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[Federal Register: February 9, 2010 (Volume 75, Number 26)]
[Rules and Regulations]               
[Page 6473-6537]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr09fe10-9]                         


[[Page 6473]]

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Part III





Environmental Protection Agency





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40 CFR Parts 50 and 58



Primary National Ambient Air Quality Standards for Nitrogen Dioxide; 
Final Rule


[[Page 6474]]


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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 50 and 58

[EPA-HQ-OAR-2006-0922; FRL 9107-9]
RIN 2060-AO19

 
Primary National Ambient Air Quality Standards for Nitrogen 
Dioxide

AGENCY: Environmental Protection Agency (EPA).

ACTION: Final rule.

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SUMMARY: Based on its review of the air quality criteria for oxides of 
nitrogen and the primary national ambient air quality standard (NAAQS) 
for oxides of nitrogen as measured by nitrogen dioxide 
(NO2), EPA is making revisions to the primary NO2 
NAAQS in order to provide requisite protection of public health. 
Specifically, EPA is establishing a new 1-hour standard at a level of 
100 ppb, based on the 3-year average of the 98th percentile of the 
yearly distribution of 1-hour daily maximum concentrations, to 
supplement the existing annual standard. EPA is also establishing 
requirements for an NO2 monitoring network that will include 
monitors at locations where maximum NO2 concentrations are 
expected to occur, including within 50 meters of major roadways, as 
well as monitors sited to measure the area-wide NO2 
concentrations that occur more broadly across communities.

DATES: This final rule is effective on April 12, 2010.

ADDRESSES: EPA has established a docket for this action under Docket ID 
No. EPA-HQ-OAR-2006-0922. All documents in the docket are listed on the 
http://www.regulations.gov Web site. Although listed in the index, some 
information is not publicly available, e.g., confidential business 
information or other information whose disclosure is restricted by 
statute. Certain other material, such as copyrighted material, will be 
publicly available only in hard copy form. Publicly available docket 
materials are available either electronically through http://www.regulations.gov or in hard copy at the Air and Radiation Docket and 
Information Center, EPA/DC, EPA West, 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 Air and Radiation Docket and Information 
Center is (202) 566-1742.

FOR FURTHER INFORMATION CONTACT: Dr. Scott Jenkins, Health and 
Environmental Impacts Division, Office of Air Quality Planning and 
Standards, U.S. Environmental Protection Agency, Mail code C504-06, 
Research Triangle Park, NC 27711; telephone: 919-541-1167; fax: 919-
541-0237; e-mail: jenkins.scott@epa.gov.

SUPPLEMENTARY INFORMATION: 

Table of Contents

    The following topics are discussed in this preamble:

