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For the reasons set forth in the preamble, part 50 of Chapter 1 of
Title 40 of the code of Federal regulations is proposed to be 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:   42 U.S.C. 7401 et seq.   ADVANCE \d4

2. Section 50.15 is revised to read as follows:

( 50.15 National primary and secondary ambient air quality standards for
ozone.

(a) The level of the national 8-hour primary ambient air quality
standard for O3 is (0.060-0.070) parts per million (ppm), daily maximum
8-hour average, measured by a reference method based on Appendix D to
this part and designated in accordance with part 53 of this chapter or
an equivalent method designated in accordance with part 53 of this
chapter.

(b) The 8-hour primary O3 ambient air quality standard is met at an
ambient air quality monitoring site when the average of the annual
fourth-highest daily maximum 8-hour average O3 concentration is less
than or equal to (0.060-0.070) ppm, as determined in accordance with
appendix P to this part.

(c) The level of the national secondary ambient air quality standard for
O3 is a cumulative index value of (7-15) ppm-hours, measured by a
reference method based on Appendix D to this part and designated in
accordance with part 53 of this chapter or an equivalent method
designated in accordance with part 53 of this chapter.

(d) The secondary O3 ambient air quality standard is a seasonal standard
expressed as a sum of weighted hourly concentrations, cumulated over
the12 hour daylight period from 8:00 a.m. to 8:00 p.m. local standard
time, during the consecutive 3-month period within the O3 monitoring
season with the maximum index value.  The secondary O3 standard is met
at an ambient air quality monitoring site when the annual maximum
consecutive 3-month cumulative index value (W126) is less than or equal
to (7-15) ppm-hours, as determined in accordance with appendix P to this
part.

3. Appendix P is revised to read as follows:

Appendix P to Part 50 -- Interpretation of the Primary and Secondary
National Ambient Air Quality Standards for Ozone.

1.  General

(a) This appendix explains the data handling conventions and
computations necessary for determining whether the 8-hour primary and
secondary national ambient air quality standards for ozone specified in
§50.15 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, 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 reporting, data handling, and
computation procedures to be used in making comparisons between reported
ozone concentrations and the levels of the ozone standards are specified
in the following sections.

(b)Whether to exclude, retain, or make adjustments to the data affected
by exceptional events, including stratospheric ozone intrusion and other
natural events, is determined by the requirements under §50.1, §50.14
and §51.930.

(c) The terms used in this appendix are defined as follows:

	8-hour average is the rolling average of eight hourly ozone
concentrations as explained in section 3 of this appendix.

	Annual fourth-highest daily maximum refers to the fourth-highest value
measured at a monitoring site during a particular year.

Annual Cumulative W126 Index is the maximum sum over three consecutive
calendar months of the monthly W126 index in a year, as explained in
section 4 of this appendix.

	Daily maximum 8-hour average concentration refers to the maximum
calculated 8-hour average for a particular day as explained in section 3
of this appendix.

	Daily W126 Index is the sum of the sigmoidally weighted hourly ozone
concentrations during the 12-hour daylight period, 8:00 a.m. to 7:59
p.m. local standard time (LST).

Design values are the metrics (i.e., statistics) that are compared to
the primary and secondary NAAQS levels to determine compliance,
calculated as shown in sections 3 and 4 of this appendix.

Monthly W126 Index is the sum of the daily W126 index over one calendar
month during the required ozone monitoring season, adjusted for
incomplete data if appropriate, as explained in section 4 of this
appendix.

	Required ozone monitoring season refers to the span of time within a
calendar year when individual States are required to measure ambient
ozone concentrations as listed in part 58 Appendix D to this chapter.

	Year refers to calendar year.

2.	Requirements for Data Used for Comparisons with the Ozone NAAQS

(a) All valid FRM/FEM ozone data submitted to EPA's Air Quality System
(AQS), or otherwise available to EPA, meeting the requirements of part
58 of this chapter including appendices A, C, and E shall be used in
design value calculations.

(b) When two or more ozone monitors are operated at a site, the state
may in advance designate one of them as the primary monitor. If the
state has not made this designation, the Administrator will make the
designation, either in advance or retrospectively. Design values will be
developed using only the data from the primary monitor, if this results
in a valid design value. If data from the primary monitor do not allow
the development of a valid design value, data solely from the other
monitor(s) will be used in turn to develop a valid design value, if this
results in a valid design value. If there are three or more monitors,
the order for such comparison of the other monitors will be determined
by the Administrator. The Administrator may combine data from different
monitors in different years for the purpose of developing a valid
primary or secondary standard design value, if a valid design value
cannot be developed solely with the data from a single monitor. However,
data from two or more monitors in the same year at the same site will
not be combined in an attempt to meet data completeness requirements,
except if one monitor has physically replaced another instrument
permanently, in which case the two instruments will be considered to be
the same monitor, or if the state has switched the designation of the
primary monitor from one instrument to another during the year.

(c) Hourly average concentrations shall be reported in parts per million
(ppm) to the third decimal place, with additional digits to the right of
the third decimal place truncated. The start of each hour shall be
identified in local standard time (LST).

