National Ambient Air Quality Standards for Particulate Matter
Related Material
[Federal Register: July 18, 1997 (Volume 62, Number 138)]
[Rules and Regulations]
[Page 38651-38701]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr18jy97-16]
=======================================================================
-----------------------------------------------------------------------
ENVIRONMENTAL PROTECTION AGENCY
40 CFR Part 50
[AD-FRL-5725-2]
RIN 2060-AE66
National Ambient Air Quality Standards for Particulate Matter
AGENCY: Environmental Protection Agency (EPA).
ACTION: Final rule.
-----------------------------------------------------------------------
SUMMARY: This document describes EPA's decision to revise the national
ambient air quality standards (NAAQS) for particulate matter (PM) based
on its review of the available scientific evidence linking exposures to
ambient PM to adverse health and welfare effects at levels allowed by
the current PM standards. The current primary PM standards are revised
in several respects: Two new PM2.5 standards are added, set
at 15 g/m3 , based on the 3-year average of annual
arithmetic mean PM2.5 concentrations from single or multiple
community-oriented monitors, and 65 g/m 3 , based
on the 3-year average of the 98th percentile of 24-hour
PM2.5 concentrations at each population-oriented monitor
within an area; and the current 24-hour PM10 standard is
revised to be based on the 99th percentile of 24-hour
PM10 concentrations at each monitor within an area. The new
suite of primary standards will provide increased protection against a
wide range of PM-related health effects, including premature mortality
and increased hospital admissions and emergency room visits, primarily
in the elderly and individuals with cardiopulmonary disease; increased
respiratory symptoms and disease, in children and individuals with
cardiopulmonary disease such as asthma; decreased lung function,
particularly in children and individuals with asthma; and alterations
in lung tissue and structure and in respiratory tract defense
mechanisms. The current secondary standards are revised by making them
identical in all respects to the new suite of primary standards. The
new secondary standards, in conjunction with a regional haze program,
will provide appropriate protection against PM-related public welfare
effects including soiling, material damage, and visibility impairment.
In conjunction with the new PM2.5 standards, a new reference
method has been specified for monitoring PM as PM2.5 .
EFFECTIVE DATE: This action is effective September 16, 1997.
ADDRESSES: A docket containing information relating to the EPA's review
of the PM primary and secondary standards (Docket No. A-95-54) is
available for public inspection in the Central Docket Section of the
U.S. Environmental Protection Agency, South Conference Center, Rm. 4,
401 M St., SW., Washington, DC. This docket incorporates the docket
established for the air quality Criteria Document (Docket No. ECAO-CD-
92-0671). The docket may be inspected between 8 a.m. and 3 p.m., Monday
through Friday, except legal holidays, and a reasonable fee may be
charged for copying. The information in the docket constitutes the
complete basis for the decision announced in this document. For the
availability of related information, see ``SUPPLEMENTARY INFORMATION.''
FOR FURTHER INFORMATION CONTACT: John H. Haines, MD-15, Air Quality
Strategies and Standards Division, Office of Air Quality Planning and
Standards, U.S. Environmental Protection Agency, Research Triangle
Park, NC 27711; telephone: (919) 541-5533; e-mail:
haines.john@epamail.epa.gov.
SUPPLEMENTARY INFORMATION:
Related Final Rules on PM Monitoring
In a separate document published elsewhere in this issue of the
Federal Register, EPA is amending its ambient air quality surveillance
requirements (40 CFR part 58) and its ambient air monitoring reference
and equivalent methods (40 CFR part 53) for PM.
Availability of Related Information
Certain documents are available from the U.S. Department of
Commerce, National Technical Information Service, 5285 Port Royal Road,
Springfield, VA 22161. Available documents include:
(1) Air Quality Criteria for Particulate Matter (Criteria Document)
(three volumes, EPA/600/P-95-001aF thru EPA/600/P-95-001cF, April 1996,
NTIS #PB-96-168224, $234.00 paper copy).
(2) Review of the National Ambient Air Quality Standards for
Particulate Matter: Policy Assessment of Scientific and Technical
Information (Staff Paper) (EPA-452/R-96-013, July 1996, NTIS #PB-97-
115406, $47.00 paper copy and $19.50 microfiche). (Add a $3.00 handling
charge per order.)
A limited number of copies of other documents generated in
connection with this standard review, such as technical support
documents pertaining to air quality, monitoring, and health risk
assessment, can be obtained from: Environmental Protection Agency
Library (MD-35), Research Triangle Park, NC 27711, telephone (919) 541-
2777. These and other related documents are also available for
inspection and copying in the EPA docket at the address under
``ADDRESSES,'' at the beginning of this document.
Electronic Availability
The Staff Paper and human health risk assessment support documents
are available on the Agency's Office of Air Quality Planning and
Standards' (OAQPS) Technology Transfer Network (TTN) Bulletin Board
System (BBS) in the Clean Air Act Amendments area, under Title I,
Policy/Guidance Documents. To access the bulletin board, a modem and
communications software are necessary. To dial up, set your
communications software to 8 data bits, no parity and one stop bit.
Dial (919) 541-5742 and follow the on-screen instructions to register
for access. After registering, proceed to choice ``(T) Gateway to TTN
Technical Areas'', then choose ``(E) CAAA BBS''. From the main menu,
choose ``(1) Title I: Attain/Maint of NAAQS'', then ``(P) Policy
Guidance Documents.'' To access these documents through the World Wide
Web, click on ``TTN BBSWeb'', then proceed to the Gateway to TTN
Technical areas, as above. If assistance is needed in accessing the
system, call the help desk at (919) 541-5384 in Research Triangle Park,
NC.
Implementation Strategy For Revised Air Quality Standards
On Wednesday, July 16, 1997, President Clinton signed a memorandum
to the Administrator specifying his goals for the implementation of the
O3 and PM standards. Attached to the President's memorandum
is a strategy prepared by an interagency Administration group outlining
the next steps that would be necessary for implementing these
standards. The EPA will prepare guidance and proposed rules consistent
with the President's memorandum. Copies of the Presidential document
are available in paper copy by contacting the U.S. Environmental
Protection Agency Library at the address under ``Availability of
Related Information'' and in electronic form as discussed above in
``Electronic Availability.''
The following topics are discussed in this preamble:
I. Background
A. Legislative Requirements
B. Related Control Requirements
C. Review of Air Quality Criteria and Standards for PM
D. Summary of Proposed Revisions to the PM Standards
II. Rationale for the Primary PM Standards
A. Introduction
B. Need for Revision of the Current Primary PM Standards
[[Page 38653]]
C. Indicators of PM
D. Averaging Time of PM2.5 Standards
E. Form of PM2.5 Standards
F. Levels for the Annual and 24-Hour PM2.5 Standards
G. Conclusions Regarding the Current PM10 Standards
H. Final Decisions on Primary PM Standards
III. Rationale for the Secondary Standards
A. Need for Revision of the Current SecondaryStandards
B. Decision on the Secondary Standards
IV. Other Issues
A. Consideration of Costs
B. Margin of Safety
C. Data Availability
D. 1990 Amendments
V. Revisions to 40 CFR Part 50, Appendix K--Interpretation of the PM
NAAQS
A. PM2.5 Computations and Data Handling Conventions
B. PM10 Computations and Data Handling Conventions
C. Changes that Apply to Both PM2.5 and
PM10 Computations
VI. Reference Methods for the Determination of Particulate Matter as
PM10 and PM2.5 in the Atmosphere
A. Revisions to 40 CFR Part 50, Appendix J--Reference Method for
PM10
B. 40 CFR Part 50, Appendix L--New Reference Method for
PM2.5
VII. Effective Date of the Revised PM Standards and Applicability of
the Existing PM10 Standards
VIII. Regulatory and Environmental Impact Analyses
A. Executive Order 12866
B. Regulatory Flexibility Analysis
C. Impact on Reporting Requirements
D. Unfunded Mandates Reform Act
E. Environmental Justice
F. Submission to Congress and the Comptroller General
IX. Response to Petition for Administrator Browner's Recusal
X. References
I. Background
A. Legislative Requirements
Two sections of the Clean Air Act (Act) govern the establishment,
review, and revision of NAAQS. Section 108 of the Act (42 U.S.C. 7408)
directs the Administrator to identify certain pollutants which ``may
reasonably be anticipated to endanger public health and welfare'' and
to issue air quality criteria for them. These air quality criteria are
to ``accurately reflect the latest scientific knowledge useful in
indicating the kind and extent of all identifiable effects on public
health or welfare which may be expected from the presence of [a]
pollutant in the ambient air * * *.''
Section 109 of the Act (42 U.S.C. 7409) directs the Administrator
to propose and promulgate ``primary'' and ``secondary'' NAAQS for
pollutants identified under section 108 of the Act. Section 109(b)(1)
of the Act defines a primary standard as one ``the attainment and
maintenance of which in the judgment of the Administrator, based on
[the] criteria and allowing an adequate margin of safety, are requisite
to protect the public health.'' The margin of safety requirement was
intended to address uncertainties associated with inconclusive
scientific and technical information available at the time of standard
setting, as well as to provide a reasonable degree of protection
against hazards that research has not yet identified. Both kinds of
uncertainties are components of the risk associated with pollution at
levels below those at which human health effects can be said to occur
with reasonable scientific certainty. Thus, by selecting primary
standards that provide an adequate margin of safety, the Administrator
is seeking not only to prevent pollution levels that have been
demonstrated to be harmful but also to prevent lower pollutant levels
that she finds may pose an unacceptable risk of harm, even if the risk
is not precisely identified as to nature or degree. The Act does not
require the Administrator to establish a primary NAAQS at a zero-risk
level, but rather at a level that reduces risk sufficiently so as to
protect public health with an adequate margin of safety. The selection
of any particular approach to providing an adequate margin of safety is
a policy choice left specifically to the Administrator's judgment. Lead
Industries Ass'n v. EPA, 647 F.2d 1130, 1161-1162 (D.C. Cir.1980).
A secondary standard, as defined in section 109 (b)(2) of the Act,
must ``specify a level of air quality the attainment and maintenance of
which in the judgment of the Administrator, based on [the] criteria,
[are] requisite to protect the public welfare from any known or
anticipated adverse effects associated with the presence of [the]
pollutant in the ambient air.'' Welfare effects as defined in section
302(h) of the Act (42 U.S.C. 7602(h)) include, but are not limited to,
``effects on soils, water, crops, vegetation, manmade materials,
animals, wildlife, weather, visibility, and climate, damage to and
deterioration of property, and hazards to transportation, as well as
effects on economic values and on personal comfort and well-being.''
Section 109(d)(1) of the Act requires periodic review and, if
appropriate, revision of existing air quality criteria and NAAQS.
Section 109(d)(2) of the Act requires appointment of an independent
scientific review committee to review criteria and standards and
recommend new standards or revisions of existing criteria and
standards, as appropriate. The committee established under section
109(d)(2) of the Act is known as the Clean Air Scientific Advisory
Committee (CASAC), a standing committee of EPA's Science Advisory
Board.
B. Related Control Requirements
States are primarily responsible for ensuring attainment and
maintenance of ambient air quality standards once EPA has established
them. Under section 110 of the Act (42 U.S.C. 7410) and related
provisions, States are to submit, for EPA approval, State
implementation plans (SIP's) that provide for the attainment and
maintenance of such standards through control programs directed to
sources of the pollutants involved. The States, in conjunction with
EPA, also administer the prevention of significant deterioration
program (42 U.S.C. 7470-7479) for these pollutants. In addition,
Federal programs provide for nationwide reductions in emissions of
these and other air pollutants through the Federal Motor Vehicle
Control Program under Title II of the Act (42 U.S.C. 7521-7574), which
involves controls for automobile, truck, bus, motorcycle, nonroad
engine, and aircraft emissions; the new source performance standards
under section 111 of the Act (42 U.S.C. 7411); and the national
emission standards for hazardous air pollutants under section 112 of
the Act (42 U.S.C. 7412).
C. Review of Air Quality Criteria and Standards for PM
Particulate matter is the generic term for a broad class of
chemically and physically diverse substances that exist as discrete
particles (liquid droplets or solids) over a wide range of sizes.
Particles originate from a variety of anthropogenic stationary and
mobile sources as well as from natural sources. Particles may be
emitted directly or formed in the atmosphere by transformations of
gaseous emissions such as sulfur oxides (SOx), nitrogen
oxides (NOX), and volatile organic compounds (VOC). The
chemical and physical properties of PM vary greatly with time, region,
meteorology, and source category, thus complicating the assessment of
health and welfare effects.
The last review of PM air quality criteria and standards was
completed in July 1987 with notice of a final decision to revise the
existing standards published in the Federal Register (52 FR 24854, July
1, 1987). In that decision, EPA changed the indicator for PM from total
suspended particles (TSP) to
[[Page 38654]]
PM10.1 Identical primary and secondary
PM10 standards were set for two averaging times: 50
g/m3, expected annual arithmetic mean, averaged
over 3 years, and 150 g/m3, 24-hour average, with
no more than one expected exceedance per year.2
---------------------------------------------------------------------------
1 PM10 refers to particles with an aerodynamic
diameter less than or equal to a nominal 10 micrometers. Technical
details further specifying the measurement of PM10 are
contained in 40 CFR part 50, Appendices J and M.
2 A more complete history of the PM NAAQS is presented in
section II.B of the OAQPS Staff Paper, Review of National Ambient
Air Quality Standards for Particulate Matter: Assessment of
Scientific and Technical Information (U.S. EPA, 1996b).
---------------------------------------------------------------------------
The EPA initiated this current review of the air quality criteria
and standards for PM in April 1994 by announcing its intention to
develop a revised Air Quality Criteria Document for Particulate Matter
(henceforth, the ``Criteria Document''). Thereafter, the EPA presented
its plans for review of the criteria and standards for PM under a
highly accelerated, court-ordered schedule3 at a public
meeting of the CASAC in December 1994. Several workshops were held by
EPA's National Center for Environmental Assessment (NCEA) to discuss
important new health effects information in November 1994 and January
1995. External review drafts of the Criteria Document were made
available for public comment and were reviewed by CASAC at public
meetings held in August and December 1995 and February 1996. The CASAC
came to closure in its review of the Criteria Document, advising the
Administrator in a March 15, 1996 closure letter (Wolff, 1996a) that
``although our understanding of the health effects of PM is far from
complete, a revised Criteria Document which incorporates the Panel's
latest comments will provide an adequate review of the available
scientific data and relevant studies of PM.'' CASAC and public comments
from these meetings, and from subsequent written comments and the
closure letter, were incorporated as appropriate in the final Criteria
Document (U.S. EPA, 1996a).
---------------------------------------------------------------------------
3 A court order entered in American Lung Association v. Browner,
CIV-93-643-TUC-ACM (D. Ariz.,October 6, 1994), as subsequently
modified, requires publication of EPA's final decision on the review
of the PM NAAQS by July 19, 1997.
---------------------------------------------------------------------------
External review drafts of a Staff Paper prepared by the Office of
Air Quality Planning and Standards (OAQPS), Review of the National
Ambient Air Quality Standards for Particulate Matter: Assessment of
Scientific and Technical Information (henceforth, the ``Staff Paper''),
were made available for public comment and were reviewed by CASAC at
public meetings in December 1995 and May 1996.4 The CASAC
came to closure in its review of the Staff Paper, advising the
Administrator in a June 13, 1996 closure letter (Wolff, 1996b) that
``the Staff Paper, when revised, will provide an adequate summary of
our present understanding of the scientific basis for making regulatory
decisions concerning PM standards.'' CASAC and public comments from
these meetings, subsequent written comments, and the CASAC closure
letter were incorporated as appropriate in the final Staff Paper (U.S.
EPA, 1996b).
---------------------------------------------------------------------------
4 The Staff Paper evaluates policy implications of the key
studies and scientific information in the Criteria Document,
identifies critical elements that EPA staff believes should be
considered, and presents staff conclusions and recommendations of
suggested options for the Administrator's consideration.
---------------------------------------------------------------------------
On November 27, 1996, EPA announced its proposed decision to revise
the NAAQS for PM (61 FR 65638, December 13, 1996) (hereafter
``proposal'') as well as its proposed decision to revise the NAAQS for
ozone (O3)(61 FR 65716, December 13, 1996). In the proposal,
EPA identified proposed revisions, based on the air quality criteria
for PM, and solicited public comments on alternative primary standards
and on the proposed forms of the standards.
To ensure the broadest possible public input on the PM and
O3 proposals, EPA took extensive and unprecedented steps to
facilitate the public comment process beyond the normal process of
providing an opportunity to request a hearing and receiving written
comments submitted to the rulemaking docket. The EPA established a
national toll-free telephone hotline to facilitate public comments on
the proposed revisions to the PM and O3 NAAQS, and on
related notices dealing with the implementation of revised PM and
O3 standards, as well as a system for the public to submit
comments on the proposals electronically via the Internet. Over 14,000
calls and over 4,000 electronic mail messages were received through
these channels. The public could also access key supporting documents
(including the Criteria Document, Staff Paper, related technical
documents and fact sheets) via the Internet.
The EPA also held several public hearings and meetings across the
country to provide direct opportunities for public comment on the
proposed revisions to the PM and O3 NAAQS and to disseminate
information to the public about the proposed standard revisions. On
January 14 and 15, 1997, EPA held concurrent, 2-day public hearings in
Boston, MA, Chicago, IL, and Salt Lake City, UT. A fourth public
hearing, which focused primarily on PM monitoring issues, was held in
Durham, NC on January 14, 1997. Over 400 citizens and organizations
testified during these public hearings. EPA also held two national
satellite telecasts to answer questions on the standards and
participated in meetings sponsored by the Air and Waste Management
Association on the proposed revisions to the standards at more than 10
locations across the country. Beyond that, several EPA regional offices
held public meetings and workshops and participated in hearings that
States and cities held around the country.
As a result of this intensive effort to solicit public input, over
50,000 written and oral comments were received on the proposed
revisions to the PM NAAQS by the close of the public comment period on
March 12, 1997. Major issues raised in the comments are discussed
throughout the preamble of this final decision. A comprehensive summary
of all significant comments, along with EPA's response to such comments
(hereafter ``Response to Comments''), can be found in the docket for
this rulemaking (Docket No. A-95-54).
The principal focus of this current review of the air quality
criteria and standards for PM is on recent epidemiological evidence
reporting associations between ambient concentrations of PM and a range
of serious health effects. Particular attention has been given to
several size-specific classes of particles, including PM10
and the principal fractions of PM10, referred to as the fine
(PM2.5)5 and coarse
(PM10-2.5)6 fractions. As discussed in the
Criteria Document, fine and coarse fraction particles can be
differentiated by their sources and formation processes and their
chemical and physical properties, including behavior in the atmosphere.
Detailed discussions of atmospheric formation, ambient concentrations,
and health and welfare effects of PM, as well as quantitative estimates
of human health risks associated with exposure to PM, can be found in
the Criteria Document and in the Staff Paper.
---------------------------------------------------------------------------
5 PM2.5 refers to particles with an aerodynamic
diameter less than or equal to a nominal 2.5 micrometers, as further
specified in 40 CFR part 50, Appendix L in this document.
6 PM10-2.5 refers to those particles with an
aerodynamic diameter less than or equal to a nominal 10 micrometers
but greater than 2.5 micrometers. In other words, it refers to the
inhalable particles that remain if fine (PM2.5) particles
are removed from a sample of PM10 particles.
---------------------------------------------------------------------------
[[Page 38655]]
D. Summary of Proposed Revisions to the PM Standards
For reasons discussed in the proposal, the Administrator proposed
to revise the current primary standards for PM (as indicated by
PM10), by adding two new primary PM2.5 standards
set at 15 g/m3, annual mean, and 50 g/
m3, 24-hour average. The proposed annual PM2.5
standard would be based on the 3-year average of the annual arithmetic
mean PM2.5 concentrations, spatially averaged across an
area. The proposed 24-hour PM2.5 standard would be based on
the 3-year average of the 98th percentile of 24-hour
PM2.5 concentrations at each population-oriented monitor
within an area. The proposal solicited comment on two alternative
approaches for selecting the levels of PM2.5 standards. The
Administrator also proposed to revise the current 24-hour primary
PM10 standard of 150 g/m3 by replacing
the 1-expected-exceedance form with a 98th percentile form,
averaged over 3 years at each monitor within an area, solicited comment
on an alternative proposal to revoke the 24-hour PM10
standard, and proposed to retain the current annual primary
PM10 standard of 50 g/m3. The proposal
also solicited comment on proposed revisions to 40 CFR part 50,
Appendix K to establish new data handling conventions for calculating
98th percentile values and spatial averages, revisions to 40
CFR part 50, Appendix J to modify the reference method for monitoring
PM as PM10, and a proposed new reference method for
monitoring PM as PM2.5 (40 CFR part 50, Appendix L).
With regard to the secondary standards, the Administrator proposed
to revise the current secondary standards by making them identical to
the suite of proposed primary standards, in conjunction with the
establishment of a regional haze program under section 169A of the Act.
II. Rationale for the Primary Standards
A. Introduction
1. Overview. This document presents the Administrator's final
decisions regarding the need to revise the current primary ambient air
quality standards for PM, and, more specifically, regarding the
establishment of new annual and 24-hour PM2.5 primary
standards and revisions to the form of the current 24-hour
PM10 primary NAAQS. These decisions are based on a thorough
review, in the Criteria Document, of the latest scientific information
on known and potential human health effects associated with exposure to
PM at levels typically found in the ambient air. These decisions also
take into account:
(1) Staff Paper assessments of the most policy-relevant information
in the Criteria Document, upon which staff recommendations for new and
revised primary standards are based.
(2) CASAC advice and recommendations, as reflected in discussions
of drafts of the Criteria Document and Staff Paper at public meetings,
in separate written comments, and in the CASAC's closure letters to the
Administrator.
(3) Public comments received during the development of these
documents, either in connection with CASAC meetings or separately.
(4) Extensive public comments received on the proposed decisions
regarding the primary PM standards.
After taking this information and comments into account, and for
the reasons discussed below in this unit, the Administrator concludes
that revisions to the current primary standards to provide increased
public health protection against a variety of health risks are
appropriate. More specifically, the Administrator has determined that
it is appropriate to establish new annual and 24-hour PM2.5
standards, to revise the current 24-hour PM10 standard, and
to retain the current annual PM10 standard. As discussed
more fully below in this unit, the rationale for the final decisions
regarding the PM primary NAAQS includes consideration of:
(1) Health effects information, and alternative views on the
appropriate interpretation and use of the information, as the basis for
judgments about the risks to public health presented by population
exposures to ambient PM.
(2) Insights gained from a quantitative risk assessment conducted
to provide a broader perspective for judgments about protecting public
health from the risks associated with PM exposures.
(3) Specific conclusions regarding the need for revisions to the
current standards and the elements of PM standards (i.e., indicator,
averaging time, form, and level) that, taken together, would be
appropriate to protect public health with an adequate margin of safety.
As with virtually any policy-relevant scientific research, there is
uncertainty in the characterization of health effects attributable to
exposure to ambient PM. As discussed in the proposal, however, there is
now a greatly expanded body of health effects information as compared
with that available during the last review of the PM standards.
Moreover, the recent evidence on PM-related health effects has
undergone an unusually high degree of scrutiny and reanalysis over the
past several years, beginning with a series of workshops held early in
the review process to discuss important new information. A number of
opportunities were provided for public comment on successive drafts of
the Criteria Document and Staff Paper, as well as for intensive peer
review of these documents by CASAC at several public meetings attended
by many knowledgeable individuals and representatives of interested
organizations. In addition, there have been a number of important
scientific conferences, symposia, and colloquia on PM issues, sponsored
by the EPA and others, in the U.S. and abroad, during this period.
While significant uncertainties exist, the review of the health effects
information has been thorough and deliberate. In the judgment of the
Administrator, this intensive evaluation of the scientific evidence has
provided an adequate basis for regulatory decision making at this time,
as well as for the comprehensive research needs document recently
developed by EPA, and reviewed by CASAC and others, for improving our
future understanding of the relationships between ambient PM exposures
and health effects.
The health effects information and human risk assessment were
summarized in the proposal and are only briefly outlined below in this
unit. Subsequent units provide a more complete discussion of the
Administrator's rationale, in light of key issues raised in public
comments, for concluding that it is appropriate to revise the current
primary standards (Unit II.B. of this preamble) and to revise the
specific elements of the standards including indicator (Unit II.C. of
this preamble); averaging time, form, and level of new PM2.5
standards (Units II.D., II.E., and II.F. of this preamble); and
averaging time, form, and level of revised PM10 standards
(Unit II.G. of this preamble).
2. Summary of the health effects evidence. In brief, since the last
review of the PM criteria and standards, the most significant new
evidence on the health effects of PM is the greatly expanded body of
community epidemiological studies. The Criteria Document stated that
these recent studies provide ``evidence that serious health effects
(mortality, exacerbation of chronic disease, increased hospital
admissions, etc.) are associated with exposures to ambient levels of PM
found in contemporary U.S. urban airsheds even at concentrations below
current U.S. PM standard'' (U.S. EPA, 1996a; p. 13-1). Although a
variety of
[[Page 38656]]
responses to constituents of ambient PM have been hypothesized to
contribute to the reported health effects, the relevant toxicological
and controlled human studies published to date have not identified any
accepted mechanism(s) that would explain how such relatively low
concentrations of ambient PM might cause the health effects reported in
the epidemiological literature.
Unit II.A. of the proposal further outlines key information
contained in the Criteria Document, Chapters 10-13, and the Staff
Paper, Chapter V, on the known and potential health effects associated
with airborne PM, alone and in combination with other pollutants that
are routinely present in the ambient air. The information highlighted
there summarizes:
(1) The nature of the effects that have been reported to be
associated with ambient PM, which include premature mortality,
aggravation of respiratory and cardiovascular disease (as indicated by
increased hospital admissions and emergency room visits, school
absences, work loss days, and restricted activity days), changes in
lung function and increased respiratory symptoms, changes to lung
tissues and structure, and altered respiratory defense mechanisms.
(2) Sensitive subpopulations that appear to be at greater risk to
such effects, specifically individuals with respiratory disease and
cardiovascular disease and the elderly (premature mortality and
hospitalization), children (increased respiratory symptoms and
decreased lung function), and asthmatic children and adults
(aggravation of symptoms).
(3) An integrated evaluation of the health effects evidence, with
an emphasis on the key issues raised in assessing community
epidemiological studies, including alternative interpretations of the
evidence, both for individual studies and for the evidence as a whole.
(4) The PM fractions of greatest concern to health.
The summary in the proposal will not be repeated here. EPA emphasizes
that the final decisions on these standards take into account the more
comprehensive and detailed discussions of the scientific information on
these issues contained in the Criteria Document and Staff Paper, which
were reviewed by the CASAC and the public.
3. Key insights from the risk assessment. The Staff Paper presents
the results of a quantitative assessment of health risks for two
example cities, including risk estimates for several categories of
health effects associated with: existing PM air quality levels,
projected PM air quality levels that would occur upon attainment of the
current PM10 standards, and projected PM air quality levels
that would occur upon attainment of alternative PM2.5
standards. The risk assessment is intended as an aid to the
Administrator in judging which alternative PM NAAQS would reduce risks
sufficiently to protect public health with an adequate margin of
safety, recognizing that such standards will not be risk-free. The risk
assessment is described more fully in the Staff Paper and summarized in
the proposal. Related technical reports and updates7 have
been placed in the docket (Abt Associates, 1996a,b; 1997a,b).
---------------------------------------------------------------------------
7 The risk assessment results that appear in the Staff Paper and
are summarized in the proposal have been updated to include analyses
of the particular forms of standard alternatives contained in the
proposal and to correct estimates for one effects category
(mortality from long-term exposure) to reflect the actual statistics
used in the study upon which they were based (Pope et al., 1995).
The corrections, which cumulatively reduce estimates of mortality
associated with long-term exposures by 20 to 35%, have no effect on
risk estimates for mortality associated with short-term exposures or
the estimates for any other effects. Because the key sensitivity
analyses that provide additional insights regarding thresholds,
copollutants, averaging time and related issues involved the short-
term exposure studies, none of these results are affected by changes
to the long-term exposure risk estimates.
---------------------------------------------------------------------------
EPA emphasizes that it places greater weight on the overall
conclusions derived from the studies--that PM air pollution is likely
causing or contributing to significant adverse effects at levels below
those permitted by the current standards--than on the specific
concentration-response functions and quantitative risk estimates
derived from them. These quantitative risk estimates include
significant uncertainty and, therefore, should not be viewed as
demonstrated health impacts. EPA believes, however, that they do
represent reasonable estimates as to the possible extent of risk for
these effects given the available information. Keeping in mind the
important uncertainties inherent in any such analyses, the key insights
from the risk assessment that are most pertinent to the current
decision include:
(1) Fairly wide ranges of estimates of the incidence of PM-related
mortality and morbidity effects and risk reductions associated with
attainment of alternative standards were calculated for the two
locations analyzed when the effects of key uncertainties and
alternative assumptions were considered. Significantly, the combined
analysis for these two cities alone found that the risk remaining after
attaining the current PM10 standards was on the order of
hundreds of premature deaths each year, hundreds to thousands of
respiratory-related hospital admissions, and tens of thousands of
additional respiratory related symptoms in children.
(2) Based on the results from the sensitivity analyses of key
uncertainties and the integrated uncertainty analyses, the single most
important factor influencing the uncertainty associated with the risk
estimates is whether or not a threshold concentration exists below
which PM-associated health risks are not likely to occur.
(3) Over the course of a year, the few peak 24-hour
PM2.5 concentrations appear to contribute a relatively small
amount to the total health risk posed by the entire air quality
distribution as compared to the aggregated risks associated with the
low to mid-range concentrations.
(4) There is greater uncertainty about both the existence and the
magnitude of estimated excess mortality and other effects associated
with PM exposures as one considers increasingly lower concentrations
approaching background levels.
B. Need for Revision of the Current Primary PM Standards
1. Introduction. The overarching issue in the present review of the
primary NAAQS is whether, in view of the advances in scientific
knowledge reflected in the Criteria Document and Staff Paper, the
existing PM standards should be revised and, if so, what revised or new
standards would be appropriate. The concluding section of the
integrative synthesis of health effects information in the Criteria
Document, which CASAC characterized as EPA's ``best ever example of a
true integrative summary of the state of knowledge about the health
effects of airborne PM,'' (Wolff, 1996b) provides the following summary
of the science with respect to this issue:
The evidence for PM-related effects from epidemiological studies
is fairly strong, with most studies showing increases in mortality,
hospital admissions, respiratory symptoms, and pulmonary function
decrements associated with several PM indices. These epidemiological
findings cannot be wholly attributed to inappropriate or incorrect
statistical methods, misspecification of concentration-effect
models, biases in study design or implementation, measurement errors
in health endpoint, pollution exposure, weather, or other variables,
nor confounding of PM effects with effects of other factors. While
the results of the epidemiological studies should be interpreted
cautiously, they nonetheless provide ample reason to be concerned
that there are detectable health effects attributable
[[Page 38657]]
to PM at levels below the current NAAQS. [U.S. EPA, 1996a, p. 13-92]
Given the nature of the health effects in question, this finding,
which is based on a large number of studies that used PM10
measurements, as well as studies using other indicators of PM, clearly
indicates that revision of the current PM NAAQS is appropriate. Quite
apart from the issue of whether PM10 should be the sole
indicator for the PM NAAQS, the extensive PM epidemiological data base
provides evidence of serious health effects (e.g., mortality,
exacerbation of chronic disease, increased hospital admissions) in
sensitive populations (e.g., the elderly, individuals with
cardiopulmonary disease), as well as significant adverse health effects
(e.g., increased respiratory symptoms, school absences, and lung
function decrements) in children. Moreover, these effects associations
are observed in areas or at times when the levels of the current
PM10 standards are met. Although the increase in relative
risk is small for the most serious outcomes, EPA believes it is
significant from an overall public health perspective, because of the
large number of individuals in sensitive populations that are exposed
to ambient PM, as well as the significance of the health effects
involved (U.S. EPA, 1996a, p. 1-21). The results of the two-city PM
risk assessment reinforce these conclusions regarding the significance
of the public health risk--even under a scenario in which the current
PM10 standards are attained.
While the lack of demonstrated mechanisms that explain the
extensive body of epidemiological findings is an important caution,
which presents difficulties in providing an integrated assessment of PM
health effects research, a number of potential mechanisms have been
hypothesized in the recent literature (U.S. EPA, 1996b; p. V-5 to V-8;
appendix D). Moreover, qualitative information from laboratory studies
of the effects of particle components at high concentrations and
dosimetry considerations suggest that the kinds of effects observed in
community studies (e.g., respiratory- and cardiovascular-related
responses) are at least plausibly related to inhalation of
PM.8 Indeed, as discussed in the Criteria Document and
section V.E of the Staff Paper, the consistency of the results of the
epidemiological studies from a large number of different locations and
the coherent nature of the observed effects9 are suggestive
of a likely causal role of ambient PM in contributing to the reported
effects.
---------------------------------------------------------------------------
8 As discussed more fully below in this unit, epidemiological
studies alone cannot be used to demonstrate mechanisms of action,
but they can provide evidence useful in making inferences with
regard to causal relationships (U.S. EPA, 1996b, p. V-9).
9 As noted in the proposal, the kinds of effects observed in the
epidemiological studies are logically related. For example, the
association of PM with mortality is mainly linked to respiratory and
cardiovascular causes, which is coherent with observed PM
associations with respiratory and cardiovascular hospital admissions
and respiratory symptoms. Further, similar categories of effects are
seen in long- and short-term exposure studies.
---------------------------------------------------------------------------
2. Comments on scientific basis for revision. A majority of the
public comments received on the proposal agreed that, based on the
available scientific information, the current PM10 standards
are not of themselves sufficient to protect public health and it would
be appropriate to revise them. Included in those calling for revisions
to the current standards are many public health professionals,
including numerous medical doctors and academic researchers. For
example, a group of 27 members of the scientific and medical community
recognized as having substantial expertise in conducting research on
the health effects of air pollution stated:
Health studies conducted in the U.S. and around the world have
demonstrated that levels of particulate and ozone air pollution
below the current U.S. National Air Quality Standards exacerbate
serious respiratory disease and contribute to early death. A large
body of scientific and medical evidence clearly indicates that the
current NAAQS are not sufficiently protective of public health.
[Thurston, 1997]
Similar conclusions were reached in a letter signed by more than
1,000 scientists, clinicians, researchers, and other health care
professionals (Dickey, 1997). The cosigners to this letter argued that
tens of thousands of hospital visits and premature deaths could be
prevented with the proposed air quality standard revisions. In fact,
these commenters argued that even stronger standards than those
proposed by EPA are needed to protect the health of the most vulnerable
residents of our communities.
A number of State and local government authorities also submitted
comments in support of adopting new air quality standards for fine
particulate matter. The commenters concurred with conclusions reached
through the EPA's peer review process that the PM standards should be
revised to protect public health. A number of these commenters
suggested that the standards proposed by EPA should be even stronger,
while several other State agencies recommended that EPA adopt
PM2.5 standards, but at less stringent levels. A number of
the comments from states supporting even stronger standards
acknowledged the lack of demonstrated mechanism(s) and other
uncertainties but stressed the strength of the other evidence in urging
EPA to set protective standards.
Many comments were also received from representatives of
environmental or community health organizations that supported the
adoption of air quality standards for PM2.5. These
commenters agreed with EPA's finding that a large body of compelling
evidence demonstrates that exposure to particulate matter pollution, in
general, is associated with premature death, aggravation of heart and
lung diseases, increased respiratory illness and reduced lung function.
They agreed with EPA that these studies present a consistent and
coherent relationship between exposure to PM and both mortality and
various measures of morbidity. However, the majority of these
commenters argued that EPA's proposed standards for PM2.5
were inadequate and recommended adoption of more stringent levels of
the 24-hour and/or annual air quality standards for PM2.5.
Many of these commenters also urged EPA to revise the NAAQS for
PM10 to be more protective of public health. These
commenters based their recommendations on the findings of the studies
that were reviewed in the preparation of the Criteria Document and
Staff Paper. One commenter used results from five of these studies as
the basis for recommending PM2.5 standards of 10 g/
m3 (annual) and 18 g/m3 (24-hour)
(Dockery et al., 1993; Pope et al., 1995; Schwartz et al., 1996;
Schwartz et al., 1994; Thurston et al., 1994). The commenters agreed
with EPA on the significance of these studies' results and the need to
revise the PM standards, while differing with EPA's interpretation of
the findings for purposes of developing the proposed PM standards.
Several commenters made reference to the conclusions of a number of
international scientific panels regarding the health effects of
exposure to airborne particulate matter--the British Expert Panel on
Air Quality Standards, the British Committee on the Medical Effects of
Air Pollutants, the World Health Organization, the Canadian Ministry of
Environment, Lands and Parks, and the Health Council of the Netherlands
-- and argued that all these panels found that PM concentrations
equivalent to the current U.S. standards for PM10 are not
protective of human health and made recommendations for greater
protection. One commenter noted that the findings of the British Health
Panel have resulted in a British
[[Page 38658]]
proposal to adopt a 24-hour PM10 standard of 50 g/
m3, which is one-third the level of the current U.S. NAAQS.
In these comments, some toxicological studies were cited as
providing evidence for toxicity of particulate pollution. These
commenters disagreed with arguments that PM standards cannot be adopted
due to a lack of a sufficient understanding of the biological mechanism
of injury. The commenters argued that there is sufficient evidence that
particulate pollution is associated with adverse health effects to make
it inappropriate to delay the establishment of standards while further
studies are undertaken. This group of commenters was also critical of
arguments against the establishment of additional PM standards based on
the possibility of confounding by other pollutants, and urged that more
attention be paid instead to the possible additive or synergistic
effects of multiple pollutant exposures.
In general, the EPA agrees with these commenters' arguments
regarding the need to revise the PM standards. The scientific studies
cited by these commenters were the same studies used in the development
of the Criteria Document and the Staff Paper, and the EPA agrees that
there is a sufficient body of evidence that the current NAAQS for PM
are not adequately protective of the public health. For reasons
detailed in Unit II.F. of this preamble and in the Response to
Comments, EPA disagrees with aspects of these commenters' views on the
level of protection that is appropriate and supported by the available
scientific information.
Another body of commenters, including almost all commenters
representing businesses and industry associations, many local
governmental groups and private citizens, and some States opposed
revising the standards. Many of these commenters argued that the
available scientific evidence does not provide an adequate basis for
revising the current standards. The central arguments made by these
commenters can be divided into two categories: (1) General comments on
the appropriateness of relying on the epidemiological evidence for
making regulatory decisions, and (2) more specific comments challenging
EPA's appraisal of the consistency and coherence of the available
information, EPA's conclusions regarding causality, and the use of
these studies for risk assessment and decisions on whether to revise
the standards. While EPA has included comprehensive responses to these
comments in the Response to Comments, certain key points are summarized
below in this unit.
a. General comments on the use of epidemiological studies. The
first category of comments was largely derived from ad hoc panels of
occupational and other epidemiological experts, consulting groups, and
individual consultants. Most of these individuals and groups commented
on the use of epidemiology in reaching scientific and policy
conclusions primarily from an occupational or hazard assessment
perspective, in contrast to the perspective of the review of ambient PM
criteria and standards, where the use of community air pollution
epidemiological studies are central. Citing accepted criteria used in
evaluating epidemiological studies to assess the likelihood of
causality (most notably those of Sir Austin Bradford Hill, 1965), these
commenters argued that in the absence of a demonstrated biological
mechanism, the relative risks of effects in the PM epidemiological
studies are too low (less than values variously cited as 1.5 to 2.0) to
reach any conclusions regarding causality or to form the basis for
regulations. In general, the commenters applied these criteria to a
subset of studies evaluated in the Criteria Document, including as few
as two long-term exposure studies (EOP Group) (API, 1997), a group of 9
selected studies (Greenland panel) (API, 1997), those studies cited in
the proposal (AIHC, 1997), or as many as 23 selected short-term
exposure studies examined in a recently published review paper (Gamble
and Lewis, 1996).
