PART 50-NATIONAL PRIMARY AND SECONDARY
AMBIENT AIR QUALITY STANDARDS
[Revised as of July 1, 2000]
PART 50--NATIONAL PRIMARY AND SECONDARY AMBIENT AIR QUALITY STANDARDS
Sec.
50.1 Definitions.
50.2 Scope.
50.3 Reference conditions.
50.4 National primary ambient air quality standards for sulfur oxides
(sulfur dioxide).
50.5 National secondary ambient air quality standard for sulfur oxides
(sulfur dioxide).
50.6 National primary and secondary ambient air quality standards for
PM10.
50.7 National primary and secondary ambient air quality standards for
particulate matter.
50.8 National primary ambient air quality standards for carbon
monoxide.
50.9 National 1-hour primary and secondary ambient air quality
standards for ozone.
50.10 National 8-hour primary and secondary ambient air quality
standards for ozone.
50.11 National primary and secondary ambient air quality standards for
nitrogen dioxide.
50.12 National primary and secondary ambient air quality standards for
lead.
40 CFR 50 contains Appendix A-N
(The following Appendix are included from 40 CFR 50.
For a complete version go to
http://www.access.gpo.gov/cgi-bin/cfrassemble.cgi?title=200040)
Appendix H to Part 50--Interpretation of the 1-Hour Primary and
Secondary National Ambient Air Quality Standards for Ozone
Appendix I to Part 50--Interpretation of the 8-Hour Primary and
Secondary National Ambient Air Quality Standards for Ozone
Appendix K to Part 50--Interpretation of the National Ambient Air
Quality Standards for Particulate Matter
Appendix N to Part 50--Interpretation of the National Ambient Air
Quality Standards for Particulate Matter
Sec. 50.1 Definitions.
(a) As used in this part, all terms not defined herein shall have
the meaning given them by the Act.
(b) Act means the Clean Air Act, as amended (42 U.S.C. 1857-18571,
as amended by Pub. L. 91-604).
(c) Agency means the Environmental Protection Agency.
(d) Administrator means the Administrator of the Environmental
Protection Agency.
(e) Ambient air means that portion of the atmosphere, external to
buildings, to which the general public has access.
(f) Reference method means a method of sampling and analyzing the
ambient air for an air pollutant that is specified as a reference method
in an appendix to this part, or a method that has been designated as a
reference method in accordance with part 53 of this chapter; it does not
include a method for which a reference method designation has been
cancelled in accordance with Sec. 53.11 or Sec. 53.16 of this chapter.
(g) Equivalent method means a method of sampling and analyzing the
ambient air for an air pollutant that has been designated as an
equivalent method in accordance with part 53 of this chapter; it does
not include a method for which an equivalent method designation has
been cancelled in accordance with Sec. 53.11 or Sec. 53.16 of this
chapter.
(h) Traceable means that a local standard has been compared and
certified either directly or via not more than one intermediate
standard, to a primary standard such as a National Bureau of Standards
Standard Reference Material (NBS SRM), or a USEPA/NBS-approved Certified
Reference Material (CRM).
(i) Indian country is as defined in 18 U.S.C. 1151.
[36 FR 22384, Nov. 25, 1971, as amended at 41 FR 11253, Mar. 17, 1976;
48 FR 2529, Jan. 20, 1983; 63 FR 7274, Feb. 12, 1998]
Sec. 50.2 Scope.
(a) National primary and secondary ambient air quality standards
under section 109 of the Act are set forth in this part.
(b) National primary ambient air quality standards define levels of
air quality which the Administrator judges are necessary, with an
adequate margin of safety, to protect the public health. National
secondary ambient air quality standards define levels of air quality
which the Administrator judges necessary to protect the public welfare
from any known or anticipated adverse effects of a pollutant. Such
standards are subject to revision, and additional primary and secondary
standards may be promulgated as the Administrator deems necessary to
protect the public health and welfare.
(c) The promulgation of national primary and secondary ambient air
quality standards shall not be considered in any manner to allow
significant deterioration of existing air quality in any portion of any
State or Indian country.
(d) The proposal, promulgation, or revision of national primary and
secondary ambient air quality standards shall not prohibit any State or
Indian country from establishing ambient air quality standards for that
State or area under a tribal CAA program or any portion thereof which
are more stringent than the national standards.
[36 FR 22384, Nov. 25, 1971, as amended at 63 FR 7274, Feb. 12, 1998]
Sec. 50.3 Reference conditions.
All measurements of air quality that are expressed as mass per unit
volume (e.g., micrograms per cubic meter) other than for the particulate
matter (PM10 and PM2.5) standards contained in
Sec. 50.7 shall be corrected to a reference temperature of 25 deg.C and
a reference pressure of 760 millimeters of mercury (1,013.2 millibars).
Measurements of PM10 and PM2.5 for purposes of
comparison to the standards contained in Sec. 50.7 shall be reported
based on actual ambient air volume measured at the actual ambient
temperature and pressure at the monitoring site during the measurement
period.
[62 FR 38711, July 18, 1997]
Sec. 50.4 National primary ambient air quality standards for sulfur
oxides (sulfur dioxide).
(a) The level of the annual standard is 0.030 parts per million
(ppm), not to be exceeded in a calendar year. The annual arithmetic mean
shall be rounded to three decimal places (fractional parts equal to or
greater than 0.0005 ppm shall be rounded up).
(b) The level of the 24-hour standard is 0.14 parts per million
(ppm), not to be exceeded more than once per calendar year. The 24-hour
averages shall be determined from successive nonoverlapping 24-hour
blocks starting at midnight each calendar day and shall be rounded to
two decimal places (fractional parts equal to or greater than 0.005 ppm
shall be rounded up).
(c) Sulfur oxides shall be measured in the ambient air as sulfur
dioxide by the reference method described in appendix A to this part or
by an equivalent method designated in accordance with part 53 of this
chapter.
(d) To demonstrate attainment, the annual arithmetic mean and the
second-highest 24-hour averages must be based upon hourly data that are
at least 75 percent complete in each calendar quarter. A 24-hour block
average shall be considered valid if at least 75 percent of the hourly
averages for the 24-hour period are available. In the event that only
18, 19, 20, 21, 22, or 23 hourly averages are available, the 24-hour
block average shall be computed as the sum of the available hourly
averages using 18, 19, etc. as the divisor. If fewer than 18 hourly
averages are available, but the 24-hour average would exceed the level
of the standard when zeros are substituted for the missing values,
subject to the rounding rule of paragraph (b) of this section, then this
shall be considered a valid 24-hour average. In this case, the 24-hour
block average shall be computed as the sum of the available hourly
averages divided by 24.
[61 FR 25579, May 22, 1996]
Sec. 50.5 National secondary ambient air quality standard for sulfur
oxides (sulfur dioxide).
(a) The level of the 3-hour standard is 0.5 parts per million (ppm),
not to be exceeded more than once per calendar year. The 3-hour averages
shall be determined from successive nonoverlapping 3-hour blocks
starting at midnight each calendar day and shall be rounded to 1 decimal
place (fractional parts equal to or greater than 0.05 ppm shall be
rounded up).
(b) Sulfur oxides shall be measured in the ambient air as sulfur
dioxide by the reference method described in appendix A of this part or
by an equivalent method designated in accordance with part 53 of this
chapter.
(c) To demonstrate attainment, the second-highest 3-hour average
must be based upon hourly data that are at least 75 percent complete in
each calendar quarter. A 3-hour block average shall be considered valid
only if all three hourly averages for the 3-hour period are available.