3.	Comparison to the Primary Standard for Ozone

(a)  Computing 8-hour averages

Running 8-hour averages shall be computed from the hourly ozone
concentration data for each hour of the year and shall be stored in the
first, or start, hour of the 8-hour period.  In the event that only 6 or
7 hourly averages are available, the valid 8-hour average shall be
computed on the basis of the hours available, using 6 or 7 as the
divisor. In the event that only 1, 2, 3, 4, or 5 hourly averages are
available, the 8-hour average shall be computed on the basis of
substituting for all the hours without hourly averages a low hourly
average value selected as follows, using 8 as the divisor. For days
within the required ozone monitoring season, the substitution value
shall be the lowest hourly average ozone concentration observed during
the same hour (local standard time) of any day in the required ozone
monitoring season of that year, or one-half of the method detection
limit of the ozone instrument, whichever is higher.  However, if the
number of same-hour concentration values available for the required
ozone monitoring season for the year, from which the lowest observed
hourly concentration would be identified for purposes of this
substitution, is less than 50% of the number of days during the required
ozone monitoring season, one-half the method detection limit of the
ozone instrument shall be used in the substitution. For days outside the
required ozone monitoring season, the substitution value shall be
one-half the method detection limit of the ozone instrument. An 8-hour
period with no available hourly averages does not have a valid 8-hour
average. The computed 8-hour average ozone concentrations are not
rounded or truncated.

(b) Daily maximum 8-hour average concentrations

There are 24 8-hour periods in each calendar day. Some of these may not
have valid 8-hour averages, under section 3(a). The daily maximum 8-hour
concentration for a given calendar day is the highest of the valid
8-hour average concentrations computed for that day. This process is
repeated, yielding a daily maximum 8-hour average ozone concentration
for each day with ambient ozone monitoring data, including days outside
the required ozone monitoring season if data are available.  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. In these cases, the maximum 8-hour average concentration
from each day is used, even if the two averages have some hours in
common.

(c)  Primary Standard Design Value

The primary standard design value is the annual fourth-highest daily
maximum 8-hour ozone concentration considering all days with monitoring
data including any days outside the required ozone monitoring season,
expressed in parts per million, averaged over three years. The 3-year
average shall be computed using the three most recent, consecutive years
of monitoring data that can yield a valid design value. For a design
value to be valid for comparison to the standard, the monitoring data
set on which it is based must meet the data completeness requirements
described in section 3(d). The computed 3-year average of the annual
fourth-highest daily maximum 8-hour average ozone concentrations shall
be rounded to three decimal places.  Values equal to or greater than
0.xxx5 ppm shall round up.

(d)  Data Completeness Requirements for a Valid Design Value

(i) A design value greater than the standard is valid if in each of the
three years there are at least four days with a daily maximum 8-hour
average concentration. Under sections 3(a) and 3(b), there will be a
daily maximum 8-hour average concentration on any day with at least one
hourly concentration. One or more of these four days may be outside the
required ozone monitoring season.

(ii) A design value less than or equal to the standard is valid if for
at least 75% of the days in the required ozone monitoring season in each
of the three years there are at least 18 8-hour averages in the day that
are based on at least 6 measured hourly average concentrations.

(iii) When computing whether the minimum data completeness requirement
in section 3(d)(ii) has been met for the purpose of showing that a
design value equal to or less than the standard is valid, meteorological
or ambient data may be sufficient to demonstrate that ozone levels on
days with missing data would not have affected the design value.  At the
request of the state, the Regional Administrator may consider
demonstrations that meteorological conditions on one or more days in the
required ozone monitoring season which do not have at least 18 8-hour
averages in the day that are based on at least 6 measured hourly average
concentrations could not have caused a daily maximum 8-hour
concentration high enough to have been one of the four highest daily
maximum 8-hour concentrations for the year.  At the request of the
state, days so demonstrated may be counted towards the 75% requirement
for the purpose of validating the design value, subject to the approval
of the Regional Administrator.

(vi) Years that do not meet the completeness criteria stated in 3(d)(ii)
may nevertheless be used to calculate a design value that will be deemed
valid with the approval of, or at the initiative of, the Administrator,
who may consider factors such as monitoring site closures/moves,
monitoring diligence, the consistency and levels of the valid
concentration measurements that are available, and nearby concentrations
in determining whether to use such data.

(e) Comparison with the Primary Ozone Standard

(i) The primary ozone ambient air quality standard is met at an ambient
air quality monitoring site when the design value is less than or equal
to [0.075] ppm.

 (ii) Comparison with the primary ozone standard is demonstrated by
examples 1 and 2 as follows:

Example 1.	Ambient monitoring site attaining the primary ozone standard.

Year	Percent

Valid Days (Within the Required Monitoring Season)

	1st

Highest

Daily Max 8-hour Conc.

(ppm)	2nd Highest

Daily Max

8-hour Conc.

(ppm)	3rd Highest

Daily Max

8-hour Conc.

(ppm)	4th Highest

Daily Max

8-hour Conc.

(ppm)	5th Highest

Daily Max

8-hour Conc.