Based on a careful review of these comments, EPA notes a number of
limitations in these commenters' evaluations of the epidemiological
studies that they considered, as discussed in detail in the Response to
Comments. In summary, EPA notes that these commenters provided
scientific advice and conclusions that are in substantial disagreement
with the conclusions of the review reflected in the Criteria Document
and Staff Paper. EPA stands behind the scientific conclusions reached
in these documents regarding the appropriate use of the available
community epidemiological studies. These documents were the product of
an extended public process that included conducting public workshops
involving the leading researchers in the field, drafts of the Criteria
Document and Staff Paper providing opportunities for public scrutiny
and comment on, and, not least, receiving the advice of an independent
panel of air pollution experts, including epidemiologists.
EPA clearly specified the key criteria by which it evaluated the
available epidemiological studies in section 12.1.2 of the Criteria
Document, with substantial reliance on those specified by Hill (1965).
In rejecting results with relative risks less than 1.5 to 2 as
meaningful absent demonstrated biological mechanisms, the commenters
fail to note that Hill and other expert groups (U.S. DHEW, 1964) have
emphasized that no one criterion is definitive by itself, nor is it
necessary that all be met in order to support a determination of
causality (U.S. EPA, 1996a, p. 12-3).
With respect to biological plausibility, Hill noted that ``this is
a feature I am convinced we cannot demand. What is biologically
plausible depends upon the biological knowledge of the day'' (Hill,
1965). This statement is clearly pertinent to the toxicological and
mechanistic understanding of the effects of PM and associated air
pollutants, especially at lower concentrations. It is also important to
stress that while the mechanistic evidence published as of the time the
Criteria Document closed does not provide quantitative support for the
epidemiological results, neither can such limited evidence refute these
findings. It is also important to stress that our understanding of
biological mechanisms for PM pollution effects is not sufficient to
explain the effects observed at much higher concentrations in air
pollution episodes, for which causality is generally accepted.
Moreover, the toxicological literature has only recently begun to
examine animal models (or controlled human studies) that might reflect
the sensitive populations in question (the elderly, individuals with
chronic respiratory and cardiovascular disease) or that adequately
reproduce all of the physico-chemical properties of particles in the
ambient atmosphere. In short, the absence of evidence of a particular
mechanism is hardly proof that there are no mechanisms that could
explain the effects observed so consistently in the epidemiological
studies. The absence of biological mechanisms did not deter CASAC from
recommending revisions to the PM standards in 1982, 1986, and again in
1996.
While Hill appropriately emphasized the strength of the association
as important (e.g., size of the relative risk), he also pointed out
that ``We must not be too ready to dismiss a cause-and-effect
hypothesis merely on the ground that the observed association appears
to be slight. There are many occasions in medicine when this in truth
is so'' (Hill, 1965). EPA believes that the effects of air pollution
containing PM is such a
[[Page 38659]]
case. Unlike the ``textbook'' examples of unlikely significant
associations provided by some commenters (e.g., ice cream consumption
correlated with heat stroke), the abundant epidemiological literature
on combustion particles documents numerous occasions in which single
short-term episodes of high air pollution produced unequivocally
elevated relative risks. For the week of the well documented 1952
London air pollution episode, for example, the relative risk of
mortality for all causes was 2.6, while the relative risk for
bronchitis mortality was as high as 9.3 (Ministry of Health, 1954).
Hospital admissions also increased by more than a factor of two.
British epidemiologists in the 1950s concluded that increased mortality
was likely when PM (as mass calibrated British Smoke <4.5 m in
aerodynamic diameter) exceeded 500 g/m3 (Martin and
Bradley, 1960). This is only about a factor of 3 higher than that
allowed by the current PM standard. Unlike the ``textbook'' and other
unlikely statistical associations noted by some commenters, where the
only evidence is for low relative risk, clear and convincing links
between high-level PM concentrations and mortality and morbidity
buttress the findings of similar associations at much lower PM
concentrations as suggested in the more recent epidemiological
literature.
These commenters also appear to ignore several epidemiological
studies conducted at low PM concentrations in U.S. and European cities,
including both short- and long-term exposures to PM air pollution, that
find statistically significant relative risks of respiratory symptom
categories in children in the range of 1.5 to 5 (Schwartz et al., 1994;
Pope and Dockery, 1992; Braun-Fahrlander et al., 1992; Dockery et al.,
1989; Dockery et al., 1996). Concentrations in these studies extend
from moderately above to well below those permitted by the current
PM10 standards. While, as noted in the proposal, most of the
recent epidemiological studies of mortality and hospital admissions
report comparatively small relative risks, the findings of relative
risks well in excess of the 1.5 to 2 criterion noted by commenters for
earlier studies of high PM episodes, as well as the relative risks of
1.5 to 5 reported in more recent studies of less serious, but still
important effects categories, lend credibility to EPA's interpretation
of the results.
In addition to basing their conclusions primarily on their own
assessment of a limited set of studies, this group of commenters
reached different conclusions about the consistency of the observed
associations because of their assumptions that all model building
strategies by all authors are equally valid. Even the most thorough of
these treatments (Gamble and Lewis, 1996) shared this flaw,
particularly in the discussion of the series of Philadelphia mortality
studies and in the discussion of modeling approaches. The authors'
treatment of modeling and confounding issues was further limited
because they did not include the most recent Philadelphia results
(Samet et al., 1996a,b) sponsored by the Health Effects Institute (HEI,
1997). One of the important functions of the Criteria Document is to
evaluate the strengths and limitations of various studies. As discussed
more fully below in this unit, the Criteria Document found that some of
the studies cited by commenters as suggesting a lack of consistency had
important limitations. In general, these commenters' analyses suffered
by ignoring the much more thorough critical review of these studies and
issues contained in the Criteria Document, notably that in section 12.6
on alternative modeling approaches.
EPA also rejects the notion advanced by these commenters that
epidemiological studies must use personal exposure monitoring to be
considered for regulatory purposes. In particular, commenters ignore
the significant strengths of the time-series studies and prospective
cohort studies relied on by EPA as compared to cross-sectional
epidemiological studies. Time-series studies, such as the daily
mortality studies, look at changes in response rate in relation to
changes in weather and air pollution over time intervals of a few days.
This controls for other factors such as smoking and socioeconomic
status, which are little changed during such short intervals.
Prospective cohort studies (e.g., Pope et al., 1995; Raizenne et al.,
1996), on the other hand, look at changes in health status in a
selected cohort of individuals, which allows direct adjustment for
smoking status, socioeconomic status, and other subject-specific
factors. The commenters also ignore the Criteria Document conclusions
on how properly conducted monitoring can provide an adequate index of
population exposure to ambient air pollution in such studies that, as
detailed below, is more relevant to establishing ambient air quality
standards (U.S. EPA 1996a, chapter 7). Although personal monitoring may
be practical for some occupational and epidemiological studies, and has
been employed in some past studies of air pollution, it is not
realistic to require personal monitors in air pollution studies of
daily mortality, which require urban scale population data over a
period of years. Furthermore, the use of community monitoring-based
epidemiological studies as a basis for establishing standards and
guidelines has a long history in air pollution, including the British
authorities' response to the London episodes and the establishment of
the original U.S. NAAQS in 1971. Rejecting the use of the vast array of
such studies on this basis alone would also go against the advice of
the independent scientific experts on every CASAC panel that has
addressed the subject of PM pollution through the years, each of which
has recommended general PM standards based primarily on the results of
community epidemiological studies (Friedlander, 1982; Lippmann, 1986;
Wolff, 1996b). As noted above in this unit, EPA has included a more
detailed discussion of its responses to these comments in the Response
to Comments.
b. Specific comments on epidemiologic studies. The second group of
commenters noted above made more specific challenges to EPA's
assessment of the epidemiological studies. These comments, although
overlapping some of those made by the first group, were generally made
by commenters who have taken a more active role in the review of the
Criteria Document and Staff Paper. These commenters asserted that the
epidemiological evidence on PM is not as consistent and coherent as EPA
has claimed, and, in particular, charged that EPA ignored or downplayed
a number of studies that the commenters argue contradict the evidence
the Agency cited as supporting the consistency and coherence of PM
effects. The studies, all of which commenters contend do a better job
of addressing one or more key issues, such as confounding pollutants,
weather, exposure misclassification, and model specification, than
earlier studies, include several that were available during preparation
of the Criteria Document, and a number that appeared after the Criteria
Document and Staff Paper were completed. Because the status of the
later studies differ from that of the earlier ones for purposes of
decisions under section 109 of the Act, the two categories are
discussed separately below in this unit. Additional responses to
comments relating to both sets of studies have been included in the
Response to Comments. In addition to the inclusion of specific studies,
commenters also raised other issues regarding the limitations of the
[[Page 38660]]
epidemiological information and the use of these studies in EPA's two-
city risk assessment. Both of these topics are also discussed below in
this unit.
(i) Studies available for inclusion in the criteria review. With
some exceptions, most of the above commenters cited somewhat similar
lists of ``negative'' studies that they argue EPA ignored or downplayed
in arriving at conclusions on consistency and coherence. Of the most
commonly cited studies, the following were available for inclusion in
the Criteria Document: daily mortality studies by Styer et al. (1995),
Lyon et al. (1995), Li and Roth (1995), Moolgavkar (1995a,b), Wyzga and
Lipfert (1995), Lipfert and Wyzga (1995), and Samet et al. (1995,
1996a,b); the long-term exposure mortality study by Abbey et al.
(1991); and the re-examination of the Six-City mortality results
(Dockery et al., 1993) by Lipfert (1995).
The written record of EPA's evaluations of these studies
effectively refutes the claim that the Agency ignored any of these
studies and supports the treatment the Agency accorded to each of them.
All of the studies available to EPA at the time of CASAC closure on the
PM Criteria Document (March 1996) were examined for inclusion in the
Criteria Document and Staff Paper, which form the basis for the PM
proposal. ``Negative''10 studies were evaluated in detail
along with ``positive'' studies when they were found to have no
critical methodological deficiencies, or to point out strengths and
limitations. Studies that had more serious problems were generally
discussed in less detail, whether positive or negative, than studies
with fewer or small deficiencies. The EPA assessments were evaluated by
peer reviewers, by CASAC, and by the public.
---------------------------------------------------------------------------
10 The term ``negative'' studies, as used in these comments,
should not be construed to mean those in which there is a negative
effects estimate (either significant or non-significant) for the
nominal cause. As used by these commenters, the term also includes
statistically non-significant positive effect estimates. In other
words, the commenters define ``positive'' studies as including only
those in which the effect estimate is both positive and
statistically significant.
---------------------------------------------------------------------------
Most of the short-term exposure studies cited above in this unit
are reanalyses and extensions of PM/mortality studies that had been
published by other investigators. In general, the Criteria Document
concluded that the most comprehensive and thorough reanalyses were
those in the series conducted for the HEI, which reanalyzed data sets
used in studies from six urban areas in Phase I.A (Samet et al.,
1995)11, with extended analyses for Philadelphia in Phase
I.B (Samet et al., 1996a,b). The most important finding in the HEI
Phase I.A reanalyses of the six areas is ``the confirmation of the
numerical results of the earlier analyses of all six data sets'' (HEI,
1995)12. After replicating the original investigators'
analyses, Samet et al. (1995) also found similar results analyzing the
data using an improved statistical model. The HEI Oversight Committee
found
[I]t is reasonable to conclude that, in these six data sets,
daily mortality from all causes combined, and from cardiovascular
and respiratory causes in particular, increases as levels of
particulate air pollution indexes increase. [HEI, 1995]
It is important to note that these reanalyses by respected
independent scientists confirm the reliability and reproducibility of
the work of the original investigators, particularly in view of the
concerns some commenters have expressed about EPA's reliance on a
number of PM studies published by these authors.
---------------------------------------------------------------------------
11 Data sets were those used in the original studies by Dockery
et al. (1992) for St. Louis and Eastern Tennessee; Pope et al.
(1992) for Utah Valley; Schwartz and Dockery (1992a) for
Philadelphia; Schwartz (1993) for Birmingham; and a portion of the
Santa Clara data from Fairley (1990). The data set from the
Moolgavkar et al. (1995a) Philadelphia reanalysis was also included
(Samet et al., 1995).
12 The HEI Board of Directors appointed an eight member
Oversight Committee consisting of leading scientists in several
disciplines relevant to air pollution epidemiology to oversee key
aspects of the project and to prepare HEI's assessment of the
results.
---------------------------------------------------------------------------
The Phase I.A HEI results for Philadelphia also found that it was
difficult to separate the effects of PM from those of co-occurring
SO2, in agreement with the Moolgavkar et al.(1995a)
analysis. Subsequent HEI work, and several of the other so-called
``negative'' studies cited above in this unit, further examined this
issue in terms of confounding or effects modification by one or more
co-occurring gaseous pollutants or weather. Contrary to commenters'
claims, this issue and these studies received considerable attention in
the Criteria Document and Staff Paper, and the overall implications and
conclusions from these assessments were summarized in the proposal. In
particular, the so-called ``negative'' and other findings of
Moolgalvkar et al. (1995a,b) in their Philadelphia and Steubenville
studies were discussed in great detail in section 12.6 of the PM
Critera Document and compared to those of the original investigators
(Schwartz and Dockery, 1992a,b) and other investigators (Li and Roth,
1995; Wyzga and Lipfert, 1995). Further analytical studies of the
Philadelphia data set were carried out by HEI (Samet et al., 1996a,b)
and have largely resolved many of the uncertainties in the earlier
analyses; in EPA's opinion, these studies supersede the results of the
original investigators (Schwartz and Dockery, 1992a) and the several
earlier reanalyses, including Moolgavkar (1995a), Moolgavkar and
Luebeck (1996), Li and Roth (1995), Wyzga and Lipfert (1995), and Samet
et al. (1995). Even though TSP is not the best PM indicator for health
effects, since it includes a substantial fraction of non-thoracic
particles, the extended Criteria Document assessment (U.S. EPA, 1996a,
pp. 12-291 to -299; 12-327) of the Phase I.B HEI analyses in
Philadelphia (Samet et al., 1996a,b) serves to support the following
findings:
(1) The mortality effects estimates for TSP do not depend heavily
on statistical methods when appropriate models are used.
(2) Estimated PM effects are not highly sensitive to appropriate
methods for adjusting for time trends and for weather.
(3) Air pollution has significant health effects above and beyond
those of weather.
(4) Copollutants such as ozone, CO, and NO2 may be
important predictors of mortality, but their effects can be
substantially separated from those of TSP and SO2.
(5) The health effects of TSP in Philadelphia cannot be completely
separated from SO2, which is itself a precursor of fine
particles, based solely on the epidemiological analyses in this single
city.
The most recent HEI Oversight Committee comments on these studies
(HEI, 1997), which were submitted to the docket by HEI, state that:
Although individual air pollutants (TSP, SO2, and
ozone) are associated with increased daily mortality in these data,
the limitations of the Philadelphia data make it impossible to
establish that particulate air pollution alone is responsible for
the widely observed associations between increased mortality and air
pollution in that city. All we can conclude is that it appears to
play a role. [HEI, 1997; p.38.]
While recognizing the limitations in the conclusions that can be made
based on studies in a single city, the Oversight Committee endorses the
approach taken by EPA in evaluating a broader set of epidemiological
studies:
Consistent and repeated observations in locales with different
air pollution profiles can provide the most convincing
epidemiological evidence to support
[[Page 38661]]
generalizing the findings from these models. This has been the
approach reported by the EPA in its recent Criteria Document and
Staff Paper. [HEI, 1997; p. 38.]
As noted in the proposal, based on this approach, EPA's assessment
of numerous mortality studies concludes that when studies are evaluated
on an individual basis, the PM-effects associations are valid and, in a
number of studies, not seriously confounded by co-pollutants (U.S. EPA,
1996a; p. 13-57); and when a collection of studies from multiple areas
with differing concentrations of PM and co-pollutants are examined
together, the association with PM10 remains reasonably
consistent across a wide range of concentrations of these potentially
influential pollutants (U.S. EPA, 1996a; p. 12-33; U.S. EPA, 1996b; p.
V-55).
In addition to relying on the most comprehensive and best analyses
in evaluating the reanalysis in Philadelphia and other areas, the
Criteria Document gave less weight to both so-called ``negative'' and
``positive'' studies with methodogical limitations. In particular, EPA
agreed with the epidemiological experts on CASAC (Lippmann et al.,
1996; Samet, 1995) that the Li and Roth (1995) study approach of using
a ``panoply'' of different modeling strategies to produce seemingly
conflicting findings provides little useful insight and is superseded
by the HEI report. The attempt by Lipfert and Wyzga (1995) to address
relative effects of different pollutants was considered inconclusive
(Lippmann et al., 1996) and flawed by the use of a metric (elasticity)
that ignores the absolute concentrations of the pollutants being
compared (see Response to Comments).
Further, the Steubenville studies and reanalyses (Schwartz and
Dockery, 1992b; Moolgavkar, 1995b) were discussed in detail to examine
methodologies, and the differences in relative risks between the two
were regarded as small (U.S. EPA, 1996a, p. 12-280 to 283). Both
studies used TSP as the PM indicator variable, and they are augmented
by the more recent findings of Schwartz et al. (1996) that examine
PM10 and its components. The mixed results by Lyon et al.
(1995) in Utah Valley are compromised by loss of information related to
the methodology (U.S. EPA, 1996a, p. 12-58). As noted above, subsequent
reanalyses of the Utah Valley study by HEI (Samet et al., 1995) as well
as by Pope and Kalkstein (1996) confirmed the original findings of Pope
et al. (1992) using different model specifications. The Salt Lake City
study by Styer et al. (1995) was mentioned in the PM Criteria Document,
but received little discussion because aspects of the methodological
approach limited its statistical power to detect effects. The analysis
of Chicago mortality data in the same paper shared these problems,
particularly for seasonal analyses; in this larger city, they
nonetheless found significant associations on an annual basis between
PM10 and mortality that are consistent with other studies.
In short, the record shows that EPA did not ignore these short-term
exposure studies cited by commenters; moreover, EPA's assessment of
these studies is consistent with the views of four researchers on the
CASAC panel who have extensive involvement in conducting population
studies of air pollution (Lippmann et al., 1996).13
---------------------------------------------------------------------------
13 Their March 20, 1996 letter to the Administrator concludes
that the HEI analysis of Philadelphia supersedes earlier analyses,
specifically Moolgavkar et al. (1995a), Lipfert and Wyzga (1995),
and Li and Roth (1995), and points out the limitations of Styer et
al. (1995).
---------------------------------------------------------------------------
Similarly, EPA believes that appropriate treatment and weight were
given to studies of long-term exposure and mortality. EPA concluded
that the lack of associations in the Abbey et al. (1991) prospective
cohort study were not inconsistent with two other such studies because
the use of days of peak TSP levels as the PM indicator (instead of
PM10 or PM2.5) is inappropriate for California
cohorts exposed to both urban smog and fugitive dust episodes, and the
overall sample size may have been too small to detect significant
effects (U.S. EPA, 1996b; pp. V-17 to -18). The inadequacy of Lipfert's
(1995) application of state-wide average sedentary lifestyle data to
adjust mortality for the six cities studied by Dockery et al. (1993),
in which superior subject-specific body mass index data had already
been considered, was also noted and addressed in the Staff Paper (U.S.
EPA, 1996b; p. V-16). Again, EPA did not ignore these studies; the
rationale for giving them less weight was clearly articulated in the
documents reviewed by CASAC and judged appropriate for use in standard
setting.
While the proposal presents only a summary discussion of key
Criteria Document and Staff Paper findings, EPA believes that
discussion is fully consistent with the state of the science.
Furthermore, the proposal highlights the nature of alternative
viewpoints on the epidemiology in a quotation from the Criteria
Document (61 FR 65644, December 13, 1996) and cites explicitly the
views of most of the authors noted above in this unit (Moolgavkar et
al., 1995b; Moolgavkar and Luebeck, 1996; Li and Roth, 1995; Samet et
al., 1996; Wyzga and Lipfert, 1995). The proposal also summarizes EPA
conclusions based on all of the literature as assessed in the Criteria
Document and Staff Paper with respect to issues raised in these and
other studies, including potential confounding by independent risk
factors such as weather and other pollutants, choice of statistical
models, use of outdoor monitors, and exposure misclassification.
More specifically, in the proposal EPA has not ignored the view
advanced by some that the results of individual studies of multiple
pollutants, such as the HEI Philadelphia studies, are more suggestive
of an ``air pollution'' effect than an effect of PM alone. Indeed, the
proposal notes that it is reasonable to expect that other pollutants
may play a role in modifying the magnitude of the estimated effects of
PM on mortality, either through pollutant interactions or independent
effects (61 FR 65645, December 13, 1996). Based on the large body of
evidence at hand, however, EPA cannot accept the suggestion that such
multi-pollutant studies are in any way ``negative'' with respect to
EPA's conclusions that PM, alone or in combination with other
pollutants, is associated with adverse effects at levels below those
allowed by the current standards. This conclusion is based not only on
the consistency of PM effects across areas with widely varying
concentrations of potentially confounding copollutants, but also on the
extended analyses of the Philadelphia studies in the Criteria Document
and Staff Paper.
Because commenters have tended to ignore the latter analyses, it is
appropriate to summarize them here briefly. As noted above in this
unit, the Criteria Document assessment of the Philadelphia studies
finds that PM can reasonably be distinguished from potential effects of
all pollutants except SO2. The Staff Paper builds on this
analysis through an integrated assessment that draws on information
from atmospheric chemistry, human exposure studies, and respiratory
tract penetration results to provide insight as to which of these two
pollutants is more likely to be responsible for mortality in the
elderly and individuals with cardiopulmonary disease (U.S. EPA 1996b;
pp. V-46 to -50). That assessment notes that the inhalable
(PM10), including the fine (PM2.5), components of
TSP are more likely than SO2 to penetrate and remain indoors
where the sensitive population resides most of the time.14
In addition, these PM
[[Page 38662]]
components, especially PM2.5, penetrate far more effectively
to the airways and gas exchange regions of the lung than does
SO2. Furthermore, in Philadelphia, it is possible that
SO2 is a surrogate for fine particulate acid sulfates. For
these reasons, even though statistical analyses of the Philadelphia
data set cannot fully distinguish between these two highly correlated
pollutants, EPA believes that the weight of the available evidence from
an integrated assessment more strongly supports the notion that PM is
playing an important direct role in the observed mortality effects
associations in Philadelphia. Moreover, as noted above in this unit, in
some other locations with significant PM-mortality associations,
ambient SO2 levels are too low to confound PM.
---------------------------------------------------------------------------
14 In response to comments on this rulemaking, some papers
submitted by industry commenters make statements that are in
substantial agreement with these staff conclusions with respect to
the likelihood of SO2 penetrating to indoor environments
and the lesser likelihood of affecting sensitive populations indoors
(Lipfert and Wyzga, 1997; Lipfert and Urch, 1997).
---------------------------------------------------------------------------
(ii) Recent studies available after completion of criteria review.
As noted above in this unit, other studies cited by some commenters as
so-called ``negative'' evidence ignored by EPA were published or
otherwise made available only after completion of the PM Criteria
Document. EPA agrees that it did not rely on these studies, based on
its long-standing practice of basing NAAQS decisions on studies and
related information included in the pertinent air quality criteria and
available for CASAC review.15 Although EPA has not relied on
such studies in this review and decision process, the Agency
nevertheless has conducted a provisional examination of these and other
recent studies to assess their general consistency with the much larger
body of literature evaluated in the Criteria Document.16 EPA
has placed its examination of recent studies in the rulemaking docket.
---------------------------------------------------------------------------
15 Since the 1970 amendments, the EPA has taken the view that
NAAQS decisions are to be based on scientific studies that have been
assessed in air quality criteria [see e.g., 36 FR 8186 (April 30,
1971) (EPA based original NAAQS for six pollutants on scientific
studies discussed in the air quality criteria and limited
consideration of comments to those concerning validity of scientific
basis); 38 FR 25678, 25679-25680 (September 14, 1973) (EPA revised
air quality criteria for sulfur oxides to provide basis for
reevaluation of secondary NAAQS)]. This longstanding interpretation
was strengthened by new legislative requirements enacted in 1977
(section 109(d)(2) of the Act; section 8(c) of the Environmental
Research, Development, and Demonstration Authorization Act of 1978)
for CASAC review of air quality criteria and reaffirmed in EPA's
decision not to revise the ozone standards in 1993. 58 FR 13008,
13013-13014 (March 9, 1993). Some of the commenters now criticizing
EPA for not considering the most recent PM studies strongly
supported the Agency's interpretation in the 1993 decision (UARG,
1992).
16 As discussed in EPA's 1993 decision not to revise the NAAQS
for ozone, new studies may sometimes be of such significance that it
is appropriate to delay a decision on revision of NAAQS and to
supplement the pertinent air quality criteria so the new studies can
be taken into account. 58 FR at 13014, March 9, 1993. In the present
case, EPA's provisional examination of recent studies suggests that
reopening the air quality criteria review would not be warranted
even if there were time to do so under the court order governing the
schedule for this rulemaking. Accordingly, EPA believes that the
appropriate course of action is to consider the newly published
studies during the next periodic review cycle.
---------------------------------------------------------------------------
Among the most frequently cited new studies relied on by commenters
were Davis et al. (1996), Moolgavkar et al. (1997), and Roth and Li
(1997). Davis et al. (1996) conducted a reanalysis of the Birmingham
mortality data set originally investigated in Schwartz (1993). At the
time of the close of the public comment period, the paper based on this
manuscript had not been accepted for publication in a peer reviewed
journal (Sacks, 1997). Commenters nevertheless highlight the authors'
claim that ``when humidity is included among the meteorological
variables (it is excluded in the analysis by Schwartz [1993]), we find
that the PM10 effect is not statistically significant.''
EPA's review found important factual errors in this study. Contrary to
Davis et al., Schwartz did include humidity in his 1993 study, and his
finding of a hot-and-humid-day effect was reported there. In addition,
the PM-related variables used by Davis et al. in their manuscript were
not, as the authors claimed, the same as those in Schwartz (1993).
Davis et al. also used a different humidity indicator, specific
humidity. Reanalysis by one of the co-authors (R. Smith, personal
communication, February 8, 1997) showed that when Schwartz's PM metric
was used, the estimated PM10 effect was of about the same
magnitude, and statistically significant at the 0.05 level, even using
the characterization of humidity effect proposed by Davis et al. It
therefore appears that the Davis et al. PM10 result was, in
fact, consistent with that of Schwartz, and robust against a very
different weather model specification.
Based on its examination of both the content and the publication
status of this study, EPA believes the heavy reliance and attention
given to it are misguided. In contrast to commenters' assertions, this
study does not contradict EPA's conclusions with respect to consistency
of the epidemiological evidence and confounding by weather variables;
indeed, the consideration of the corrected results would actually
support EPA's conclusions. EPA believes this example reinforces the
importance of relying on peer reviewed studies and also conducting the
kind of critical examination of such studies that takes place in the
criteria and standards review process.
Several commenters note that Roth and Li (1997) also reexamined the
Birmingham mortality data, as well as hospital admissions data from
Schwartz (1994), and produced a number of negative and inconsistent
results that depend on temperature effects and choice of statistical
model. Preliminary findings from this study were presented by Roth at
the May 1996 CASAC meeting. CASAC epidemiologists and statisticians at
the meeting pointed out a number of shortcomings, both in the
analytical strategy and in details of the models being
evaluated.17 As discussed in more detail in the Response to
Comments, the materials from Roth and Li (1997) recently provided to
EPA as attachments to public comments show that the deficiencies
pointed out at the May 1996 CASAC meeting have not been adequately
addressed. EPA concludes that this study does not support commenters'
claims.
---------------------------------------------------------------------------
17 For example, commenting on the Roth examination of
alternative model specifications, Dr. Stolwijk noted ``If you select
out of his [Roth's] matrix the things that other people have done,
he comes to a different conclusion than when he takes his whole
matrix * * *. [Y]ou are going to get a random effect that shows that
there is no effect. He [Roth] did this, I think, on purpose in this
case. Most epidemiologists, I think, have been trained to limit
their observations to something that they can state or would have
stated before they started and observe that and base their
conclusions on it'' [U.S. EPA 1996(c); May 17, 1996 Transcript,
pages 45-46].
---------------------------------------------------------------------------
The paper recently accepted for publication by Moolgavkar et al.
(1997) examines hospital admissions and air pollution in Minneapolis
and Birmingham and comes to different conclusions than earlier
investigators with respect to the role of PM10. While the
paper is a useful addition to the literature, the authors clearly do
not attempt to replicate the original studies, making the kind of
direct comparisons suggested by commenters difficult. The paper finds
an air pollution effect in one city that implicates ozone but is unable
to separate effects of PM from a group of other pollutants. EPA's
provisional examination of this study raises some questions about the
methodology, which might usefully be supplemented to further separate
pollutants as was done by Samet et al. (1996a,b) in Philadelphia, and
about the authors' interpretation of the results in both cities. In any
event, EPA does not believe this study negates the PM associations with
hospital admissions
[[Page 38663]]
reported in a number of other studies cited in the Criteria Document.
Another recent paper by Lipfert and Wyzga (1997) provides analyses
suggesting that differential measurement error might account for some
or all of the observation by Schwartz et al. (1996) that daily
mortality is more strongly associated with fine (PM2.5) than
with coarse (PM10-2.5) PM. EPA staff and CASAC accounted for
this possibility, however, and it was factored into both the Staff
Paper and CASAC recommendations.18
---------------------------------------------------------------------------
18 CASAC panelists recommended a discussion of this issue in the
Staff Paper. The Staff Paper notes: ``While greater measurement
error for the coarse fraction could depress a potential coarse
particle effect, this would not explain the results in Topeka
relative to other cities. Even considering relative measurement
error, these results provide no clear evidence implicating coarse
particles in the reported effects.'' (U.S. EPA, 1996b p. V-64).
EPA's provisional examination of the Lipfert and Wyzga (1997) paper
in the Response to Comments, finds that it is implausible that most
of the effect attributed to PM2.5 could in fact be due to
PM10-2.5, since differential measurement error cannot
make a weaker effect appear stronger than a stronger one, except
under extremely unusual circumstances.
---------------------------------------------------------------------------
Some commenters have highlighted selected individual papers or
summaries from the APHEA19 project conducted in Europe, and
from Roth (1996), calling attention particularly to negative results
found in heavily polluted regions of Eastern Europe. EPA notes that a
number of the recent APHEA and other studies in Western Europe have
shown significant associations between mortality and air pollution
including PM, and that a meta-analysis of 12 Western and Central-
eastern European studies ``is supportive of a causal association
between PM and SO2 exposure and all-cause mortality''
(Katsouyanni et al., 1997). The Eastern and Western European studies
used differing measurement methods for PM, including PM10,
gravimetric ``suspended particles,'' and the British Smoke
method.20 The differences in aerometry and the substantial
differences in location and strength of primary PM emissions sources in
central and eastern Europe as compared to western Europe or the U.S.
might well explain the different results in these unique areas.
Consequently, integration of these results would involve comprehensive
examination of the various PM instruments used, monitor siting in
relation to sources, mass calibration procedures and other aspects of
these studies.21 EPA notes that a number of European
authorities, who are familiar with this recent literature, have
proceeded with recommendations to strengthen their health guidelines,
risk assessments, or regulations for PM.22
---------------------------------------------------------------------------
19 The APHEA (Air Pollution and Health: a European Approach)
project was supported by the European Union Environment 1991-1994
Programme to investigate the possible short-term health effects of
exposure to low or moderate levels of ambient air pollutants. Eleven
European research groups carried out studies in 15 cities
(Amsterdam, Athens, Barcelona, Bratislava, Cracow, Helsinki, Koln,
Lodz, London, Lyon, Milan, Paris, Poznan, Rotterdam and Wroclaw) in
which air pollutant concentration data had been collected for at
least 5 years. Initial findings of studies on mortality and hospital
admissions were published in a series of papers in Supplement 1 to
the Journal of Epidemiology and Community Health in 1996 and a meta-
analysis of the mortality data from 12 cities is currently in press
(Katsouyanni et al., 1997).
20 The Roth et al. (1997) study in Prague used a measurement
termed ``suspended particles'' that appears to be close to TSP. The
relation of this indicator to PM10 or PM2.5 in
this city is not reported. Moreover, this study uses a variant of
the problematic methodology in the Roth analyses cited above.
21 These concerns are consistent with EPA's treatment of a
number of European and South American studies that are included in
the Criteria Document and contributed to the evaluation of the
epidemiology in Chapter 12. Because of differences in aerometry
methods and characteristic source classes between North America and
other regions of the world, however, the integrative assessment
chapter reported results only from studies conducted in the U.S. and
Canada (cf. Tables 13-3 to 13-5) in reaching quantitative
conclusions for effects estimates.
22 See, for example, the United Kingdom Air Quality Strategy,
1997; Swiss Federal Commission of Air Hygiene, 1996; World Health
Organization Revised Air Quality Guidelines for Europe, In Press).
---------------------------------------------------------------------------
Aside from the recent literature cited by these commenters, there
are a number of other recent epidemiological studies that, if
considered in today's decision, would tend to support EPA's conclusions
about the effects of PM at lower concentrations, assuming their results
were accepted following a full review in the criteria and CASAC
process. For example, in addition to the APHEA studies, several other
recent epidemiologic studies have reported significant positive
associations between PM and health effects (Lipsett et al., 1997;
Peters et al., 1997; Borja-Aburto et al., 1997; Delfino et al., 1997;
Scarlett et al., 1996; Woodruff et al., 1997; Wordley et al., 1977). In
addition, a number of recent toxicologic papers have been accepted or
appear in proceedings (Costa and Dreher, 1997; Killingsworth et al.,
1997; Godleski et al., 1997) that involve exposure to concentrated
ambient fine particles or PM constituents and appear to provide
supportive evidence as to the plausibility of the effects that have
been reported epidemiologically. If considered in this decision, these
studies would also provide biological support for the epidemiological
observation that certain susceptible groups (notably those with
cardiopulmonary disease) are most likely to be affected by PM, again
assuming the results were sustained in the full criteria and CASAC
review process.
In summary, EPA has conducted a provisional assessment of the more
recent scientific literature. Based on this provisional assessment, EPA
disagrees with commenters' assertion that full consideration of
selected new studies in this decision would materially change the
Criteria Document and Staff Paper conclusions on the consistency and
coherence of the PM data, or on the need to revise the current
standards.
(iii) Other specific comments on the epidemiological studies. Aside
from their assertion that EPA ignored or downplayed particular studies,
this second group of commenters raise additional objections, based on
the statistical modeling strategies used and the potential importance
of personal exposure misclassification, to EPA's conclusions regarding
the consistency of the epidemiological evidence. EPA conclusions on
these topics were summarized in the proposal and supported by extensive
treatments in the Criteria Document and Staff Paper. With respect to
the first issue, commenters argued that sufficient flexibility exists
in the analyses of large data sets that it may be possible to obtain
almost any result desired through choice of statistical method.
Analytical choices include the specific statistical model; methods used
to adjust for seasonal variation and the trends in the data; treatment
of other variables (e.g., other pollutants, weather, and day of week);
``lag'' structure; and study population.
A more detailed discussion of this issue, which expands on the
assessment summarized in the Criteria Document, is included in the
Response to Comments. In summary, EPA must reject commenters'
contention that legitimate alternative analyses can obtain ``almost any
result.'' As outlined above in this unit, EPA's detailed reviews of
individual studies have shown that not all methods are equally valid or
legitimate. Moreover, strong arguments can be made that the methods and
analytical strategies in the studies EPA relied upon are more
appropriate approaches than those cited by commenters (e.g., Li and
Roth, 1995; Lipfert and Wyzga, 1995; Davis et al., 1996; Roth and Li,
1997). While not all studies have addressed each of the above issues in
this unit equally well, the most comprehensive analyses of these issues
(e.g., Samet et al., 1995, 1996a,b; Pope and Kalkstein, 1996), as well
as the EPA analyses comparing study results for each issue (U.S. EPA,
1996a, pp. 12-261 to 12-305) found that the authors of studies on which
EPA
[[Page 38664]]
chiefly relied made appropriate modeling choices. The Criteria Document
concludes that: ``[T]he largely consistent specific results, indicative
of significant positive associations of ambient PM exposures and human
mortality/morbidity effects, are not model specific, nor are they
artifactualy derived due to misspecification of any specific model. The
robustness of the results of different modeling strategies and
approaches increases our confidence in their validity [U.S. EPA, 1996a,
p. 13-54].'' While it is true, as evidenced in Li and Roth (1995), that
PM-effects data can be randomly manipulated to produce apparently
conflicting results, commenters have provided no evidence that
different plausible model specifications could lead to markedly
different conclusions.
Some commenters have expressed concerns about the reliability of
the epidemiological results because some studies showed a lack of
correlation in cross-sectional comparisons between outdoor PM measured
at central locations and indoor or personal exposures to PM (which
includes PM from the outdoor, indoor and personal
environments).23 EPA acknowledged and responded to this
issue in chapter 7 of the Criteria Document and the proposal (61 FR
65645, December 13, 1996). The major premise underlying commenters'
arguments on this issue is incorrect.24 The question is not
whether central monitoring site measurements contain a signal
reflecting actual exposures to total PM from both outdoor and indoor
sources at the individual level; the relevant question is whether
central monitoring site measurements contain a signal reflecting actual
exposures to ambient PM for the subject population, including both
ambient PM, while individuals are outdoors, and ambient PM that has
infiltrated indoors, while individuals are indoors. The PM standards
are intended to protect the public from exposure to ambient PM, not PM
generated by indoor or personal sources. There is ample evidence, as
discussed in chapter 7 of the Criteria Document, that personal exposure
to ambient PM, while outdoors and while in indoor micro-environments,
does correlate on a day-to-day basis with concentrations measured at
properly sited central monitors (U.S. EPA, 1996a, p. 1-10). EPA has,
therefore, concluded that it is reasonable to presume that a reduction
in ambient PM concentrations will reduce personal exposure to ambient
PM, and that this will protect the public from adverse health outcomes
associated with personal exposure to ambient PM.
---------------------------------------------------------------------------
23 Paradoxically, some commenters have argued (e.g., Valdberg,
1997) that the PM results are confounded because the weather and
other factors that cause daily variations in outdoor pollution will
cause similar daily variations in indoor generated air pollution.
For this to be true, outdoor ambient pollution concentrations would
have to be correlated with personal exposure to indoor generated air
pollution such as that from smoking, cleaning, and cooking. This
argument is logically inconsistent with the other comments on the
lack of any such correlation with personal exposure, and these
commenters have offered no scientific evidence to support their
claim. In response, EPA has performed and included in the Response
to Comments a numerical analysis of the relevant information from
the PTEAM exposure study that finds no evidence for such a
correspondence in the actual data.