If only one or two hourly averages are available, but the 3-hour average
would exceed the level of the standard when zeros are substituted for
the missing values, subject to the rounding rule of paragraph (a) of
this section, then this shall be considered a valid 3-hour average. In
all cases, the 3-hour block average shall be computed as the sum of the
hourly averages divided by 3.
[61 FR 25580, May 22, 1996]
Sec. 50.6 National primary and secondary ambient air quality standards
for PM10.
(a) The level of the national primary and secondary 24-hour ambient
air quality standards for particulate matter is 150 micrograms per cubic
meter (ug/m3), 24-hour average concentration. The standards
are attained when the expected number of days per calendar year with a
24-hour average concentration above 150 ug/m3, as determined
in accordance with appendix K to this part, is equal to or less than
one.
(b) The level of the national primary and secondary annual standards
for particulate matter is 50 micrograms per cubic meter ug/m3,
annual arithmetic mean. The standards are attained when the
expected annual arithmetic mean concentration, as determined in
accordance with appendix K to this part, is less than or equal to 50
ug/m3.
(c) For the purpose of determining attainment of the primary and
secondary standards, particulate matter shall be measured in the ambient
air as PM10 (particles with an aerodynamic diameter less than
or equal to a nominal 10 micrometers) by:
(1) A reference method based on appendix J and designated in
accordance with part 53 of this chapter, or
(2) An equivalent method designated in accordance with part 53 of
this chapter.
(d) The PM10 standards set forth in this section will no
longer apply to an area not attaining these standards as of September
16, 1997, once EPA takes final action to promulgate a rule pursuant to
section 172(e) of the Clean Air Act, as amended (42 U.S.C. 7472(e))
applicable to the area. The PM10 standards set forth in this
section will no longer apply to an area attaining these standards as of
September 16, 1997, once EPA approves a State Implementation Plan (SIP)
applicable to the area containing all PM10 control measures
adopted and implemented by the State prior to September 16, 1997, and a
section 110 SIP implementing the PM standards published on July 18,
1997.
SIP approvals are codified in 40 CFR part 52.
[52 FR 24663, July 1, 1987, as amended at 62 FR 38711, July 18, 1997]
Sec. 50.7 National primary and secondary ambient air quality standards
for particulate matter.
(a) The national primary and secondary ambient air quality standards
for particulate matter are:
(1) 15.0 micrograms per cubic meter (ug/m3)
annual arithmetic mean concentration, and 65 ug/m3
24-hour average concentration measured in the ambient air as
PM2.5 (particles with an aerodynamic diameter less than or
equal to a nominal 2.5 micrometers) by either:
(i) A reference method based on appendix L of this part and
designated in accordance with part 53 of this chapter; or
(ii) An equivalent method designated in accordance with part 53 of
this chapter.
(2) 50 micrograms per cubic meter (ug/m3) annual
arithmetic mean concentration, and 150 ug/m3 24-hour
average concentration measured in the ambient air as PM10
(particles with an aerodynamic diameter less than or equal to a nominal
10 micrometers) by either:
(i) A reference method based on appendix M of this part and
designated in accordance with part 53 of this chapter; or
(ii) An equivalent method designated in accordance with part 53 of
this chapter.
(b) The annual primary and secondary PM2.5 standards are
met when the annual arithmetic mean concentration, as determined in
accordance with Appendix N of this part, is less than or equal to 15.0
micrograms per cubic meter.
(c) The 24-hour primary and secondary PM2.5 standards are
met when the 98th percentile 24-hour concentration, as
determined in accordance with Appendix N of this part, is less than or
equal to 65 micrograms per cubic meter.
(d) The annual primary and secondary PM10 standards are
met when the annual arithmetic mean concentration, as determined in
accordance with Appendix N of this part, is less than or equal to 50
micrograms per cubic meter.
(e) The 24-hour primary and secondary PM10 standards are
met when the 99th percentile 24-hour concentration, as
determined in accordance with Appendix N of this part, is less than or
equal to 150 micrograms per cubic meter.
[62 FR 38711, July 18, 1997]
Sec. 50.8 National primary ambient air quality standards for carbon
monoxide.
(a) The national primary ambient air quality standards for carbon
monoxide are:
(1) 9 parts per million (10 milligrams per cubic meter) for an 8-
hour average concentration not to be exceeded more than once per year
and
(2) 35 parts per million (40 milligrams per cubic meter) for a 1-
hour average concentration not to be exceeded more than once per year.
(b) The levels of carbon monoxide in the ambient air shall be
measured by:
(1) A reference method based on appendix C and designated in
accordance with part 53 of this chapter, or
(2) An equivalent method designated in accordance with part 53 of
this chapter.
(c) An 8-hour average shall be considered valid if at least 75
percent of the hourly average for the 8-hour period are available. In
the event that only six (or seven) hourly averages are available, the 8-
hour average shall be computed on the basis of the hours available using
six (or seven) as the divisor.
(d) When summarizing data for comparision with the standards,
averages shall be stated to one decimal place. Comparison of the data
with the levels of the standards in parts per million shall be made in
terms of integers with fractional parts of 0.5 or greater rounding up.
[50 FR 37501, Sept. 13, 1985]
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
ug/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 ug/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.
[62 FR 38894, July 18, 1997]
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 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.
[62 FR 38894, July 18, 1997]
Sec. 50.11 National primary and secondary ambient air quality standards
for nitrogen dioxide.
(a) The level of the national primary ambient air quality standard
for nitrogen dioxide is 0.053 parts per million (100 micrograms per
cubic meter), annual arithmetic mean concentration.
(b) The level of national secondary ambient air quality standard for
nitrogen dioxide is 0.053 parts per million (100 micrograms per cubic
meter), annual arithmetic mean concentration.
(c) The levels of the standards shall be measured by:
(1) A reference method based on appendix F and designated in
accordance with part 53 of this chapter, or
(2) An equivalent method designated in accordance with part 53 of
this chapter.
(d) The standards are attained when the annual arithmetic mean
concentration in a calendar year is less than or equal to 0.053 ppm,
rounded to three decimal places (fractional parts equal to or greater
than 0.0005 ppm must be rounded up). To demonstrate attainment, an
annual mean must be based upon hourly data that are at least 75 percent
complete or upon data derived from manual methods that are at least 75
percent complete for the scheduled sampling days in each calendar
quarter.
[50 FR 25544, June 19, 1985]
Sec. 50.12 National primary and secondary ambient air quality standards
for lead.
National primary and secondary ambient air quality standards for
lead and its compounds, measured as elemental lead by a reference method
based on appendix G to this part, or by an equivalent method, are: 1.5
micrograms per cubic meter, maximum arithmetic mean averaged over a
calendar quarter.
(Secs. 109, 301(a) Clean Air Act as amended (42 U.S.C. 7409, 7601(a)))
[43 FR 46258, Oct. 5, 1978]
Appendix H To Part 50--Interpretation of The 1-Hour Primary and
Secondary National Ambient Air Quality Standards for Ozone.
1. General
This appendix explains how to determine when the expected
number of days per calendar year with maximum hourly average
concentrations above 0.12 ppm (235 ug/m3) is equal to or less
than 1. An expanded discussion of these procedures and associated
examples are contained in the "Guideline for Interpretation of
Ozone Air Quality Standards." For purposes of clarity in the
following discussion, it is convenient to use the term
"exceedance" to describe a daily maximum hourly average ozone
measurement that is greater than the level of the standard.