(ppm)

2006	80%	0.092500	0.090375	0.085125	0.078375	0.078125

2007	96%	0.084750	0.083500	0.075375	0.071875	0.070625

2008	98%	0.080875	0.079750	0.077625	0.075500	0.060375

Average

	0.075250

	Rounded

	0.075

As shown in Example 1, this monitoring site meets the primary ozone
standard because the 3-year average of the annual fourth-highest daily
maximum 8-hour average ozone concentrations (i.e., 0.075256 ppm, rounded
to 0.075 ppm) is less than or equal to [0.075] ppm.  The data
completeness requirement is also met because no single year has less
than 75% data completeness.  In Example 1, the individual 8-hour
averages and the 3-year average are shown with six decimal digits. In
actual calculations, all digits supported by the calculator or
calculation software must be retained.

Example 2.  Ambient monitoring site failing to meet the primary ozone
standard.

Year	Percent

Valid Days

(Within the Required Monitoring Season)

	1st

Highest

Daily Max 8-hour Conc.

(ppm)	2nd Highest

Daily Max

8-hour Conc.

(ppm)	3rd Highest

Daily Max

8-hour Conc.

(ppm)	4th Highest

Daily Max

8-hour Conc.

(ppm)	5th Highest

Daily Max

8-hour Conc.

(ppm)

2006	96%	0.105125	0.103500	0.101125	0.078625	0.072375

2007	74%	0.104250	0.103625	0.093000	0.080250	0.069500

2008	98%	0.103125	0.101875	0.101750	0.075375	0.074625

Average

	0.078083

	Rounded

	0.078

As shown in Example 2, the data capture in 2007 is less than 75%. The
primary ozone standard is not met for this monitoring site because the
3-year average of the fourth-highest daily maximum 8-hour average ozone
concentrations (i.e., 0.078083 ppm, rounded to 0.078 ppm) is greater
than [0.075] ppm and is therefore valid despite this incompleteness. In
Example 2, the individual 8-hour averages and the 3-year average are
shown with six decimal digits. In actual calculations, all digits
supported by the calculator or calculation software must be retained.

4.	Secondary Ambient Air Quality Standard for Ozone

(a)	Computing the daily W126 index value.

The secondary ozone ambient air quality standard is a seasonal standard
expressed as a sum of weighted hourly concentrations, cumulated over the
12 hour daylight period from 8:00 a.m. to 8:00 p.m. local standard time,
during the consecutive 3-month period within the ozone monitoring season
with the maximum index value. The first step in determining whether the
standard is met at a monitoring site is to compute the daily W126 index
value for each day by applying the sigmoidal weighting function in
Equation 1 to each reported measurement of hourly average concentration.

Equation 1

 .

The computed value of the sigmoidally weighted hourly concentration is
not rounded or truncated.  The daily W126 index is formed by summing the
twelve computed hourly values, retaining all decimal places.  An
illustration of computing a daily W126 index value is below:

Example 3.	Daily W126 index value calculation for an ambient ozone
monitoring site.

Start of hour	Concentration (ppm)	Weighted Concentration (ppm)

8:00 a.m.	0.045	0.002781

9:00 a.m.	0.060	0.018218

10:00 a.m.	0.075	0.055701

11:00 a.m.	0.080	0.067537

12:00 p.m.	0.079	0.065327

1:00 p.m.	0.082	0.071715

2:00 p.m.	0.085	0.077394

3:00 p.m.	0.088	0.082448

4:00 p.m.	0.083	0.073683

5:00 p.m.	0.081	0.069667

6:00 p.m.	0.065	0.029260

7:00 p.m.	0.056	0.011676

Sum=Daily W126  index value

0.625406 ppm-hours

In Example 3, the individual weighted concentrations and their sum are
shown with six decimal digits. In actual calculations, all digits
supported by the calculator or calculation software must be retained.
There are no data completeness requirements for the daily index.  If
fewer than 12 hourly values are available, only the available hours are
weighted and summed. However, there are data completeness requirements
for the monthly W126 index values and a required adjustment for
incomplete data, as describe in the next section.

(b) Computing the Monthly W126 Index

As described in section 4(a), the daily index value is computed at each
monitoring site for each calendar day in each month during the required
ozone monitoring season with no rounding or truncation.  The monthly
W126 index is the sum of the daily index values over one calendar month.
 At an individual monitoring site, a monthly W126 index is valid if
hourly average ozone concentrations are available for at least 75% of
the possible daylight hours in the month.  For months with more than 75%
but less than 100% data completeness, the monthly W126 value shall be
adjusted for incomplete data by multiplying the unadjusted monthly W126
index value by the ratio of the number of possible reporting hours to
the number of hours with reported ambient hourly concentrations using
Equation 2 in this appendix:

Equation 2

where,

	M.I.	=	the adjusted monthly W126 index,

	D.I.	=	daily W126 index (i.e., the daily sum of the sigmoidally
weighted daylight hourly concentrations),

	n	=	the number of days in the calendar month,

	v	=	the number of daylight reporting hours (8:00 a.m. – 7:59 p.m.
LST) in the month with reported valid hourly ozone concentrations.

The resulting adjusted value of the monthly W126 index shall not be
rounded or truncated.

(b)	Secondary Standard Design Value

	The secondary standard design value is the 3-year average of the annual
maximum consecutive 3-month sum of adjusted monthly W126 index values
expressed in ppm-hours.   Specifically, the annual W126 index value is
computed on a calendar year basis using the three highest, consecutive
adjusted monthly W126 index values.   The 3-year average shall be
computed using the most recent, consecutive three calendar years of
monitoring data meeting the data completeness requirements described in
section 4(c).  The computed 3-year average of the annual maximum
consecutive 3-month sum of adjusted monthly W126 index values in
ppm-hours shall be rounded to a whole number with decimal values equal
to or greater than 0.500 rounding up.