24 As documented in Chapter 7 of the Criteria Document, time-
series community studies observe the effects of varying levels of
ambient air pollution; therefore the effects of indoor-generated air
pollution would be independent of and in addition to the effects
found in these epidemiological studies. Commenters apparently
believe EPA is claiming such studies are detecting the effects of
daily variations in total PM personal exposure from indoor and
outdoor sources. This misunderstanding is evidenced, for example, by
Wyzga and Lipfert's (1995) treatment of the difference between
ambient monitors and actual personal exposures as ``exposure
errors'' and Brown's comment for API that ``if (ambient) PM is
causally related to mortality/morbidity, then it is personal PM
exposure that must be reduced to have an effect.'' On the contrary,
it is personal exposure to ambient PM that must be reduced to
address the risk identified in community air pollution studies. Any
lack of significant correlation between outdoor PM concentrations
and personal exposure to total PM from all sources is irrelevant,
except to the extent it may decrease the power of time-series
studies to detect the effects of ambient pollution.
---------------------------------------------------------------------------
Commenters have also restated theoretically based concerns on a
related issue, namely errors in the measurement of the concentrations
of air pollutants, that was summarized in the proposal. In multiple
pollutant analyses, measurement error or, more generally, exposure
misclassification, could theoretically bias effects estimates of PM or
co-pollutants in either direction, introducing further uncertainties in
the estimated concentration-response relationships for all pollutants
(U.S. EPA, 1996b, pp. V-39 to V-43). Relevant insights on this issue in
material appended to public comments (Ozkaynak and Spengler, 1996) have
prompted an expanded statistical analysis of the conditions under which
such errors could inflate the magnitude of the effects estimates or the
significance of PM relative to gaseous pollutants, as has been
suggested by Lipfert and Wyzga (1995). This analysis, which is
summarized in the Response to Comments, finds that the conditions under
which measurement error could inflate the effects estimates or
significance of PM relative to other pollutants are restricted to a
limited set of statistical relationships. Commenters have not provided
evidence that suggest such conditions are likely to occur with respect
to the measurement of ambient PM in relation to those for gaseous co-
pollutants commonly used in epidemiological studies.25
Therefore, it appears unlikely that measurement and exposure errors for
PM and other pollutants have inflated the estimated effects of PM, even
in multivariate analyses. More importantly, the available evidence on
the consistency of the PM-effects relationships in multiple urban
locations, with widely varying indoor/outdoor conditions and a variety
of monitoring approaches, makes it less likely that the observed
associations of PM with serious health effects at levels allowed under
the current NAAQS are an artifact of errors in measurement of pollution
or of exposure (U.S. EPA 1996b, pp. V-39 to V-43).
---------------------------------------------------------------------------
25 The EPA analysis finds that in order for measurement errors
in one pollutant variable to significantly bias the estimated effect
of another pollutant, three conditions are necessary: (1) The
measurement error in the poorly measured pollutant must be very
large, roughly at least the same size as the population variability
in that pollutant; (2) the poorly measured pollutant must be highly
correlated with the other pollutant, either positively or
negatively; and (3) the measurement errors for the two pollutants
must be highly negatively correlated (Response to Comments, Appendix
D). This important factor was not considered in Lipfert and Wyzga
(1995) or by commenters.
---------------------------------------------------------------------------
(iv) Comments on the PM risk assessment. As noted in the proposal,
uncertainties about measurement errors, exposure misclassification, and
the relative effects of copollutants are more important to the
quantitative estimates of risk associated with PM than to the existence
of valid PM-effects associations at levels found in recent studies. A
number of commenters argued that EPA's risk assessment is flawed and
incomplete. Chief among the reasons they advanced is that the
assessment is based on the same epidemiological studies these
commenters argued are inadequate for the reasons summarized and
responded to above. Specific comments also addressed the extent to
which the risk assessment might overstate risk estimates because it
assumes a linear no-threshold relationship and the use of studies that
might inflate PM risk due to inadequate consideration of co-pollutants
and other potential confounders. The full risk assessment acknowledges
these issues and uncertainties, however, and it illustrates the
potential influence of such uncertainties in sensitivity analyses (U.S.
EPA 1996b; chapter 6, appendix F; Abt Associates, 1996a,b; 1997a,b).
For example, Figure 2c in the proposal (61 FR 65653, December 13, 1996)
[[Page 38665]]
illustrates the potential influence of what appears to be the most
significant uncertainty in current information, whether a population
threshold exists below which the effects of PM no longer occur (61 FR
65653, December 13, 1996). EPA notes that a full consideration of the
uncertainties, including the analysis summarized above on measurement
error, suggests that the epidemiological studies might well have
understated the total effects of air pollution; thus, both the
direction and the extent of any bias in the risk estimates are less
clear than commenters suggest.
EPA believes that, even recognizing the large uncertainties, the
key qualitative insights derived from the risk assessment and
summarized in Unit II.A.3. of this preamble remain appropriate. While
not placing great weight on the specific numerical estimates, EPA
believes that the risk analysis confirms the general conclusions drawn
primarily from the epidemiological results themselves, that there is
ample reason to be concerned that exposure to ambient PM at levels
allowed under the current air quality standards presents a serious
public health problem.
3. Key considerations informing the decision. Having carefully
considered the public comments on the above matters, EPA believes the
fundamental scientific conclusions on the effects of PM reached in the
Criteria Document and Staff Paper, and restated in the introduction to
this unit, remain valid. That is, the epidemiological evidence for
ambient PM, alone or in combination with other pollutants, shows
associations with premature mortality, hospital admissions, respiratory
symptoms, and lung function decrements. Despite extensive critical
examination in the criteria and standards review, these findings cannot
be otherwise explained by analytical, data, or other problems inherent
in the conduct of such studies. Although the evidence from
toxicological studies available during the criteria review has not
revealed demonstrated mechanisms that explain the range of effects
reported in epidemiological studies, it does not and cannot refute the
observation of such effects in exposed populations. Moreover, the
effects observed in the recent epidemiological studies at lower PM
concentrations are both coherent with each other and plausible based on
the categories of effects observed at much higher concentrations in
historic air pollution episodes, laboratory studies of PM effects at
high doses, and particle dosimetry studies. The consistency of the
results from a large number of locations and the coherent nature of the
observed results suggest a likely causal role of ambient PM in
contributing to the reported effects (U.S. EPA, 1996a; p. 13-1). Many
of the studies showing PM effects were conducted in areas where the
current PM10 standards are largely met, and both the studies
and EPA's risk assessment suggest that the collective magnitude of the
effects reflects a significant public health problem.
For these reasons, and having considered public comments on this
issue, the Administrator concludes that the review of the criteria and
standards provides strong evidence that the current PM10
standards do not adequately protect public health, and that revision of
the standards is not only appropriate, but necessary.
Aside from that conclusion, the appropriateness of continuing to
rely on the use of PM10 as the sole indicator for revised PM
standards is also relevant here. While the basis for decisions on
specific indicators is discussed more fully in Unit II.C. of this
preamble, this issue is related to the Administrator's decision on the
need to revise the standards. Based on both the staff review (U.S. EPA,
1996b, p. VII-3) and the recommendations of some commenters (e.g.,
California EPA), there are two alternative approaches for providing
additional health protection in revising the standards: Adopt tighter
PM10 standards and/or recognize the fundamental differences
between fine and coarse particles and develop separate standards for
the major components of PM10, including fine particles.
Conceptually, the first approach would give weight to comments that
standards should be based on pollutant indicators for which the most
data have been collected, with less consideration of the evidence that
suggests that the current standards provide adequate protection against
the effects of coarse particles, and that tightening the current
PM10 standards in an attempt to control fine particles would
place unnecessary requirements on coarse particles. Because the
PM10 network is in place, a more stringent PM10
standard would also respond to commenters who have expressed a desire
for more immediate implementation of revised standards. The second
approach is based on the view that, in the long run, more effective and
efficient protection can be provided by separately targeting
appropriate levels of controls to fine and coarse PM.
The Staff Paper examined this issue in detail (U.S. EPA 1996b, pp.
VII-3 to VII-11), and concluded that the available information was
sufficient to develop separate indicators for fine and coarse fractions
of PM10, based on the recent health evidence, the
fundamental differences between fine- and coarse-fraction particles,
and implementation experience with PM10. Further, the staff
concluded that:
[C]onsideration of comparisons between fine and coarse fractions
suggests that fine fraction particles are a better surrogate for
those particle components linked to mortality and morbidity effects
at levels below the current standards. In contrast, coarse fraction
particles are more likely linked with certain effects at levels
above those allowed by the current PM10 standards. In
examining alternative approaches to increasing the protection
afforded by PM10 standards, the staff concludes that
reducing the levels of the current PM10 standards would
not provide the most effective and efficient protection from these
health effects. [U.S. EPA 1996b; p. 7-45]
As discussed in Unit II.C. of this preamble, the Administrator
believes that it is more appropriate to provide additional protection
against the risk posed by PM by adding new standards for the fine
fraction of PM10, as opposed to tightening the current
PM10 standards. Although fewer epidemiological studies have
used PM2.5 and other fine particle indicators (e.g.,
sulfates, acids), there are nonetheless significant indications from
the scientific evidence - drawn from the physicochemical studies of PM,
air quality and exposure information, toxicological studies, and
respiratory tract deposition data - that this approach will provide the
most effective and efficient protection of public health.
Several commenters have argued that the decision on whether to
revise the PM standards should be deferred, particularly with regard to
fine particle standards, pending establishment and operation of a
national monitoring network to characterize fine PM and a research
program to reduce uncertainties in the effects information. These
commenters expressed concerns that establishing fine PM standards now
might result in needless regulation of PM components that may be
unrelated to observed health effects. As discussed more fully in Unit
II.F. of this preamble, such commenters recommended, at most, that if
fine PM standards were established, they should be set at a level
``equivalent'' to the current PM standards.
EPA strongly disagrees that the decision on revising the standards
should be delayed to await the results of new PM monitoring and
research programs. Under section 109(d) of the Act, EPA's obligation
after reviewing the
[[Page 38666]]
existing criteria and standards for PM is to make such revisions in the
standards and to promulgate such new standards as are appropriate under
section 109(b) of the Act. Based on her review of the criteria and
standards for PM, the Administrator has concluded that the current
standards are not adequate to protect public health and that revisions
are appropriate. In the face of the available evidence, a delay in
revising the standards would not only be inconsistent with the statute
but -- even under the optimistic assumption that the same extensive
monitoring and strategy assessment as now contemplated would occur in
the absence of a revised standard -- would add approximately 2 years to
the time when significant health benefits can be realized, resulting in
potentially significant numbers of additional premature deaths and even
larger numbers of children and individuals with air pollution-related
illness and symptoms. On the other hand, establishing standards now
will set into motion the development of implementation programs and
monitoring that can be conducted in parallel with additional scientific
research, without undue delays inherent in waiting for the research.
The question of which pollutant components to regulate has been an
issue since the inception of the first PM standards. Other ambient
pollutants (e.g., NO2 or CO) are uniquely defined as
individual chemicals, whether or not they serve as proxies for a larger
class of substances (e.g., ozone as an index of photochemical
oxidants). Regulating general PM, as opposed to multiple chemical
components of PM, raises the spectre of a host of particulate materials
of varying composition, size, and other physicochemical properties, not
all of which are likely to produce identical effects.
Both EPA's past and present regulatory experience with PM control
programs and its successive reviews of the standards have reaffirmed
the wisdom of retaining standards that control particles as a group,
rather than eliminating such standards and waiting for scientific
research to develop information needed to identify more precise limits
for the literally thousands of particle components. Each such decision
recognized the possibility that potentially less harmful particles
might be included in the mix that was regulated, but concluded that the
need to provide protection against serious health effects nonetheless
required action under section 109 of the Act. The success of this
approach is evident in early U.S. control programs that dramatically
reduced ``smoke'' and ``TSP'' in major cities in the 1960's and 1970's
and in the continued improvement in air quality through the current PM
standards. The major refinements that have been recommended through the
course of reviews of PM standards have been to improve the focus of
control efforts by defining scientifically based size classes (i.e.,
moving from TSP to PM10 and now, PM2.5) that will
permit more effective and efficient regulation of those fractions most
likely to present significant risks to health and the environment.
As discussed in Unit II.C. of this preamble, the current review has
examined the available evidence to determine whether it would tend to
support inclusion or exclusion of any physical or chemical classes of
PM, for example sulfates, nitrates, or ultra-fine particles. That
examination concludes that, while both fine and coarse particles can
produce health effects, the fine fraction appears to contain more of
the reactive substances potentially linked to the kinds of effects
observed in the recent epidemiological studies (U.S. EPA 1996b, section
V.F.). However, the available scientific information does not rule out
any one of these components as contributing to fine particle effects.
Indeed, it is reasonable to anticipate that no single component will
prove to be responsible for all of the effects of PM.
EPA recognizes that whether the standards are set for
PM10 only or also for fine particles, there are
uncertainties with respect to the relative risk presented by various
components of PM. In this regard, the Administrator places greater
weight on the concern that by failing to act now, the PM NAAQS would
not control adequately those components of air pollution that are most
responsible for serious effects, than on the possibility they might
also control some component that is not. EPA believes that moving
simultaneously to establish standards based on the best available
scientific evidence and to conduct an aggressive monitoring and
scientific research program designed to help resolve current
uncertainties is a prudent and responsible approach for addressing both
the risks and the uncertainties inherent in this important public
health issue.
In summary, given the evidence that PM-related health effects
appear likely to occur at levels below the current standards, the
serious nature and potential magnitude of the public health risks
involved, and the need to consider the fine and coarse fractions as
distinct classes of particles, the Staff Paper and the CASAC (Wolff,
1996b) concluded that revision of the current standards is clearly
appropriate. Moreover, at their May 1996 public meeting (U.S. EPA,
1996c), and in separate written comments (including Lippmann et al.,
1996), a majority of CASAC panel members recommended revisions that
would strengthen the health protection provided by the current PM
standards. Based on the rationale and recommendations contained in the
Staff Paper and the advice of CASAC, and taking into account public
comments, the Administrator concludes that it is appropriate at this
time to revise the current PM standards to increase the public health
protection provided against the known and potential effects of PM
identified in the air quality criteria.
C. Indicators of PM
In establishing adequately protective, effective, and efficient PM
standards, it is necessary to specify the fraction of particles found
in the ambient air that should be used as the indicator(s) for the
standards. In this regard, EPA concludes that the most recent
assessment of scientific information in the Criteria Document,
summarized in chapters IV and V of the Staff Paper, continues to
support past staff and CASAC recommendations regarding the selection of
size-specific indicators for PM standards. More specifically, EPA
continues to find that the following conclusions reached in the Staff
Paper and in the 1987 review remain valid:
(1) Health risks posed by inhaled particles are influenced both by
the penetration and deposition of particles in the various regions of
the respiratory tract and by the biological responses to these
deposited materials.
(2) The risks of adverse health effects associated with deposition
of ambient fine and coarse fraction particles in the thoracic
(tracheobronchial and alveolar) regions of the respiratory tract are
markedly greater than for deposition in the extrathoracic (head)
region. Maximum particle penetration to the thoracic region occurs
during oronasal or mouth breathing.
(3) The risks of adverse health effects from extrathoracic
deposition of general ambient PM are sufficiently low that particles
which deposit only in that region can safely be excluded from the
standard indicator.
(4) The size-specific indicator(s) should represent those particles
capable of penetrating to the thoracic region, including both the
tracheobronchial and alveolar regions.
[[Page 38667]]
These conclusions, together with information on the dosimetry of
particles in humans, were the basis for the promulgation in 1987 of a
new size-specific indicator for the PM NAAQS, PM10, that
includes particles with an aerodynamic diameter smaller than or equal
to a nominal 10 m. The recent information on human particle
dosimetry contained in the Criteria Document provides no basis for
changing 10 m as the appropriate cut point for particles
capable of penetrating to the thoracic regions.
As noted in Unit II.B. of this preamble, however, the Staff Paper
concludes that continued use of PM10 as the sole indicator
for the PM standards would not provide the most effective and efficient
protection from the health effects of PM (U.S. EPA, 1996b, pp. VII-4 to
VII-11). Based on the recent health effects evidence and the
fundamental physical and chemical differences between fine and coarse
fraction particles, the Criteria Document and Staff Paper conclude that
fine and coarse fractions of PM10 should be considered
separately (U.S. EPA, 1996a, p. 13-93; 1996b, p. VII-18). Taking into
account such information, CASAC found sufficient scientific and
technical bases to support establishment of separate standards relating
the Administrator that ``there is a consensus that retaining an annual
PM10 NAAQS * * * is reasonable at this time'' and that there
is ``also a consensus that a new PM2.5 NAAQS be
established'' (Wolff, 1996b).
Some commenters have noted that it is often difficult to
distinguish the effects of either fine or coarse fraction particles
from those of PM10; this is to be expected because both
fractions are themselves components of PM10, and hence not
fully independent. EPA believes that it is more meaningful to examine
comparisons between the fine and coarse fraction components. Such
comparisons presented in the Staff Paper suggest that fine particles
are a better surrogate for those components of PM that are linked to
mortality and morbidity effects at levels below the current standards
(U.S. EPA, 1996b, p. VII-18). Moreover, a regulatory focus on fine
particles would likely also result in controls on gaseous precursors of
fine particles (e.g., SOx, NOX, VOC), which are
all components of the complex mixture of air pollution that has most
generally been associated with mortality and morbidity effects. The
Staff Paper concludes that, in contrast to fine particles, coarse
fraction particles are more clearly linked with certain morbidity
effects at levels above those allowed by the current 24-hour standard.
Public comments received on the proposed indicators were
overwhelmingly in favor of EPA's proposal to maintain PM10
as an indicator for PM, whether as an indicator of coarse particles in
conjunction with a fine PM standard, or as the sole PM indicator. This
near unanimity shows strong support for retaining general PM standards.
While a substantial number of commenters supported EPA's proposal to
add an indicator for fine PM, a number of other commenters objected to
any standard revisions, including addition of a fine PM indicator.
Beyond the general points about the basis for any revisions discussed
in Unit II.B. of this preamble, these commenters argued either that the
available epidemiological data did not provide a basis for separating
fine and coarse fraction particles, or that there were not enough fine
particle studies to support selecting standard levels. Most of these
commenters also expressed concerns that there were insufficient ambient
fine particle data by which to evaluate the relative protection
afforded by new standards.
EPA notes that issues relating to the basis for separating
PM10 fractions were addressed in the Criteria Document and/
or Staff Paper assessments, and these perspectives were also available
for CASAC consideration in developing its recommendations. The proposal
states that the main basis for separating the fine and coarse fractions
of PM10 is that, because they are fundamentally different PM
components with significantly different physico-chemical properties and
origins (U.S. EPA 1996b, section V.D), separate standards would permit
more effective and efficient regulation of PM. While the difficulty in
separating these classes in the epidemiological studies is noted above,
the preponderance of the available evidence suggests that strategies to
control fine particles will more effectively reduce population exposure
to substances associated with health effects in the recent
epidemiological studies. Although the number of studies using fine PM
indicators is more limited than for PM10, there are more
than 20 community studies showing significant associations for a
consistent set of mortality and morbidity effects. A substantial subset
of these studies (Tables V-12 to V-13; U.S. EPA, 1996b) provides a
sufficient quantitative basis for selecting standard levels, without
the need to rely on estimates based on PM2.5/PM10
ratios.
Having considered the public comments on this issue, the
Administrator concurs with staff and CASAC recommendations to control
particles of health concern (i.e., PM10) through separate
standards for fine and coarse fraction particles. The following units
outline the basis for the Administrator's decision on specific
indicators for fine and coarse fraction particle standards.
1. Indicators for the fine fraction of PM10. The
Administrator continues to conclude that it is appropriate to control
fine particles as a group, as opposed to singling out particular
components or classes of fine particles. The more qualitative
scientific literature, evaluated in Chapter 11 of the Criteria Document
and summarized in section V.C of the Staff Paper, has reported various
health effects associated with high concentrations of a number of fine
particle components (e.g., sulfates, nitrates, organics, transition
metals), alone or in some cases in combination with gases. Community
epidemiolgical studies have found significant associations between fine
particles or PM10 and health effects in various areas across
the U.S. where such fine particle components correlate significantly
with particle mass. As noted above in this unit, it is not possible to
rule out any one of these components as contributing to fine particle
effects.26 Thus, the Administrator finds that the present
data more readily support a standard based on the total mass of fine
particles. EPA will conduct additional research, in cooperation with
other Federal agencies and in partnership with State and local agencies
and the private sector, to better identify which species are of concern
for human health, and the sources and relative magnitude of such
species.
---------------------------------------------------------------------------
26 As discussed above, a number of commenters expressed concerns
that various portions of fine particles might not be responsible for
any observed effects. One group (PG&E, 1997) recommended that
nitrates should be excluded from fine PM mass collected on the basis
of their assessment of available effects literature on particulate
and gas phase inorganic nitrates. Based on an examination of this
information as well as the earlier staff assessment, EPA maintains
its conclusion that the available evidence is not sufficient to
exclude nitrates or any other class of fine particles that are
collected by PM monitors comparable to those used in the recent
epidemiological studies.
---------------------------------------------------------------------------
In specifying a precise size range for a fine particle standard,
both the staff and CASAC recommended PM2.5 as the indicator
of fine particles (Wolff, 1996b). The particle diameter reflecting the
mass minimum between the fine and coarse modes typically lies between 1
and 3 m, and the scientific data support a sampling ``cut
point'' to delineate fine particles somewhere in this range. Because of
the potential
[[Page 38668]]
overlap of fine and coarse particle mass in this intermodal region, EPA
recognizes that any specific sampling cut point would result in only an
approximation of the actual fine-mode particle mass. Thus, the choice
of a specific diameter within this size range is largely a policy
judgment. The staff and CASAC recommendations for a 2.5 m
sampling cut point were based on considerations of consistency with the
community health studies, the limited potential for intrusion of coarse
fraction particles into the fine fraction, and availability of
monitoring technology.27 PM2.5 encompasses all of
the potential agents of concern in the fine fraction, including most
sulfates, acids, fine particle transition metals, organics, and
ultrafine particles, and includes most of the aggregate surface area
and particle number in the entire distribution of atmospheric
particles.
---------------------------------------------------------------------------
27 The National Mining Association (NMA) and related companies
submitted comments favoring ultimate selection of a smaller cutpoint
of 1 m (PM1) to further reduce coarse particle
intrusion. EPA considered this approach in developing the Staff
Paper and proposal. PM1 has not been used in health
studies, although in most cases collected mass should be similar to
those for cutpoints of 2.1 or 2.5 m. While a PM1
indicator could reduce intrusion of coarse particles, it might also
omit portions of hygroscopic PM components such as acid sulfates,
nitrates, and some organic compounds in higher humidity environments
picked up by PM2.5 measurements. PM1 sampling
technologies have been developed, but have not been widely used in
the field to date; there are some concerns about loss of certain
organic materials in available models relative to an instrument with
a larger size cut. NMA has also recommended consideration of a
methodology that could subtract coarse mass from PM2.5
measurements where undue coarse particle intrusion resulted in fine
standard violations. EPA will evaluate this recommendation in the
context of implementation policies.
---------------------------------------------------------------------------
The Administrator concurs with the staff and CASAC recommendations
and concludes that PM2.5 is the appropriate indicator for
fine particle standards. As discussed in Unit VI.B. of this preamble,
technical details of how PM2.5 is to be measured in the
ambient air are specified in the Federal Reference Method (40 CFR part
50, Appendix L).
2. Indicators for the coarse fraction of PM10.
The Criteria Document and Staff Paper conclude that
epidemiological information, together with dosimetry and toxicological
information, support the need for a particle indicator that addresses
the health effects associated with coarse fraction particles within
PM10 (i.e., PM10-2.5). As noted above, coarse
fraction particles can deposit in those sensitive regions of the lung
of most concern. Although the role of coarse fraction particles in much
of the recent epidemiological results is unclear, limited evidence from
studies where coarse fraction particles are the dominant fraction of
PM10 suggest that significant short-term effects related to
coarse fraction particles include aggravation of asthma and increased
upper respiratory illness. In addition, qualitative evidence suggests
that potential chronic effects may be associated with long-term
exposure to high concentrations of coarse fraction particles.
In selecting an indicator for coarse fraction particles, the
Administrator took into account the views of several CASAC panel
members who suggested using the coarse fraction directly (i.e.,
PM10-2.5) as the indicator. However, the Administrator notes
that the existing ambient data base for coarse fraction particles is
smaller than that for fine particles, and that the only studies of
clear quantitative relevance to effects most likely associated with
coarse fraction particles have used undifferentiated PM10.
In fact, it was the consensus of CASAC that it is reasonable to
consider PM10 itself as a surrogate for coarse fraction
particles, when used together with PM2.5 standards. The
monitoring network already in place for PM10 is large.
Therefore, in conjunction with the decision to have separate standards
for PM2.5, the Administrator concludes, consistent with
CASAC recommendations and public comments, that it is appropriate to
retain PM10 as the indicator for PM standards intended to
protect against the effects most likely associated with coarse fraction
particles.
D. Averaging Time of PM2.5 Standards
As discussed above in this unit, the Administrator has concluded
that PM2.5 is an appropriate indicator for standards
intended to provide protection from effects associated primarily with
fine particles. The recent health effects information includes reported
associations with both short-term (from less than 1 day to up to 5
days) and long-term (from a year to several years) measures of PM.
On the basis of this information, summarized in chapter V of the
Staff Paper and in the rationale presented in the proposal, the
Administrator has considered both short- and long-term PM2.5
standards.
1. Short-term PM2.5 standard. The current 24-hour
averaging time is consistent with the majority of community
epidemiological studies, which have reported associations of health
effects with 24-hour concentrations of various PM indicators such as
PM10, fine particles, and TSP. Such health effects,
including premature mortality and increased hospital admissions, have
generally been reported with same-day, previous day, or longer lagged
single-day concentrations, although some studies have reported stronger
associations with multiple-day average concentrations. In any case, the
Administrator recognizes that a 24-hour PM2.5 standard can
effectively protect against episodes lasting several days, since
attainment of such a standard would provide protection on each day of a
multi-day episode, while also protecting sensitive individuals who may
experience effects after even a single day of exposure.
Although most reported effects have been associated with daily or
longer measures of PM, evidence also suggests that some effects may be
associated with PM exposures of shorter durations. For example,
controlled human and animal exposures to specific components of fine
particles, such as acid aerosols, suggest that bronchoconstriction can
occur after exposures of minutes to hours. Some epidemiological studies
of exposures to acid aerosols have also found changes in respiratory
symptoms in children using averaging times less than 24 hours. However,
such reported results do not provide a satisfactory quantitative basis
for setting a fine particle standard with an averaging time of less
than 24 hours, nor do current gravimetric mass monitoring devices make
such shorter durations generally practical at present. Further, the
Administrator recognizes that a 24-hour average PM2.5
standard which leads to reductions in 24-hour average concentrations is
likely to lead as well to reductions in shorter-term average
concentrations in most urban atmospheres, thus providing some degree of
protection from potential effects associated with shorter duration
exposures.
2. Long-term PM2.5 standard. Community epidemiological
studies have reported associations of annual and multi-year average
concentrations of PM10, PM2.5, sulfates, and TSP
with an array of health effects, notably premature mortality, increased
respiratory symptoms and illness (e.g., bronchitis and cough in
children), and reduced lung function. The relative risks associated
with such measures of long-term exposures, although highly uncertain,
appear to be larger than those associated with short-term exposures.
Based on the available epidemiology, and consistent with the limited
relevant toxicological and dosimetric information, the Administrator
concludes that significant, and potentially independent, health
consequences are likely associated with long-term PM exposures.
[[Page 38669]]
The Administrator has considered this evidence, which suggests that
some health endpoints reflect the cumulative effects of PM exposures
over a number of years. In such cases, an annual standard would provide
effective protection against persistent long-term (several years)
exposures to PM. Requiring a much longer averaging time would also
complicate and unnecessarily delay control strategies and attainment
decisions.
The Administrator has also considered the seasonality of emissions
of fine particles and their precursors in some areas (e.g., wintertime
smoke from residential wood combustion, summertime regional acid
sulfate and ozone formation), which suggests that some effects
associated with annual average concentrations might be the result of
repeated seasonally high exposures. However, different seasons are
likely of concern in different parts of the country, and the current
evidence does not provide a satisfactory quantitative basis for setting
a national fine particle standard in terms of a seasonal averaging
time.
In addition, the Administrator recognizes that an annual standard
would have the effect of improving air quality broadly across the
entire annual distribution of 24-hour PM2.5 concentrations,
although such a standard would not as effectively limit peak 24-hour
concentrations as would a 24-hour standard. The risk assessment
summarized above found that because such 24-hour peaks contribute much
less to the total health risk over a year than the more numerous low-
to mid-range PM2.5 levels, an annual standard could also
provide effective protection from health effects associated with short-
term exposures to PM2.5 as well as those associated with
long-term exposures (see figure 2; 61 FR 65652-65653, December 13,
1996).
3. Combined effect of annual and 24-hour standards. For the reasons
outlined in Units II.C.1. and 2. of this preamble, the Administrator
concluded in the proposal that a short-term PM2.5 standard
with a 24-hour averaging time can serve to control short-term ambient
PM2.5 concentrations, thus providing protection from health
effects associated with short-term (from less than 1-day to up to 5-
day) exposures to PM2.5. Further, a long-term
PM2.5 standard with an annual averaging time can serve to
control both long- and short-term ambient PM2.5
concentrations, thus providing protection from health effects
associated with long-term (seasonal to several years) and, to some
degree, short-term exposures to PM2.5.
EPA received comparatively few public comments on these proposed
averaging times. Those supporting PM2.5 standards also
strongly supported adopting both annual and 24-hour averaging times.
Many of those opposing PM2.5 standards, for the reasons
discussed in Unit II.B. of this preamble, provided contingent comments
that variously supported both averaging times for PM2.5
standards in the event the Administrator disagreed with their overall
recommendations. Other opponents of PM2.5 standards
disagreed with having two standards on administrative grounds, or
because some CASAC members did not support both averaging times.
The relationship between standards for the two averaging times is
discussed below in this unit. In essence, based on its examination of
the effects data and air quality relationships, EPA believes that a
single PM2.5 standard (24-hour or annual) either would not
provide adequate protection against effects of concern for all
averaging times, or would be inefficient in the sense that it was more
stringent than necessary for at least one averaging time. Contrary to
commenters who focused on minority CASAC opinions, EPA notes that a
clear majority of CASAC supported both 24-hour and annual
standards28. After considering public comments on averaging
time and the rationale outlined above, the Administrator has concluded
that both 24-hour and annual PM2.5 standards are
appropriate.
---------------------------------------------------------------------------
28 Of the 19 panel members who joined in the consensus for
PM2.5 standards, 17 (90 percent) recommended a 24-hour
standard and 13 (70 percent) recommended an annual standard (Wolff,
1996b).
---------------------------------------------------------------------------
The Administrator next considered the potential combined effects of
such standards on PM concentration levels and distributions. The
existing health effects evidence could, of course, be used to assess
the form and level of each standard independently, with short-term
exposure health effects evidence being used as the basis for a 24-hour
standard and the long-term exposure health effects evidence as the
entire basis for an annual standard. Some CASAC panel members
apparently used this approach as a basis for their views on appropriate
averaging times and standard levels. In particular, a few members
focused only on a 24-hour PM2.5 standard in light of the
relative strength of the short-term exposure studies. On the other
hand, two members focused only on an annual standard, recognizing that
strategies to meet an annual standard would provide protection against
effects of both short- and long-term exposures.
As noted above in this unit, attempting to provide protection for
all of the effects identified in long- and short-term PM exposure
studies with a single averaging time would result in either inadequate
protection for some effects, or unnecessarily stringent control for
others. The Administrator has, instead, emphasized a policy approach
that considers the consistency and coherence, as well as the
limitations, of the body of evidence as a whole, and recognizes that
there are various ways to combine two standards to achieve an
appropriate degree of public health protection. Such an approach to
standard setting, which integrates the body of health effects evidence
and air quality analyses, and considers the combined effect of the
standards, has the potential to result in a more effective and
efficient suite of standards than an approach that only considers
short- and long-term exposure evidence, analyses, and standards
independently.
In considering the combined effect of such standards, the
Administrator notes that while an annual standard would focus control
programs on annual average PM2.5 concentrations, it would
also result in fewer and lower 24-hour peak concentrations.
Alternatively, a 24-hour standard that focuses controls on peak
concentrations could also result in lower annual average
concentrations. Thus, either standard could be viewed as providing both
short- and long-term protection, with the other standard serving to
address situations where the daily peaks and annual averages are not
consistently correlated.
The Administrator proposed that the suite of PM2.5
standards could most effectively and efficiently be defined by treating
the annual standard as the generally controlling standard for lowering
both short- and long-term PM2.5 concentrations. In
conjunction with the annual standard, the 24-hour standard would serve
to provide protection against days with high peak PM2.5
concentrations, localized ``hot spots,'' and risks arising from
seasonal emissions that would not be well controlled by a national
annual standard.
Relatively few public comments were addressed specifically to the
proposal that the annual standard be directed toward controlling both
24-hour and annual levels (thereby basing the annual standard on an
evaluation of both the short- and long-term health effects
information), with the 24-hour standard being used to address more
localized short-term peaks. A number of commenters, notably some among
the groups opposing any revised PM
[[Page 38670]]
standards, appeared to have ignored this fundamental aspect of the
proposal, judging by their assertions that the sole basis for EPA's
proposed annual standards was two long-term exposure studies (Dockery
et al., 1993; Pope et al. 1995). This is incorrect; as the proposal
states, EPA based the proposed annual standard level on a wider range
of short- and long-term exposure studies. Other commenters, including
some environmental groups, reserved comment on this specific issue, but
expressed concerns that the specific levels for both standards were not
stringent enough, regardless of which standard is intended to be
controlling. Issues regarding specific levels are discussed below in
Unit II.F. of this preamble.
Some commenters, however, disagreed with the proposition that EPA's
proposed approach would necessarily provide the most effective and
efficient standards. In the view of some who opposed PM2.5
standards, the likelihood that there are thresholds below which no
effects occur means that a 24-hour standard would be more efficient
than an annual standard. In this view, the reductions made on days that
were below the threshold would provide no protection.29 Some
commenters also noted that while a majority of CASAC members favored
both annual and 24-hour standards, more recommended 24-hour standards.
---------------------------------------------------------------------------
29 A related comment criticized the risk assessment conclusion
that peak 24-hour concentrations contribute much less to the total
risk over a year as inconsistent with the experience in historic air
pollution episodes. EPA disagrees. While the historic London
episodes were quantitatively different from those assumed in the
risk assessment, the record over 14 London winters indicates a
continuum of effects down to the lowest levels. It is therefore
likely that the cumulative increase in mortality calculated for all
the days in the whole 14-year period would not be dominated by the
more limited number of episode days.
---------------------------------------------------------------------------
While the available epidemiological studies provide strong evidence
suggesting that PM causes or contributes to health effects at levels
below the current standards, EPA agrees, as stated previously, that
uncertainties increase markedly at lower concentrations. Nevertheless,
the level or even existence of population thresholds below which no
effects occur cannot be reliably determined by an examination of the
results from the available studies. Analyses have placed some limits,
however, and EPA has considered hypothetical thresholds in its risk
assessment. As noted in Unit II.A. of this preamble, even assuming an
example threshold of 18 g/m3, the risk assessment
(see Figure 2c; 61 FR 65653, December 13, 1996) finds that most of the
annual aggregate risk associated with short-term exposures still
results from the large number of days at lower to mid-range values
above the mean. Given that neither the Criteria Document nor commenters
have provided quantitative evidence regarding the likelihood of a
threshold at levels much higher than the above example, EPA believes
that the evidence provided in the risk assessment does not support the
commenters' position. As noted above, EPA believes that most CASAC
opinions on averaging time reflect panelists' judgments on the relative
strength of the short-term exposure epidemiological studies, a judgment
that EPA shares. Although most CASAC panel members did not offer an
opinion on the use of short-term exposure studies in specifying annual
standards, two panelists did support this notion. EPA therefore
believes this approach is neither inconsistent with the underlying
science nor discordant with the advice of CASAC.
Another concern was raised by some air pollution control officials
who otherwise supported revised PM standards. These commenters state
that, from an implementation perspective, it is often easier to design
control strategies for single short-term events than for annual
averages. Aside from whether this is a proper consideration in
establishing NAAQS, the point in fact highlights one of the important
strengths of an annual standard in addressing short-term risks
associated with PM2.5. As noted by the commenters, risk
management for a short-term standard focuses on a characteristic
``design value'' episode responsible for peak concentrations. For PM,
such peak values can be associated with single source contributions.
Meteorology, relative source contributions, and resulting particle
composition for that day may or may not be typical for the area or for
the year. Yet the short-term exposure epidemiological results are
largely drawn from studies that associated variations in area-wide
effects with monitor(s) that gauged the variation in daily levels over
the course of up to 8 years. The strength of the associations in these
data is demonstrably in the numerous ``typical'' days in the upper to
middle portion of the annual distribution, not on the peak
days.30 For these reasons, strategies that focus only on
reducing peak days are less likely to achieve reduction of the mix and
sources of urban and regional-scale PM pollution most strongly
associated with health effects. Although designing control strategies
to reduce annual levels may be more difficult than for 24-hour
standards, the available short- and long-term epidemiological data
suggest it is also likely to result in a greater reduction in area-wide
population exposure and risk.
---------------------------------------------------------------------------
30 This point is buttressed by studies that have taken out a
limited number of higher PM concentration days with little effect on
the effects estimates or significance of the association (e.g.,
Schwartz et al., 1996; Pope and Dockery, 1992).
---------------------------------------------------------------------------
The Administrator concludes that the most effective and efficient
approach to establishing PM2.5 standards is to treat the
annual standard as the generally controlling standard for lowering both
short- and long-term PM2.5 concentrations, while the 24-hour
standard would serve to provide protection against days with high peak
PM2.5 concentrations, localized ``hot spots,'' and risks
arising from seasonal emissions that would not be well controlled by a
national annual standard. In reaching this view, the Administrator took
into account the public comments and the factors discussed below in
this unit.
(1) Based on one of the key observations from the quantitative risk
assessment summarized above (see Figures 2a,b,c; 61 FR 65652-65653,
December 13, 1996), the Administrator notes that much if not most of
the aggregate annual risk associated with short-term exposures results
from the large number of days during which the 24-hour average
concentrations are in the low- to mid-range, below the peak 24-hour
concentrations. As a result, lowering a wide range of ambient 24-hour
PM2.5 concentrations, as opposed to focusing on control of
peak 24-hour concentrations, is the most effective and efficient way to
reduce total population risk. Further, there is no evidence suggesting
that risks associated with long-term exposures are likely to be
disproportionately driven by peak 24-hour concentrations. Thus, an
annual standard that controls an area's attainment status is likely to
reduce aggregate risks associated with both short- and long-term
exposures with more certainty than a 24-hour standard.