Therefore, the phrase "expected number of days with maximum
hourly average ozone concentrations above the level of the
standard" may be simply stated as the "expected number of
exceedances."
The basic principle in making this determination is
relatively straightforward. Most of the complications that arise
in determining the expected number of annual exceedances relate
to accounting for incomplete sampling. In general, the average
number of exceedances per calendar year must be less than or
equal to 1. In its simplest form, the number of exceedances at a
monitoring site would be recorded for each calendar year and then
averaged over the past 3 calendar years to determine if this
average is less than or equal to 1.
2. Interpretation of Expected Exceedances
The ozone standard states that the expected number of
exceedances per year must be less than or equal to 1. The
statistical term "expected number" is basically an arithmetic
average. The following example explains what it would mean for an
area to be in compliance with this type of standard. Suppose a
monitoring station records a valid daily maximum hourly average
ozone value for every day of the year during the past 3 years. At
the end of each year, the number of days with maximum hourly
concentrations above 0.12 ppm is determined and this number is
averaged with the results of previous years. As long as this
average remains "less than or equal to 1," the area is in
compliance.
3. Estimating the Number of Exceedances for a Year
In general, a valid daily maximum hourly average value may
not be available for each day of the year, and it will be
necessary to account for these missing values when estimating
the number of exceedances for a particular calendar year. The
purpose of these computations is to determine if the expected
number of exceedances per year is less than or equal to 1. Thus,
if a site has two or more observed exceedances each year, the
standard is not met and it is not necessary to use the procedures
of this section to account for incomplete sampling.
The term "missing value" is used here in the general sense
to describe all days that do not have an associated ozone
measurement. In some cases, a measurement might actually have
been missed but in other cases no measurement may have been
scheduled for that day. A daily maximum ozone value is defined to
be the highest hourly ozone value recorded for the day. This
daily maximum value is considered to be valid if 75 percent of
the hours from 9:01 a.m. to 9:00 p.m. (LST) were measured or if
the highest hour is greater than the level of the standard.
In some areas, the seasonal pattern of ozone is so
pronounced that entire months need not be sampled because it is
extremely unlikely that the standard would be exceeded. Any such
waiver of the ozone monitoring requirement would be handled under
provisions of 40 CFR, Part 58. Some allowance should also be made
for days for which valid daily maximum hourly values were not
obtained but which would quite likely have been below the
standard. Such an allowance introduces a complication in that it
becomes necessary to define under what conditions a missing value
may be assumed to have been less than the level of the standard.
The following criterion may be used for ozone:
A missing daily maximum ozone value may be assumed to be
less than the level of the standard if the valid daily maxima on
both the preceding day and the following day do not exceed 75
percent of the level of the standard.
Let z denote the number of missing daily maximum values that
may be assumed to be less than the standard. Then the following
formula shall be used to estimate the expected number of
exceedances for the year:
e=v+[(v/n)*(N-n-z)] (1)
(* Indicates multiplication.)
where:
e=the estimated number of exceedances for the year,
N=the number of required monitoring days in the year,
n=the number of valid daily maxima,
v=the number of daily values above the level of the standard,
and
z=the number of days assumed to be less than the standard
level.
This estimated number of exceedances shall be rounded to one
decimal place (fractional parts equal to 0.05 round up).
It should be noted that N will be the total number of days
in the year unless the appropriate Regional Administrator has
granted a waiver under the provisions of 40 CFR part 58.
The above equation may be interpreted intuitively in the
following manner. The estimated number of exceedances is equal to
the observed number of exceedances (v) plus an increment that
accounts for incomplete sampling. There were (N-n) missing values
for the year but a certain number of these, namely z, were
assumed to be less than the standard. Therefore, (N-n-z) missing
values are considered to include possible exceedances. The
fraction of measured values that are above the level of the
standard is v/n. It is assumed that this same fraction applies to
the (N-n-z) missing values and that (v/n) x (N-n-z) of these
values would also have exceeded the level of the standard.
[44 FR 8220, Feb. 8, 1979, as amended at 62 FR 38895, July 18, 1997]
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 90%, and no single year has less than 75% data
completeness.
Example 1. Ambient monitoring site attaining the primary
and secondary ozone standards
Percent Highest Daily Maximum 8-hour
Valid Concentration (ppm)
Year Days 1st 2nd 3rd 4th 5th
---------------------------------------------
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
[Examples 1 and 2 have been reformatted to fit on a 8.5" by 11"
page in letter size (portrait).]
(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
Percent Highest Daily Maximum 8-hour
Valid Concentration (ppm)
Year Days 1st 2nd 3rd 4th 5th
---------------------------------------------
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
[Examples 1 and 2 have been reformatted to fit on a 8.5" by 11"
page in letter size (portrait).]
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.
[62 FR 38895, July 18, 1997]
APPENDIX K TO PART 50-INTERPRETATION OF THE NATIONAL AMBIENT AIR QUALITY
STANDARDS FOR PARTICULATE MATTER
1.0 General.
(a) This appendix explains the computations necessary for
analyzing particulate matter data to determine attainment of the 24-
hour and annual standards specified in 40 CFR 50.6. For the primary
and secondary standards, particulate matter is measured in the
ambient air as PM10 (particles with an aerodynamic
diameter less than or equal to a nominal 10 micrometers) by a
reference method based on appendix J of this part and designated in
accordance with part 53 of this chapter, or by an equivalent method
designated in accordance with part 53 of this chapter. The required
frequency of measurements is specified in part 58 of this chapter.
(b) The terms used in this appendix are defined as follows:
Average refers to an arithmetic mean. All particulate matter
standards are expressed in terms of expected annual values: Expected
number of exceedances per year for the 24-hour standards and
expected annual arithmetic mean for the annual standards.
Daily value for PM10 refers to the 24-hour average
concentration of PM10 calculated or measured from
midnight to midnight (local time).
Exceedance means a daily value that is above the level of the
24-hour standard after rounding to the nearest 10 ug/m3
(i.e., values ending in 5 or greater are to be rounded up).
Expected annual value is the number approached when the annual
values from an increasing number of years are averaged, in the
absence of long-term trends in emissions or meteorological
conditions.
Year refers to a calendar year.
(c) Although the discussion in this appendix focuses on
monitored data, the same principles apply to modeling data, subject
to EPA modeling guidelines.
2.0 Attainment Determinations.
2.1 24-Hour Primary and Secondary Standards.
(a) Under 40 CFR 50.6(a) the 24-hour primary and secondary
standards are attained when the expected number of exceedances per
year at each monitoring site is less than or equal to one. In the
simplest case, the number of expected exceedances at a site is
determined by recording the number of exceedances in each calendar
year and then averaging them over the past 3 calendar years.
Situations in which 3 years of data are not available and possible
adjustments for unusual events or trends are discussed in sections
2.3 and 2.4 of this appendix. Further, when data for a year are
incomplete, it is necessary to compute an estimated number of
exceedances for that year by adjusting the observed number of
exceedances. This procedure, performed by calendar quarter, is
described in section 3.0 of this appendix. The expected number of
exceedances is then estimated by averaging the individual annual
estimates for the past 3 years.
(b) The comparison with the allowable expected exceedance rate
of one per year is made in terms of a number rounded to the nearest
tenth (fractional values equal to or greater than 0.05 are to be
rounded up; e.g., an exceedance rate of 1.05 would be rounded to
1.1, which is the lowest rate for nonattainment).