I. Background
    A. Summary of Revisions to the NO2 Primary NAAQS
    B. Legislative Requirements
    C. Related NO2 Control Programs
    D. Review of the Air Quality Criteria and Standards for Oxides 
of Nitrogen
    E. Summary of Proposed Revisions to the NO2 Primary 
NAAQS
    F. Organization and Approach to Final NO2 Primary 
NAAQS Decisions
II. Rationale for Final Decisions on the NO2 Primary 
Standard
    A. Characterization of NO2 Air Quality
    1. Current Patterns of NO2 Air Quality
    2. NO2 Air Quality and Gradients Around Roadways
    B. Health Effects Information
    1. Adverse Respiratory Effects and Short-Term Exposure to 
NO2
    2. Other Effects With Short-Term Exposure to NO2
    a. Mortality
    b. Cardiovascular Effects
    3. Health Effects With Long-Term Exposure to NO2
    a. Respiratory Morbidity
    b. Mortality
    c. Carcinogenic, Cardiovascular, and Reproductive/Developmental 
Effects
    4. NO2-Related Impacts on Public Health
    C. Human Exposure and Health Risk Characterization
    D. Approach for Reviewing the Need To Retain or Revise the 
Current Standard
    E. Adequacy of the Current Standard
    1. Rationale for Proposed Decision
    2. Comments on the Adequacy of the Current Standard
    a. Comments on EPA's Interpretation of the Epidemiologic 
Evidence
    b. Comments on EPA's Interpretation of the Controlled Human 
Exposure Evidence
    c. Comments on EPA's Characterization of NO2-
Associated Exposures and Health Risks
    3. Conclusions on the Adequacy of the Current Standard
    F. Elements of a New Short-Term Standard
    1. Indicator
    a. Rationale for Proposed Decision
    b. Comments on Indicator
    c. Conclusions Regarding Indicator
    2. Averaging Time
    a. Rationale for Proposed Decision
    b. Comments on Averaging Time
    c. Conclusions on Averaging Time
    3. Form
    a. Rationale for Proposed Decision
    b. CASAC and Public Comments on Form
    c. Conclusions on Form
    4. Level
    a. Rationale for Proposed Decisions on Approach and Level
    b. Rationale for Alternative Decisions on Approach and Level
    c. Comments on Approach and Level
    i. CASAC Comments on the Approach to Setting the Standard
    ii. Public Comments on the Approach To Setting the Standard
    iii. CASAC Comments on Standard Level
    iv. Public Comments on Standard Level
    d. Conclusions on Approach and Standard Level
    G. Annual Standard
    H. Summary of Final Decisions on the Primary NO2 
Standard
III. Amendments to Ambient Monitoring and Reporting Requirements
    A. Monitoring Methods
    1. Chemiluminescence FRM and Alternative Methods
    2. Allowable FRM and FEMs for Comparison to the NAAQS
    a. Proposed Changes to FRM and FEMs That May Be Compared to the 
NAAQS
    b. Comments
    c. Decisions on Allowable FRM and FEMs for Comparison to the 
NAAQS
    B. Network Design
    1. Two-Tiered Network Design
    a. Proposed Two-Tier Network Design
    b. Comments
    c. Conclusions Regarding the Two-Tier Network Design
    2. First Tier (Near-road Monitoring Component) of the 
NO2 Network Design
    a. Proposed First Tier (Near-road Monitoring Component) of the 
Network Design
    b. Comments
    c. Conclusions Regarding the First Tier (Near-road Monitoring 
Component) of the Network Design
    3. Second Tier (Area-wide Monitoring Component) of the Network 
Design
    a. Proposed Second Tier (Area-wide Monitoring Component) of the 
Network Design
    b. Comments
    c. Conclusions on the Second Tier (Area-wide Monitoring 
Component) of the Network Design
    4. Regional Administrator Authority
    a. Proposed Regional Administrator Authority
    b. Comments
    c. Conclusions on Regional Administrator Authority
    5. Monitoring Network Implementation
    a. Proposed Monitoring Network Implementation Approach
    b. Comments
    c. Conclusions on Monitoring Network Implementation
    6. Near-Road Site Selection
    a. Proposed Near-Road Site Selection Criterion
    b. Comments
    c. Conclusions on Near-Road Site Selection
    7. Near-Road Siting Criteria
    a. Proposed Near-Road Siting Criteria
    b. Comments
    c. Conclusions on Near-Road Siting Criteria
    8. Area-wide Monitor Site Selection and Siting Criteria

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    a. Proposed Area-wide Monitor Site Selection and Siting Criteria
    b. Comments
    c. Conclusions on Area-Wide Monitor Site Selection and Siting 
Criteria
    9. Meteorological Measurements
    a. Proposed Meteorological Measurements
    b. Comments
    c. Conclusions on Meteorological Measurements
    C. Data Reporting
    1. Proposed Data Quality Objectives and Measurement Uncertainty
    2. Comments
    3. Conclusions on Data Quality Objectives and Measurement 
Uncertainty
IV. Appendix S--Interpretation of the Primary NAAQS for Oxides of 
Nitrogen and Revisions to the Exceptional Events Rule
    A. Interpretation of the Primary NAAQS for Oxides of Nitrogen 
for the Annual Primary Standard
    1. Proposed Interpretation of the Annual Standard
    2. Comments on Interpretation of the Annual Standard
    3. Conclusions on Interpretation of the Annual Standard
    B. Interpretation of the Primary NAAQS for Oxides of Nitrogen 1-
Hour Primary Standard
    1. Proposed Interpretation of the 1-Hour Standard
    2. Comments on Interpretation of the 1-Hour Standard
    3. Conclusions on Interpretation of the 1-Hour Standard
    C. Exceptional Events Information Submission Schedule
V. Designation of Areas
    A. Proposed Process
    B. Public Comments
    C. Final Designations Process
VI. Clean Air Act Implementation Requirements
    A. Classifications
    1. Proposal
    2. Public comments
    3. Final
    B. Attainment Dates
    1. Attaining the NAAQS
    a. Proposal
    b. Final
    2. Consequences of Failing to Attain by the Statutory Attainment 
Date
    a. Proposal
    b. Final
    C. Section 110(a)(2) NAAQS Infrastructure Requirements
    1. Proposal
    2. Final
    D. Attainment Planning Requirements
    1. Nonattainment Area SIPs
    a. Proposal
    b. Public Comments
    c. Final
    2. New Source Review and Prevention of Significant Deterioration 
Requirements
    a. Proposal
    b. Public Comments
    c. Final
    3. General Conformity
    a. Proposal
    4. Transportation Conformity
    a. Proposal
    b. Public Comments
    c. Final
VII. Communication of Public Health Information
VIII. 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 & Safety Risks
    H. Executive Order 13211: Actions Concerning Regulations 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
    K. Congressional Review Act
References