(2) The consistency and coherence of the health effects data base
are, therefore, more directly related to the more frequently occurring
PM exposures reflected in study period mean measures of air quality
(e.g., the annual distributions of 24-hour PM concentrations), than to
the potentially site-specific and/or otherwise infrequent PM exposures
reflected in a limited number of peak 24-hour concentrations. More
specifically, judgments about the quantitative consistency of the large
number of short-term exposure studies
[[Page 38671]]
reporting associations with 24-hour concentrations arise from comparing
the relative risk results per PM increment as derived from analyzing
the associations across the entire duration of the studies. These
studies typically spanned at least an annual time frame and the
reported associations are most strongly influenced by the large number
of days toward the middle of the distribution.
(3) An annual average measure of air quality is more stable over
time than are 24-hour measures. Thus, a controlling annual standard is
likely to result in the development of more consistent risk reduction
strategies over time, since an area's attainment status will be less
likely to change due solely to year-to-year variations in
meteorological conditions that affect the formation of fine particles,
than under a controlling 24-hour standard.
Under this policy approach, the annual PM2.5 standard
would serve in most areas as the target for control programs designed
to be effective in lowering the broad distribution of PM2.5
concentrations, thus protecting not only against long-term effects but
also short-term effects as well. In combination with such an annual
standard, the 24-hour PM2.5 standard would be set so as to
protect against the occurrence of peak 24-hour concentrations,
particularly peak concentrations that present localized or seasonal
exposures of concern in areas where the highest 24-hour-to-annual mean
PM2.5 ratios are appreciably above the national average.
E. Form of PM2.5 Standards
1. Annual standard. As discussed in some detail during the last
review of the PM NAAQS (see 49 FR 10408, March 20, 1984; 52 FR 24634,
July 1, 1987) and in the December 13, 1996 proposal, the annual
arithmetic mean form of the current annual PM10 standard
(i.e., the annual arithmetic mean averaged over 3 years) is a
relatively stable measure of air quality that reflects the total
cumulative dose of PM to which an individual or population is exposed.
Short-term peaks have an influence on the arithmetic mean that is
proportional to their frequency, magnitude, and duration, and, thus,
their contribution to cumulative exposure and risk. As a result, the
annual arithmetic mean form of an annual standard provides protection
across a wide range of the air quality distribution contributing to
exposure and risk, in contrast to other forms, such as the geometric
mean, that de-emphasize the effects of short-term peak concentrations.
While almost no commenters took specific issue with use of an
annual arithmetic mean, a number of commenters disagreed with averaging
over 3 years for both the annual and 24-hour standards because of their
desire for quick action in the initial implementation of
PM2.5 controls. The Administrator recognizes the importance
of promptly implementing appropriate control programs, but she does not
believe that implementation start-up concerns are an adequate basis for
adopting a form (e.g., a single year annual average) that would provide
less stable risk reduction in the long-run. Therefore, the
Administrator continues to concur with the Staff Paper recommendation,
supported by CASAC, to use the annual arithmetic mean, averaged over 3
years, as the form for an annual PM2.5 standard consistent
with the current form of the annual PM10 standard.
Nevertheless, EPA intends to address the concerns of those who
commented that the 3-year form might prevent the public from being
informed about the air quality status of their communities. As outlined
in Unit II.H. of this preamble, EPA plans to issue revised Pollutant
Standard Index criteria for PM2.5, to ensure the public is
informed promptly about air quality status.
The Staff Paper and some CASAC panel members also recommended that
consideration be given to calculating the PM2.5 annual
arithmetic mean for an area by averaging the annual arithmetic means
derived from multiple monitoring sites within a monitoring planning
area. In proposing a calculation method for annual arithmetic averages
that involves spatial averaging of monitoring data, the Administrator
reasoned as follows:
(1) Many of the community-based epidemiological studies examined in
this review used spatial averages, when multiple monitoring sites were
available, to characterize area-wide PM exposure levels and the
associated population health risk. In those studies that used only one
monitoring location, the selected site was chosen to represent
community-wide exposures, not the highest value likely to be
experienced within the community. Thus, spatial averages are most
directly related to the epidemiological studies used as the basis for
the proposed revisions to the PM NAAQS.
(2) As a part of the overall policy approach discussed in Unit
II.D. of this preamble, the annual PM2.5 standard would be
intended to reduce aggregate population risk from both long- and short-
term exposures by lowering the broad distribution of PM2.5
concentrations across the community. An annual standard based on
spatially averaged concentrations would better reflect area-wide PM
exposure levels than would a standard based on concentrations from a
single monitor with the highest measured values.
(3) Under this policy approach, the 24-hour PM2.5
standard would be intended to work in conjunction with a spatially
averaged annual PM2.5 standard by providing protection
against peak 24-hour concentrations, localized ``hot spots,'' and
higher PM2.5 concentrations arising from seasonal emissions
and meteorology that would not be as well controlled by an annual
standard. Accordingly, the 24-hour PM2.5 standard should be
based on the single population-oriented monitoring site within the
monitoring planning area with the highest measured values.
Based on these considerations, the Administrator proposed that the
form of an annual PM2.5 standard be expressed as the annual
arithmetic mean, temporally averaged over 3 years and spatially
averaged over all designated monitoring sites,31 which, in
conjunction with a 24-hour PM2.5 standard, was intended to
provide the most appropriate target for reducing area-wide population
exposure to fine particle pollution. Recognizing the complexities that
spatial averaging might introduce into risk management programs, in the
proposal the Administrator also requested comment on the alternative of
basing the annual standard for PM2.5 solely on the single
population-oriented monitor site within the monitoring planning area
with the highest 3-year average annual mean.
---------------------------------------------------------------------------
31 The notice of proposed revisions to 40 CFR part 58 recognized
that a single appropriately sited monitor could suffice for an area
in place of an average of multiple monitors.
---------------------------------------------------------------------------
The proposed approach to designating sites that are appropriate for
spatial averaging was based on criteria and constraints contained in
the proposed revision to the monitoring siting and network planning
requirements in 40 CFR part 58. In proposing this approach, the
Administrator noted concerns regarding the development and
implementation of appropriate and effective criteria for the selection
of sites and designations of areas for spatial averaging.
A number of commenters who otherwise favored setting
PM2.5 standards objected to the concept of population-
oriented monitors and expressed the view that any monitor regardless of
where it was sited should be eligible for comparison to the annual
PM2.5 standard. They further maintained that the proposed
provisions for spatial averaging would fail to provide adequate health
protection because
[[Page 38672]]
``clean areas'' and ``dirty areas'' would be averaged together. Some
commenters expressed concern that the proposed constraints on spatial
average would not be sufficient to prevent use of such averaging to
avoid pollution abatement. Others may not have fully understood the
implications of the specific constraints and siting requirements
discussed in the proposed revisions to 40 CFR part 58, which were
intended to ensure that the population-oriented monitors used for the
annual standard were actually reflective of community-wide exposures
and that the spatial averages did not include non-representative
monitored values from either ``clean areas'' or ``dirty
areas.''32 In order to clarify the intent that the spatially
averaged annual standard protect those in smaller communities, as well
as those in larger population centers, the final revisions to 40 CFR
part 58 adopt the term ``community-oriented'' monitors.
---------------------------------------------------------------------------
32 The 40 CFR part 58 proposed rule identified the proposed
criteria for monitors to be averaged; namely, monitors must be
properly sited to reflect population-orientation, primarily
influenced by similar sources, and within +/-20 percent of the
average levels and a specific degree of correlation (or meet a
``homogeneity'' constraint). Additional criteria include
demonstrations that the monitors to be averaged are influenced
primarily by similar sources (e.g., to prevent the placement of
monitors upwind in unrepresentative locations), EPA oversight of the
monitoring program which includes regular review and approval of the
State PM monitoring network design, and other criteria to ensure
proper monitor siting. The final rule includes the addition of
provisions that the State PM monitoring network design be available
for public inspection.
---------------------------------------------------------------------------
Other commenters, who supported PM2.5 annual standards,
endorsed the concept of spatial averaging as being more reflective of
the air quality data used in the underlying health studies and because
there is general uniformity of fine particle concentrations across an
area. Opponents of the PM2.5 standards expressed contingent
support for spatial averaging in concept, again citing the linkage to
the underlying health studies. Indeed, they advocated the extension of
spatial averaging to the daily form of the standard, and/or recommended
less constrained spatial averaging to allow for averaging across entire
metropolitan areas.
The Administrator, of course, shares commenters' concerns that the
form of the standards, in conjunction with other components of the
standards, must protect public health adequately against risks
associated with PM. It was for this reason that EPA proposed a policy
approach providing for greatest overall risk reduction for all citizens
in the community from exposures to the mix of urban and regional scale
PM pollution most strongly associated with health effects. In
specifically considering whether to allow for the use of spatial
averaging, the Administrator placed great weight on consistency with
the underlying body of health effects evidence. The Administrator is
mindful that some community studies relied inherently on exposure and
effects estimates that reflect comparatively broad spatial scales, as
highlighted by those commenters desiring to extend permissible
averaging; however, this type of exposure characterization may not be
appropriate for all circumstances and might leave some areas without
adequate protection.33
For these reasons, the 40 CFR part 58 proposal package contained
criteria and constraints on spatial averaging. These criteria and
constraints were intended to ensure that spatial averaging would not
result in inequities in the level of protection provided by the PM
standards. The Administrator again recognizes that either a single
properly sited community-oriented monitor, or an average of more than
one such monitors, are both appropriate indices of area-wide population
exposures. Both are consistent with monitoring approaches used in
community epidemiological studies upon which the standards are based.
On the other hand, comparing the annual PM2.5 standard to
the maximum concentrations at a site that is not representative of
community exposures, as some have suggested, would be inconsistent with
the Administrator's goal of using the annual standard to reduce urban
and regional scale exposures and risks. Further, the Administrator
believes that the criteria and, siting requirements contained in 40 CFR
part 58, provide adequate safeguards against inappropriate application
of spatial averaging. Therefore, the Administrator continues to believe
that an annual PM2.5 standard reflective of area-wide
exposures, in conjunction with a 24-hour standard designed to provide
adequate protection against localized peak or seasonal PM2.5
levels, reflects the most appropriate approach for public health
against the effects of PM reported in the scientific
literature.34
---------------------------------------------------------------------------
33 Daily mortality studies generally use urban or metro-areawide
effects statistics in conjunction with single or multiple monitors
that index day-to-day pollution changes across the area. Ito et al.
(1995) found that spatial averages from multiple PM monitors in
Chicago were better correlated with daily mortality than were most
single monitors, but that single monitors were also associated. A
number of morbidity studies (e.g., Schwartz et al., 1994; Neas et
al., 1995; Raizenne et al.; 1996) used community scale monitors and
effects information from a defined group of subjects from the
community, who were more closely represented by the monitor.
34 Because the 24-hour standard is designed to address localized
peaks, it would be inappropriate to extend spatial averaging forms
to this standard.
---------------------------------------------------------------------------
The majority of comments from States stressed the need for
flexibility in specifying network designs and spatial averaging, given
that the nature and sources of particle pollution vary from one area to
another. One State agency specifically requested the flexibility to
choose whether to use a single community-oriented monitor or a spatial
average of several of such monitors, arguing that it is appropriate to
provide this flexibility as PM2.5 monitoring networks evolve
and to address the diversity of local conditions.
As a result of EPA's evaluation of these comments, the requirements
of 40 CFR part 50, Appendix K, and 40 CFR part 58 have been revised to
clarify that the implementing agencies have the flexibility to compare
the annual PM2.5 standard either to the measured value at a
single representative community-oriented monitoring site, or to the
value resulting from an average of community-oriented monitoring sites
that meet the revised criteria and constraints enumerated in the 40 CFR
part 58 final rule.
In the Administrator's view, the final criteria and siting
requirements contained in 40 CFR part 58 and in the new 40 CFR part 50,
Appendix N, address the concerns raised by these commenters about the
protection afforded by the form of the annual standard. Therefore, the
Administrator continues to believe that the form of a PM2.5
annual standard should be expressed as an annual arithmetic mean,
averaged over 3 years, from single or multiple community-oriented
monitors, in accordance with 40 CFR part 50, Appendix N and 40 CFR part
58. In her judgment, an annual standard expressed in this manner and
set at an appropriate level, in conjunction with a 24-hour
PM2.5 standard, will adequately protect public health.
2. 24-hour standard. The current 24-hour PM10 standard
is expressed in a ``1-expected-exceedance'' form. That is, the standard
is formulated on the basis of the expected number of days per year
(averaged over 3 years) on which the level of the standard will be
exceeded. The test for determining attainment of the current 24-hour
standard is presented in Appendix K to 40 CFR part 50.
As discussed in the proposal, since promulgation of the current 24-
hour PM10 standard in 1987, a number of concerns have been
raised about the 1-
[[Page 38673]]
expected-exceedance form. These include, in particular, the year-to-
year stability of the number of exceedances, the stability of the
attainment status of an area, and the complex data handling conventions
specified in 40 CFR part 50, Appendix K, including the procedures for
making adjustments for missing data and less-than-every-day monitoring.
In light of these concerns, the Staff Paper and several CASAC panel
members (Wolff, 1996b) recommended that consideration be given to
adoption of a more stable and robust form for 24-hour standards. In
considering this recommendation for the proposal, the Administrator
noted that the use of a concentration-based percentile form would have
several advantages over the current 1-expected-exceedance form:
(1) Such a concentration-based form would be more directly related
to the ambient PM concentrations that are associated with health
effects. Given that there is a continuum of effects associated with
exposures to varying levels of PM, the extent to which public health is
affected by exposure to ambient PM is related to the actual magnitude
of the concentration, not just whether the concentration is above a
specified level. With an exceedance-based form, days on which the
ambient concentration is well above the level of the standard are given
equal weight to those days on which the concentration is just above the
standard (i.e., each day is counted as one exceedance), even though the
public health impact on the 2 days is significantly different. With a
concentration-based form, days on which higher concentrations occur
would weigh proportionally more than days with lower concentrations for
the design value, since the actual concentrations would be used
directly in determining whether the standard is attained.
(2) A concentration-based percentile form would also compensate for
missing data and less-than-every-day monitoring, thereby reducing or
eliminating the need for complex data handling procedures in the 40 CFR
part 50, Appendix K test for attainment. As a result, an area's
attainment status would be based directly on monitoring data rather
than on a calculated value adjusted for missing data or less-than-
every-day monitoring.
(3) Further, a concentration-based form, averaged over 3 years,
would also have greater stability than the expected exceedance form
and, thus, would facilitate the development of more stable
implementation programs by the States.
The proposal discussed various specific percentile values for such
a form (e.g., 90th to 99th percentiles), taking
into account two factors. First, the 24-hour PM2.5 standard
is intended to supplement the annual PM2.5 standard by
providing additional protection against extremely high peak days,
localized ``hot spots,'' and risks arising from seasonal emissions.
Second, given an appropriate level of health protection, the form of
the 24-hour PM2.5 standard should provide an appropriate
degree of increased stability relative to the current form. The
Administrator noted in the proposal that a more stable statistic would
reduce the impact of a single high exposure event that may be due to
unusual meteorological conditions alone, and thus would provide a more
stable basis upon which to design effective control programs.
With these purposes in mind, the Administrator observed in the
proposal that while a percentile value such as the 90th or
95th would provide substantially increased stability when
compared to a more extreme air quality statistic (e.g., the current 1-
expected-exceedance form), it would likely not serve as an effective
supplement to the annual standard, because it would allow a large
number of days with peak PM2.5 concentrations above the
standard level. For example, in a 365-day data base, the
90th and 95th percentiles would equal the
37th and 19th highest 24-hour concentrations,
respectively. On the other hand, a percentile value selected much
closer to the tail of the air quality distribution (e.g. a
99th or greater percentile) would not likely provide
significantly more health protection or significantly increased
stability as compared to a 1-exceedance form. In balancing these issues
in the proposal, the Administrator ultimately proposed a
98th percentile value form of the standard.
Some commenters maintained that EPA should retain the current 1-
expected-exceedance form for the 24-hour PM2.5 standard to
limit the number of days per year that the standard is exceeded. These
commenters apparently gave little weight to EPA's rationale that a
concentration-based form is more directly related to ambient PM
concentrations that are associated with health effects because it takes
into account the magnitude of PM concentrations, not just whether the
concentrations are above a specific level. These commenters also
discounted the other advantages of a concentration-based percentile
form outlined above in this unit. A number of other commenters
supported the concentration-based percentile form for the reasons
outlined in the proposal but, as discussed below in this unit, argued
for alternative percentile values that were higher or lower than the
proposed 98th percentile value.
EPA continues to believe that a concentration-based percentile form
is more reflective of the health risk posed by elevated PM
concentrations, because it gives proportionally greater weight to days
when concentrations are well above the level of the standard than to
days when the concentrations are just above the standard. This factor,
coupled with the other advantages outlined above in this unit, leads
EPA to conclude that a concentration-based percentile form will provide
for more effective health protection than a 1-expected-exceedance form.
Some commenters supporting a single exceedance form or a more
restrictive concentration-based percentile form (e.g. a 99th
percentile) expressed concern that the proposed 98th
percentile form could allow too many high concentration excursions, and
thus fail to provide adequate protection against seasonal emissions
problems or localized peaks. In particular, some commenters expressed
concerns that in areas with strongly seasonal emissions, such as
western areas with winter inversions, over a three year period an area
could experience several excursions in which levels could reach as high
as 250 g/m3 and still comply with both the annual
and daily standards if the remainder of the days had low levels (e.g.,
10 g/m3). Although this combination of events is
theoretically possible, EPA believes it is unlikely. Moreover, if such
episodic events did occur, the Act provides for emergency State or
Federal action to address them.35 In view of the limits on
truely episodic peak concentrations, EPA believes that an appropriately
selected 24-hour standard with a concentration-based 98th
percentile form can provide a stable and adequately protective
supplement to the annual standard in areas with periodic peak
concentrations.
---------------------------------------------------------------------------
35 See sections 303, 110(a)(2)(y); 40 CFR part 51. EPA intends
to establish a significant harm level for PM2.5 and
associated guidance so States can develop appropriate emergency
episode plans. The significant harm and episode criteria will be
included in forthcoming proposed revisions to 40 CFR part 51 and 40
CFR part 58 implementation guidance. In the interim, existing
PM10 emergency episode plans should be triggered by
events of this magnitude.
---------------------------------------------------------------------------
Other commenters who were also concerned with monitoring
requirements associated with spatial averaging in the annual standard,
argued that a 98th percentile form, coupled with the
proposed monitoring requirements that would limit
[[Page 38674]]
compliance monitors for the 24-hour standard to population-oriented
sites, would not protect people residing in or near localized ``hot
spots'' in some areas.36 The Administrator believes that the
siting requirements as proposed and finalized in 40 CFR part 58 for
population-oriented sites will provide adequate safeguards for such
residential areas.
---------------------------------------------------------------------------
36 The 40 CFR part 58 monitoring rule proposed to limit sites
that would be eligible for comparisons to the 24-hour standard to
population-oriented monitoring sites.
---------------------------------------------------------------------------
Other commenters, who otherwise opposed setting PM2.5
standards, recommended that alternative lower percentiles (e.g.,
95th percentiles) be used, if EPA proceeds to set such
standards. As discussed above in this unit, however, EPA continues to
hold the view that a 90th to 95th percentile form
would not provide an adequate limit against periodic peak values in
areas with low annual values and periodic high seasonal or source-
oriented peaks.
After carefully assessing the comments received, the Administrator
is persuaded that the adoption of a 98th percentile form for
the 24-hour PM2.5 standard measured at each population-
oriented monitoring site in an area would provide an effective
supplement to the annual PM2.5 standard. This form will
provide adequate protection against 24-hour peak PM2.5
levels in locations dominated by single point sources, as well as in
areas dominated by seasonal emissions. The Administrator also believes
that a 98th percentile form, with more frequent sampling and
averaged over 3 years, will provide increased stability and robustness
as recommended by several members of the CASAC panel. For these
reasons, the Administrator has decided to adopt the 98th
percentile form for the final PM2.5 24-hour standard. The
24-hour PM2.5 standard would be attained when the 3-year
average of the 98th percentile of 24-hour concentrations at
each populated oriented monitor within an area is less than or equal to
the level of the standard. Further details regarding the interpretation
of the form, as well as associated calculations and other data handling
conventions are specified in the new 40 CFR part 50, Appendix N.
F. Levels for the Annual and 24-Hour PM2.5 Standards
As discussed in Unit II.D. of this preamble, the Administrator
believes that an annual PM2.5 standard can provide the
requisite reduction in risk associated with both annual and 24-hour
averaging times in most areas of the United States. Under this
approach, the 24-hour standard would be intended to provide
supplemental protection against extreme peak fine particle levels that
may occur in some localized situations or in areas with distinct
variations in seasonal fine particle levels. In reaching judgments as
to appropriate levels to propose for both the annual and 24-hour
PM2.5 standards, the Administrator has considered the
combined protection afforded by both the annual and 24-hour standards,
taking into account the forms discussed in Unit II.E. of this preamble.
With this approach in mind, the Administrator has considered the
available health effects evidence and related air quality information
presented in the Criteria Document and summarized in chapters IV--VII
of the Staff Paper, which provides the basis for decisions on standard
levels that would reduce risk sufficiently to protect public health
with an adequate margin of safety, recognizing that such standards will
not be risk-free. In so doing, the Administrator has considered both
the strengths and the limitations of the available evidence and
information, as well as alternative interpretations of the scientific
evidence advanced by various CASAC panel members (Wolff, 1996b;
Lippmann et al., 1996) and public commenters, arising primarily from
the inherent uncertainties and limitations in the health effects
studies.
Beyond those factors, but clearly related to them, a range of views
have been expressed by CASAC panel members and the public as to the
appropriate policy response to the available health effects evidence
and related air quality information. Toward one end of the spectrum,
the view has been expressed that only a very limited policy response is
appropriate in light of the many key uncertainties and unanswered
questions that, taken together, call into question the fundamental
issue of causality in the reported associations between ambient levels
of PM2.5 and mortality and other serious health effects.
Toward the other end, the view has been expressed that the consistency
and coherence of the epidemiological evidence should be interpreted as
demonstrating causality in the relationships between PM2.5
and health endpoints that are clearly adverse, and that uncertainties
in the underlying health effects information should be treated,
regardless of their nature, as warranting a maximally precautionary
policy response. A third view would suggest an alternative policy
response, taking into account not only the consistency and coherence of
the health effects evidence, but also the recognition of key
uncertainties and unanswered questions that increasingly call into
question the likelihood of PM-related effects as PM2.5
concentrations decrease below the mean values in areas where effects
have been observed and/or as such concentrations approach background
levels.
Reflecting these divergent views, both of the science itself and of
how the science should be used in making policy decisions on proposed
standards, the Administrator considered three alternative approaches to
selecting appropriate standard levels, as described in the proposal,
ultimately deciding to propose standards based on a balanced view of
the strengths and uncertainties of the scientific information that
reflects the intermediate approach.
Judging by the public comments received, EPA accurately reflected
the bases for divergent views. A substantial body of public comments
supported revising the PM standards by adding PM2.5
standards with levels at least as stringent as those proposed by the
Administrator. In general, however, comments on levels for
PM2.5 standards revealed a strong dichotomy between those
who recommended even stronger standards than proposed, and those who
counseled against revising the standards at all. As noted above in this
unit, many in this latter group made contingent recommendations with
respect to the levels and other aspects of PM2.5 standards,
if the Administrator concluded that any revisions were appropriate.
This latter group of ``contingent'' commenters recommended levels
well above those proposed by the Administrator. These commenters placed
great weight on factors outlined in Units II.B. and II.C. of this
preamble that led them to oppose any revisions to the PM standards,
including the uncertainties and limitations in the available health
effects studies considered individually, such as the possible existence
of effects thresholds and unanswered questions regarding the causal
agent(s) responsible for the reported health effects. Further, they
emphasized the limited amount of research currently available that has
measured PM2.5 directly. A substantial group recommended
that PM2.5 standards be selected so as to be equivalent or
close in stringency to the current PM10 standards, and cited
the opinions of some CASAC PM panel members as support. Some of these
commenters provided supplemental analyses of air quality data, arguing
that they demonstrate that ``equivalent'' standards would be at
PM2.5 levels as
[[Page 38675]]
high as approximately 95 g/m3 24-hour average and
27 g/m3 annual average.
Having evaluated these comments, the Administrator rejects both
their underlying rationale and the specific recommendations for
PM2.5 standard levels that result in similar or only
marginally more protection than that afforded by the current
PM10 standards. Aside from technical problems in the
commenters' supporting analyses on the issue of defining ``equivalent''
standards,37 the Administrator finds this approach
inconsistent with her conclusions regarding the adequacy of the current
standards and the need to provide additional protection as articulated
in Unit II.B. of this preamble. The Administrator believes that,
despite well recognized uncertainties, the consistency and coherence of
the epidemiological evidence and the seriousness of the health effects
require a more protective response than provided by ``equivalence'' or
a marginal strengthening of the standards. Moreover, EPA believes that
the standard levels should be based on the most recent assessment of
the scientific criteria for PM, not on applying uncertain ratios to
standard decisions based on much more limited evidence in 1987. The
Administrator also rejects the premise of some38 who suggest
that adopting a standard that prompts little or no additional control
would cause no delay in risk reduction as compared to conducting
monitoring and research now and setting a more stringent standard after
the next review. These comments do not consider the realities of
implementing air quality standards, which ensure that such an approach
would add several years to the risk reduction process. Thus, aside from
her obligations under the statute,39 the Administrator
believes that the most prudent and appropriate course is to establish
appropriately protective standards now that put into motion monitoring
and strategy development programs, while at the same time pursuing an
expanded research program to improve implementation and to inform the
next periodic review of the criteria and standards.
---------------------------------------------------------------------------
37 Nationwide PM2.5 estimates have been derived from
the current PM air quality data base, but reflect a significant
degree of uncertainty due to the highly variable relationship
between PM2.5 and PM10 air quality values
across locations and seasons (Fitz-Simons et al., 1996). The
American Iron and Steel Institute (AISI) submitted a useful data
base (Cooper Associates, 1997) on PM2.5/PM10
relationships that examines both these predictions and the issue of
equivalence. An EPA examination of this material, which found some
problems with the analysis and with commenters' conclusions that
appear inconsistent with the Cooper report, is included in the
Response to Comments.
38 Some commenters suggest that CASAC and EPA support for
PM2.5 standards is based on the need to stimulate
additional monitoring and research. While the Administrator agrees
that the additional monitoring and research that would accompany
establishment of equivalent or marginally tighter PM2.5
standards are very important goals, they do not form an adequate
rationale for establishing air quality standards.
39 As stated previously, section 109(d) of the Act requires
that, after reviewing the existing criteria and standards for PM,
the Administrator make such revisions in the standards and
promulgate such new standards as are appropriate under section
109(b) of the Act.
---------------------------------------------------------------------------
In sharp contrast to the commenters discussed immediately above, a
number of other commenters strongly supported standard levels more
stringent than those proposed by EPA. These commenters supported EPA's
conclusions regarding the epidemiological studies, but would place much
less weight on uncertainties related to the concentration-response
relationships for PM2.5 as a surrogate for PM and the
relative importance of various PM components. Based on their evaluation
of the information, and citing the support of some CASAC panel members,
these commenters variously recommended 24-hour PM2.5
standards as low as 18 to 20 g/m3 and annual
standards of 10 to 12 g/m3.40
---------------------------------------------------------------------------
40 This range of levels for a 24-hour PM2.5 standard
is close to the lower bound levels recommended by four CASAC panel
members (20 g/m3); no member supported an annual
PM2.5 standard as low as 10 to 12 g/
m3.
---------------------------------------------------------------------------
EPA notes that setting such standards would result in commensurate
reductions in health risks only if, in fact, there is a continuum of
health risks down to the lower end of the ranges of air quality
observed in the key epidemiological studies, and only if the reported
associations are, in fact, causally related to PM2.5 at the
lowest concentrations measured. Setting standards at low levels where
the possibility of effects thresholds is greater, and where there is
greater potential that other elements in the air pollution mix (or some
subset of particles within the fine fraction) become more responsible
for (or modify) the effects being causally attributed to
PM2.5, might result in regulatory programs that go beyond
those that are needed to effectively reduce risks to public health.
While placing substantial weight on the results of the key health
studies in the higher range of concentrations observed, EPA is
persuaded that the inherent scientific uncertainties are too great to
support standards based on the lowest concentrations measured in such
studies, which approach the maximum range of PM2.5 values
estimated for short-term background conditions.
Having considered the comments reflecting the two contrasting views
summarized above in this unit, the Administrator concludes that the
approach she set forth in the proposal is the most appropriate for
selecting levels for annual and 24-hour PM2.5 standards.
This approach focuses primarily on standard levels designed to limit
annual PM2.5 concentrations to somewhat below those where
the body of epidemiological evidence is most consistent and coherent,
in recognition of both the strengths and the limitations of the full
range of scientific and technical information on the health effects of
PM, as well as associated uncertainties, as interpreted by the Criteria
Document, Staff Paper, and CASAC. The Administrator believes that this
approach appropriately reflects the weight of the evidence as a whole.
In identifying PM2.5 standard levels consistent with
this overall approach, the Administrator has placed greatest weight on
those epidemiological studies reporting associations between health
effects and direct measures of fine particles, most notably those
recent studies conducted in North America (summarized in Tables V-12
and V-13 of the Staff Paper).41 Key considerations and study
results upon which this approach is based are presented as follows.
---------------------------------------------------------------------------
41 Some confusion is apparent in comments regarding the basis on
which the Administrator selected levels for the proposed
PM2.5 standards, with some commenters suggesting two or
at most three studies were used, and others suggesting that EPA
relied extensively on uncertain conversion factors to estimate
levels for the standards. These comments are in error. To clarify,
as stated in the proposal, the Administrator is basing her decision
to revise the standards on the full range of PM health effects
studies summarized in the Criteria Document and Staff Paper, but in
selecting specific levels for PM2.5 standards, is relying
chiefly on U.S. and Canadian studies, listed in Tables V-12 and V-13
of the Staff Paper, that measured fine PM levels. To ease
identification and use of these key studies, the short-term exposure
studies and key PM air quality statistics are cited in Koman (1996)
and all long-term exposure studies are cited in this preamble. The
referenced memorandum (Koman, 1996) has been updated (Koman, 1997)
to clarify key aspects of the studies cited and relevant air quality
statistics. In accordance with EPA and CASAC views on the relative
strength of these studies, greater weight is placed on short-term
exposure studies than on long-term exposure studies. Where studies
found statistically significant associations with PM2.5
components (e.g., sulfates and/or acids, in Thurston et al., 1994;
Dockery et al., 1996), the corresponding PM2.5 or
PM2.1 values from the study are cited. No conversions
were made from the original measurements used in these studies.
---------------------------------------------------------------------------
As previously discussed, the Administrator has concluded that it is
appropriate to select the level of the annual standard so as to protect
against the range of effects associated with both short- and long-term
exposures to PM,
[[Page 38676]]
with the 24-hour standard level selected to provide supplemental
protection against peak concentrations that might occur over limited
areas and/or for limited time periods. In selecting the level for the
annual standard, therefore, the Administrator has considered both
short- and long-term exposure studies.
In accordance with EPA staff and CASAC views on the relative
strengths of the epidemiological studies, the Administrator has placed
greater emphasis on the short-term exposure studies in selecting the
level of the annual standard. The approach she took to this issue
consisted of determining a provisional level based on the short-term
exposure studies, and then determining whether the long-term exposure
studies are consistent with that level or, instead, suggest the need
for a lower level. The effects estimates from the short-term exposure
studies (in Table V-12 of the Staff Paper) are based on analyses of
daily PM2.5 concentrations that occurred over the course of
the study period. While effects may occur over the full range of
concentrations observed in the studies, consistent with the discussion
of this issue in Unit II.D. of this preamble, the strongest evidence
for short-term PM2.5 effects occurs at concentrations near
the long-term (e.g., annual) average. More specifically, the strength
of the evidence of effects increases for concentrations that are at or
above the long-term (e.g., annual) mean levels reported for these
studies.42 Given the serious nature of the potential
effects, the Administrator believes it is both prudent and appropriate
to select a level for an annual standard at or below such
concentrations. An examination of the long-term means from the combined
six city analyses of daily mortality (Schwartz et al., 1996a) and
morbidity (Schwartz et al., 1994), together with those from studies in
individual cities for which statistically significant PM-effects
associations are reported (from Table V-12 in the Staff Paper), finds
mean concentrations ranging from about 16 to about 21 g/
m3 (Koman, 1996; 1997). In addition, the mean concentrations
in cities where short-term exposure associations are characterized in
the Criteria Document as nearly statistically significant (U.S. EPA,
1996a, p. 13-40) range from about 11 g/m3 to 30
g/m3. Taken together, and placing greatest weight
on those studies that were clearly statistically significant, this
evidence suggests that an annual standard level of 15 g/
m3 is appropriate to reduce the risk of effects from short-
term exposure to fine particles.
---------------------------------------------------------------------------
42 As discussed in the proposal and Appendix E of the Staff
Paper (U.S. EPA, 1996b, p. E-4), there is generally greatest
statistical confidence in observed associations for levels at and
above the mean concentration.
---------------------------------------------------------------------------
Before reaching a final conclusion, the Administrator also examined
this level in light of the effects reported in epidemiological studies
of long-term exposures to fine particles (Table V-13 in the Staff
Paper), which may reflect the accumulation of daily effects over time
as well as potential effects uniquely associated with long-term
exposures. Even though subject to additional uncertainties, the long-
term exposure studies provide important insights with respect to the
overall protection afforded by an annual standard. These studies were
examined for general consistency and support for the levels derived
from the short-term exposure studies, and to determine whether they
provide evidence that a more stringent level is needed.
The most direct comparison with the daily fine particle mortality
studies is provided by two long-term prospective cohort studies
(Dockery et al., 1993; Pope et al., 1995). The annual mean
PM2.5 concentration for the multiple cities included in
these studies (6 and 50 cities, respectively) was 18 g/
m3 (Dockery et al., 1993), and about 21-22 g/
m3 for the larger Pope et al. (1995) study.43 The
Staff Paper assessment of the concentration-response results from
Dockery et al. (1993) concluded that the evidence for increased risk
was more apparent at annual concentrations at or above 15 g/
m3 (Table E-3; U.S. EPA; 1996b).44 EPA notes that
the estimated mean values for most of the cities in Pope et al. (1995)
are above 15 g/m3. As noted in the Staff Paper and
the Criteria Document, the estimated magnitude of effects in both long-
term exposure mortality studies may be related to higher historical
concentrations than the affected communities experienced during the
time period of the studies; this consideration suggests that a level of
15 g/m3 would incorporate a margin of safety. An
examination of morbidity effects and long-term exposures is provided by
the recent ``24 city'' studies, which found that reduced lung function
and increased respiratory symptoms in children followed the gradient in
annual mean concentrations of fine particles and/or acid-sulfate
components of fine particles (Raizenne et al., 1996; Dockery et al.,
1996). The results indicate a greater likelihood of effects at annual
mean PM2.1 levels above about 15 g/m3
(U.S. EPA, 1996b; Figure V-7). In the judgment of the Administrator,
these studies are consistent with a standard level of 15 g/
m3. While they provide some suggestion of risks extending to
lower concentrations, they do not provide a sufficient basis for
establishing a lower annual standard level.
---------------------------------------------------------------------------
43 Based on a public comment, EPA found that the mean of 18
g/m3 in Pope et al. (1995) reported in the
Criteria Document and elsewhere was actually the mean of median
values. Based on typical air quality relationships, the conventional
arithmetic mean would be approximately 21 to 22 g/
m3 (Freas, 1997). The lowest median concentration
measured in this study (9 g/m3), which was
relied upon by some commenters as a basis for annual standards of 10
g/m3, is about 11 to 12 g/m3
as an arithmetic mean.
44 Based on public comments and a further evaluation of the
underlying study, EPA concludes that the comparable assessment of
the concentration-response function summarized in Table E-3 for Pope
et al. (1995) is not appropriate, because it was based on a
supplemental ``ecologic'' comparison for these cities and not on the
far more reliable prospective-cohort analysis that was the main
focus of the paper.
---------------------------------------------------------------------------
Taking the epidemiological studies of both short- and long-term
exposures together, the Administrator believes the concordance of
evidence for PM effects and associated levels provides clear support
for an annual PM2.5 standard level of 15 g/
m3. This level is below the range of annual data most
strongly associated with both short- and long-term exposure effects,
and because even small changes in annual means in this concentration
range can make significant differences in overall risk reduction and
total population exposures, the Administrator believes it will provide
an adequate margin of safety against the effects observed in these
epidemiological studies. Moreover, the means in areas where
PM2.5 concentrations were statistically significantly
associated with daily mortality (about 16 to 21 g/
m3) reflect a 7 to 9-year average; thus, the use of a 3-year
mean will provide additional protection. Although the possibility of
effects at lower annual concentrations cannot be excluded, the evidence
for that possibility is highly uncertain and, as previously discussed,
the likelihood of significant health risk, if any, becomes smaller as
concentrations approach the lower end of the range of air quality
observed in the key epidemiological studies and/or background levels.
The final annual standard will provide substantial protection
against short-term as well as long-term exposures to particles.
Nevertheless, for the reasons specified above, a spatially averaged
annual standard cannot be expected to offer an adequate margin of
safety against the effects of all potential short-term exposures in
areas with strong local or seasonal sources. The
[[Page 38677]]
broad-based community studies considered in this review generally could
not evaluate such peak exposure conditions directly. Given the public
health purposes of the 24-hour standard, the Administrator believes it
should be set at a level that generally supplements the control
afforded by an annual standard and proposed an approach based on
providing a reasonable degree of protection against the peak levels
observed or expected in communities where health effects have been
associated with daily levels of fine particles.
For the reasons specified in the previous unit, the Administrator
has decided to use a 98th percentile concentration-based
form of the standard. As noted in the proposal, the 98th
percentile 24-hour PM2.5 concentrations in cities with
statistically significant or nearly significant short-term fine
particle exposure-effects associations ranged from 34 g/
m3 to as high as 90 g/m3 (Koman, 1996,
1997). Based on an examination of these results, EPA originally
proposed a level for the 24-hour standard of 50 g/
m3, and solicited comments on higher and lower alternative
levels.
In considering comments on alternative levels for the purpose of
making a final decision on the 24-hour standard, the Administrator
recognizes the significant uncertainties in identifying the extent of
the incremental risk associated with single peak exposures to
PM2.5 in areas where the annual standard is met. Clearly,
the risks associated with the 98th percentile air quality
data used in the selecting the proposed level are from the same study
cities that experienced long-term levels at varying amounts above that
selected for the annual standard. It is unclear what risks might have
been associated with such peak levels had the long-term averages in
these areas been below that selected for the annual standard.
Regardless of this uncertainty, it is clear that reducing the annual
concentrations in such areas to that of the annual standard would
reduce the risk associated with peak days, whatever the magnitude, as
well as that associated with the far more numerous days with
concentrations near the annual average. Given these uncertainties and
the significant degree of protection afforded by the annual standard,
the Administrator is persuaded that it is appropriate to adopt a
different approach for selecting the levels of the 24-hour standard
than the one proposed.
