Ambient Ozone Monitoring Regulations: Revisions to Network Design Requirements, 34525-34539 [E9-16802]

Agencies

• ENVIRONMENTAL PROTECTION AGENCY

[Federal Register Volume 74, Number 135 (Thursday, July 16, 2009)]
[Proposed Rules]
[Pages 34525-34539]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: E9-16802]


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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 58

[EPA-HQ-OAR-2008-0338; FRL-8930-7]
RIN 2060-AP15


Ambient Ozone Monitoring Regulations: Revisions to Network Design 
Requirements

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: The EPA is proposing to revise the monitoring network design 
requirements for ozone to assist in implementing changes to the primary 
and secondary National Ambient Air Quality Standards (NAAQS) for ozone 
that were promulgated on March 27, 2008. EPA is proposing to modify 
minimum monitoring requirements in urban areas, add new minimum 
monitoring requirements in non-urban areas, and extend the length of 
the required ozone monitoring season in some States.

DATES: Comments must be received on or before September 14, 2009.

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-HQ-
OAR-2008-0338, by one of the following methods:
     https://www.regulations.gov: Follow the on-line 
instructions for submitting comments.
     E-mail: Comments may be sent by electronic mail (e-mail) 
to a-and-r-docket@epa.gov, Attention Docket ID No. EPA-HQ-OAR-2008-
0338.
     Fax: Fax your comments to (202) 566-9744, Attention Docket 
ID No. EPA-HQ-OAR-2008-0338.
     Mail: Send your comments to Air and Radiation Docket and 
Information Center, Environmental Protection Agency, Mailcode 2822T, 
1200 Pennsylvania Ave., NW., Washington, DC 20460, Attention Docket ID 
No. EPA-HQ-OAR-2008-0338. Please include a total of two copies. In 
addition, please mail a copy of your comments on the information 
collection provisions to the Office of Information and Regulatory 
Affairs, Office of Management and Budget (OMB), Attn: Desk Officer for 
EPA, 725 17th St., NW., Washington, DC 20503.
     Hand Delivery: Deliver your comments to EPA Docket Center, 
1301 Constitution Ave., NW., Room 3334, Washington, DC 20460. Such 
deliveries are only accepted during the Docket's normal hours of 
operation, and special arrangements should be made for deliveries of 
boxed information.
    Instructions: Direct your comments to Docket ID No. EPA-HQ-OAR-
2008-0338. EPA's policy is that all comments received will be included 
in the public docket without change and may be made available online at 
https://www.regulations.gov, including any personal information 
provided, unless the comment includes information claimed to be 
Confidential Business Information (CBI) or other information whose 
disclosure is restricted by statute. Do not submit information that you 
consider to be CBI or otherwise protected through https://www.regulations.gov or e-mail. The https://www.regulations.gov Web site 
is an ``anonymous access'' system, which means EPA will not know your 
identity or contact information unless you provide it in the body of 
your comment. If you send an e-mail comment directly to EPA without 
going through https://www.regulations.gov your e-mail address will be 
automatically captured and included as part of the comment that is 
placed in the public docket and made available on the Internet. If you 
submit an electronic comment, EPA recommends that you include your name 
and other contact information in the body of your comment and with any 
disk or CD ROM you submit. If EPA cannot read your comment due to 
technical difficulties and cannot contact you for clarification, EPA 
may not be

[[Page 34526]]

able to consider your comment. Electronic files should avoid the use of 
special characters, any form of encryption, and be free of any defects 
or viruses. For additional information about EPA's public docket, visit 
the EPA Docket Center homepage at https://www.epa.gov/epahome/dockets.htm.
    Docket: All documents in the docket are listed in the https://www.regulations.gov index. Although listed in the index, some 
information is not publicly available, e.g., CBI or other information 
whose disclosure is restricted by statute. Certain other material, such 
as copyrighted material, will be publicly available only in hard copy. 
Publicly available docket materials are available either electronically 
in https://www.regulations.gov or in hard copy at the Ambient Ozone 
Monitoring Regulations: Revisions to Network Design Requirements 
Docket, EPA/DC, EPA West Building, Room 3334, 1301 Constitution Ave., 
NW., Washington, DC. The Public Reading Room is open from 8:30 a.m. to 
4:30 p.m. Monday through Friday, excluding legal holidays. The 
telephone number for the Public Reading Room is (202) 566-1744, and the 
telephone number for the Ambient Ozone Monitoring Regulations: 
Revisions to Network Design Requirements Docket is (202) 566-1742.

FOR FURTHER INFORMATION CONTACT: For technical questions, please 
contact Mr. Lewis Weinstock, U.S. Environmental Protection Agency, 
Office of Air Quality Planning and Standards, Air Quality Assessment 
Division, Ambient Air Monitoring Group (C304-06), Research Triangle 
Park, North Carolina 27711; telephone number: (919) 541-3661; fax 
number: (919) 541-1903; e-mail address: weinstock.lewis@epa.gov. For 
general questions, please contact Ms. Lula Melton, U.S. Environmental 
Protection Agency, Office of Air Quality Planning and Standards, Air 
Quality Assessment Division (C304-02), Research Triangle Park, North 
Carolina 27711; telephone number: (919) 541-2910; fax number: (919) 
541-4511; e-mail address: melton.lula@epa.gov.

SUPPLEMENTARY INFORMATION:

I. General Information

A. Does This Action Apply to Me?

    Categories and entities potentially regulated by this action 
include:

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           Category            NAICS \a\  Examples of regulated entities
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Federal government...........     924110  Federal agencies that conduct
                                           ambient air monitoring
                                           similar to that conducted by
                                           States under 40 CFR part 58
                                           and that wish EPA to use
                                           their monitoring data in the
                                           same manner as State data.
State/local/tribal government     924110  State, territorial, and local
                                           air quality management
                                           programs that are responsible
                                           for ambient air monitoring
                                           under 40 CFR part 58. The
                                           proposal may also affect
                                           tribes that conduct ambient
                                           air monitoring similar to
                                           that conducted by States and
                                           that desire that EPA use
                                           their monitoring data in the
                                           same manner as State
                                           monitoring data.
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\a\ North American Industry Classification System.