I. Background

A. Summary of Revisions to the NO2 Primary NAAQS

    Based on its review of the air quality criteria for oxides of 
nitrogen and the primary national ambient air quality standard (NAAQS) 
for oxides of nitrogen as measured by nitrogen dioxide 
(NO2), EPA is making revisions to the primary NO2 
NAAQS in order to provide requisite protection of public health as 
appropriate under section 109 of the Clean Air Act (Act or CAA). 
Specifically, EPA is supplementing the existing annual standard for 
NO2 of 53 parts per billion (ppb) by establishing a new 
short-term standard based on the 3-year average of the 98th percentile 
of the yearly distribution of 1-hour daily maximum concentrations. EPA 
is setting the level of this new standard at 100 ppb. EPA is making 
changes in data handling conventions for NO2 by adding 
provisions for this new 1-hour primary standard. EPA is also 
establishing requirements for an NO2 monitoring network. 
These new provisions require monitors at locations where maximum 
NO2 concentrations are expected to occur, including within 
50 meters of major roadways, as well as monitors sited to measure the 
area-wide NO2 concentrations that occur more broadly across 
communities. EPA is making conforming changes to the air quality index 
(AQI).

B. Legislative Requirements

    Two sections of the CAA govern the establishment and revision of 
the NAAQS. Section 108 of the Act directs the Administrator to identify 
and list air pollutants that meet certain criteria, including that the 
air pollutant ``in [her] judgment, cause[s] or contribute[s] to air 
pollution which may reasonably be anticipated to endanger public health 
and welfare'' and ``the presence of which in the ambient air results 
from numerous or diverse mobile or stationary sources.'' 42 U.S.C. 21 
7408(a)(1)(A) & (B). For those air pollutants listed, section 108 
requires the Administrator to issue air quality criteria that 
``accurately reflect the latest scientific knowledge useful in 
indicating the kind and extent of all identifiable effects on public 
health or welfare which may be expected from the presence of [a] 
pollutant in ambient air * * *'' 42 U.S.C. 7408(2).
    Section 109(a) of the Act directs the Administrator to promulgate 
``primary'' and ``secondary'' NAAQS for pollutants for which air 
quality criteria have been issued. 42 U.S.C. 7409(1).\1\ Section 
109(b)(1) defines a primary standard as one ``the attainment and 
maintenance of which in the judgment of the Administrator, based on 
[the air quality] criteria and allowing an adequate margin of safety, 
are requisite to protect the public health.'' \2\ 42 U.S.C. 7409(b)(1). 
A secondary standard, in turn, must ``specify a level of air quality 
the attainment and maintenance of which, in the judgment of the 
Administrator, based on [the air quality] criteria, is requisite to 
protect the public welfare from any known or anticipated adverse 
effects associated with the presence of such pollutant in the ambient 
air.'' \3\ 42 U.S.C. 7409(b)(2).
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    \1\ EPA notes that as the promulgation of a NAAQS is identified 
in section 307(d)(1) of the Clean Air Act, all of the provisions of 
this rulemaking are subject to the requirements of section 307(d) of 
the Clean Air Act.
    \2\ 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).
    \3\ EPA is currently conducting a separate review of the 
secondary NO2 NAAQS jointly with a review of the 
secondary SO2 NAAQS.
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    The requirement that primary standards include an adequate margin 
of safety is intended to address uncertainties associated with 
inconclusive scientific and technical information available at the time 
of standard setting. It is also intended to provide a reasonable degree 
of protection against hazards that research has not yet identified. 
Lead Industries Association v. EPA, 647 F.2d 1130, 1154 (DC Cir 1980), 
cert. denied, 449 U.S.

[[Page 6476]]