In making a final decision on an appropriate level for the 24-hour
standard, the Administrator considered several key factors: the
significant protection afforded against short-term exposures by the
annual PM2.5 standard; the role of the 24-hour standard in
providing supplemental protection against peak exposures not addressed
by the annual standard; the air quality and effects information in the
studies cited above; the uncertainties in the risks associated with
infrequent and isolated peak exposures in areas that meet the annual
standard; the range of levels recommended by EPA staff and CASAC panel
members; and the extensive public comment on the alternative levels
proposed, which ranged between 20 and 65 g/m3.
Because of the approach of establishing the annual standard as the
controlling standard, and, in particular, the decision to set the level
at the lower end of the annual range, there is no need to consider
levels in the lower portion of the 24-hour range below the level
proposed. Therefore, the Administrator focused on evaluating the margin
of safety associated with levels between 50 and 65 g/
m3.
As has been discussed in previous units, the extent of total risk
over the course of a year associated solely with a limited number of
peak exposures is uncertain, but it is considerably smaller than that
associated with the entire air quality distribution. Further, the risk
associated with infrequent peak 24-hour exposures in otherwise clean
areas is not well enough understood at this time to provide a basis for
selecting the more restrictive levels in the range of 50 to 65
g/m3. On the other hand, it is clear that any
standard level within this range would provide some margin of safety.
Taking into account the factors outlined above, the Administrator has
concluded that a 24-hour standard at the level of 65 g/
m3 would provide an effective limit in the role as a
supplement to the annual standard. This level is at the upper end of
the range recommended by staff and most CASAC panel members, and below
the levels suggested by some CASAC panel members and by a number of
public commenters. Although this level is not risk free, the
Administrator believes that it would provide an appropriate degree of
additional protection over that provided by the annual PM2.5
standard. Accordingly, after weighing these factors in light of the
scientific uncertainties, the Administrator believes that a
98th percentile 24-hour PM2.5 standard of 65
g/m3 would provide an adequate margin of safety
against infrequent or isolated peak concentrations that could occur in
areas that attain the annual standard of 15 g/m3.
In the Administrator's judgment, the factors discussed above
provide ample reason to believe that both annual and 24-hour
PM2.5 standards are appropriate to protect public health
from adverse health effects associated with short- and long-term
exposures to ambient fine particles. Further, she believes these
factors provide a clear basis for judging that an annual
PM2.5 standard set at 15 g/m3, in
combination with a 24-hour standard set at 65 g/m3,
will protect public health with an adequate margin of safety.
G. Conclusions Regarding the Current PM10 Standards
1. Averaging time and form. In conjunction with
PM2.5 standards, the new function of PM10
standard(s) is to protect against potential effects associated with
coarse fraction particles in the size range of 2.5 to 10 m.
Coarse fraction particles are plausibly associated with certain effects
from both long- and short-term exposures (EPA 1996a,b). Based on
qualitative considerations, deposition of coarse fraction particles in
the respiratory system could be expected to aggravate effects in
individuals with asthma. The Criteria Document and Staff Paper found
support for this expectation in limited epidemiological evidence on the
effects of coarse fraction particles, suggesting that aggravation of
asthma and respiratory infections and symptoms may be associated with
daily or episodic increases in PM10 that are dominated by
coarse fraction particles. The potential build-up of insoluble coarse
fraction particles in the lung after long-term exposures to high levels
should also be considered.
Based on assessments of the available information in the Criteria
Document and Staff Paper, both the staff and CASAC recommended
retention of an annual PM10 standard. The staff, with CASAC
concurrence, recommended retention of the current annual arithmetic
mean form of the standard, which is the same form being adopted for the
annual PM2.5 standard. As noted in the staff assessment, the
current annual PM10 standard offers substantial protection
against the effects of both long- and short-term exposure to coarse
fraction particles. Public comment was nearly unanimous in recommending
retention of this standard. The Administrator therefore has decided to
continue a long-term PM10 standard as an annual arithmetic
mean, averaged over 3 years.
The staff and CASAC also recommended that consideration be
[[Page 38678]]
given to retention of a 24-hour standard to provide additional
protection against potential effects of short-term exposures to coarse
fraction particles. The staff, with CASAC concurrence, also recommended
that if a 24-hour standard is retained, the form of the standard should
be revised to provide a more robust target for coarse fraction particle
controls. The Administrator originally proposed a 98th
percentile form for the 24-hour PM10 standard based
primarily on the reasons outlined above in this unit regarding the
proposed form of the 24-hour PM2.5 standard.
The EPA received few comments supporting elimination of the 24-hour
PM10 standard. The main exceptions were some industries,
most notably the mining industry, which as noted above in this unit,
argued that the available data provide little evidence for coarse
particle effects at current ambient levels. These groups, who generally
opposed PM2.5 standards, also argued that the daily
PM10 standard could be eliminated if PM2.5
standards were set. Based on the potential aggravation of respiratory
symptoms from short-term exposure to coarse fraction particles
discussed in the Criteria Document and by numerous commenters, as well
as the recommendations of a majority of CASAC panelists who also
supported PM2.5 standards, the Administrator concludes it is
appropriate to retain a 24-hour PM10 standard.
In general, comments received on the form of the 24-hour
PM10 standard paralleled those on the form of the
PM2.5 standard. Substantial concerns were expressed by
environmental groups, some States, and others that the 98th
percentile would not provide an adequate limit on the number and
magnitude of 24-hour peak PM10 excursions. While a number of
these commenters suggested keeping the current 1-expected-exceedance
form, EPA believes that a concentration- based percentile form offers
significant advantages, as outlined above in this unit, for both PM
indicators. Some air pollution control officials, who were concerned
about the extent to which the 24-hour PM10 standard would be
relaxed under the proposed form, suggested consideration of a
99th percentile form with increased monitoring as an
appropriately protective form. Other commenters, particularly some
industry groups and some States, strongly supported concentration-based
percentile forms, with some recommending consideration of the
95th percentile form.
The proposal noted that a percentile value selected closer to the
``tail'' of the air quality distribution (e.g., a 99th or
greater percentile) would not significantly increase stability as
compared to the current form. However, an association of 8 State air
pollution agencies commented that a 99th percentile form
could provide increased stability if combined with a daily or 1-in-3-
day sampling frequency and with greater data capture. In addition, EPA
notes that this concentration-based form is inherently more stable than
the current exceedance-based form.
Many of these and other commenters were concerned that the
uncertainties in the available scientific information on the effects of
coarse particles were a reason to be concerned that, assuming the
current standard level was kept, a 98th percentile form
would represent a significant relaxation in protection relative to the
current standards. Unlike the situation for the new
PM2.5 standards, in the case of the PM10
standards, the 24-hour standard has generally been the ``controlling''
standard, making changes to the form of the 24-hour standard
potentially more significant to the overall national level of
protection afforded. Given the uncertainties in the available
scientific evidence with respect to the potential health effects of
short-term exposures to coarse fraction particles, the Administrator is
persuaded that the somewhat more cautious approach with respect to
revising the 24-hour PM10 standard recommended by many
commenters is appropriate. The only approaches available for increasing
the extent of protection for this standard as compared to that of the
proposed standard involve modifying the form or reducing the level. For
reasons discussed in the following section, the Administrator believes
it is not appropriate to revise the level of the standard. In order to
provide adequate protection against the potential risk associated with
multiple short-term peak exposures to coarse fraction particles, the
Administator accepts commenters' recommendations to decrease the
frequency of peak values, while still providing for a more stable
control target than afforded by the current 1-expected-exceedance form.
Therefore, the Administrator concludes that the 99th
percentile concentration-based form, averaged over 3 years, and
combined with more frequent sampling, would be an appropriate form for
a 24-hour PM10 standard.
2. Levels for the annual and 24-hour PM10 standards--a.
Annual PM10 standard. As a result of the more limited
information for coarse fraction particles, the Administrator's approach
for selecting a level of the standard is directly related to the
approach taken in the last review of the PM NAAQS. In that review,
evidence from limited quantitative studies was used in conjunction with
support from the qualitative literature in selecting the level of the
current annual PM10 standard. In the current review, the
staff assessment of the major quantitative basis for the level of that
standard (Ware et al., 1986), together with a more recent related study
(Dockery et al., 1989), recommended the same range of levels of concern
(40 to 50 g/m3) as in the 1986 staff paper. The
staff concludes that it is possible, but not certain, that coarse
fraction particles, in combination with fine particles, may have
influenced the observed effects at these levels. Based on particle
deposition considerations, it is possible that cumulative deposition of
coarse fraction particles could be of concern in children, who are more
prone to be active outdoors than sensitive adult populations.
Qualitative evidence of other long-term coarse particle effects,
most notably from long-term build-up of silica-containing materials,
supports the need for a long-term standard, but does not provide
evidence of effects below the range of 40 to 50 g/
m3 (U.S. EPA, 1996a, p. 13-79). The staff concludes that the
qualitative evidence with respect to biological aerosols also supports
the need to limit coarse materials, but should not form the major basis
for a national standard (U.S. EPA, 1996a, p. 13-79). In addition, staff
notes that the nature and distribution of such materials, which vary
from endemic fungi (e.g., valley fever) to pollens larger than 10
m, are not appropriately addressed by traditional air
pollution control programs.
Based on its review of the available information, CASAC found ``a
consensus that retaining an annual PM10 NAAQS at the current
level is reasonable at this time'' (Wolff, 1996b). With few exceptions,
public comments supported levels at least as stringent as the current
annual PM10 standard.45 Taking into account these
comments and the above considerations, as more fully detailed in the
Staff Paper and the
[[Page 38679]]
CASAC recommendations, the Administrator has decided to retain the
current annual PM10 standard of 50 g/m3
to protect against the known and potential effects of long-term
exposure to coarse fraction particles.
---------------------------------------------------------------------------
45 Some commenters, including some environmental groups and the
State of California (Cal EPA, 1997), suggested that the large number
of recent studies showing effects at PM10 levels below
the current standards provides a basis for establishing stricter
annual and 24-hour PM10 standards, in conjunction with
PM2.5 standards. As discussed in Units II.B. and C. of
this preamble, while these studies could be used either to tighten
the PM10 standards or to add standards that tighten
control of the fine fraction of PM10, the weight of
evidence from all of the relevant information more readily supports
the development of additional protection for the PM2.5
fraction.
---------------------------------------------------------------------------
b. 24-hour PM10 standard. As discussed above in this
unit, EPA staff and CASAC also recommended that consideration be given
to a 24-hour standard for coarse fraction particles as measured by
PM10. Unlike the case for the annual standard, however, the
staff found that the original quantitative basis for the level of the
current 24-hour PM10 standard (150 g/m3)
is no longer appropriate. Instead, the staff found that the main
quantitative basis for a short-term standard is provided by the two
recent community studies of exposure to fugitive dust (Gordian et al.,
1996; Hefflin et al., 1994). Because these studies reported multiple
large exceedances of the current 24-hour standard, and because of
limitations in the studies themselves, the staff concluded that they
provide no basis to lower the level of the standard below 150
g/m3. Moreover, staff concluded that none of the
qualitative literature regarding the potential effects of short-term
exposure to coarse particles provides a basis for a lower standard
level. Both EPA staff and CASAC recommended that if a 24-hour
PM10 standard is retained, the level of the standard should
be maintained at 150 g/m3, although with a revised
form. Beyond the comments summarized above recommending elimination of
the 24-hour standard, no commenters recommended a less stringent level,
while some others, as summarized above in this unit, recommended more
stringent levels. Most comments favored the current level.
Having considered these factors and the public comments, the
Administrator judges that, retention of a 24-hour PM10
standard at the level of 150 /m3 with a
99th percentile form is appropriate and will provide
adequate protection against the known and potential effects of short-
term coarse fraction particle exposures that have been identified to
date in the scientific literature.
H. Final Decisions on Primary PM Standards
For the reasons discussed above in this unit, and taking into
account the information and assessments presented in the Criteria
Document and the Staff Paper, the advice and recommendations of CASAC,
and public comments received on the proposal, the Administrator is
revising the current PM NAAQS by adding new PM2.5 standards
and by revising the form of the current 24-hour PM10
standard. Specifically, the Administrator is making the following
revisions:
(1) The suite of PM standards is revised to include an annual
primary PM2.5 standard and a 24-hour PM2.5
standard.
(2) The annual PM2.5 standard is met when the 3-year
average of the annual arithmetic mean PM2.5 concentrations,
from single or multiple community-oriented monitors (in accordance with
EPA's final rule on monitoring siting guidance, 40 CFR part 58,
published in a separate document elsewhere in this issue of the Federal
Register) is less than or equal to 15 g/m3, with
fractional parts of 0.05 or greater rounding up.
(3) The 24-hour PM2.5 standard is met when the 3-year
average of the 98th percentile of 24-hour PM2.5
concentrations at each population-oriented monitor within an area is
less than or equal to 65 g/m3, with fractional
parts of 0.5 or greater rounding up.
(4) The form of the current 24-hour PM10 standard is
revised to be based on the 3-year average of the 99th
percentile of 24-hour PM10 concentrations at each monitor
within an area.
In addition, the Administrator is retaining the current annual
PM10 standard at the level of 50 g/m3,
which is met when the 3-year average of the annual arithmetic mean
PM10 concentrations at each monitor within an area is less
than or equal to 50 g/m3, with fractional parts of
0.5 or greater rounding up.
As discussed below in Units V. and VI. of this preamble, data
handling conventions and completeness criteria for the revised
standards are being established (40 CFR part 50, Appendix N). The
reference method for monitoring PM as PM10 for the revised
standards has been established (40 CFR part 50, Appendix M). A new
reference method is being established for monitoring PM as
PM2.5 (40 CFR part 50, Appendix L). In a separate document
published elsewhere in this issue of the Federal Register, EPA is
providing opportunity for public comment on supplemental information
relating to the new reference method for monitoring PM as
PM2.5 (40 CFR part 50, Appendix L).
As indicated previously, EPA plans to propose related revisions to
the Pollutant Standards Index for PM (40 CFR 58.50) and the significant
harm level program (40 CFR 51.66) at a later date.
III. Rationale for the Secondary Standards
The Criteria Document and Staff Paper examined the effects of PM on
such aspects of public welfare as visibility, materials damage, and
soiling. The following discussion of the rationale for revising the
secondary standards for PM focuses on those considerations most
influential in the Administrator's decision.
A. Need for Revision of the Current Secondary Standards
1. Visibility impairment. This unit of the document presents the
Administrator's decision to address the welfare effects of PM on
visibility by setting secondary standards identical to the suite of
PM2.5 primary standards, in conjunction with the
establishment of a regional haze program under section 169A of the
Act.46 In the Administrator's judgment, this approach is the
most effective way to address visibility impairment given the regional
variations in concentrations of non-anthropogenic PM as well as other
regional factors that affect visibility, such as humidity. By
augmenting the protection provided by secondary standards set identical
to the suite of PM2.5 primary standards with a regional haze
program, the Administrator believes that an appropriate degree of
visibility protection can be achieved in the various regions of the
country.
---------------------------------------------------------------------------
46 Congress adopted section 169A of the Act because of concern
that the NAAQS and Prevention of Significant Deterioration programs
might not provide adequate visibility protection nationally,
particularly for ``areas of great scenic importance.'' See H.R. Rep.
No. 95-294,at 203-205 (1977).
---------------------------------------------------------------------------
In coming to this decision, the Administrator took into account
several factors, including: The pertinent scientific and technical
information in the Criteria Document and Staff Paper, difficulties
inherent in attempting to establish national secondary standards to
address visibility impairment, the degree of visibility improvement
expected through attainment of secondary standards equivalent to the
suite of PM2.5 primary standards, the effectiveness of
addressing the welfare effects of PM on visibility through the
combination of a regional haze program and secondary standards for
PM2.5 equivalent to the suite of primary standards, and
comments received during the public comment period. The Administrator's
consideration of each of these factors is discussed below in this unit.
The Administrator first concluded, based on information presented
and referenced in the Criteria Document and
[[Page 38680]]
Staff Paper, that particulate matter can and does produce adverse
effects on visibility in various locations, depending on the PM
concentrations involved and other factors discussed below. It has been
demonstrated that impairment of visibility is an important effect of PM
on public welfare, and that it is experienced throughout the United
States, in multi-state regions, urban areas, and remote mandatory Class
I Federal areas47 alike. Visibility is an important welfare
effect because it has direct significance to people's enjoyment of
daily activities in all parts of the country. Individuals value good
visibility for the well-being it provides them directly, both where
they live and work, and in places where they enjoy recreational
opportunities. Visibility is highly valued in significant natural
areas, such as national parks and wilderness areas, because of the
special emphasis given to protecting these lands now and for future
generations. The Criteria Document cites many studies designed to
quantify the benefits associated with improvements in visibility.
---------------------------------------------------------------------------
47 There are 156 mandatory Class I Federal areas protected by
the visibility provisions in sections 169A and 169B of the Act.
These areas are defined in section 162 of the Act as those national
parks exceeding 6,000 acres, wilderness areas and memorial parks
exceeding 5,000 acres, and all international parks which were in
existence on August 7, 1977.
---------------------------------------------------------------------------
The Administrator considered information from the Staff Paper and
Criteria Document regarding the effect of the composition of
particulate matter on visibility. Visibility conditions are determined
by the scattering and absorption of light by particles and gases, from
both natural and anthropogenic sources. Visibility can be described in
terms of visual range, light extinction, or deciview48. The
classes of fine particles principally responsible for visibility
impairment are sulfates, nitrates, organic matter, elemental carbon
(soot), and soil dust. Fine particles are more efficient per unit mass
at scattering light than coarse particles. The scattering efficiency of
certain classes of fine particles, such as sulfates, nitrates, and some
organics, increases as relative humidity rises because these particles
can absorb water and grow to sizes comparable to the wavelength of
visible light. In addition to limiting the distance that one can see,
the scattering and absorption of light caused by air pollution can also
degrade the color, clarity, and contrast of scenes.
---------------------------------------------------------------------------
48 Visual range can be defined as the maximum distance at which
one can identify a black object against the horizon sky. It is
typically described in miles or kilometers. Light extinction is the
sum of light scattering and absorption by particles and gases in the
atmosphere. It is typically expressed in terms of inverse megameters
(Mm-1), with larger values representing poorer
visibility. The deciview metric describes perceived visual changes
in a linear fashion over its entire range, analogous to the decibel
scale for sound. A deciview of 0 represents pristine conditions.
Under many scenic conditions, a change of 1 deciview is considered
perceptible by the average person.
---------------------------------------------------------------------------
The Administrator next considered what would be an appropriate
level for a secondary standard to address adverse effects of
particulate matter on visibility. The determination of a single
national level is complicated by regional differences in visibility
impairment due to several factors, including background and current
levels of PM, composition of particulate matter, and average relative
humidity.
The Criteria Document and Staff Paper describe estimated background
levels of PM and natural light extinction. In the United States,
estimated annual mean background levels of PM2.5 are
significantly lower in the West than in the East. Based on estimated
background fine particle and light extinction levels summarized in
Table VIII-2 of the Staff Paper, naturally occurring visual range in
the East is approximately 105 to 195 kilometers, whereas in the West it
is approximately 190 to 270 kilometers. This significant regional
difference in estimated background conditions results from two main
factors. First, in the western United States, visibility is more
sensitive to an additional 1-2 g/m3 of
PM2.5 in the atmosphere than in the eastern United States.
Secondly, light scattering is increased for certain particles (e.g.,
sulfates, nitrates, and some organics) due to higher average relative
humidity in the East.
The combination of naturally occurring and manmade emissions also
leads to significant differences in current visibility conditions
between the eastern United States, 23-39 kilometers average visual
range, and western United States, 55-150 kilometers average visual
range. Table VIII-4 of the Staff Paper indicates that the current level
of annual average light extinction in several western locations, such
as the Colorado Plateau, is about equal to the level of background
light extinction, i.e., the level generally regarded as representing
the absence of anthropogenic emissions in North America, in the East.
This regional difference is due to higher background particle
concentrations in the East, a composition of fine particles in the East
that, in association with higher eastern humidity levels, is more
efficient at light scattering, and significantly lower concentrations
of anthropogenic PM in remote western locations as compared with remote
eastern sites.
Because of these regional differences, it is the Administrator's
judgment that a national secondary standard intended to maintain or
improve visibility conditions on the Colorado Plateau or other parts of
the West would have to be set at or even below natural background
levels in the East, which would effectively require elimination of all
eastern anthropogenic emissions. Conversely, a national secondary
standard that would achieve an appropriate degree of visibility
improvement in the East would permit further degradation in the West.
Due to this regional variability in visibility conditions created by
differing background fine particle levels, fine particle composition,
and humidity effects, the Administrator finds that addressing
visibility solely through setting more stringent national secondary
standards would not be an appropriate means to protect the public
welfare from adverse impacts of PM on visibility in all parts of the
country.49 Aside from the problem of regional variability,
the Administrator has also determined that the Agency currently lacks
sufficient information to establish a level for a national secondary
standard that would represent a threshold above which visibility
conditions would always be adverse and below which visibility
conditions would always be acceptable. Because visibility varies not
only with PM concentration, but also with PM composition and humidity
levels, attaining even a low concentration of fine particles might or
might not provide adequate protection, depending on these factors.
---------------------------------------------------------------------------
49 Congress adopted a visibility protection program in section
169A of the Act because it recognized the impracticability of
revising the NAAQS to protect visibility in all areas of the
country: ``It would be impracticable to require a major city such as
New York or Los Angeles to meet the same visibility standards as the
Grand Canyon and Yellowstone Park.'' See H.R. Rep. No. 95-294 at
205. (1977)
---------------------------------------------------------------------------
The Administrator next assessed potential visibility
improvements50 that would result from attainment of the new
primary standards for PM2.5. The spatially averaged form of
the annual standard is well suited to the protection of visibility,
which involves effects of PM throughout an extended viewing distance
across an urban area. Indeed, as
[[Page 38681]]
the generally controlling standard focused on reducing urban and
regional scale fine particle levels, most of the visibility protection
provided by the PM2.5 primary standards would be derived
from the annual standard. In many cities having annual mean
PM2.5 concentrations exceeding 17 g/m3,
improvements in annual average visibility resulting from attainment of
the new annual PM2.5 primary standard are expected to be
perceptible (i.e., to exceed 1 deciview). Based on annual mean
PM2.5 data reported in Table 12-2 of the Criteria Document
and Table V-12 in the Staff Paper, many cities in the Northeast,
Midwest, and Southeast, as well as Los Angeles, would be expected to
see perceptible improvement in visibility if the annual
PM2.5 primary standard is attained.
---------------------------------------------------------------------------
50 Estimates of annual average visibility improvements assume
that, on a percentage basis, the reduction for each fine particle
component is equal to the % reduction in the mass of fine particles,
and that the overall light extinction efficiency of the fine
particle pollutant mix does not change. Further, for the estimates
presented here, the reductions in fine mass at monitored locations
are assumed to reflect the spatial average concentrations through
the viewing distance. (Damberg and Polkowsky, 1996.)
---------------------------------------------------------------------------
In Washington, DC, for example, where the IMPROVE
network51 shows annual mean PM2.5 concentrations
at about 19 g/m3 during 1992-1995, approximate
annual average visibility would be expected to improve from 21 km
visual range (29 deciview) to 27 km (27 deciview). Annual average
visibility in Philadelphia, where annual PM2.5 levels have
been recently measured at 17 g/m3, would be
expected to change from about 24 to 27 km, an improvement of about 1
deciview. In Los Angeles, where recent data shows annual mean
PM2.5 concentrations at approximately 30 g/
m3, visibility would be expected to improve from about 19 to
34 km (30 to 24 deciview) if the new annual primary PM2.5
standard is attained.
---------------------------------------------------------------------------
51 IMPROVE (Interagency Monitoring of PROtected Visual
Environments) is a visibility monitoring network managed
cooperatively by EPA, Federal land management agencies, and State
representatives. An analysis of IMPROVE data for 1992-1995 is found
in Sisler et al. (1996).
---------------------------------------------------------------------------
It is important to note that some urban areas, many in the eastern
United States, would be expected to have annual mean PM2.5
concentrations reduced below the primary standard level of 15
g/m3 when implementation of regional control
strategies for PM and other air quality programs, such as those
addressing acid rain and mobile sources, are taken into account
together. On the other hand, some urban areas with annual
PM2.5 levels at or below the 15 g/m3
level would be expected to see little, if any, improvement in annual
average visibility. This may be particularly true of certain western
urban areas that are dominated by coarse rather than fine particles.
The Administrator also considered the potential effect on urban
visibility if the 24-hour 98th percentile PM2.5 standard of
65 m3 is attained. In areas with violations caused by
localized hot spots, the 24-hour standard might have little effect
other than on visible source emissions. In other areas, for example,
with seasonally high woodsmoke, a more areawide improvement is
possible. In such urban areas, attainment of the 24-hour standard would
be expected to reduce, to some degree, the number and intensity of
``bad visibility'' days, i.e., the 20% of days having the greatest
impairment over the course of a year. For example, maximum 24-hour
PM2.5 concentrations have been recorded in recent years at
over 140 g/m3 at several California locations. If
the level and frequency of peak PM concentrations are reduced,
improvements would be expected in those days where visibility is worst,
even in urban areas having annual averages below the annual
PM2.5 primary standard.
Having concluded that attainment of the annual and 24-hour
PM2.5 primary standards would lead to visibility
improvements in many eastern and some western urban areas, the
Administrator also considered potential improvements to visibility on a
regional scale. In the rural East, attainment of the PM2.5
primary standards could result in regional visibility improvement,
e.g., in certain mandatory Class I Federal areas such as Shenandoah and
Great Smoky Mountains National Park, if regional control strategies are
adopted and carried out in order to reduce the impact of long-range
transport of fine particles such as sulfates. Fine particle emission
reductions achieved by other air quality programs, such as those to
reduce acid rain or mobile source emissions, are also expected to
improve Eastern regional visibility conditions (U.S. EPA, 1993). In the
West, strategies to attain the primary PM2.5 standards are
less likely to significantly improve visibility on a regional basis.
However, areas downwind from large urban areas, such as Southern
California, would likely see some improvement in annual average
visibility.
Based on the foregoing, the Administrator concludes that attainment
of PM2.5 secondary standards set at the level of the primary
standards for PM2.5 would be expected to result in
visibility improvements in the eastern United States at both urban and
regional scales, but little or no change in the western United States
except in and near certain urban areas. Additionally, the Administrator
determined that attainment of secondary standards equivalent to the
suite of PM2.5 primary standards for particulate matter
would address some but not all of the effects of particulate matter on
visibility. The extent to which these effects would be addressed is
expected to vary regionally.
The Administrator then considered the potential effectiveness of a
regional haze program to address the remaining effects of particulate
matter on visibility (i.e., those that would not be addressed through
attainment of secondary standards identical to the suite of
PM2.5 primary standards). A program to address the
widespread, regionally uniform type of haze caused by a multitude of
sources is required by sections 169A and 169B of the Act. In 1977,
Congress established as a national goal ``the prevention of any future,
and the remedying of any existing, impairment of visibility in
mandatory Class I Federal areas which impairment results from manmade
air pollution'', section 169A(a)(1) of the Act. The EPA is required by
section 169A(a)(4) of the Act to promulgate regulations to ensure that
``reasonable progress'' is achieved toward meeting the national goal.
EPA originally deferred establishment of a program to address regional
haze in 1980 due to the need for greater scientific and technical
knowledge, but the current Criteria Document and Staff Paper cite
information supporting the Administrator's conclusion that the
scientific state of understanding and analytical tools are now adequate
to develop such a program. Because regional emission reductions are
needed to make visibility improvements in mandatory Class I Federal
areas, the structure and requirements of sections 169A and 169B of the
Act, provide for visibility protection programs that can be more
responsive to the factors contributing to regional differences in
visibility than can programs addressing a nationally applicable
secondary NAAQS. The visibility goal is more protective than a
secondary NAAQS since the goal addresses any man-made impairment rather
than just impairment at levels determined to be adverse.
Thus, an important factor considered in this review is whether a
regional haze program, in conjunction with secondary standards set
identical to the suite of PM2.5 primary standards, would
provide appropriate protection for visibility in non-Class I areas. The
Administrator continues to believe that the two programs and associated
control strategies should provide such protection due to the regional
approaches needed to manage emissions of pollutants that impair
visibility in many of these areas. Regional strategies implemented to
attain the NAAQS, meet other air program goals, and make reasonable
progress toward the national visibility goal in mandatory Class I
Federal areas are expected to improve
[[Page 38682]]
visibility in many urban and non-Class I areas as well. The following
recommendation from the 1993 report of the National Research Council,
Protecting Visibility in National Parks and Wilderness Areas, addresses
this point:
Efforts to improve visibility in Class I areas also would
benefit visibility outside these areas. Because most visibility
impairment is regional in scale, the same haze that degrades
visibility within or looking out from a national park also degrades
visibility outside it. Class I areas cannot be regarded as potential
islands of clean air in a polluted sea.
Before making a final decisions on the secondary standards, the
Administrator also considered a number of public comments that
addressed this aspect of the proposal. Some commenters suggested
setting secondary standards for PM2.5 more stringent than
the proposed primary standards for the purpose of addressing visibility
impairment and other environmental effects. For the reasons discussed
above in this unit, however, the Administrator has concluded that this
may not be an effective and would not be an appropriate means of
protecting against visibility impairment in all parts of the country.
Other commenters raised the possibility of establishing a nationally
applicable secondary standard defined as a ``floor,'' or increment,
above regionally specific background levels of PM2.5 or
associated visibility. Although this idea is of interest and may
warrant further study, the Administrator determined that it was not
appropriate to pursue such an approach at this time for two principal
reasons. First, the Agency does not currently have adequate scientific
information to establish a specific floor or increment level that would
protect against adverse effects nationally, nor is it clear as a
conceptual matter whether further information would support selection
of a single, uniform increment as providing an appropriate degree of
protection in all areas of the country. Second, there are serious,
unresolved questions about whether such an approach is consistent with
the statutory language and purposes of section 109 of the Act.
Other commenters argued that national secondary standards
equivalent to the proposed PM2.5 primary standards are not
necessary or not supported by the Administrator's findings. As noted
earlier, however, it is clear that coarse and fine particles can cause
adverse effects on visibility and significant quantitative data exist
to demonstrate that visibility impairment occurs at small
concentrations of PM2.5. Substantial efforts have been put
forth to assess the effects of PM on visibility. For example, the Grand
Canyon Visibility Transport Commission52 spent several years
and significant effort studying the effects of pollution on 16
mandatory Class I Federal areas on the Colorado plateau and has made
recommendations to the Administrator for actions to improve visibility
in these areas (GCVTC, 1996). All of the mandatory Class I Federal
areas studied by the GCVTC with monitoring data have annual mean
PM2.5 concentrations below 5 g/m3
(Sisler, 1996) while also documenting anthropogenic visibility
impairment. The Southern Appalachian Mountain Initiative53
is currently assessing air pollution impacts on visibility, terrestrial
resources, and aquatic resources in the southeastern U.S. in order to
recommend measures to remedy existing and prevent future adverse
effects on these air quality related values. The IMPROVE network shows
that all of the mandatory Class I Federal areas in the SAMI region have
annual mean PM2.5 concentrations for 1992-95 between 11.0-
13.5 g/m3 (Sisler, 1996). The inclusion in section
169A of the Act of a national visibility goal of no manmade impairment
also places significant value on reducing PM concentrations and
resulting visibility impairment to low levels.54 The
differences between the fine particle levels associated with visibility
impairment in eastern and western mandatory Class I Federal areas
provide further impetus to act under the provisions of sections 169A
and 169B enabling the Administrator to establish a regionally-tailored
visibility program to address impairment of visibility in mandatory
Class I Federal areas. For these reasons, the Administrator has
concluded that a national regional haze program allowing for regional
approaches to addressing fine particle pollution, combined with a
nationally applicable level of protection achieved through secondary
PM2.5 standards set equal to the suite of primary standards,
would be more effective in addressing regional variations in the
adverse effects of PM2.5 on visibility than establishing
national secondary standards for particulate matter that are lower than
the suite of PM2.5 primary standards. The Administrator
emphasizes that in order to appropriately address the regional
differences in adverse effects of particulate matter on visibility, it
is essential to establish secondary standards for PM2.5
equivalent to the primary standards and an effective new regional haze
program. A regional haze program will be particularly important in
those areas of the country that do not exceed any of the primary
standards for PM2.5, yet still experience significant
visibility impairment due to particulate matter. The EPA will propose a
regional haze regulation in the near future.
---------------------------------------------------------------------------
52 EPA established the Grand Canyon Visibility Transport
Commission (GCVTC) in 1991 under section 169B of the Act. Section
169B(d) requires visibility transport commissions to assess the
``adverse impacts on visibility from potential or projected growth
in emissions'' and to recommend to EPA measures to remedy such
adverse impacts. The Commission issued its final report in June
1996.
53 The Southern Appalachian Mountain Initiative is a voluntary
effort begun in 1993. Participants include eight southeastern
States, Federal land managers, EPA, and representatives from
industry and environmental groups. A final report has not been
issued to date.
54 Indeed, Congress recognized when it adopted section 169A that
the ``visibility problem is caused primarily by emission into the
atmosphere of sulfur dioxide, oxides of nitrogen and particulate
matter, especially fine particulate matter, from inadequately
controlled sources.'' H.R. Rep. No. 95-294 at 204 (1977).
---------------------------------------------------------------------------
In addition to providing a more regionally tailored approach than
establishing a more stringent national secondary standard, an effective
regional haze program will also fulfill the Administrator's regulatory
responsibility under sections 169A and 169B of the Act to address both
reasonably attributable impairment and regional haze impairment in
mandatory Class I Federal areas. Indeed, regional haze has been shown
to be the principal cause of visibility impairment in mandatory Class I
Federal areas today. Thus, the promulgation of a regional haze program
in conjunction with secondary standards for PM2.5 equivalent
to the suite of primary standards will serve as an appropriate approach
for addressing adverse effects of visibility that vary regionally, and
it will also establish a comprehensive program for making reasonable
progress toward the national visibility goal in mandatory Class I
Federal areas by addressing visibility impairment in the form of both
source-specific impacts and regional haze. Further, the regional haze
rulemaking will fulfill the Administrator's responsibilities to address
the visibility protection recommendations of the Grand Canyon
Visibility Transport Commission, pursuant to section 169B(e) of the
Act.
The Administrator recognizes that people living in certain urban
areas may place a high value on unique scenic resources in or near
these areas, and as a result might experience visibility problems
attributable to sources that would not necessarily be addressed by the
combined effects of a regional haze program and secondary standards
identical to the suite of primary standards for PM2.5.
Commenters from
[[Page 38683]]
certain western cities and States raised this issue. In the
Administrator's judgment, State or local regulatory approaches, such as
past action in Colorado to establish a local visibility standard for
the City of Denver, would be more appropriate and effective in
addressing these special situations because of the localized and unique
characteristics of the problems involved. Visibility in an urban area
located near a mandatory Class I Federal area can also be improved
through State implementation of the current visibility regulations, by
which emission limitations can be imposed on a source or group of
sources found to be contributing to ``reasonably attributable''
impairment in the mandatory Class I Federal area. EPA also intends to
pursue opportunities to obtain information on urban and non-Class I
area visibility through examination of available fine particle
monitoring data. Current or planned monitoring networks and
initiatives, such as monitoring and chemical analysis of
PM2.5 in urban and background sites, efforts to better
characterize real-time environmental conditions in major populations
centers, and new automated airport visibility monitoring networks
should provide data needed to evaluate trends in these areas. This
information should help to better characterize the nature and spatial
extent of urban and non-Class I visibility problems and thus serve to
inform future decisions on NAAQS revisions or other appropriate
measures.
Based on all of the considerations discussed, the Administrator has
decided to establish secondary standards identical to the suite of
PM2.5 primary standards, in conjunction with a regional haze
program under sections 169A and 169B of the Act, as the most
appropriate and effective means of addressing the welfare effects
associated with visibility impairment. Together, the two programs and
associated control strategies should provide appropriate protection
against the effects of PM on visibility and enable all regions of the
country to make reasonable progress toward the national visibility
goal.
2. Materials damage and soiling effects. Annual and 24-hour
secondary standards for materials damage and soiling effects of PM were
established in 1987 at levels equal in all respects to the primary
standards. As discussed in the Criteria Document and Staff Paper,
particles affect materials by promoting and accelerating the corrosion
of metals, by degrading paints, and by deteriorating building materials
such as concrete and limestone. Soiling is found to reduce the
aesthetic quality of buildings and objects of historical or social
interest. Past studies have found that residential properties in highly
polluted areas typically have lower values than those in less polluted
areas. Thus, at high enough concentrations, particles become a nuisance
and result in increased cost and decreased enjoyment of the
environment.
In the proposal, EPA proposed to establish secondary standards for
PM10 and PM2.5 identical to the suite of proposed
primary standards. Several comments recommended setting secondary
standards at levels more stringent than the proposed primary standards
in order to address various welfare effects of PM, including soiling
and materials damage, acid deposition, and visibility. Some commenters
specifically suggested changing the form or level of the proposed 24-
hour, 98th percentile PM standards to better protect against elevated
PM episodes and associated soiling, materials damage, and visibility
effects.
After reviewing the extent of relevant studies and other
information provided since the 1987 review of the PM standards, the
Administrator concurs with staff and CASAC conclusions that the
available data do not provide a sufficient basis for establishing a
separate secondary standard based on soiling or materials damage alone.
In the Administrator's judgment, however, setting secondary standards
identical to the suite of PM2.5 and PM10 primary
standards would provide increased protection against the effects of
fine particles and retain an appropriate degree of control on coarse
particles. Accordingly, the Administrator establishes the secondary
standards for PM2.5 identical to the suite of primary
standards to protect against materials damage and soiling effects of
PM.
B. Decision on the Secondary Standards
The Administrator establishes secondary standards identical to the
suite of primary standards. In the Administrator's judgment, the
establishment of these standards, in conjunction with implementation of
a regional haze program, will provide appropriate protection against
the welfare effects associated with particle pollution.
IV. Other Issues
Commenters have raised a number of legal and procedural issues that
are discussed in this unit. These include:
(1) Whether EPA must give consideration to costs and similar
factors in setting NAAQS.
(2) Whether EPA erred in its selection of a methodology for
determining the level of a NAAQS that protects public health with an
adequate margin of safety.
(3) Whether EPA committed a procedural error by not entering into
the rulemaking docket underlying data from certain epidemiological
studies.
(4) Whether the 1990 amendments to the Act preclude EPA from
revising the PM NAAQS to establish a new PM2.5 indicator.
Responses to other legal and procedural issues are included in the
Response-to-Comments Document.
A. Consideration of Costs
For more than a quarter of a century, EPA has interpreted section
109 of the Act as precluding consideration of the economic costs or
technical feasibility of implementing NAAQS in setting them. As
indicated in the proposal, a number of judicial decisions have
confirmed this interpretation. Natural Resources Defense Council v.
Administrator, 902 F.2d 962, 972-973 (D.C. Cir. 1990)(PM
NAAQS)(``PM10''), vacated, in part, dismissed, 921 F.2d 326
(D.C. Cir.), certs. dismissed, 498 U.S. 1075, and cert. denied, 498
U.S. 1082 (1991); Natural Resources Defense Council v. EPA, 824 F.2d
1146, 1157-1159 (D.C. Cir. 1987)(en banc)(CAA section 112 standards for
vinyl chloride)(``Vinyl Chloride''); American Petroleum Institute v.