B. What Should I Consider as I Prepare My Comments for EPA?

    Do not submit information containing CBI to EPA through https://www.regulations.gov or e-mail. Send or deliver information identified 
as CBI only to the following address: Roberto Morales, OAQPS Document 
Control Officer (C404-02), U.S. EPA, Office of Air Quality Planning and 
Standards, Research Triangle Park, North Carolina 27711, Attention 
Docket ID No. EPA-HQ-OAR-2008-0338. Clearly mark the part or all of the 
information that you claim to be CBI. For CBI information in a disk or 
CD ROM that you mail to EPA, mark the outside of the disk or CD ROM as 
CBI, and then identify electronically within the disk or CD ROM the 
specific information that is claimed as CBI. In addition to one 
complete version of the comment that includes information claimed as 
CBI, a copy of the comment that does not contain the information 
claimed as CBI must be submitted for inclusion in the public docket. 
Information so marked will not be disclosed except in accordance with 
procedures set forth in 40 CFR part 2.

C. Where Can I Get a Copy of This Document and Other Related 
Information?

    In addition to being available in the docket, an electronic copy of 
this proposed rule is also available on the Worldwide Web (WWW) through 
the Technology Transfer Network (TTN). Following the Administrator's 
signature, a copy of this proposed rule will be placed on the TTN's 
policy and guidance page for newly proposed or promulgated rules at 
https://www.epa.gov/ttn/oarpg. The TTN provides information and 
technology exchanges in various areas of air pollution control.

D. How Is This Document Organized?

    The information presented in this preamble is organized as follows:

I. General Information
    A. Does This Action Apply to Me?
    B. What Should I Consider as I Prepare My Comments for EPA?
    C. Where Can I Get a Copy of This Document and Other Related 
Information?
    D. How is This Document Organized?
II. Summary of Proposed Ozone Network Design Requirements and 
Rationale
    A. What Are the Proposed Revisions to Urban Network Design 
Requirements?
    B. What Are the Proposed Revisions to Non-Urban Network Design 
Requirements?
    C. What Are the Proposed Revisions to the Length of the Required 
O3 Monitoring Season?
III. Statutory and Executive Order Reviews
    A. Executive Order 12866: Regulatory Planning and Review
    B. Paperwork Reduction Act
    C. Regulatory Flexibility Act
    D. Unfunded Mandates Reform Act
    E. Executive Order 13132: Federalism
    F. Executive Order 13175: Consultation and Coordination With 
Indian Tribal Governments
    G. Executive Order 13045: Protection of Children From 
Environmental Health Risks and Safety Risks
    H. Executive Order 13211: Actions That Significantly Affect 
Energy Supply, Distribution, or Use
    I. National Technology Transfer and Advancement Act
    J. Executive Order 12898: Federal Actions To Address 
Environmental Justice in Minority Populations and Low-Income 
Populations

II. Summary of Proposed Ozone Network Design Requirements and Rationale

A. What Are the Proposed Revisions to Urban Network Design 
Requirements?

    Presently, States (including the District of Columbia, Puerto Rico, 
and the Virgin Islands) and local air quality management agencies when 
so delegated by the State are required to operate minimum numbers of 
EPA-approved ozone (O3) monitors based on the population of 
each of their Metropolitan Statistical Area (MSA) and the most recently 
measured O3 levels for each area. These requirements are 
contained in 40 CFR part 58 Appendix

[[Page 34527]]

