National Ambient Air Quality Standards for Ozone

[Federal Register: July 18, 1997 (Volume 62, Number 138)]
[Page 38855-38896]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr18jy97-21]
[Page 38856]

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ENVIRONMENTAL PROTECTION AGENCY
40 CFR Part 50
[ADA-95-58; FRL-5725-3]
RIN-2060-AE57

AGENCY: Environmental Protection Agency (EPA).
ACTION: Final rule.

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SUMMARY: This document describes EPA's decision to revise the national
ambient air quality standards (NAAQS) for ozone (O₃) based
on its review of the available scientific evidence linking exposures to
ambient O₃ to adverse health and welfare effects at levels
allowed by the current O₃ standards. The current 1-hour
primary standard is replaced by an 8-hour standard at a level of 0.08
parts per million (ppm) with a form based on the 3-year average of the
annual fourth-highest daily maximum 8-hour average O₃
concentrations measured at each monitor within an area. The new primary
standard will provide increased protection to the public, especially
children and other at-risk populations, against a wide range of
O₃-induced health effects, including decreased lung
function, primarily in children active outdoors; increased respiratory
symptoms, particularly in highly sensitive individuals; hospital
admissions and emergency room visits for respiratory causes, among
children and adults with pre-existing respiratory disease such as
asthma; inflammation of the lung, and possible long-term damage to the
lungs. The current 1-hour secondary standard is replaced by an 8-hour
standard identical to the new primary standard. The new secondary
standard will provide increased protection to the public welfare
against O₃-induced effects on vegetation, such as
agricultural crop loss, damage to forests and ecosystems, and visible
foliar injury to sensitive species.

EFFECTIVE DATE: This rule is effective September 16, 1997.

ADDRESSES: A docket containing information relating to the EPA's review
of the O₃ primary and secondary standards (Docket No. A-95-
58) is available for public inspection in the Central Docket Section of
the U.S. Environmental Protection Agency, South Conference Center, Room
4, 401 M St., SW., Washington, DC. This docket incorporates the docket
from the previous review of the O₃ standards (Docket No. A-
92-17) and the docket established for the air quality criteria document
(Docket No. ECAO-CD-92-0786). The docket may be inspected between 8
a.m. and 3 p.m. on weekdays, and a reasonable fee may be charged for
copying. The information in the docket constitutes the complete basis
for the decision announced in this final rule. For the availability of
related information, see ``SUPPLEMENTARY INFORMATION.''
FOR FURTHER INFORMATION CONTACT: David McKee, MD-15, Air Quality
Standards and Strategies Division, Office of Air Quality Planning and
Standards, U.S. Environmental Protection Agency, Research Triangle
Park, NC 27711; telephone: (919) 541-5288; e-mail:
mckee.dave@epamail.epa.gov.
SUPPLEMENTARY INFORMATION:

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 O₃ and Other Photochemical
Oxidants (``Criteria Document'') (three volumes, EPA/600/P-93-004aF
through EPA/600/P-93-004cF, July 1996, NTIS # PB-96-185574, $169.50
paper copy, $58.00 microfiche).
(2) The Review of the National Ambient Air Quality Standards for
O₃: Assessment of Scientific and Technical Information
(``Staff Paper'')(EPA-452/R-96-007, June 1996, NTIS # PB-96-203435,
$67.00 paper copy and $21.50 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 documents pertaining to
human exposure and health risk assessments, and vegetation exposure,
risk, and benefits analyses can be obtained from: U.S. 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 identified under
``ADDRESSES''.

Electronic Availability

The Staff Paper and human exposure and health risk assessment
support documents are now 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 O₃
D. Summary of Proposed Revisions to the O₃ Standards
II. Rationale for the Primary O₃ Standard
A. Introduction
B. Elements of the Primary Standard
C. Communication of Public Health Information
III. Rationale for the Secondary O₃ Standard
A. Introduction
B. Need for Revision of Current Secondary Standard
C. Final Decision on the Secondary Standard
IV. Other Issues
A. Cost Considerations
B. Margin of Safety
C. Comment Period
D. 1990 Act Amendments
V. Technical Changes to Part 50
VI. Revisions to Appendices D, E, and H
VII. Regulatory and Environmental Impact Analyses

[[Page 38857]]

A. Executive Order 12866
B. Regulatory Flexibility Analysis
C. Impact of Reporting Requirements
D. Unfunded Mandates Reform Act
E. Environmental Justice
F. Submission to Congress and Comptroller General
VIII. Response to Petition for Administrator Browner's Recusal
IX. References

I. Background

A. Legislative Requirements

Two sections of the Act govern the establishment, review, and
revision of NAAQS. Section 108 (42 U.S.C. 7408) directs the
Administrator to identify certain pollutants which ``may reasonably be
anticipated to endanger public health or 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 (42 U.S.C. 7409) directs the Administrator to propose
and promulgate ``primary'' and ``secondary'' NAAQS for pollutants
identified under section 108. Section 109(b)(1) 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
Association v. EPA. (647 F.2d 1130, 1161-62 (D.C. Cir. 1980)).
A secondary standard, as defined in section 109(b)(2), 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) (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) 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) 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
programs (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 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 (42 U.S.C. 7411); and the
national emission standards for hazardous air pollutants under section
112 (42 U.S.C. 7412).

C. Review of Air Quality Criteria and Standards for O₃

The last review of O₃ air quality criteria and standards
was completed in March 1993 with notice of a final decision not to
revise the existing primary and secondary standards (58 FR 13008). The
current primary and secondary standards are each set at a level of 0.12
ppm, with a 1-hour averaging time and a 1-expected-exceedance form,
such that the standards are attained when the expected number of days
per calendar year with maximum hourly average concentrations above 0.12
ppm is equal to or less than 1, averaged over 3 years (as determined by
40 CFR part 50, Appendix H).¹
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1 A more complete history of the O₃ NAAQS is
presented in section II.B. of the Office of Air Quality Planning and
Standards Staff Paper, Review of National Ambient Air Quality
Standards for O₃: Assessment of Scientific and Technical
Information (U.S. EPA, 1996b).
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The EPA initiated this current review of the air quality criteria
and standards in August 1992 with the development of a revised Air
Quality Criteria Document for O₃ and Other Photochemical
Oxidants, henceforth the ``Criteria Document.'' Several workshops were
held by EPA's National Center for Environmental Assessment (NCEA) to
discuss health and welfare effects information during the summer and
fall of 1993. An external review draft of the Criteria Document made
available to the public and to the CASAC in the spring of 1994 was
reviewed at a public CASAC meeting held on July 20-21, 1994. Based on
comments made at the meeting, NCEA staff prepared a second external
review draft, which was reviewed at a public CASAC meeting on March 21-
22, 1995. At the same meeting, the CASAC also reviewed draft portions
of a staff paper prepared by the OAQPS, Review of National Ambient Air
Quality Standards for O₃: Assessment of Scientific and
Technical Information (henceforth, the ``Staff Paper''), focusing on
health effects and the primary NAAQS.² Taking into account
CASAC and public comments, staff revised both documents and made new
drafts available for public and CASAC review during the summer of 1995.
The OAQPS staff also prepared and made available draft portions of the
Staff Paper focusing on welfare effects and the secondary standard.
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2 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.

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[[Page 38858]]

A public CASAC meeting was held on September 19-20, 1995, at which
time CASAC came to closure in its review of the draft Criteria Document
and the primary standard sections of the draft Staff Paper. In a
November 28, 1995 letter from the CASAC chair to the Administrator,
CASAC advised that the final draft Criteria Document ``provides an
adequate review of the available scientific data and relevant studies
of O₃ and related photochemical oxidants'' (Wolff, 1995a).
Further, in a November 30, 1995 letter, CASAC advised the Administrator
that the primary standard portion of the draft Staff Paper ``provides
an adequate scientific basis for making regulatory decisions concerning
a primary O₃ standard'' (Wolff, 1995b). The final Criteria
Document (U.S. EPA, 1996a) reflects CASAC and public comments received
at and subsequent to the September 1995 CASAC meeting.
Based on comments on the Staff Paper from the September 1995 CASAC
meeting, revisions were made to the secondary standard sections of the
Staff Paper, which were reviewed at a public CASAC meeting held on
March 21, 1996. At that meeting and in a subsequent letter to the
Administrator, CASAC concluded that the secondary standard sections of
the draft Staff Paper ``provide an appropriate scientific basis for
making regulatory decisions concerning a secondary O₃
standard'' (Wolff, 1996). The final Staff Paper (U.S. EPA, 1996b)
reflects CASAC and public comments received at and subsequent to the
September 1995 and March 1996 meetings on the primary standard and
secondary standard sections, respectively.
On November 27, 1996 EPA announced its proposed decision to revise
the NAAQS for O₃ (61 FR 65716, December 13, 1996,
hereinafter ``proposal'') as well as its proposed decision to revise
the NAAQS for particulate matter (PM). In the proposal, EPA identified
proposed revisions, based on the air quality criteria for
O₃, and solicited public comments on alternative primary and
secondary standards and on the proposed forms of the standards.
To ensure the broadest possible public input on the O₃
and PM 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 O₃ and PM NAAQS, and on
related notices dealing with the implementation of revised
O₃ and PM 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 O₃ and PM 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 verbal comments were received on the proposed
revisions to the O₃ NAAQS by the close of the public comment
period on March 12, 1997. The major issues raised in the comments are
discussed throughout the preamble of this final rule. 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-95-58).
The focus of this current review of the air quality criteria and
standards for O₃ and related photochemical oxidants is on
public health and welfare effects associated with exposure to ambient
levels of tropospheric O₃. Tropospheric O₃ is
chemically identical to stratospheric O₃, which is produced
miles above the earth's surface and provides a protective shield from
excess ultraviolet radiation. In contrast, tropospheric O₃
at sufficient concentrations has been associated with harmful effects
due to its oxidative properties and its presence in the air that people
and plants take up during respiratory processes. Ozone is not emitted
directly from mobile or stationary sources but, like other
photochemical oxidants, commonly exists in the ambient air as an
atmospheric transformation product. Ozone formation is the result of
chemical reactions of volatile organic compounds (VOC), nitrogen oxides
(NO_x), and oxygen in the presence of sunlight and generally
at elevated temperatures. A detailed discussion of atmospheric
formation, ambient concentrations, and health and welfare effects
associated with exposure to O₃ can be found in the Criteria
Document and in the Staff Paper.

D. Summary of Proposed Revisions to the O₃ Standards

For reasons discussed in the proposal, the Administrator proposed
to replace the current 1-hour primary standard for O₃ with
an 8-hour standard set at 0.08 ppm, which would be met at an ambient
air quality monitoring site when the 3-year average of the annual
third-highest daily maximum 8-hour average O₃ concentration
is less than or equal to 0.08 ppm. The proposal solicited comments on
alternative 8-hour standards set at 0.09 ppm, which generally
represents the continuation of the present level of protection, and
0.07 ppm, which would be highly precautionary in nature, as well as on
retaining the current primary standard. The proposal also solicited
comments on alternative forms of the standard, specific data handling
and rounding conventions used in determining attainment with the standard,
and issues related to the communication of public health information.
With regard to the secondary standard, the Administrator proposed
to replace the current 1-hour secondary standard with one of two
alternative standards: either one set identical to the proposed primary
standard or a new seasonal standard expressed as a sum of hourly
O₃ concentrations greater than or equal to 0.06 ppm,
cumulated over 12 hours per day during the consecutive 3-month period
of maximum concentrations during the O₃ monitoring season,
set at a level of 25 ppm-hour. The proposal solicited comments on these
two alternatives, as well as on specific issues related to the form of
a seasonal standard and on an enhanced rural air quality monitoring
network.

[[Page 38859]]

II. Rationale for the Primary Standard

A. Introduction

1. Overview . This notice presents the Administrator's final
decision regarding the need to revise the current primary O₃
standard, and, more specifically, regarding the averaging time, level,
and form of a new primary standard to replace the current 1-hour
standard. This decision is based on a thorough review, in the Criteria
Document, of the scientific information on human health effects
associated with exposure to ambient levels of O₃, including
evaluation of key studies published through 1995. This decision also
takes into account:
(1) Staff Paper assessments of the most policy-relevant information
in the Criteria Document and analyses of human exposure and risk,
presented in the Staff Paper and supporting technical reports.
(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 CASAC's 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 proposal regarding
the primary O₃ standard.
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 standard to provide increased public
health protection are appropriate at this time to protect public health
with an adequate margin of safety. Further, the Administrator
determines that it is appropriate to establish a revised 8-hour, 0.08
ppm primary standard with a form based on the 3-year average of the
annual fourth-highest daily maximum 8-hour average O₃
concentrations measured at each monitor within an area.
As discussed more fully below in this unit, the rationale for the
final decision regarding the O₃ primary NAAQS includes
consideration of:
(1) Health effects information to inform judgments as to the
likelihood that exposures to ambient O₃ result in adverse
health effects for exposed individuals.
(2) Insights gained from human exposure and risk assessments to
provide a broader perspective for judgments about protecting public
health from the risks associated with O₃ exposure.
(3) Specific conclusions with regard to the elements of a standard
(i.e., averaging time, level, and form) that, taken together, would be
appropriate to protect public health with an adequate margin of safety.
(4) Alternative views of the significance of the effects and
factors to be considered in policy judgments about the appropriate
elements of the standard.
The health effects information and human exposure and risk
assessments were summarized in the proposal and are only briefly
outlined below. More fully discussed in the following units of this
preamble is the Administrator's rationale, in light of key issues
raised in public comments, for concluding that it is appropriate to
revise the specific elements of the current standard including
averaging time (Unit II.B.1.), level (Unit II.B.2.), and form (Unit
II.B.3.). Finally, the related subject of the communication of public
health information, and the public comments received on this subject,
are summarized in Unit II.C.
2. Health effects information. The last review of the air quality
criteria for O₃ included an evaluation of key studies
published through early 1989 and was the basis for EPA's 1993 decision
not to revise the primary standard at that time. However, in
recognition of the large number of new studies, particularly on 6- to
8-hour exposures to O₃, that had become available since
early 1989 but had not undergone rigorous assessment and review by
CASAC, the EPA made clear in the 1993 final decision notice that it
would proceed with the next review as rapidly as possible to consider
this new information. Thus, the current review of health effects
information focused on a large body of information published since 1989
that would lead to a more informed decision than was possible in 1993
as to whether an O₃ primary standard with a longer averaging
time was appropriate to protect public health.
The proposal reviewed the human health effects associated with
exposure to ambient levels of O₃ based on an integrative
assessment of human clinical, epidemiological, and animal toxicological
studies available through 1995, as assessed in the Criteria Document
and Staff Paper. Based on this information, an array of health effects
has been attributed to short-term (1 to 3 hours), prolonged (6 to 8
hours), and long-term (months to years) exposures to O₃.
Acute health effects³ are induced by short-term
exposures to O₃ (observed at concentrations as low as 0.12
ppm), generally while individuals are engaged in moderate or heavy
exertion, and by prolonged exposures to O₃ (observed at
concentrations as low as 0.08 ppm), typically while individuals are
engaged in moderate exertion. Moderate exertion levels are more
frequently experienced by individuals than heavy exertion levels. The
acute health effects include transient pulmonary function responses,
transient respiratory symptoms, effects on exercise performance,
increased airway responsiveness, increased susceptibility to
respiratory infection, increased hospital admissions and emergency room
visits, and transient pulmonary inflammation. Based in particular on
new information available since the last review of the air quality
criteria for O₃ was completed, such acute health effects
have been observed following prolonged exposures at moderate levels of
exertion at concentrations of O₃ as low as 0.08 ppm. Groups
at increased risk of experiencing such effects include active children
and outdoor workers who regularly engage in outdoor activities and
individuals with preexisting respiratory disease (e.g., asthma, chronic
obstructive lung disease). Further, it is recognized that some
individuals are unusually responsive to O₃ and may
experience much greater functional and symptomatic effects from
exposure to O₃ than the average individual.
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3 ``Acute health effects'' of O₃ are defined as those
effects induced by short-term and prolonged exposures to
O₃. Examples of these effects are functional,
symptomatic, biochemical, and physiologic changes.
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With regard to chronic health effects⁴, the collective
data from studies of laboratory animals and human populations have many
ambiguities, but provide suggestive evidence of such effects in humans.
It is clear from toxicological data that O₃-induced lung
injury is roughly similar across species (including monkeys, rats, and
mice) with responses that are concentration dependent. The currently
available information provides at least a biologically plausible basis
for considering the possibility that repeated inflammation associated
with exposure to O₃ over a lifetime may result in sufficient
damage to respiratory tissue such that individuals later in life may
experience a reduced quality of life,

[[Page 38860]]

although such relationships remain highly uncertain.
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4 ``Chronic health effects'' of O₃ are defined as
those effects induced by long-term exposures to O₂.
Examples of these effects are structural damage to lung tissue and
accelerated decline in baseline lung function.
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EPA's consideration of this health effects information necessarily
included judgments with respect to when these physiological effects
become so significant that they should be regarded as adverse to the
health of individuals experiencing the effects. In making these
judgments, the Administrator looked to guidelines published by the
American Thoracic Society (1985) and the advice of CASAC. The proposal
summarized the criteria and reasoning for EPA's judgments on this
issue, upon which the CASAC panel expressed a consensus view that these
``criteria for the determination of an adverse physiological response
was reasonable'' (Wolff, 1995b). The criteria take into account the
degree of severity of the effects; the likelihood that the effects
would interfere with normal activity for individuals with impaired
respiratory systems or active healthy individuals; the likelihood that
the effects would result in additional or more frequent use of
medication, medical treatment, or emergency room visits for individuals
with impaired respiratory systems; and the implications of single or
repeated occurrences of the effects for an individual.
Some commenters raised concerns regarding the criteria used by EPA
to make determinations as to when effects become adverse, citing
CASAC's closure letter (Wolff, 1995b) stating that ``there was
considerable concern that the criteria for grading physiological and
clinical responses to O₃ was confusing if not misleading.''
These concerns with the draft criteria were discussed at length during
a public CASAC meeting, resulting in very specific agreements as to how
to revise the draft criteria so as to be consistent with CASAC's advice
(Transcript of CASAC meeting, September 19-20, 1995, pp. 242-248).
Having reached such specific agreement, CASAC advised that further
review of the final version of these criteria, subsequently incorporated
in both the final Criteria Document and Staff Paper, was unnecessary.
Other commenters have questioned whether judgments made in this
review are consistent with those made in the last review with regard to
when physiological and clinical effects become adverse to individuals
experiencing such effects. Specifically, the commenters focused on the
judgment stated in the 1993 final decision notice (58 FR 13008, March
9, 1993) that ``lesser effects associated with [1- to 3-hour] exposure
to O₃ in the range of 0.12 ppm to 0.15 ppm observed in the
controlled human studies did not constitute adverse effects for
purposes of section 109 of the Act.'' The ``lesser effects'' referred
to in that notice involved responses of a maximum decrease in lung
function [as measured by forced expiratory volume in 1 second
(FEV₁)] of from 9 percent to 16 percent for the most
sensitive individuals exposed in this range, with few, if any,
symptoms. The EPA notes that this judgment is, in fact, consistent with
judgments presented in the 1996 proposal, which identify moderate and
large lung function decrements (as reflected in EPA's risk assessment
by FEV₁ decreases of ³ 15 percent and ³
20 percent, respectively, with the most sensitive individuals
experiencing FEV₁ decreases as large as 40 percent to 50
percent at 6- to 8-hour exposures in the range of 0.08 ppm to 0.10 ppm
in controlled human studies), and moderate to severe symptoms as being
adverse.
3. Exposure and risk assessments. To put judgments about health
effects that are adverse for individuals into a broader public health
context, EPA conducted quantitative assessments to estimate
O₃ exposures and related risks for the general population
and two at-risk groups, ``outdoor children'' and ``outdoor workers,''
living in nine representative U.S. urban areas. This broader context
included consideration, to the extent possible, of the size of the
particular population groups identified as at risk for various effects,
the estimated number of people within at-risk groups likely to
experience O₃-related adverse effects, the estimated number
of occurrences of such effects, and the estimated number of people who
would experience exposures of concern⁵ associated with
various air quality scenarios representing attainment of the current
and alternative 8-hour standards. Consideration was also given to the
kind and degree of uncertainties inherent in assessing such exposures
and risks. Such considerations provided a basis for judgments discussed
in the proposal about the levels of exposure and risk associated with
the current and alternative standards, which helped inform judgments
about the adequacy of public health protection afforded by the current
and alternative standards.
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5 ``Exposures of concern'' refer throughout to exposures at and
above 0.08 ppm, 8-hour average, at which a range of health effects
have been observed in controlled human studies, but for which data
were too limited to allow for quantitative risk assessment.
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Risk estimates were developed for those effects for which
sufficient concentration-response information was available from
studies evaluated in the Criteria Document, including adverse lung
function and respiratory symptom responses. In a separate analysis,
excess respiratory hospital admissions for individuals with asthma
associated with attainment of alternative standards were also
estimated, using a risk model for this health endpoint based on the
results of an epidemiological study in New York City (Thurston et al.,
1992) for which adequate air quality information was available to
assess population risk⁶. These quantitative risk estimates
(for that subset of O₃-related effects for which information
is sufficient to conduct such quantitative analyses) add to our
understanding of the broader array of health effects that are
associated with exposure to O₃ but for which quantitative
risk estimates could not be developed.
---------------------------------------------------------------------------

6 This study is one of several studies, mainly conducted in the
northeastern portion of the United States and southeastern Canada,
reporting excess daily respiratory-related hospital admissions
associated with elevated O₃ levels within the general
population and, more specifically, for individuals with asthma.
---------------------------------------------------------------------------

The methodology, results, and key observations from these
assessments were presented in the proposal. The EPA believes, and CASAC
concurred, that the models selected to estimate exposure and risk were
appropriate and that the methods used to conduct the health risk
assessment for adverse lung function and respiratory symptom responses
represent the state of the art. Nevertheless, the Administrator and
CASAC recognized that there are many uncertainties inherent in such
analyses, and that not all uncertainties inherent in such analyses
could be quantified and reflected in ranges of risk estimates (Wolff,
1995b), as discussed in the proposal and the referenced technical
support documents.
The exposure and risk assessments available at the time of proposal
had been conducted to evaluate the O₃ exposures and risks
associated with attainment of the current 1-hour standard and various
alternative 8-hour standards under consideration early in the standards
review process when the assessments were initiated. The EPA and CASAC
recognized at that time that additional alternative standards might
need to be analyzed later in the review process. Upon deciding to
propose a standard with a concentration-based form in the Fall of 1996,
EPA staff initiated supplemental analyses to estimate exposures and
risks⁷ for the

[[Page 38861]]

specific standard to be proposed and alternative standards on which the
proposal solicited comment. In conducting these supplemental analyses,
several technical changes were made based on insights gained from the
initial analyses.⁸ The supplemental assessment (Richmond,
1997) was placed in the docket and on the TTN on February 12, 1997, and
its availability was announced in the Federal Register notice extending
the public comment period on the proposal, providing the public the
opportunity to comment on the supplemental assessment (61 FR 7743,
February 20, 1997).
---------------------------------------------------------------------------

7 The analyses were conducted for the at-risk population of
outdoor children, the group with the highest exposures and risks.
Outdoor children are the subset of children between the ages of 6
and 18 years old who tend to be active outdoors, and include
approximately over 30 percent to 45 percent of all children in this
age group in the nine urban areas analyzed.
8 These changes primarily focused on the air quality data used
in the exposure analysis and on the air quality adjustment
procedures used to simulate ambient O₃ concentrations
upon attainment of alternative standards.
---------------------------------------------------------------------------

Key observations and results from the initial and supplemental
exposure and risk assessments that are most pertinent to the decision
to revise the current primary standard are highlighted in the following
unit, together with discussion of the key issues raised in public
comments on the methodology and public health implications of these
assessments.