1042 (1980); American Petroleum Institute v. Costle, 665 F.2d 1176, 
1186 (DC Cir. 1981), cert. denied, 455 U.S. 1034 (1982). Both kinds of 
uncertainties are components of the risk associated with pollution at 
levels below those at which human health effects can be said to occur 
with reasonable scientific certainty. Thus, in selecting primary 
standards that include an adequate margin of safety, the Administrator 
is seeking not only to prevent pollution levels that have been 
demonstrated to be harmful but also to prevent lower pollutant levels 
that may pose an unacceptable risk of harm, even if the risk is not 
precisely identified as to nature or degree.
    In addressing the requirement for a margin of safety, EPA considers 
such factors as the nature and severity of the health effects involved, 
the size of the at-risk population(s), and the kind and degree of the 
uncertainties that must be addressed. The selection of any particular 
approach to providing an adequate margin of safety is a policy choice 
left specifically to the Administrator's judgment. Lead Industries 
Association v. EPA, supra, 647 F.2d at 1161-62.
    In setting standards that are ``requisite'' to protect public 
health and welfare, as provided in section 109(b), EPA's task is to 
establish standards that are neither more nor less stringent than 
necessary for these purposes. In so doing, EPA may not consider the 
costs of implementing the standards. Whitman v. American Trucking 
Associations, 531 U.S. 457, 471, 475-76 (2001).
    Section 109(d)(1) of the Act requires the Administrator to 
periodically undertake a thorough review of the air quality criteria 
published under section 108 and the NAAQS and to revise the criteria 
and standards as may be appropriate. 42 U.S.C. 7409(d)(1). The Act also 
requires the Administrator to appoint an independent scientific review 
committee composed of seven members, including at least one member of 
the National Academy of Sciences, one physician, and one person 
representing State air pollution control agencies, to review the air 
quality criteria and NAAQS and to ``recommend to the Administrator any 
new * * * standards and revisions of existing criteria and standards as 
may be appropriate under section 108 and subsection (b) of this 
section.'' 42 U.S.C. 7409(d)(2). This independent review function is 
performed by the Clean Air Scientific Advisory Committee (CASAC) of 
EPA's Science Advisory Board.

C. Related NO2 Control Programs

    States are primarily responsible for ensuring attainment and 
maintenance of ambient air quality standards once EPA has established 
them. Under section 110 of the Act, 42 U.S.C. 7410, and related 
provisions, States are to submit, for EPA approval, State 
implementation plans (SIPs) that provide for the attainment and 
maintenance of such standards through control programs directed to 
sources of the pollutants involved. The States, in conjunction with 
EPA, also administer the prevention of significant deterioration 
program that covers these pollutants. See 42 U.S.C. 7470-7479. In 
addition, Federal programs provide for nationwide reductions in 
emissions of these and other air pollutants under Title II of the Act, 
42 U.S.C. 7521-7574, which involves controls for automobile, truck, 
bus, motorcycle, nonroad engine and equipment, and aircraft emissions; 
the new source performance standards under section 111 of the Act, 42 
U.S.C. 7411; and the national emission standards for hazardous air 
pollutants under section 112 of the Act, 42 U.S.C. 7412.
    Currently there are no areas in the United States that are 
designated as nonattainment of the NO2 NAAQS. With the 
revisions to the NO2 NAAQS that result from this review, 
however, some areas could be classified as non-attainment. Certain 
States will be required to develop SIPs that identify and implement 
specific air pollution control measures to reduce ambient 
NO2 concentrations to attain and maintain the revised 
NO2 NAAQS, most likely by requiring air pollution controls 
on sources that emit oxides of nitrogen (NOX).\4\
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    \4\ In this document, the terms ``oxides of nitrogen'' and 
``nitrogen oxides'' (NOX) refer to all forms of oxidized 
nitrogen (N) compounds, including NO, NO2, and all other 
oxidized N-containing compounds formed from NO and NO2. 
This follows usage in the Clean Air Act Section 108(c): ``Such 
criteria [for oxides of nitrogen] shall include a discussion of 
nitric and nitrous acids, nitrites, nitrates, nitrosamines, and 
other carcinogenic and potentially carcinogenic derivatives of 
oxides of nitrogen.'' By contrast, within the air pollution research 
and control communities, the terms ``oxides of nitrogen'' and 
``nitrogen oxides'' are restricted to refer only to the sum of NO 
and NO2, and this sum is commonly abbreviated as 
NOX. The category label used by this community for the 
sum of all forms of oxidized nitrogen compounds including those 
listed in Section 108(c) is NOY.
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    While NOX is emitted from a wide variety of source 
types, the top three categories of sources of NOX emissions 
are on-road mobile sources, electricity generating units, and non-road 
mobile sources. EPA anticipates that NOX emissions will 
decrease substantially over the next 20 years as a result of the 
ongoing implementation of mobile source emissions standards. In 
particular, Tier 2 NOX emission standards for light-duty 
vehicle emissions began phasing into the fleet beginning with model 
year 2004, in combination with low-sulfur gasoline fuel standards. For 
heavy-duty engines, new NOX standards are phasing in between 
the 2007 and 2010 model years, following the introduction of ultra-low 
sulfur diesel fuel. Lower NOX standards for nonroad diesel 
engines, locomotives, and certain marine engines are becoming effective 
throughout the next decade. In future decades, these lower-
NOX vehicles and engines will become an increasingly large 
fraction of in-use mobile sources, effecting large NOX 
emission reductions.