D, SLAMS Minimum O3 Monitoring Requirements, Table D-2. 
These requirements were last revised on October 17, 2006, as part of a 
comprehensive review of ambient monitoring requirements for all 
criteria pollutants. (See 71 FR 61318 for the specific Table D-2 
referenced above.)
    Currently, the minimum number of O3 monitors required in 
an MSA ranges from zero (for an area with a population of at least 
50,000 and under 350,000 and no recent history of an O3 
design value greater than 85 percent of the level of the NAAQS) to four 
(for an area with a population greater than 10 million and an 
O3 design value greater than 85 percent of the level of the 
NAAQS). Because these requirements apply at the MSA level, large urban 
areas consisting of multiple MSAs can be required to have more than 
four monitors.
    Currently, there are 369 MSAs in the U.S. subject to minimum 
O3 monitoring requirements.\1\ Of these MSAs, 251 are 
required to have one or more monitors based on their 2005 population 
estimates \2\ and 2005 to 2007 O3 design values compared to 
the revised O3 NAAQS, and the other 118 MSAs are not 
required to have monitors. The specific size range of MSAs that are not 
required to have monitors have urban area populations between 50,000 
and less than 350,000, and have O3 design values less than 
85 percent of the level of the NAAQS. Some of the MSAs do not have 
current design values due to the lack of monitors. Also note that 
monitoring requirements do not apply to Micropolitan Statistical 
Areas.\3\
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    \1\ MSA must contain an urbanized area of 50,000 or more 
population.
    \2\ https://www.census.gov/population/www/estimates/metropop/2005/cbsa-01-fmt.xls.
    \3\ Micropolitan Statistical Areas must have at least one urban 
cluster of at least 10,000 but less than 50,000 population.
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    In the 251 MSAs with one or more required O3 monitors, a 
total of 392 monitors are required to meet the minimum requirements 
listed in Table D-2. In actuality, 992 monitors were in operation 
during 2005 to 2007 representing these MSAs.\4\ This monitor count 
exceeds the minimum requirements based on Table D-2, indicating the 
typical practice of operating more than the minimum required number of 
monitors to support the basic monitoring objectives described in part 
58, Appendix D. In addition, State and local agencies operated 55 
monitors during 2005 to 2007 in MSAs that were not required to have 
monitors.\5\
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    \4\ Of these 992 monitors, 873 monitors provided complete data 
for calculation of design values.
    \5\ Of these 55 monitors, 20 monitors provided complete data for 
calculation of design values.
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    We note that many of the O3 monitors that are operated 
in excess of minimum requirements are necessary to characterize the 
O3 concentrations that occur in metropolitan areas and in 
downwind areas that are potentially impacted by transport from MSAs. As 
noted in Appendix D (see 71 FR 61318), O3 minimum monitoring 
requirements do not account for the full breadth of additional factors 
that would be considered in designing a complete O3 
monitoring program for an area. Some of these additional factors 
include geographic size, population density, complexity of terrain and 
meteorology, adjacent O3 monitoring programs, air pollution 
transport from neighboring areas, and measured air quality in 
comparison to all forms of the O3 NAAQS (i.e., 8-hour and 1-
hour forms). States and EPA Regional Administrators work together to 
design and/or maintain the most appropriate O3 network to 
service the variety of data needs in an area. The results of these 
negotiations are documented in annual monitoring network plans that are 
made available for public inspection and then approved by the EPA 
Regional Administrator, and the O3 monitoring requirements 
in approved plans become the basis for State O3 monitoring 
requirements for the one-year period following plan approval.
    Because existing minimum monitoring requirements include a factor 
based on the comparison of an area's design value to the O3 
NAAQS (see 71 FR 61318), the recent revisions to the O3 
NAAQS (see 73 FR 16436) may already necessitate that some States make 
changes to their O3 monitoring network independent of the 
proposed changes described below. The requirements listed in Table D-2 
of 40 CFR part 58 Appendix D are based on how close measured ambient 
concentrations are to the level of the O3 NAAQS, with a 
design value threshold at 85 percent of the NAAQS. For an MSA of a 
given population size, there are a greater number of required monitors 
when the design value is greater than or equal to 85 percent of the 
O3 NAAQS than when the design value is less than 85 percent 
of the O3 NAAQS. With the recent decision to revise the 8-
hour primary and secondary standards from a level of 0.08 ppm to a 
level of 0.075 ppm, the 8-hour O3 design value that will 
trigger increased minimum monitoring requirements for an MSA decreased 
from 0.068 ppm to 0.064 ppm. Therefore, MSAs with 8-hour design values 
between 0.064 ppm and 0.067 ppm are now required to increase the number 
of monitors operating to meet minimum requirements based on existing 
monitoring requirements.\6\ A total of 15 MSAs have O3 
design values between 0.064 ppm and 0.067 ppm based on 2005 to 2007 
design values. Of those 15 MSAs, 13 MSAs are already meeting 
requirements based on the operation of additional monitors by the 
affected States. Thus, current data indicate that only two areas may 
need additional monitors \7\ on the grounds that their design values 
are now greater than or equal to 85 percent of the revised NAAQS.
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    \6\ States should document the required changes to O3 
networks in their annual monitoring network plans that are required 
by 40 CFR part 58.10. Such plans are due by July 1 of each year and 
required to be made available for public inspection prior to 
submission to EPA Regional Offices for review and approval.
    \7\ Based on 2005 to 2007 O3 design values and 2005 
Census Bureau population estimates, these MSAs are Port St. Lucie-
Fort Pierce, Florida, and Salem, Oregon.
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    There are 105 MSAs with populations between 50,000 and less than 
350,000 that are presently without any O3 monitors 
supporting design value calculations for either 2004 to 2006 or 2005 to 
2007.\8\ These unmonitored MSAs have a total population of 
approximately 18 million people and include areas in 37 States and 
Puerto Rico. The existing regulations do not require these MSAs to 
begin monitoring for O3. Comments that were received from 
State air monitoring agencies and from multi-State air planning 
organizations in response to the O3 NAAQS proposal expressed 
concern that these requirements ignore the needs that States and 
localities have for additional monitors to measure O3 levels 
in a variety of locations, particularly in areas with populations under 
350,000. The commenters stated that unless this deficiency is 
corrected, the health benefits of EPA's O3 NAAQS revision 
would likely be limited to those living in MSAs having populations of 
more than 350,000. Other commenters noted the difficulty in defining 
the boundaries of new attainment/nonattainment areas without additional 
monitoring in the MSAs below 350,000 population.\9\
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    \8\ Approximately 18 of these MSAs have operating O3 
monitors but incomplete data for the purposes of calculating design 
values for the 2004 to 2006 and 2005 to 2007 time periods.
    \9\ See the O3 NAAQS Response to Comments document in 
docket EPA-HQ-OAR-2005-0172, document number 7185, available online 
at https://www.regulations.gov/fdmspublic/component/main?main=DocketDetail&d=EPA-HQ-OAR-2005-0172.

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[[Page 34528]]