B. Elements of the Primary Standard

In selecting a primary standard for O₃, the
Administrator must specify: Averaging time, O₃ concentration
(i.e., level), and form (i.e., the air quality statistic to be used as
a basis for determining compliance with the standard).⁹ All
three of these elements are necessary to define a standard and to
determine the degree of public health protection afforded by the
standard. The proposal outlined the key factors considered in selecting
each of these elements for the proposed standard, as well as the range
of options for each element on which the EPA solicited comment. The
factors reflect an integration of information on acute and chronic
health effects associated with exposure to ambient O₃;
expert judgments on the adversity of such effects for individuals; and
policy judgments, informed by air quality and exposure analyses and
quantitative risk assessment when possible, as to the point at which
risks would be reduced sufficiently to achieve protection of public
health with an adequate margin of safety.
---------------------------------------------------------------------------

9 This review focused only on a standard for O₃, as
the most appropriate surrogate for photochemical oxidants.
---------------------------------------------------------------------------

This approach to selecting a primary standard was endorsed by CASAC
(Wolff, 1995b), particularly through its advice to the Administrator
that ``EPA's risk assessments must play a central role in identifying
an appropriate level'' and its recognition that ``the selection of a
specific level and [form] is a policy judgment.'' Further, it was the
consensus view of CASAC that the ranges of 8-hour average levels (0.07
to 0.09 ppm) and forms (concentration-based forms that generally allow
for 1 to 5 exceedances) on which the proposal solicited comment were
appropriate.
The following discussion focuses primarily on those considerations
that were most influential in the Administrator's final decisions on
these elements, taking into account the comments received on the range
of options identified in the proposal.
1. Averaging time. In proposing to change the averaging time of the
primary standard from 1 to 8 hours, the Administrator was concurring
with the unanimous recommendation of CASAC (Wolff, 1995b) ``that the
present 1-hour standard be eliminated and replaced with an 8-hour
standard,'' and that more research is needed to resolve uncertainties
about potential chronic effects before appropriate consideration can be
given to establishing a long-term (e.g., seasonal or annual) primary
standard. The Administrator's proposed decision was supported by the
following key observations and conclusions:
(1) The 1-hour averaging time specified in the current NAAQS was
originally selected primarily on the basis of health effects associated
with short-term (i.e., 1- to 3-hour) exposures, with qualitative
consideration given to preliminary information on potential
associations with longer exposure periods.
(2) Substantial new health effects information available for
consideration in this review demonstrates associations between a wide
range of health effects and prolonged (i.e., 6- to 8-hour) exposures
below the level of the current 1-hour NAAQS.
(3) Results from the quantitative risk analyses show that attaining
a standard with a 1-hour averaging time reduces the risk of
experiencing health effects associated with both 1-hour and 8-hour
exposures. Likewise, attaining an 8-hour standard reduces the risk of
experiencing health effects associated with both 8-hour and 1-hour
exposures. Thus, reductions in risks from both short-term and prolonged
exposures can be achieved through a primary standard with an averaging
time of either 1 or 8 hours. As a result, establishment of both 1-hour
and 8-hour standards would not be necessary to reduce risks associated
with the full range of observed acute health effects.
(4) The 8-hour averaging time is more directly associated with
health effects of concern at lower O₃ concentrations than is
the 1-hour averaging time. It was thus the consensus of CASAC ``that an
8-hour standard was more appropriate for a human health-based standard
than a 1-hour standard.'' (Wolff, 1995b)
(5) While there is a large animal toxicology database providing
clear evidence of associations between long-term (e.g., from several
months to years) exposures and lung tissue damage, with additional
evidence of reduced lung elasticity and accelerated loss of lung
function, there is no corresponding evidence for humans. Moreover, the
state of the science has not progressed sufficiently to permit
quantitative extrapolation of the animal-study findings to humans.
Thus, the Administrator concluded that consideration of a separate
long-term primary O₃ standard is not appropriate at this
time. As discussed below, however, the Administrator considered the
possibility of long-term effects in selecting the level of an 8-hour
standard, which will provide protection against such effects to the
extent they may occur in humans, by lowering overall air quality
distributions and, thus, reducing cumulative long-term exposures.
The public comments reflect broad support for a standard with an 8-
hour averaging time, either alone or in conjunction with a 1-hour
standard. This support was typically based on references to:
(1) Evidence of health effects from 6- to 8-hour exposures to
O₃ concentrations down to 0.08 ppm, which are lower than
those concentrations that have induced such effects after 1- to 3-hour
exposures, and which are lower than the 0.12 ppm level of the current
standard.
(2) Analyses indicating that an 8-hour standard would limit both 1-
and 8-hour exposures.
(3) CASAC's unanimous agreement that the current 1-hour standard
should be replaced by an 8-hour standard. In considering the adequacy
of the current 1-hour standard alone in light of the health effects
evidence, some commenters have highlighted the statement in the
Criteria Document that there is ``strong evidence that ambient
exposures to O₃ can cause significant exacerbations of
preexisting respiratory disease in the general public at concentrations
below 0.12 ppm.'' (U.S. EPA, 1996a, p. 7-171)
Commenters expressing support for an 8-hour averaging time included
not only those who supported a level of public health protection
consistent with

[[Page 38862]]

or greater than that reflected by EPA's proposed standard, but also
many who disagreed for various reasons with the need for increased
public health protection beyond that provided by the current standard.
Of those supporting an 8-hour averaging time but not supporting the
need for increased protection, some expressed the view that the
averaging time of a health-based standard should be consistent with the
exposures of most concern, while others were simply neutral between the
choices of retaining the current 1-hour standard and replacing it with
an ``equivalent'' 8-hour standard.
The EPA agrees with the considerations raised by those commenters
who favor an 8-hour standard. Further, in considering the
appropriateness of an 8-hour standard as compared to a 1-hour standard,
EPA also notes the results of its exposure and risk assessments which
show variability across the nine urban areas analyzed with regard to
the extent to which the current 1-hour standard, and alternative 8-hour
standards, limit 8-hour exposures of concern and associated risks of
adverse health effects. As noted in the proposal and in the
supplemental risk assessment, there is much greater variability across
urban areas, particularly in looking at the seven current nonattainment
areas examined, in the extent to which the current 1-hour standard
limits such exposures of concern and risks than for the alternative 8-
hour standards. For example, the updated assessment estimates that the
current 1-hour standard results in 8-hour exposures of concern at and
above 0.08 ppm¹0 that vary by almost two orders of magnitude
across these areas. In contrast, alternative 8-hour standards at the
proposed level of 0.08 ppm result in estimated 8-hour exposures of
concern and risks that are much more consistent.¹1 In EPA's
view, the fact that an averaging time of 8 hours results in a
significantly more uniformly protective national standard than the
current 1-hour standard is an important public health policy
consideration that supports the selection of an 8-hour averaging time.
---------------------------------------------------------------------------

10 More precisely, exposures at and above 0.08 ppm refers to
estimates of exposures to O₃ concentrations ³
0.081 ppm from the exposure assessment.
11 In terms of the percent of outdoor children estimated to be
exposed to O₃ concentrations at and above 0.08 ppm while
engaged in moderate exertion, the current 1-hour standard results in
a range across the seven nonattainment areas of approximately 0.3
percent to 24 percent of such children, whereas alternative 8-hour
standards, at the proposed level of 0.08 ppm, result in a
significantly more uniform degree of protection, with ranges of
approximately 2 percent to 9 percent, third-highest concentration
form, and 3 percent to 11 percent, fifth-highest concentration form,
across the areas.
---------------------------------------------------------------------------

Those commenters who did not support EPA's proposal for an 8-hour
averaging time generally did not support any revision to the current
standard. These commenters predominantly focused on two basic points:
The generally improving trends in air quality under the current
standard and associated air quality management programs, which,
commenters argued, suggest that there is no need for EPA to adopt any
more stringent standard; and observations made in CASAC's closure
letter (Wolff, 1995b) with regard to EPA's risk assessment not
demonstrating any ``bright line'' threshold of effects or acceptable
risk. With regard to the first issue, EPA agrees that air quality
trends are improving as a consequence of ongoing control programs
designed to attain the current NAAQS. The EPA does not, however,
believe that these trends relieve the Agency of its statutory mandate
to review and, if appropriate, revise the NAAQS on the basis of the
best available scientific evidence to establish standards that protect
public health with an adequate margin of safety. The fact that current
control programs are resulting in progress toward improving air quality
does suggest that it is important to ensure that such progress is
maintained during any transition to a revised standard.
With regard to the second issue, commenters very frequently quoted
from the CASAC closure letter (Wolff, 1995b) stating ``that there is no
bright line' which distinguishes any of the proposed standards (either
the level or the number of allowable exceedances) as being
significantly more protective of public health'' and that ``the
selection of a specific level and number of allowable exceedances is a
policy judgment.'' These commenters have variously interpreted these
statements as a CASAC consensus that the differences in the public
health protection afforded by any of the alternative standards were too
small to be important from a public health perspective, not
statistically significantly different, or simply not different at all.
Based on these interpretations, the commenters argued that it is not
appropriate to revise the standard in any way, because a revised
standard would result in disruption to ongoing programs, additional
planning requirements, and increased implementation costs, but would
provide no or only very little improvement in public health protection.
The EPA believes that these commenters have misconstrued or too
narrowly interpreted CASAC's advice to the Administrator by not
considering the entire range of views and recommendations included in
its closure letter. Specifically, CASAC began its summary of
recommendations to the Administrator (Wolff, 1995b) by stating that
``[t]he Panel was in unanimous agreement that the present 1-hour
standard be eliminated and replaced with an 8-hour standard.'' This
agreement was based on ``the consensus of the Panel that an 8-hour
standard was more appropriate for a human health-based standard than a
1-hour standard.'' Thus, CASAC was unequivocal in its advice to the
Administrator with regard to which averaging time the health effects
evidence more strongly supports. While some commenters have also quoted
statements by individual Panel members at CASAC meetings suggesting
that choosing between a 1- or 8-hour averaging time is a ``policy''
choice, these individual statements during the course of CASAC's review
do not contradict nor supersede the clear and unanimous agreement of
CASAC on averaging time as conveyed to the Administrator in its closure
letter.
In considering these comments, EPA also believes it is important to
put into a public health perspective CASAC's observations about the
differences among alternative standards in protecting the public from
the health effects that were quantitatively estimated in EPA's risk
assessment. In the closure letter (Wolff, 1995b), CASAC observed that
``the differences in the percent of outdoor children *** responding
between the present standard and the most stringent proposal *** are
small and their ranges overlap for all health endpoints.'' Most
importantly, EPA notes that the primary standard would provide
protection from a broader array of health effects than it was possible
to consider in its quantitative risk assessment. This perspective is
clearly shared in particular by those CASAC panel members who
personally favored a level or range of levels that included the
proposed level of 0.08 ppm, in that the closure letter characterizes
their views as reflecting, in part, their ``concern over the evidence
for chronic deep lung inflammation from the controlled human and animal
exposure studies.'' While the risk of this effect, as well as other
effects related to 6- to 8-hour exposures in the Criteria Document and
Staff Paper (including increased airway responsiveness, impairment of host

[[Page 38863]]

defenses suggesting an increased susceptibility to respiratory
infection, and increased emergency room visits, doctor visits, and
frequency of medication use by individuals with impaired respiratory
systems) could not be quantitatively estimated in EPA's risk
assessment, EPA believes that consideration of these effects is
nevertheless important in making public health policy judgments.
Further, in interpreting CASAC's statements on EPA's risk
assessment report (Whitfield et al., 1996) that there is no ``bright
line'' which distinguishes any of the standards as being
``significantly'' more protective, and that the ``ranges overlap,'' EPA
notes that there are statistically significant differences in the
estimated risks for the standards analyzed with 1- and 5-exceedance
forms. This information was presented to CASAC at its September 1995
meeting (CASAC meeting transcript, September 19-20, 1995, pp. 108-109).
Further, EPA again notes that whether one judges the differences to be
significant or small can depend on whether one focuses on percentages,
as CASAC's letter did, or on total numbers of times that children or
other at-risk individuals experience such effects. The overlap in the
ranges of risk referred to in the CASAC letter reflect differences
among urban areas used in EPA's risk analysis (e.g., air quality,
exposure patterns, environmental factors), not random uncertainties in
risk estimates within any given urban area. Thus, the fact that the
ranges overlap does not mean that there are no real or statistically
significant differences in protection among alternative standards. To
the extent that the quoted statements from CASAC's closure letter are
read as implying that CASAC considered the differences not to be
statistically significant (or that there are no differences at all in
the protection afforded by the alternative standards), EPA disagrees
with that reading.
Another group of commenters, while supporting an 8-hour standard,
specifically opposed replacing the current 1-hour standard with an 8-
hour standard, but favored instead both 8-hour and 1-hour standards.
These commenters generally felt that a greater degree of public health
protection than that provided by the proposed standard was warranted,
and that standards based on both averaging times were necessary to
provide the requisite protection from 1- and 8-hour exposures of
concern. These commenters generally argued that an 8-hour standard
alone could still allow for high 1-hour exposures of concern, or that
the retention of the current 1-hour standard was critical to
maintaining current pollution control measures. As an initial matter,
EPA is delaying revocation of the 1-hour standard to ensure an
effective transition to the 8-hour standard, as discussed in Unit
II.B.4 of this preamble. While EPA agrees that it is possible that an
8-hour standard alone could allow for high 1-hour exposures of concern,
at and above 0.12 ppm,¹2 EPA's exposure assessments estimate
that alternative 8-hour standards, at the proposed level of 0.08 ppm
but with different forms, would be very effective in limiting 1-hour
exposures, and generally even more effective in limiting 1-hour
exposures of concern than is the current 1-hour standard. More
specifically, the updated assessment estimates that upon attainment of
alternative 8-hour, 0.08 ppm standards, with forms ranging up to the
fifth-highest concentration form, less than 0.1 percent of outdoor
children are likely to experience any 1-hour exposures greater than
0.12 ppm while at heavy exertion levels in four to seven of the nine
urban areas analyzed, whereas this is true for only two of the nine
areas upon attainment of the current 1-hour standard. In all nine areas
both the current and alternative 8-hour, 0.08 ppm standards are
estimated to limit such exposures to less than 1 percent of the outdoor
children. Thus, EPA concludes that an 8-hour averaging time does
effectively limit both 1- and 8-hour exposures of concern.
---------------------------------------------------------------------------

12 The EPA recognizes this possibility exists especially in the
very few areas with unusually ``peaky'' air quality patterns (i.e.,
in which the ratio of the 1- and 8-hour average design values for
the current and proposed standards is greater than 1.5).
---------------------------------------------------------------------------

For the reasons discussed above in this unit, and after taking into
account the range of views expressed in the public comments, the
Administrator finds that replacing the current 1-hour standard with an
8-hour standard, in combination with the decisions on level and form
described below, is appropriate to provide adequate and more uniform
protection of public health from both short-term (1 to 3 hours) and
prolonged (6 to 8 hours) exposures to O₃ in the ambient air.
2. Level. Taken together, the level and form of the standard, for a
given averaging time, determine the degree of public health protection
afforded by the standard. Consideration of the level of the standard
discussed in this unit of the preamble reflects a recognition of this
linkage between level and form (discussed separately below in Unit II.B.3).
The Administrator's decision to propose the level of an 8-hour
primary O₃ standard at 0.08 ppm, and to solicit comment on
alternative levels, necessarily reflected a recognition, as emphasized
by CASAC, that it is likely that ``O₃ may elicit a continuum
of biological responses down to background concentrations'' (Wolff,
1995b). Thus, in the absence of any discernible threshold, it is not
possible to select a level below which absolutely no effects are likely
to occur. Nor does it seem possible, in the Administrator's judgment,
to identify a level at which it can be concluded with confidence that
no ``adverse'' effects are likely to occur. In such a case, as CASAC
has advised, the traditional paradigm for standard-setting cannot be
applied in the usual way, and assessments of risk ``must play a central
role in identifying an appropriate level'' (Wolff, 1995b). Thus, the
Administrator's task became one of attempting to select a standard
level that would reduce risks sufficiently to protect public health
with an adequate margin of safety, since a zero-risk standard is
neither possible nor required by the Act. In this and other NAAQS
reviews the CASAC has generally recognized that the selection of
specific standards requires that the Administrator make public health
policy judgments in addition to determinations of a strictly scientific
nature. The Administrator's public health policy judgment on the level
of the proposed standard was framed by the considerations discussed
above in this unit and informed by the following key observations and
conclusions:
(1) During the last review of the O₃ criteria and
standards, CASAC concluded that the existing 1-hour standard set at
0.12 ppm O₃ provided ``little, if any, margin of safety,''
and that the upper end of the range of consideration for a 1-hour
standard should be 0.12 ppm (McClellan, 1989). In addition, several
members of the CASAC panel recommended that consideration should be
given to a lower 1-hour level of 0.10 ppm to offer some protection
against effects for which there was preliminary information at that
time of associations with 8-hour exposures to O₃.
Regarding currently available evidence of O₃-related effects:
(2) Based on a significant body of information available since the
last review, there is now clear evidence from human clinical studies
that O₃ effects of concern are associated with the 6- to 8-
hour exposures tested. Studies were done at 6- to 8-hour exposure
levels of 0.12, 0.10, and 0.08 ppm. This includes evidence of the
following statistically significant responses at 6- to 8-hour exposures
to the lowest concentration evaluated, 0.08 ppm O₃, at moderate

[[Page 38864]]

exertion: lung function decrements, respiratory symptoms (e.g., cough,
pain on deep inspiration), nonspecific bronchial responsiveness, and
biochemical indicators of pulmonary inflammation. Field studies provide
evidence of similar functional and symptomatic effects at ambient
O₃ exposures that are consistent with the clinical findings.
Laboratory animal studies provide supporting evidence of O₃-
induced biochemical indicators of inflammation and functional changes.
(3) Numerous epidemiological studies have reported excess hospital
admissions and emergency department visits for respiratory causes (for
asthmatic individuals and the general population) attributed primarily
to ambient O₃ exposures, including O₃
concentrations below the level of the current standard, with no
discernible threshold at or below this level. The biological
plausibility of attributing such effects to ambient O₃
exposures is supported by human studies showing increased nonspecific
bronchial responsiveness, laboratory animal studies showing pulmonary
changes that decrease the effectiveness of the lung's defenses against
bacterial respiratory infections, and the reasonable anticipation that
O₃ exposures also increase the risk of respiratory
infections in humans, based on the many similarities between animal and
human defense mechanisms.
(4) Long-term laboratory animal studies suggest that changes in
lung biochemistry and structure may, under certain circumstances,
become irreversible, although it is unclear whether long-term exposures
to ambient O₃ levels result in similar chronic health
effects in humans.
Regarding the types and severity of O₃-induced
physiological effects that are considered to be adverse to the health
status of individuals experiencing such effects:
(5) With regard to lung function decrements and respiratory
symptoms, the Administrator recognized that these O₃-induced
effects are transient and reversible, and concluded that the extent to
which such effects are adverse to the health status of an individual
depends upon the severity, duration, and frequency with which an
individual experiences such effects throughout the O₃
season. While group mean responses in clinical studies at the lowest
exposure level tested of 0.08 ppm are typically small or mild in
nature, responses of some sensitive individuals are sufficiently severe
and extended in duration to be considered adverse. This would
especially be true to the extent that those individuals likely to
experience such effects would, on average, experience them several
times a year.
(6) With regard to increased hospital admissions and emergency room
visits, the Administrator judged that such effects are clearly adverse
to individuals.
(7) With regard to pulmonary inflammation, the Administrator
recognized that singular occurrences of inflammation are likely
reversible and potentially of little health significance. On the other
hand, based on laboratory animal studies, repeated inflammatory
responses associated with exposure to O₃ over a lifetime
have the potential to result in damage to respiratory tissue such that
individuals later in life may experience a reduced quality of life.
Furthermore, there is the possibility that repeated pulmonary
inflammatory responses could adversely affect asthmatic individuals by
resulting in increased medication use, medical treatment, and/or
emergency room visits and hospital admission. Such effects in
asthmatics are of special concern particularly in light of the growing
asthma problem in the United States and the increasing rates of asthma-
related mortality and hospitalizations, especially among children in
general and black children in particular. While O₃ has not
been shown to cause asthma, the available evidence suggests that
O₃ may exacerbate asthma. Accordingly, the Administrator
judged that repeated exposures to O₃ levels that produce
inflammation of the lungs are adverse to individuals likely to
experience such exposures over long periods of time.
The Administrator considered the results of the exposure and risk
analyses and the following key observations and conclusions from these
analyses in putting effects considered to be adverse to individuals
into a broader public health perspective and in making judgments about
the level of a standard that would reduce risk sufficiently to protect
public health with an adequate margin of safety:
(8) The median risk estimates for respiratory functional and
symptomatic effects, as well as for excess hospital admissions of
asthmatics for respiratory causes, are approximately the same or only
marginally smaller for some of the 8-hour, 0.09 ppm standard options
evaluated (including those with forms ranging from 1- to 3-expected-
exceedances¹3) as compared to the current 1-hour, 0.12 ppm
NAAQS (risk estimates are somewhat larger for an 8-hour, 0.09 ppm, 5-
expected-exceedance standard as compared to those for the current NAAQS).
---------------------------------------------------------------------------

13 The upper end of this range, 3-expected-exceedances, was
based on air quality comparisons, since risk estimates were only
available at the time of proposal for the 1- and 5-expected-
exceedance forms of a 0.09 ppm standard. This range is consistent
with the results of the updated risk assessment.
---------------------------------------------------------------------------

(9) Within any given urban area, statistically significant
reductions in exposure and risk associated with respiratory functional
and symptomatic effects result from alternative 8-hour standards as the
level changes from 0.09 ppm to 0.08 ppm to 0.07 ppm. These reductions
represent differences of hundreds of thousands of times that children
in the nine urban areas included in the analysis would likely
experience such effects under the range of alternative standards
considered relative to the current standard. There are significant
uncertainties in such quantitative estimates, however, and there is no
break point or bright line that differentiates between acceptable and
unacceptable risks within this range.
(10) Similarly, reductions in hospital admissions for respiratory
causes for asthmatic individuals and the general population are
estimated to occur with each change in the level of the standard from
0.09 ppm to 0.08 ppm to 0.07 ppm. However, hospital admissions for
asthmatic individuals associated with ambient O₃ exposures
within the range of standard levels under consideration represent a
relatively small fraction of the total respiratory-related hospital
admissions for asthmatics over the O₃ season.
(11) Estimated exposures to O₃ concentrations at and
above 0.08 ppm (at which increased nonspecific bronchial
responsiveness, decreased pulmonary defense mechanisms, and indicators
of pulmonary inflammation have been observed in humans) while engaged
in moderate exertion are essentially zero at the 0.07 ppm standard
level (with a 1-expected-exceedance form) for the seven nonattainment
areas evaluated in the exposure analyses for the at-risk population of
outdoor children. Such exposures of outdoor children increase to
approximately 0 to 1 percent at the 0.08 ppm standard level, while the
estimated range at the 0.09 ppm standard level increases to
approximately 3 to 7 percent of outdoor children for these areas.
(12) While recognizing that sensitive individuals may experience
adverse but transient effects with a standard set at 0.08 ppm, no CASAC
panel member supported selection of 0.07 ppm as the level of a primary
standard. Of the

[[Page 38865]]

members who expressed their personal views, three indicated a
preference for a level of 0.08 ppm, one for a range of 0.08 to 0.09
ppm, three for a level of 0.09 ppm (with one of the three expressing a
preference for selecting a form that would result in equivalent
protection to the current standard), and one for a range of 0.09 to
0.10 ppm, associated with public advisories for O₃ levels at
and above 0.07 ppm. Other CASAC panel members also expressed support
for such public notices or advisories reflecting potential effects for
extremely sensitive individuals associated with O₃ levels as
low as 0.07 ppm.
These observations and conclusions resulted in the Administrator
focusing in particular on the alternative levels of 0.08 ppm and 0.09
ppm, having placed great weight on the fact that none of the CASAC
panel members expressed support for a standard set below 0.08 ppm. In
deciding between these two levels, the Administrator took into account
quantitative estimates of the risks associated with attaining standards
set at these levels for those effects for which such quantitative risk
estimates could be developed. Other factors that were important in the
Administrator's proposed decision include:
(1) Quantitative estimates of 8-hour exposures of concern (i.e., at
and above 0.08 ppm) associated with these standard levels.
(2) The consistency of the clinical, field, and epidemiological
studies, in which effects were seen not only from controlled exposures
to 0.08 ppm, but also in ambient environments in which 8-hour average
O₃ concentrations ranged from above to below the 0.08 ppm level.
(3) The importance of increased protection for those sensitive
individuals who may experience respiratory symptomatic and functional
effects at lower O₃ concentrations than the population as a
whole.
(4) The uncertainties in considering the potentially more serious
but as yet uncertain chronic effects.
As discussed above in Unit II.A.3., EPA completed and made
available for public comment supplemental exposure and risk assessments
subsequent to the proposal. For any of the alternative standards
considered in the assessment, the new estimates of exposures at and
above 0.08 ppm are somewhat higher than those available at the time of
proposal, while the new estimates of risks, for adverse effects
including moderate and large decreases in lung function, moderate to
severe respiratory symptoms, and hospital admissions for asthmatics,
are lower. However, the relative differences in estimated exposures and
risks between alternative standard levels remain about the same as at
the time of proposal. Thus, while the Administrator's final decision
takes into account the more recent assessments, the differences in the
quantitative results between the initial and supplemental assessments
do not fundamentally alter the basis for the judgments expressed at the
time of proposal.
To aid in comparing the public health protection associated with 8-
hour standards at the 0.08 ppm and 0.09 ppm levels, observations from
the updated exposure and risk assessments for all nine urban areas
evaluated are summarized below (assuming the third-highest
concentration form, which was the upper end of the range of
consideration for forms for the 0.09 ppm level).
(1) The percentages of outdoor children exposed to O₃
concentrations at and above 0.08 ppm (at which increased nonspecific
bronchial responsiveness, decreased pulmonary defense mechanisms, and
indicators of pulmonary inflammation have been observed in humans)
while engaged in moderate exertion are estimated to be approximately 3
percent at the 0.08 ppm standard level, ranging from approximately 2
percent to 10 percent in the nine areas, increasing to approximately 11
percent at a standard level of 0.09 ppm, ranging from approximately 7
percent to 29 percent in the nine areas.
Updated risk estimates in terms of the percentages¹4 and
numbers of outdoor children estimated to experience various health
effects, and the total numbers of occurrences of these effects in
outdoor children, upon attainment of these two alternative standards
for all nine urban areas combined¹5 are as follows:
---------------------------------------------------------------------------

14 These updated risk estimates in terms of the percentage of
outdoor children in the nine urban areas are roughly comparable to
the range of original estimates presented in Table 1 of the proposal
for 1- and 5-expected-exceedance forms of the standards.
15 Approximately 3.1 million outdoor children reside in these
nine urban areas.
---------------------------------------------------------------------------

(2) For moderate lung function (FEV₁) decreases
³ 15 percent, approximately 6 percent of outdoor children
(180,000 children) would experience this effect one or more times per
year (650,000 occurrences) at the 0.08 ppm standard level, increasing
to approximately 8 percent of outdoor children (250,000 children and
1,100,000 occurrences) at the 0.09 ppm standard level.
(3) For large lung function (FEV₁) decreases ³
20 percent, approximately 2 percent of outdoor children (58,000
children) would experience this effect one or more times per year
(100,000 occurrences) at the 0.08 ppm standard level, increasing to
approximately 3 percent of outdoor children (97,000 children and
220,000 occurrences) at the 0.09 ppm standard level.
(4) For moderate or severe pain on deep inspiration, approximately
0.9 percent of outdoor children (27,000 children) would experience this
effect one or more times per year (120,000 occurrences) at the 0.08 ppm
standard level, increasing to over 1 percent of outdoor children
(41,000 children and 220,000 occurrences) at the 0.09 ppm standard level.
Many public commenters supported EPA's proposed level of 0.08 ppm
for an 8-hour standard, including most public health associations and
groups of medical professionals, many citizens, and some States and
regional associations. There were also large numbers of commenters who
expressed strong views in opposition to the proposed level. Of those
who did not support the proposed 8-hour level, almost all commenters
representing businesses and industry associations, many local
governmental groups and private citizens, and some States either
supported no change to the current standard or, if EPA were to replace
the current 1-hour standard with an 8-hour standard, supported a level
of 0.09 ppm directly or simply one that would be ``equivalent'' to the
current standard. On the other hand, environmental groups, many
citizens, and some medical professionals and researchers supported a
level of 0.07 ppm for an 8-hour standard.
In general, the issues raised by these groups of commenters can be
addressed in three categories: Comments on the strength and adequacy of
the health effects evidence upon which the proposed decision was based,
comments on the quantitative exposure and risk assessments and the
extent to which the assessments either over- or under-predict exposures
and risks among sensitive populations, and judgments as to whether the
differences in public health protection provided by alternative
standards are significant from a public health perspective. Each of
these categories of key issues is discussed separately below.
With regard to the first category of comments, on the strength and
adequacy of the health effects evidence, commenters who did not support
the need for any increased protection beyond that provided by the
current standard questioned the adequacy or highlighted the limitations
of the