2.2 Annual Primary and Secondary Standards. Under 40 CFR
50.6(b), the annual primary and secondary standards are attained
when the expected annual arithmetic mean
PM10 concentration is less than or equal to the level of
the standard. In the simplest case, the expected annual arithmetic
mean is determined by averaging the annual arithmetic mean
PM10 concentrations for the past 3 calendar years.
Because of the potential for incomplete data and the possible
seasonality in PM10 concentrations, the annual mean shall
be calculated by averaging the four quarterly means of
PM10 concentrations within the calendar year. The
equations for calculating the annual arithmetic mean are given in
section 4.0 of this appendix. Situations in which 3 years of data
are not available and possible adjustments for unusual events or
trends are discussed in sections 2.3 and 2.4 of this appendix. The
expected annual arithmetic mean is rounded to the nearest 1
ug/m3 before comparison with the annual standards
(fractional values equal to or greater than 0.5 are to be rounded
up).
2.3 Data Requirements.
(a) 40 CFR 58.13 specifies the required minimum frequency of
sampling for PM10. For the purposes of making comparisons
with the particulate matter standards, all data produced by National
Air Monitoring Stations (NAMS), State and Local Air Monitoring
Stations (SLAMS) and other sites submitted to EPA in accordance with
the Part 58 requirements must be used, and a minimum of 75 percent
of the scheduled PM10 samples per quarter are required.
(b) To demonstrate attainment of either the annual or 24-hour
standards at a monitoring site, the monitor must provide sufficient
data to perform the required calculations of sections 3.0 and 4.0 of
this appendix. The amount of data required varies with the sampling
frequency, data capture rate and the number of years of record. In
all cases, 3 years of representative monitoring data that meet the
75 percent criterion of the previous paragraph should be utilized,
if available, and would suffice. More than 3 years may be
considered, if all additional representative years of data meeting
the 75 percent criterion are utilized. Data not meeting these
criteria may also suffice to show attainment; however, such
exceptions will have to be approved by the appropriate Regional
Administrator in accordance with EPA guidance.
(c) There are less stringent data requirements for showing that
a monitor has failed an attainment test and thus has recorded a
violation of the particulate matter standards. Although it is
generally necessary to meet the minimum 75 percent data capture
requirement per quarter to use the computational equations described
in sections 3.0 and 4.0 of this appendix, this criterion does not
apply when less data is sufficient to unambiguously establish
nonattainment. The following examples illustrate how nonattainment
can be demonstrated when a site fails to meet the completeness
criteria. Nonattainment of the 24-hour primary standards can be
established by the observed annual number of exceedances (e.g., four
observed exceedances in a single year), or by the estimated number
of exceedances derived from the observed number of exceedances and
the required number of scheduled samples (e.g., two observed
exceedances with every other day sampling). Nonattainment of the
annual standards can be demonstrated on the basis of quarterly mean
concentrations developed from observed data combined with one-half
the minimum detectable concentration substituted for missing values.
In both cases, expected annual values must exceed the levels allowed
by the standards.
2.4 Adjustment for Exceptional Events and Trends.
(a) An exceptional event is an uncontrollable event caused by
natural sources of particulate matter or an event that is not
expected to recur at a given location. Inclusion of such a value in
the computation of exceedances or averages could result in
inappropriate estimates of their respective expected annual values.
To reduce the effect of unusual events, more than 3 years of
representative data may be used. Alternatively, other techniques,
such as the use of statistical models or the use of historical data
could be considered so that the event may be discounted or weighted
according to the likelihood that it will recur. The use of such
techniques is subject to the approval of the appropriate Regional
Administrator in accordance with EPA guidance.
(b) In cases where long-term trends in emissions and air quality
are evident, mathematical techniques should be applied to account
for the trends to ensure that the expected annual values are not
inappropriately biased by unrepresentative data. In the simplest
case, if 3 years of data are available under stable emission
conditions, this data should be used. In the event of a trend or
shift in emission patterns, either the most recent representative
year(s) could be used or statistical techniques or models could be
used in conjunction with previous years of data to adjust for
trends. The use of less than 3 years of data, and any adjustments
are subject to the approval of the appropriate Regional
Administrator in accordance with EPA guidance.
3.0 Computational Equations for the 24-hour Standards.
3.1 Estimating Exceedances for a Year.
(a) If PM10 sampling is scheduled less frequently
than every day, or if some scheduled samples are missed, a
PM10 value will not be available for each day of the
year. To account for the possible effect of incomplete data, an
adjustment must be made to the data collected at each monitoring
location to estimate the number of exceedances in a calendar year.
In this adjustment, the assumption is made that the fraction of
missing values that would have exceeded the standard level is
identical to the fraction of measured values above this level. This
computation is to be made for all sites that are scheduled to
monitor throughout the entire year and meet the minimum data
requirements of section 2.3 of this appendix. Because of possible
seasonal imbalance, this adjustment shall be applied on a quarterly
basis. The estimate of the expected number of exceedances for the
quarter is equal to the observed number of exceedances plus an
increment associated with the missing data. The following equation
must be used for these computations:
Equation 1
>>>>40387131 See the accompanying hardcopy volume for non-
machine-readable data that appears at this point. <<<<
where:
eq=the estimated number of exceedances for calendar
quarter q;
vq=the observed number of exceedances for calendar
quarter q;
Nq=the number of days in calendar quarter q;
nq=the number of days in calendar quarter q with
PM10 data; and
q=the index for calendar quarter, q=1, 2, 3 or 4.
(b) The estimated number of exceedances for a calendar quarter
must be rounded to the nearest hundredth (fractional values equal to
or greater than 0.005 must be rounded up).
(c) The estimated number of exceedances for the year, e, is the
sum of the estimates for each calendar quarter.
Equation 2
>>>>40387132 See the accompanying hardcopy volume for non-
machine-readable data that appears at this point. <<<<
(d) The estimated number of exceedances for a single year must
be rounded to one decimal place (fractional values equal to or
greater than 0.05 are to be rounded up). The expected number of
exceedances is then estimated by averaging the individual annual
estimates for the most recent 3 or more representative years of
data. The expected number of exceedances must be rounded to one
decimal place (fractional values equal to or greater than 0.05 are
to be rounded up).
(e) The adjustment for incomplete data will not be necessary for
monitoring or modeling data which constitutes a complete record,
i.e., 365 days per year.
(f) To reduce the potential for overestimating the number of
expected exceedances, the correction for missing data will not be
required for a calendar quarter in which the first observed
exceedance has occurred if:
(1) There was only one exceedance in the calendar quarter;
(2) Everyday sampling is subsequently initiated and maintained
for 4 calendar quarters in accordance with 40 CFR 58.13; and
(3) Data capture of 75 percent is achieved during the required
period of everyday sampling. In addition, if the first exceedance is
observed in a calendar quarter in which the monitor is already
sampling every day, no adjustment for missing data will be made to
the first exceedance if a 75 percent data capture rate was achieved
in the quarter in which it was observed.