(c) Data Completeness Requirement

(i) The annual W126 index is valid for purposes of calculating a 3-year
design value if each full calendar month in the required ozone
monitoring season has at least 75% data completeness for daylight hours.

(ii) If one or more months during the ozone monitoring seasons of three
successive years has less than 75% data completeness, the three years
shall nevertheless be used in the computation of a valid design value
for the site if substituting the lowest hourly ozone concentration
observed during daylight hours in the required ozone monitoring season
of each year, or one-half of the method detection limit of the ozone
instrument, whichever is higher, for enough of the missing hourly
concentrations within each incomplete month to make the month 75%
complete, and then adjusting for the remaining missing data using
Equation 2, above results in a design value greater than the level of
the standard.

 (d)	Comparisons with the Secondary Ozone Standard

(i) The secondary ambient ozone air quality standard is met at an
ambient air quality monitoring site when the design value is less than
or equal to [15] ppm-hours.

(ii) Comparison with the secondary ozone standard is demonstrated by
example 4 as follows:

Example 4.	Ambient Monitoring Site Failing to Meet the Secondary Ozone
Standard

	April	May	June	July	August	September	October	Overall

2006

Adjusted monthly W126 index	4.442	9.124	12.983	16.153	13.555	4.364	1.302

	3-Month sum	na	na	26.549	38.260	42.691	34.072	19.221

	2006 Maximum

	42.691

	42.691

2007

Adjusted monthly W126 index	3.114	7.214	8.214	8.111	7.455	7.331	5.115

	3-Month sum	na	na	18.542	23.539	23.780	22.897	19.901

	2007 Maximum

	23.780

	23.780

2008

Adjusted monthly W126 index	4.574	5.978	6.786	8.214	5.579	4.331	2.115

	3-Month sum	na	na	17.338	20.978	20.579	18.124	12.025

	2008 Maximum

20.978

20.978

3-Year average W126 index

29.149666

Rounded

29

As shown in example 4, the secondary ozone standard is not met for this
monitoring site because the 3-year average of the annual W126 index
value for this site is greater than [15] ppm-hours:

3-year average W126 index = (42.691+ 23.780+ 20.978)/3 = 29.149666,
which rounds to 29 ppm-hours.

In Example 4, the adjusted monthly W126 index values and the 3-month
sums of the adjusted monthly W126 index values are shown with three
decimal digits.  In actual calculations, all digits supported by the
calculator or calculation software must be retained.

4. Section 50.14 is amended by adding entries for "Primary and Secondary
Ozone Standards” to the end of the table in paragraph (c)(2)(vi) to
read as follows:

§ 50.14 Treatment of air quality monitoring data influenced by
exceptional events.

* * * * *

(c) ***

(2) ***

(vi) ***

Table 1.  Schedule for Exceptional Event Flagging and Documentation
Submission for Data to be Used in Designations Decisions for New NAAQS

NAAQS Pollutant/

Standard/(Level)/

Promulgation Date	Air Quality Data Collected for Calendar Year	Event
Flagging & Initial Description Deadline	Detailed Documentation
Submission Deadline

*******

	Primary Ozone/8-Hr Standard (Level TBD) Promulgated by August 31, 2010
2007-2009	November 1, 2010b	November 1, 2010b

	2010	60 Days after the end of the calendar quarter in which the event
occurred or March 1, 2011, whichever date occurs firstb	60 Days after
the end of the calendar quarter in which the event occurred or March 1,
2011, whichever date occurs firstb

Secondary Ozone/ (Level TBD)Alternative 2-year Schedule- to be
Promulgated by August 31, 2010 	2008	July 1, 2011b	July 1, 2011a

	2009-2010	July 1, 2011b	July 1, 2011b

	2011	60 Days after the end of the calendar quarter in which the event
occurred or March 1, 2012, whichever occurs firstb	60 Days after the end
of the calendar quarter in which the event occurred or March 1, 2012,
whichever occurs firstb

Secondary Ozone/ (Level TBD)- Alternative Accelerated Schedule -to be
Promulgated by August 31, 2010	2007-2009	November 1, 2010b	November 1,
2010b

	2010	60 Days after the end of the calendar quarter in which the event
occurred or March 1, 2011, whichever date occurs firstb	60 Days after
the end of the calendar quarter in which the event occurred or March 1,
2011, whichever date occurs firstb

a These dates are unchanged from those published in the original
rulemaking.

b Indicates change from general schedule in 40 CFR 50.14.

Note:  EPA notes that the table of revised deadlines only applies to
data EPA will use to establish the final initial designations for new
NAAQS.  The general schedule applies for all other purposes, most
notably, for data used by EPA for redesignations to attainment.

 *****

5. Section 58.50 (c) is revised and (d) is added to read as follows:

§ 58.50  Index reporting.

 (c) The population of a metropolitan statistical area for purposes of
index reporting is the latest available U.S. census population.

(d) For O3, reporting is required in metropolitan and micropolitan
statistical areas wherever monitoring is required under Appendix D to
Part 58—SLAMS Minimum O3 Monitoring Requirements.