[[Page 38866]]

various types of health effects studies that have related O₃
exposures to adverse effects. For example, some commenters questioned
the controlled human exposure studies, arguing that: Many such studies
used patterns of exposures and exercise levels that are not
representative of normal population exposures to ambient O₃;
some exposure chambers using artificially generated O₃ may
have been contaminated with other pollutants that could have accounted
for some of the observed effects; and responses to elevated
O₃ levels were compared to responses to air with essentially
no O₃ rather than to background levels typical of ambient
air. Some commenters argued that these flaws in the study designs would
result in overestimating responses to non-background levels of ambient
O₃ or in erroneous findings of statistical significance. In
contrast, others commented that because the chambers did not contain
other pollutants and natural pulmonary irritants (e.g., pollens, dust)
or a full range of environmental conditions (e.g., high temperatures
and humidity) typical of ambient air, the results may underestimate the
true impact of O₃ in the ambient air.
Some commenters also questioned the summer camp and other field
studies and epidemiological studies reporting increased hospital
admissions and emergency room visits, arguing that: The responses in
these studies were inherently confounded by exposures to other
pollutants, the camp studies did not differentiate activity levels of
the participants, and linear regression down to or below background
levels was unjustifiably used to analyze the results of the hospital
admission studies. These commenters expressed the view that these and
other flaws call into question any conclusions about whether the
reported associations are causal. In contrast, other commenters argued
that the hospital admissions reported in these studies are indicative
of a pyramid of adverse health effects, including increased mortality,
increased visits to emergency and outpatient departments and
physicians, increased numbers of asthma attacks resulting in increased
medication use, and increased numbers of restricted activity days and
acute respiratory symptom days, that EPA has not adequately taken into
account. The EPA notes that these comments are consistent with
statistics published by the U.S. Department of Health and Human
Services, which indicate that for every hospital admission of an
individual with asthma for respiratory causes, there are more than five
emergency and outpatient department visits and more than 20 office-
based physician visits (U.S. DHHS, 1996).
With regard to studies related to pulmonary inflammation and
chronic respiratory damage, some commenters argued that the linkage
between repeated inflammatory responses and chronic respiratory damage
was merely speculation, and, therefore, should not be considered as
part of the basis for decisions on the primary standard. In contrast,
others commented that animal studies had demonstrated that repeated
pulmonary inflammation leads to degenerative or irreversible lung
damage, that these studies are consistent with observations in human
exposure studies, and, therefore, that they should be considered in
decisions on the standard.
The EPA notes that many of these comments did not reflect an
integrative assessment of the evidence--the approach CASAC has
historically urged EPA to follow--but rather a piecemeal look at each
individual study or type of study, which tends to miss the strength of
the entire body of evidence taken together. Other commenters did
consider the body of evidence in a more integrative manner, and many of
these commenters expressed the view that the body of evidence as a
whole provided clear evidence of O₃-related effects at and
below O₃ concentrations allowed by the current standard.
Some commenters highlighted the large number of studies that
demonstrate evidence of effects for prolonged exposures at and below
0.08 ppm, and criticized EPA for giving too little weight to those
studies which reported serious effects, but for which the data were not
sufficient to do quantitative risk assessments.
With regard to the second category of comments, on the exposure and
risk assessments, a number of commenters raised concerns about key
aspects of the assessments, including the exposure model, the
development of concentration-response functions, the application of the
risk model, and the measures of risk used to characterize the results
of the assessments. With regard to the exposure model, a number of
commenters claimed that: The model overestimates the exertion level
that can be achieved by most children and outdoor workers and the
fraction of time that these groups spend in moderate or heavy exertion;
the model overestimates outdoor ambient exposures because fixed-site
monitors overestimate outdoor personal exposures; and the air quality
adjustment procedures used to simulate attainment of the standards are
inappropriate or highly uncertain. Other commenters expressed concern
that the exposure model may be significantly underestimating exposures
for children and outdoor workers who repeatedly exercise due to
limitations in the available human activity pattern data.
As discussed in the proposal, EPA recognizes that the exposure
model necessarily contains many sources of uncertainty, although every
effort has been made to account for such uncertainties to the extent
possible. In particular, the model incorporates and is sensitive to
analytical procedures used to simulate spatial and temporal
distributions of O₃ concentrations that would occur as a
result of an area just attaining any of the alternative standards
addressed in the exposure assessment. These air quality adjustment
procedures are based on generalized models intended to reflect the
patterns of changes in distributions of O₃ concentrations
that have historically been observed in areas implementing control
programs designed to attain the O₃ NAAQS. The EPA recognizes
that future changes in air quality distributions are area-specific, and
will be affected by whatever specific control strategies are
implemented in the future to attain the revised NAAQS. Thus,
generalized models are expected to be more uncertain for any given area
than when exposure results are aggregated across many areas (as was
done across the nine urban areas analyzed in EPA's exposure assessment).
Some commenters questioned the specific air quality adjustment
procedure used in the initial and supplemental assessment¹6,
and a few of these commenters recommended revisions or alternative
procedures that they believed would be more representative of
historical or projected future air quality patterns. As discussed in
more detail in the Response to Comments, EPA acknowledges that both
procedures used in the assessments result in projections of air quality
that deviate to some degree from historical patterns of air quality
changes observed in specific urban areas, and that other procedures may
be more representative of air quality patterns in specific areas. While
EPA will take these comments into account as future refinements are
made to the air quality adjustment

[[Page 38867]]

procedures used in the exposure model, EPA believes, and CASAC
concurred, that the procedures used in the assessments conducted as
part of this review are reasonable given the uncertainties inherent in
projecting future changes in air quality patterns.
---------------------------------------------------------------------------

16 The initial risk assessment used both ``Weibull'' and
``proportional'' air quality adjustment procedures, whereas the
supplemental risk assessment used a ``proportional'' air quality
adjustment procedure for all nine urban areas. In responding to
comments on the air quality adjustment procedures, EPA also
evaluated an alternative ``quadratic'' procedure (as discussed in
the Response to Comments), which generally resulted in risk
estimates between those from the Weibull and proportional procedures.
---------------------------------------------------------------------------

In commenting on the air quality adjustment procedure used in the
supplemental assessment, some commenters particularly focused on the
results for two of the nine areas analyzed in which, contrary to
results from the initial assessment, lower risks were estimated for the
current standard as compared to the proposed standard. As discussed
more fully in the Response to Comments, EPA believes that these results
for each area cannot be distinguished within the sensitivity of the
alternative air quality adjustment procedures used in the initial and
supplemental assessments. Further, EPA notes that these two areas have
much higher ratios of peak 1-hour to 8-hour O₃
concentrations than the vast majority of areas in which O₃
is monitored¹7, and it is thus reasonable to expect that
generalized air quality adjustment procedures would be particularly
uncertain for such areas.
---------------------------------------------------------------------------

17 The two areas are Houston and parts of Los Angeles county,
which are two of only six areas nationwide with peak 1- to 8-hour
design value ratios greater than 1.5.
---------------------------------------------------------------------------

Comments focusing on the development of concentration- response
functions for use in the risk model have included a number of claims.
Some commenters claimed that EPA inappropriately selected studies for
developing the functions by excluding studies that reported lower
response rates and by using only studies conducted by EPA scientists.
Some commenters asserted that contaminants in the controlled exposure
chambers may be responsible for some of the effects incorporated into
the concentration-response functions for O₃. Further, some
commenters asserted that it was inappropriate to extrapolate the
concentration-response functions to background levels or to develop
concentration-response functions for symptomatic responses in children
based on studies of such responses in adults.
Of the comments focusing on the application of the risk model, some
commenters claimed that the aggregate risk results were overstated
because of: Many of the methodological problems noted in the above
summary of comments, the failure to take into account the known
attenuation of effects, and the assumption of an inappropriately low
background concentration in calculating risks attributable to non-
background sources of O₃. On the other hand, other
commenters claimed that aggregate risk results were understated because
of: Methodological problems, noted above, that underestimate exposures,
limiting the analyses to only a subset of adverse health effects rather
than estimating the full range of effects that have been attributed to
O₃, and by focusing only on nine urban areas rather than
projecting risk reductions from alternative standards nationally.
While EPA has included comprehensive responses to these comments in
the Response to Comments, most of the issues and concerns raised by
commenters concerning the health effects evidence and the methods used
in the exposure and risk assessments are essentially restatements of
concerns raised during the review of the Criteria Document and the
development and review of these quantitative assessments as part of the
preparation and review of the Staff Paper. EPA presented and the CASAC
reviewed in detail the approaches used to assess exposure and health
risk, the studies and health effect categories selected for which
concentration-response functions were estimated, and the presentation
of the exposure and risk results summarized in the Staff Paper. As
stated in the proposal, EPA believes and CASAC concurred, that the
general models selected to estimate exposure and risk are appropriate
and that the methods used to conduct the exposure and risk assessments
represent the state of the art. EPA does not believe that the exposure
or risk assessments are fundamentally biased in one direction or the
other as claimed in some of the comments.
The Administrator and CASAC have recognized, however, that there
are many uncertainties inherent in such assessments and that the
resulting ranges of quantitative risk estimates do not reflect all of
the uncertainties associated with the numerous assumptions inherent in
such analyses (Wolff, 1995b). EPA summarized some of the most important
caveats and limitations concerning both the exposure analyses and the
risk assessments for lung function changes, respiratory symptoms, and
hospital admissions in the proposal. A more complete discussion of
assumptions and uncertainties is contained in the Staff Paper and
technical support documents (Johnson et al., 1996 a,b; Whitfield et
al., 1996; Richmond, 1997).
With regard to the third category of comments, reflecting
commenters' judgments as to whether the differences in public health
protection of alternative standards are significant from a public
health perspective, EPA notes that highly divergent judgments were
expressed by different groups of commenters. A large number of
commenters who expressed the view that the differences in public health
protection were not significant or important enough to warrant any
standard more stringent than the current standard used CASAC as the
basis for their position, as discussed above in Unit II.B.1. on
averaging time. Others cited small percentages of outdoor children and
other sensitive groups likely to be affected based on EPA's assessment,
or even smaller percentages as modified by analyses conducted by the
commenter to correct perceived errors in the analyses. In contrast,
other commenters cited large total numbers of children likely to be
affected, not only for the subset of O₃-related effects and
the nine areas analyzed in EPA's assessments, but also for a broader
array of related effects projected nationally.
The core issue in this review of the primary O₃
standard, as stated by the Administrator at the time of proposal, is
who is to be protected, and from what. Clearly, for pollutants, such as
O₃, that have no discernible thresholds for health effects,
no standard can be risk-free. The Administrator's task is to select a
standard level that will reduce risks sufficiently to protect public
health with an adequate margin of safety since a zero-risk standard is
neither possible nor required by the Act. As CASAC and the
Administrator recognize, the selection of a specific standard level for
such pollutants requires public health policy judgments in addition to
determinations of a strictly scientific nature.
In making such judgments, the Administrator rejects the notion that
because standards cannot be risk-free they should not be revised to
provide increased protection for sensitive populations, particularly
including children in this case, when available evidence points to
greater impacts on public health than had previously been demonstrated.
In carefully reassessing both those risks to public health that can be
quantified as well as those for which quantitative risk information is
more limited, the Administrator has focused on the following
comparisons between the degree of public health protection likely to be
afforded by an 8-hour standard at the proposed level of 0.08 ppm and an
alternative standard set at a level of 0.09 ppm (assuming the same
third-highest concentration form):
(1) Based on EPA's updated analyses of estimated moderate or large
decreases

[[Page 38868]]

in lung function and moderate to severe pain on deep inspiration in
outdoor children in nine urban areas (Richmond, 1997), a standard set
at 0.09 ppm would allow approximately 40 percent to 65 percent more
outdoor children to experience such effects than would a 0.08 ppm
standard, and approximately 70 percent to 120 percent more occurrences
of such effects in outdoor children per year.
(2) While only relatively small percentages of outdoor children are
estimated to experience such effects, the differences in these
percentages between the two standard levels represent tens of thousands
more children, and hundreds of thousands more occurrences of adverse
effects in these children, in these nine urban areas alone, for a 0.09
ppm standard as compared to a 0.08 ppm standard.
(3) Based on EPA's updated risk assessment of increased hospital
admissions in New York City (Richmond, 1997), a standard set at 0.09
ppm would allow approximately 40 more excess hospital admissions of
asthmatics within an O₃ season in New York City for
respiratory causes as compared to a 0.08 ppm standard, which represents
approximately a 40 percent increase in excess O₃-related
admissions, but only approximately a 0.3 percent increase in total
admissions of asthmatics. The EPA believes that while these numbers of
hospital admissions are relatively small from a public health
perspective, they are indicative of a pyramid of much larger numbers of
related O₃-induced effects, including respiratory-related
hospital admissions among the general population, emergency and
outpatient department visits, doctors visits, and asthma attacks and
related increased use of medication that are important public health
considerations.
(4) Based on EPA's exposure analyses in the nine urban areas, a
standard set at 0.09 ppm would allow more than three times as many
children to experience 8-hour average exposures of concern as would a
0.08 ppm standard, with the number of outdoor children likely to
experience such exposures increasing from approximately 100,000 to more
than 300,000 in the nine urban areas alone, representing an increase
from approximately 3 percent to approximately 11 percent of the outdoor
children likely to experience such exposures.
(5) These exposures of concern are judged by EPA to be an important
indicator of the public health impacts of those O₃-related
effects for which information is too limited to develop quantitative
estimates of risk, but which have been observed in humans at a level of
0.08 ppm for 6- to 8-hour exposures. Such effects include the
following: increased nonspecific bronchial responsiveness (related, for
example, to aggravation of asthma), decreased pulmonary defense
mechanisms (suggestive of increased susceptibility to respiratory
infection), and indicators of pulmonary inflammation (related to potential
aggravation of chronic bronchitis or long-term damage to the lungs).
(6) To put these risks and exposures into broader perspective, EPA
notes that approximately 46 million more people, including
approximately 13 million more children and 3 million more individuals
with asthma, live in areas that would not attain a 0.08 ppm standard
compared to a 0.09 ppm standard. The general population as well as
children and asthmatics would breathe cleaner air as a direct result of
control measures designed to bring areas into attainment with the
proposed standard.¹8
---------------------------------------------------------------------------

18 The EPA anticipates that additional people would be protected
through regional measures adopted for purposes of an 8-hour, 0.08
ppm standard.
---------------------------------------------------------------------------

While recognizing the inherent uncertainties in these estimates,
and after taking into account the range of views and judgments
expressed in the public comments, the Administrator finds the public
health impacts described in the proposal, as updated above, to be
important and sufficiently large as to warrant a standard set at a
level of 0.08 ppm, as proposed.
The Administrator recognizes the views of those who argue that
similarly large improvements in public health protection would result
from a standard set at 0.07 ppm as compared to the proposed standard,
such that, based on the same reasoning, the evidence warrants a
standard set at 0.07 ppm. In considering these views, the Administrator
gives significant weight to the following considerations:
(1) No member of the CASAC panel of experts supported a standard
set lower than 0.08 ppm, specifically after considering a range of
alternative standards that included 0.07 ppm.
(2) The most certain O₃-related effects, while judged to
be adverse, are transient and reversible (particularly at O₃
exposures below 0.08 ppm), and the more serious effects with greater
immediate and potential long-term impacts on health are less certain,
both as to the percentage of individuals exposed to various
concentrations who are likely to experience such effects and as to the
long-term medical significance of these effects.
(3) As many commenters have noted, based on information in the
Criteria Document with regard to ambient concentrations of
O₃ from background sources, an 8-hour standard set at a 0.07
ppm level would be closer to peak background levels that infrequently
occur in some areas due to nonanthropogenic sources of O₃
precursors, and thus more likely to be inappropriately targeted in some
areas on such sources.
After taking into account the public comments, and for the reasons
outlined above, the Administrator finds that a standard set at a level
of 0.07 ppm is not requisite to protect public health with an adequate
margin of safety.
3. Form. The form of the current 1-hour, 0.12 ppm standard is a
``1-expected-exceedance'' form. That is, the current standard is based
on the expected¹9 number of days per year, on average over 3
years, on which the level of the standard is exceeded, and limits that
number of expected exceedances to be less than or equal to 1.0.
---------------------------------------------------------------------------

19 The term ``expected'' means that the numbers of exceedances
per year are averaged over 3 years and may be calculated using
specific adjustments to account for missing data.
---------------------------------------------------------------------------

In evaluating alternative forms for the primary standard, the
adequacy of the public health protection provided was the
Administrator's foremost consideration. The Administrator also
recognized, however, that concerns have been raised with the current
form since it was promulgated in 1979 due to the inherent lack of year-
to-year stability in the measure of air quality on which the 1-
expected-exceedance form is based.²⁰ The CASAC specifically
took such concerns into account in recommending that the current form
be revised and in noting that a more robust, concentration-based form
would minimize such instability and provide some insulation from the
impacts of extreme meteorological events that are conducive to
O₃ formation (Wolff, 1995b). Such instability can have the
effect of reducing public health protection by disrupting ongoing
implementation plans and associated control programs.
---------------------------------------------------------------------------

20 The 1-expected-exceedance form essentially requires the
fourth-highest air quality value in 3 years, based on adjustments
for missing data, to be less than or equal to the level of the
standard for the standard to be met at an air quality monitoring site.
---------------------------------------------------------------------------

As discussed in the proposal, based on information presented in
sections IV. and V.I of the Staff Paper and the advice of CASAC, the
Administrator focused her consideration on the following alternatives:
(1) Revising the current 1-expected-exceedance form of the standard to

[[Page 38869]]

allow for multiple (up to five) expected exceedances per year, averaged
over 3 years. A multiple-exceedance form would be based on a less
extreme air quality statistic and, thus, would increase the stability
of the expected-exceedance form.
(2) Adopting a concentration-based statistic, such as the 3-year
average of the nth-highest daily maximum 8-hour average O₃
concentration, as an alternative to an expected exceedance statistic.
Air quality analyses presented in the Staff Paper indicate that the 3-
year averages of the annual third-, fourth-, and fifth-highest daily
maximum 8-hour concentrations would provide approximately the same
health protection as the 3-, 4-, and 5-expected-exceedance forms
averaged over the same period, respectively.
It was the consensus of the CASAC Panel that this range of
allowable exceedances (i.e., up to 5 exceedances), and the
consideration of comparable concentration-based forms, was appropriate.
Further, CASAC acknowledged that selecting from within this range of
alternative forms is a policy judgment, especially given the nature of
the health effects and the absence of a ``bright line'' that clearly
differentiates between acceptable and unacceptable risks within this
range. All 10 CASAC Panel members who expressed specific opinions on
the form of the standard favored one that would allow for multiple
exceedances (Wolff, 1995b).
In reaching her proposed decision on the form of an 8-hour standard
set at 0.08 ppm, the Administrator had to choose a specific form within
the range of up to 5 allowable exceedances or up to the comparable
fifth-highest concentration, and either an exceedance-based or a
concentration-based form. As discussed in the proposal, in considering
possible forms within the range of 1 to 5 exceedances (or their
concentration-based counterparts) the Administrator took into
consideration aggregate risk estimates for those health effects for
which quantitative risk analyses have been done; estimated exposures
associated with those effects for which no quantitative risk estimates
could be developed; and the magnitude of peak measurements of 8-hour
average O₃ concentrations, and the number of days on which
the level of the standard would likely be exceeded, based on an
analysis of historical air quality data (Freas, 1996). In considering
exposure and risk estimates available at the time of proposal for 1-
and 5-expected-exceedance forms, the Administrator noted that the level
of the standard is a more dominant factor in determining the degree of
exposure and risk reductions achieved, with the form being associated
with smaller differences in risk estimates within a continuum of risk.
In considering air quality comparisons for standards across the range
of forms considered, the Administrator focused in particular on the
extent to which alternative forms would limit the number of days in
which the level of the standard would be exceeded in areas that just
attain the standard²¹, and the magnitude of peak 8-hour
average O₃ concentrations²² that would occur in
such areas.²³ More specifically, the Administrator took into
consideration the percentage of monitoring sites just attaining an 8-
hour, 0.08 ppm standard that would have 8-hour peak O₃
concentrations above a benchmark level of 0.09 ppm. This benchmark
level is the upper end of the range of levels endorsed by CASAC for an
8-hour O₃ standard. The Administrator believes, given the
uncertainties associated with this kind of complex health decision,
that it is an appropriate goal to limit the percentages of areas
experiencing such daily peaks.
---------------------------------------------------------------------------

21 Areas that ``just attain the standard'' are defined as those
whose design value falls between 0.075 and 0.084 ppm.
22 Peak 8-hour average concentrations are defined in terms of
the fourth-highest daily maximum concentration in 3 years (i.e., the
design value for the current 1-expected-exceedance form of the standard).
23 The results of these air quality analyses are presented in
Freas (1996) and summarized in the proposal for the third- and
fifth-highest concentration forms and the 3- and 5-expected-
exceedance forms. Based on these considerations, and the air quality
comparisons in particular, the Administrator judged that the middle
of the range of exceedances considered, three expected exceedances,
or the comparable third-highest concentration, represented a
reasonable policy choice, and proposed the 3-year average of the
annual third-highest daily maximum 8-hour average O₃
concentrations as the form of the standard. In recognition of a
range of views on the degree of health protection that would be
appropriate, she also solicited comment on other concentration-based
forms, including the second-, fourth-, and fifth-highest
concentration forms.
---------------------------------------------------------------------------

In choosing to propose a concentration-based form, the
Administrator recognized the advantages of a concentration-based form
over an exceedance-based form. As discussed in the proposal, the
principal advantage of a concentration-based form is that it is more
directly related to the ambient O₃ concentrations that are
associated with health effects. That is, given that there is a
continuum of effects associated with exposures to varying levels of
O₃, the extent to which public health is affected by
exposure to ambient O₃ is related to the actual magnitude of
the O₃ concentration, not just whether the concentration is
above a specified level. With an exceedance-based form, days on which
the ambient O₃ concentration is well above the level of the
standard are given equal weight to those days on which the
O₃ concentration is just above the standard (i.e., each day
is counted as 1 exceedance), even though the public health impact on
the two days is significantly different. With a concentration-based
form, days on which higher O₃ concentrations occur would
weigh proportionally more than days with lower O₃
concentrations, since the actual concentrations are used directly in
determining whether the standard is attained. A concentration-based
form also has greater temporal stability than the expected-exceedance
form and, thus, would facilitate the development of more stable
implementation programs by the States.
As discussed above in Units II.A.3. and II.B.2., EPA completed and
made available for public comment supplemental exposure and risk
assessments subsequent to the proposal. These updated assessments,
which specifically analyzed the third- and fifth-highest concentration-
based forms, aid in comparing the differences in public health
protection among alternative concentration-based forms within the range
considered in the proposal for 8-hour, 0.08 ppm standards. Based on
these updated assessments, the Administrator again notes that the level
of the standard is the more dominant factor in determining the degree
of risk reduction achieved, with these alternative forms being
associated with much smaller differences in risk estimates within a
continuum of risk. For example, within the nine urban areas included in
the risk assessment, approximately 180,000 outdoor children would
experience moderate lung function (FEV₁) decreases
³ 15 percent upon attainment of an 8-hour, 0.08 ppm standard
with a third-highest concentration form, compared to approximately
200,000 outdoor children with a fourth-highest concentration form and
220,000 outdoor children with a fifth-highest concentration form.
The public comments include a large number that specifically
addressed the form of the standard. Those commenters who expressed
views on the form of the standard can be divided into three groups,
according to the level of 8-hour standard and the relative degree of
public health protection that the commenter supported. These groups
include: Commenters who supported an 8-hour, 0.08 ppm standard to provide
increased public health protection relative to the current standard;

[[Page 38870]]

commenters who supported either an 8-hour, 0.09 ppm standard, or simply
an 8-hour standard ``equivalent'' to the current standard; and
commenters who supported an 8-hour, 0.07 ppm standard to provide a
greater margin of safety than that afforded by the proposed standard.
The first group included many private citizens, some medical
professionals and researchers, and some States and local governmental
groups. While a number of commenters in the first group specifically
supported the proposed third-highest concentration form, generally for
the reasons presented in the proposal, others supported either a 1-
expected-exceedance form or a concentration-based form in the upper
part of the range (i.e., the fourth- or fifth-highest forms). The
second group of commenters, which included many local governmental
groups and private citizens, some States, and most commenters
representing businesses and industry associations, almost exclusively
supported a concentration-based form in general, and a form in the
upper part of the range (or above the range) in particular. In sharp
contrast, the third group of commenters, which included environmental
groups, many private citizens, and some medical professionals and
researchers, almost exclusively supported a 1-expected-exceedance form
in conjunction with an 8-hour, 0.07 ppm standard to provide the largest
margin of safety within the range of alternative standards considered.
To the extent that the second and third groups of commenters argued
for a different level than the Agency adopts today, the Administrator
disagrees with their comments for the reasons set forth in the
discussion of the standard level above in Unit II.B.2. To the extent
that they argued for more than 5 exceedances (or the concentration-
based equivalent), the Administrator disagrees with their views because
such forms fall outside the range recommended by CASAC and would
provide less public health protection than she deems appropriate. To
the extent that the second and third groups of commenters addressed the
merits of particular forms within the range of forms considered in the
proposal, they raised points similar to those raised by commenters in
the first group. These points are discussed below.
Among the commenters in the first group (i.e., those supporting an
8-hour, 0.08 ppm standard to provide increased public health
protection), many felt that there was no compelling basis for selecting
the third-highest rather than the fourth- or fifth-highest
concentration-based form. These commenters frequently quoted CASAC's
closure letter (Wolff, 1995b) as stating ``that there is no bright
line' which distinguishes any of the proposed standards (either the
level or the number of exceedances) as being significantly more
protective of public health,'' and that ``the selection of a specific
level and number of allowable exceedances is a policy judgment.'' In
general, these commenters did not give weight to the air quality
comparisons that were a major consideration in the Administrator's
decision to propose the third-highest concentration form. Some
commenters seem to view such air quality comparisons, particularly with
regard to pollutants such as O₃ that have no discernible
threshold of effects, as relating more to people's perceptions of how
well air pollution is controlled than to any objective measure of
actual risks to public health.
These commenters made a number of points in questioning the need to
specify an 8-hour, 0.08 ppm standard in terms of the third-highest
rather than the fourth- or fifth-highest concentration form. Many noted
that a change to an 8-hour averaging time in and of itself would
appropriately focus air quality management programs on prolonged
exposures of most concern. Further, many noted that a level of 0.08
ppm, regardless of the form within the range of forms considered in the
proposal, would provide significantly increased protection from
O₃-related risks to public health associated with acute
effects (i.e., those resulting from short-term and prolonged exposures)
for which they believe there is sufficient evidence to be used as a
basis for a standard at this time. Some of these commenters expressed
the view that the potential for chronic effects (i.e., those resulting
from long-term exposures) would be better addressed through continued
research, rather than by adding a greater margin of safety to a revised
standard based primarily on effects of short-term and prolonged
exposures. Many of these commenters recognized, as did EPA in the
proposal, that there is a continuum of risks associated with
O₃ exposures, that no standard can therefore be risk-free,
and that there are large uncertainties in any estimates of the degree
of protection associated with alternative forms. In general, these
commenters also noted that, for the same reasons, CASAC advised that
the selection of a form from within the range considered in the
proposal was a policy judgment, not one that could be decided on the
basis of science alone. In essence, these commenters argued that a more
restrictive form than the upper part of the range endorsed by CASAC is
not requisite to protect public health.
In contrast, other commenters in the first group (i.e., those
supporting an 8-hour, 0.08 ppm standard) supported either the proposed
third-highest or second-highest concentration form or a 1-expected-
exceedance form. These commenters generally gave greater weight to
limiting the magnitude of peak O₃ concentrations and the
number of days on which the standard level would be exceeded in areas
meeting such a standard, and, in some cases, to providing a greater
margin of safety to account for potential chronic effects. Such views
suggest that limiting the number of days on which the standard level
would be exceeded, for example, is an important factor in risk
communication and in the public's understanding of the degree to which
a standard protects people from exposures to O₃ that may
interfere with their ability to engage in normal activities or may
result in the need for increased medication or medical treatment,
especially for those individuals with asthma or other respiratory
diseases. As discussed above in this unit, although some of these
commenters felt that the third-highest concentration form would protect
public health while also providing increased stability, others
expressed concern that public health could be compromised by any form
that allowed for multiple exceedances of the standard. The advantages
of forms that allow for multiple exceedances, thus providing increased
stability as discussed in the proposal, and the views of the CASAC
panel members who expressed opinions, all of whom favored such forms,
were not given weight by commenters within this group who supported a
1-expected-exceedance form.
The Administrator has carefully reassessed the relative risks to
public health of specific forms within the range of the second- to
fifth-highest concentration forms or their exceedance-based
equivalents, taking into account the public comments summarized above,
and the advice from CASAC Panel members that the current form be
replaced by a form that allows multiple exceedances. In doing so, the
Administrator focused on the following considerations:
(1) The CASAC advised that concentration-based forms, within the
range considered up to the fifth-highest concentration form, are
appropriate for a health-based primary O₃ standard, and that
selection from within this range is a policy judgment that cannot be based