Example 1
a. During a particular calendar quarter, 39 out of a possible 92
samples were recorded, with one observed exceedance of the 24-hour
standard. Using Equation 1, the estimated number of exceedances for
the quarter is:
eq=1 x 92/39=2.359 or 2.36.
b. If the estimated exceedances for the other 3 calendar
quarters in the year were 2.30, 0.0 and 0.0, then, using Equation 2,
the estimated number of exceedances for the year is
2.362.300.00.0 which equals 4.66 or 4.7. If no exceedances were
observed for the 2 previous years, then the expected number of
exceedances is estimated by: (1/3) x (4.700)=1.57 or 1.6. Since
1.6 exceeds the allowable number of expected exceedances, this
monitoring site would fail the attainment test.
Example 2
In this example, everyday sampling was initiated following the
first observed exceedance as required by 40 CFR 58.13. Accordingly,
the first observed exceedance would not be adjusted for incomplete
sampling. During the next three quarters, 1.2 exceedances were
estimated. In this case, the estimated exceedances for the year
would be 1.01.20.00.0 which equals 2.2. If, as before, no
exceedances were observed for the two previous years, then the
estimated exceedances for the 3-year period would then be (1/
3) x (2.20.00.0)=0.7, and the monitoring site would not fail the
attainment test.
3.2 Adjustments for Non-Scheduled Sampling Days.
(a) If a systematic sampling schedule is used and sampling is
performed on days in addition to the days specified by the
systematic sampling schedule, e.g., during episodes of high
pollution, then an adjustment must be made in the eqution for the
estimation of exceedances. Such an adjustment is needed to eliminate
the bias in the estimate of the quarterly and annual number of
exceedances that would occur if the chance of an exceedance is
different for scheduled than for non-scheduled days, as would be the
case with episode sampling.
(b) The required adjustment treats the systematic sampling
schedule as a stratified sampling plan. If the period from one
scheduled sample until the day preceding the next scheduled sample
is defined as a sampling stratum, then there is one stratum for each
scheduled sampling day. An average number of observed exceedances is
computed for each of these sampling strata. With nonscheduled
sampling days, the estimated number of exceedances is defined as:
Equation 3
>>>>40387133 See the accompanying hardcopy volume for non-
machine-readable data that appears at this point. <<<<
where:
eq=the estimated number of exceedances for the quarter;
Nq=the number of days in the quarter;
mq=the number of strata with samples during the quarter;
vj=the number of observed exceedances in stratum j; and
kj=the number of actual samples in stratum j.
(c) Note that if only one sample value is recorded in each
stratum, then Equation 3 reduces to Equation 1.
Example 3
A monitoring site samples according to a systematic sampling
schedule of one sample every 6 days, for a total of 15 scheduled
samples in a quarter out of a total of 92 possible samples. During
one 6-day period, potential episode levels of PM10 were
suspected, so 5 additional samples were taken. One of the regular
scheduled samples was missed, so a total of 19 samples in 14
sampling strata were measured. The one 6-day sampling stratum with 6
samples recorded 2 exceedances. The remainder of the quarter with
one sample per stratum recorded zero exceedances. Using Equation 3,
the estimated number of exceedances for the quarter is:
eq=(92/14) x (2/60. . .0)=2.19.
4.0 Computational Equations for Annual Standards.
4.1 Calculation of the Annual Arithmetic Mean. (a) An annual
arithmetic mean value for PM10 is determined by averaging
the quarterly means for the 4 calendar quarters of the year. The
following equation is to be used for calculation of the mean for a
calendar quarter:
Equation 4
>>>>40387141 See the accompanying hardcopy volume for non-
machine-readable data that appears at this point. <<<<
where:
xq= the quarterly mean concentration for quarter q, q=1,
2, 3, or 4,
nq= the number of samples in the quarter, and
xi= the ith concentration value recorded in the quarter.
(b) The quarterly mean, expressed in ug/m3, must be
rounded to the nearest tenth (fractional values of 0.05 should be
rounded up).
(c) The annual mean is calculated by using the following
equation:
Equation 5
>>>>40387142 See the accompanying hardcopy volume for non-
machine-readable data that appears at this point. <<<<
where:
x=the annual mean; and
xq=the mean for calendar quarter q.
(d) The average of quarterly means must be rounded to the
nearest tenth (fractional values of 0.05 should be rounded up).
(e) The use of quarterly averages to compute the annual average
will not be necessary for monitoring or modeling data which results
in a complete record, i.e., 365 days per year.
(f) The expected annual mean is estimated as the average of
three or more annual means. This multi-year estimate, expressed in
ug/m3, shall be rounded to the nearest integer for
comparison with the annual standard (fractional values of 0.5 should
be rounded up).
Example 4
Using Equation 4, the quarterly means are calculated for each
calendar quarter. If the quarterly means are 52.4, 75.3, 82.1, and
63.2 ug/m3, then the annual mean is:
x = (1/4) x (52.475.382.163.2)= 68.25 or 68.3.
4.2 Adjustments for Non-scheduled Sampling Days. (a) An
adjustment in the calculation of the annual mean is needed if
sampling is performed on days in addition to the days specified by
the systematic sampling schedule. For the same reasons given in the
discussion of estimated exceedances, under section 3.2 of this
appendix, the quarterly averages would be calculated by using the
following equation:
Equation 6
>>>>40387143 See the accompanying hardcopy volume for non-
machine-readable data that appears at this point. <<<<
where:
xq=the quarterly mean concentration for quarter q, q=1,
2, 3, or 4;
xij=the ith concentration value recorded in stratum j;
kj=the number of actual samples in stratum j; and
mq=the number of strata with data in the quarter.
(b) If one sample value is recorded in each stratum, Equation 6
reduces to a simple arithmetic average of the observed values as
described by Equation 4.
Example 5
a. During one calendar quarter, 9 observations were recorded.
These samples were distributed among 7 sampling strata, with 3
observations in one stratum. The concentrations of the 3
observations in the single stratum were 202, 242, and 180
ug/m3. The remaining 6 observed concentrations were 55,
68, 73, 92, 120, and 155 ug/m3. Applying the weighting
factors specified in Equation 6, the quarterly mean is:
xq = (1/7) x [(1/3) x (202 242 180) 155 68
73 92 120 155] = 110.1
b. Although 24-hour measurements are rounded to the nearest 10
ug/m3 for determinations of exceedances of the 24-hour
standard, note that these values are rounded to the nearest 1
ug/m3 for the calculation of means.
[52 FR 24667, July 1, 1987; 52 FR 26402, July 14, 1987; 52 FR
29382, Aug. 7, 1987; 52 FR 31701, Aug. 21, 1987; 62 FR 38652, July
18, 1997]
Appendix N to Part 50--Interpretation of the National Ambient Air
Quality Standards for Particulate Matter
1.0 General.
(a) This appendix explains the data handling conventions and
computations necessary for determining when the annual and 24-hour
primary and secondary national ambient air quality standards for PM
specified in Sec. 50.7 of this chapter are met. Particulate matter
is measured in the ambient air as PM10 and
PM2.5 (particles with an aerodynamic diameter less than
or equal to a nominal 10 and 2.5 micrometers, respectively) by a
reference method based on Appendix M of this part for
PM10 and on Appendix L of this part for PM2.5,
as applicable, and designated in accordance with part 53 of this
chapter, or by an equivalent method designated in accordance with
part 53 of this chapter. Data handling and computation procedures to
be used in making comparisons between reported PM10 and
PM2.5 concentrations and the levels of the PM standards
are specified in the following sections.