6.  Appendix G of Part 58 (3) is revised to read as follows:

Appendix G to Part 58—Uniform Air Quality Index (AQI) and Daily
Reporting

3. Must I Report the AQI?

You must report the AQI daily if yours is a metropolitan statistical
area (MSA) with a population over 350,000.  For O3, reporting is
required in metropolitan and micropolitan statistical areas wherever
monitoring is required under Appendix D to Part 58—SLAMS Minimum O3
Monitoring Requirements.

 The legislative history of section 109 indicates that a primary
standard is to be set at “the maximum permissible ambient air level .
. . which will protect the health of any [sensitive] group of the
population,” and that for this purpose “reference should be made to
a representative sample of persons comprising the sensitive group rather
than to a single person in such a group” [S. Rep. No. 91-1196, 91st
Cong., 2d Sess. 10 (1970)].

 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, man-made 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.”

  See EPA report, Evaluating Ozone Control Programs in the Eastern
United States: Focus on the NOx Budget Trading Program, 2004.

 American Lung Association v. Whitman (No. 1:03CV00778, D.D.C. 2003).

 The level of the 8-hour primary ozone standard was set at 0.075 ppm,
while CASAC unanimously recommended a range between 0.060 and 0.070 ppm.

 The Administrator also noted the exchange that had occurred between EPA
and the Office of Management and Budget (OMB) with regard to the final
decision on the secondary standard, as discussed in the 2008 final rule
(73 FR 16497).

 The EPA also separately announced that it will move quickly to
implement any new standards that might result from this reconsideration.
 To reduce the workload for states during the interim period of
reconsideration, the Agency intends to propose to defer compliance with
the CAA requirement to designate areas as attainment or nonattainment.
EPA will work with states, local governments and tribes to ensure that
air quality is protected during that time.

 The use of O3 as the indicator for photochemical oxidants was adopted
in the 1979 final rule and retained in subsequent rulemaking.  An 8-hour
averaging time and a form based on the annual fourth-highest daily
maximum 8-hour concentration, averaged over 3 years, were adopted in the
1997 final rule and retained in the 2008 rulemaking.

 In its assessment of the epidemiological evidence judged to be most
relevant to making decisions on the level of the O3 primary standard,
EPA has placed greater weight on U.S. and Canadian epidemiologic
studies, since studies conducted in other countries may well reflect
different demographic and air pollution characteristics.

 The exposure assessment done as part of the 2008 final rulemaking
considered several air quality scenarios, including just meeting what
was then the current standard set at a level of 0.084 ppm, as well as
just meeting alternative standards at levels of 0.080, 0.074, 0.070, and
0.064 ppm.

 Exposures of concern were also considered in the 1997 review of the O3
NAAQS, and were judged by EPA to be an important indicator of the public
health impacts of those O3-related effects for which information was too
limited to develop quantitative estimates of risk but which had been
observed in humans at and above the benchmark level of 0.08 ppm for 6-
to 8-hour exposures . . . including increased nonspecific bronchial
responsiveness (for example, 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).  (62 FR 38868)

 While most of the available evidence addresses mechanisms for O3, O3
clearly serves as an indicator for the total photochemical oxidant
mixture found in the ambient air.  Some effects may be caused by one or
more components in the overall pollutant mix, either separately or in
combination with O3.  However, O3 clearly dominates these other oxidants
with their concentrations only being a few percent of the O3
concentration.

 In previous Staff Papers and Federal Register notices announcing
proposed and final decisions on the O3 and other NAAQS, EPA has used the
phrase “sensitive population groups” to include both population
groups that are at increased risk because they are more intrinsically
susceptible and population groups that are more vulnerable due to an
increased potential for exposure.  In this notice, we use the phrase,
“at risk” populations to include both types of population groups.

 Health effects discussions are also drawn from the more detailed
information and tables presented in the Criteria Document’s annexes.

 This study and other studies (Folinsbee et al., 1988; Horstman et al,
1990; and McDonnell et al., 1991), conducted in EPA’s human studies
research facility in Chapel Hill, NC, measured ozone concentrations to
within +/- 5 percent or +/- 0.004 ppm at the 0.080 ppm exposure level.

 These studies, conducted at a facility at the University of California,
in Davis, CA, reported O3 concentrations to be accurate within +/- 0.003
ppm over the range of concentrations included in these studies.

 These distributional results presented in the Criteria Document and
Staff Paper for the Adams (2006) study are based on data for squate-wave
exposures to 0.080 ppm that were not included in the publication but
were obtained from the author.

 Dr. Adams submitted comments on EPA’s reanalysis in which he
concluded that the FEV1 response in healthy young adults at the 0.060
ppm exposure level in his study (Adams, 2006a) does not demonstrate a
significant mean effect by ordinarily acceptable statistical analysis,
but is rather in somewhat of a gray area, both in terms of a
biologically meaningful response and a statistically significant
response (Adams, 2007).    The EPA responded to these comments in the
2008 final rule (73 FR 16455) and in the Response to Comments (EPA,
2008, pp. 26-28).

 Graham and Koren (1990) compared inflammatory mediators present in NL
and BAL fluids of humans exposed to 0.4 ppm O3 for 2 hours and found
similar increases in PMNs in both fluids, suggesting a qualitative
correlation between inflammatory changes in the lower airways (BAL) and
upper respiratory tract (NL).