Costle, 665 F.2d 1176, 1185-1186 (D.C. Cir. 1981)(ozone
NAAQS)(``Ozone''), cert. denied, 455 U.S. 1034 (1982); Lead Industries
Ass'n v. EPA, 647 F.2d 1130, 1148-1151 (D.C. Cir.)(lead NAAQS)(Lead
Industries), cert. denied, 449 U.S. 1042 (1980).
Some commenters have argued that costs and similar factors should,
nonetheless, be considered, both in this rulemaking and in the
rulemaking on proposed revisions to the NAAQS for ozone. Although most
of the commenters' arguments are inconsistent with the judicial
decisions cited in this unit, several commenters have argued that those
decisions are not dispositive. For reasons discussed in this unit and
in the Response-to-Comments Document, EPA disagrees with these comments
and maintains its longstanding interpretation of the Act as precluding
consideration of costs and similar factors in setting NAAQS.
1. Background. Given the nature of the points raised, a brief
review of the issue seems useful before addressing the comments. The
requirement that EPA establish national ambient air quality standards
for certain pollutants, to be implemented by the States, was enacted in
1970 as part of a set of comprehensive amendments that established the
basic framework for
[[Page 38684]]
Federal, State, and local air pollution control. When EPA promulgated
the original NAAQS in 1971, its first Administrator, William D.
Ruckelshaus, concluded that costs and similar factors could not be
considered in that decision.55 This conclusion was not
challenged in litigation on the original NAAQS. It has been confirmed
since then, however, by every judicial decision that has considered the
issue.
---------------------------------------------------------------------------
55 36 FR 8186, April 30, 1971. EPA has maintained this
interpretation consistently since then.
---------------------------------------------------------------------------
As discussed in this unit, EPA's interpretation rests primarily on
the language, structure, and legislative history of the statutory
scheme adopted in 1970. It is also supported by the judicial decisions
cited in this unit, as well as by legislative developments since 1970
that reaffirm Congress' original approach to the issue.
Without cataloguing all relevant aspects of the 1970 amendments and
their legislative history, several basic points should be noted. Under
section 109(b) of the Act, NAAQS are to be ``based on'' the air quality
criteria issued under section 108 of the Act. Under section 108(a)(2)
of the Act, the kind of information EPA is required to include in
criteria documents is limited to information about health and welfare
effects ``which may be expected from the presence of [a] pollutant in
the ambient air * * * .'' There is no mention of the costs or
difficulty of implementing the NAAQS, nor of ``effects'' that might
result from implementing the NAAQS (as opposed to effects of pollution
in the air).56 By contrast, Congress explicitly provided for
consideration of costs and similar factors in decisions under other
sections of the Act.57 Moreover, States were permitted to
consider economic and technological feasibility in developing plans to
implement the NAAQS to the extent such consideration did not interfere
with meeting statutory deadlines for attainment of the
standards.58 Finally, the legislative history indicated that
Congress had considered the issue and had deliberately chosen to
mandate NAAQS that would protect health regardless of concerns about
feasibility.59
---------------------------------------------------------------------------
56 That consideration of such factors was not intended in NAAQS
decisions is also supported by section 109(a)(1) of the Act. For
pollutants for which air quality criteria had been issued prior to
the 1970 amendments, that provision required EPA to propose NAAQS
within 30 days after enactment and to take final action 90 days
later. The criteria issued previously did not include information on
costs and similar factors, and it would have been difficult if not
impossible for EPA to supplement them in time to include meaningful
consideration of such factors in NAAQS proposed 30 days after
enactment.
57 See, e.g., sections 110(e)(1), 111(a)(1), 231(b) of the 1970
Act; see also, e.g., sections 113(d)(4)(C)(ii), 125(a)(3),
202(a)(3)(C), 317 of the 1977 Act.
58 Union Electric Co. v. EPA, 427 U.S. 246, 257-58 (1976).
59 The Senate report on the 1970 amendments stated: ``In the
Committee discussions, considerable concern was expressed regarding
the use of the concept of technical feasibility as the basis of
ambient air standards. The Committee determined that (1) the health
of people is more important than the question of whether the early
achievement of ambient air quality standards protective of health is
technically feasible; and, (2) the growth of pollution load in many
areas, even with application of available technology, would still be
deleterious to public health.''
``Therefore, the Committee determined that existing sources of
pollutants either should meet the standard of the law or be closed
down * * * .''
S. Rep. No. 91-1196, at 2-3 (1970).
---------------------------------------------------------------------------
The first judicial decision on the issue came in the Lead
Industries case. An industry petitioner argued that EPA should have
considered economic and technological feasibility in allowing a
``margin of safety'' in setting primary standards for lead. Based on a
detailed review of the language, structure, and legislative history of
the statutory scheme, the U.S. Court of Appeals for the District of
Columbia Circuit concluded that:
This argument is totally without merit. [The petitioner] is
unable to point to anything in either the language of the Act or its
legislative history that offers any support for its claim * * * . To
the contrary, the statute and its legislative history make clear
that economic considerations play no part in the promulgation of
ambient air quality standards under section 109.
647 F.2d at 1148.
The Court cited a number of reasons for this conclusion. Id. at
1148-1150. Among other things, it noted the contrast between section
109(b) of the Act and other provisions in which Congress had explicitly
provided for consideration of economic and technological feasibility,
as well as the requirement that NAAQS be based on air quality criteria
defined without reference to such factors. Id. at 1148-1149 and n.37.
The Court also noted that, in developing plans to implement NAAQS,
States may consider economic and technological feasibility only to the
extent that this does not interfere with meeting the statutory
deadlines for attainment of the standards; and that EPA may not
consider such factors at all in deciding whether to approve State
implementation plans. Id. at 1149 n.37 (citing Union Electric Co. v.
EPA, 427 U.S. 246, 257-258, 266 (1976)).60
---------------------------------------------------------------------------
60 These limitations would, of course, make little sense if such
factors could be considered in setting the NAAQS themselves.
---------------------------------------------------------------------------
As to the legislative history of the 1970 amendments, the Court
observed that:
[T]he absence of any provision requiring consideration of these
factors was no accident; it was the result of a deliberate decision
by Congress to subordinate such concerns to the achievement of
health goals.
Id. at 1149. Citing several leading Supreme Court decisions, as well as
the Senate report quoted in this unit, the Court noted that Congress
had intended a drastic change in approach toward the control of air
pollution in the 1970 amendments and was well aware that sections 108-
110 of the Act imposed requirements of a ``technology-forcing''
character. Id.61
---------------------------------------------------------------------------
61 Such requirements ``are expressly designed to force regulated
sources to develop pollution control devices that might at the time
appear to be economically or technologically infeasible.''' Id.
(quoting Union Electric Co. v. EPA, 427 U.S. at 257).
---------------------------------------------------------------------------
The Court also noted that Congress had already acted, in further
amendments adopted in 1977, to relieve some of the burdens imposed by
the 1970 amendments. Id. at 1150 n.38. Observing that Congress had,
however, declined to amend section 109(b) of the Act to provide for
consideration of costs and similar factors as requested by industrial
interests, Id. n.39, the Court concluded:
A policy choice such as this is one which only Congress, not the
courts and not EPA, can make. Indeed, the debates on the [1970
amendments] indicate that Congress was quite conscious of this fact
* * * .
* * * [I]f there is a problem with the economic or technological
feasibility of the lead standards, [the petitioner], or any other
party affected by the standards, must take its case to Congress, the
only institution with the authority to remedy the problem.
Id. at 1150.
After the decision in Lead Industries, Supreme Court review was
sought on the question whether costs and similar factors could be
considered in setting NAAQS, among other issues. The Supreme Court
declined to review the decision. Lead Industries Ass'n v. EPA, 449 U.S.
1042 (1980). The subsequent decisions in Ozone, Vinyl Chloride, and
PM10, cited in this unit, strongly reaffirmed the
interpretation adopted in Lead Industries.62 Supreme Court
[[Page 38685]]
review of the Ozone and PM10 decisions was sought but
denied. American Petroleum Institute v. Gorsuch, 455 U.S. 1034 (1984);
American Iron and Steel Institute v. EPA, 498 U.S. 1082 (1991).
---------------------------------------------------------------------------
62 In the PM10 case, for example, the Court
considered an argument that EPA should have considered potential
health consequences of unemployment that might result from revision
of the primary NAAQS for PM:
``This claim is entirely without merit. In three previous cases,
this court has emphatically stated that Sec. 109 does not permit EPA
to consider such costs in promulgating national ambient air quality
standards * * * . It is only health effects relating to pollutants
in the air that EPA may consider * * * . Consideration of costs
associated with alleged health risks from unemployment would be
flatly inconsistent with the statute, legislative history and case
law on this point.''
902 F.2d at 973 (emphasis in original; citations omitted).
---------------------------------------------------------------------------
The Lead Industries opinion focused largely, though not
exclusively, on the 1970 amendments and their legislative history.
Perhaps as a result, it did not canvass all the factors that, in fact,
supported its conclusions at the time. For example, when Congress
enacted major amendments to the Act in 1977, it was clearly aware that
some areas of the country had experienced difficulty in attempting to
attain some of the NAAQS.63 It was also aware that there
might be no health-effects thresholds for the pollutants involved, and
that significant uncertainties are inherent in setting health-based
standards under the Act.64 In response, Congress made
significant changes in the provisions for implementation of the NAAQS,
including changes intended to ease the burdens of attainment. It also
amended sections 108 and 109 of the Act in several ways; for example,
by requiring periodic review and, if appropriate, revision of air
quality criteria and NAAQS and by establishing a special scientific
advisory committee (CASAC) to advise EPA on such reviews. Notably,
Congress recognized that implementation of NAAQS could cause ``adverse
public health, welfare, social, economic, or energy effects'' and
charged CASAC with advising EPA on such matters.65 Yet it
made no changes in section 109(b) or section 108(a)(2) of the Act; that
is, in the substantive criteria for setting or revising NAAQS. In other
words, Congress chose to address economic and other difficulties
associated with attainment of the NAAQS by adjusting the scheme for
their implementation, rather than by changing the instructions for
setting them.66
---------------------------------------------------------------------------
63 See, e.g., H.R. Rep. No. 95-294, at 207-217 (l977).
64 See, e.g., Id. at 110-112; Id. at 43-51.
65 Section 109(d)(2)(C)(iv) of the Act. Some commenters have
argued that this provision requires EPA to consider such effects in
setting NAAQS. From the language and structure of section 109(d) of
the Act, however, it is clear that CASAC's responsibility to advise
on these factors is separate from its responsibility to review and
recommend revision of air quality criteria and NAAQS, and that the
advice pertains to the implementation of NAAQS rather than to
setting them. The legislative history confirms this view, indicating
that the advice was intended for the benefit of the States and
Congress. See H.R. Rep. No. 95-294, at 183 (1977).
66 The 1977 amendments also required EPA to prepare economic
impact assessments for specified actions but limited the requirement
to non-health-based standards, excluding decisions under sections
109 and 112 of the Act. Section 317; H.R. Rep. No. 95-294, at 51-52
(1977). In this and other respects, Congress continued the approach
it took in the l970 amendments, making careful choices as to when
consideration of costs and similar factors would be required and
giving paramount priority to protection of health. See 123 Cong.
Rec. H8993 (daily ed. Aug. 4, 1977) (Clean Air Conference Report
(1977); Statement of Intent; Clarification of Select Provisions),
reprinted in 3 Senate Committee on Environment and Public Works,
95th Cong., A Legislative History of the Clean Air Act Amendments of
1977, at 319 (1978).
---------------------------------------------------------------------------
Congress enacted major amendments to the Act again in 1990, well
after the Lead Industries and Ozone decisions that interpreted section
109 of the Act as precluding consideration of costs in NAAQS
decisions.67 In doing so, Congress was clearly aware of
intervening developments such as EPA's decision to revise the PM NAAQS
in 1987--the result of an elaborate review in which the Administrator
strongly underscored the scientific uncertainties
involved68--and the Vinyl Chloride case drawing a sharp
distinction between sections 109 and 112 of the Act with regard to
consideration of costs and similar factors.69 Indeed, the
legislative history of the 1990 amendments reflects Congress'
understanding that primary NAAQS were to be based on protection of
health ``without regard to the economic or technical feasibility of
attainment.''70 Again, however, Congress chose to respond to
severe, widespread, and persistent problems with attaining the NAAQS by
adjusting the scheme for their implementation rather than by changing
the basis for setting them. See, e.g., sections 181-192 of the Act.
---------------------------------------------------------------------------
67 In the interim, the National Commission on Air Quality had
also submitted its report to Congress as required by a provision of
the 1977 amendments. Among other things, the Commission recommended
that the statutory approach of requiring NAAQS to be set at levels
necessary to protect public health, without consideration of
economic factors, be continued without change. National Commission
on Air Quality, To Breathe Clean Air 55 (1981).
68 As the Administrator indicated in EPA's proposal to revise
the PM standards:
``[T]hat review has revealed a highly limited data base--
particularly where quantitative studies are concerned--and a wide
range of views among qualified professionals about the exact
pollution levels at which health effects are likely to occur. The
setting of an `adequate margin of safety' below these levels calls
for a further judgment--in an area for which the scientific data
base is even more sparse and uncertain * * * .''
``* * * [L]ong and expert review of public health issues has to
date revealed no scientific method of assessing exactly what level
of standards public health requires. The scientific review indicates
substantial uncertainties concerning the health risks associated
with lower levels of particulate matter.'' (49 FR 10408, 10409,
March 20, l984)
69 Congress was clearly aware of the 1987 decision to revise the
PM NAAQS, which among other things involved changing the indicator
for particulate matter from ``total suspended particulate'' to
PM10, because it enacted special nonattainment
provisions, as well as provisions for PSD increments, applicable to
PM10. Sections 188-190 of the Act; section 166(f) of the
Act. It was clearly aware of the Vinyl Chloride decision because it
amended section 112 of the Act in response to that decision,
essentially creating a new scheme for setting emission standards for
hazardous pollutants.
70 H.R. Rep. No. 101-490, pt. 1, at 145 (1990). See also S. Rep.
No. 101-228, at 5 (1989).
---------------------------------------------------------------------------
2. Public comments. As noted previously, a number of commenters
have argued that costs and similar factors should be considered in
EPA's final decisions on revision of both the particulate and ozone
NAAQS. Aside from arguments that are simply inconsistent with the
judicial decisions cited in this unit, some of the commenters argue
that those decisions are not dispositive for a variety of reasons. One
commenter submitted a particularly comprehensive version of this
argument; the following discussion focuses primarily on points raised
by that commenter, among others.71
---------------------------------------------------------------------------
71 Additional responses to points raised by this commenter and
others are included, as appropriate, in the Response-to-Comments
Document.
---------------------------------------------------------------------------
As a general matter, the commenter acknowledges that Congress
intended to preclude consideration of economic costs and similar
factors in setting NAAQS. The commenter argues, however, that this is
so only when the scientific basis for NAAQS is ``clear and compelling''
or ``unambiguous.'' From that premise, the commenter advances three key
assertions:
a. Where non-threshold pollutants are involved and the health
evidence is ambiguous, section 109 of the Act must be interpreted to
allow consideration of all relevant factors, including the practical
consequences of EPA's decisions.
b. To the extent the judicial decisions cited in this unit are read
as precluding this, they rest on a faulty analysis that pre-dates and
cannot survive scrutiny under Chevron, U.S.A. v. Natural Resources
Defense Council, 467 U.S. 837 (1984).72
---------------------------------------------------------------------------
72 Several other commenters argue that the cited decisions are
not dispositive because they held only that EPA is not required to
consider costs and similar factors in setting NAAQS. As discussed in
this unit in connection with Chevron, however, the decisions clearly
concluded that Congress intended to preclude consideration of such
factors, and that EPA is not free to alter that congressional
choice. Although these conclusions are technically dicta, nothing in
the Court's opinions suggests that it would have interpreted section
109 of the Act differently had EPA claimed authority to consider
costs and similar factors in NAAQS decisions. Indeed, the tone of
the opinions argues to the contrary. See, e.g., PM10, 902
F.2d at 973. Cf. Ethyl Corp. v. EPA, 51 F.3d 1053 (D.C. Cir. 1995).
---------------------------------------------------------------------------
c. Because EPA has discretion to consider costs and similar factors
where the health evidence is ambiguous, it must do so in light of
Executive Order 12866 (58 FR 51735, October 4, 1993), and two recent
statutes, the Unfunded
[[Page 38686]]
Mandate Reform Act of 1995, 2 U.S.C. 1501-1571 (UMRA), and the Small
Business Regulatory Enforcement Fairness Act of 1996, Pub. L. 104-121,
110 Stat. 857 (SBREFA), which in part amended the Regulatory
Flexibility Act, 5 U.S.C. 601-808.
EPA believes all three assertions are clearly incorrect. Regarding
the first point, it should be evident, both from previous NAAQS
decisions and from the court opinions upholding them, that the
scientific basis for NAAQS decisions has never pointed clearly and
unambiguously to a single ``right answer.''73 This is
inherent in the statutory scheme for the establishment and revision of
NAAQS, which in effect requires them to be based on the ``latest
scientific knowledge'' on potential health and welfare effects of the
pollutant in question. See sections 109(b) and 108(a)(2) of the Act.
Although advances in science increase our understanding of such
effects, they also raise new questions. For this reason, the key
studies for any given decision on revision of a NAAQS are, almost by
definition, ``at the very `frontiers of scientific
knowledge.'''73 That is, studies that call into question the
adequacy of a standard are always those that go beyond previous
studies--by reporting new kinds of effects, for example, or effects at
lower concentrations than those at which effects have been reported
previously.
---------------------------------------------------------------------------
73 See, e.g., Lead Industries, 647 F.2d at 1146-1147, 1153-1156,
1160-1161, 1167 n.106. In enacting the 1970 amendments, Congress was
aware that there were gaps in the scientific information available
then as a basis for establishing the original NAAQS. See, e.g., S.
Rep. No. 91-1196, at 9-11 (1970). If anything, Congress had an even
greater understanding of the point when it enacted the 1977
amendments without changing the substantive criteria for setting
NAAQS. See H.R. Rep. No. 95-294, at 43-51, 181-182 (1977).
74 Lead Industries, 647 F.2d at 1147 (quoting Ethyl Corp. v.
EPA, 541 F.2d 1, 24-27 (D.C. Cir.) (en banc), cert. denied, 426 U.S.
941 (1976)).
---------------------------------------------------------------------------
As with pioneering work in other fields, such studies may have a
variety of strengths and limitations.875 As a result, the
validity and implications of such studies may be both uncertain and
highly controversial. Given the precautionary nature of section 109 of
the Act,76 however, it is precisely these kinds of studies
that the Administrator must grapple with when advances in science
suggest that revision of a NAAQS is appropriate.
---------------------------------------------------------------------------
75 They may have methodological flaws, for example, but
nonetheless report effects that are of serious medical significance;
or they may be of impeccable quality but involve effects of
uncertain significance. Others may involve results that are striking
but hard to explain in terms of previous knowledge, or results that
seem plausible and important but are not yet replicated by other
studies.
76 See, e.g., Lead Industries, 647 F.2d at 1155-1156; H.R. Rep.
No. 94-295, at 43-51 (1977).
---------------------------------------------------------------------------
As a result, the EPA staff typically recommends for consideration,
and the Administrator may propose for comment, a range of alternatives
based on what the commenter would call ``ambiguous'' science. In this
respect, the current reviews of the NAAQS for ozone and particulate
matter are not unusual and do not differ, for example, from the review
that led to adoption of the PM10 NAAQS in 1987.77
Indeed, the NAAQS that were upheld in the Lead Industries, Ozone, and
PM10 decisions were all based on highly controversial health
evidence; the Lead Industries decision took note of congressional
statements recognizing that there may be no thresholds for criteria
pollutants; and the Ozone and PM10 decisions noted the
Administrator's findings that clear thresholds could not be identified
for ozone and particulate matter, respectively.78 Thus, the
present decisions on revision of the NAAQS for ozone and particulate
matter cannot be distinguished from those past decisions in terms of
the nature of the health evidence or pollutants involved.78
---------------------------------------------------------------------------
77 As previously discussed, the Administrator strongly
emphasized the uncertainties involved in that review. As a result of
the uncertainties, he proposed ``relatively broad'' ranges for
comment, though he focused on lower levels within the ranges as
providing greater margins of safety against the health risks
involved. See 49 FR 10408, 10409, March 20, l984.
78 See, e.g., Lead Industries, 647 F.2d at 1152-53 and n. 43,
1159-60; Ozone, 665 F.2d at 1185, 1187; PM10, 902 F.2d at
969-71, 972.
79 Indeed, the present decisions on the NAAQS for PM and ozone
are based on some of the best scientific information the Agency has
ever been able to rely on in NAAQS decision-making. In particular,
the science underlying these decisions is much more extensive and of
much better quality than the science underlying the existing NAAQS
for PM and ozone.
---------------------------------------------------------------------------
Regarding the second of the commenter's key assertions, EPA
determines it is clear that the judicial decisions cited in this unit
were correctly decided and continue to be good law under Chevron. In
Chevron, the Supreme Court essentially reaffirmed the principle that
courts must defer to reasonable agency interpretations of the statutes
they administer where Congress has delegated authority to them to
elucidate particular statutory provisions. Where the intent of Congress
on an issue is clear, however, it must be given effect by the agency
and the courts. See 467 U.S. at 842-45. Thus, the first question on
review of an agency's interpretation under Chevron is ``whether
Congress has directly spoken to the precise question at issue.'' If the
court determines that it has not, the remaining question for the court
is ``whether the agency's answer is based on a permissible construction
of the statute.'' 467 U.S. at 842-843 (footnote omitted). In
determining whether Congress ``had an intention on the precise question
at issue,'' a court employs ``traditional tools of statutory
construction.'' Id. at 843 n.9.80
---------------------------------------------------------------------------
80 In practice, analysis of this question is sometimes referred
to as a ``Chevron step one'' analysis.
---------------------------------------------------------------------------
In essence, the commenter's argument here is that the Lead
Industries decision did not address whether Congress had ``spoken
directly'' to the precise issue posed by the commenter; that is,
whether section 109 of the Act must be interpreted differently for
NAAQS decisions involving non-threshold pollutants and ``ambiguous''
health evidence. The Lead Industries opinion, which pre-dated Chevron,
did not pose the question in those terms. Its focus, however, was
clearly on what Congress intended to be the basis for NAAQS decisions,
in a context the Court understood to involve considerable uncertainty
and debate about the health evidence, as well as the possibility that
there was no threshold for health effects of the
pollutant.81 In short, the health evidence was hardly
``unambiguous,'' yet the Court interpreted section 109 of this Act as
precluding consideration of costs and similar factors even in allowing
a margin of safety. Nothing in the Lead Industries decision or in the
subsequent cases suggests in any way that section 109 of the Act should
be interpreted differently based on the nature of the pollutants or
health evidence involved, and the Court's findings on congressional
intent admit of no exceptions:
* * * [T]he statute and its legislative history make clear that
economic considerations play no part in the promulgation of ambient
air quality standards under Section 109.
647 F.2d at 1148.
---------------------------------------------------------------------------
81 See, e.g., 647 F.2d at 1148-51, 1152-53 and n.43, 1160-61.
---------------------------------------------------------------------------
Alternatively, the commenter argues that the Lead Industries case
decided the issue incorrectly in light of the principles announced
subsequently in Chevron. In this context, the commenter essentially
argues that the Lead Industries decision rested on two factors that are
no longer probative:
(1) That there was no indication that Congress meant to allow
consideration of costs in NAAQS decisions, and
(2) That Congress specifically provided for such consideration in
other sections of the Act but not in section 109.
[[Page 38687]]
On the first point, the commenter argues that EPA is free under
Chevron to consider costs and similar factors (by reinterpreting
section 109 of the Act) unless there is evidence that Congress intended
to restrict its discretion. As to the second point, the commenter
argues that similar reasoning was rejected in Vinyl Chloride.
In Vinyl Chloride, however, an en banc decision that post-dated
Chevron, the Court essentially underscored the point that such issues
cannot be decided mechanically but must turn, instead, on more
analytical attention to relevant indicia of congressional intent. See,
e.g., 824 F.2d at 1157 n.4; Id. at 1157-1163. With reference to NAAQS
decisions in particular, the Court concluded that there were concrete
indications of congressional intent to preclude consideration of costs
and similar factors; for example, the fact that section 108 of the Act
``enumerate[s] specific factors to consider and pointedly exclude[s]
feasibility.'' 824 F.2d at 1159. In a later case, moreover, the same
Court held that EPA could not consider certain factors, in decisions
under section 211(f)(4) of the Act, for reasons exactly parallel to
those that the commenter criticizes in Lead Industries. See Ethyl Corp.
v. EPA, 51 F.3d 1053, 1057-1063 (D.C. Cir. 1995).
Beyond this, the commenter's characterization of the Lead
Industries decision ignores or discounts much of the key evidence cited
by the Court, including the language, structure, and legislative
history of the statutory scheme established in 1970, for its conclusion
that Congress intended to preclude consideration of costs and similar
factors in NAAQS decisions.82 As indicated in this unit, the
Vinyl Chloride and PM10 cases, both of which post-dated
Chevron, reached the same conclusion.
---------------------------------------------------------------------------
82 See 647 F.2d at 1148-51. By contrast, the commenter's
argument that Congress actually intended EPA to consider such
factors relies heavily on statements made in subsequent legislative
history, most of which were made in floor debate, that sought to
justify controversial amendments to establish a different program
than the NAAQS and did not involve any proposed changes in section
109 of the Act or related provisions; and statements in early
judicial decisions involving programs under other statutory
provisions. In context, EPA determines these and other statements
cited by the commenter are consistent with and do not alter the
conclusion that Congress intended to preclude consideration of costs
and similar factors under section 109 of the Act.
---------------------------------------------------------------------------
Moreover, this series of decisions went far beyond mere deference
to an agency interpretation. As indicated in the Vinyl Chloride case,
the Lead Industries court found ``clear evidence'' of Congressional
intent, which was to limit the factors EPA may consider under section
109 of the Act. 824 F.2d 1159. Consistent with Chevron, these findings
were based on traditional tools of statutory construction. See Id. at
1157-1159; Lead Industries, 647 F.2d at 1148-1151. In terms of the
analytical framework later established by Chevron, these were Chevron
step one findings, meaning that the statute spoke directly to the issue
and that the courts, as well as the agency, must give effect to
Congress' intent as so ascertained. See 467 U.S. at 842-
843.83 Thus, absent a more recent legislative enactment
overriding that intent, EPA has no discretion to alter its longstanding
interpretation that consideration of costs and similar factors is
precluded in NAAQS decisions under section 109 of the Act.84
---------------------------------------------------------------------------
83 The commenter argues that the post-Chevron cases accepted the
Lead Industries analysis uncritically rather than re-examining it
under Chevron. Clearly, this elevates form over substance. It is
true that neither case referred to Chevron in discussing the point
at issue. In Vinyl Chloride, however, the Court retraced the steps
in the Lead Industries analysis in some detail, characterized some
of the key evidence reviewed in that analysis in terms going beyond
mere rote repetition (e.g., ``a far clearer statement than anything
in the present case that Congress considered the alternatives''),
and used Chevron-like language in discussing the significance of
that evidence; that is, that it demonstrated congressional intention
on the point at issue. E.g., 824 F.2d at 1159. Given that the Vinyl
Chloride case was decided three years after Chevron, that it was an
en banc decision of the D.C. Circuit involving interpretation of
statutory language very similar to that in Lead Industries, and that
the Court cited Chevron twice in analyzing the language and history
of section 112 of the Act, it seems highly unlikely that the Court
was unmindful of Chevron principles in concluding that Congress
intended to preclude consideration of costs under section 109 of the
Act but not under section 112 of the Act.
In the PM10 decision, the Court confirmed the sharp
distinction it had drawn, based on such evidence of congressional
intent, between sections 109 and 112 of the Act in Vinyl Chloride.
902 F.2d at 972-973. Although discussion of the point was brief and
did not mention Chevron, the industry petitioner raising the point
had cited Chevron in arguing that the Lead Industries interpretation
was not binding, and that EPA's decision on the PM10
standards should be reversed on the ground that it rested on a legal
position that EPA unjustifiably believed was mandated by Congress.
Reply Brief of the American Iron and Steel Institute at 11 and n.10,
Natural Resources Defense Council v. Administrator, 902 F.2d 962
(D.C. Cir. 1990) (Nos. 87-1438 et al.). Thus, Chevron issues were
properly before the Court and were brought squarely to its
attention.
84 See also 52 FR 24854, July 1, 1987.
---------------------------------------------------------------------------
As to the commenter's third key assertion, Executive Order 12866,
UMRA sections 202 and 205, and the Regulatory Flexibility Act (RFA), as
amended by SBREFA, do not conflict with this interpretation or require
a different result. Basically, the commenter argues that the Executive
Order, UMRA, and the RFA (as amended by SBREFA) require agencies to use
cost (or similar factors) as a decisional criterion in making
regulatory decisions, and that this modifies the Clean Air Act's
directive that EPA is precluded from considering costs when setting a
NAAQS. The commenter's argument is flawed on a number of grounds.
First, UMRA and the RFA (as amended by SBREFA) do not conflict with
section 109 of the Act because they do not apply to this decision, as
discussed in Unit VIII. of this preamble. Second, the Executive Order
and both statutes are quite clear that they do not override the
substantive provisions in an authorizing statute. Third, the
commenter's premise that UMRA and the RFA (as amended by SBREFA)
establish substantive decisional criteria that agencies are required to
follow is wrong.
As a matter of law, the Executive Order cannot (and does not
purport to) override the Clean Air Act. The Executive Order does not
conflict with section 109 of the Act because the requirement that
agencies ``select approaches that maximize net benefits'' does not
apply if a ``statute requires another regulatory approach.'' Executive
Order 12866, section (1)(a), (58 FR 51735, October 4, 1993). More
generally, the Executive Order provides that agencies are to adhere to
its regulatory principles only ``to the extent permitted by law.'' Id.,
section (1)(b).
UMRA sections 202 and 205 do not apply to this decision, as
discussed in Unit VIII. of this preamble. Even when they do apply to a
regulatory action, they do not establish decisional criteria that an
agency must follow, much less override decisional criteria established
in the statute authorizing the regulatory action. UMRA does not require
an agency to select any particular alternative. Rather, an agency can
select an alternative that is not the least costly, most cost-effective
or least burdensome if the agency explains why. Section 205(b)(1) of
UMRA. Such an explanation is not required if the least costly, most
cost-effective or least burdensome alternative would have been
``inconsistent with law,'' section 205(b)(2) of UMRA, and the only
alternatives that an agency should consider are ones that ``achieve[]
the objectives of the rule,'' section 205(a) of UMRA. The UMRA
Conference Report confirms that UMRA does not override the authorizing
statute. ``This section [202] does not require the preparation of any
estimate or analysis if the agency is prohibited by law from
considering the estimate or analysis in adopting the rule.'' 141 Cong.
Rec. H3063 (daily ed. March 13, 1995).
The RFA (as amended by SBREFA) also does not apply to this
decision, as
[[Page 38688]]
discussed in Unit VIII. of this preamble. As is the case with UMRA,
even when the RFA (as amended by SBREFA) does apply to a regulatory
action, it does not establish decisional criteria that an agency must
follow, much less override the underlying substantive statute. When the
RFA was adopted in 1980, Congress made clear that it did not alter the
substantive standards contained in authorizing statutes: ``The
requirements of section 603 and 604 of this title [to prepare initial
and final regulatory flexibility analyses] do not alter in any manner
standards otherwise applicable by law to agency action.'' Section 606
of the RFA. The legislative history further explains that section 606
``succinctly states that this bill does not alter the substantive
standard contained in underlying statutes which defines the agency's
mandate.''85 When Congress passed SBREFA in 1996 and amended
parts of the RFA, it did not amend section 606.
---------------------------------------------------------------------------
85 126 Cong. Rec. 21452, 21455 (1980) (Description of Major
Issues and Section-By-Section Analysis of Substitute for S. 299).
---------------------------------------------------------------------------
Even when a regulatory decision is subject to sections 603 and 604
of the RFA and an agency is therefore required to analyze alternatives
that minimize significant economic impacts on small entities, the RFA
(as amended by SBREFA) does not establish decisional criteria that an
agency is required to follow. Both section 603 and 604 of the RFA
provide that the alternatives an agency should consider are to be
``consistent with the stated objectives of applicable statutes.''
Section 603(c) and 604(a)(5) of the RFA. Furthermore, although the RFA
(as amended by SBREFA) requires agencies to consider alternatives that
minimize impacts on small entities subject to the rules' requirements
and to explain their choice of regulatory alternatives, it does not
require agencies to select such alternatives. For these reasons, the
RFA (as amended by SBREFA) does not conflict with or override the Clean
Air Act's preclusion of considering costs and similar factors in
setting NAAQS.
3. Conclusion. In summary, EPA determines that the judicial
decisions cited in this unit are both correct and dispositive on the
question of considering costs in setting NAAQS, and that the Agency is
not free to reinterpret the Act on that question.
B. Margin of Safety
Several commenters questioned the approach used by the
Administrator in specifying PM standards that protect public health
with an adequate margin of safety. Rather than the integrative approach
applied by the Administrator, these commenters maintained that EPA must
employ a two-step process. One line of argument was that the
Administrator must first determine a ``safe level'' and then apply a
margin of safety taking into account costs and societal impacts. It was
argued that this was the only approach that would enable the
Administrator to reach a reasoned decision on a standard level that
protects public health against unacceptable risk of harm, such that any
remaining risk was ``acceptable.'' In effect, these commenters adopted
the two-step methodology endorsed by Vinyl Chloride, 824 F.2d 1146, for
setting hazardous air pollutant standards under section 112 of the Act.
Another commenter also maintained that the Administrator must apply a
two-step process but from a different perspective. It was argued that
EPA should first identify the lowest observed effect level and then
apply a margin of safety to address uncertainties and to protect the
most sensitive individuals within the at-risk population(s). This
commenter also maintained that the use of risk assessment in
establishing a NAAQS was a departure from past practice, and that this
departure was not adequately explained.
In recognition of the complexities facing the Administrator in
determining a standard that protects public health with an adequate
margin of safety, the courts have declined to impose any specific
requirements on the Administrator's methodological approach. Thus, in
Lead Industries the court held that the selection of any particular
approach to providing an adequate margin of safety ``is a policy choice
of the type Congress specifically left to the Administrator's judgment.
This court must allow him the discretion to determine which approach
will best fulfill the goals of the Act.'' 647 F.2d at 1161-1162. As a
result, the Administrator is not limited to any single approach to
determining an adequate margin of safety and, in the exercise of her
judgment, may choose an integrative approach, a two-step approach, or
perhaps some other approach, depending on the particular circumstances
confronting her in a given NAAQS review.
With respect to the approaches advanced in comment, the
PM10 case made clear that the two-step process endorsed in
Vinyl Chloride was necessary because of the need under section 112 of
the Act to ``sever determinations that must be based solely on health
considerations from those that may include economic and technical
considerations.'' 902 F.2d at 973. Because the Administrator may not
consider cost and technological feasibility under section 109 of the
Act, however, the Court concluded that ``the rationale for parsing the
Administrator's determination into two steps is inapposite.'' Id.
The claim that EPA must follow a two-step process of first
identifying the lowest observed effects level and then applying a
margin of safety has also been rejected by the courts. In Lead
Industries, the Court specifically held that the Administrator need not
apply a margin of safety at the end of the analytical process but may
take into account margin of safety considerations throughout the
process as long as such considerations are fully explained and
supported by the record. 647 F.2d 1161-1162. Accord, PM10,
902 F.2d at 973-974.
Because such factors as the nature and severity of the health
effects involved, the size of the sensitive population(s) at risk, the
types of health information available, and the kind and degree of
uncertainties that must be addressed will vary from one pollutant to
another, the most appropriate approach to establishing a NAAQS with an
adequate margin of safety may be different for each standard under
review. Thus, no generalized paradigm such as that imbedded in EPA's
cancer risk policy can substitute for the Administrator's careful and
reasoned assessment of all relevant health factors in reaching such a
judgment. As noted in this unit, both Congress and the courts have left
to the Administrator's discretion the choice of analytical approaches
and tools, including risk assessments, rather than prescribing a
particular formula for reaching such determinations.86
Because of the inherent uncertainties that the Administrator must
address in margin of safety determinations, they are largely judgmental
in nature, particularly with respect to non-threshold pollutants, and
may not be amenable to quantification in terms of what risk is
``acceptable'' or any other metric. In view of these considerations,
the task of the Administrator is to select an approach that best takes
into account the nature of the health effects and other information
assessed in the air quality criteria for the pollutant in question and
to apply appropriate and reasoned analysis to ensure that scientific
[[Page 38689]]
uncertainties are taken into account in an appropriate manner.
---------------------------------------------------------------------------
86 Contrary to one of the comments received, EPA's use of risk
assessment in this rulemaking is by no means a departure from past
practice. The EPA first considered and began applying risk
assessment methods in the late 1970's (44 FR 8210, 8211, February 8,
1979).
---------------------------------------------------------------------------
In this instance, the Administrator has clearly articulated the
factors she has considered, the judgments she has had to make in the
face of uncertain and incomplete information, and alternative views as
to how such information should be interpreted, in reaching her decision
on standard specifications that will protect public health with an
adequate margin of safety. See Unit II. of this preamble. Her
conclusions on these matters are fully supported by the record.
C. Data Availability
Several commenters questioned EPA's ability to rely on studies
demonstrating an association between PM and excess mortality without
obtaining and disclosing the raw ``data'' underlying these studies for
public review and comment. In particular, a number of commenters cited
Dockery, D.W., et al. 1993 and Pope, C.A. III, et al., 1995, as studies
upon which EPA relied without obtaining and disclosing the underlying
raw data. One commenter also cited J. Schwartz et al., 1996 in the same
context.87 According to the commenters, without the
underlying data used in these studies, the reliability of these studies
cannot be assessed accurately. These commenters requested that EPA
obtain the relevant data and make it available for public review. In
light of the court-ordered requirement that EPA publish its rule by
July 19, 1997, the commenters argued that EPA must retain the current
PM10 NAAQS pending additional review of the raw data and the
studies at issue. One commenter, the American Petroleum Institute (API)
requested that EPA remove the studies from the docket, unless the
underlying data was also included in the docket.88
---------------------------------------------------------------------------
87 Contrary to this commenter's assertion, both the health and
air quality data used in the 1996 Schwartz study are available to
interested parties. EPA's Office of Research and Development
maintains a copy of the air pollution database used in the Schwartz
study and it has previously been made available in response to
Freedom of Information Act requests from interested parties, such as
the American Iron and Steel Institute (AISI). The Harvard School of
Public Health has also made this data available to several
collaborators and to the Health Effects Institute. With regard to
the health data underlying the Schwartz study, that mortality data
was compiled by the National Center for Health Statistics (NCHS) and
can be purchased from the NCHS by interested parties. Thus, there is
no real data availability concern with regard to the 1996 Schwartz
study. However, even were this not the case, for the reasons
discussed more fully in this unit and elsewhere in the preamble, EPA
believes it would be entitled to rely upon this study and other
studies, including the Dockery and Pope studies, regardless of the
availability of the underlying health data.