[[Page 38871]]

on science alone. This advice reflects CASAC's recognition that
O₃ exhibits a continuum of effects, such that there is no
discernible threshold above which public health protection requires
that no exposures be allowed or below which all risks to public health
can be avoided. The CASAC also recognized that a concentration-based
form would increase the stability of the standard by providing some
insulation from the impacts of extreme meteorological events (Wolff, 1995b).
(2) Estimates of the differences in risk to public health, for
those effects that could be considered quantitatively, within a range
of alternative forms from the second- to fifth-highest concentrations
(for an 8-hour, 0.08 ppm standard) are relatively small compared to the
differences between alternative levels. In other words, the choice of
level is substantially more important to the degree of public health
protection afforded by the standard than the choice of form from within
this range of forms.
(3) Measures that distinguish between the alternatives within the
range of the second- to fifth-highest forms, based on air quality
analyses, reflect considerations related to how some individuals
understand the degree to which an air quality standard protects public
health. These considerations are a distinct aspect of risk
communication to individual citizens even though the days on which
exceedances occur are accounted for in EPA's quantitative assessments
of risks to public health.
(4) To assess the comparative effect of all forms within the range
of the second- to fifth-highest concentration forms, EPA considered air
quality comparisons for all such forms (Freas, 1996). These comparisons
(based on 1993 to 1995 data) show that 8-hour, 0.08 ppm second- and
third-highest concentration standards are very similar in that each
standard limits the percent of monitoring sites that would experience
peak days above the benchmark level of 0.09 ppm to 1 percent of such
sites, and the number of days on which the standards would likely be
exceeded in the worst of 3 years would be no more than 6 and 7,
respectively. While less restrictive than either of these standards, an
8-hour, 0.08 ppm fourth-highest concentration standard would be
significantly more restrictive than a fifth-highest standard. For
example, the 8-hour, 0.08 ppm fourth-highest concentration standard
would limit the percent of monitoring sites that would experience peak
days about the benchmark level of 0.09 ppm to 8 percent of such sites,
and the number of days on which the standards would likely be exceeded
in the worst of 3 years would be no more than nine. In comparison, the
fifth-highest concentration standard would limit the percent of
monitoring sites that would experience peak days about the benchmark
level of 0.09 ppm to 17 percent of such sites, and the number of days
on which the standards would likely be exceeded in the worst of 3 years
would be no more than 11.
(5) The extent to which the alternatives within the range of the
second- to fifth-highest concentration forms provide protection against
the more serious, but less certain effects that have been associated
with exposure to O₃, including potential chronic effects,
cannot be quantitatively assessed at this time. Given that all such
forms would result in significant reductions in exposures to
O₃ at and above 0.08 ppm (the level where suggestive
evidence of such effects is available), any form within this range
would provide some margin of safety against these effects.
Based on these considerations, the available health effects
evidence, the quantitative assessments contained in the Criteria
Document, Staff Paper, and supplemental analyses and supporting
documents, and the range of views and judgments expressed in the public
comments on the appropriate form, the Administrator has reconsidered
the form of the standard that is requisite to protect public health
with an adequate margin of safety. As an initial matter, the
Administrator has decided to adopt a concentration-based form which
allows for more than one exceedance. While the Adminstrator understands
the views of the many citizens who are concerned about a standard that
would allow for multiple days on which the level of the standard may be
exceeded, the Administrator concludes that such concerns are more
relevant for pollutants that exhibit a clear threshold of effects than
for pollutants such as O₃ that exhibit a continuum of
effects. The Administrator believes that the public health risks
associated with such pollutants can be appropriately addressed through
a standard that allows for multiple exceedances to provide increased
stability, but that also significantly limits both the number of days
on which the level may be exceeded and the magnitude of such
exceedances. This approach recognizes that exposures associated with
such exceedances are already reflected in the exposure and risk

ppm level for the primary O₃ standard, and that increased
stability in the standard is important to avoid disruption to ongoing
control programs, and thus to maintain ongoing public health protection.
Having again concluded that a concentration-based O₃
standard that allows for multiple exceedances is appropriate, the
Administrator considered the extent to which the form of an 8-hour
standard should be selected so as to provide a margin of safety against
possible, but uncertain chronic effects. The Administrator carefully
considered the views of the many commenters who emphasized the
uncertainties in the evidence, primarily from laboratory animal
studies, that was available in this review of the criteria and
standards to relate long-term exposures to ambient levels of
O₃ to possible chronic effects in humans. These commenters,
as did CASAC, advised that further research into potential chronic
effects in humans should be continued, and the results considered in
the next review of the O₃ standard. The Administrator is
persuaded that the difference between the margins of safety for these
potential chronic effects afforded by the alternatives within the range
of the second- to fifth-highest concentration forms is not well enough
understood at this time to use as the basis for choosing the most
restrictive forms (i.e., the second- or third-highest concentration
form). On the other hand, the Administrator also judges that the
relatively large percentage of sites that would experience
O₃ peaks above a benchmark level of 0.09 ppm even when
attaining a fifth-highest concentration standard and the number of days
on which the level of a fifth-highest concentration standard may be
exceeded argue against choosing that form, which is the least
restrictive within the range considered.
For the reasons outlined above, and taking into account the range
of views in the public comments, the Administrator concludes that an
intermediate form, the fourth-highest concentration form, would serve
to appropriately balance these public health considerations in
conjunction with the 8-hour averaging time and 0.08 ppm level selected,
as discussed above in Units II.B.1. and II.B.2., that are of primary
importance in determining the degree of public health protection
afforded by the standard. In addition, the Administrator notes that
based on an analysis of air quality in counties that would attain an 8-
hour, 0.08 ppm fourth-highest concentration standard (based on 1993-
1995 data), over 99 percent of such counties would be expected to have
four or fewer days on which the level of the standard is exceeded in an
average year (Freas,

[[Page 38872]]

1997). This number of exceedances is clearly within the range of
multiple exceedances that CASAC judged to be appropriate for a health-
based primary O₃ standard. Thus, in the Administrator's
judgment, based on the information currently available, an 8-hour, 0.08
ppm standard with a fourth-highest concentration form will protect
public health with an adequate margin of safety.
In the proposal, which maintained the current approach of using air
quality data from the monitor measuring the highest O₃
concentrations in an area to determine whether the primary standard for
O₃ is attained, the Administrator solicited comment on the
alternative of using some form of averaging across monitors. As
discussed in the proposal, EPA recognized that during the review of the
Staff Paper, a number of commenters suggested that averaging across
monitors might be appropriate to increase the degree to which
monitoring data used in determining attainment of the standard reflects
population exposure and aggregate population health risk. Further,
these commenters suggested that averaging data from multiple monitors
in an area would produce a more stable measure of air quality and would
take into account broader population exposure patterns across an area
than would the current approach of considering data from each monitor
independently.
The Administrator did not propose the use of spatial averaging
because of concerns outlined in the proposal including: The difficulty
in determining an appropriate level for a spatially averaged primary
standard given that the bulk of the human health effects evidence
supporting a decision on an appropriate O₃ standard is based
on controlled human exposure studies that relate known O₃
exposures directly to responses in individuals; and questions as to
whether adequate health protection would be provided to individuals
within the populations that live or work in communities that routinely
experience higher O₃ concentrations within a broad
metropolitan area.
To address these two concerns, it would be necessary to define
criteria for geographic locations or communities (e.g., spatial
averaging zones) within which the use of spatially averaged
O₃ data would be acceptable. Such criteria would be
important since O₃ air quality concentrations can vary
significantly across most urban areas. The lowest concentrations
typically occur in the urban center and in locations near O₃
precursor sources, mid-range concentrations in neighborhoods and
locations surrounding the urban center, and peak concentrations are
typically measured downwind along the outermost suburban regions of the
urban area. Also, the location of residences, schools, parks, and other
places where individuals might be exposed more frequently to ambient
O₃ concentrations of concern would be an important
consideration. Unless the O₃ concentration gradients within
each spatial averaging zone were relatively homogeneous, there may be
significant numbers of sensitive individuals exposed to high
O₃ concentrations in areas where the spatial average
indicates that the overall air quality is acceptable.
In the proposal, EPA also noted the need to help State and local
governments devise different O₃ monitoring networks by
revising relevant regulations and guidance, should spatial averaging be
adopted. This would likely involve defining general criteria for
monitoring network design, siting, and spatial averaging zones in
nationally implementable terms, with case-by-case evaluation of each
monitoring network. The EPA recognized that this activity would place
additional burdens on State and local air quality management districts.
In soliciting comment on whether it would be desirable to adopt
some form of spatial air quality averaging for O_3, the
Administrator also solicited comment on specific alternative approaches
that could be used to address the issues of concern. In particular, the
Administrator was interested in analyses that inform questions about
monitoring network design, siting requirements, and approaches for
specification of spatial averaging zones; the distribution of public
health protection that would result from such alternative approaches;
and the extent to which the level of the standard would need to be
adjusted, if any, to provide public health protection consistent with
the level of protection contemplated in the proposal.
The EPA received many comments on the subject of using spatially
averaged data to determine when the primary standard for O₃
is attained. Commenters from business and industry associations
frequently supported the use of spatially averaged data, as did many
local governments and a small number of States, principally because it
would provide a more stable air quality indicator and would better
represent population exposure and risk. Some of these commenters felt
that the use of spatial averaging would be consistent with the use of
risk assessment as a policy tool for standard setting. Many of these
commenters agreed that the heterogeneity of O₃
concentrations across geographic areas would need to be addressed by
network design, with a few expressing the opinion that this would not
be an insurmountable problem given that there is continual movement of
monitors within existing networks. Some commenters suggested averaging
approaches that included the use of population weighting of monitored
data, and some supported the use of a public health information system
to allow individuals residing in ``hot spot'' areas to reduce their
exposures to O₃ concentrations of concern.
In contrast, environmental associations, public health
professionals, most States, and many individuals voiced strong concerns
that the use of spatially averaged data would routinely allow
individuals who live or work in communities with consistently higher
O₃ levels than those occurring across the broader urban area
to be exposed to concentrations of concern. Many of these commenters
raised the issue of environmental equity, expressing the view that
communities with consistently higher O₃ concentrations
typically are composed predominantly of individuals of lower
socioeconomic status, or are composed of a predominantly minority
population. The EPA notes that this view is not consistent with the air
quality data discussed earlier in this unit, in that O₃
concentrations are typically lower in urban centers than in locations
surrounding or downwind of urban centers. Some commenters also raised
concerns about the complexity and burdens associated with redesigning
existing monitoring networks.
Taking into account the comments received, the Administrator does
not find that the issues of concern, as outlined in the proposal and
above, have been adequately addressed in this review of the
O₃ standard. In particular, while EPA strongly agrees with
the importance of public health advisories in addition to adequately
protective standards, relying on the use of public health advisories to
provide information for at-risk populations who may consistently be
exposed to localized O₃ concentrations of concern is
considered by the Administrator to be an insufficient approach to
protecting public health with an adequate margin of safety. Further,
the suggested use of population weighting of monitored data may, in
many cases, be insufficiently sensitive to local O₃
variations to ensure adequate protection of these populations from
localized O₃ concentrations. Thus, the revised O₃
standard will maintain the current

[[Page 38873]]

approach of using air quality data from the monitor measuring the
highest O₃ concentrations in an area to determine whether
the standard is attained within an area.
The EPA has also considered spatial averaging in the context of the
decision to revise the PM NAAQS, in part, by adopting a form of an
annual standard for fine particles (i.e., PM_2.5) that allows
for spatial averaging within appropriate criteria. It is important to
note that different considerations apply in these two cases. One
principal difference is the nature of the health effects evidence for
O₃ and PM_2.5. When considering averaging
approaches for O₃, it should be recognized that much of the
human health effects evidence supporting the O₃ standard is
based on controlled human exposure studies that relate individual
O₃ exposures directly to responses in individuals, whereas
the health effects evidence supporting the PM_2.5 standards
is from epidemiological studies relating community measures of
PM_2.5 concentrations to population-wide responses. Thus,
information available for determining an appropriate level of a
standard in these two cases is predominantly individual-oriented in the
case of O₃ and community-oriented in the case of
PM_2.5. As a consequence, additional research and exposure
and risk assessments beyond those available in this review would be
necessary to provide a basis for further consideration of a spatially
averaged standard for O₃. The EPA will continue to explore
this approach.
Another important difference between the O₃ and PM
standards is that the suite of annual and 24-hour PM_2.5
standards permits the use of the 24-hour PM_2.5 standard,
which would not be spatially averaged, as a backstop to control
localized ``hot spots,'' whereas a single O₃ standard does
not allow for such a dual approach. Also, EPA notes that the existence
of an established, extensive O₃ monitoring network would
require substantial redesigning and relocation of monitors for the
purpose of spatial averaging, in contrast to the current absence of
such a network for PM_2.5 which can be newly designed to
address community-oriented monitoring from the outset.
As discussed in the proposal, the Administrator recognizes that no
standard within the range of levels and forms considered in this
review, including the selected standard, is risk free, due to the
continuum of risk likely posed by exposures to ambient O₃
potentially down to background levels. Accordingly, consistent with
CASAC advice, the Administrator solicited comment in the proposal on
elements of an enhanced public health advisory system. The
Administrator believes that the information that could be made
available through such a public health advisory system would be
particularly useful to extremely sensitive individuals in making
personal decisions about avoiding exposures with the potential to cause
transient adverse effects on days when 8-hour average O₃
concentrations are predicted to be at or near the level of the
standard. Approaches to developing an enhanced system, and comments
received on such approaches, are discussed in Unit II.C. of this preamble.
4. Final decision on the primary standard. After carefully
considering the information presented in the Criteria Document and the
Staff Paper, the advice and recommendations of CASAC, public comments
received on the proposal, and for the reasons discussed above, the
Administrator is replacing the existing 1-hour, 0.12 ppm primary
standard with a new 8-hour, 0.08 ppm primary standard. The new 8-hour
standard will become effective September 16, 1997.
The 8-hour, 0.08 ppm primary standard will be met at an ambient air
quality monitoring site when the 3-year average of the annual fourth-
highest daily maximum 8-hour average O₃ concentration is
less than or equal to 0.08 ppm. Data handling conventions are specified
in a new Appendix I to 40 CFR part 50 as discussed in Unit VI below.
In the proposal, EPA proposed that the revocation of the existing
1-hour O₃ standard be delayed for certain purposes until EPA
had approved State Implementation Plans to implement the new 8-hour
O₃ standard. EPA had proposed continuing the applicability
of the 1-hour standard in this way in order to facilitate continuity in
public health protection during the transition to a new standard. (See
Memorandum from John S. Seitz to Mary D. Nichols, November 20, 1996;
Docket No. A-95-58, item II-B-3.) Also, at the time of the proposal of
the new O₃ standard, EPA had proposed an interpretation of
the Act in the proposed Interim Implementation Policy (61 FR 65764,
December 13, 1996) under which the provisions of subpart 2 of part D of
Title I of the Act would not apply to existing O₃
nonattainment areas once a new O₃ standard becomes effective.
In light of comments received regarding the interpretation proposed
in the Interim Implementation Policy, EPA has reconsidered that
interpretation and now believes that the Act should be interpreted such
that the provisions of subpart 2 continue to apply to O₃
nonattainment areas for purposes of achieving attainment of the current
1-hour standard. As a consequence, the provisions of subpart 2, which
govern implementation of the 1-hour O₃ standard in
O₃ nonattainment areas, will continue to apply as a matter
of law for so long as an area is not attaining the 1-hour standard.
Once an area attains that standard, however, the purpose of the
provisions of subpart 2 will have been achieved and those provisions
will no longer apply. However, the provisions of subpart 1 of part D of
Title I of the Act would apply to the implementation of the new 8-hour
O₃ standards.
To facilitate the implementation of those provisions and to ensure
a smooth transition to the implementation of the new 8-hour standard,
the 1-hour standard should remain applicable to areas that are not
attaining the 1-hour standard. Therefore, the 1-hour standard will
remain applicable to an area until EPA determines that it has attained
the 1-hour standard, at which point the 1-hour standard will no longer
apply to that area.

C. Communication of Public Health Information

Information on the public health implications of ambient
concentrations of criteria pollutants is currently made available
primarily through two EPA programs. The first program is designed to
prevent ambient pollutant concentrations from reaching the significant
harm level (i.e., an exposure level that constitutes an imminent and
substantial endangerment to public health). The second program is the
Pollutant Standards Index (PSI),²⁴ which is a health
advisory system. The proposal focused on the potentially expanded use
of the PSI in regard to allowing sensitive individuals to reduce their
risk of exposure. Currently, EPA and local officials use the PSI as a
public information tool to advise the public about the general health
effects associated with different pollution levels and to describe
whatever precautionary steps may need to be taken if air pollution
levels rise into the unhealthful range. By notifying the public when a
PSI value exceeds 100 (which corresponds to the NAAQS for each criteria
pollutant)²⁵, citizens are given the opportunity to take
appropriate steps to avoid exposures of concern. This use of the PSI
could be expanded to provide more specific health information for
O₃ concentrations

[[Page 38874]]

close to the level of the primary standard. Given the continuum of
risks associated with exposure to O₃, this information,
while perhaps of interest to all citizens, would be particularly useful
to those individuals who are extremely sensitive to relatively low
O₃ concentrations. As an example, the proposal mentioned the
possibility of expanding the PSI to include two new descriptive
categories in the Index, one including concentrations within a range
somewhat below the level of the new primary standard (with a possible
descriptor of ``moderately good''), the other including concentrations
within a range somewhat above the level of the standard (with a
possible descriptor of ``moderately unhealthful''). Such an approach
could better reflect the increased understanding of health effects
associated with O₃ exposure developed during this review,
and would be consistent with the recommendation of a number of CASAC
panel members ``that an expanded air pollution warning system be
initiated so that sensitive individuals can take appropriate 'exposure
avoidance' behavior'' (Wolff, 1995b).
---------------------------------------------------------------------------

24 For a discussion of these programs, see the proposal.
25 Currently, a PSI value of 100 for O₃ corresponds
to an ambient concentration of 0.12 ppm, averaged over 1 hour.
---------------------------------------------------------------------------

The proposal also discussed the use of forecasting in combination
with this expanded use of the PSI. For a health advisory system to be
effective, citizens need to be notified as early as possible to be able
to avoid exposures of concern. The notice indicated that if the current
1-hour primary NAAQS for O₃ is replaced with an 8-hour
standard, there would clearly be increased value in using forecasted
O₃ concentrations in providing cautionary statements to the
public. Currently, when a health advisory indicates that the 1-hour
O₃ PSI value of 100 has been exceeded, citizens generally
have time to avoid exposures of concern because O₃ levels
tend to remain elevated for several hours during the day. With the new
8-hour standard, however, this would likely not be the case, since by
the time a PSI value is reported, the potential for prolonged exposures
of concern would likely have passed for that day. Forecasting 8-hour
maximum O₃ concentrations would facilitate the risk-
reduction function of the PSI by giving citizens more time to limit or
avoid exposures of concern.
The EPA did not formally propose revisions to the PSI in the
proposal. Instead, the Administrator requested comment, and indicated
that the Agency might propose revisions to the PSI in conjunction with
future proposals associated with the implementation of a revised NAAQS.
The EPA received a large number of comments from a wide variety of
commenters on the usefulness of both an expanded health advisory system
and the forecasting of 8-hour ambient O₃ concentrations.
Commenters representing State and local agencies, business and industry
associations, as well as environmental associations overwhelmingly
endorsed the use of an expanded public health advisory system and many
noted the importance of forecasting 8-hour O₃ concentrations
in conjunction with the PSI, while recognizing a number of issues that
would need to be addressed.
Comments from environmental associations endorsed increasing the
specificity of warnings with regard to the health effects that could
occur as a result of exposure, and noted that citizens are capable of
dealing with complex information. These commenters also took exception
to describing O₃ levels around the level of the standard
that have been shown to result in decreased lung function and increased
respiratory symptoms, as ``moderately good,'' stating that this
descriptor is misleading and might not be heeded by people who could,
if they fully understood the nature of the health risk, take action to
minimize their exposures. Other commenters felt that the descriptors
``moderately good'' and ``moderately unhealthful'' were unnecessarily
confusing.
Industry commenters were uniformly supportive of enhancing the risk
reduction function of the PSI by issuing health advisories with
specific health information at and above the level of the standard.
Several industry commenters also recommended that the function of the
PSI be combined with the function of an O₃ action system,
which would recommend voluntary actions to reduce ambient O₃
concentrations when the level of the standard is forecasted to be
exceeded. This would result in a system that not only could provide
accurate health effects information specific to the members of the
population likely to experience effects, but also could help prevent
exposures to levels of O₃ at or above the level of the standard.
Commenters from State and local air pollution control authorities
strongly endorsed expanding the use of the PSI and the utilization of
forecasted 8-hour O₃ concentrations. These commenters
encouraged EPA to develop any such approaches to revise the PSI in
consultation with State and local agencies, specifically in the areas
of sharing real-time O₃ monitoring data among neighboring
States, risk communication with the public, and coordination of a
national program. States also expressed the need for flexibility in the
implementation of such approaches and for guidance from EPA on
technical aspects such as forecasting.
The EPA will take all of these comments into consideration when
developing a proposal to revise the PSI (40 CFR 58.50) for O₃. The
EPA plans to propose these revisions, as well as revisions to the
significant harm level program (40 CFR 51.16), at a later date.