 Discussion of the reasons for focusing on warm season studies is found
in the section 2.A.3.a below.

 In commenting on the Criteria Document, the CASAC Ozone Panel raised
questions about the implications of these time-series results in a
policy context, emphasizing that “…while the time-series study
design is a powerful tool to detect very small effects that could not be
detected using other designs, it is also a blunt tool” (Henderson,
2006b).  They note that “. . .not only is the interpretation of these
associations complicated by the fact that the day-to-day variation in
concentrations of these pollutants is, to a varying degree, determined
by meteorology, the pollutants are often part of a large and highly
correlated mix of pollutants, only a very few of which are measured”
(Henderson, 2006b).  Even with these uncertainties, the CASAC Ozone
Panel, in its review of the Staff Paper, found “…premature total
non-accidental and cardiorespiratory mortality for inclusion in the
quantitative risk assessment to be appropriate.” (Henderson, 2006b)

 This reanalysis report and the original prospective cohort study
findings are discussed in more detail in section 8.2.3 of the Air
Quality Criteria for Particulate Matter (EPA, 2004).

 Results for studies of respiratory symptoms are presented as odds
ratios; an odds ratio of 1.0 is equivalent to no effect, and thus is
presented as equivalent to the zero effect estimate line.

 In the Staff Paper and documents from previous O3 NAAQS reviews,
"at-risk" groups have also been called "sensitive" groups, to mean both
groups with greater inherent susceptibility and those more likely to be
exposed.

 Similar to animal toxicology studies referred above, a polymorphism in
a specific proinflammatory cytokine gene has been implicated in
O3-induced lung function changes in healthy, mild asthmatics and
individuals with rhinitis.  These observations suggest a potential role
for these markers in the innate susceptibility to O3, however, the
validity of these markers and their relevance in the context of
prediction to population studies requires additional research.

 In 2000, the American Thoracic Society (ATS) published an official
statement on “What Constitutes an Adverse Health Effect of Air
Pollution?” (ATS, 2000), which updated its earlier guidance (ATS,
1985). Overall, the new guidance does not fundamentally change the
approach previously taken to define adversity, nor does it suggest a
need at this time to change the structure or content of the tables
describing gradation of severity and adversity of effects described
below.

 Modeling that projects whether and how areas might attain alternative
standards in a future year is presented in the Regulatory Impact
Analysis being prepared in connection with this rulemaking.

 EPA made available corrected versions of the final 2007 Staff Paper,
and human exposure and health risk assessment technical support
documents in July 2007 on the EPA web site listed in the Availability of
Related Information section of this notice.

 The 12 CSAs modeled are:  Atlanta-Sandy Springs-Gainesville, GA-AL;
Boston-Worcester-Manchester, MA-NH;  Chicago-Naperville-Michigan City,
IL-IN-WI;  Cleveland-Akron-Elyria, OH;  Detroit-Warren-Flint, MI;
Houston-Baytown-Huntsville, TX;  Los Angeles-Long Beach-Riverside, CA;
New York-Newark-Bridgeport, NY-NJ-CT-PA;  Philadelphia-Camden-Vineland,
PA-NJ-DE-MD;  Sacramento--Arden-Arcade--Truckee, CA-NV;  St. Louis-St.
Charles-Farmington, MO-IL;  Washington-Baltimore-N. Virginia,
DC-MD-VA-WV

 All 12 of the CSAs modeled did not meet the 0.084 ppm O3 NAAQS for the
three year period examined.

 The general approach used in the human exposure assessment was
described in the draft Health Assessment Plan (EPA, 2005d) that was
released to the CASAC and general public in April 2005 and was the
subject of a consultation with the CASAC O3 Panel on May 5, 2005.  In
October 2005, OAQPS released the first draft of the Staff Paper
containing a chapter discussing the exposure analyses and first draft of
the Exposure Analyses TSD for CASAC consultation and public review on
December 8, 2005.  In July 2006, OAQPS released the second draft of the
Staff Paper and second draft of the Exposure Analyses TSD for CASAC
review and public comment which was held by the CASAC O3 Panel on August
24-25, 2006.

 The 8-hour O3 standard established in 1997 was 0.08 ppm, but the
rounding convention specified that the average of the 4th daily maximum
8-hour average concentrations over a three-year period must be at 0.084
ppm or lower to be in attainment of this standard.  When EPA staff
selected alternative standards to analyze, it was presumed that the same
type of rounding convention would be used, and thus alternative
standards of 0.084, 0.074, 0.064 ppm were chosen.

 A design value is a statistic that describes the air quality status of
a given area relative to the level of the NAAQS.  Design values are
often based on multiple years of data, consistent with specification of
the NAAQS in Part 50 of the CFR.  For the 8-hour O3 NAAQS, the 3-year
average of the annual 4th-highest daily maximum 8-hour average
concentrations, based on the monitor within (or downwind of) an urban
area yielding the highest 3-year average, is the design value.

 The quadratic rollback approach and evaluation of this approach are
described by Johnson (1997), Duff et al. (1998) and Rizzo (2005, 2006).