(b) Data resulting from uncontrollable or natural events, for
example structural fires or high winds, may require special
consideration. In some cases, it may be appropriate to exclude these
data because they could result in inappropriate values to compare
with the levels of the PM standards. In other cases, it may be more
appropriate to retain the data for comparison with the level of the
PM standards and then allow the EPA to formulate the appropriate
regulatory response. Whether to exclude, retain, or make adjustments
to the data affected by uncontrollable or natural events is subject
to the approval of the appropriate Regional Administrator.
(c) The terms used in this appendix are defined as follows:
Average and mean refer to an arithmetic mean.
Daily value for PM refers to the 24-hour average concentration
of PM calculated or measured from midnight to midnight (local time)
for PM10 or PM2.5.
Designated monitors are those monitoring sites designated in a
State PM Monitoring Network Description for spatial averaging in
areas opting for spatial averaging in accordance with part 58 of
this chapter.
98th percentile (used for PM2.5) means the
daily value out of a year of monitoring data below which 98 percent
of all values in the group fall.
99th percentile (used for PM10) means the
daily value out of a year of monitoring data below which 99 percent
of all values in the group fall.
Year refers to a calendar year.
(d) Sections 2.1 and 2.5 of this appendix contain data handling
instructions for the option of using a spatially averaged network of
monitors for the annual standard. If spatial averaging is not
considered for an area, then the spatial average is equivalent to
the annual average of a single site and is treated accordingly in
subsequent calculations. For example, paragraph (a)(3) of section
2.1 of this appendix could be eliminated since the spatial average
would be equivalent to the annual average.
2.0 Comparisons with the PM2.5 Standards.
2.1 Annual PM2.5 Standard.
(a) The annual PM2.5 standard is met when the 3-year
average of the spatially averaged annual means is less than or equal
to 15.0 ug/m3. The 3-year average of the
spatially averaged annual means is determined by averaging quarterly
means at each monitor to obtain the annual mean PM2.5
concentrations at each monitor, then averaging across all designated
monitors, and finally averaging for 3 consecutive years. The steps
can be summarized as follows:
(1) Average 24-hour measurements to obtain quarterly means at
each monitor.
(2) Average quarterly means to obtain annual means at each
monitor.
(3) Average across designated monitoring sites to obtain an
annual spatial mean for an area (this can be one site in which case
the spatial mean is equal to the annual mean).
(4) Average 3 years of annual spatial means to obtain a 3-year
average of spatially averaged annual means.
(b) In the case of spatial averaging, 3 years of spatial
averages are required to demonstrate that the standard has been met.
Designated sites with less than 3 years of data shall be included in
spatial averages for those years that data completeness requirements
are met. For the annual PM2.5 standard, a year meets data
completeness requirements when at least 75 percent of the scheduled
sampling days for each quarter have valid data. However, years with
high concentrations and more than a minimal amount of data (at least
11 samples in each quarter) shall not be ignored just because they
are comprised of quarters with less than complete data. Thus, in
computing annual spatially averaged means, years containing quarters
with at least 11 samples but less than 75 percent data completeness
shall be included in the computation if the resulting spatially
averaged annual mean concentration (rounded according to the
conventions of section 2.3 of this appendix) is greater than the
level of the standard.
(c) Situations may arise in which there are compelling reasons
to retain years containing quarters which do not meet the data
completeness requirement of 75 percent or the minimum number of 11
samples. The use of less than complete data is subject to the
approval of the appropriate Regional Administrator.
(d) The equations for calculating the 3-year average annual mean
of the PM2.5 standard are given in section 2.5 of this
appendix.
2.2 24-Hour PM2.5 Standard.
(a) The 24-hour PM2.5 standard is met when the 3-year
average of the 98th percentile values at each monitoring
site is less than or equal to 65 ug/m3. This
comparison shall be based on 3 consecutive, complete years of air
quality data. A year meets data completeness requirements when at
least 75 percent of the scheduled sampling days for each quarter
have valid data. However, years with high concentrations shall not
be ignored just because they are comprised of quarters with less
than complete data. Thus, in computing the 3-year average
98th percentile value, years containing quarters with
less than 75 percent data completeness shall be included in the
computation if the annual 98th percentile value (rounded
according to the conventions of section 2.3 of this appendix) is
greater than the level of the standard.
(b) Situations may arise in which there are compelling reasons
to retain years containing quarters which do not meet the data
completeness requirement. The use of less than complete data is
subject to the approval of the appropriate Regional Administrator.
(c) The equations for calculating the 3-year average of the
annual 98th percentile values is given in section 2.6 of
this appendix.
2.3 Rounding Conventions. For the purposes of comparing
calculated values to the applicable level of the standard, it is
necessary to round the final results of the calculations described
in sections 2.5 and 2.6 of this appendix. For the annual
PM2.5 standard, the 3-year average of the spatially
averaged annual means shall be rounded to the nearest 0.1
ug/m3 (decimals 0.05 and greater are rounded up
to the next 0.1, and any decimal lower than 0.05 is rounded down to
the nearest 0.1). For the 24-hour PM2.5 standard, the 3-
year average of the annual 98th percentile values shall
be rounded to the nearest 1 ug/m3 (decimals 0.5
and greater are rounded up to nearest whole number, and any decimal
lower than 0.5 is rounded down to the nearest whole number).
2.4 Monitoring Considerations.
(a) Section 58.13 of this chapter specifies the required minimum
frequency of sampling for PM2.5. Exceptions to the
specified sampling frequencies, such as a reduced frequency during a
season of expected low concentrations, are subject to the approval
of the appropriate Regional Administrator. Section 58.14 of 40 CFR
part 58 and section 2.8 of Appendix D of 40 CFR part 58, specify
which monitors are eligible for making comparisons with the PM
standards. In determining a spatial mean using two or more
monitoring sites operating in a given year, the annual mean for an
individual site may be included in the spatial mean if and only if
the mean for that site meets the criterion specified in Sec. 2.8 of
Appendix D of 40 CFR part 58. In the event data from an otherwise
eligible site is excluded from being averaged with data from other
sites on the basis of this criterion, then the 3-year mean from that
site shall be compared directly to the annual standard.
(b) For the annual PM2.5 standard, when designated
monitors are located at the same site and are reporting
PM2.5 values for the same time periods, and when spatial
averaging has been chosen, their concentrations shall be averaged
before an area-wide spatial average is calculated. Such monitors
will then be considered as one monitor.
2.5 Equations for the Annual PM2.5 Standard.
(a) An annual mean value for PM2.5 is determined by
first averaging the daily values of a calendar quarter:
Equation 1
[GRAPHIC] [TIFF OMITTED] TR18JY97.000
where:
xq,y,s = the mean for quarter q of year y for site s;
nq = the number of monitored values in the quarter; and
xi,q,y,s = the ith value in quarter q for year
y for site s.
(b) The following equation is then to be used for calculation of
the annual mean:
Equation 2
[GRAPHIC] [TIFF OMITTED] TR18JY97.001
where:
xy,s = the annual mean concentration for year y (y = 1,
2, or 3) and for site s; and
xq,y,s = the mean for quarter q of year y for site s.
(c) (1) The spatially averaged annual mean for year y is
computed by first calculating the annual mean for each site
designated to be included in a spatial average, xy,s, and
then computing the average of these values across sites:
Equation 3
[GRAPHIC] [TIFF OMITTED] TR18JY97.002
where:
xy = the spatially averaged mean for year y;
xy,s = the annual mean for year y and site s; and
ns = the number of sites designated to be averaged.