III. Rationale for the Secondary O₃ Standard

A. Introduction

1. Overview. This notice presents the Administrator's final
decision regarding the need to revise the current secondary
O₃ standard, and more specifically, to replace the existing
1-hour, 0.12 ppm O₃ secondary NAAQS with a secondary
standard equal in form, level, and averaging time to the new 8-hour,
0.08 ppm primary standard. This decision is based on a thorough review
of the scientific information on vegetation effects associated with
exposure to ambient levels of O₃ as assessed in the Criteria
Document. This decision also takes into account:
(1) Staff Paper assessments of the most policy-relevant information
in the Criteria Document and staff analyses of air quality, vegetation
exposure and risk, and economic values presented in the Staff Paper,
upon which staff recommendations for a new O₃ secondary
standard were based.
(2) Consideration of the degree of protection to vegetation
potentially afforded by the new 8-hour, 0.08 ppm primary standard
compared to alternative secondary standards.
(3) CASAC advice and recommendations as reflected in discussion of
drafts of the Criteria Document and Staff Paper at public meetings, in
separate written comments, and in CASAC's letter to the Administrator
(Wolff, 1996).
(4) Public comments received during development of these documents
either in conjunction with CASAC meetings or separately.
(5) Extensive public comments received on the proposed decision
regarding the secondary O₃ standard.
After taking this information into account and for the reasons
discussed in this Unit, the Administrator concludes that revisions to
the current secondary standard are appropriate at this time to provide
increased protection against adverse effects to public welfare, and
that it is appropriate to set the new secondary standard identical to
the new primary standard.
This review has focused on O₃ effects on vegetation
since these public welfare effects are of most concern at O₃

[[Page 38875]]

concentrations typically occurring in the United States. By affecting
commercial crops and natural vegetation, O₃ may also
indirectly affect natural ecosystem components such as soils, water,
animals, and wildlife. Based on the scientific literature assessed in
the Criteria Document, the Administrator believes it is reasonable to
conclude that a secondary standard that protects the public welfare
categories of commercial crops and natural vegetation from known or
anticipated adverse effects would also afford increased protection to
these other related public welfare categories. With regard to
O₃ effects on manmade materials and deterioration of
property, the scientific literature assessed in the Criteria Document
contains little new information since the last review. Accordingly, EPA
again concludes for the reasons set forth in 1993 (58 FR 13008, March
9, 1993) that O₃-related effects on materials do not provide
a basis for selecting an averaging time and level for a secondary
standard. In addition, since the effects of O₃ on personal
comfort and well-being (e.g., nose and throat irritation, chest
discomfort, and cough) have been accounted for in the review of the
primary standard, these effects are not considered in this review of
the secondary standard.
The vegetation effects information, exposure and risk assessment,
and economic analyses presented in the Staff Paper and proposal are
briefly outlined in the remainder of Unit III.A. of this preamble. The
key issues raised in public comments with regard to: Whether revisions
to the current secondary standard are requisite to protect public
welfare from adverse effects and the specific elements of a revised
secondary standard are discussed in Unit III.B. along with the
Administrator's rationale for concluding that it is appropriate to
revise the current secondary standard to be identical to the new
primary standard.
2. Vegetation effects information. Exposures to O₃ have
been associated quantitatively and qualitatively with a wide range of
vegetation effects such as visible foliar injury, growth reductions and
yield loss in annual crops, growth reductions in tree seedlings and
mature trees, and effects that can have impacts at the forest stand and
ecosystem level. Summarized below are key findings for each of the
above effects categories that are discussed in more detail in the
Criteria Document, Staff Paper, and proposal.
Visible foliar injury can represent a direct loss of the intended
use of the plant, ranging from reduced yield and/or marketability for
some agricultural species to impairment of the aesthetic value of urban
ornamental species. On a larger scale, foliar injury is occurring on
native vegetation in national parks, forests, and wilderness areas, and
may be degrading the aesthetic quality of the natural landscape, a
resource important to public welfare.
Ozone can interfere with carbon gain (photosynthesis) and
allocation of carbon with or without the presence of visible foliar
injury. As a result of decreased carbohydrate availability, remaining
carbohydrates may be allocated to sites of injured tissue or employed
in other repair or compensatory processes, thus reducing the
carbohydrates available for plant growth and/or yield. Growth and yield
effects of O₃ have been well documented for numerous
species, including commodity crops, fruits and vegetables, and
seedlings of both coniferous and deciduous tree species.
Due to a number of differences between seedlings and mature trees
in their responses to O₃ exposures, data from tree seedling
studies cannot, at this time, be extrapolated to quantify responses to
O₃ in mature trees. However, long-term observational studies
of mature trees have shown growth reductions in the presence of
elevated O₃ concentrations. Where these growth reductions
are not attributed to O₃ alone, due to the presence of many
other environmental variables, it has been reported that O₃
is a significant contributor that potentially exacerbates the effects
of other environmental stresses (e.g., pests). In addition, studies
show that sensitivity to O₃ with respect to visible foliar
injury and growth and yield effects can vary significantly within and
between species for both crops and trees.
Growth reductions can indicate that plant vigor is being
compromised such that the plant can no longer compete effectively for
essential nutrients, water, light, and space. When many O₃-
sensitive individuals make up a population, the whole population may be
affected. Changes occurring within sensitive populations, or stands, if
they are severe enough, ultimately can change community and ecosystem
structure. Structural changes that alter the ecosystem functions of
energy flow and nutrient cycling can alter ecosystem succession.
In the CASAC closure letter, all CASAC panel members agreed that
``damage is occurring to vegetation and natural resources at
concentrations below the present 1-hour national ambient air quality
standard (NAAQS) of 0.12 ppm,'' and the vegetation experts agreed that
``plants appear to be more sensitive to O₃ than humans''
(Wolff, 1996). Further, the CASAC panel agreed ``that a secondary
NAAQS, more stringent than the present primary standard, was necessary
to protect vegetation from O₃'' (Wolff, 1996). The
Administrator concurred in the proposal with the unanimous view of
CASAC that the current standard of 0.12 ppm, 1-hour average, does not
provide adequate protection to vegetation from the adverse effects of
O₃, based on the following specific observations that were
taken from key studies and other biological effects information
reported in the O₃ Criteria Document and Staff Paper:
(1) O₃ concentrations ³ 0.10 ppm can be
phytotoxic to a large number of plant species, and can produce acute
foliar injury responses and reduced crop yield and biomass production.
(2) O₃ concentrations within the range of 0.05 to 0.10
ppm have the potential over a longer duration of creating chronic
stress on vegetation that can result in reduced plant growth and yield,
shifts in competitive advantages in mixed populations, decreased vigor
leading to diminished resistance to pest and pathogens, and injury from
other environmental stresses. Some sensitive species can experience
foliar injury and growth and yield effects even when concentrations
never exceed 0.08 ppm.
The Administrator further concluded that the available scientific
information supports the conclusion that a cumulative seasonal exposure
index, such as the proposed SUM06 index,²⁶ is more
biologically relevant than a single event or mean index.
---------------------------------------------------------------------------

26 The SUM06 exposure index cumulates over a given time period
and diurnal window all hourly O₃ concentrations greater
than or equal to 0.06 ppm.
---------------------------------------------------------------------------

3. Vegetation exposure and risk analyses. In reaching a judgment in
the proposal as to a standard requisite to protect crops and vegetation
against the adverse effects of O₃, the Administrator took
into account several additional considerations including the extent of
exposure of O₃-sensitive species, potential risks of adverse
effects to such species, and monetized and nonmonetized categories of
increased vegetation protection associated with reductions in
O₃ exposures. In so doing, the Administrator recognized that
markedly improved air quality, and thus significant reductions in
O₃ exposures would result from attainment of the alternative
0.08 ppm, 8-hour primary standards within the range of 1- and 5-
expected exceedance forms. Thus, as a matter of policy, the Agency
estimated the increased protection from O₃-related

[[Page 38876]]

effects on vegetation associated with attainment of alternative 8-hour,
0.08 ppm primary standards, and then considered the incremental
protection associated with attainment of a seasonal secondary standard.
The ability of EPA to characterize O₃ air quality in
rural and remote sites was limited by the available rural O₃
monitoring network. Therefore, EPA conducted national analyses using
geographic information systems (GIS) and data from existing air quality
monitoring sites to estimate seasonal O₃ air quality for the
year 1990, in terms of the 3-month, 12-hour, SUM06 exposure index. The
year 1990 was selected because it was a fairly typical year in terms of
O₃ air quality. The estimated 1990 air quality was then used
as a baseline from which to roll back O₃ concentrations to
project O₃ air quality that would be expected to occur when
alternative standards were just attained.
The regulatory scenarios examined included just attaining the
existing 1-hour secondary standard, alternative 8-hour primary
standards in the range of 0.07 to 0.09 ppm, including standards set at
0.08 ppm, with 1- and 5-expected-exceedance forms, and a range of
seasonal standards using the SUM06 index, based on a single year of
data. Estimates of air quality associated with alternative 8-hour
primary standards with 1- and 5-expected-exceedance forms were used to
roughly bound air quality estimates for 8-hour standards with
concentration-based forms ranging from the annual second- to the fifth-
highest concentration-based forms, and including the proposed third-
highest concentration-based form.
By comparing these projected air quality scenarios for alternative
standards with maps showing the growing regions for O₃-
sensitive crops and tree seedling species, estimates of exposures of
concern and risks of adverse effects for various species were developed
for alternative standards. Taking into account the body of information
concerning O₃ effects on vegetation, as presented in the
Criteria Document and Staff Paper and summarized in the proposal, EPA
considered both quantifiable risks (when exposure-response functions
were available) as well as those risks that could only be qualitatively
characterized.
The Administrator concluded in the proposal that attaining a 8-
hour, 0.08 ppm primary standard within the range of forms under
consideration would provide substantially improved protection of
vegetation from seasonal O₃ exposures of concern. The
Administrator recognized, however, that some areas may continue to have
elevated seasonal exposures, including forested park lands and other
natural areas and Class I areas that are federally mandated to preserve
certain air quality related values.
In its discussions of uncertainties, described in the proposal, the
CASAC Panel members expressed concerns about the use of the GIS
methodology to project national O₃ air quality and exposures
of O₃-sensitive species. As is the case with other analytic
methods (e.g., Krieging, inverse distance weighting), the GIS
methodology contains numerous assumptions and uncertainties, and
incorporates various databases each with their own set of
uncertainties. As noted in the Staff Paper and proposal, the EPA and
CASAC recognized that the uncertainties in exposure and risk estimates
derived from the GIS methodology are large and unquantifiable, but that
the method provides useful information that is appropriate to consider
in comparing the relative protection afforded by alternative standards.
Further, EPA noted in the Staff Paper and proposal that the GIS-
generated air quality estimates compare reasonably well with the
limited available O₃ monitoring data. In taking the results
from these analyses into account, the Administrator recognized these
inherent limitations and primarily considered the comparative results
in assessing the degree of protection afforded by alternative standards.
While the analyses discussed above indicated that an 8-hour, 0.08
ppm primary standard within the range of alternatives considered, would
provide increased protection for commercial and natural vegetation, it
remained uncertain as to the extent to which air quality improvements
designed to reduce 8-hour O₃ concentrations would reduce
O₃ exposures measured by a seasonal SUM06 index. To further
explore this question, EPA also examined the design values for
alternative 8-hour, 0.08 ppm standards, within the range of 1- and 5-
expected exceedances, averaged over 3 years, and a 3-month, 12-hour
SUM06 standard for 581 counties (those having sufficient monitoring
data for the period 1991 - 1993). As discussed in the Staff Paper and
proposal, this analysis revealed that almost all areas that are within
or above a SUM06 range of 25-38 ppm-hours would also have an 8-hour
daily maximum design value of greater than 0.08 ppm. Thus, in those
areas in which air quality monitoring is being conducted, areas that
would likely be of most concern for effects on vegetation, as measured
by the SUM06 exposure index, would also be addressed by an 8-hour
primary standard set at a 0.08 ppm level.
4. Monetized estimates of vegetation protection. As discussed in
section VII.F. of the Staff Paper and in the proposal, EPA developed
monetized estimates of increased protection associated with several
alternative standards for economically important commodity crops
nation-wide²⁷ and for fruit and vegetable crops in
California.²⁸ These analyses were based on the GIS-generated
projections of O₃ air quality for various alternative
standards. Monetized estimates of increased protection could not be
developed for other important categories of vegetation, such as urban
ornamentals, Class I areas, and commercial and other forests because of
a lack of available concentration-response functions and appropriate
economic valuation models. The available data suggested, however, that
reductions in ambient O₃ concentrations resulting from
attainment of alternative standards would confer increased protection
for these categories as well by reducing biomass loss, protecting
functional, aesthetic, and existing values, and by preserving
biodiversity and native habitats.
---------------------------------------------------------------------------

27 Including 15 species, representing approximately 75% of the
U.S. sales of agricultural crops, evaluated in the National Crop
Loss Assessment Network (NCLAN) studies undertaken in the early to
mid-1980's, which provide the largest, most uniform database on the
effects of O₃ on agricultural crop species.
28 These fruit and vegetable crops constitute approximately 50%
of the Nation's fruits and vegetable markets.
---------------------------------------------------------------------------

As summarized in the proposal, most of the monetized estimates of
increased protection would accrue from attainment of an 8-hour, 0.08
ppm primary standard, with a smaller incremental improvement obtained
by the addition of a seasonal secondary standard. In contrast, the
incremental protection obtained from the addition of a seasonal
secondary standard would be considerably more significant when compared
to an alternative 8-hour primary standard at a level of 0.09 ppm.

B. Need for Revision of the Current Secondary Standard

Based on the above considerations and the rationale in the
proposal, the Administrator proposed and sought comment on two
alternative standards, either of which in her judgment would be
appropriate to protect public welfare from known or anticipated adverse
effects given the available scientific knowledge. The two alternatives
were setting the revised secondary standard

[[Page 38877]]

identical to the proposed 8-hour, 0.08 ppm primary standard, or
establishing a 3-month, 12-hour, SUM06 seasonal secondary standard at
the level of 25 ppm-hours. The Administrator recognized that it would
be a reasonable policy choice to set the revised secondary standard
identical to an 0.08, 8-hour ppm primary standard, but also recognized
that a SUM06 seasonal standard is more biologically relevant and,
therefore, was also appropriate to consider.
In reaching her final decision on a revised secondary standard, the
Administrator has taken into account several factors. First, she again
concludes based on information presented in the Criteria Document and
Staff Paper, and summarized in the proposal and in this preamble, that
the existing secondary standard does not provide adequate protection
for vegetation against the adverse welfare effects of O₃.
Second, she has considered the comments made by the CASAC Panel
members during their reviews of these documents and in CASAC's closure
letter, ``that a secondary NAAQS, more stringent than the present
primary standard, was necessary to protect vegetation from
O₃'' (Wolff, 1996). These statements provide strong support
to the Administrator's judgment that the body of scientific evidence on
O₃ effects on vegetation provides sufficient and compelling
evidence that the current secondary standard is not adequately
protective and should be revised.
Third, the Administrator recognizes that significant uncertainties
remain with respect to exposure dynamics, air quality relationships,
and estimates of increased vegetation protection which are important
factors in selecting an appropriate secondary standard, as described
more fully in the Criteria Document, Staff Paper and proposal. The
CASAC closure letter highlighted key uncertainties that hampered the
Panel's ability to make any recommendations as to an appropriate form
or level for a secondary standard that would be protective against
adverse effects on vegetation from exposure to ambient levels of
O₃. The Panel stated that ``agreement on the level and form
of such a standard is still elusive'' and ``***there remain important
limitations to our understanding of the extent of the response of
vegetation to O₃ under field conditions'' (Wolff, 1996).
These uncertainties are largely a result of inadequate rural and remote
O₃ air quality data that would allow with greater certainty
determination of the relationships between O₃-related
effects being observed in the field and ambient O₃
exposures. Nevertheless, the alternative standards proposed by the
Administrator are consistent with the range of views expressed by the
CASAC panel members, and CASAC recognized that choosing between the two
alternatives is a policy decision that cannot be based solely on
science (Wolff, 1996).
Fourth, the Administrator recognized that just attaining the 8-
hour, 0.08 ppm, 1- and 5-expected exceedance alternatives results in
markedly improved air quality when compared to just attaining the
existing secondary standard, with only slight improvements associated
with going from a 5- to 1-expected exceedance form.
Fifth, the Administrator has carefully considered the information
and views provided in the public comments. Though these comments
yielded no new scientific information relevant to choosing between the
two alternative proposed standards, many commenters repeated the
CASAC's concerns over the significant uncertainties remaining in the
database. Many of these commenters expressed the view that EPA should
wait to set a seasonal secondary standard until better rural air
quality data were available, which would allow for better
characterization of the magnitude of improvements in public welfare
protection likely to be afforded by such a standard compared to a
revised primary standard.
In sharp contrast, other commenters expressed the view that the
available data were sufficient to demonstrate a need to set a seasonal
secondary standard to protect vegetation against the adverse effects of
O₃, and many such commenters recommended the proposed SUM06
form for such a standard. A significant number of these commenters also
made recommendations on the appropriate level for a seasonal SUM06,
generally recommending levels lower than the proposed 25 ppm-hours,
ranging from 8 to 20 ppm-hours. The key source frequently cited in
support of these recommendations is an article by Heck and Cowling
(1997) which summarizes the outcome of a consensus-building workshop
sponsored by the Southern Oxidant Study group on the secondary standard
held in January 1996.
This workshop was attended by 16 scientists with backgrounds in
agricultural, managed forest, natural systems, and air quality, all of
whom are leaders in their fields and whose research formed the basis of
much of the research examined in the Criteria Document. These
scientists expressed their judgements on what standard level(s) would
provide vegetation with adequate protection from O₃-related
adverse effects.
Though the report identified no new data in support of the
scientists' recommendations, the Administrator believes that the report
lends important support to the view that the current secondary standard
is not adequately protective of vegetation. Further, the Administrator
believes that the report foreshadows the direction of future scientific
research in this area, the results of which could be important in
future reviews of the O₃ secondary standard.
As the results of such research become available, EPA will be in a
better position to characterize rural air quality and the improvements
in vegetation protection that would result from a seasonal secondary
standard, and to select a standard level that would provide adequate
protection for vegetation. However, given the present limits of the
scientific evidence of O₃-related effects and of rural air
quality data, as discussed in the Criteria Document, Staff Paper, the
proposal, and by CASAC, the Administrator has decided that it is not
appropriate to move forward with a seasonal secondary standard at this
time for the reasons described below. In coming to this conclusion, the
Administrator specifically considered the significant improvements in
public welfare protection that are expected to be afforded by the new
8-hour primary standard, as well as the value of obtaining additional
information to better characterize O₃-related effects on
vegetation under field conditions.

C. Final Decision on the Secondary Standard

Based on the scientific evidence, CASAC advice and recommendations,
comments received on the proposal, and the considerations summarized
above, the Administrator is replacing the current secondary
O₃ standard with an 8-hour standard, set at a level of 0.08
ppm, identical in all respects to the new primary standard. The
Administrator judges that this standard will provide substantially
improved protection for vegetation from O₃-related adverse
effects as compared to that provided by the current 1-hour, 0.12 ppm
secondary standard, while allowing time for additional research and the
development of a more complete rural monitoring network and air quality
database from which to evaluate the elements of an appropriate seasonal
secondary standard.
The decision not to set a seasonal secondary standard at this time
is based

[[Page 38878]]

in large part on the Administrator's recognition that the exposure,
risk, and monetized valuation analyses presented in the proposal
contain substantial uncertainties, resulting in only rough estimates of
the increased public welfare protection likely to be afforded by each
of the proposed alternative standards. These uncertainties were
discussed in the proposal and the Staff Paper and were noted by CASAC
(Wolff, 1996). In light of these uncertainties, the Administrator has
decided it is not appropriate at this time to establish a new separate
seasonal secondary standard given the potentially small incremental
degree of public welfare protection that such a standard may afford.
Instead, the Administrator finds it a reasonable policy choice to set a
new secondary standard identical to the new primary standard, while
focusing additional research on key areas for consideration in the next
review of the O₃ criteria and standards.
Continued research on the effects of O₃ on vegetation
under field conditions and on better characterizing the relationship
between O₃ exposure dynamics and plant response will be
important in the next review because:
(1) The available biological database highlights the importance of
cumulative, seasonal exposures as a primary determinant of plant responses.
(2) The association between daily maximum 8-hour O₃
concentrations and plant responses has not been specifically examined
in field tests.
(3) The impacts of attaining an 8-hour, 0.08 ppm primary standard
in upwind urban areas on rural air quality distributions cannot
currently be characterized with confidence due to limited monitoring
data and air quality modeling in rural and remote areas.
Setting the secondary standard equal to the primary standard will
allow EPA the opportunity to evaluate more specifically the improvement
in rural air quality and in O₃-related vegetation effects
resulting from measures designed to attain the new primary standard.
This information in turn will allow for better evaluation of the
incremental need for a separate seasonal secondary standard in the next
review of the O₃ criteria and standards.
In the proposal, the Administrator solicited comment on the
appropriate spatial scale of an expanded rural monitoring network.
Relatively few comments were received regarding an expanded rural
monitoring network, but those who did submit comments were generally in
favor of an expanded network to allow for improved modelling of long-
range transport of O₃ and its precursors and for better
characterization of O₃ air quality in rural and remote
areas. Those comments will serve to inform EPA's development of revised
air quality surveillance requirements (40 CFR part 58) that will be
proposed at a later date.
With respect to the proposed seasonal secondary standard only, the
proposal sought comment on whether O₃ concentrations from
several monitors should be spatially integrated when determining
compliance with the standard. Only a few comments were received, with
some supporting and some opposing spatial integration of O₃
concentrations from several monitors.
In view of the Administrator's decision to replace the current
secondary standard with a secondary standard which is identical in
form, level, and averaging time to the new 8-hour, 0.08 ppm primary
standard, rather than with a seasonal standard, EPA is not adopting the
use of spatial averaging for the new secondary standard.
To decrease some of the uncertainties discussed above and to remedy
the lack of air quality data in rural and remote areas of commercial or
ecological importance for vegetation, the Administrator reiterates her
intention, expressed in the proposal, to expand the rural O₃
monitoring network. The EPA will propose revised O₃ air
quality surveillance requirements (40 CFR part 58) at a later date. The
EPA is exploring opportunities to work with other Federal agencies to
develop a coordinated and long-term rural monitoring network.

IV. Other Issues

Several commenters raised key legal and procedural issues that are
discussed below. 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 extending the comment
period; and (4) whether the 1990 amendments to the Act preclude EPA
from revising the O₃ NAAQS to establish a new 8-hour
standard. Responses to other legal and procedural issues are included
in the Response-to-Comments Document.

A. Cost Considerations

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, 972-73 (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-
59 (D.C. Cir. 1987)(en banc)(CAA section 112 standards for vinyl
chloride)(``Vinyl Chloride''); American Petroleum Institute v. Costle,
665 F.2d 1176, 1185-86 (D.C. Cir. 1981)(ozone NAAQS)(``Ozone''), cert.
denied, 455 U.S. 1034 (1982); Lead Industries Ass'n v. EPA, 647 F.2d
1130, 1148-51 (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 particulate matter.
Although most of the commenters' arguments are inconsistent with the
judicial decisions cited above, several commenters have argued that
those decisions are not dispositive. For reasons discussed below 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 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.²⁹ 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.
---------------------------------------------------------------------------

29 36 FR 8186, Apr. 30, 1971. EPA has maintained this
interpretation consistently since then.
---------------------------------------------------------------------------

As discussed below, 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
above, as well as by legislative developments since 1970 that reaffirm
Congress' original approach to the issue.

[[Page 38879]]

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. Under section 108(a)(2), 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).³⁰ By contrast, Congress
explicitly provided for consideration of costs and similar factors in
decisions under other sections of the Act.³¹ 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.³² 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.³³
---------------------------------------------------------------------------

30 That consideration of such factors was not intended in NAAQS
decisions is also supported by section 109(a)(1). 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.
31 See, e.g., sections 110(e)(1), 111(a)(1), 231(b) (1970 Act);
see also, e.g., sections 113(d)(4)(C)(ii), 125(a)(3), 202(a)(3)(C),
317 (1977 Act).
32 Union Electric Co. v. EPA, 427 U.S. 246, 257-58 (1976).
33 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
1148-50. Among other things, it noted the contrast between section
109(b) 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 1148-49 & 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, 257-58,
266 (1976)).³⁴
---------------------------------------------------------------------------

34 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 above, 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 imposed requirements of a ``technology-forcing'' character.
Id.³⁵
---------------------------------------------------------------------------

35 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) 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 above, strongly reaffirmed the interpretation
adopted in Lead Industries.³⁶ Supreme Court 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).
---------------------------------------------------------------------------

36 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 section 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.³⁷ 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.³⁸ In response, Congress made

[[Page 38880]]

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 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.³⁹ Yet it made no changes in
sections 109(b) or 108(a)(2); 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.⁴⁰
---------------------------------------------------------------------------

37 See, e.g., H.R. Rep. No. 95-294, at 207-17 (l977).
38 See, e.g., id. at 110-12; id. at 43-51.
39 Section 109(d)(2)(C)(iv). 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), 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).
40 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. 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 as precluding consideration of costs in NAAQS
decisions.⁴¹ 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
involved⁴²--and the Vinyl Chloride case drawing a sharp
distinction between sections 109 and 112 with regard to consideration
of costs and similar factors.⁴³ 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.''⁴⁴
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.
---------------------------------------------------------------------------

41 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).]
42 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, Mar. 20, l984.
43 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; section 166(f). It was clearly
aware of the Vinyl Chloride decision because it amended section 112
in response to that decision, essentially creating a new scheme for
setting emission standards for hazardous pollutants.
44 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 ozone and particulate
NAAQS. Aside from arguments that are simply inconsistent with the
judicial decisions cited above, 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 in the
rulemaking on proposed revisions to the particulate NAAQS; the
following discussion focuses primarily on points raised by that
commenter, among others.⁴⁵
---------------------------------------------------------------------------

45 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:
(1) Where non-threshold pollutants are involved and the health
evidence is ambiguous, section 109 must be interpreted to allow
consideration of all relevant factors, including the practical
consequences of EPA's decisions;
(2) To the extent the judicial decisions cited above 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);⁴⁶ and
---------------------------------------------------------------------------

46 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
below 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 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).
---------------------------------------------------------------------------

(3) 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, Oct. 4, 1993, and two recent
statutes, the Unfunded Mandate Reform Act of 1995, 2 U.S.C. secs. 1501-
1571 (UMRA), and the Small Business Regulatory Enforcement Fairness Act
of 1996, Pub. L. No. 104-121, 110 Stat. 857 (SBREFA), which in part
amended the Regulatory Flexibility Act, 5 U.S.C. secs. 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.''⁴⁷ 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

[[Page 38881]]

scientific knowledge'' on potential health and welfare effects of the
pollutant in question. See sections 109(b), 108(a)(2). 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.' ''⁴⁸ 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.
---------------------------------------------------------------------------

47 See, e.g., Lead Industries, 647 F.2d at 1146-47, 1153-56,
1160-61, 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 that 1977
amendments without changing the substantive criteria for setting
NAAQS. See H.R. Rep. No. 95-294, at 43-51, 181-82 (1977).
48 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.⁴⁹ As a result, the
validity and implications of such studies may be both uncertain and
highly controversial. Given the precautionary nature of section
109,⁵⁰ 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.
---------------------------------------------------------------------------

49 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.]
50 See, e.g., Lead Industries, 647 F.2d at 1155-56; 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 1987.⁵¹
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.⁵² 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.⁵³
---------------------------------------------------------------------------

51 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, Mar. 20, l984.
52 See, e.g., Lead Industries, 647 F.2d at 1152-53 & n. 43,
1159-60; Ozone, 665 F.2d at 1185, 1187; PM₁₀, 902 F.2d at
969-71, 972.
53 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
believes it is clear that the judicial decisions cited above 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 842-43 (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.9.⁵⁴
---------------------------------------------------------------------------

54 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 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.⁵⁵ In short,
the health evidence was hardly ``unambiguous,'' yet the Court
interpreted section 109 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 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:
---------------------------------------------------------------------------

55 See, e.g., 647 F.2d at 1148-51, 1152-53 & n.43, 1160-61.

[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.
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. On the first point, the commenter
argues that EPA is free under Chevron to consider costs and similar
factors (by reinterpreting section 109) 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 1157-63. 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
``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, 1057-63 (D.C. Cir. 1995).