 As discussed above in Section II.A, O3 health responses observed in
controlled human exposure studies are associated with exposures while
engaged in moderate or greater exertion and, therefore, these are the
exposure measures of interest.  The level of exertion of individuals
engaged in particular activities is measured by an equivalent
ventilation rate (EVR), ventilation normalized by body surface area
(BSA, in m2), which is calculated as VE/BSA, where VE is the ventilation
rate (liters/minute). Moderate and greater exertion levels were defined
as EVR > 13 liters/min-m2 (Whitfield et al., 1996) to correspond to the
exertion levels measured in most subjects studied in the controlled
human exposure studies that reported health effects associated with 6.6
hour O3 exposures.

	 The full range of quantitative exposure estimates associated with just
meeting the 0.084 ppm and alternative O3 standards are presented in
chapter 4 and Appendix 4A of the 2007 Staff Paper.

 The methodology, scope, and results from the risk assessment conducted
in the last review are described in Chapter 6 of the 1996 Staff Paper
(EPA, 1996) and in several technical reports (Whitfield et al., 1996;
Whitfield, 1997) and publication (Whitfield et al., 1998).

 The 9 urban study areas included in the exposure and risk analyses
conducted during the last review were: Chicago, Denver, Houston, Los
Angeles, Miami, New York City, Philadelphia, St. Louis, and Washington,
D.C.

 The general approach used in the health risk assessment was described
in the draft Health Assessment Plan (EPA, 2005d) that was released to
the CASAC and general public in April 2005 and was the subject of a
consultation with the CASAC O3 Panel on May 5, 2005.  In October 2005,
OAQPS released the first draft of the Staff Paper containing a chapter
discussing the risk assessment and first draft of the Risk Assessment
TSD for CASAC consultation and public review on December 8, 2005.  In
July 2006, OAQPS released the second draft of the Staff Paper and second
draft of the Risk Assessment TSD for CASAC review and public comment
which was held by the CASAC O3 Panel on August 24-25, 2006.

 The 12 urban areas are the same urban areas evaluated in the exposure
analysis discussed in the prior section.  However, for most of the
health endpoints based on findings from epidemiological studies, the
geographic areas and populations examined in the health risk assessment
were limited to those counties included in the original epidemiological
studies that served as the basis for the concentration-response
relationships.

 EPA notes that the estimated level of policy-relevant background O3
used in the prior risk assessment was a single concentration of 0.04
ppm, which was the midpoint of the range of levels for policy-relevant
background that was provided in the 1996 Criteria Document.

 As discussed above in section II.B.1, the urban areas were defined
using the consolidated statistical areas definition and the total
population residing in the 12 urban areas was approximately 88.5 million
people.

 For 9 of the 12 urban areas, the O3 season is defined as a period
running from March or April to September or October.  In 3 of the urban
areas (Houston, Los Angeles, and Sacramento), the O3 season is defined
as the entire year.

 The geographic boundaries for the urban areas included in this portion
of the risk assessment were generally matched to the geographic
boundaries used in the epidemiological studies that served as the basis
for the concentration-response functions.  In most cases, the urban
areas were defined as either a single county or a few counties for this
portion of the risk assessment.

 Due to time constraints, lung function risk estimates for asthmatic
school age children were developed for only 5 of the 12 urban areas, and
the areas were selected to represent different geographic regions.  The
5 areas were: Atlanta, Chicago, Houston, Los Angeles, and New York City.

 For example, assuming lower background levels resulted in increased
estimates of non-accidental mortality incidence per 100,000 that were
often 50 to 100 percent greater than the base case estimates; assuming
higher background levels resulted in decreased estimates of
non-accidental mortality incidence per 100,000 that were less than the
base case estimates by 50 percent or more in many of the areas.

 Bell et al. (2006) referred to this level as being approximately
equivalent to 120 µg/m3, daily 8-hour maximum, the World Health
Organization guideline and European Commission target value for O3.

 As described in the 2007 Staff Paper (section 4.5.8) and discussed
above in section II.B, recent O3 air quality distributions have been
statistically adjusted to simulate just meeting the then current 0.084
ppm standard and selected alternative standards.  These simulations do
not represent predictions of when, whether, or how areas might meet the
specified standards.  Modeling that projects whether and how areas might
attain alternative standards in a future year is presented in the
Regulatory Impact Analysis being prepared in connection with this
rulemaking.

 The abbreviated notation used to identify the then current 0.084 ppm
standard and alternative standards in this section and in the risk
assessment section of the Staff Paper is in terms of ppm and the nth
highest daily maximum 8-hour average.  For example, the 8-hour standard
established in 1997 is identified as “0.084/4.”

 As discussed above at the beginning of section II, the Administrator
has focused her reconsideration of the primary O3 standard set in the
2008 final rule on the level of the standard, having decided not to
reopen the 2008 final rule with regard to the need to revise the 1997
primary O3 standard to provide increased public health protection nor
with regard to the indicator, averaging period, and form of the 2008
standard.

 The EPA responded to these comments in the 2008 final rule (73 FR
16454-5).

 As noted in section II.C.1.b.above, the Administrator focused on
alternative standards with different levels but the same form and
averaging time as the primary standard set in 2008.

 In its assessment of the evidence judged to be most relevant to making
decisions on the level of the O3 secondary standard, however, EPA has
placed greater weight on U.S. studies, due to the often species-, site-
and climate-specific nature of O3-related vegetation response.