88 API's letter stated that ``API petitions EPA to identify all
studies that rely, in any way, on data not available for public
review as part of the rulemaking process and remove those studies
from the record.'' To the extent this letter constitutes a
``petition'' for EPA action, EPA hereby denies the ``petition'' for
the reasons stated in this unit and elsewhere in this preamble.
---------------------------------------------------------------------------
A few commenters argued that section 307(d) of the Act requires
that EPA obtain the raw data underlying these studies and that a
failure to do so contradicts the plain language of section 307(d)(3) of
the Act, which requires EPA to place in the docket any ``factual data
on which the proposed rule is based.'' Other commenters argued that
under section 307(d)(8) of the Act, a failure to obtain and disclose
the underlying raw data used in the studies would constitute an error
``so serious and related to matters of such central relevance to the
rule that there is a substantial likelihood that the rule would have
been significantly changed if such errors had not been made.'' Id.
According to one commenter, without the raw data and an opportunity for
an analysis of it, ``EPA has no legal alternative other than to
conclude that no new air quality standard would be appropriate within
the meaning of CAA section 109(a)(1)(B).'' Finally, a number of
commenters have argued that recent caselaw under the Clean Air Act and
other statutes makes clear that EPA has a legal obligation to obtain
and disclose the data used in these studies.89
---------------------------------------------------------------------------
89 One commenter argued that the failure to obtain and disclose
the underlying data was a violation of the Administrative Procedure
Act (APA). The NAAQS rulemaking is promulgated under section 307(d)
of the Act; the APA generally does not apply to such rulemakings.
See section 307(d)(1) of the Act.
---------------------------------------------------------------------------
In developing the proposed revisions to the PM NAAQS, the
Administrator relied on the scientific studies cited in the rulemaking
record, rather than on the raw data underlying them.90 In
this case, the raw data consists of responses to health questionnaires
based on information supplied by individual citizens, or computer
tabulations of this information, which remains confidential, and air
quality and monitoring data, most of which is now publicly available.
EPA does not generally undertake evaluations of raw, unanalyzed
scientific data as part of its public health standard setting process.
Only in extreme cases--for example where there are credible allegations
of fraud, abuse or misconduct--would a review of raw data be warranted.
It would be impractical and unnecessary for EPA to review underlying
data for every study upon which it relies as support for every proposed
rule or standard. If EPA and other governmental agencies could not rely
on published studies without conducting an independent analysis of the
enormous volume of raw data underlying them, then much plainly relevant
scientific information would become unavailable to EPA for use in
setting standards to protect public health and the environment. In
addition, such data are often the property of scientific investigators
and are often not readily available because of the proprietary
interests of the investigators or because of arrangements made to
maintain confidentiality regarding personal health status and lifestyle
information of individuals included in such data. Without provisions of
confidentiality, the possibility of conducting such studies could be
severely compromised.91
---------------------------------------------------------------------------
90 It is important to note that while EPA did use the Dockery
and Pope studies to confirm its conclusions regarding the health
effects of fine particulate air pollution and thus as support for
its decision to revise the PM standard, these studies do not provide
the sole (or even primary) basis for EPA's decision regarding
PM2.5, despite the assertions of numerous commenters. The
proposed standards are based on a consideration of a large body of
epidemiological studies, a clear majority of which suggest PM is
strongly linked to mortality and other serious health effects at
concentrations permitted under the current standards. Although the
specific levels of the PM2.5 standards are based on a
more limited number of studies that actually measured fine particles
and/or components of fine particles, the Dockery and Pope studies
were not used in initially selecting the annual fine particle
standard level, which was principally based on examination of other
daily mortality and respiratory effects studies (Koman, 1996, 1997)
that found significant associations between fine PM and effects in
cities with annual average PM2.5 concentrations of about
16 to 21 g/m3. Only then were the long-term Dockery and
Pope studies examined and used to help corroborate this result; in
the opinion of the Administrator, neither study alone (or together)
provided sufficient evidence to support more stringent levels below
those identified from the daily studies. Thus, removal of the
Dockery and Pope studies would not affect the conclusions about the
significance of the risks and therefore, while these long-term
studies tend to strengthen the need for fine particle control and
provide important insights into the nature of PM effects, removal of
these two studies from consideration would not have changed the
selected standard level.
91 Some commenters noted that with regard to the health data
underlying the 1993 Dockery and 1995 Pope studies, since EPA
provided partial funding for these studies, EPA has access to this
data and cannot shield itself from the duty to obtain this data by
claiming that it is not in its possession. Although a legal argument
potentially exists that EPA may obtain access to such data, this
legal argument has not been tested in the courts. More importantly,
EPA's ability to rely on studies without reviewing the raw data
should not depend on whether some Agency of the Federal government
funded the science.
---------------------------------------------------------------------------
In this case, the merits of the studies considered and used in
developing the PM2.5 standard have been discussed and
debated extensively over the past several years, both as part of the
EPA review of the pertinent science and in a number of other public
forums. The studies at issue were critically evaluated
[[Page 38690]]
by the Agency's Office of Research and Development (ORD) and by the
EPA's independent Clean Air Scientific Advisory Committee (CASAC), in a
multi-year process for assessment of the science at issue. As with
other studies on which EPA relied, particular attention was given to
the strengths and limitations of the Dockery, Schwartz and Pope studies
during this process, which involved numerous opportunities for public
participation and extensive input from interested parties. The results
of these studies are not only consistent with each other, but they are
also consistent with the results of other studies demonstrating
significant associations between long-term exposure to fine particle
indicators and mortality. See U.S. EPA, 1996b, p. V-62. The CASAC
concluded that EPA's assessments of the pertinent science properly
characterized both the current state of knowledge and the range of
policy options for revising the standards.
In fact, many peer reviewed studies have reported associations
between PM and premature death; the Dockery, Schwartz and Pope studies
are among the most recent studies to corroborate this association. In
the early 1990s, several studies were published showing associations at
levels below the current PM standards. Some critics began raising
questions about the extent to which the results could be reproduced and
the unavailability of underlying data. In response, an independent
group of investigators under the auspices of the Health Effects
Institute (HEI), a highly respected research organization jointly
funded by EPA and several motor vehicle manufacturers, undertook a
reanalysis of several such studies. The original investigators of
several studies, including studies conducted at Harvard University,
Brigham Young University, and the San Francisco Bay Area Air Quality
Management District provided their raw air quality data sets to the HEI
investigation team for reanalysis. HEI's reanalysis produced numerical
results from the data sets for all six cities that closely agree with
and, in general, confirm the results of the original investigators.
Thus, as noted in Unit II. of this preamble, these reanalyses by
respected independent scientists confirmed the reliability and
reproduceability of prior work of the original investigators, including
work by Dockery et al. (1992), Pope et al. (1992), Schwartz and Dockery
(1992a), and Schwartz (1993).
Thus, the 1993 Dockery and 1995 Pope studies build upon previous
studies done by a number of different researchers and have been subject
to an extensive peer review process by EPA's ORD, CASAC and HEI. They
also underwent a peer review process at the time of their publication
in reputable scientific journals. Given the consistency and coherence
of the scientific evidence and the scrutiny the studies have received
in peer review and in the extensive scientific review process described
in this unit, EPA does not agree that review of the underlying data for
these studies is also necessary. Considering the various reviews
described in this unit and the fact that EPA has received no specific
and substantiated reason, such as plausible allegations of fraud or
scientific abuse, to doubt the overall validity of their conclusions,
EPA agrees with CASAC that revision of the standard is appropriate,
based on these and other studies.
In spite of EPA and CASAC's conclusion that it is appropriate to
rely on the Pope, Dockery and other studies to establish a
PM2.5 NAAQS, EPA also believes in public disclosure and
supports efforts to seek appropriate release of data underlying the
studies in question. On January 31, 1997, EPA wrote to the principal
scientific investigators at the Harvard School of Public Health and at
Brigham Young University and urged them to make the data associated
with their studies available to interested parties. Studies conducted
by these investigators relied on data compiled as part of the Harvard
Six-Cities Study and data compiled by the American Cancer Society (ACS)
as part of the Cancer Prevention Study II.
The studies in question combined health data on individuals with
air pollution data. The air pollution data are publicly available. The
health data consist of personal and confidential information, e.g. age,
sex, weight, eduction level, smoking history, occupational exposures,
medical history. These data are not publicly available. In compiling
these data, researchers have promised study participants that private,
personal information would be kept confidential under signed assurances
of confidentiality. Data-sharing arrangements with outside parties
must, therefore, accommodate interests both in making data accessible
and in protecting the confidentiality of the information contained
within them.
Both the Harvard School of Public Health and the American Cancer
Society have made such arrangements. Both have processes which allow
ouside scientists, in collaboration with Harvard and ACS researchers,
to access their databases for the conduct of legitimate scientific
research. Scientists from all over the world have applied for and have
been granted such access and numerous studies have been conducted and
published using the databases.
Because of increased interest resulting from EPA's rulemaking on PM
standards and at the request of the Harvard School of Public Health,
HEI is taking additional steps to provide a forum for outside
researchers to access health data associated with the Harvard-Six
Cities Study and perhaps others. HEI has convened an expert panel of
esteemed scientists to access underlying data and to conduct additional
reanalyses. This arrangement appears to provide a constructive venue
for testing legitimate scientific hypotheses while protecting the
confidentiality of the underlying data.
Nevertheless, as noted previously, EPA has full confidence in the
scientific integrity of the Dockery, Schwartz, and Pope studies and
their suitability for use in the Agency's rulemaking on PM, without
undertaking a separate or additional review and analysis of the
underlying raw data. The decision to propose revisions of the current
PM standards was based on careful assessment of the scientific and
technical information presented in the PM Criteria Document and Staff
Paper. The decision was also consistent with the consensus of CASAC
that ``although an understanding of health effects of PM is far from
complete, the Staff Paper, when revised, will provide an adequate
summary of our present understanding of the scientific basis for making
regulatory decisions concerning PM standards.'' The extensive PM
epidemiological data base provides evidence that serious adverse health
effects, e.g., mortality, exacerbation of chronic disease, increased
hospital admissions, respiratory symptoms, and pulmonary function
decrements, in sensitive subpopulations, e.g., the elderly, individuals
with cardiopulmonary disease and children, are attributable to PM at
levels below the current standards. The increase in risk is significant
from an overall public health perspective because of the large number
of individuals in sensitive subpopulations that are exposed to ambient
PM and the significance of the health effects. These considerations, as
well as others discussed in the proposal and Staff Paper, such as the
need to consider fine and coarse particles as distinct classes, led
both the Administrator and CASAC to conclude that revision of the
current standards is clearly appropriate. This conclusion remains
unchanged despite the fact that EPA is without the actual raw and
[[Page 38691]]
unanalyzed health data underlying the studies.
A number of commenters cited section 307(d) of the Act in support
of their position that EPA is required to obtain and disclose the
underlying raw data. Under section 307(d)(3) of the Act, EPA is
required to issue a notice of proposed rulemaking in the Federal
Register that is accompanied by a ``statement of basis and purpose''
that includes ``a summary'' of:
(A) The factual data on which the proposed rule is based.
(B) The methodology used in obtaining the data and in analyzing
the data.
Thus, it is clear from the language of section 307(d) of the Act
that where EPA relies on any ``data'' as support in its rulemakings
under the Clean Air Act, it has an obligation to include such data or
information in the rulemaking docket that is open to the public. Where
EPA fails to do so and the error is ``so serious and related to matters
of such central relevance to the rule that there is a substantial
likelihood that the rule would have been significantly changed if such
errors had not been made,'' a reviewing court may overturn the rule.
In this case, as noted previously, EPA did not rely upon the raw
health data supporting the Dockery and Pope studies; it relied instead
upon the studies themselves. These studies may properly be considered
``data.'' The EPA has never had the raw health data in its possession;
thus EPA has neither reviewed it nor had an opportunity to place it in
the docket. The EPA did rely on the studies and these studies are
included in the docket and are available for public review. Because EPA
neither reviewed nor relied upon the raw data, there is no obligation
to obtain it or to make it available.
Some commenters argued that the language of section 307(d) of the
Act, which refers to the ``factual data'' and which also discusses the
``methodology used in obtaining and analyzing the data'' distinguishes
between raw data and studies. In the view of these and other
commenters, the plain language of section 307(d) of the Act requires
that EPA obtain and disclose the raw data used in the Dockery and Pope
studies. According to these commenters, without such raw ``data,'' EPA
cannot legally promulgate its rule.
The EPA disagrees with this narrow interpretation of the word
``data'' and of section 307(d) of the Act. Data can take many forms,
including studies, reports, tabulations, graphs and summaries, as well
as more raw forms, such as questionnaire responses, test results and
even actual physical specimens. The ``factual data'' called for by
section 307(d) of the Act may clearly include peer-reviewed scientific
studies. Nor does section 307(d) of the Act prohibit EPA from relying
on a study for standard setting without obtaining the raw, underlying
data supporting a study. Indeed, as noted in the legislative history to
section 307(d) of the Act,
* * * [t]he [House Commerce] Committee recognizes that the
factual support needed for a rule may vary greatly according to the
subject being addressed and that rules on some subjects, such as
procedures, may not require any factual basis at all. There is no
intention to increase the amount of `factual' support now required
to support `policy judgments where no factual certainties exist or
where facts alone do not provide the answer,' Industrial Union
Department, AFL-CIO v. Hodgson, 499 F.2d 467, 476 (D.C. Cir. 1974).
Nor is there any intent to diminish the Administrator's authority to
adopt precautionary regulations based on a showing of risk * * * .
H.R. Rep. No. 95-294, at 323 (1977) (footnote omitted). As this
legislative history makes clear, the language in section 307(d) of the
Act is not intended to require EPA to change the amount of ``factual
support'' that EPA must assemble in order to promulgate a rule and EPA
may adopt ``precautionary'' regulations ``where no factual certainties
exist.'' Given this clarification in the legislative history, it is
evident that EPA is entitled under section 307(d) of the Act to rely on
studies rather than raw data in developing its Clean Air Act rules,
despite the arguably ambiguous use of the term ``data.''92
---------------------------------------------------------------------------
92 EPA also does not agree that because the language of section
307(d) of the Act mentions ``factual data'' as well as ``the
methodology used in obtaining and analyzing the data,'' EPA cannot
rely on a study alone. In this case, the study is the ``factual
data'' and EPA's methodology used in obtaining and analyzing the
``factual data'' is the method that EPA used to review and rely upon
the studies. This methodology is discussed extensively in the staff
paper and summarized in some detail elsewhere in this preamble. In
fact, as is clear from the overall structure of section 307(d) of
the Act, as well as the legislative history cited in this unit,
section 307(d) of the Act merely requires that EPA summarize and
disclose the information and methodology that it relied upon in
developing its rule. It leaves unchanged the ``level'' of support
that an agency must bring to bear in drafting a proposed rule.
---------------------------------------------------------------------------
Moreover, EPA has relied on studies in the past (including studies
using the undisclosed Six Cities data) without obtaining or disclosing
the underlying raw data, and EPA's reliance on such studies to set
Clean Air Act standards has been upheld in court. In NRDC v. EPA, 902
F. 2d 962 (D.C. Cir. 1990), the D.C. Circuit declined to delay its
review of the PM10 NAAQS rulemaking due to concerns raised
by the American Iron and Steel Institute about the integrity of the Six
Cities data base. 902 F.2d at 974. In that case, EPA had relied upon an
earlier Dockery study based on the Six Cities data base. Although the
National Institutes of Health (NIH) undertook a review of the
allegations regarding the Six Cities database, the court nevertheless
upheld EPA's reliance on that Dockery study without waiting for the
results of the NIH review. NIH eventually concluded that the
allegations were without merit. According to the court in the NRDC
case:
AISI claims that the EPA relied too much on the Six Cities
Study, which is comprised of the Dockery study and the Ware study *
* * . We do not agree that the Administrator's selection of the
twenty-four hour standard lacks the necessary reasoned analysis and
supportive evidence * * * . After carefully reviewing the record, we
find EPA's selection of the twenty four hour standard reasonable in
light of the divergent results in the studies and the agency's
mandate to provide an adequate margin of safety. Studies contained
in the record provided evidence of adverse health effects at levels
below 250 g/m3.
902 F.2d at 969 (footnotes omitted; emphasis in original). The court
also stated that:
In setting a standard under section 109 of the Act, the
Administrator must ``take into account all the relevant studies
revealed in the record`` and ``make an informed judgment based on
available evidence.'' American Petroleum Institute v. Costle, 665
F.2d at 1187. The record shows that the Administrator did so. The
Administrator relied on studies which showed adverse effects at and
below the 250 g/m3 level. AISI essentially asks this court
to give different weight to the studies than did the Administrator.
We must decline. It is simply not the court's role to ``second-guess
the scientific judgments of the EPA. * * * [T]he Administrator did
not act arbitrarily in drawing conclusions from the uncertain and
conflicting data. The Administrator may reasonably apply his
expertise to draw conclusions from ``imperfect data,'' Ethyl Corp.,
541 F.2d at 28, as he did here.
Id. at 971.
As this language makes plain, the term ``data'' may include a study
relied upon by EPA. It should be equally plain that EPA may properly
rely on such a study in setting a standard despite the fact that such
``data'' may be ``imperfect,'' ``conflicting,'' and ``uncertain.''
There are numerous other cases in which EPA has relied on studies in
setting standards under the Clean Air Act. See, e.g., Engine
Manufacturers Association v. EPA, 88 F. 3d 1075, 1099 (D.C. Cir.
1996)(upholding EPA's use of the 1993 Dockery study for setting mobile
source standards); API v. Costle, 665 F.2d 1176, 1185 (D.C. Cir.
1981)(Administrator's conclusion that normal body functions
[[Page 38692]]
are disrupted by ozone is ``supported by the studies'').
A number of commenters cited Endangered Species Committee v.
Babbitt, 852 F. Supp. 32 (D.D.C. 1994) (hereafter ``Gnatcatcher'') in
support of the proposition that EPA must obtain and disclose the raw
data underlying the Dockery and Pope studies. Relying on cases such as
Connecticut Light and Power Co. v. NRC, 673 F.2d 525 (D.C. Cir. 1982),
Portland Cement v. Ruckelshaus, 486 F.2d 375 (D.C. Cir. 1973), and
United States v. Nova Scotia Food Processing Corp, 568 F.2d 240 (2nd
Cir. 1977), these commenters suggest that ``a body of legal decisions
is emerging whereby federal courts are increasingly dubious of final
regulatory decisions that are being made absent public scrutiny of the
data underlying and purportedly supporting such decisions.'' According
to these commenters, based on Gnatcatcher and other cases, failure by
EPA to obtain and place in the docket the raw unanalyzed data used in
the Dockery and Pope studies constitutes serious procedural error under
the Clean Air Act.
Under Connecticut Light and Power, agencies must make available
technical studies and data that have been relied upon during the
rulemaking process in order for the public to have an adequate
opportunity for notice and comment. There is no question that EPA has
done this with regard to the Dockery and Pope studies, which are
included in the rulemaking docket. The Portland Cement case makes clear
that where an agency actually relies on factual data it cannot
``promulgate rules on the basis of inadequate data, or on data that,
[to a] critical degree, is known only to the agency.'' 486 F.2d at 393.
See also, Nova Scotia, 568 F.2d 240, at 251 (where all of the research
was collected by the agency, and none of it was disclosed ``as the
material upon which the proposed rule would be fashioned,'' error
resulted); CMA v. EPA, 870 F.2d 177, 200 (5th Cir. 1989) (``fairness
requires that the agency afford interested parties an opportunity to
challenge the underlying factual data relied on by the agency'').
However, in this case, EPA did not rely on, nor did it ever have
or review, the underlying data used in the Dockery and Pope studies.
Instead, it relied upon the studies themselves. Thus, the cases cited
in this unit are inapposite. They stand only for the proposition that
where an agency actually reviews and relies on ``data,'' which may be
raw data, a study or a variety of other forms of information, it must
make these data available. They do not and cannot stand for the
proposition that an agency may not rely on a study alone and must
always obtain the raw and unanalyzed data underlying a study. Indeed,
as one D.C. Circuit case noted: ``Portland Cement and Nova Scotia
simply cannot be twisted so as to require notices of proposed or
interim rules to contain elaborate reproductions of underlying
studies.'' Petry v. Block, 737 F.2d 1193, 1198 (D.C. Cir. 1984).
Requiring EPA to obtain, analyze and disclose the data underlying the
Pope and Dockery studies, which EPA neither reviewed nor relied upon,
would be to require EPA to attempt such an ``elaborate reproduction.''
Such a step is not required under the law and would make it extremely
difficult, if not impossible, for EPA to regulate in complex, technical
areas ``at the frontiers of science.'' Baltimore Gas and Electric Co.
v. NRC, 462 U.S. 87 (1983).
The district court's decision in the Gnatcatcher case is similarly
inapposite. That case concerned a scientific study regarding the range
of the California Gnatcatcher, a small insectivorous songbird. As the
Gnatcatcher opinion itself notes, ``courts have generally allowed
agencies to rely on scientific reports.'' Gnatcatcher, 852 F.Supp. at
37. Thus, the question at issue in Gnatcatcher was whether specific
circumstances exist in which an agency may not be entitled to rely on
studies alone. In the Gnatcatcher case, a single author had published
two directly contradictory studies on the same issue, while relying on
the same data. In light of this clear contradiction, commenters in that
rulemaking argued that without the underlying data it was impossible to
determine whether the conclusions in either study were correct. The
district court noted that:
The Secretary had before him a report by an author who, two
years before had analyzed the same data and come to an opposite
conclusion. It is the disputed nature of this report that
distinguishes this from other cases where a scientific report alone
has been considered sufficient for ESA purposes.
Id. Thus, according to the court: ``While courts have generally allowed
agencies to rely on scientific reports * * * this is not sufficient in
this case because the report itself is under serious question.'' Id.
The EPA's current reliance on the Dockery and Pope studies bears
no resemblance to the circumstances present in the Gnatcatcher
decision. As noted previously, these studies have been subject to
extensive peer review and scrutiny, and neither researcher has
published a contradictory study on the same issue, much less using the
same data base. The EPA is not aware of, nor have any of the commenters
raised any particular issues relating to either gross error, fraud or
scientific abuse arising from the data. Indeed, as noted previously,
the prior work of these particular researchers has been subject to
extensive independent scrutiny and reanalysis, which has confirmed,
rather than called into question, the underlying validity of their
conclusions and the integrity of their research methods. Reading
Gnatcatcher to suggest that EPA cannot rely on such a study, where the
study and its methods have been subject to extensive peer review, would
place the district court's rationale in Gnatcatcher in conflict with
applicable D.C. Circuit precedent that makes evident the right of
agencies to rely on studies alone. See, e.g., Engine Manufacturers
Association v. EPA, 88 F.3d 1075, 1099 (D.C. Cir 1996); API v. Costle,
665 F.2d 1176, 1185 (D.C. Cir. 1981), ``studies discussed in the
Criteria Document constitute a rational basis for the finding that
adverse health effects occur at ozone levels of 0.15-0.25 ppm for
sensitive individuals''; see also, NRDC v. Thomas, 805 F.2d 410, 418
(D.C. Cir. 1986)(EPA use of a summary of confidential data that was not
disclosed provides ``a reasoned explanation for moving from a 4.0 to
5.0 long term NOx standard'').
In addition, to require EPA to obtain and analyze the data prior
to revising the standard would also contradict the ``common sense
notion that Congress, in providing for notice and comment under the
APA, could not have intended to subject the agencies--and the public on
whose behalf they regulate--to [a] sort of interminable back and
forth.'' International Fabricare Institute v. EPA, 972 F.2d 384, 399
(D.C. Cir. 1992). In the view of some commenters, EPA has no choice but
to either postpone its decision for a year or more awaiting a review of
data or choose to retain the current standard. Yet were EPA to adopt
such an approach, these commenters would undoubtedly insist that EPA be
required to include an analysis of the data in the docket; further
questions would likely be raised regarding the re-analysis and once
again EPA might find itself unable to promulgate its rule pending
review of further hypothetical questions. This type of unending inquiry
is not required under the law. As the D.C. Circuit has noted:
* * * [D]isagreement among the experts is inevitable when the
issues involved are at the ``very frontiers of scientific
knowledge,'' and such disagreement does not prevent us from finding
that the Administrator's decisions are adequately supported by the
evidence in the record * * * . It is not our function to resolve
disagreement among the experts or to judge
[[Page 38693]]
the merits of competing expert views * * * . Cf. Hercules, Inc. v.
EPA, 598 F.2d 91,115 (D.C. Cir. 1978) (``[c]hoice among scientific
test data is precisely the type of judgment that must be made by
EPA, not this court'').
Lead Industries Association v. EPA, 647 F.2d 1130, 1160 (D.C. Cir.
1980).
Neither Gnatcatcher, nor any other case can fairly be read to
suggest that EPA has an obligation to respond to all possible questions
that might be raised regarding its scientific conclusions or that where
EPA relies on a study, it must engage in a multi-phased and possibly
unending re-examination of the data supporting such a study until all
commenters are satisfied in full with the details of the underlying
science. Even assuming that EPA could obtain the confidential Six
Cities data through litigation, a substantial delay of many months, if
not years, would likely result, in order for both EPA and industry to
reanalyze the data. In the meantime, some tens of thousands of
premature deaths could result. Neither the Clean Air Act nor relevant
case law requires or permits such a result.
Indeed, the suggestion that EPA cannot and should not rely upon
the Pope, Dockery, and Schwartz studies, unless and until interested
parties have had an opportunity to examine and reanalyze the underlying
raw data, is extraordinary. Given the precautionary nature of section
109 of the Act and the need to allow an adequate margin of safety, see
Lead Industries, 647 F.2d at 1154, 1155, there are limits on EPA's
discretion to disregard even studies that are clearly flawed, if they
are nonetheless ``useful'' in indicating the kind and extent of health
effects that may result from the presence of a pollutant in the ambient
air. See sections 109(b)(1) and 108(a)(2) of the Act.
A few commenters cited Kennecott v. EPA, 684 F.2d 1007 (D.C. Cir.
1982) and argued that under sections 307(d)(8) and 307(d)(9)(D) of the
Act, a failure by EPA to obtain and include in the docket the data
underlying the Pope and Dockery studies would constitute an ``error''
that is ``so serious and related to matters of such central relevance
to the rule that there is a substantial likelihood that the rule would
have been significantly changed if such error[] had not been
made.''93 EPA disagrees. Peer reviewed studies conducted by
outside parties were not at issue in Kennecott. Kennecott involved a
dispute over financial analyses that EPA itself had previously
conducted and used in earlier rulemakings. The court determined that
the financial analyses at issue must have provided at least part of the
factual basis for EPA's rule, and EPA referenced these analyses in the
preamble to the final rule without placing them in the docket until one
week before promulgation. The factual circumstances in Kennecott are
substantially different than the current situation and thus, Kennecott
cannot fairly be read to establish the applicable legal standard with
regard to EPA's reliance on peer reviewed studies for use in setting
the NAAQS.
---------------------------------------------------------------------------
93 One commenter argued that EPA's failure to place the ``data''
in the docket was not an ``error'' but a ``refusal to comply with
the clear language of the law that should be reviewed by the courts
under section 307(d)(9)(C), rather than 307(d)(9)(D).'' As noted
previously, EPA does not agree with this interpretation of section
307(d)(3) of the Act. Under applicable caselaw, the term ``data''
may include information in many forms, including studies that EPA
has placed in the docket. See Endangered Species Committee v.
Babbitt, 852 F. Supp. 32, 37 (D.D.C., 1994) (``data can come in many
forms: it can be a scientific report, it can be graphs and
tabulations * * * it can be raw numbers'').
---------------------------------------------------------------------------
In this case, EPA--well before proposal--has placed the information
that it relied upon in the docket. This information is in the form of
studies. These studies have been subject to extensive scrutiny and peer
review. To date no specific allegation has been made that the studies
are clearly in error or that the data underlying them are the subject
of fraud, scientific misconduct, or gross error going to the basic
validity of the studies.94 Instead, various commenters have
merely stated their view that were the raw data behind these studies
available, they would be able to better verify and assess the results
reached in the studies.
---------------------------------------------------------------------------
94 A number of commenters did argue these studies do not form a
sufficient basis for EPA's decision to revise the NAAQS and that
attempts to replicate these studies have not been universally
successful. These same commenters also listed a number of
hypothetical questions and issues that might be resolved through a
review of the underlying data and suggested that before EPA may
properly rely on these studies to revise the NAAQS, a variety of
confounders (such as smoking) should also be ruled out by reviewing
the data. As set forth more fully in Unit II. of this preamble,
neither EPA nor CASAC agrees that any of these factors precludes
reliance on the studies in question.
---------------------------------------------------------------------------
As one commenter noted, ``In the absence of data on which EPA's
proposal is based, [key scientific] issues remain shrouded in
uncertainty and skepticism. The disclosure of the data would allow for
robust scientific analysis and discussion of these issues.'' A
similarly hypothetical concern is raised by another commenter who
stated that ``seeing the data would clarify substantial questions of
methodology'' and ``had the Harvard data been available, a far broader
evaluation of the defects of the Harvard Studies would have been
possible with the same expenditure of time and money.'' Yet, despite
having spent ``in the neighborhood of a million dollars to duplicate
and reanalyze the Harvard data set'' this commenter was unable to
allege any particular defect in the methodology or results of these
studies and noted instead that ``the track record to date suggests that
the claimed associations to PM2.5 and health effects would
not have held up under such a broader evaluation.''
EPA is not required to await the results of such an inquiry before
proceeding to regulate to protect human health and the environment. The
concerns raised by the commenters regarding these studies remain
hypothetical; the comments themselves raise no allegations of fraud,
scientific misconduct or gross error that calls into question the
fundamental validity of the studies. Given this fact, EPA does not
agree with the commenters that reliance on these studies and/or a
failure to place the underlying data in the docket constitutes an
error, much less an error that is ``so serious and related to matters
of such central relevance that there is a substantial likelihood that
the rule would have been significantly changed.'' EPA is entitled to
rely upon these studies and it has satisfied its obligation to provide
the ``factual data'' upon which the proposed rule is based by placing
these studies in the docket.
In fact, the concerns raised by the commenters ultimately boil down
to a disagreement with EPA over the level of scientific certainty
necessary to adopt the NAAQS revisions. In setting standards under the
Clean Air Act, EPA is not required to resolve all scientific issues to
the complete satisfaction of every interested party. As noted by the
D.C. Circuit in Lead Industries Association v. EPA, 647 F.2d 1130, 1160
(D.C. Cir. 1980):
To be sure, the Administrator's conclusions were not
unchallenged; both LIA and the Administrator are able to point to an
impressive array of experts supporting each of their respective
positions. However, disagreement among the experts is inevitable
when the issues involved are at the ``very frontiers of scientific
knowledge,'' and such disagreement does not preclude us from finding
that the Administrator's decisions are adequately supported by the
evidence in the record. It may be that LIA expects this court to
conclude that LIA's experts are right, and the experts whose
testimony supports EPA are wrong. If so, LIA has seriously
misconceived our role * * * . It is not our function to resolve
disagreement among the experts or to judge the merits of competing
expert views * * * . Cf. Hercules, Inc., v. EPA, 598 F.2d 91, 115
(D.C. Cir. 1978) (``[c]hoice among scientific test data is precisely
the type of judgment that must be made by EPA, not this court'').
[[Page 38694]]
647 F.2d at 1160 (footnotes omitted).
The EPA's rationale for proposing to add a fine particle standard
was detailed in the preamble to the proposed rule, most notably at 61
FR 65654-65662, December 13, 1996. This decision is based on the
extensive review of the science and policy issues contained in the PM
Criteria Document and Staff Paper; the CASAC concluded, after extensive
review, that both of these documents were appropriate for use in
decision making on standards. These documents contain a full discussion
of both what is known about PM and the information gaps and
uncertainties. Considering the full weight of the scientific evidence,
including the uncertainties, the CASAC recommended that the
Administrator adopt fine particle standards and a number of panel
members based their support for a PM2.5 standard on the
following reasoning:
[T]here is strong consistency and coherence of information
indicating that high concentrations of urban air pollution adversely
affect human health, there are already NAAQS that deal with all of
the major components of that pollution except PM2.5, and
there are strong reasons to believe that PM2.5 is at
least as important as PM10-2.5 in producing adverse
health effects.
Wolff, 1996.
Given the consistency and coherence of the evidence that premature
mortality and sickness occur in large numbers of Americans at
concentrations permitted by the current standards, it would be
irresponsible to delay action that would put more appropriate air
quality goals into place based on the most recent scientific
information. After a review of the comments submitted, the Agency's
conclusion that it is appropriate to rely on the existing studies
remains unchanged.
D. 1990 Amendments
Contrary to the view expressed in some public comments, the
provisions of subpart 4 of Part D of Title I of the Act, enacted in
1990, do not preclude EPA from adopting PM2.5 as an
additional indicator for PM and establishing standards for
PM2.5. The provisions of subpart 4 of Part D of Title I of
the Act simply do not limit EPA's clear authority under section 109 of
the Act to revise the PM standards.
The basic contention is that because the provisions of subpart 4
of Part D of Title I of the Act refer to PM10, they prohibit
EPA from regulating any other type of PM, for example, by revising the
existing NAAQS for PM by adopting an ambient air quality standard for
PM2.5. These provisions, however, do not lead to such a
conclusion. Moreover, this view ignores provisions indicating that
Congress believed that EPA could revise any existing NAAQS or adopt a
new NAAQS.
At the outset, it should be noted that Congress expressly
authorized EPA to revise any ambient air quality standard and to adopt
a new NAAQS in section 109 of the Act. That section, which requires EPA
to review and revise, as appropriate, each NAAQS every five years,
contains no language expressly or implicitly prohibiting EPA from
revising a NAAQS or adopting a new NAAQS. If Congress had intended to
preclude EPA from reviewing and revising a NAAQS or adopting a new
NAAQS, which are part of EPA's fundamental functions, Congress would
have specifically done so. Clearly, Congress knew how to preclude EPA
from exercising otherwise existing regulatory authority and did so in
other instances. See section 202(b)(1)(C) of the Act (expressly
precluding EPA from modifying certain motor vehicle standards prior to
model year 2004); section 112(b)(2) of the Act (preventing EPA from
adding to the list of hazardous air pollutants any air pollutants that
are listed under section 108(a) of the Act unless they meet the
specific exceptions of section 112(b)(2) of the Act); section
249(e)(3), (f) and section 250(b) (limiting EPA's authority regarding
certain clean-fuel vehicle programs). No such language was included
either in section 109 of the Act or elsewhere in the Act and no such
implication may properly be based on the provisions of subpart 4 of
Part D of Title I of the Act.
Second, other provisions of the Act expressly contemplate EPA's
ability to promulgate a new or revised NAAQS, and provide no indication
that such ability is limited to standards other than those whose
implementation is the subject of subparts 2, 3 and 4 of Part D of Title
I of the Act. For example, section 110(a)(2)(H)(i) of the Act provides
that SIPs are to provide for revisions ``from time to time as may be
necessary to take account of revisions of such national primary or
secondary ambient air quality standard * * * .'' Section 107(d)(1)(A)
of the Act provides a process for designating areas as attainment,
nonattainment, or unclassifiable ``after promulgation of a new or
revised standard for any pollutant under section 109 * * * .'' Section
172(e) of the Act addresses modifications of national primary ambient
air quality standards. Finally, section 172(a)(1) of the Act expressly
contemplates that EPA may revise a standard in effect at the time of
enactment of the 1990 Clean Air Act Amendments. Section 172(a)(1)(A) of
the Act provides EPA with authority to classify nonattainment areas on
or after the designation of an area as nonattainment with respect to
``any revised standard, including a revision of any standard in effect
on the date of the enactment of the Clean Air Act Amendments of 1990.''
Plainly, Congress had no intention of prohibiting EPA from revising any
of the ambient standards in effect at the time of the enactment of the
1990 amendments.
Third, the provisions of subpart 4 of Part D of Title I of the Act
do not support the contention that they somehow preclude EPA from
exercising its authority to adopt a revised PM NAAQS based on a metric
other than PM10. The fact that Congress laid out an
implementation program for the PM standard existing at the time of the
1990 amendments in no way suggests that Congress intended to preclude
EPA from exercising the authority it provided EPA to revise the NAAQS
when the health data on which EPA bases such decisions warranted a
change in the standard.
The fact that Congress drafted subpart 4 of Part D of Title I of
the Act in 1990 to specify the implementation regime for the PM
standard then in effect, a PM10 standard, in terms that
explicitly refer to PM10 in no way suggests that Congress
meant to preclude EPA from adopting a PM standard based on another
metric if scientific information supported such a change. Obviously,
PM10 was the standard in existence in 1990 and Congress
drafted subpart 4 of Part D of Title I of the Act, the purpose of which
was to delineate an implementation regime for that standard, in terms
of that standard. There is simply no language in subpart 4 of Part D of
Title I of the Act that limits EPA's ability to establish a different
PM standard if such a standard were warranted under section 109 of the
Act or indicates any implicit intent on the part of Congress to limit
EPA's authority under section 109 of the Act in such a way. Subpart 4
of Part D of Title I of the Act simply does not speak to the question
of whether EPA may establish a PM standard based on a different metric.
In addition, section 107(d)(4) of the Act, the only provision outside
of subpart 4 of Part D of Title I of the Act invoked as a basis for the
view that the Act prohibits EPA from adopting a PM2.5
standard, does not support that view. That provision simply preserved
pre-existing designations for ``total suspended particulates,'' the PM
metric utilized prior to PM10, for certain purposes. It
provides no suggestion that Congress intended to prohibit EPA from
adopting
[[Page 38695]]
a metric other than PM10. Indeed, if anything, it indicates
that Congress was fully aware that EPA had previously changed the PM
metric used in the PM NAAQS and confirms the view that Congress would
have explicitly barred EPA from changing the metric had it intended to
do so.
Finally, for the reasons stated in this unit, EPA's analysis of
its ability to implement a PM2.5 standard under the
provisions of subpart 1 of Part D of Title I does not support the view
that Congress prohibited EPA from promulgating such a standard.
Congress clearly specified an approach to the implementation of the
PM10 standard in the provisions of subpart 4 of Part D of
Title I of the Act. The EPA believes that the clear and express linkage
of that approach to the PM10 standard indicates that a
different PM standard should be implemented under the general
principles of subpart 1 of Part D of Title I of the Act. That Congress
directed specifically how EPA and the States should implement the
PM10 standard does not carry with it the implication that
Congress intended to prohibit EPA from exercising its otherwise clear
and express authority to adopt a PM standard based on a different
metric in order to carry out one of its fundamental missions, the
establishment of ambient air quality standards to protect public health
with an adequate margin of safety. It is entirely reasonable and
logical for Congress to, on the one hand, specify an implementation
regime for the PM standard in effect at the time of enactment of the
1990 amendments, but, on the other hand, leave EPA free to exercise the
authority provided it by Congress in section 109 of the Act to adopt a
new or revised standard when EPA determined that such a standard was
needed to protect public health with an adequate margin of safety.
Congress explicitly required EPA to review and revise as appropriate
the NAAQS every five years. If Congress did not intend for EPA to
revise the NAAQS when warranted, it would not have required EPA to
review and revise them. If Congress had intended to prohibit EPA from
exercising such a fundamental authority it would have clearly
specified, as it did in other instances, that EPA could not do so.