[[Page 38882]]

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.⁵⁶ As indicated above, the Vinyl
Chloride and PM₁₀ cases, both of which post-dated Chevron,
reached the same conclusion.
---------------------------------------------------------------------------

56 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 (1) 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 or related provisions; and (2) statements in early
judicial decisions involving programs under other statutory
provisions. In context, EPA believes 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.
---------------------------------------------------------------------------

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. 824 F.2d 1159. Consistent with Chevron, these findings were based
on traditional tools of statutory construction. See id. at 1157-59;
Lead Industries, 647 F.2d at 1148-51. 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 842-43.⁵⁷ 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 109.⁵⁸
---------------------------------------------------------------------------

57 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 3 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, 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 but not under
section 112.
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 in Vinyl Chloride. 902 F.2d at
972-73. 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 & 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.
58 See also 52 FR 24854, July 1, 1987.
---------------------------------------------------------------------------

As to the commenter's third key assertion, Executive Order 12866
(58 FR 51735, October 4, 1993) 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 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 because the requirement that agencies
``select approaches that maximize net benefits'' does not apply if a
``statute requires another regulatory approach.'' EO 12866, sec.
(1)(a), 58 FR 51735, Oct. 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., sec. (1)(b).
UMRA sections 202 and 205 do not apply to this decision, as
discussed in Unit VII 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, sec. 205(b)(1). Such an
explanation is not required if the least costly, most cost-effective or
least burdensome alternative would have been ``inconsistent with law,''
sec. 205(b)(2), and the only alternatives that an agency should
consider are ones that ``achieve[] the objectives of the rule,'' sec.
205(a). 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 discussed in Unit VII 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.''⁵⁹ When Congress passed SBREFA in 1996
and amended parts of the RFA, it did not amend section 606.
---------------------------------------------------------------------------

59 126 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
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 provide that the

[[Page 38883]]

alternatives an agency should consider are to be ``consistent with the
stated objectives of applicable statutes.'' Sec. 603 and 604(a)(5).
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 believes that the judicial
decisions cited above 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 O₃ 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. The 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 argued
that the Administrator must adopt the two-step methodology endorsed in
Vinyl Chloride, 824 F.2d 1146, for setting hazardous air pollutant
standards under section 112.
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 1161-62. As a
result, the Administrator is not limited to any single approach to
determining an adequate margin of safety and may, in the exercise of
her judgment, 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 approach 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, however,
the court concluded that ``the rationale for parsing the
Administrator's determination into two steps is inapposite.'' Id.
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 above, 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. 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 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 the scientific uncertainties are taken into
account in an appropriate manner.
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. Comment Period

A number of commenters maintained that EPA erred by not extending
the comment period for the review of the O₃ standards by at
least 60 days. The commenters further maintained there was no
justification for keeping the O₃ standard review on the same
schedule as the PM NAAQS, since the O₃ review is not subject
to a court-ordered deadline as is PM.
The EPA believes that there are benefits to reviewing the
O₃ and PM NAAQS on the same schedule, for the reasons set
forth in the proposal, and that the period available for public comment
was sufficient. All interested parties have had ample notice that EPA
intended to complete this review of the O₃ standards on an
expedited basis. The EPA first announced its intention in a March 9,
1993, Federal Register notice (58 FR 13008) when the Administrator
announced her commitment to expedite the review in light of new
scientific evidence of the effects of O₃ on human health. In
a February 3, 1994, Federal Register notice (59 FR 5164), the
Administrator announced a schedule for completion of the scientific
assessment and review of the standards, including opportunities for
public comment. This schedule called for proposal in mid-1996 and a
final decision as to whether to revise the O₃ standard by
mid-1997. On June 12, 1996, in an advance notice of proposed rulemaking
(61 FR 29719), the Administrator announced her decision to delay the
O₃ proposal schedule in order to place it on the same
schedule as the PM standard review. In that notice, she explained her
rationale for reviewing the O₃ and PM NAAQS on the same
schedule and pointed to the benefits of developing integrated
implementation strategies. She also provided advance notice of the
kinds of revisions to the primary and secondary O₃ NAAQS
that she was considering proposing. In effect, the delay of the
O₃ proposal provided interested parties an additional 5
months to review EPA's assessments of the scientific and technical
information, as well as staff and CASAC recommendations as to whether
revisions were appropriate. With this background, EPA believes all
interested parties had ample opportunity to develop specific

[[Page 38884]]

comments on the O₃ proposal during the 89 days allotted for
public comment.⁶⁰
---------------------------------------------------------------------------

60 This comment period reflects an extension of 22 days beyond
the 67-day comment period originally announced in the proposal.
---------------------------------------------------------------------------

Another commenter raised a more specific issue in requesting a 60-
day extension of the public comment period. This commenter maintained
that such an extension was necessary because EPA did not make publicly
available certain O₃ exposure and health risk assessment
reports and an explanatory memoranda in a timely manner. In response,
EPA notes that the documents in question were entered into the docket
on February 12, 1997, and placed on the OAQPS Technology Transfer
Bulletin Board on February 13, 1997, so that they would have wide
public circulation. Because this commenter's organization was aware
that the reports were under preparation and had expressed interest in
receiving them, copies were sent directly to the responsible staff
person on February 12, 1997. Given that these reports build on analyses
and methodologies that were available to the public during the
scientific phase of the O₃ NAAQS review, well in advance of
the proposal, and that the new analyses and explanatory memorandum were
only 120 pages in length, EPA believes that this commenter had
sufficient time to review the material and prepare comments before the
close of the comment period on March 12, 1997.

D. 1990 Act Amendments

Contrary to the view expressed in some public comments, EPA
maintains that the provisions of subpart 2 of Part D of Title I of the
Clean Air Act, enacted in 1990, do not preclude EPA from revising the
O₃ standard. The provisions of subpart 2 simply do not limit
EPA's clear authority under section 109 to revise the standard.
The basic contention of the commenters is that because the
provisions of subpart 2 are linked to the current 1-hour, 0.12 ppm
O₃ standard, they prohibit EPA from revising the
O₃ standard. These provisions, however, do not lead to such
a conclusion. Moreover, the view expressed in these comments ignores
provisions indicating that Congress believed that EPA could revise the
O₃ NAAQS.
At the outset, it should be noted that Congress expressly
authorized EPA to revise any ambient air quality standard in section
109. That section, which requires EPA to review and revise, as
appropriate, each NAAQS every 5 years, contains no language expressly
or implicitly prohibiting EPA from revising a NAAQS. If Congress had
intended to preclude EPA from reviewing and revising a NAAQS, which is
one 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)(expressly precluding EPA from modifying
certain motor vehicle standards prior to model year 2004); section
112(b)(2)(preventing EPA from adding to the list of hazardous air
pollutants any air pollutants that are listed under section 108(a)
unless they meet the specific exceptions of section 112(b)(2)); section
249(e)(3), (f) and section 250(b)(limiting EPA's authority regarding
certain clean-fuel vehicle programs). No such language was included in
either section 109 or elsewhere in the Act and no such implication may
properly be based on the provisions of subpart 2 of Part D of Title I.
Second, other provisions of the Act expressly contemplate EPA's
ability to revise any 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. For example, section
110(a)(2)(H)(i) 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) 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) addresses modifications of national primary ambient air
quality standards. Finally, section 172(a)(1) 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) 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 2 of Part D do not support the
contention that they somehow preclude EPA from exercising its authority
to revise the NAAQS under section 109. The fact that Congress laid out
an implementation program for the O₃ 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. Contrary to this
contention, section 181(a) does not preclude the designation of areas
as nonattainment for O₃ that have design values less than
0.121 ppm. EPA has designated as nonattainment numerous areas whose
design value was less than 0.121 ppm, but which violated the existing
1-hour, 0.12 ppm O₃ standard. These areas, referred to as
``nonclassifiable nonattainment areas,'' include ``submarginal'' areas
(i.e., O₃ nonattainment areas with design values below 0.121
ppm), (See 57 FR 13498, 13524-27, April 16, 1992). These areas include
areas that were designated nonattainment prior to the 1990 amendments
and whose nonattainment designation Congress required to be continued
after 1990. See section 107(d)(1)(C)(i). Clearly, Congress did not
prohibit the designation of areas as nonattainment for O₃
with design values below 0.121 ppm; in fact, in some cases, Congress
required it. Furthermore, the position advanced by the commenters would
mean that, in effect, Congress in the 1990 amendments legislatively
revised the then-existing 1-hour, 0.12 ppm O₃ standard to a
0.121 ppm standard. There is no indication that Congress intended to do
that.
In addition, the fact that Congress directed EPA to use ``the
interpretation methodology issued by the Administrator most recently''
before the date of the enactment of the Clean Air Act Amendments of
1990 in the context of subpart 2 does not add any support to the
commenters' position; it merely shows that Congress intended the
existing 1-hour, 0.12 ppm standard to be implemented in a specified
way, not that Congress intended to preclude EPA from using its
otherwise applicable authority to revise the standard.
The EPA also disagrees with the contention that sections
172(a)(1)(C) and (a)(2)(D), which provide that the general
classification and attainment date provisions of section 172 do not
apply to areas for which classifications or attainment dates ``are
specifically provided under other provisions of this part,'' support
the conclusion that Congress intended to prohibit EPA from revising the
O₃ standard. These provisions simply mean that where
Congress elsewhere provided for specific classifications and attainment
dates, as in the case of subpart 2 regarding the 1-hour, 0.12 ppm
standard, EPA is not to modify those

[[Page 38885]]

classifications or dates. The EPA is not purporting to do this. These
provisions do not lead to the conclusion that because Congress
established them for the O₃ standard in effect at the time
of the 1990 amendments, Congress meant that EPA could not revise that
standard in order to appropriately protect public health.
EPA does not accept the thesis that revising the O₃
standard forces EPA to violate other provisions of the Act and,
therefore, is not an ``appropriate'' revision of the standard under
section 109. Revising the O₃ standard in accordance with the
language of section 109 does not result in EPA violating any provision
of the Act. On the other hand, a determination by EPA that the
O₃ standard should not be revised, even though EPA concludes
that it needs to be revised to protect public health with an adequate
margin of safety, would violate section 109.
Also, EPA does not believe that carrying out the provisions of
section 109 to set a new O₃ standard to protect public
health with an adequate margin of safety somehow ``risks undermining
both perceptions and reality of the functioning of our democratic form
of government.'' EPA is merely implementing the words of the Clean Air
Act, a statute passed by the Congress and signed by the President. To
refuse to revise the standard notwithstanding the need to protect
public health as enunciated in section 109 would thwart the objectives
of those who passed and signed the Clean Air Act on behalf of the
American public.
Finally, for the reasons stated above, EPA's analysis of its
ability to implement the revised O₃ standard under the
provisions of subpart 1 of Part D of Title I does not support the view
that Congress prohibited EPA from revising the standard. Congress
clearly specified an approach to the implementation of the 1-hour, 0.12
ppm O₃ standard in the provisions of subpart 2 of Part D.
EPA believes that the clear and express linkage of that approach to the
1-hour, 0.12 ppm standard indicates that it may implement a revised
O₃ standard in accord with the general principles of subpart
1 of Part D, as informed by the no-backsliding principle embodied in
section 172(e). That Congress directed specifically how EPA and the
States should implement the 1-hour, 0.12 ppm O₃ standard
does not carry with it the implication that Congress intended to
prohibit EPA from exercising its otherwise clear and express authority
to revise that standard in order to carry out one of its fundamental
missions, the establishment of ambient air quality standards to protect
public health with an ample margin of safety. 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.
The EPA also disagrees with the contention that a revised
O₃ standard may not be implemented for so long as the
current 1-hour, 0.12 ppm O₃ standard remains in effect. The
fact that the provisions of subpart 2 of Part D are focused on the
implementation of the current standard does not mean that, if a new or
revised O₃ standard is promulgated pursuant to section 109,
the new standard could not simultaneously be implemented under the
provisions of section 110 and subpart 1 of Part D, which apply
regardless of the criteria pollutant of concern. There is no language
in sections 181 or 182 that precludes the implementation of a different
standard under other authority; those provisions simply govern the
implementation of the 1-hour, 0.12 ppm O₃ standard. EPA
further notes that it has historically had more than one primary
standard for criteria pollutants (e.g., annual and 24-hour
PM₁₀ and sulfur dioxide standards, and 8-hour and 1-hour CO
standards) and believes that had Congress wanted to preclude EPA from
implementing two primary O₃ standards simultaneously it
would have expressly precluded EPA from doing so. Thus, EPA does not
believe that it must repeal the 1-hour, 0.12 ppm O₃ standard
before it can promulgate and implement a new primary O₃ standard.

V. Technical Changes to Part 50

In the proposal, the EPA proposed two alternative secondary
standards: (1) A secondary standard set identical to the proposed 0.08
ppm, 8-hour primary standard; or (2) a seasonal secondary standard
expressed in the SUM06 form. For the reasons discussed in Unit III, the
EPA has decided to promulgate a secondary ambient air quality standard
for O₃ that is identical to the primary ambient air quality
standard. Accordingly, the language adopted in the final regulation (40
CFR 50.10) has been revised to reflect this change.
In the proposal, the regulatory text in Sec. 50.9 inadvertently
included language about what it means when the standard is not met,
that should have been discussed in 40 CFR part 50, Appendix H.
Therefore this sentence has been removed from Sec. 50.10(b), and the
discussion moved to the new Appendix I to 40 CFR part 50, which now
provides additional clarification on calculations for sites with less
than complete data, as discussed in Unit VI. of this preamble.

VI. Revisions to Appendices D, E, and H

The EPA is finalizing the changes to Appendices D and E to 40 CFR
part 50, that were proposed and described in the proposal. No adverse
comments were received on these changes.
Because the revocation of the existing 1-hour standard will become
effective at a later date (as discussed above in Unit II.B.4.), EPA is
retaining Appendix H in its current form. A new Appendix I explains the
computations necessary for determining when the new 8-hour primary and
secondary standards are met.
The new Appendix I addresses data completeness requirements, data
reporting, handling, and rounding conventions, and example
calculations. The discussion in this unit sometimes refers to the
contents of the new Appendix I as revisions to Appendix H, so as to
highlight how the new Appendix I differs from the current Appendix H.
For example, the example calculations in Appendix I differ from those
in Appendix H to reflect the final form of the new 8-hour primary standard.
In the proposal, two alternative secondary standards were proposed,
and the proposed changes to Appendix H addressed both alternatives: A
secondary standard set identical to the proposed 0.08 ppm, 8-hour
primary standard; or a seasonal secondary standard expressed in the
SUM06 form. For the reasons discussed above, the Administrator has
decided to set the secondary standard identical to the primary standard
as reflected in Appendix I.
Key elements of Appendix I, particularly as they differ from those
of Appendix H, are outlined below.

A. Data Completeness

One key change to Appendix H, incorporated into Appendix I, for the
new 0.08 ppm, 8-hour primary and secondary standards is that no
numerical adjustment is made to the measured 8-hour concentrations to
account for missing or incomplete data as was the case with the 1-hour
standard. Instead, the EPA has decided to replace the methodology used
to adjust the computation of estimated exceedances for missing data
under the 1-hour standard with new data completeness requirements for
the 8-hour standards.
The EPA proposed that, in order to determine that the 8-hour
standards have been met at a monitoring site

[[Page 38886]]

during the current 3-year period, revisions to Appendix H would require
90 percent data completeness, on average, with no single year at the
site having less than 75 percent data completeness. A site could be
found not to have met the standards with less than complete data.
Almost all commenters supported deleting the estimated exceedances
missing data adjustment procedure of the current 1-hour standard and
replacing it with minimum data completeness requirements. Several
commenters felt that the proposed data completeness requirement might
be too stringent and would be difficult to attain. Other commenters
recommended that some consideration be made for hours lost due to
instrument calibration. A few commenters thought that EPA should
establish higher minimum data completeness requirements.
Based on its analysis of available air quality data, the EPA
believes that, with the changes to the proposal described below, the
data completeness requirement in Appendix I is reasonable given that 90
percent of all monitoring sites that currently operate on a continuous
basis meet this objective. The EPA believes that a missing hour during
the day resulting from instrument calibration should not negatively
impact the ability of a monitoring site to meet the data completeness
requirements because data completeness is based on the number of days
with valid daily maximum 8-hour concentrations, not on the number of
non-missing hours.
In the proposal, the EPA sought comment on whether meteorological
data could provide an objective basis for determining, on a day for
which there is missing data, that the meteorological conditions were
not conducive to high O₃ concentrations, and therefore, that
the day could be assumed to have an 8-hour daily maximum O₃
concentration less than 0.08 ppm. Under the 0.12 ppm 1-hour standard, a
missing day is assumed less than the level of the standard only if the
two adjacent days are non-missing, and the daily maximum 1-hour
concentration on each of those days is less than or equal to 0.09 ppm.
In the proposal, the EPA specifically requested comment on the
appropriateness of using data on meteorological conditions, as well as
on other information that would permit better definition of those
necessary conditions likely to result in peak 8-hour O₃
concentrations in the ranges of concern. Most commenters expressing an
opinion supported the use of meteorological data, as well as ambient
data from nearby monitoring sites to establish that missing hours could
be assumed less than the level of the standard. Days assumed less than
the level of the standard would be counted as non-missing when
computing whether the data completeness requirements have been met at
the site. Taking these comments into account, EPA has revised the
proposed revisions to Appendix H, as reflected in Appendix I, to count
missing days assumed less than the standard when computing whether the
data completeness requirement has been met. EPA will develop guidance
on methodologies necessary for using meteorological data and ambient
measurements to make such determinations.
Several commenters expressed concerns about the possibility that
stratospheric O₃ intrusion from aloft or forest fires may
lead to exceedances of the level of the standard, particularly within
the context of peak O₃ concentrations that have been
observed at background sites. Commenters expressed concern that such
events could lead to violations of the 8-hour standard and, therefore,
they questioned the attainability of the proposed standard. Consistent
with a forthcoming update to EPA's policy on natural events for the new
8-hour standard, EPA has revised Appendix H to specifically address
this concern by stating that whether to use data affected by
stratospheric O₃ intrusion or other natural events when
determining if the standards have been met is subject to the approval
of the appropriate Regional Administrator.

B. Data Handling and Rounding Conventions

For the reasons cited above, and taking into account the advice of
CASAC, the Administrator has set the level of the new 8-hour primary
and secondary standards at 0.08 ppm. As EPA explained in the proposal,
the level of the 8-hour standard is expressed to the second decimal
place, 0.08 ppm, with the support of CASAC and in part to reflect
uncertainties in the health effects evidence upon which the proposed
standard is based. More specifically, these uncertainties include the
measurement uncertainty and representativeness inherent in the reported
ambient O₃ concentrations used in field and epidemiological
studies and the uncertainty in the exposure estimates upon which
quantitative risk assessments have been based. In the proposal, EPA
stated its belief that expressing the proposed standard to the second
decimal place is also consistent with the quality assurance guidelines
that indicate the precision⁶¹ for such O₃
measurements shall be within 15 percent.
---------------------------------------------------------------------------

61 The term precision is used to denote both the reproducibility
of a measurement under a constant set of conditions, as well as
other components of measurement uncertainty such as instrument drift
and relative bias.
---------------------------------------------------------------------------

To determine whether the standard is met, EPA proposed that the
calculated value of the third-highest maximum 8-hour average
concentrations, averaged over 3 years, is compared to the level of the
standard. It is the level of the standard, 0.08 ppm, expressed to two
decimal places that determines the number of significant digits to be
used when comparing air quality measurements to the standard. The EPA
proposed that, for hourly data, 8-hour average O₃
concentrations computed from such hourly data, and the 3-year averages
of the third highest maximum 8-hour average concentrations, that the
third decimal place is carried forward as the rounding digit, and the
insignificant digits are truncated. To compare the calculated 3-year
average O₃ concentration to the level of the standard, the
third decimal place of the calculated value is rounded. The current
rounding convention is to round up digits equal to or greater than 5.
In the proposal, EPA recognized that the level of public health
protection afforded by the use of the current rounding convention could
be increased by replacing the current rounding convention with a
convention that defined the smallest increment above the level of the
standard to be 0.001 ppm for the purposes of determining whether the
standard has been met. The EPA solicited comment on the use of such an
alternative rounding convention, with regard to potential increased
public health protection, as well as to potential effects on the
probability of attainment misclassifications and on the stability of
the standard.
Of the many States that commented specifically on the rounding
convention, most State agencies cited concerns by their monitoring
staffs about the precision and accuracy of measured O₃
concentrations in ambient environments and recommended maintaining the
current rounding convention. A tribal association also supported the
current rounding convention. Other State agencies felt that newer
instruments were capable of supporting a rounding convention set at
0.001 ppm. Of those environmental and health associations that
commented, all supported replacing the current rounding convention with

[[Page 38887]]

the alternative 0.001 ppm convention.⁶² All industry and
trade associations that commented on rounding recommended that EPA
retain the current rounding convention.
---------------------------------------------------------------------------

62 One individual commenter provided an analysis of current
monitoring technology and suggested that the precision and accuracy
data supported setting the standard to three decimal places and
rounding the annual average third-highest 8-hour average
concentration up at 0.001 ppm. EPA believes that the precision and
accuracy data cited by the commenter does not capture all of the
uncertainty inherent in ambient air quality measurements.
---------------------------------------------------------------------------

After taking these comments into account, EPA has decided that the
current rounding approach is appropriate for comparing monitoring data
to the level of the standard expressed to two decimal places. The
current rounding procedure has the effect of reducing the probability
of misclassifying an attainment area as nonattainment and of producing
a more stable attainment test. The EPA believes that measures that
promote a stable control program will lead to greater long-term health
protection and risk reduction. For the reasons stated above, and taking
into account the uncertainty in the exposure estimates upon which
quantitative risk assessments have been based, measurement uncertainty,
data representativeness, and the desirability of these resulting
effects, EPA is retaining the current rounding convention and finalizing
the data handling and rounding conventions, in Appendix I, as proposed.

VII. Regulatory and Environmental Impact Analyses

As discussed in Unit IV of this preamble, the Clean Air Act and
judicial decisions make clear that the economic and technological
feasibility of attaining ambient standards are not to be considered in
setting NAAQS, although such factors may be considered in the
development of State plans to implement the standards. Accordingly,
although, as described below, a Regulatory Impact Analysis (RIA) has
been prepared, neither the RIA nor the associated contractor reports
have been considered in issuing this final rule.

A. Executive Order 12866

Under Executive Order 12866, 58 FR 51735 (October 4, 1993), the
Agency must determine whether a regulatory action is ``significant''
and, therefore, subject to Office of Management and Budget (OMB) review
and other requirements of the Executive Order. The order defines
``significant regulatory action'' as any regulatory action that is
likely to result in a rule that may:
(1) Have an annual effect on the economy of $100 million or more or
adversely affect in a material way the economy, a sector of the
economy, productivity, competition, jobs, the environment, public
health or safety, or State, local, or tribal governments or communities.
(2) Create a serious inconsistency or otherwise interfere with an
action taken or planned by another Agency.
(3) Materially alter the budgetary impact of entitlements, grants,
user fees, or loan programs or the rights and obligations of recipients
thereof.
(4) Raise novel legal or policy issues arising out of legal
mandates, the President's priorities, or the principles set forth in
the Executive Order.
In view of its important policy implications, this action has been
judged to be a ``significant regulatory action'' within the meaning of
the Executive Order. As a result, under section 6 of the Executive
Order, EPA has prepared an RIA, entitled ``Regulatory Impact Analysis
for Particulate Matter and Ozone National Ambient Air Quality Standards
and Proposed Regional Haze Rule (July 1997).'' This RIA assesses the
costs, economic impacts, and benefits associated with potential State
implementation strategies for attaining the PM and O₃ NAAQS
and the proposed Regional Haze Rule. Changes made in response to OMB
suggestions or recommendations will be documented in the public docket
and made available for public inspection at EPA's Air and Radiation
Docket Information Center (Docket No. A-95-58). The RIA will be
publicly available in hard 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.''

B. Regulatory Flexibility Analysis

The Regulatory Flexibility Act (RFA), 5 U.S.C. 601 et seq.,
provides that, whenever an agency is required to publish a general
notice of rulemaking for a proposed rule, the agency must prepare an
initial regulatory flexibility analysis for the proposed rule unless
the head of the agency certifies that the rule ``will not, if
promulgated, have a significant economic impact on a substantial number
of small entities'' (section 605(b)). The EPA certified each of the
proposed NAAQS rules based on its conclusion that the rule would not
establish requirements applicable to small entities and therefore would
not have a significant economic impact on small entities within the
meaning of the RFA. See 61 FR 65638, 65668 (PM proposal); 61 FR 65716,
65746 (ozone proposal), both published on December 13, 1996.
Accordingly, the Agency did not prepare an initial regulatory
flexibility analysis for the proposed rule, but it did conduct a more
general analysis of the potential impact on small entities of possible
State strategies for implementing any new or revised NAAQS.
At the heart of EPA's certification of the proposed NAAQS rule was
the Agency's interpretation of the word ``impact'' as used in the RFA.
Is the ``impact'' to be analyzed under the RFA a rule's impact on the
small entities that will be subject to the rule's requirements, or the
rule's impact on small entities in general, whether or not they will be
subject to the rule? In the case of NAAQS rules, the question arises
because of the congressionally-designed mixture of Federal and State
responsibilities in setting and implementing the NAAQS.
As EPA explained in the proposal, NAAQS rules establish air quality
standards that States are primarily responsible for meeting. Under
section 110 and part D of Title I of the CAA, every State develops a
State Implementation Plan (SIP) containing the control measures that
will achieve a newly promulgated NAAQS. States have broad discretion in
the choice of control measures. As the U.S. Supreme Court noted in
Train v. NRDC:

[P]rimary [NAAQS] deal with the quality of outdoor air and are
fixed on a nationwide basis at a level which the agency determines
will protect the public health. It is the attainment and maintenance
of these standards which section 110(a)(2)(A) requires that State
plans provide. In complying with this requirement, a State's plan
must include ``emission limitations'' which are regulations of the
composition of substances emitted into the ambient air from such
sources as power plants, service stations and the like. They are the
specific rules to which operators of pollution sources are subject
and which, if enforced, should result in ambient air which meets the
national standards.
The Agency is plainly charged by the Act with the responsibility
for setting the national ambient air standards. Just as plainly, it
is relegated to a secondary role in the process of determining and
enforcing the specific, source-by-source emission limitations which
are necessary if the national standards are to be met. Under
110(a)(2), the Agency is required to approve a State plan which
provides for the timely attainment and maintenance of the ambient
air standards, and which also satisfies that section's other general
requirements. The Act gives the agency no authority to question the
wisdom of a State's choices of emission limitations if they are part
of a plan which satisfies the standards of 110(a)(2) and the Agency
may devise and promulgate a plan of

[[Page 38888]]

its own only if the state fails to submit an implementation plan
which satisfies those standards. Section 110(c).

421 U.S. 60, at 78-79 (1975) (emphasis in original). In short, NAAQS
rules themselves do not establish any control requirements applicable
to small entities. State rules implementing the NAAQS may establish
such requirements and the extent to which they do depends primarily on
each State's strategy for meeting the NAAQS.⁶³
---------------------------------------------------------------------------

63 It is worth noting that Federal rules that apply nationally
also play a role in reducing emissions governed by NAAQS. For
instance, EPA rules under Title II of the CAA require reductions in
ozone-forming emissions from on and off-road vehicles and the fuels
that power them. When EPA issues such rules, it conducts the
analysis required under the RFA. For example, EPA performed
regulatory flexibility analyses for the reformulated gasoline rule
issued under section 211(k) of the CAA. See 59 FR 7716, February 16, 1994.
---------------------------------------------------------------------------

To determine the proper interpretation of ``impact'' under the RFA,
EPA considered the RFA's stated purpose, its requirements for
regulatory flexibility analyses, its legislative history, the
amendments made by the Small Business Regulatory Enforcement Fairness
Act of 1996 (SBREFA)(Pub. L. 104-121), and caselaw. The EPA concluded
that all of these traditional tools of statutory construction point in
one direction--that an agency is required to assess the impact of a
rule on the small entities that will be subject to the rule's
requirements, because the purpose of a regulatory flexibility analysis
is to consider ways of easing or even waiving a rule's requirements as
they will apply to small entities, consistent with the statute
authorizing the rule. That purpose cannot be served in the case of the
rules like the NAAQS that do not have requirements that apply to small
entities.
More specifically, EPA noted that its interpretation of ``impact''
flows from the express purpose of the RFA itself. As the RFA's
``Findings and Purposes'' section (Pub. L. 96-354, section 2) makes
clear, Congress enacted the RFA in 1980 out of concern that agencies
were writing one-size-fits-all regulations that in fact did not fit the
size and resources of small entities. Congress noted that it is
generally easier for big businesses to comply with regulations, and
that small businesses are therefore at a competitive disadvantage in
complying with uniform rules. Congress also noted that small entities'
relative contribution to the problem a rule is supposed to solve may
not warrant applying the same requirements to large and small entities
alike. In the RFA itself, Congress therefore stated:

It is the purpose of this Act to establish as a principle of
regulatory issuance that agencies shall endeavor, consistent with
the objectives of the rule and of applicable statutes, to fit
regulatory and informational requirements to the scale of the businesses,
organizations, and governmental jurisdictions subject to regulation.