    EPA notes that States already have the discretion to add 
O3 monitors in these locations and in any currently 
unmonitored areas where applicable siting criteria can be satisfied, 
although they are not currently required to do so in the unmonitored 
MSAs below 350,000 population based on existing O3 minimum 
monitoring requirements.
    EPA has conducted a review of 8-hour design values obtained from 
existing monitors that are in proximity to these unmonitored MSAs of 
population below 350,000. Based on 2005 to 2007 data reported to the 
Air Quality System (AQS), approximately 25 percent of these unmonitored 
MSAs (26 of 105 areas) had an O3 monitor within 20 
kilometers (approximately 12 miles) that violated the revised NAAQS. 
Approximately 42 percent (44 of 105 areas) of the unmonitored MSAs had 
a violating O3 monitor within 50 kilometers (approximately 
31 miles). The close proximity of violating O3 monitors to 
unmonitored MSAs indicates a reasonable likelihood that monitors placed 
in many of these unmonitored areas would have recorded violating 
concentrations over the same time period. When these unmonitored MSAs 
are evaluated in comparison to the locations of non-violating 
O3 monitors that measured a level of greater than or equal 
to 85 percent of the revised NAAQS, approximately 34 percent (36 of 105 
areas) were within 20 kilometers of such a monitor and 63 percent (66 
of 105 areas) were within 50 kilometers. Concentrations of greater than 
or equal to 85 percent of the NAAQS to 100 percent of the NAAQS level 
obtained from many of the monitors in close proximity to these 
unmonitored MSAs indicates a reasonable likelihood that monitors placed 
in the unmonitored MSAs would have measured similar concentrations at 
levels over the same time period. This suggests the need for 
O3 monitoring in these unmonitored MSAs of between 50,000 
and 350,000 population to ensure that potential NAAQS violations are 
measured.
    Based on these analyses, EPA believes it is important to monitor 
O3 concentrations in the smaller MSAs with populations 
between 50,000 and less than 350,000 in light of the revised level of 
the standards. While it was less likely that violating concentrations 
of the former 0.08 parts per million (ppm \10\) primary standard were 
being missed due to the lack of a monitoring requirement in these MSAs, 
the likelihood of missing violating concentrations of the 0.075 ppm 
primary standard is greater, and the public comments in regard to the 
potential need to revise applicable O3 monitoring 
regulations have merit.
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    \10\ Due to the data handling regulations associated with the 
1997 O3 NAAQS level, an 8-hour design value of 0.085 ppm 
was required to exceed the level of the NAAQS.
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    Accordingly, EPA is proposing to modify the minimum O3 
monitoring requirements to require one monitor to be placed in MSAs of 
populations ranging from 50,000 to less than 350,000 in situations 
where there is no current monitor and no history of O3 
monitoring within the previous 5 years indicating a design value of 
less than 85 percent of the revised NAAQS. We propose to modify Table 
D-2 of 40 CFR part 58 Appendix D by moving the current footnote 4 from 
the right column of the table to the middle column of the table. By 
doing so, we propose to require greater numbers of O3 
monitors for MSAs that do not have design values compared with the 
requirements that were promulgated in the October 17, 2006 revisions to 
ambient monitoring regulations (see 71 FR 61318). Functionally, this 
modification should mainly impact MSAs in the population range between 
50,000 and 350,000 since virtually all MSAs of population 350,000 or 
greater currently have at least two O3 monitors in 
operation.\11\
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    \11\ Three MSAs with a population of at least 350,000 appear to 
have no design values for either the 2004-2006 or 2005-2007 periods. 
These MSAs include Anchorage, Alaska; Kileen-Temple-Fort Hood, 
Texas; and San Juan-Caguas-Guaymabo, Puerto Rico. The Alaska and 
Texas MSAs reached the 350,000 level based on the difference in the 
2005 population estimate compared with the 2000 decennial census 
figure and would therefore be subject to minimum requirements of two 
monitors in each of these MSAs.
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    EPA solicits comment on whether the proposed 5-year historical data 
period is appropriate for demonstrating that O3 design 
values in a currently unmonitored MSA of population ranging from 50,000 
to less than 350,000 have been less than 85 percent of the revised 
NAAQS, or whether the time period for allowing the use of historical 
data should be longer or shorter than 5 years.
    States may wish to relocate an existing O3 monitor to 
the unmonitored MSA to meet the proposed requirements. Opportunities 
for relocation may exist in areas where the current number of 
O3 monitors in another MSA in the same State exceeds minimum 
requirements and the relocation of one or more of the non-required 
monitors meets one or more of the conditions described in 40 CFR part 
58.14(c). States may also relocate a non-required O3 monitor 
from a location outside of an MSA to an unmonitored MSA that is subject 
to the proposed requirements. Relocations of monitors to meet the 
proposed requirements would be subject to EPA Regional Administrator 
approval, based on a review of State-supplied information such as the 
ambient data trend from the monitor being proposed for relocation, the 
potential impact on data stakeholders with the monitor discontinuance, 
and the ability of other nearby O3 monitors to characterize 
the O3 conditions in the area from which the monitor is 
being proposed to be removed.
    While States will be required to add some new monitors or relocate 
existing monitors to meet the proposed requirements, EPA notes that 
many of these unmonitored MSAs already have existing O3 
monitors in close proximity to their geographic boundaries. Based on 
the siting characteristics and data record from the existing 
O3 monitors near the unmonitored MSAs, it is plausible that 
some of these monitors may adequately represent O3 
concentrations in the unmonitored areas based on analyses of ambient 
concentrations, O3 precursor emissions, meteorology, 
photochemical modeling, and/or topography. Analyses based on these 
factors or other available information could be used to support case-
by-case waivers from the requirement for monitoring within some of 
these unmonitored MSAs, as described below, thereby mitigating the 
expense and logistical hurdles involved with establishing new 
O3 monitors or relocating non-required existing monitors 
from other areas.
    In some cases where an existing monitor is located close to an 
unmonitored MSA that would be required to site a new monitor based on 
the proposed rule modification, the affected State may propose and EPA 
Regional Administrators may consider approving a waiver of monitoring 
requirements for the unmonitored MSA. When seeking such a waiver, the 
State must provide relevant information including the siting 
characteristics and data record from the existing O3 
monitors near the unmonitored MSA, or other information sources that 
the Regional Administrator must consider in evaluating the estimation 
of current and future O3 levels in the unmonitored MSAs. The 
Regional Administrator may approve such requests under the waiver 
authority provided in paragraph 4.1.1(c) of 40 CFR part 58, Appendix D 
of the proposed regulatory text. Any deviations based on the Regional 
Administrator's waiver of requirements

[[Page 34529]]

must be described in the annual monitoring network plan.
    Such waiver requests must be accompanied by a letter documenting 
the State's commitment to propose a nonattainment designation for the 
unmonitored MSA based on violating readings from the nearby monitor(s) 
and a commitment to modify a State Implementation Plan (SIP) to provide 
for a specific, reproducible approach to representing the O3 
concentration of the unmonitored MSA in the absence of the actual 
monitoring data that would have been supplied by the required monitor. 
We request comment on the practicality of allowing States to enter into 
agreements with EPA Regional Administrators to use nearby O3 
monitors to represent the conditions within unmonitored MSAs, the 
specific commitments that must be included in these agreements and/or 
submitted plans, and the implementation challenges that may arise 
during the O3 designation process if the EPA Regional 
Administrator approves of such arrangements.
    In all cases described above, proposed changes to O3 
networks in response to the proposed new requirement would have to be 
documented in the annual monitoring network plans that are required by 
40 CFR part 58.10 and are subject to approval by the EPA Regional 
Administrator.
    Based on the proposed requirements described above, EPA estimates 
that approximately 109 new O3 monitors would be required in 
the national O3 network if the proposed urban requirement 
was satisfied solely with new monitors installed in the unmonitored 
MSAs. In actuality, we expect the net addition of new monitors to the 
national O3 network to be less than 109 monitors due to the 
mitigating factors that have been previously described. These factors 
include the presence of existing monitors that could satisfy the 
proposed requirement in these unmonitored MSAs with improved data 
completeness, the proposed flexibility for States to relocate non-
required O3 monitors to the unmonitored MSAs, and the 
possibility of States proposing that existing monitors in close 
proximity to the unmonitored MSAs be used to represent O3 
concentrations within the unmonitored MSAs.
    It has been EPA's recent practice to allow at least a one-year 
period for States to install new monitors when monitoring requirements 
are revised through rulemaking (see 71 FR 61241). Consistent with this 
practice and based on the projected schedule of completing a final 
O3 monitoring rulemaking in early 2010, EPA proposes that 
new O3 monitors be required to be installed and operating by 
the first day of the required O3 monitoring season that is 
effective in 2012 as described in Table D-3 of Appendix D to part 58 
(see Section II.C of this proposal for the proposed changes to the 
required O3 monitoring seasons). For some States, new 
monitors would be required to be installed and operating as early as 
January 1, 2012, while other States would have later deadlines based on 
their respective O3 monitoring seasons.
    States would be required to identify how their monitoring networks 
would be modified to meet the proposed new O3 requirements 
in the annual monitoring network plan due on July 1, 2011.
    EPA also recognizes the logistical difficulty in siting new 
O3 monitors or in relocating existing O3 monitors 
that have been approved for discontinuation and subsequent relocation 
to meet the proposed requirements. Accordingly, we solicit comment on 
the proposed requirement for having new monitors operating in 2012, 
specifically whether States might need additional time to site all the 
new monitors (e.g., a staggered 2-year deployment schedule accomplished 
in 2012 and 2013) versus the single-year deadline described above. We 
note that the deployment schedule would be applicable to the proposed 
urban monitoring requirements as well as the proposed non-urban 
monitoring requirements described in the following section.