V. Revisions to 40 CFR Part 50, Appendix K--Intrepretation of the
PM NAAQS
Because the revocation of the existing PM10 standards
will become effective at a later date (as discussed in Unit VII. of
this preamble), EPA is retaining 40 CFR part 50, Appendix K, although
it is being published today in revised format to conform with the
format of the other appendices in this part. A new Appendix N to 40 CFR
part 50 explains the computations necessary for determining when the
primary and secondary PM2.5 and PM10 standards
being adopted today are met. The discussion in this unit sometimes
refers to the contents of the new Appendix N as revisions to Appendix
K, so as to highlight how the new Appendix N differs from the current
Appendix K.
Key elements of the new 40 CFR part 50, Appendix N, particularly as
they differ from those of Appendix K, are outlined in this unit.
A. PM2.5 Computations and Data Handling Conventions
As discussed in Unit II.E. of this preamble, the form of the annual
PM2.5 standard is a spatially averaged annual mean averaged
over 3 years, and the form of the 24-hour PM2.5 standard is
a 98th percentile concentration averaged over 3 years.
With regard to the annual PM2.5 standard, the EPA
proposed a form expressed as the annual arithmetic mean, averaged over
3 years and spatially averaged over all designated monitoring sites to
represent population exposures. As discussed in Unit II.E.1. of this
preamble, the form of the annual PM2.5 standard has been
clarified to make explicit that implementing agencies have the
flexibility to base comparison of the standard level with measured
values from either a single community-oriented site or an average of
measured values from such monitors within the constraints enumerated in
40 CFR part 58. The new Appendix N of 40 CFR part 50 reflects this
clarification. The spatial average, if used, is to be carried out using
data from monitoring sites designated in a State PM Monitoring Network
Description in accordance with the provisions of 40 CFR part 58.
Also, the EPA proposed that, for spatial averaging, the
requirements for 3 years of data for comparison with the standard be
fulfilled by the spatial averaging network as a whole, not by
individual monitors within the network. The EPA received comments
regarding the application of the 75 percent data completeness
requirement to spatial averaging. The commenters stated that the
inclusion or exclusion of a site not meeting the data completeness
requirements from a spatial average, based on the level of the single
site average, would bias the spatial average for that year. The EPA has
responded to the comment by demonstrating in Example 1 in 40 CFR part
50, Appendix N the application of the data completeness criterion that
is consistent with a spatially averaged network. Specifically, the
application of the data completeness requirement has been altered in
the example if a particular site has quarters in a year that do not
meet the minimum data completeness requirement. Instead of comparing a
site's annual average to the level of the standard to decide whether or
not to keep the site in the calculations, the annual average for all
the sites (the spatial average) is compared to the level of the
standard. If the spatial average is above the level of the standard,
the site is kept in the calculations. If it is below, the site is
omitted from the calculations.
The EPA also proposed that averaging over calendar quarters be
retained for the annual average form of the standard. Although several
commenters stated that the step of calculating quarterly averages to
obtain the annual average was unnecessary, the EPA maintains that
quarterly averages are important to ensure representative sampling in
areas with extreme seasonal variation.
Regarding the 75 percent data completeness requirement, the
proposal stated that a given year meets data completeness requirements
when at least 75 percent of the scheduled sampling days for each
quarter have valid data, and high values measured in incomplete
quarters shall not be ignored but shall be included if their value
causes the annual calculation to be above the level of the standard.
Some commenters felt that this treatment was unfair in that measured
data below the standard in incomplete quarters are not retained. In
addition, the commenters felt that this could create a bias where a
single sample could inflate an annual average to a level above the
standard. The EPA agrees and has incorporated in 40 CFR part 50,
Appendix N the following provisions.
(1) A statement has been added that less than complete data may be
used in certain cases subject to the approval of the appropriate
Regional Administrator in accordance with EPA guidance for dealing with
less than complete data. This statement was considered necessary for
those situations where measured data and air quality analyses would
indicate that the area met or did not meet the standard although it did
not exactly meet the data completeness requirements.
(2) A provision has been added that a minimal amount of data is
needed before the requirement to retain high values in an incomplete
quarter comes into effect for the annual standards. Sites with at least
11 samples but less than 75 percent data completeness in a quarter will
have to include high values
[[Page 38696]]
if they result in calculated values which are above the level of the
standard. This provision is based upon the change in sampling frequency
set forth in the revisions to 40 CFR part 58 which effectively doubles
the minimum sampling frequency from 1-in-6 day sampling to 1-in-3 day
sampling. The data completeness requirement for the annual form of the
standard under the original 1-in-6 day sampling schedule is equivalent
to a minimum of 37.5 percent under the new sampling schedule of 1-in-3
days. This is equivalent to a minimum of 11 samples in each quarter.
Therefore, a minimum of 11 samples in a quarter should be sufficient
for an annual average above the level of the standard to be used under
the new sampling schedule.
(3) In sharp contrast, this minimum requirement was considered
unnecessary for the 24-hour form of the standard when the
98th percentile is above the level of the standard. That is,
for a site with a 98th percentile above the level of the
standard that does not meet the 75 percent data completeness
requirement, the 98th percentile would be equivalent to the
maximum or second maximum daily concentration in that year. While
adding more data samples up to the minimum data completeness
requirement of 75 percent could help to ensure that the second maximum
value (rather than the maximum value) corresponds to the
98th percentile, this difference is not considered
significant enough to require some minimal number of data samples when
dealing with the form of the 24-hour standard.
With regard to the 24-hour PM2.5 standard, the proposed
revision to 40 CFR part 50, Appendix K defined the 98th
percentile as the daily value out of a year of monitoring data below
which 98 percent of all values in the group fall. The calculation of
the percentile form has been revised to reflect general comments that
the form of the standard and its calculation should be simplified. The
EPA maintains that the revised calculation is consistent with the
definition of the percentile being that number below which a certain
percent of the data fall.
Regarding the expression of the annual standard to the nearest 0.1
g/m3 and the 24-hour standard to the nearest 1
g/m3, virtually no commenters disagreed with the
EPA's proposed approach. The few that did, however, took issue with the
overall stringency of the standards, not the rationale discussed in the
proposal. The EPA maintains its position that instrument sensitivity
and the number of measured values used in calculating the values to be
compared to the standard, as discussed at length in the proposal, point
to keeping the expressions of the standards stated in this unit.
B. PM10 Computations and Data Handling Conventions
As discussed in Unit II.G. of this preamble, the EPA proposed
retaining the current annual arithmetic mean, averaged over 3 years, as
the form of the annual PM10 standard, and changing the form
of the 24-hour PM10 standard to a 98th percentile
value form, averaged over 3 years. As discussed in Unit II.G. of this
preamble, the form of the daily PM10 standard has been
revised to a 99th percentile instead of the 98th
percentile, and the related calculations have been revised accordingly.
The same revision described above in Unit V.A. of this preamble to
simplify the formula used to calculate the percentile form of the 24-
hour PM2.5 standard also applies to the PM10
99th percentile calculation.
The revisions made to the annual and 24-hour PM2.5
standards regarding the 75 percent data completeness requirement also
apply to the annual and 24-hour PM10 standards. Appendix N
of 40 CFR part 50 reflects this change.
As with the PM2.5 standards, the EPA maintains its
position that instrument sensitivity and the number of measured values
used in calculating the values to be compared to the standard, as
discussed in detail in the proposal, point to keeping the expressions
of the standards to the nearest 1 g/m3 for the
annual standard and to the nearest 10 g/m3 for the
24-hour standard.
C. Changes That Apply to Both PM2.5 and PM10
Computations
In the proposal, the EPA stated that revisions to 40 CFR part 50,
Appendix K would not address the treatment of exceptional events data,
which are considered part of the standards implementation process.
Since several commenters mentioned the handling of these events in
conjunction with the proposed revisions to Appendix K, the EPA has
addressed this concern in Appendix N of 40 CFR part 50, which states
that whether to exclude, retain, or make adjustments to data affected
by uncontrollable or natural events is subject to the approval of the
appropriate Regional Administrator.
Comments were also received expressing the desire of some areas to
conduct seasonal sampling, reducing the frequency of monitoring during
a period of expected low concentrations to save resources. The proposed
revision to 40 CFR part 50, Appendix K did not prohibit this course of
action, and referred matters of sampling frequency to 40 CFR 58.13. For
clarification, 40 CFR part 50, Appendix N adds that exceptions to
specified sampling frequencies, such as a reduced frequency during a
season of expected low concentrations, shall be subject to the approval
of the appropriate Regional Administrator.
VI. Reference Methods for the Determination of Particulate Matter
as PM10 and PM2.5 in the Atmosphere
A. Revisions to 40 CFR Part 50, Appendix J--Reference Method for
PM10
Because the revocation of the existing PM10 standards
will become effective at a later date (as discussed in Unit VII. of
this preamble), EPA is retaining Appendix J in its current form. A new
Appendix M to 40 CFR part 50 establishes the reference method for
measuring PM10 in the ambient air for the revised
PM10 standards. The discussion in this unit sometimes refers
to the contents of the new Appendix M as revisions to Appendix J, so as
to highlight how the new Appendix M differs from the current Appendix
J. As discussed below, the only revision to the Reference Method for
PM10 relates to the calculation of the volume of air
sampled.
During the course of this standards review, EPA has received a
number of comments regarding the appropriateness of the current
practice of adjusting measured PM10 concentrations to
reflect standard conditions of temperature and pressure (25 deg. C and
760 mm Hg, respectively), as required by 40 CFR part 50, Appendix J.
The practice was originally adopted to provide a standard basis for
comparing all pollutants measured in terms of mass per unit volume
(e.g., g/m3). As EPA has reviewed the ambient
standards for gaseous pollutants, however, technical changes have been
made to express them on a pollutant volume/air volume basis (i.e., ppm)
that is insensitive to differences in altitude and temperature. Such an
approach is not applicable to particulate pollutants. The question
arises whether continuing the past practice of making temperature and
pressure adjustments for PM is appropriate or necessary.
Information in the Criteria Document on the health and welfare
effects of PM provides no clear basis for making such adjustments.
Recent health effects studies have been conducted in cool and warm
climates, and in cities at high altitude, e.g., Denver, as well as near
to these two fractions of PM10. Specifically, CASAC advised
no evidence that risk associated with PM exposures is affected by
variations in
[[Page 38697]]
altitude. Accordingly, any effect that would be accounted for by
temperature and pressure adjustments would be below the detection
limits of epidemiological studies. While extremes of altitude might be
expected to increase the delivered dose of PM in those not acclimatized
to such locations, the dosimetric studies summarized in the Criteria
Document provide no clear support for any quantitative adjustment to
standard conditions. With respect to welfare effects, visibility is
directly related to the actual mass of fine particles in the
atmosphere. Adjustment of PM concentrations collected at higher
altitudes to standard conditions would therefore lead to an
overstatement of the effect of PM on visibility in such locations.
Similarly, there is no evidence in the Criteria Document suggesting
that effects on materials damage and soiling are dependent on altitude.
Based on this assessment, EPA proposed to delete the requirement to
adjust PM10 concentrations to standard conditions of
temperature and pressure from 40 CFR part 50, Appendix J for the
revised standards and to make corresponding revisions in 40 CFR 50.3.
Comments received on this issue were divided. A number of commentors
supported EPA's proposal for the reasons set forth above. A few States
opposed the change because the lack of adjustment for very cold
temperature in areas near sea level could make the standard more
stringent. Some commentors were concerned that the proposed change
would relax protection afforded for areas at high altitude. A few
commentors expressed concern that ``sojourners'' who visit high
altitude area would have higher ventilation rates and receive reduced
protection as compared to local residents whose ventilation patterns
were more adapted to these conditions.
The EPA does not believe that the localized comparisons regarding
increased or decreased stringency of standards relative to the proposed
change are an appropriate rationale for keeping the current adjustment
for temperature and pressure. The issue is whether the available
scientific evidence on the health and welfare effects of PM provides a
basis for continuing with the traditional adjustments. The comments
with respect to sojourners at altitude are relevant, but this issue was
considered in reaching the proposed decision. Furthermore, commentors
provided neither laboratory nor epidemiologic evidence that would
support their theoretical concerns regarding increased annual or 24-
hour PM effects at altitudes typical of mountainous urban areas in the
United States.
Based on its assessment of the available evidence and public
comments, EPA concludes that a continuation of the practice of
adjusting PM10 concentrations to standard conditions of
temperature and pressure is not warranted or appropriate. Accordingly,
this requirement is not included in 40 CFR part 50, Appendix M and
corresponding revisions are made in 40 CFR 50.3. In addition, EPA is
also incorporating the proposed minor modifications to 40 CFR part 50,
Appendix J in Appendix M.
B. 40 CFR Part 50, Appendix L - New Reference Method for
PM2.5
1. Introduction. A new reference method for the measurement of fine
particles (as PM2.5) in the ambient air has been developed
for the primary purpose of determining attainment of the new
PM2.5 standards. The method is described in the new 40 CFR
part 50, Appendix L, and joins the other reference methods (or
measurement principles) specified for other criteria pollutants in
other appendices to 40 CFR part 50.
In developing the proposed new reference method for
PM2.5, EPA staff consulted with a number of individuals and
groups in the monitoring community, including instrument manufacturers,
academics, consultants, and experts in State and local agencies. The
approach and key specifications were submitted to the CASAC Technical
Subcommittee for Fine Particle Monitoring, which held a public meeting
to discuss the proposed new reference method for PM2.5 and
related monitoring issues on March 1, 1996. Comments on the proposed
method were provided orally and in writing by interested parties. The
Technical Subcommittee indicated their overall satisfaction with the
method in a letter (Price, 1996) forwarded by CASAC to the
Administrator.
On December 13, 1996, EPA proposed the new 40 CFR part 50, Appendix
L at 61 FR 65676 for public comment. The proposal described in detail
the approach taken and the design specifications and performance
requirements for the new PM2.5 sampler. On January 14, 1997,
EPA held a public hearing on the proposed new 40 CFR part 50, Appendix
L and associated 40 CFR parts 53 and 58 requirements.
2. Basic reference method approach. In addition to the primary
purpose of the new PM2.5 reference method (determining
attainment of the standards), EPA considered a variety of possible
secondary goals and objectives that the PM2.5 reference
method might also fulfill. Subsequently, various alternative
PM2.5 measurement techniques were evaluated. From this
analysis, EPA proposed to base its PM2.5 reference method on
a conventional type sampler that collects 24-hour integrated
PM2.5 samples on a 47 mm Teflon filter that is subsequently
moisture and temperature conditioned and analyzed gravimetrically. The
sampler is a low volume sampler that operates at a flow rate of 1 cubic
meter per hour, for a total sample volume of 24 m3 for the
specified 24-hour sample collection period. The sampler is easy to
operate, operates over a wide range of ambient conditions, produces a
measurement that is comparable to large sets of previously collected PM
data in existing databases, and provides a physical sample that can be
further analyzed for chemical composition.
3. Public comments and responses--a. Sampler design. The EPA
received many general comments concerning the proposed sampler design.
Commenters suggested the use of a different indicator, use of a
different size cut, inclusion of additional constituents (e.g., acid
aerosols, carbon, metals, and semi-volatiles), and/or use of a multi-
filter method. Early in the development process, design decisions were
based on public input and the advice of CASAC on these and other basic
design issues. Other factors affecting the basic design of the method
were the need for historical continuity, high measurement precision,
and simplicity of operation, all in response to current national
monitoring objectives and available resources. In selecting the basic
measurement approach, substantial weight was given to maintaining
comparability to PM2.5 samplers, such as the ``dichotomous
sampler,'' that were widely used to obtain the data upon which the new
standards are based. Given this objective, EPA concludes that the
conventional PM measurement approach is appropriate and will provide
PM2.5 measurements that are comparable to the air quality
data used in the health studies that provide the basis for the
PM2.5 standards.
Although the sampler is conventional in configuration, its design
is much more sophisticated than that of previous PM samplers. This more
sophisticated sampler, together with improved manufacturing and
operational quality assurance, is necessary to achieve the more
stringent data quality objectives established for PM2.5
monitoring data. To meet precision requirements, the critical
mechanical components of the inlet, particle size separator, downtube,
and upper portion of the filter holder
[[Page 38698]]
are specified by design. All other aspects of the sampler are specified
by performance-based specifications.
Several commenters felt that the portions of the sampler that were
specified by design would stifle further improvements and innovations.
Although the EPA specifies methods by performance whenever possible,
for the PM2.5 reference method, development of adequate
performance specifications for inlet aspiration and particle size
discrimination would have been a very difficult, costly, lengthy, and
problematic process. Moreover, manufacturer testing of proposed inlet
and particle size discrimination devices against such performance
specifications would require elaborate specialized facilities and would
be extremely costly. For these reasons, the EPA believes that
specification of these critical components by design is a prudent and
very cost-effective way to ensure good inter-manufacturer and intra-
manufacturer precision of the PM2.5 measurements. Therefore,
these components are specified by design, and other aspects of the
sampler are specified by performance, as proposed. Innovations and
improved samplers or measurement methods are encouraged and provided
for as Class II and III equivalent methods (see 40 CFR part 53).
b. Inlet and impactor design. Several commenters addressed the
inlet design, noting that the inlet could allow entrance of
precipitation and possibly insects. In fact, the inlet selected for the
sampler has been used effectively for many years to obtain many of the
PM2.5 measurements that formed the basis of the
epidemiological studies. While EPA acknowledges that there have been
some reports of intrusion of precipitation, the Agency believes the
problem is relatively minor. Nevertheless, a modification of the inlet
has been developed to further reduce the possibility of precipitation
(and possibly small insects) reaching the sample filter to damage the
PM2.5 sample. Extensive wind tunnel tests have shown no
significant compromise in the PM2.5 aspiration performance
of the modified inlet.
In addition, a new provision has been added, in 40 CFR part 50,
Appendix L, section 7.3.8, to require that the sampling air entrance of
the inlet be at a height of 2 0.2 meters above the
supporting surface to help ensure homogeneous air samples when
collocated samplers of different types are operated simultaneously.
Other commenters addressed the sharpness of the size cut and how it
is obtained, e.g., whether more than two stages should be used and what
size cut should be used for each stage. These aspects were carefully
considered in selecting the sampler configuration. The selection by EPA
of the previously used PM10 inlet established the size cut
for the first stage, and the second stage was designed to be simple,
reliable, and low in cost for user agencies. In EPA's estimation, the
advantages of this configuration outweigh any modest advantage that
might have been gained by designing a new inlet/separation
configuration that would further refine the cut points at each of two
(or more) stages.
A few commenters questioned whether the inlet was wind speed
dependent at high wind speeds. The selected inlet has been shown to
perform well up to 24 km/hr with 10 m aerosols and is expected
to perform well at higher speeds with 2.5 m aerosols. The EPA
again determined that the advantages of using the selected inlet
outweighed the possible minor improvement in wind-speed characteristics
that might have been obtained by a newly-designed inlet.
Some commenters felt that other types of particle discrimination
techniques such as cyclones and virtual impactors, should be allowed.
Again, these alternatives were evaluated previously and the specified
inlet and impactor were determined to best meet the various objectives
of the sampler. However, EPA has provided for considerations of other
particle size selection techniques or devices for approval if
incorporated into candidate equivalent methods for PM2.5.
Several commenters addressed the impactor design, noting that the
impactor should be changed to sharpen the size-cut characteristic, to
address concerns regarding possible contamination and/or performance
loss due to impactor oil, and to improve ease of access to service. To
address the first concern, the initial prototype impactor has been
modified slightly to sharpen its size-cut. The current impactor is
designed to lower cost and to optimize cut sharpness, loading capacity,
manufacturing simplicity, manufacturing quality control,
serviceability, and reliability. A report containing the penetration
efficiency of the impactor is available in Docket No. A-95-54. With
regard to impactor oil concerns, the impactor oil selected has a very
low vapor pressure, and testing has indicated no contamination of the
sample filters with impactor oil. The EPA believes that the impactor
design is as accessible as possible, given the design objectives. Some
flexibility may be allowed for manufacturers to develop improved
closure devices or other external modifications. Proper maintenance
will, of course, be very important and will be stressed in the
associated operator instruction manuals and in other training and
guidance materials. The EPA has been performing field and laboratory
tests that will provide detailed guidance for all necessary preventive
maintenance. Proper installation procedures for the oil and the
impactor filter, as well as all other maintenance requirements, will be
available in the quality assurance procedures and guidance contained in
the new section 2.12 of Appendix L to be added to EPA's Quality
Assurance Handbook for Air Pollution Measurement Systems (EPA/600/R-94/
038b).
c. Anodized aluminum surface. All internal surfaces exposed to
sample air prior to the filter are required to be anodized aluminum as
stated in 40 CFR part 50, Appendix L, section 7.3.7. A few commenters
expressed concern that the anodized aluminum surfaces in high volume
PM10 samplers have shown substantial pitting, particularly
in the venturi flow control device. The anodized aluminum surfaces are
required in the PM2.5 sampler to maintain comparability to
previously used samplers. The EPA believes that the much lower flow
rate in the PM2.5 sampler will greatly reduce the pitting
tendency, and the active flow control in the PM2.5 sampler
is not dependent on the physical dimensions of a critical orifice as it
is in a venturi flow control device.
d. Filter for PM2.5 sample collection. The proposed
reference method called for the sample to be collected on a 47 mm
Teflon filter. Many of the comments received on the measurement method
concerned the proposed filter medium and its performance. Commenters
expressed concerns with the use of Teflon filters and with the
selection of a single-filter method. Several commenters recommended
that alternative filter media be allowed, in most cases to support
speciation and/or to allow the capture of all PM components. Other
comments noted potential advantages of other media in operating
characteristics or chemistry requirements. Operational concerns
expressed about Teflon filters included tearing, possible loss of
integrity, and high cost. Other concerns were that Teflon is generally
not conducive to carbon analysis, and that Teflon filters may not hold
deposited PM. Many commenters recommended use of a multi-filter sampler
to support chemical speciation in addition to compliance determination.
[[Page 38699]]
To address some of these general concerns about the performance of
the specified filter material, some minor refinements to the filter
specifications concerning the filter diameter and the filter support
ring have been made to ensure proper performance of the filter in the
specified filter holder. Additional clarifications have been made to
the maximum moisture pickup and the filter weight stability
requirements. Although Teflon may preclude certain chemical analyses
(e.g., elemental and organic carbon), the EPA believes that Teflon
filter material is the best overall choice to meet the objectives of
compliance monitoring and to provide good measurement precision. Other
filter media are likely to provide reduced gravimetric precision and
preclude more types of subsequent chemical analysis. Additional or
alternative samplers or filter types can be considered as candidate
equivalent methods under 40 CFR part 53 and can be used for non-
compliance monitoring, where necessary.
Compliance monitoring based on mass concentration of
PM2.5 is the primary objective of the reference method.
Multi-filter capability would have substantially increased the cost and
complexity of the sampler. However, multi-filter samplers can be
considered as candidate equivalent methods. In addition, multi-filter
samplers can be used as special purpose monitors (SPMs) to perform
characterization studies, develop control strategies, and conduct other
special studies as has been done previously for PM10.
In response to numerous comments received on 40 CFR part 50,
Appendix L and on the provisions of 40 CFR part 58 regarding the need
for chemical speciation, the EPA is assigning a high priority to a
chemical speciation trends network through section 105 of the Act grant
allocation program and will issue guidance describing the monitoring
methods and scenarios under which speciation should be performed. The
program will incorporate additional PM2.5 samplers that
allow for the simultaneous collection of aerosols on multiple filter
media.
The associated requirement for archiving filters has been removed
from 40 CFR part 50, Appendix L, section 10.17 and relocated to 40 CFR
part 58, Appendix A. This change has been made because this is a
supplemental monitoring requirement and not an integral part of the
reference method for determining compliance with the PM2.5
NAAQS.
Provisions of 40 CFR part 50, Appendix L have been clarified to
apply not only to a single-sample sampler, but also to a sequential-
sample sampler, provided that all specifications are met and no
deviations, modifications, or exceptions are made to the inlet,
downtube, impactor, or the upper portion of the filter holder. Samplers
that have minor changes or modifications in these components, have
changes that alter the aerosol's flow path, or contain other
significant deviations will be required to meet the requirements of
Class I equivalent methods, in the amendments to 40 CFR part 53.
Further, a provision has been added to require that sequential sample
filters stored in a sequential sampler be adequately covered and
protected from contamination during storage periods in the sampler.
A few commenters expressed concern about who must carry out filter
tests to determine if they meet the filter specifications. In response,
the filter specifications have been clarified to indicate that filter
manufacturers should generally carry out most or all of the filter
performance tests in order to certify that their filters meet the
filter specifications for the PM2.5 reference method. In
addition, EPA conducts acceptance tests on filters procured for NAMS/
SLAMS networks prior to distribution to State and local agencies.
Some commenters requested additional information on the requirement
that an ID number be attached to each filter. Preliminary information
indicates that it is not practical at this time for either filter
manufacturers or users to print an ID number directly on the filter.
However, EPA is continuing to pursue this goal. In the meantime,
alternative means, such as attaching an appropriate ID number to the
filter's storage container, will be necessary. Additional details and
possible alternative filter identification methods will be provided in
new section 2.12 of the Quality Assurance Handbook for Air Pollution
Measurement Systems.
e. Filter handling/weighing/conditioning requirements. Many
commenters felt that the filter handling requirements for collected
PM2.5 samples were too burdensome. However, handling of the
exposed filter between retrieval from the sampler and commencement of
the conditioning period is expected to be one of the most significant
sources of PM2.5 measurement variability. Thus, EPA
concludes that specific requirements for this activity are necessary,
and this position was supported by several commenters.
Some commenters felt that the samples should be kept cold until
analysis to prevent volatile losses. In response to this concern, the
restriction on the maximum temperature exposure for collected samples
has been reduced from 32 to 25 deg. C, and a recommendation has been
added for sampler operators to keep the samples as cool as practical
between retrieval from the sampler and delivery to the conditioning
environment. Further, the length of time permitted between retrieval of
the filter and post-collection weighing is increased from 10 to 30
days, provided that the sample is maintained at 4 deg. C or less
between retrieval and the start of the conditioning period. The new
section 2.12 of the Quality Assurance Handbook for Air Pollution
Measurement Systems will provide guidance and techniques for keeping
samples cool during this period and may suggest devices to document
maximum temperature exposure of the sample.
Commenters also requested additional specifications and guidance
for field blanks. The EPA will provide additional clarification and
detailed procedures and guidance regarding field blanks in the new
section 2.12 of the Quality Assurance Handbook for Air Pollution
Measurement Systems.
Other commenters felt that the filter weighing requirements were
too restrictive. Because filter weighing is one of the most significant
sources of PM2.5 measurement variability, specific
requirements and restrictions are deemed necessary. However, in
response to some of the concerns expressed, the proposed requirement
that both pre- and post-weighings be carried out by the same analyst
has been reduced to a non-mandatory recommendation. Detailed
recommendations and guidance on filter weighing, based on information
obtained in current field tests, will be provided in the new section
2.12 of the Quality Assurance Handbook for Air Pollution Measurement
Systems.
Several commenters questioned the filter conditioning requirements,
with some requesting a lower humidity range. Since humidity can
profoundly affect the weight of the PM2.5 on the filter, EPA
maintains that filter conditioning requirements need to be tight to
control measurement variability and to ensure satisfactory precision.
But in response to at least one of the concerns, the filter
conditioning humidity requirement has been changed to allow
conditioning at a relative humidity within 5 RH percent of
the mean ambient humidity during sampling (down to a minimum of 20 RH
percent) for samples collected at average ambient humidities lower than
30
[[Page 38700]]
percent. The EPA will provide further details on filter conditioning
controls in the new section 2.12 of the Quality Assurance Handbook for
Air Pollution Measurement Systems.
f. Sampler performance requirements. Several commenters addressed
sampler performance requirements, including sampler flow control
specifications, filter temperature control, sampler performance under
extreme conditions, and data reporting. In response to concerns that
various sampler flow control specifications are too tight, EPA contends
that good flow control is necessary to maintain uniform sampling, to
ensure correct particle size discrimination, and to control measurement
variability. Sampler manufacturers have been able to meet the specified
flow control requirements, and field studies to date confirm that
prototype samplers are able to meet these flow control requirements.
In response to comments about the ambient temperature plus 3 deg. C
filter temperature control requirement, EPA believes that fairly tight
control of the sample filter temperature is necessary to minimize
losses of semi-volatile components over a wide temperature range, and
tight temperature control has been strongly recommended by the CASAC.
Monitoring of the filter temperature difference from ambient
temperature is necessary to verify that the sampler filter temperature
control is functioning properly. Testing to date indicates that the
proposed 3 deg. C (above ambient temperature) limit is somewhat
difficult to meet; however, a 5 deg. C limit can be reasonably met.
Therefore, the filter temperature control requirement has been relaxed
slightly from 3 deg. C to not more than 5 deg. C above the concurrent
ambient temperature. Ambient and filter temperature sensors will
require periodic calibration or verification of accuracy. In response
to a frequent comment, the method has been clarified to indicate that
exceedance of the filter temperature difference limit would not
necessarily invalidate the sample.
In response to concerns about the performance of the sampler under
extreme weather conditions (e.g., high or low temperatures, low
pressures, high winds, high or low humidity, fog, dust storms), the EPA
has established sampler specifications that are intended to cover
reasonably normal environmental conditions at about 95 percent of
expected monitoring sites. Qualification test requirements in 40 CFR
part 53 address most, if not all, of these operational requirements.
Specification of the sampler performance for sites with extreme
environmental conditions would substantially raise the cost of the
sampler for other users, most of whom do not require the extra
capability. Users requiring operation of samplers under extreme
conditions are encouraged to develop supplemental specifications for
modified samplers to cover those specific conditions. Sampler
manufacturers have indicated a commitment to respond to the need for
modified samplers for such extreme conditions.
Although concerns were expressed that the amount of data required
to be reported from each sampler is excessive, EPA stresses that only a
portion of the data collected by the sampler needs to be reported to
AIRS. These limited data reporting requirements (i.e., ambient and
filter temperature, barometric pressure, sample volume, variation in
sample run flow rate) are important to establish or verify the
reliability and confidence of the PM2.5 measurements and to
aid in utilization of those data. The substantial amount of additional
data generated by the sampler are of use to the site operator to
provide confirmation of a given sample's validity, and to aid in
troubleshooting should outlier measurements appear in the monitoring
data. A variety of current electronic devices and systems may be used
to acquire and handle the data, and these devices can easily
accommodate the amount of data required to be reported, as well as the
additional, optional data. Printers, modem connections, and alternative
data output connections or devices are not precluded.
4. Additional changes. Additional clarifying changes have also been
made throughout 40 CFR part 50, Appendix L, based on comments received
or recently obtained field test information. In 40 CFR part 50,
Appendix L, section 3.1, the lower concentration of the method has been
revised from 1 to 2 g/m3, based on the results of
field blanks associated with available field test data. In 40 CFR part
50, Appendix L, section 3.3, the sample period specification has been
augmented to clarify that a measured PM2.5 concentration for
a sample period less than 23 hours that is greater than the NAAQS
level(s) is to be considered a valid measurement for comparison to the
NAAQS, even though not valid for other purposes. Sections 4 (Accuracy)
and 5 (Precision) have been revised to properly reflect associated
changes to the data quality and method performance assessment
requirements set forth in 40 CFR part 58, Appendix A.
A provision has been added in 40 CFR part 50, Appendix L, section
7.4.17 to require sampler manufacturers to make available computer
software to input sampler output data and translate the data into a
standard spreadsheet format (since no specific format is specified for
output of the sample data acquired by the sampler).
The requirements for the sampler to display current flow rate,
temperature, filter temperature, and barometric pressure readings have
been changed to require updating of these readings at least every 30
seconds. This change is based on operational experience of prototype
samplers in 40 CFR part 50, Appendix L, section 7.4.5.1, and will make
it easier for the operators to perform status checks and calibrations.
In 40 CFR part 50, Appendix L, section 7.4.8.1, the requirements for
the ambient temperature sensor have been changed to specify an external
sensor with a passive sun shield, to provide better uniformity in the
ambient temperature measurements among different types of reference
method samplers. The reference method has also been clarified to
indicate that PM2.5 samples for which the sampler reported
an out-of-specification (FLAG) occurrence during or after the sample
period are not necessarily invalid, and that such samples should be
reviewed by a quality assurance officer (40 CFR part 50, Appendix L,
section 10.12). Finally, a new reference has been added in section 13
of the Act to provide applicable standards for meteorological
measurements and measurement systems.
5. Decision on 40 CFR part 50, Appendix L. After fully considering
the public comments on the proposed new reference method for
PM2.5, EPA has concluded that the proposed design and
performance specifications for the reference sampler, with the
modifications discussed in this unit, will achieve the design
objectives set forth in the proposal and outlined above. Therefore, EPA
is adopting the sampler and other method requirements specified in 40
CFR part 50, Appendix L as the reference method for measuring
PM2.5 in the ambient air.
Since proposal, a series of field tests have been performed using
prototype samplers manufactured in accordance with the proposed design
and performance specifications. The results of these field tests
confirm that the prototype samplers perform in accordance with design
expectations. Operational experience gained through these field tests
did, however, identify the need for minor modifications as discussed
above in this unit. In addition, EPA made other modifications to the
proposed design and performance specification in response to public
[[Page 38701]]
comment as discussed above. As part of this process, EPA performed
laboratory tests to ensure that the modifications achieved the intended
objective.
While the results of these field tests and laboratory tests were
largely confirmatory in nature and did not indicate a need to alter the
basic design and performance specifications, they did identify areas
that needed further refinement. Given that these tests were performed,
by necessity, during and after the close of the public comment period
and because the results were not available for placement in the docket
until late in the rulemaking process, EPA is announcing, in a separate
Federal Register notice being signed today, a supplemental comment
period for the limited purpose of taking comments on these field and
laboratory test results.
VII. Effective Date of the Revised PM Standards and Applicability
of the Current PM10 Standards
In summary, the primary and secondary NAAQS for PM have been
revised by establishing annual and 24-hour PM2.5 standards;
and by changing the form of the existing 24-hour PM10
standards. The existing PM10 annual standards have been
retained. Section 50.3 (reference conditions) of 40 CFR part 50 has
been revised to remove the adjustment of measured PM10
concentrations to standard conditions of temperature and pressure with
respect to the revised PM standards. (Although EPA is retaining the
current annual PM10 standards, the revision of 40 CFR 50.3
potentially may affect the effective stringency of the annual
standards.) A new Appendix M has been added to 40 CFR part 50 that
reflects the revision of 40 CFR 50.3. A new Appendix N to 40 CFR part
50 has been added to reflect the forms of the PM2.5 and
revised PM10 standards. Finally, a new Appendix L to 40 CFR
part 50 has been added that specifies the reference method for
measuring PM2.5 in the ambient air.
The revised PM NAAQS, the revisions to 40 CFR 50.3, and the new
Appendices M, N, and L to 40 CFR part 50 will become effective
September 16, 1997. Inherent in the establishment of this revised set
of PM standards and related provisions is the revocation of the current
set of PM10 standards and associated provisions. To provide
for an effective transition from the existing PM standards to the
revised PM standards --in light of the need to establish
PM2.5 monitoring networks, designate areas, and develop
control strategies for PM2.5--the Administrator has
determined that the effective date of the revocation of the current set
of PM10 standards and associated provisions should be
delayed so that the existing standards and associated provisions will
continue to apply for an interim period. The duration of the interim
period would depend on whether the area in question has attained the
current PM10 standards, as described below in this unit.
First, section 172(e) of the Act provides that, if the
Administrator relaxes a national primary ambient air quality standard,
she shall, within 12 months after the relaxation, promulgate
requirements applicable to all areas that have not attained that
standard as of the date of the relaxation. Those requirements shall
provide for controls that are not less stringent than the controls
applicable to areas designated nonattainment before such relaxation.
Although the set of revised PM standards, viewed as a whole, is more
stringent than the set of current PM standards, it appears that the
shift from the current PM10 standards to the revised
PM10 standards, viewed in and of itself, represents a
relaxation of the current PM10 standards. As a result,
section 172(e) of the Act requires EPA to issue a rule within 12 months
to apply implementation requirements no less stringent than the
currently applicable requirements for those areas that have not yet
attained the current PM10 standard(s) by today's
promulgation. However, the Act does not specifically provide how to
ensure that States with current PM10 problems should
maintain the necessary public health protection in the interim between
promulgation of a relaxed standard and issuance of a rule under section
l72(e) of the Act. For that reason, EPA believes that it is both
necessary and appropriate to defer the effective date of the revocation
of the current PM10 standards, for areas that have not
attained those standards, until EPA issues the rule called for by
section 172(e) of the Act.
Second, since it will take many years for States to identify PM
problems under the revised standards and to develop effective means for
addressing those problems, EPA believes it is necessary for even those
areas that have already attained the current PM10 standards
(and hence are not subject to the terms of section 172(e) of the Act)
to continue their current PM10 implementation efforts for
the purpose of protecting public health in the transition to
implementation of the revised standards.
In order to deal with both of these categories of areas--those that
are not attaining the current PM10 standards and those that
are in attainment of the current PM10 standards--EPA is
taking a two-pronged approach towards deferral of the effective date of
the revocation of the current PM10 standards. For those
areas that are not attaining the current PM10 standards at
the time of the promulgation of the revised PM10 standards,
the current standards will continue to apply until EPA has completed
its rulemaking under section 172(e) of the Act to prevent backsliding
in those areas. This will assure that no backsliding can occur in the
interim period between the promulgation of the revised standards and
the completion of the rulemaking under section 172(e) of the Act. For
those areas that are attaining the current PM10 standards at
the time of promulgation of the revised PM10 standards, the
existing PM10 standards will continue to apply until the
areas have an approved SIP that includes any control measures that had
been adopted and implemented at the State level to meet the current
PM10 NAAQS and have an approved section 110 SIP for purposes
of implementing the revised PM standards. If an area has already
received approval of a PM10 SIP embodying all of the
measures that had been adopted and implemented at the State level, no
further Part D submission or approval would be necessary. If an area
has already submitted such measures, EPA would need to take action to
approve them. Finally, if an area has not yet submitted such measures
to EPA for inclusion in the SIP, the area would need to submit them and
EPA would need to approve them. This submission and approval would
serve to satisfy both the area's remaining subpart D obligations and,
in part, its new obligations under section 110(a)(1) of the Act
regarding the implementation of the revised PM NAAQS. EPA emphasizes
that it is not requiring an approval of a modeled attainment
demonstration for the current PM10 NAAQS, only an approval
of the control measures that had in fact been adopted and implemented
and that, therefore, were responsible for the area's attainment of the
current PM10 standards.
The existing definition of reference conditions and 40 CFR part 50,
Appendices J and K will remain in force as long as the current
PM10 standards apply to an area. Additional policies and
guidance for assuring an effective transition will be set forth in
future EPA guidance, policies, and/or rules.
VIII. Regulatory and Environmental Impact Analyses
As discussed in Unit IV of this preamble, the Clean Air Act and
judicial
[[Continued on page 38702]]
![[logo] US EPA](https://webarchive.library.unt.edu/eot2008/20090513121351im_/http://www.epa.gov/epafiles/images/logo_epaseal.gif){kind=logo}