(2) In the event that an area designated for spatial averaging
has two or more sites at the same location producing data for the
same time periods, the sites are averaged together before using
Equation 3 by:
Equation 4
[GRAPHIC] [TIFF OMITTED] TR18JY97.003
where:
xy,s* = the annual mean for year y for the sites at the
same location (which will now be considered one site);
nc = the number of sites at the same location designated
to be included in the spatial average; and
xy,s = the annual mean for year y and site s.
(d) The 3-year average of the spatially averaged annual means is
calculated by using the following equation:
Equation 5
[GRAPHIC] [TIFF OMITTED] TR18JY97.004
where:
x = the 3-year average of the spatially averaged annual means; and
xy = the spatially averaged annual mean for year y.
Example 1--Area Designated for Spatial Averaging That Meets the
Primary Annual PM2.5 Standard.
a. In an area designated for spatial averaging, four designated
monitors recorded data in at least 1 year of a particular 3-year
period. Using Equations 1 and 2, the annual means for
PM2.5 at each site are calculated for each year. The
following table can be created from the results. Data completeness
percentages for the quarter with the fewest number of samples are
also shown.
Table 1.--Results from Equations 1 and 2
--------------------------------------------------------------------------------------------------------------------------------------------------------
Site #1 Site #2 Site #3 Site #4 Spatial mean
--------------------------------------------------------------------------------------------------------------------------------------------------------
Year 1......................................... Annual mean (ug/m\3\)............ 12.7 ............ ............ ............ 12.7
% data completeness.............. 80 0 0 0 ............
Year 2......................................... Annual mean (ug/m\3\)............ 12.6 17.5 15.2 ............ 15.05
% data completeness.............. 90 63 38 0 ............
Year 3......................................... Annual mean (ug/m\3\).... 12.5 18.5 14.1 16.9 15.50
% data completeness.............. 90 80 85 50 ............
3-year mean.................................... ................................. ............ ............ ............ ............ 14.42
--------------------------------------------------------------------------------------------------------------------------------------------------------
b. The data from these sites are averaged in the order described
in section 2.1 of this appendix. Note that the annual mean from site
#3 in year 2 and the annual mean from site #4 in year 3 do not meet
the 75 percent data completeness criteria. Assuming the 38 percent
data completeness represents a quarter with fewer than 11 samples,
site #3 in year 2 does not meet the minimum data completeness
requirement of 11 samples in each quarter. The site is therefore
excluded from the calculation of the spatial mean for year 2.
However, since the spatial mean for year 3 is above the level of the
standard and the minimum data requirement of 11 samples in each
quarter has been met, the annual mean from site #4 in year 3 is
included in the calculation of the spatial mean for year 3 and in
the calculation of the 3-year average. The 3-year average is rounded
to 14.4 ug/m3, indicating that this area meets
the annual PM2.5 standard.
Example 2--Area With Two Monitors at the Same Location That Meets
the Primary Annual PM2.5 Standard.
a. In an area designated for spatial averaging, six designated
monitors, with two monitors at the same location (#5 and #6),
recorded data in a particular 3-year period. Using Equations 1 and
2, the annual means for PM2.5 are calculated for each
year. The following table can be created from the results.
Table 2.--Results From Equations 1 and 2
--------------------------------------------------------------------------------------------------------------------------------------------------------
Average of Spatial
Annual mean (ug/m\3\) Site #1 Site #2 Site #3 Site #4 Site #5 Site #6 #5 and #6 mean
--------------------------------------------------------------------------------------------------------------------------------------------------------
Year 1............................................ 12.9 9.9 12.6 11.1 14.5 14.6 14.55 12.21
Year 2............................................ 14.5 13.3 12.2 10.9 16.1 16.0 16.05 13.39
Year 3............................................ 14.4 12.4 11.5 9.7 12.3 12.1 12.20 12.04
3-Year mean....................................... ........... ........... ........... ........... ........... ........... .......... 12.55
--------------------------------------------------------------------------------------------------------------------------------------------------------
b. The annual means for sites #5 and #6 are averaged together
using Equation 4 before the spatial average is calculated using
Equation 3 since they are in the same location. The 3-year mean is
rounded to 12.6 ug/m3, indicating that this area
meets the annual PM2.5 standard.
Example 3--Area With a Single Monitor That Meets the Primary Annual
PM2.5 Standard.
a. Given data from a single monitor in an area, the calculations
are as follows. Using Equations 1 and 2, the annual means for
PM2.5 are calculated for each year. If the annual means
are 10.28, 17.38, and 12.25 ug/m3, then the 3-
year mean is:
[GRAPHIC] [TIFF OMITTED] TR18JY97.005
b. This value is rounded to 13.3, indicating that this area
meets the annual PM2.5 standard.
2.6 Equations for the 24-Hour PM2.5 Standard.
(a) When the data for a particular site and year meet the data
completeness requirements in section 2.2 of this appendix,
calculation of the 98th percentile is accomplished by the
following steps. All the daily values from a particular site and
year comprise a series of values (x1, x2,
x3, ..., xn), that can be sorted into a series
where each number is equal to or larger than the preceding number
(x[1], x[2], x[3], ...,
x[n]). In this case, x[1] is the smallest
number and x[n] is the largest value. The 98th
percentile is found from the sorted series of daily values which is
ordered from the lowest to the highest number. Compute (0.98) x
(n) as the number "i.d", where "i" is the integer part of the
result and "d" is the decimal part of the result. The
98th percentile value for year y, P0.98, y, is
given by Equation 6:
Equation 6
[GRAPHIC] [TIFF OMITTED] TR18JY97.006
where:
P0.98,y = 98th percentile for year y;
x[i+1] = the (i+1)th number in the ordered
series of numbers; and
i = the integer part of the product of 0.98 and n.
(b) The 3-year average 98th percentile is then
calculated by averaging the annual 98th percentiles:
Equation 7
[GRAPHIC] [TIFF OMITTED] TR18JY97.007
(c) The 3-year average 98th percentile is rounded
according to the conventions in section 2.3 of this appendix before
a comparison with the standard is made.
Example 4--Ambient Monitoring Site With Every-Day Sampling That
Meets the Primary 24-Hour PM2.5 Standard.
a. In each year of a particular 3 year period, varying numbers
of daily PM2.5 values (e.g., 281, 304, and 296) out of a
possible 365 values were recorded at a particular site with the
following ranked values (in ug/m3):
Table 3.--Ordered Monitoring Data For 3 Years
----------------------------------------------------------------------------------------------------------------
Year 1 Year 2 Year 3
----------------------------------------------------------------------------------------------------------------
j rank Xj value j rank Xj value j rank Xj value
----------------------------------------------------------------------------------------------------------------
275.............. 57.9 296 54.3 290 66.0
276.............. 59.0 297 57.1 291 68.4
277.............. 62.2 298 63.0 292 69.8
----------------------------------------------------------------------------------------------------------------
b. Using Equation 6, the 98th percentile values for
each year are calculated as follows:
[GRAPHIC] [TIFF OMITTED] TR18JY97.008
[GRAPHIC] [TIFF OMITTED] TR18JY97.009
[GRAPHIC] [TIFF OMITTED] TR18JY97.010
c. 1. Using Equation 7, the 3-year average 98th
percentile is calculated as follows:
[GRAPHIC] [TIFF OMITTED] TR18JY97.011
2. Therefore, this site meets the 24-hour PM2.5
standard.