B. What Are the Proposed Revisions to Non-Urban Network Design 
Requirements?

    The newly established secondary standard was put into place 
specifically to provide protection to sensitive vegetation in less 
urbanized areas, in particular those Class I Wilderness Areas set aside 
by Congress to be protected so as to conserve the scenic value and the 
natural vegetation and wildlife within such areas, and to leave them 
unimpaired for the enjoyment of future generations. The secondary 
O3 NAAQS also considered the benefits that would be provided 
to the public welfare from increased protection of sensitive vegetation 
in other Federal, State, Tribal and/or public interest lands that have 
been set aside for a similar purpose. These areas are characterized by 
the presence of O3-sensitive species of native vegetation 
that have been shown to be subject to O3-induced visible 
foliar injury, impaired growth, and/or other adverse impacts to a 
degree that could be considered adverse.
    Currently, existing O3 monitoring requirements and 
current State monitoring practices are primarily oriented towards 
protecting against human health effects and therefore towards reporting 
compliance with the primary NAAQS. This accounts for the current focus 
of the monitoring requirements on urban areas, where large populations 
reside, in which significant emissions of O3-forming 
precursors are found, and where O3 concentrations of concern 
have been historically measured. EPA believes that the previously 
described proposed changes to urban monitoring requirements will be 
adequate for determining compliance with the secondary NAAQS in MSAs, 
noting that the assessment of welfare effects has not been a 
traditional objective of urban-based O3 monitoring networks.
    It is now known, however, that O3 concentrations of 
concern for vegetation can also occur in areas far downwind of urban 
areas. In addition, the new more stringent level of the primary and 
secondary NAAQS make it likely that O3 levels of concern for 
both plants and people will be found outside of urban areas. Thus, EPA 
believes that there is merit in proposing additional limited monitoring 
requirements in non-urban areas to address both secondary and primary 
standard needs.
    Although there are currently no EPA requirements for O3 
monitoring other than in or adjacent to MSAs\12\, there are at present 
about 200 State-operated O3 monitors in counties that are 
not part of MSAs, and these monitors can be categorized in several 
ways. States commonly locate O3 monitors both upwind and 
downwind of major urban areas to evaluate the spatial gradient or 
extent of transported O3 pollution and the lag time 
typically associated with photochemical production. In some cases, 
these O3 monitors are located in non-urban or rural areas 
within MSAs or physically outside the MSA boundary if the expected 
location of maximum downwind O3 concentration is outside the 
MSA. These monitors are counted toward meeting the minimum urban 
O3 monitoring requirements listed in Table D-2 of Appendix D 
since they provide information about the air quality status of an urban 
MSA.
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    \12\ States affected by Photochemical Assessment Monitoring 
Stations (PAMS) requirements may be required to establish 
O3 monitors outside of MSAs to characterize upwind or 
downwind concentrations. See 40 CFR part 58 Appendix D, section 5.
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    States may also operate monitors in non-urban or rural areas to 
meet other objectives such as the support of research programs 
including studies of

[[Page 34530]]