[Pub. L. 96-354, section 2(b).]

The EPA further noted that the RFA sections governing initial and
final regulatory flexibility analyses reflect this statement of
purpose. RFA sections 603 and 604 require that initial and final
regulatory flexibility analyses identify the types and estimate the
numbers of small entities ``to which the proposed rule will apply''
(sections 603(b)(3) and 604(a)(3)). Similarly, they require a
description of the ``projected reporting, recordkeeping and other
compliance requirements of the proposed rule, including an estimate of
the classes of small entities which will be subject to the
requirement'' (sections 603(b)(4) and 604(a)(4)). At the core of the
analyses is the requirement that agencies identify and consider
``significant regulatory alternatives'' that would ``accomplish the
stated objectives of applicable statutes and which minimize any
significant economic impact of the proposed rule on small entities''
(section 603(c) and 604(a)(5)). Among the types of alternatives
agencies are to consider are the establishment of different
``compliance or reporting requirements or timetables'' for small
entities and the exemption of small entities ``from coverage of the
rule, or any part'' of the rule (section 603(c)(1) and (4)). The RFA
thus makes clear that regulatory flexibility analyses are to focus on
how to minimize rule requirements on small entities.
As EPA further explained, since regulatory flexibility analyses are
not required for a rule that will not have a ``significant economic
impact on a substantial number of small entities,'' it makes sense to
interpret ``impact'' in light of the requirements for such analyses.
Regulatory flexibility analyses, as described above, are to consider
how a rule will apply to small entities and how its requirements may be
minimized with respect to small entities. In this context, ``impact''
is appropriately interpreted to mean the impact of a rule on the small
entities subject to the rule's requirements.
The Agency cited two Federal court cases in support of its
interpretation. In Mid-Tex Elec. Co-op v. FERC, 773 F.2d 327, 342 (D.C.
Cir. 1985), petitioners claimed that the RFA required an agency to
analyze the effects of a rule on small entities that were not regulated
by the rule but might be indirectly impacted by it. Petitioners noted
that the Small Business Administration (SBA) also interpreted the RFA
to require analysis of a rule's impact on small entities not regulated
by the rule, and argued that the court should defer to the SBA's
position in light of its compliance monitoring role under the RFA.
After reviewing the RFA's ``Findings and Purposes'' section, its
legislative history, and its requirements for regulatory flexibility
analyses, the Mid-Tex court rejected petitioners' interpretation. As
the court explained:

The problem Congress stated it discerned was the high cost to
small entities of compliance with uniform regulations, and the
remedy Congress fashioned--careful consideration of those costs in
regulatory flexibility analyses--is accordingly limited to small
entities subject to the proposed regulation. *** [W]e conclude that
an agency may properly certify that no regulatory flexibility
analysis is necessary when it determines that the rule will not have
a significant economic impact on a substantial number of small
entities that are subject to the requirements of the rule.

Id. at 342. Notably, Congress let this interpretation stand when it
recently amended the RFA in enacting the SBREFA.
The EPA also cited a recent case affirming the Mid-Tex court's
interpretation. In United Distribution Companies v. FERC, 88 F.3d 1105,
1170 (D.C. Cir. 1996), the court noted that the Mid-Tex court:

*** conducted an extensive analysis of the RFA provisions
governing when a regulatory flexibility analysis is required and
concluded that no analysis is necessary when an agency determines
``that the rule will not have a significant economic impact on a
substantial number of small entities that are subject to the
requirements of the rule''.

Id., citing and quoting Mid-Tex (emphasis added by United Distribution
court).
The Agency went on to explain that given the Federal/State
partnership for attaining healthy air, the proposed NAAQS, if adopted,
would not establish any requirements applicable to small entities.
Instead, any new or revised standard would establish levels of air
quality that States would be primarily responsible for achieving by
adopting plans containing specific control measures for that purpose.
The proposed NAAQS rule was thus not susceptible to regulatory
flexibility analysis as prescribed by the amended RFA. Since it would
establish no requirements applicable to small entities, it afforded no
opportunity for EPA to fashion for small entities less burdensome
compliance or reporting requirements or timetables, or

[[Page 38889]]

exemptions from all or part of the rule. For these reasons, EPA
certified that the proposed rule ``will not, if promulgated, have a
significant economic impact on a substantial number of small
entities,'' within the meaning of the RFA. Because EPA was not required
to prepare an initial regulatory flexibility analysis for the rule, it
was also not required to convene a Small Business Advocacy Review Panel
for the rule under RFA section 609(b) as added by SBREFA.
Notwithstanding its certification of the proposed rule, EPA
recognized that the proposed NAAQS, if adopted, would begin a process
of State implementation that could eventually lead to small entities
having to comply with new or different control measures, depending on
the implementation plans developed by the States. EPA also recognized
that the CAA does not allow EPA to dictate or second-guess how States
should exercise their discretion in regulating to attain any new or
revised NAAQS. Under those circumstances, EPA concluded that the best
way to take account of small entity concerns regarding any new or
revised NAAQS was to work with small entity representatives and States
to provide information and guidance on how States could address small
entity concerns when they write their implementation plans.
In line with this approach, as part of the RIA it prepared for the
proposed NAAQS, EPA analyzed how hypothetical State plans for
implementing the proposed rule might affect small entities. The
analysis was necessarily speculative and limited, since it depended on
projections about what States might do several years in the future and
did not take into account any new strategies that might be developed
and recommended by the FACA subcommittee formed to help devise
potential strategies for implementing a new or revised NAAQS (see
discussion of RIA and FACA process in the previous Unit of this
notice). Nevertheless, the analysis provided as much information on
potential small entity impacts as was reasonably available at the time
of the proposed rule.
The Agency also took steps to ensure that small entities' voices
were heard in the NAAQS rulemaking itself. With Jere Glover, Chief
Counsel for Advocacy of the SBA, EPA convened outreach meetings modeled
on the SBREFA panel process to solicit and convey small entities'
concerns with the proposed NAAQS. Two meetings were held as part of
that process, on January 7 and February 28, 1997, with a total
attendance of 41 representatives of small businesses, small governments
and small nonprofit organizations. Both meetings were attended by
representatives of SBA and the Office of Management and Budget, as well
as of EPA. The key concerns raised by small entities at those meetings
related to the scientific foundation of the proposed NAAQS and the
potential cost of implementing it, the same concerns raised by other
industry commenters on the proposed rule. The Agency produced a report
on the meetings to ensure that small entity concerns were part of the
rulemaking record when EPA made its final decision on the proposal.
In light of States' pivotal role in NAAQS implementation, EPA also
undertook a number of additional activities to assist and encourage the
States to be sensitive to small entity impacts as they implement any
new or revised NAAQS. With the SBA, EPA began an interagency panel
process to collect advice and recommendations from small entity
representatives on how States could lessen any impacts on small
entities. The EPA plans to issue materials in two phases to help States
develop their implementation plans. In view of States' discretion in
implementing the NAAQS, these materials will mostly take the form of
guidance, which is not subject to the RFA's requirement for initial
regulatory flexibility analysis. (Under RFA section 603, that
requirement applies only to binding rules that are required to undergo
notice-and-comment rulemaking procedures.) But regardless of the form
such materials take, EPA is employing panel procedures to ensure that
small entities have an opportunity to raise any concerns prior to the
materials being issued in draft form.
To supplement the input the Agency receives from the ongoing CAAAC
process (described earlier in this Unit of this preamble), EPA also
added more small entity representatives to the subcommittee on
implementation of any new or revised NAAQS. These representatives have
formed a small entity caucus to develop and bring to the subcommittee a
focused approach to small entity issues. These new subcommittee members
are also part of the group in the aforementioned panel process. By
means of these various processes, EPA hopes to promote the
consideration of small entity concerns and advice throughout the NAAQS
implementation process.
In response to the proposed rule, a number of commenters questioned
EPA's decision to certify that the proposed NAAQS will not have a
significant impact on a substantial number of small entities. Some
commenters disagreed with EPA's view that the proposed NAAQS would not
establish regulatory requirements applicable to small entities. These
commenters argued that a number of control requirements applicable to
small entities would automatically result from promulgation of the
proposed NAAQS, such as new reasonable further progress, SIP and
Federal Implementation Plan (FIP) requirements. Other commenters stated
that it is possible for EPA to assess the impacts of the NAAQS revision
on small entities and that, to a limited extent, EPA has already done
so. Further, a number of commenters argued that EPA has a legal
obligation under the RFA, as amended by SBREFA, to choose a NAAQS
alternative that minimizes the impact on small entities. Some
commenters questioned EPA's interpretations of the Mid-Tex and United
Distribution cases. In addition, other commenters stated that EPA's
position regarding the NAAQS and the RFA is inconsistent with its past
practice and the legislative history of the RFA. Finally, a few
commenters noted that the panel process EPA conducted for the proposed
NAAQS did not satisfy the requirements of SBREFA.
EPA disagrees that promulgation of the NAAQS will automatically
result in control requirements applicable to small entities that EPA
can and must analyze under the RFA. As noted previously, a NAAQS rule
only establishes a standard of air quality that other CAA provisions
call on States (or in case of State inaction, the Federal government)
to achieve by adopting implementation plans containing specific control
measures for that purpose. Following promulgation of a new or revised
NAAQS, section 110 of the CAA requires States and EPA to engage in a
designation process to determine what areas within each State's borders
are attaining or not attaining the NAAQS. Under section 110 and parts C
and D of Title I of the CAA, States then conduct a planning process to
develop and adopt their SIPs. Depending on an area's designation for
the particular NAAQS, these and other Title I provisions require a
State's SIP to contain certain control programs in addition to the
control measures that the State decides are also needed to attain and
maintain the NAAQS.
The fact that the CAA requires SIPs to contain certain control
programs under certain circumstances does not mean that EPA either can
or must conduct a regulatory flexibility analysis of a rule
establishing a NAAQS. Just from the standpoint of feasibility, EPA cannot
know which areas will be subject to what mandatory SIP programs until

[[Page 38890]]

after the designation process is completed. Beyond that, any mandatory
SIP programs are still implemented by the States, and States have
considerable discretion in how they implement them. For instance, the
reasonable further progress requirement under section 172 leaves States
broad discretion to determine the rate of progress and the control
measures to achieve that progress.⁶⁴ As a result, EPA cannot
be certain where and how any mandatory programs will be implemented
with respect to small (or large) entities. Much less can EPA know about
how States will exercise their discretion to develop additional
controls needed to attain and maintain the NAAQS.
---------------------------------------------------------------------------

64 Contrary to what some commenters assumed, the SIP
requirements of subpart 2 of part D of Title I will not apply to
SIPs to implement the revised ozone NAAQS. Those requirements were
enacted by Congress in 1990 to address nonattainment of a 0.12 ppm
1-hour ozone NAAQS. To the extent those requirements remain in
effect, they apply only to SIPs for areas still in nonattainment
with that standard; they do not apply to SIPs for areas in
nonattainment only with respect to the ozone NAAQS adopted today.
Further, to the extent SIPs for areas in nonattainment with the
previous ozone standard remain subject to subpart 2 requirements,
there will be no incremental change in the impact on sources
regulated by the States' SIPs pursuant to the requirements as a
result of today's promulgation.
---------------------------------------------------------------------------

Even if EPA could know exactly how any mandatory SIP programs would
apply to small entities, the purpose of the RFA is not served by
attempting a regulatory flexibility analysis of State implementation of
those programs. As explained previously, the RFA and the caselaw
interpreting it clearly establish that the purpose of the RFA is to
promote Federal agency efforts to tailor a rule's requirements to the
scale of the small entities that will be subject to it. That purpose
cannot be served in the case of a NAAQS rule since the rule does not
establish requirements applicable to small entities. In promulgating a
NAAQS, the only choice before EPA concerns the level of the standard,
not its implementation. While mandatory SIP programs may ultimately
follow from promulgation of the NAAQS, there is nothing EPA can do in
setting the NAAQS to tailor those programs as they apply to small
entities. Whether and how the programs will apply in particular
nonattainment areas is beyond the scope of the NAAQS rulemaking and,
indeed, beyond EPA's reach in any rulemaking to the extent the
applicability and terms of the programs are prescribed by
statute.⁶⁵ Moreover, any mandatory SIP programs are
supplemented by discretionary State controls that EPA has no power to
tailor under the RFA or the CAA (see Train v. NRDC, quoted previously).
---------------------------------------------------------------------------

65 If and when the Agency issues any rules addressing State
implementation of any statutorily required actions, EPA would
analyze and address the impact of those rules on small entities as
appropriate under the RFA.
---------------------------------------------------------------------------

The commenters' suggestions for minimizing the potential impact of
the NAAQS rule on small entities run afoul of both the RFA and the CAA.
Some suggested that EPA set a less stringent standard (or no standard
at all in the case of PM_2.5) to reduce the chance that small
entities would become subject to new or tighter SIP requirements.
Others suggested that EPA require States to exempt small entities from
new or tighter SIP requirements. However, as explained in a previous
Unit of this notice addressing the Agency's authority to consider
factors other than public health in setting primary NAAQS, the RFA
neither requires nor authorizes EPA to set a less stringent NAAQS than
the applicable CAA provisions allow in order to reduce potential small
entity impacts. Indeed, the RFA provides that any means of providing
regulatory flexibility to small entities be consistent with the statute
authorizing the rule. Moreover, even if EPA set a less stringent
standard, States could still exercise their discretion to obtain any
needed emission reductions from small entities. As the Supreme Court in
Train v. NRDC made clear, EPA has no authority to forbid States from
obtaining reductions from any particular category of stationary
sources, including small entities. See also, Virginia v. EPA, No. 108
F.3d 1397, 1408 (D.C. Cir. 1997), quoting Union Electric v. EPA, 427
U.S. 246, 269 (1976) (``section 110 left to the states the power to
determine which sources would be burdened by regulations and to what
extent'').
EPA's approval of SIPs for the new or revised NAAQS also will not
establish new requirements, but will instead simply approve
requirements that a State is already imposing. And again, EPA does not
have authority to disapprove a State's plan except to the extent that
the plan fails to demonstrate attainment and maintenance of the NAAQS
as required by Title I of the CAA. In cases where EPA promulgates a
FIP, EPA might establish control requirements applicable to small
entities, and in such a circumstance, EPA would conduct the analyses
required by the RFA.
Some commenters argued that under the RFA as amended by SBREFA, EPA
now has an obligation to choose the alternative that minimizes the
impact on small entities when setting the NAAQS. As indicated above,
EPA disagrees with the commenters' argument for the reasons stated in
the Unit of this notice discussing the Agency's authority to consider
costs and other factors not related to public health in setting and
revising primary NAAQS. In a nutshell, both the text and legislative
history of the RFA make clear that the RFA does not override the
substantive provisions of the statute authorizing the rule, but only
requires agencies to identify and consider ways of minimizing the
economic impact on small entities subject to the rule in a manner
consistent with the authorizing statute.
Some commenters disagreed with EPA's interpretation of the Mid-Tex
and United Distribution cases. In particular, these commenters noted
that in those cases the relevant regulatory agency, FERC, wholly lacked
jurisdiction to regulate the small entities at issue. According to
these commenters, EPA does have the ability and jurisdiction to
regulate small entities in the case of the NAAQS, and therefore EPA's
reliance on Mid-Tex and United Distribution is misplaced.
The commenters' attempt to distinguish the FERC cases from the
NAAQS rulemaking wholly overlooks the courts' reasoning, which in fact
fully supports EPA's certification of the proposed NAAQS. As described
above, the Mid-Tex court exhaustively reviewed the relevant sections of
the RFA and its legislative history. Its analysis revealed that
Congress passed the RFA out of concern with one-size-fits-all
regulations and fashioned a remedy limited to regulations that apply to
small entities. This principle is fully applicable to the NAAQS, which
creates no rule requirements that apply to small entities.
The fact that FERC had no regulatory authority over the small
entities indirectly affected by its rules played no essential role in
the court's rationale. FERC could (and apparently did in the Mid-Tex
rulemaking) estimate the potential indirect impact of its rules on
small entities. Presumably, FERC could have also mitigated any indirect
impact by changing some aspect of the rule (or else the small entities
would have had no incentive to sue the agency). The court nevertheless
found it unnecessary for FERC to do either, based on its reading of the
RFA as limited to analysis of a rule's impact on the small entities
subject to the rule's requirements. In reaching its decision, the court
noted that requiring agencies to ``consider every indirect effect that
any regulation might have on small businesses *** is a very broad and
ambitious agenda, *** that Congress is unlikely to have embarked on ***
without airing the matter.'' Mid-Tex, 773 F.d. at 343.
The commenters also overstate EPA's regulatory authority over small
entities

[[Page 38891]]

with respect to the regulation of criteria pollutants. Various CAA
provisions authorize EPA to regulate various types of sources at the
Federal level to accomplish specified goals. However, EPA's authority
to more generally regulate sources, including small entities, in the
manner of SIPs is limited to instances of State default of SIP
responsibilities. When that occurs, EPA may issue a FIP containing
specific control measures, and to the extent a proposed FIP would
establish control measures applicable to small entities, EPA would
analyze the small entity impact of those measures as required by the
RFA. In 1994, for example, EPA prepared an initial regulatory
flexibility analysis when it proposed a FIP for Los Angeles. See 59 FR
23264, May 5, 1994.
As noted above, Congress let the Mid-Tex interpretation stand when
it recently amended the RFA in enacting SBREFA. If it had disagreed
with the court's decision, it would have revised the relevant statutory
provisions or otherwise indicated its disagreement when it enacted
SBREFA. Instead, Congress actually reinforced the Mid-Tex court's
interpretation of the RFA in enacting section 212(a) of SBREFA. That
section requires that an agency issue a ``small entity compliance
guide'' for ``each rule *** for which an agency is required to prepare
a final regulatory flexibility analysis under section 604'' of the RFA.
The guide is ``to assist small entities in complying with the rule'' by
``explain[ing] the actions a small entity is required to take to
comply'' with the rule (SBREFA section 212(a)). Obviously, it makes no
sense to prepare a small entity compliance guide for a rule that does
not apply to small entities. SBREFA thus stands as further confirmation
that Congress intended regulatory flexibility analyses to address only
rules that establish requirements small entities must meet. Since
SBREFA's passage, the United Distribution court has affirmed the Mid-
Tex court's interpretation.
Some commenters noted that EPA's informal panel process did not
comply with the requirements of SBREFA. The EPA did not convene a
SBREFA panel because such a panel is not required for rules like the
NAAQS that do not apply to small entities. Under the RFA as amended by
SBREFA, since the Agency certified the proposal, it was not required to
convene a panel for it. Nevertheless, EPA conducted the voluntary panel
process described above, as well as other voluntary small business
outreach efforts. The process could not comply with the analytical
requirements of the RFA for the reasons given above. However, it could
and did ensure that EPA heard directly from small entities about the
NAAQS proposals.
A few commenters stated that EPA's view of the NAAQS and the RFA is
inconsistent with EPA's past positions regarding the RFA and NAAQS
revisions. Some commenters also cited the Regulatory Impact Analysis
for the proposed NAAQS and noted that this analysis demonstrates EPA's
ability to estimate the impact of the NAAQS on small entities, thereby
undercutting EPA's argument that it is not able to perform a regulatory
flexibility analysis when setting the NAAQS.
Past Federal Register notices make clear that the nature of the
NAAQS makes a regulatory flexibility analysis inapplicable to NAAQS
rulemakings. For instance, in 1984, EPA stated that a ``NAAQS for NOx
by itself has no direct impact on small entities. However, it forces
each State to design and implement control strategies for areas not in
attainment.'' 49 FR 6866, 6876, February 23, 1984; see also, 50 FR
37484, 37499, September 13, 1985; 50 FR 25532, 25542, June 19, 1985
(NAAQS for NO₂ do not impact small entities directly). EPA
stated again in 1987 that the NAAQS ``themselves do not contain
emission limits or other pollution controls. Rather, such controls are
contained in State implementation plans.'' 52 FR 24634, 24654, July 1,
1987.
EPA has typically performed an analysis to assess, to the extent
practicable, the potential impact of retaining or revising the NAAQS on
small entities, depending on possible State strategies for implementing
the NAAQS. These analyses have provided as much insight into the
potential small entity impacts of implementing revised NAAQS as could
be provided at the NAAQS rulemaking stage. In some instances, these
preliminary ``analyses'' were described as ``regulatory flexibility
analys[es]'' or as analyses ``pursuant to this [Regulatory Flexibility]
Act.'' See, e.g., 52 FR 24634, 24654, July 1, 1987; 50 FR 37484, 37499,
September 13, 1985.
However, these analyses were based on hypothetical State control
strategies, and EPA made the point on various occasions that any
conclusions to be drawn from such analyses were ``speculative,'' given
that the NAAQS themselves do not impose requirements on small entities.
Although these past analyses reflected the Agency's best efforts to
evaluate potential impacts, they were not regulatory flexibility
analyses containing the necessary elements required by the RFA. These
analyses, for example, did not describe the ``reporting, recordkeeping
and other compliance requirements'' of the proposed NAAQS rules that
would apply to small entities, since the NAAQS rules did not apply to
small entities. Nor did they determine how the proposed NAAQS rules
could be eased or waived for small entities. Such an analysis is not
possible in the case of the NAAQS. To the extent EPA labeled these
analyses regulatory flexibility analyses in the past, that label was
inappropriate. EPA's current practice is to describe such an analysis
more accurately as a ``general analysis of the potential cost impacts
on small entities.'' See, e.g., 61 FR 65638, 65669, 65747, December 13,
1996 (current O₃ and PM NAAQS proposals).⁶⁶ EPA's
analytical approach to small entity impacts of the NAAQS has thus
remained consistent over time.
---------------------------------------------------------------------------

66 As commenters pointed out, the RIA for the proposed PM NAAQS
does state that ``[t]he screening analysis *** provides enough
information for an initial regulatory flexibility analysis (RFA) if
such an analysis were to be done.'' That statement was mistaken and
was not made in the RIA for the proposed ozone NAAQS. While both
RIAs attempted to gauge the potential impact on small entities of
State implementation of the proposed NAAQS, neither could or did
identify any specific control or information requirements contained
in the NAAQS rule that would apply to small entities. Indeed, both
RIAs made clear that the impact being analyzed was that of potential
State measures to attain the NAAQS, and that such an analysis was
inherently speculative and uncertain. Thus, the RIAs actually
confirm EPA's statement in the preambles for the proposed NAAQS that
conducting a complete regulatory flexibility analysis is not
feasible for rules setting or revising a NAAQS.
---------------------------------------------------------------------------

One commenter noted that the legislative history of the RFA
suggests that the RFA was intended to apply to the NAAQS. As noted
previously, EPA's reading of both the RFA and SBREFA, based on the
language of the statute as amended and its legislative histories and
applicable caselaw, is that the RFA requirements at issue do not apply
to the NAAQS. The legislative history cited by the commenter does not
change this conclusion.
In fact, the statement by Senator Culver on which the commenter
relies does not indicate that the NAAQS should be subject to regulatory
flexibility analyses. Rather, Senator Culver uses the NAAQS as an
example of the type of standard that agencies would not change as a
result of the Regulatory Flexibility Act. According to Senator Culver,
Section 606 ``succinctly states that this bill does not alter the
substantive standard contained in underlying statutes which defines the
agency's mandate.'' 126 Cong. Rec. S 21455 (Aug. 6, 1980) daily ed.
After citing CAA section 109, Senator Culver goes on to describe EPA's
bubble policy

[[Page 38892]]

(which addresses the limits on emissions from a particular facility) as
the type of flexible regulation that agencies should consider, once EPA
has set a NAAQS. ``The important point for purposes of this discussion
is that the `bubble concept', a type of flexible regulation, in no
manner altered the basic statutory substantive standard of the EPA ***
. No regulatory flexibility analysis alters the substantive standard
otherwise applicable by law to agency action.'' Id. Thus, contrary to
the suggestion of the commenter, Senator Culver's statement actually
confirms that the time to consider regulatory flexibility is when
regulations applicable to sources are being established, not when a
NAAQS itself is being set.
Under section 604 of the RFA, whenever an agency promulgates a
final rule under section 553 of the Administrative Procedure Act, after
being required by that section or any other law to publish a general
notice of proposed rulemaking (NPRM), the agency is required to prepare
a final regulatory flexibility analysis. RFA section 605(b) provides,
however, that section 603 (re initial regulatory flexibility analyses)
and section 604 do not apply if the agency certifies that the rule will
not have a significant economic impact on a substantial number of small
entities and publishes such certification at the time of publication of
the NPRM or at the time of the final rule.
As noted above, EPA certified today's rule at the time of the NPRM.
After considering the public comments on the certification, EPA
continues to believe that today's rule will not have a significant
economic impact on a substantial number of small entities for the
reasons explained above and that it therefore appropriately certified
the rule. Further, as required by the CAA, EPA is promulgating today's
rule under CAA section 307(d). For all the foregoing reasons, EPA has
not prepared a final regulatory flexibility analysis for the rule. The
Agency has nonetheless analyzed in the final RIA for the rule the
potential impact on small entities of hypothetical State plans for
implementing the NAAQS. The Agency also plans to issue guidance to the
States on reducing the potential impact on small entities of
implementing the NAAQS.

C. Impact on Reporting Requirements

There are no reporting requirements directly associated with the
finalization of ambient air quality standards under section 109 of the
Act (42 U.S.C. 7409). There are, however, reporting requirements
associated with related sections of the Act, particularly sections 107,
110, 160, and 317 (42 U.S.C. 7407, 7410, 7460, and 7617).