 The SUM06 index is defined as the sum of all hourly O3 concentrations
greater or equal to 0.06 ppm over a specified time.

 The CMAQ model is a multi-pollutant, multiscale air quality model that
contains state-of-the-science techniques for simulating atmospheric and
land processes that affect the transport, transformation, and deposition
of atmospheric pollutants and/or their precursors on both regional and
urban scales.  It is designed as a science-based modeling tool for
handling many major pollutants (including photochemical oxidants/O3,
particulate matter, and nutrient deposition) holistically.  The CMAQ
model can generate estimates of hourly O3 concentrations for the
contiguous U.S., making it possible to express model outputs in terms of
a variety of exposure indices (e.g., W126, 8-hour average).

 This analysis was updated using 2003-2005 air quality as it became
available, finding similar results.

	 Principal crops as defined by the USDA include corn, sorghum, oats,
barley, winter wheat, rye, Durum wheat, other spring wheat, rice,
soybeans, peanuts, sunflower, cotton, dry edible beans, potatoes, sugar
beets, canola, proso millet, hay, tobacco, and sugarcane.  Acreage data
for the principal crops were taken from the USDA NASS 2005 Acreage
Report (  HYPERLINK
"http://usda.mannlib.cornell.edu/reports/nassr/field/pcp-bba/acrg0605.pd
f"
http://usda.mannlib.cornell.edu/reports/nassr/field/pcp-bba/acrg0605.pdf
).

 While the term “averaging time” is used, for the cumulative,
seasonal standard the seasonal and diurnal time periods at issue are
those over which exposures during a specified period of time are
cumulated, not averaged.

 Prior to publication of the 2008 final rule, EPA did further analysis
of the degree of overlap to extend the 2007 Staff Paper analyses, and
that analysis was available in the docket.

 The AOT40 index used in Europe is a cumulative index that incorporates
a threshold at 0.04 ppm (40 ppb).  This index is calculated as the area
over the threshold (AOT) by subtracting 40 ppb from the value of each
hourly concentration above that threshold and then cumulating each
hourly difference over a specified window.

 While the term “averaging time” is used, for the cumulative,
seasonal standard the seasonal and diurnal time periods at issue are
those over which exposures during a specified period of time are
cumulated, not averaged.

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shall be administered for the use and enjoyment of the American people
in such manner as will leave them unimpaired for future use as
wilderness, and so as to provide for the protection of these areas, the
preservation of their wilderness character” (The Wilderness Act,
1964).

 Because only enough missing 1-hour ozone values would be substituted as
needed to meet the 75 percent completeness requirement, to avoid
unreasonable underestimation of the true W126 index, tying the the
selection of the substitution value to the hour of the missing value, as
is proposed for data substitution for the purpose of the primary
standard (see section V.D), would introduce considerable complexity  by
requiring an algorithm for determining which specific missing values
would be substituted. Therfore, EPA is proposing this simpler
substitution approach for the secondary standard.

 At present, EPA’s Air Quality System (AQS) for storing and reporting
air quality data provides a completeness report that is based on yet a
third approach, in which the period for reporting data completeness is
the required monitoring season plus any extension needed to encompass
any exceedances that may have occurred outside the required season.
However, EPA’s practice for regulatory purposes has been to consider
completeness only over the required ozone monitoring season.

 Actually, it is an interpretation of the text of Appendix P, section
2.1, that the average resulting from the data substitution is to be
taken as the “8-hour” average, rather than the average of the
available 5 or fewer hours of data, which would be higher.  The text is
not entirely clear on this point.

 EPA also is proposing eliminate this 90 percent requirement, see
section V.E. The point made in this paragraph applies with or without
the 90 percent requirement in place.

 EPA notes that in the current versions of Appendix I and P, it is not
explicit that this provided exception also applies in the case of three
years which each have 75 percent or more of days with valid data but
less than 90 percent across three years. Because EPA is proposing to
remove the 90 percent requirement (see section V.E) this ambiguity does
not need correction.

 Appendix P now provides that in the event that only 6 or 7 hourly
averages are available, the valid 8-hour average shall be computed on
the basis of the hours available, using 6 or 7 as the divisor.  We are
not proposing to change this provision.

 The requirement that there be at least four days with at least one
hourly measurement is actually redundant and is stated only for ease of
understanding, since there would be no annual fourth-highest daily
maximum 8-hour concentration unless there are at least four days with
monitoring data, and a single hourly data point is necessary and
sufficient (with the proposed substitution step) to generate a daily
maximum 8-hour concentration.

 EPA has recently proposed to amend the completeness requirements for
sulfur dioxide and nitrogen dioxide to add quarterly 75 percent
completeness requirements in connection with proposals to establish
1-hour primary NAAQS for these pollutants, still with no requirement for
90 percent completeness across three years.

 The requirements specified in Table D-2 of Appendix D to part 58, as
noted in the third footnote of Table D-2, are applicable to the levels
of the O3 NAAQS as defined in 40 CFR part 50.  Accordingly, the 85
percent threshold for requiring higher minimum monitoring requirements
within MSAs would apply to the proposed levels for the cumulative,
seasonal secondary standard as well as to the proposed levels of the
8-hour primary standard.

 These MSAs are not currently required to monitor for O3.

 Defined as areas having at least one urban cluster of at least 10,000
but less than a population of 50,000.

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