atmospheric chemistry and ecosystem impacts, and these monitors are not 
typically counted toward meeting minimum monitoring requirements 
applicable to urban areas. States often categorize these non-required 
monitors as special purpose monitors (SPMs). This provides inherent 
flexibility because States are allowed to discontinue operation of SPMs 
without EPA Regional Administrator approval, subject to the conditions 
of 40 CFR 58.20. Furthermore, SPMs can be operated for a period of up 
to 24 months without being considered in NAAQS compliance 
determinations.
    As part of the Clean Air Status and Trends Network (CASTNET), the 
EPA operates 57 O3 monitors, and the National Park Service 
(NPS) operates 23 monitors across the eastern and western U.S. The NPS 
also operates additional O3 monitors independent of CASTNET 
stations. CASTNET O3 monitors operate year-round and are 
primarily located in rural areas; siting criteria require distances of 
at least 40 kilometers from cities of greater than 50,000 population as 
well as other separation requirements from air pollution sources.\13\
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    \13\ https://www.epa.gov/castnet/library/qapp_v4/QAPP_v4_Main_Body.pdf, page 105.
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    Taking into account both State and EPA/NPS-operated non-urban 
O3 monitors, an analysis of the distribution of these 
monitors indicates a relatively uniform spatial density in the eastern 
one-third of the U.S. and in California, with significant gaps in 
coverage elsewhere across the country. Virtually all States east of the 
Mississippi River have at least two to four non-urban O3 
monitors, while many large mid-western and western States have one or 
no non-urban monitors.\14\
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    \14\ Based on an AQS retrieval of O3 monitors 
reporting any data in 2007, regardless of data completeness 
requirements, the following States had one or zero non-urban 
O3 monitors: Georgia, Idaho, Louisiana, Nebraska, Nevada, 
Montana, and Oregon. If data completeness is taken into 
consideration, a total of 13 States had zero non-urban O3 
monitors that could provide a design value for either 2004-2006 or 
2005-2007.
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    Comments that were received from State monitoring agencies, State 
organizations, and private individuals in response to the O3 
NAAQS proposal noted the voluntary nature of most rural O3 
monitoring and the resulting relative lack of rural O3 
monitors in some areas. These commenters stated that EPA should 
consider adding monitoring requirements to support the secondary NAAQS 
by requiring O3 monitors in locations that contain 
O3-sensitive plants or ecosystems. These commenters also 
noted that the placement of current O3 monitors may not be 
appropriate for evaluating issues such as vegetation exposure since 
many of these monitors were likely located to meet other objectives.
    As explained in the following paragraphs, EPA agrees with the 
public input received on this issue and believes that several important 
objectives would be served by having additional non-urban monitoring 
requirements. These objectives include: (1) Provide better 
characterization of O3 exposures to O3-sensitive 
vegetation and ecosystems in rural/remote areas to ensure that 
potential secondary NAAQS violations are measured. This objective would 
also serve the purpose of providing more consistent support for studies 
examining the impact of elevated O3 levels in wilderness 
areas, locations with O3-sensitive natural vegetation, and 
in areas such as National Parks; (2) assessment of population exposure 
due to elevated ambient O3 levels in smaller communities 
located outside of the larger urban MSAs covered by the monitoring 
requirements described in Section II.A; and (3) the assessment of the 
location and severity of maximum O3 concentrations that 
occur in non-urban areas and may be attributable to upwind urban 
sources. Each of these three objectives is described below.
    With regard to the first objective, there is evidence that ambient 
concentrations of O3 in rural and other non-urban areas may 
be adversely affecting sensitive natural vegetation. As noted 
previously by the public commenters, this objective addresses the 
uncertainties that remain about the impact that O3 
concentrations have on sensitive natural vegetation, ecosystems, and 
wilderness areas. Additional monitors in National Parks and as well as 
State and/or tribal areas set aside to provide similar public welfare 
benefits would support evaluation of the revised secondary NAAQS as 
well as future reviews of the secondary O3 NAAQS by 
providing a more robust data set with which to assess actual vegetation 
exposure in rural areas, and thereby reducing the need for 
interpolations of rural air quality.
    With regard to the second objective as noted earlier in Section 
II.A, O3 monitoring requirements do not currently apply to 
Micropolitan Statistical Areas, defined as areas having at least one 
urban cluster of at least 10,000 but less than a population of 50,000. 
The lack of such monitoring requirements for smaller communities has 
historically been based on the concept that the concentrations of 
O3 in these non-urban areas would not be high enough 
relative to the NAAQS to justify the imposition of national monitoring 
requirements in less populated areas. However, in light of the revised 
level of the O3 NAAQS, it is far more likely that these 
smaller communities could be exposed to elevated concentrations that 
approach or exceed the NAAQS due to the transport of O3 from 
upwind areas and/or the formation of O3 due to precursor 
emissions from industrial sources outside of urban areas. We note that 
there are 582 Micropolitan Statistical Areas in the U.S. with a total 
population of just under 2 million people based on the 2005 census 
estimate. Although States are not required to monitor in these areas, 
over 90 monitors providing 2005 to 2007 O3 design values 
were operated. Of these 90 monitors, 45 monitors recorded design values 
exceeding the level of the revised NAAQS. A total of 86 of these 90 
monitors recorded design values greater than or equal to 85 percent of 
the revised NAAQS. These data from monitors located in Micropolitan 
Statistical Areas clearly indicate the potential for violations of the 
NAAQS in some smaller communities located outside the boundaries of 
MSAs that currently have minimum monitoring requirements.
    The third objective is the assessment of the location and severity 
of maximum O3 concentrations that occur outside of urban 
areas. Although the location of maximum non-urban O3 
concentrations could occur within the boundary of a Micropolitan 
Statistical Area or sensitive ecosystem, it is also possible that such 
concentrations could occur in an unpopulated and unmonitored area. 
Without specific information about the location and distribution of 
such potentially violating maximum O3 concentration areas, 
it would be difficult to ensure that all parts of a State meet the 
revised NAAQS and that all necessary emission control strategies have 
been accounted for in SIPs. We believe that the identification of such 
non-urban maximum concentration areas would support objectives 
including: (1) The understanding of the role of upwind urban-generated 
O3 transport and impact in locations between MSAs, (2) the 
verification of photochemical models at various time-scales (i.e., 
diurnal fluctuations, seasonal patterns) used for assessing the 
effectiveness of control measures as well as real-time models 
supporting O3 forecasts, and (3) the understanding of the 
role of O3 precursor emissions from industrial sources and 
development in more remote areas in the potential creation of high-
O3 areas in lightly

[[Page 34531]]