3.0 Comparisons with the PM10 Standards.
3.1 Annual PM10 Standard.
(a) The annual PM10 standard is met when the 3-year
average of the annual mean PM10 concentrations at each
monitoring site is less than or equal to 50 ug/
m3. The 3-year average of the annual means is determined
by averaging quarterly means to obtain annual mean PM10
concentrations for 3 consecutive, complete years at each monitoring
site. The steps can be summarized as follows:
(1) Average 24-hour measurements to obtain a quarterly mean.
(2) Average quarterly means to obtain an annual mean.
(3) Average annual means to obtain a 3-year mean.
(b) For the annual PM10 standard, a year meets data
completeness requirements when at least 75 percent of the scheduled
sampling days for each quarter have valid data. However, years with
high concentrations and more than a minimal amount of data (at least
11 samples in each quarter) shall not be ignored just because they
are comprised of quarters with less than complete data. Thus, in
computing the 3-year average annual mean concentration, years
containing quarters with at least 11 samples but less than 75
percent data completeness shall be included in the computation if
the annual mean concentration (rounded according to the conventions
of section 2.3 of this appendix) is greater than the level of the
standard.
(c) Situations may arise in which there are compelling reasons
to retain years containing quarters which do not meet the data
completeness requirement of 75 percent or the minimum number of 11
samples. The use of less than complete data is subject to the
approval of the appropriate Regional Administrator.
(d) The equations for calculating the 3-year average annual mean
of the PM10 standard are given in section 3.5 of this
appendix.
3.2 24-Hour PM10 Standard.
(a) The 24-hour PM10 standard is met when the 3-year
average of the annual 99th percentile values at each
monitoring site is less than or equal to 150 ug/
m3. This comparison shall be based on 3 consecutive,
complete years of air quality data. A year meets data completeness
requirements when at least 75 percent of the scheduled sampling days
for each quarter have valid data. However, years with high
concentrations shall not be ignored just because they are comprised
of quarters with less than complete data. Thus, in computing the 3-
year average of the annual 99th percentile values, years
containing quarters with less than 75 percent data completeness
shall be included in the computation if the annual 99th
percentile value (rounded according to the conventions of section
2.3 of this appendix) is greater than the level of the standard.
(b) Situations may arise in which there are compelling reasons
to retain years containing quarters which do not meet the data
completeness requirement. The use of less than complete data is
subject to the approval of the appropriate Regional Administrator.
(c) The equation for calculating the 3-year average of the
annual 99th percentile values is given in section 2.6 of
this appendix.
3.3 Rounding Conventions. For the annual PM10
standard, the 3-year average of the annual PM10 means
shall be rounded to the nearest 1 ug/m3 (decimals
0.5 and greater are
rounded up to the next whole number, and any decimal less than 0.5
is rounded down to the nearest whole number). For the 24-hour
PM10 standard, the 3-year average of the annual
99th percentile values of PM10 shall be
rounded to the nearest 10 ug/m3 (155 ug/
m3 and greater would be rounded to 160 ug/
m3 and 154 ug/m3 and less would be
rounded to 150 ug/m3).
3.4 Monitoring Considerations. Section 58.13 of this chapter
specifies the required minimum frequency of sampling for
PM10. Exceptions to the specified sampling frequencies,
such as a reduced frequency during a season of expected low
concentrations, are subject to the approval of the appropriate
Regional Administrator. For making comparisons with the
PM10 NAAQS, all sites meeting applicable requirements in
part 58 of this chapter would be used.
3.5 Equations for the Annual PM10 Standard.
(a) An annual arithmetic mean value for PM10 is
determined by first averaging the 24-hour values of a calendar
quarter using the following equation:
Equation 8
[GRAPHIC] [TIFF OMITTED] TR18JY97.012
where:
xq,y = the mean for quarter q of year y;
nq = the number of monitored values in the quarter; and
xi,q,y = the ith value in quarter q for year
y.
(b) The following equation is then to be used for calculation of
the annual mean:
Equation 9
[GRAPHIC] [TIFF OMITTED] TR18JY97.013
where:
xy = the annual mean concentration for year y, (y=1, 2,
or 3); and
xq,y = the mean for a quarter q of year y.
(c) The 3-year average of the annual means is calculated by
using the following equation:
Equation 10
[GRAPHIC] [TIFF OMITTED] TR18JY97.014
where:
x = the 3-year average of the annual means; and
xy = the annual mean for calendar year y.
Example 5--Ambient Monitoring Site That Does Not Meet the Annual
PM10 Standard.
a. Given data from a PM10 monitor and using Equations
8 and 9, the annual means for PM10 are calculated for
each year. If the annual means are 52.42, 82.17, and 63.23
ug/m3, then the 3-year average annual mean is:
[GRAPHIC] [TIFF OMITTED] TR18JY97.015
b. Therefore, this site does not meet the annual PM10
standard.
3.6 Equation for the 24-Hour PM10 Standard.
(a) When the data for a particular site and year meet the data
completeness requirements in section 3.2 of this appendix,
calculation of the 99th percentile is accomplished by the
following steps. All the daily values from a particular site and
year comprise a series of values (x1, x2,
x3, ..., xn) that can be sorted into a series
where each number is equal to or larger than the preceding number
(x[1], x[2], x[3], ...,
x[n]). In this case, x[1] is the smallest
number and x[n] is the largest value. The 99th percentile
is found from the sorted series of daily values which is ordered
from the lowest to the highest number. Compute (0.99) x (n) as the
number "i.d", where "i" is the integer part of the result and
"d" is the decimal part of the result. The 99th
percentile value for year y, P0.99,y, is given by
Equation 11:
Equation 11
[GRAPHIC] [TIFF OMITTED] TR18JY97.016
where:
P0.99,y = the 99th percentile for year y;
x[i+1] = the (i+1)th number in the ordered
series of numbers; and
i = the integer part of the product of 0.99 and n.
(b) The 3-year average 99th percentile value is then
calculated by averaging the annual 99th percentiles:
Equation 12
[GRAPHIC] [TIFF OMITTED] TR18JY97.017
(c) The 3-year average 99th percentile is rounded
according to the conventions in section 3.3 of this appendix before
a comparison with the standard is made.
Example 6--Ambient Monitoring Site With Sampling Every Sixth Day
That Meets the Primary 24-Hour PM10 Standard.
a. In each year of a particular 3 year period, varying numbers
of PM10 daily values (e.g., 110, 98, and 100) out of a
possible 121 daily values were recorded at a particular site with
the following ranked values (in ug/m3):
Table 4.--Ordered Monitoring Data For 3 Years
----------------------------------------------------------------------------------------------------------------
Year 1 Year 2 Year 3
----------------------------------------------------------------------------------------------------------------
j rank Xj value j rank Xj value j rank Xj value
----------------------------------------------------------------------------------------------------------------
108.............. 120 96 143 98 140
109.............. 128 97 148 99 144
110.............. 130 98 150 100 147
----------------------------------------------------------------------------------------------------------------
b. Using Equation 11, the 99th percentile values for
each year are calculated as follows:
[GRAPHIC] [TIFF OMITTED] TR18JY97.018
[GRAPHIC] [TIFF OMITTED] TR18JY97.019
[GRAPHIC] [TIFF OMITTED] TR18JY97.020
c. 1. Using Equation 12, the 3-year average 99th
percentile is calculated as follows:
[GRAPHIC] [TIFF OMITTED] TR18JY97.021
2. Therefore, this site meets the 24-hour PM10
standard.
[62 FR 38755, July 18, 1997]