D. Unfunded Mandates Reform Act

Title II of the Unfunded Mandates Reform Act of 1995 (UMRA), Pub.
L. 104-4, establishes requirements for Federal agencies to assess the
effects of their regulatory actions on State, local, and tribal
governments and the private sector. Under section 202 of the UMRA, EPA
generally must prepare a written statement, including a cost-benefit
analysis, for proposed and final rules with ``Federal mandates'' that
may result in expenditures by State, local, and tribal governments, in
the aggregate, or by the private sector, of $100 million or more in any
one year. This requirement does not apply if EPA is prohibited by law
from considering section 202 estimates and analyses in adopting the
rule in question. Before promulgating an EPA rule for which a written
statement is needed, section 205 of the UMRA generally requires EPA to
identify and consider a reasonable number of regulatory alternatives
and adopt the least costly, most cost-effective, or least burdensome
alternative that achieves the objectives of the rule. These
requirements do not apply when they are inconsistent with applicable
law. Moreover, section 205 allows EPA to adopt an alternative other
than the least costly, most cost-effective, or least burdensome
alternative if the Administrator publishes with the final rule an
explanation of why that alternative was not adopted. Before EPA
establishes any regulatory requirements that may significantly or
uniquely affect small governments, including tribal governments, it
must have developed under section 203 of the UMRA a small government
agency plan. The plan must provide for notifying potentially affected
small governments, enabling officials of affected small governments to
have meaningful and timely input in the development of EPA regulatory
proposals with significant Federal intergovernmental mandates, and
informing, educating, and advising small governments on compliance with
the regulatory requirements. Section 204 of UMRA requires each agency
to develop ``an effective process to permit elected officers of State,
local and tribal governments *** to provide meaningful and timely
input'' in the development of regulatory proposals containing a
significant Federal intergovernmental mandate.⁶⁷
---------------------------------------------------------------------------

67 As noted in Unit VII.B. of this preamble, a NAAQS rule only
establishes a standard of air quality that other provisions of the
Act call on States (or in the case of State inaction, the Federal
government) to achieve by adopting implementation plans containing
specific control measures for the purpose. Thus, it is questionable
whether the NAAQS itself imposes an enforceable duty and thus
whether it is a significant Federal mandate within the meaning of
UMRA. EPA need not and does not reach this issue today. For the
reasons given in this unit, even if the NAAQS were determined to be
a significant Federal mandate, EPA does not have any obligations
under sections 202 and 205 of UMRA, and EPA has met any obligations
it would have under section 204 of UMRA.
---------------------------------------------------------------------------

The EPA has determined that the provisions of sections 202 and 205
of the UMRA do not apply to this decision. ``Unless otherwise
prohibited by law,'' EPA is to prepare a written statement under
Section 202 of UMRA that is to contain assessments and estimates of the
costs and benefits of a rule containing a Federal mandate. Congress
clarified that ``unless otherwise prohibited by law'' referred to
whether an agency was prohibited from considering the information in
the rulemaking process, not to whether an agency was prohibited from
collecting the information. The Conference Report on UMRA states,
``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). Because the Clean Air Act prohibits EPA,
when setting the NAAQS, from considering the types of estimates and
assessments described in section 202, UMRA does not require EPA to
prepare a written statement under section 202.⁶⁸ The
requirements in section 205 do not apply because those requirements
only apply to rules ``for which a written statement is required under
section 202 ***.''
---------------------------------------------------------------------------

68 In addition to the estimates and assessments described in
section 202 of UMRA, written statements are also to include an
identification of the Federal law under which the rule is
promulgated (section 202(a)(1) of UMRA) and a description of
outreach efforts under section 204 of UMRA (section 202(a)(5) of
UMRA). Although these requirements do not apply here because a
written statement is not required under section 202 of UMRA, this
preamble identifies the Federal law under which this rule is being
promulgated and a written statement describing EPA's outreach efforts with
State, local, and tribal governments will be placed in the docket.
---------------------------------------------------------------------------

The EPA has determined that the provisions of section 203 of UMRA
do not apply to this decision. Section 203 only requires the
development of a small government agency plan for requirements with
which small governments might have to comply. Since setting the NAAQS
does not establish requirements with which small governments might have
to comply, section 203 does not apply. The

[[Page 38893]]

EPA acknowledges, however, that any corresponding revisions to
associated State implementation plan requirements and air quality
surveillance requirements, 40 CFR part 51 and 40 CFR part 58,
respectively, might result in such effects. Accordingly, EPA will
address unfunded mandates as appropriate when it proposes any revisions
to 40 CFR parts 51 and 58.
With regard to the outreach described in UMRA section 204, EPA did
follow a process for providing elected officials with an opportunity
for meaningful and timely input into the proposed NAAQS revisions,
although EPA did not describe this process in the proposal. The EPA
conducted a series of pre-proposal outreach meetings with State and
local officials and their representatives that permitted these
officials to provide meaningful and timely input on issues related to
the NAAQS and the monitoring issues associated with them. Beginning in
January, 1996, EPA briefed State and local air pollution control
officials at national meetings with State and Territorial Air Pollution
Program Administrators (STAPPA)/Association of Local Air Pollution
Control Officials (ALAPCO) in Washington DC, North Carolina, Chicago
and Nevada. The EPA also held briefings for the Washington DC
representatives of several State and local organizations, including
National Conference of State Legislators, U.S. Conference of Mayors,
National Governors Association, and National League of Cities, and
STAPPA/ALAPCO. EPA also held separate briefings and discussions with
State and local officials at meetings set up by the National Governors
Association, the U.S. Conference of Mayors and the Council of State
Governments. The EPA also conducted in-depth briefings at each EPA
regional office and regional staff also had several meetings and
discussions with their State counterparts about the standards. The
efforts described above, which provided elected officials with
opportunity for meaningful and timely input into the proposed NAAQS
revisions, met any requirements imposed by section 204. The docket will
contain a written statement describing these outreach efforts,
including a summary of the comments and concerns presented by State,
local, and tribal governments and a summary of EPA's evaluation of
those comments and concerns.
Several commenters disagreed with EPA that UMRA sections 202, 203
and 205 do not apply to this decision. These commenters argued that EPA
is not prohibited from considering costs in setting NAAQS under the
Clean Air Act and applicable judicial decisions. Some commenters also
expressed the view that there is no conflict between UMRA and the Clean
Air Act with regard to the NAAQS. These commenters argued that UMRA and
the NAAQS can be ``harmonized'' by reading UMRA as an information
gathering statute and that EPA should therefore perform the analyses
required by UMRA, regardless of whether costs may be considered.
Finally, at least one commenter argued that in past NAAQS reviews, EPA
did not dispute its UMRA obligations.
As discussed more fully in Unit IV of this preamble, EPA is
prohibited from considering cost in setting the NAAQS. Given that fact
(as noted in Unit IV preamble), sections 202 and 205 do not
apply.⁶⁹ As the Conference Report clarifies, UMRA itself
states that the section 202 estimates and analyses are not required in
cases such as the NAAQS, where an agency is prohibited by law from
considering section 202 estimates and analyses. Reading UMRA in the
manner suggested by the commenters would effectively read this
provision out of UMRA; UMRA contains an exception for rules like the
NAAQS, it must be given effect.
---------------------------------------------------------------------------

69 One commenter argued that in reviewing the SO₂
NAAQS, EPA determined that it need not revise the SO₂
NAAQS, but could instead pursue an alternative regulatory program
under other authority. This commenter argued that EPA has similar
flexibility in reviewing the PM and Ozone NAAQS, and thus UMRA
requires EPA to identify the least burdensome alternative (such as
retaining the current NAAQS) as part of that process. As discussed
more fully above at Unit IV of this preamble, EPA does not agree
that it has flexibility to choose such an alternative; nor does EPA
agree with the commenter's characterization of the action it took in
deciding not to revise the SO₂ NAAQS. In fact, in
deciding not to revise the SO₂ NAAQS, EPA determined, for
reasons independent of section 303 of the Clean Air Act that a NAAQS
revision was not warranted. See 61 FR 25566, 25575, May 22, 1996.
---------------------------------------------------------------------------

With regard to EPA's position regarding UMRA in previous NAAQS
review exercises, EPA simply made plain in those situations that
because it did not plan on revising the NAAQS, it determined, without
further review, that UMRA sections 202, 203 and 205 did not apply. EPA
thus stated that:

Because the Administrator has decided not to revise the existing
primary NAAQS for SO₂, this action will not impose any
new expenditures on governments or on the private sector, or
establish any new regulatory requirements affecting small
governments. Accordingly, EPA has determined that the provisions of
section 202, 203 and 205 do not apply to this final decision.

61 FR 25566, 25577, May 22, 1996; See also 61 FR 52852, 52856, October
8, 1996 (Same statement for NO₂ NAAQS). As this statement
makes clear, EPA only determined that UMRA sections 202, 203 and 205
did not apply to the NAAQS when EPA fails to revise the standard.
Having made that determination, EPA had no reason to catalogue
additional bases for finding UMRA inapplicable. Nothing in that
statement was intended to preclude EPA, or precludes EPA, from
concluding for other reasons (such as those discussed above) that UMRA
also does not apply when EPA in fact revises an applicable NAAQS.

E. Environmental Justice

Executive Order 12848 requires that each Federal agency make
achieving environmental justice part of its mission by identifying and
addressing, as appropriate, disproportionately high and adverse human
health or environmental effects of its programs, policies, and
activities on minorities and low-income populations. These requirements
have been addressed to the extent practicable in the RIA cited above.

F. Submission to Congress and the Comptroller General

Under 5 U.S.C. 801(a)(1)(A), as added by the Small Business
Regulatory Enforcement Fairness Act of 1996 (SBREFA), EPA submitted a
report containing this rule and other required information to the U.S.
Senate, the U.S. House of Representatives, and the Comptroller General
of the United States prior to publication of the rule in today's
Federal Register. This rule is a ``major rule'' for purposes of SBREFA.

VIII. Response to Petition for Administrator Browner's Recusal

On March 13, 1997, the Washington Legal Foundation (WLF), filed a
petition with EPA asking that I, Carol Browner, disqualify myself in
rulemaking regarding the NAAQS for PM and O₃. The petition
claims that my public statements indicate a ``clear and convincing
showing'' that I had ``already decided to revise the NAAQS for PM and
ozone'' and that I therefore ``could not give meaningful
consideration'' to comments adverse to the proposed rule. On May 12,
1997, EPA's General Counsel, Jonathan Z. Cannon, sent a letter to WLF
regarding the petition. This letter and the WLF petition were then
placed in the dockets for the proposed O₃ and PM standards
pending ``consideration and final response in connection with the
Agency's final actions.''
Contrary to WLF's assertions, I have maintained an open mind
throughout these proceedings, and have based today's decisions on the
rulemaking

[[Page 38894]]

record--including consideration of comments opposed to the proposal.
The law does not require the Administrator of EPA to disqualify herself
merely for expressing views on a proposed regulation; in fact, it is
part of my responsibility to engage in the public debate on the
proposals. Moreover, the assertions in WLF's petition do not accurately
represent my views. The petition takes quotes out of context and
repeatedly misinterprets my statements. For example, WLF quotes a
statement that I made at the Children's Environmental Health Network
Research Conference as an indication that I had ``prejudged the
issue.'' However, my statement that ``I will not be swayed'' did not
refer to adopting the NAAQS as proposed. Instead, as is clear from
reviewing the entire speech, I was addressing my broader concern about
children's health and the range of EPA standards affecting children's
health. I also appeared at several congressional hearings and testified
before members of Congress, some of whom were strongly opposed to the
proposals. At those hearings, I explained the basis for the proposals
and put forward the reasons why I concluded the proposals were
appropriate, given the information before me at the time. At the same
time, I made clear that I took very seriously my obligation to keep an
open mind, and to consider fully and fairly all significant comments
that the Agency received. For these reasons and others, as set forth in
Mr. Cannon's May 12, 1997 response to WLF, which I adopt in full, I
have decided not to recuse myself from any aspect of considering
revisions to the NAAQS for O₃ and PM. Accordingly, I am
hereby denying WLF's petition.

IX. References

(1) American Thoracic Society. (1985) Guidelines as to what
constitutes an adverse respiratory health effect, with special
reference to epidemiologic studies of air pollution. American Review
of Respiratory Disease.. 131: 666-668.
(2) Freas (1996) Ambient air quality relationships among
alternative ozone air quality standards. Internal memorandum from
Warren P. Freas to file, U.S. EPA, EMAD/OAQPS/OAR, RTP, NC, dated
October 30, 1996. Docket No. A-95-58 Item II-B-6.
(3) Freas (1997) Ambient air quality relationships for counties
meeting alternative air quality standards. Internal memorandum from
Warren P. Freas to file, U.S. EPA, EMAD/OAQPS/OAR, RTP, NC, dated
July 1, 1997. Docket No. A-95-58 Item xxx.
(4) Heck, Walter W. And Ellis B. Cowling. January, 1997. EM
Journal. ``The Need for a Long Term Cumulative Secondary Ozone
Standard - An Ecological Perspective.'' Air and Waste Management
Association, Pittsburgh, PA.; pp. 23-33.
(5) Johnson, T; Capel, J.; Mozier, J.; McCoy, M. (1996a)
Estimation of ozone exposures experienced by outdoor children in
nine urban areas using a probabilistic version of NEM. Prepared by
IT/Air Quality Services for U.S. EPA, OAQPS; Research Triangle Park,
NC, August.
(6) Johnson, T.; Capel, J.; McCoy, M.; Mozier, J. (1996b)
Estimation of ozone exposures experienced by outdoor workers in nine
urban areas using a probabilistic version of NEM. Prepared by IT/Air
Quality Services for U.S. EPA, OAQPS; Research Triangle Park, NC, August.
(7) McClellan, R. O., (1989) Letter from Chairman of Clean Air
Scientific Advisory Committee to the EPA Administrator, dated May 1,
1989. EPA-SAB-CASAC-LTR-89-019.
(8) Richmond (1997) Supplemental ozone exposure and health risk
analyses. Internal memorandum from Harvey M. Richmond to Karen M.
Martin, U.S. EPA, AQSSD/OAQPS/OAR, RTP, NC, dated February 11, 1997.
Docket No. A-95-58 Item IV-A-1.
(9) Seitz (1996) Revocation date for the existing 1-hour ozone
standards. Internal memorandum from John S. Seitz to Mary D.
Nichols, U.S. EPA, OAQPS/OAR, RTP, NC, dated November 20, 1996.
Docket No. A-95-59 Item II-B-3.
(10) Thurston, G.D.; Ito, K.; Kinney, P.L.; Lippmann, M. (1992)
A multi-year study of air pollution and respiratory hospital
admissions in three New York State metropolitan areas: results for
1988 and 1989 summers. Journal of Exposure Analysis and
Environmental Epidemiology. 2:429-450.
(11) U.S. Department of Health and Human Services (1996) Vital
and health statistics: current estimates from the national health
interview survey, 1994. Hyattsville, MD: Public Health Service,
National Center for Health Statistics; DHHS publication no. (PHS) 96-278.
(12) U.S. Environmental Protection Agency (1996a) Air quality
criteria for Ozone and related photochemical oxidants. Research
Triangle Park, NC: Office of Health and Environmental Assessment,
Environmental Criteria and Assessment Office; EPA report nos. EPA/
600/AP-93/004a-c.
(13) U.S. Environmental Protection Agency (1996b) Review of the
national ambient air quality standards for ozone: assessment of
scientific and technical information. OAQPS staff paper. Research
Triangle Park, NC: Office of Air Quality Planning and Standards; EPA
report no. EPA-452/R-96-007. Available from: NTIS, Springfield, VA;
PB96-203435.
(14) Whitfield, R.G.; Biller, W.F.; Jusko, M.J.; Keisler, J.M.
(1996) A probabilistic assessment of health risks associated with
short-term exposure to tropospheric ozone. Report prepared for U.S.
EPA, OAQPS. Argonne National Laboratory; Argonne, IL, June. (For
copies, contact Harvey M. Richmond, U.S. Environmental Protection
Agency, OAQPS, MD-15, Research Triangle Park, N.C. 27711, (919) 541-5271.)
(15) Wolff, G. T., (1995a) Letter from Chairman of Clean Air
Scientific Advisory Committee to the EPA Administrator, dated
November 28, 1995. EPA-SAB-CASAC-LTR-96-001.
(16) Wolff, G. T., (1995b) Letter from Chairman of Clean Air
Scientific Advisory Committee to the EPA Administrator, dated
November 30, 1995. EPA-SAB-CASAC-LTR-96-002.
(17) Wolff, G. T., (1996) Letter from Chairman of Clean Air
Scientific Advisory Committee to the EPA Administrator, dated April
4, 1996. EPA-SAB-CASAC-LTR-96-006.

List of Subjects in 40 CFR Part 50

Environmental protection, Air pollution control, Carbon monoxide,
Lead, Nitrogen dioxide, Ozone, Particulate matter, Sulfur oxides.

Dated: July 16, 1997.

Carol M. Browner,
Administrator.

Therefore, for the reasons set forth in the preamble, title 40,
chapter I, part 50 of the Code of Federal Regulations is amended as
follows:

PART 50--NATIONAL PRIMARY AND SECONDARY AMBIENT AIR QUALITY STANDARDS

1. The authority citation for part 50 continues to read as follows:
Authority: Secs. 109 and 301(a), Clean Air Act, as amended (42
U.S.C. 7409, 7601(a)).

2. Section 50.9 is revised to read as follows:

Sec. 50.9 National 1-hour primary and secondary ambient air quality
standards for ozone.

(a) The level of the national 1-hour primary and secondary ambient
air quality standards for ozone measured by a reference method based on
Appendix D to this part and designated in accordance with part 53 of
this chapter, is 0.12 parts per million (235 g/m³).
The standard is attained when the expected number of days per calendar
year with maximum hourly average concentrations above 0.12 parts per
million (235 g/m³) is equal to or less than 1, as
determined by Appendix H to this part.
(b) The 1-hour standards set forth in this section will no longer
apply to an area once EPA determines that the area has air quality
meeting the 1-hour standard. Area designations are codified in 40 CFR
part 81.
3. Section 50.10 is added to read as follows:

Sec. 50.10 National 8-hour primary and secondary ambient air quality
standards for ozone.

(a) The level of the national 8-hour primary and secondary ambient
air quality standards for ozone, measured

[[Page 38895]]

by a reference method based on Appendix D to this part and designated
in accordance with part 53 of this chapter, is 0.08 parts per million
(ppm), daily maximum 8-hour average.
(b) The 8-hour primary and secondary ozone ambient air quality
standards are met at an ambient air quality monitoring site when the
average of the annual fourth-highest daily maximum 8-hour average ozone
concentration is less than or equal to 0.08 ppm, as determined in
accordance with Appendix I to this part.
4. Appendix D is amended by revising references 8 and 9 and by
removing all of the text and figures immediately following ``Figure 2,
Schematic Diagram of a Typical UV Photometric Calibration System
(Option 1), through the end of Appendix D.

Appendix D to Part 50--Measurement Principle and Calibration
Procedure for the Measurement of Ozone in the Atmosphere

* * * * *
6. References.
* * * * *
8. Transfer Standards for Calibration of Ambient Air Monitoring
Analyzers for Ozone, EPA publication number EPA-600/4-79-056, EPA,
National Exposure Research Laboratory, Department E, (MD-77B),
Research Triangle Park, NC 27711.
9. Technical Assistance Document for the Calibration of Ambient
Ozone Monitors, EPA publication number EPA-600/4-79-057, EPA,
National Exposure Research Laboratory, Department E, (MD-77B),
Research Triangle Park, NC 27711.
* * * * *

Appendix E [Removed and Reserved]

5. Appendix E is removed and reserved.
6. Appendix H is amended by revising the appendix heading to read
``Appendix H To Part 50--Interpretation of The 1-Hour Primary and
Secondary National Ambient Air Quality Standards for Ozone''.
7. Appendix I is added to read as follows:

Appendix I to Part 50--Interpretation of the 8-Hour Primary and
Secondary National Ambient Air Quality Standards for Ozone

1. General.
This appendix explains the data handling conventions and
computations necessary for determining whether the national 8-hour
primary and secondary ambient air quality standards for ozone
specified in Sec. 50.10 are met at an ambient ozone air quality
monitoring site. Ozone is measured in the ambient air by a reference
method based on Appendix D of this part. Data reporting, data
handling, and computation procedures to be used in making
comparisons between reported ozone concentrations and the level of
the ozone standard are specified in the following sections. Whether
to exclude, retain, or make adjustments to the data affected by
stratospheric ozone intrusion or other natural events is subject to
the approval of the appropriate Regional Administrator.
2. Primary and Secondary Ambient Air Quality Standards for Ozone.
2.1 Data Reporting and Handling Conventions.
2.1.1 Computing 8-hour averages. Hourly average concentrations
shall be reported in parts per million (ppm) to the third decimal
place, with additional digits to the right being truncated. Running
8-hour averages shall be computed from the hourly ozone
concentration data for each hour of the year and the result shall be
stored in the first, or start, hour of the 8-hour period. An 8-hour
average shall be considered valid if at least 75% of the hourly
averages for the 8-hour period are available. In the event that only
6 (or 7) hourly averages are available, the 8-hour average shall be
computed on the basis of the hours available using 6 (or 7) as the
divisor. (8-hour periods with three or more missing hours shall not
be ignored if, after substituting one-half the minimum detectable
limit for the missing hourly concentrations, the 8-hour average
concentration is greater than the level of the standard.) The
computed 8-hour average ozone concentrations shall be reported to
three decimal places (the insignificant digits to the right of the
third decimal place are truncated, consistent with the data handling
procedures for the reported data.)
2.1.2 Daily maximum 8-hour average concentrations. (a) There
are 24 possible running 8-hour average ozone concentrations for each
calendar day during the ozone monitoring season. (Ozone monitoring
seasons vary by geographic location as designated in part 58,
Appendix D to this chapter.) The daily maximum 8-hour concentration
for a given calendar day is the highest of the 24 possible 8-hour
average concentrations computed for that day. This process is
repeated, yielding a daily maximum 8-hour average ozone
concentration for each calendar day with ambient ozone monitoring
data. Because the 8-hour averages are recorded in the start hour,
the daily maximum 8-hour concentrations from two consecutive days
may have some hourly concentrations in common. Generally,
overlapping daily maximum 8-hour averages are not likely, except in
those non-urban monitoring locations with less pronounced diurnal
variation in hourly concentrations.
(b) An ozone monitoring day shall be counted as a valid day if
valid 8-hour averages are available for at least 75% of possible
hours in the day (i.e., at least 18 of the 24 averages). In the
event that less than 75% of the 8-hour averages are available, a day
shall also be counted as a valid day if the daily maximum 8-hour
average concentration for that day is greater than the level of the
ambient standard.
2.2 Primary and Secondary Standard-related Summary Statistic.
The standard-related summary statistic is the annual fourth-highest
daily maximum 8-hour ozone concentration, expressed in parts per
million, averaged over three years. The 3-year average shall be
computed using the three most recent, consecutive calendar years of
monitoring data meeting the data completeness requirements described
in this appendix. The computed 3-year average of the annual fourth-
highest daily maximum 8-hour average ozone concentrations shall be
expressed to three decimal places (the remaining digits to the right
are truncated.)
2.3 Comparisons with the Primary and Secondary Ozone Standards.
(a) The primary and secondary ozone ambient air quality standards
are met at an ambient air quality monitoring site when the 3-year
average of the annual fourth-highest daily maximum 8-hour average
ozone concentration is less than or equal to 0.08 ppm. The number of
significant figures in the level of the standard dictates the
rounding convention for comparing the computed 3-year average annual
fourth-highest daily maximum 8-hour average ozone concentration with
the level of the standard. The third decimal place of the computed
value is rounded, with values equal to or greater than 5 rounding
up. Thus, a computed 3-year average ozone concentration of 0.085 ppm
is the smallest value that is greater than 0.08 ppm.
(b) This comparison shall be based on three consecutive,
complete calendar years of air quality monitoring data. This
requirement is met for the three year period at a monitoring site if
daily maximum 8-hour average concentrations are available for at
least 90%, on average, of the days during the designated ozone
monitoring season, with a minimum data completeness in any one year
of at least 75% of the designated sampling days. When computing
whether the minimum data completeness requirements have been met,
meteorological or ambient data may be sufficient to demonstrate that
meteorological conditions on missing days were not conducive to
concentrations above the level of the standard. Missing days assumed
less than the level of the standard are counted for the purpose of
meeting the data completeness requirement, subject to the approval
of the appropriate Regional Administrator.
(c) Years with concentrations greater than the level of the
standard shall not be ignored on the ground that they have less than
complete data. Thus, in computing the 3-year average fourth maximum
concentration, calendar years with less than 75% data completeness
shall be included in the computation if the average annual fourth
maximum 8-hour concentration is greater than the level of the standard.
(d) Comparisons with the primary and secondary ozone standards
are demonstrated by examples 1 and 2 in paragraphs (d)(1) and (d)
(2) respectively as follows:
(1) As shown in example 1, the primary and secondary standards
are met at this monitoring site because the 3-year average of the
annual fourth-highest daily maximum 8-hour average ozone
concentrations (i.e., 0.084 ppm) is less than or equal to 0.08 ppm.
The data completeness requirement is also met because the average
percent of days with valid ambient monitoring data is greater than

[[Page 38896]]

90%, and no single year has less than 75% data completeness.

Example 1. Ambient monitoring site attaining the primary and secondary ozone standards
----------------------------------------------------------------------------------------------------------------
1st Highest 2nd Highest 3rd Highest 4th Highest 5th Highest
Percent Daily Max 8- Daily Max 8- Daily Max 8- Daily Max 8- Daily Max 8-
Year Valid Days hour Conc. hour Conc. hour Conc. hour Conc. hour Conc.
(ppm) (ppm) (ppm) (ppm) (ppm)
----------------------------------------------------------------------------------------------------------------
1993.............................. 100% 0.092 0.091 0.090 0.088 0.085
----------------------------------------------------------------------------------------------------------------
1994.............................. 96% 0.090 0.089 0.086 0.084 0.080
----------------------------------------------------------------------------------------------------------------
1995.............................. 98% 0.087 0.085 0.083 0.080 0.075
================================================================================================================
Average....................... 98% 0.084
----------------------------------------------------------------------------------------------------------------

(2) As shown in example 2, the primary and secondary standards
are not met at this monitoring site because the 3-year average of
the fourth-highest daily maximum 8-hour average ozone concentrations
(i.e., 0.093 ppm) is greater than 0.08 ppm. Note that the ozone
concentration data for 1994 is used in these computations, even
though the data capture is less than 75%, because the average
fourth-highest daily maximum 8-hour average concentration is greater
than 0.08 ppm.

Example 2. Ambient Monitoring Site Failing to Meet the Primary and Secondary Ozone Standards
----------------------------------------------------------------------------------------------------------------
1st Highest 2nd Highest 3rd Highest 4th Highest 5th Highest
Percent Daily Max 8- Daily Max 8- Daily Max 8- Daily Max 8- Daily Max 8-
Year Valid Days hour Conc. hour Conc. hour Conc. hour Conc. hour Conc.
(ppm) (ppm) (ppm) (ppm) (ppm)
----------------------------------------------------------------------------------------------------------------
1993.............................. 96% 0.105 0.103 0.103 0.102 0.102
----------------------------------------------------------------------------------------------------------------
1994.............................. 74% 0.090 0.085 0.082 0.080 0.078
----------------------------------------------------------------------------------------------------------------
1995.............................. 98% 0.103 0.101 0.101 0.097 0.095
================================================================================================================
Average....................... 89% 0.093
----------------------------------------------------------------------------------------------------------------

3. Design Values for Primary and Secondary Ambient Air Quality
Standards for Ozone.
The air quality design value at a monitoring site is defined as
that concentration that when reduced to the level of the standard
ensures that the site meets the standard. For a concentration-based
standard, the air quality design value is simply the standard-
related test statistic. Thus, for the primary and secondary ozone
standards, the 3-year average annual fourth-highest daily maximum 8-
hour average ozone concentration is also the air quality design
value for the site.

[FR Doc. 97-18580 Filed 7-17-97; 8:45 am]
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