inhabited areas that historically have been unmonitored.
    Given the three objectives described above, EPA believes that there 
is strong justification for proposing additional limited monitoring 
requirements in non-urban areas to evaluate compliance with both the 
secondary and primary NAAQS. EPA proposes to modify 40 CFR part 58 
Appendix D by adding the requirement (in proposed rule section 4.1.2) 
that each State operate non-urban O3 monitors in addition to 
the current and proposed urban O3 monitoring requirements 
detailed in Table D-2 and described in section II.A of this preamble. 
The first required non-urban monitor is proposed to be located in areas 
such as some Federal, State, or Tribal lands, including wilderness 
areas that have O3-sensitive natural vegetation and/or 
ecosystems; lands with other ownership may also be appropriate. The 
second required non-urban monitor is proposed to be required to be 
placed in a Micropolitan Statistical Area expected to have 
O3 design value concentrations of at least 85 percent of the 
NAAQS.\15\ The third required non-urban monitor is proposed to be in 
the area of expected maximum O3 concentration outside of any 
MSA, potentially including the far-downwind transport zones of 
currently well-monitored urban areas.
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    \15\ Monitors installed to meet the Micropolitan Statistical 
Area requirement could be discontinued, with Regional Administrator 
approval, after demonstrating an O3 design value of less 
than 85 percent of the NAAQS.
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    EPA proposes to require that States will propose new non-urban 
O3 monitoring sites to meet each of the distinct monitoring 
objectives, and that the resulting expanded network will provide the 
foundation for an improved level of characterization of O3 
concentrations outside of urban areas in support of the secondary and 
primary NAAQS. In some cases, States may wish to operate additional 
non-urban monitors beyond the proposed minimum requirements where, for 
example, there are multiple sensitive ecosystems or wilderness areas 
impacted by O3, multiple Micropolitan Statistical Areas 
exposed to high levels of O3, or in States with multiple 
isolated locations of similarly high projected O3 
concentrations.
    EPA solicits comment on the proposed non-urban O3 
monitoring requirements including the total number of required monitors 
per State, the appropriateness of the distinct non-urban objectives, 
the ability of such an expanded network to improve characterization of 
O3 concentrations in support of the revised secondary and 
primary NAAQS, and the capability of the proposed network to support 
other objectives such as model validation.
    States will likely need to perform additional analyses to help 
determine the appropriate locations for non-urban monitors meeting the 
proposed requirements. States are encouraged to confer with partners 
familiar with the patterns of vegetation damage and distribution of 
O3 sensitive species in their areas, such as Federal Land 
Managers, State, local, or Tribal ecosystem assessment experts, or 
academic researchers who have established experience in the field.\16\ 
Resources and analyses such as the availability of photochemical 
modeling, spatial interpolation of ambient data from existing 
O3 monitors, or other quantitative assessment tools are 
useful to determine the areas where there are projected maximum non-
urban O3 concentrations, and where these regions with 
elevated O3 (typically greater than or equal to 85 percent 
of the revised NAAQS) might overlap locations with O3-
sensitive ecosystems and other important wilderness areas and 
Micropolitan Statistical Areas. The availability of regional 
photochemical modeling based on updated emissions inventories is a very 
useful tool to inform proposed non-urban and/or rural O3 
monitoring locations in areas, such as the western U.S., where national 
assessments have not fully accounted for recent changes in emissions 
from industrial activities. EPA plans to update the current 
O3 network design guidance document \17\ in time to support 
the siting of new urban and non-urban O3 monitors that are 
required by the final monitoring rule.
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    \16\ An example of available resources is posted by the National 
Park Service at https://www.nature.nps.gov/air/Pubs/pdf/flag/NPSO3sensppFLAG06.pdf.
    \17\ Guideline on Ozone Monitoring Site Selection, EPA-454/R-98-
002, August 1998, https://www.epa.gov/ttn/amtic/files/ambient/criteria/reldocs/r-98-002.pdf.
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    Monitors counted toward satisfying these proposed non-urban 
requirements would have to be operated in compliance with all 
requirements of 40 CFR part 58 and Appendices A, C, D, and E. EPA 
recognizes that a different set of monitor placement criteria from the 
current Appendix E requirements might be appropriate for locating non-
urban O3 monitors compared with urban O3 
monitors. For example, in less populated areas, States may wish to 
establish different setback requirements from roadways, minimum 
distances from urban areas or significant pollution sources, or 
consider a different set of vertical probe height requirements. EPA is 
not proposing specific changes to the monitoring regulations to support 
non-urban O3 monitoring other than the changes already noted 
to Appendix D. EPA encourages States to consider guidelines such as the 
previously noted siting guidelines used for the CASTNET network. We 
solicit comment on the need and substance of alternative non-urban 
O3 siting requirements and what changes would be appropriate 
for sites that will support the previously stated non-urban monitoring 
objectives.
    EPA also acknowledges that there may be a logistical challenge in 
operating monitors that are more physically remote than the monitors 
that States have typically run to satisfy urban monitoring 
requirements. The operation of such monitors could, in some cases, 
create additional challenges for monitoring agencies. EPA solicits 
comment on any changes to the monitoring requirements that apply 
specifically to non-urban monitors that might be appropriate to 
mitigate any increased challenges potentially associated with their 
operation.
    As noted earlier in section II.A, States may wish to relocate 
existing O3 monitors to appropriate non-urban locations to 
meet the proposed requirements. Relocations of State and local air 
monitoring station (SLAMS) monitors must meet the applicable monitoring 
requirements and would be subject to EPA Regional Administrator 
approval. States may also propose that existing non-required 
O3 monitors or those O3 monitors at existing 
candidate or approved rural national core (NCore) stations be counted 
toward meeting the proposed requirements if these monitors are located 
in areas that satisfy the proposed non-urban monitoring objectives.
    EPA expects that some States may be interested in the possibility 
of existing CASTNET or NPS O3 monitors, or monitors operated 
by some other organization, being counted towards meeting the proposed 
non-urban minimum monitoring requirements. In these cases, EPA would 
require States to enter into agreements with the operators \18\ of the 
candidate sites to insure that the sites are operated according to all 
40 CFR part 58 monitoring regulations that apply to monitors 
categorized as SLAMS while also maintaining the monitoring requirements 
of the existing program. Candidate O3 sites (e.g., CASTNET 
or NPS) utilized for meeting minimum monitoring requirements would be

[[Page 34532]]

required to be included in a State's annual monitoring network plan and 
would be subject to EPA Regional Administrator review and approval as 
with all other SLAMS monitors. Of the currently operating CASTNET 
O3 monitors, the 23 NPS-operated monitors are meeting 
applicable quality assurance requirements and currently reporting data 
to AQS. The remaining CASTNET monitors are in the process of being 
upgraded to meet the quality assurance requirements of 40 CFR part 58 
and all sites are expected to be upgraded and reporting to AQS by the 
latter part of 2009.
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    \18\ CASTNET O3 monitors are operated by the Clean 
Air Markets Division of EPA's Office of Atmospheric Programs (OAP). 
Some CASTNET sites are operated by the National Park Service in a 
cooperative agreement with OAP.
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    In certain cases, it may be difficult to identify suitable areas to 
meet each of the proposed non-urban monitoring objectives. For example, 
in a small relatively urbanized State, it may be difficult to 
distinguish between monitoring requirements for a Micropolitan 
Statistical Area versus a rural area impacted by maximum O3 
concentrations. In a remote or isolated area without significant local 
pollution sources or likelihood of being impacted by transport of 
O3 precursors from another area (e.g., Guam or American 
Samoa), it may be unwarranted to require the placement of additional 
non-urban monitors. States with historically lower ambient 
O3 levels may not have Micropolitan Statistical Areas likely 
to experience O3 concentrations of at least 85 percent of 
the NAAQS. It is also plausible that a State may not have ecosystems 
characterized by O3-sensitive natural vegetation that have 
been designated for providing specific public welfare amenities or 
benefits. States might expect in some cases that the establishment of 
multiple non-urban O3 monitors to meet one or two of the 
proposed non-urban monitoring objectives (e.g., three monitors located 
in areas with sensitive ecosystems), would be more important than 
allocating an additional monitor to meet each of the three distinct 
monitoring objectives. In addition, one monitor could conceivably serve 
multiple purposes so that fewer than three monitors would be needed to 
meet these objectives.
    In situations like those described above, States may choose to seek 
from the EPA Regional Administrator a deviation from such requirements 
that either modify or waive these requirements, consistent with the 
authority to approve deviations from non-urban O3 minimum 
monitoring requirements stated in the proposed regulatory language in 
paragraph 4.1.2(e) of 40 CFR part 58, Appendix D. When seeking approval 
of such deviations, the State must provide relevant information 
specific to the basis for which the waiver is sought. Any deviations 
based on the Regional Administrator's waiver of requirements must be 
described in the annual monitoring network plan.
    Based on the proposed requirements described above, EPA estimates 
that approximately 159 new non-urban O3 monitors would be 
required in the national O3 network if the proposed non-
urban requirements were satisfied solely with new monitors. In 
actuality, we expect the net addition of less than 159 additional 
monitors to the national O3 network due to the mitigating 
factors that have been previously described. These factors include the 
presence of existing non-urban monitors that are satisfactorily located 
to meet one or more of the proposed monitoring objectives, the proposed 
flexibility for States to relocate existing non-required O3 
monitors to non-urban areas, the option of States proposing that some 
existing CASTNET or NPS monitors be counted towards meeting the 
proposed non-urban requirements, and the possibility of States 
obtaining Regional Administrator waivers of certain non-urban minimum 
requirements based on the situations described above.
    EPA solicits comment on the appropriateness of these proposed 
minimum non-urban monitoring requirements, including the distinct 
monitoring objectives, the required number of monitors, the criteria 
for placement, and the need to allow EPA Regional Administrators 
discretion to waive or modify siting criteria or minimum requirements.

C. What Are the Proposed Revisions to the Length of the Required 
O3 Monitoring Season?

    Unlike the ambient monitoring requirements for other criteria 
pollutants that mandate year-round monitoring, O3 monitoring 
is currently only required during the seasons of the year that are 
conducive to O3 formation. These seasons vary in length from 
place to place as the conditions that determine the likely 
O3 formation (i.e., seasonally-dependent factors such as 
ambient temperature, strength of solar insolation, and length of day) 
differ by location.\19\ In some locations, conditions conducive to 
O3 formation are limited to a few summer months of the year. 
For example, in States with colder climates such as Montana and South 
Dakota, the currently required O3 monitoring season has a 
length of 4 months. However, in other States with warmer climates such 
as California, Nevada, and Arizona, the currently required 
O3 monitoring season for most sites continues all 12 months 
of the year.\20\
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    \19\ See 40 CFR Part 58 Appendix D, section 2.5 for a table of 
required O3 seasons.
    \20\ Certain States, such as California and Arizona, have been 
approved for shorter seasons for a subset of O3 sites, 
based on Regional Administrator review and approval (see 71 FR 61319 
for the waiver authority).
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    With the recent revision of the primary and secondary NAAQS to a 
more stringent level, the issue arises of whether in some areas the 
required O3 monitoring season should be made longer. 
Lengthening the season in certain States may be appropriate as ambient 
O3 concentrations could approach or exceed the level of the 
revised standard more frequently and during more months of the year 
than before. As noted later in this section, a related issue is the 
status of any currently effective Regional Administrator-granted waiver 
approvals to O3 monitoring seasons, and the impact of 
proposed changes to monitoring requirements on such waiver approvals.
    EPA has done an analysis to address the issue of whether extensions 
of currently required monitoring seasons are appropriate in light of 
the revised NAAQS.\21\ In the analysis, we determined the number of 
exceedences of the revised NAAQS (i.e., daily maximum 8-hour 
O3 averages above 0.075 ppm) in the months falling outside 
the currently required local O3 monitoring season using 
monitors in areas that collected O3 data year-round in 2004-
2006.\22\ Additionally, we examined occurrences of daily maximum 8-hour 
O3 averages of at least 0.060 ppm. This threshold represents 
80 percent of the 0.075 ppm NAAQS level and provides an indicator of 
ambient conditions that may be conducive to the formation of 
O3 concentrations that approach or exceed the revised 
NAAQS.\23\
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    \21\ Camalier, L. and Weinstock, L. (2008) Documentation of 
O3 Monitoring Season Analysis for the Proposed 
O3 Monitoring Rule, available in docket.
    \22\ Approximately 530 O3 monitors are currently 
operated year-round, representing 45 percent of the total 
O3 monitoring network. They include monitors that are 
mandated to operate year-round due to the required O3 
season and other monitors that are voluntarily operated year-round 
by States and other organizations including EPA-operated monitors at 
CASTNET sites.
    \23\ We note that an 8-hour concentration of 0.060 ppm also 
corresponds to the threshold defining the revised Air Quality Index 
(AQI) breakpoint between the Good and Moderate indicator level (see 
73 FR 16484).
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    While proposals for revising each State's required monitoring 
season have been based on observed data in and surrounding the State, 
statistically predicted exceedences were used to

[[Page 34533]]

validate conclusions for each State. For States where year-round data 
were not available, EPA developed and employed a regression model to 
predict the frequency of exceedences in areas during unmonitored 
months. The model was fit separately for each major urban area and uses 
the relationship between daily maximum 8-hour O3 
concentrations and certain meteorological variables, including 
temperature and relative humidity, to predict exceedences of a 
particular O3 level.\24\
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    \24\ See: Camalier, L., Cox, B., and Dolwick, P., 2007. The 
effects of meteorology on O3 in urban areas and their use 
in assessing O3 trends. Atmospheric Environment 41, 7127-
7137.
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    In reviewing the year-round or close to year-round O3 
data between 2004 and 2006, EPA's analysis found observed exceedences 
of the revised O3 NAAQS in eight States during months 
outside of the current required monitoring season. The eight States are 
Maine, Massachusetts, New Hampshire, New Jersey, New York, South 
Carolina, Vermont, and Wyoming. With the exception of Wyoming, the 
exceedances occurred in a very limited manner and timeframe, just 
before the beginning of these States' required O3 monitoring 
season (beginning in these States on April 1). Every exceedance in the 
aforementioned States was found to occur either on March 30 or March 
31. In Wyoming, the frequency of O3 exceedances before the 
beginning of the required O3 season was higher, with 
multiple occurrences noted at several sites up to 2 months before the 
April 1 startup of required O3 monitoring.\25\
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    \25\ Additional information on this O3 situation is 
available on the Wyoming DEQ Web site: https://deq.State.wy.us/aqd/Monitoring%20Data.asp.
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    The frequency of observed occurrences of maximum 8-hour average 
O3 readings of at least 0.060 ppm was quite high across the 
country in months outside of the current required monitoring season. A 
total of 32 States experienced such occurrences; 22 States had such 
readings only before the required monitoring season; 9 States h