D. Review of the Air Quality Criteria and Standards for Oxides of 
Nitrogen

    On April 30, 1971, EPA promulgated identical primary and secondary 
NAAQS for NO2 under section 109 of the Act. The standards 
were set at 0.053 parts per million (ppm) (53 ppb), annual average (36 
FR 8186). EPA completed reviews of the air quality criteria and 
NO2 standards in 1985 and 1996 with decisions to retain the 
standard (50 FR 25532, June 19, 1985; 61 FR 52852, October 8, 1996).
    EPA initiated the current review of the air quality criteria for 
oxides of nitrogen and the NO2 primary NAAQS on December 9, 
2005 (70 FR 73236) with a general call for information. EPA's draft 
Integrated Review Plan for the Primary National Ambient Air Quality 
Standard for Nitrogen Dioxide (EPA, 2007a) was made available in 
February, 2007 for public comment and was discussed by the CASAC via a 
publicly accessible teleconference on May 11, 2007. As noted in that 
plan, NOX includes multiple gaseous (e.g., NO2, 
NO) and particulate (e.g., nitrate) species. Because the health effects 
associated with particulate species of NOX have been 
considered within the context of the health effects of ambient 
particles in the Agency's review of the NAAQS for particulate matter 
(PM), the current review of the primary NO2 NAAQS is focused 
on the gaseous species of NOX and is not intended to address 
health effects directly associated with particulate species.
    The first draft of the Integrated Science Assessment for Oxides of 
Nitrogen-Health Criteria (ISA) and the Nitrogen Dioxide Health 
Assessment Plan: Scope and Methods for Exposure and Risk Assessment 
(EPA, 2007b) were reviewed by CASAC at a public meeting held on October 
24-25, 2007. Based on comments received from CASAC and the public, EPA 
developed the second

[[Page 6477]]

draft of the ISA and the first draft of the Risk and Exposure 
Assessment to Support the Review of the NO2 Primary National 
Ambient Air Quality Standard (Risk and Exposure Assessment (REA)). 
These documents were reviewed by CASAC at a public meeting held on May 
1-2, 2008. Based on comments received from CASAC and the public at this 
meeting, EPA released the final ISA in July of 2008 (EPA, 2008a). In 
addition, comments received were considered in developing the second 
draft of the REA, which was released for public review and comment in 
two parts. The first part of this document, containing chapters 1-7, 9 
and appendices A and C as well as part of appendix B, was released in 
August 2008. The second part of this document, containing chapter 8 
(describing the Atlanta exposure assessment) and a completed appendix 
B, was released in October of 2008. This document was the subject of 
CASAC reviews at public meetings on September 9 and 10, 2008 (for the 
first part) and on October 22, 2008 (for the second part). In preparing 
the final REA (EPA, 2008b), EPA considered comments received from the 
CASAC and the public at those meetings.
    In the course of reviewing the second draft REA, CASAC expressed 
the view that the document would be incomplete without the addition of 
a policy assessment chapter presenting an integration of evidence-based 
considerations and risk and exposure assessment results. CASAC stated 
that such a chapter would be ``critical for considering options for the 
NAAQS for NO2'' (Samet, 2008a). In addition, within the 
period of CASAC's review of the second draft REA, EPA's Deputy 
Administrator indicated in a letter to the chair of CASAC, addressing 
earlier CASAC comments on the NAAQS review process, that the risk and 
exposure assessment will include ``a broader discussion of the science 
and how uncertainties may effect decisions on the standard'' and ``all 
analyses and approaches for considering the level of the standard under 
review, including risk assessment and weight of evidence 
methodologies'' (Peacock, 2008, p. 3; September 8, 2008).
    Accordingly, the final REA included a new policy assessment 
chapter. This policy assessment chapter considered the scientific 
evidence in the ISA and the exposure and risk characterization results 
presented in other chapters of the REA as they relate to the adequacy 
of the current NO2 primary NAAQS and potential alternative 
primary NO2 standards. In considering the current and 
potential alternative standards, the policy assessment chapter of the 
final REA focused on the information that is most pertinent to 
evaluating the basic elements of national ambient air quality 
standards: Indicator, averaging time, form,\5\ and level. These 
elements, which together serve to define each standard, must be 
considered collectively in evaluating the health protection afforded. 
CASAC discussed the final version of the REA, with an emphasis on the 
policy assessment chapter, during a public teleconference held on 
December 5, 2008. Following that teleconference, CASAC offered comments 
and advice on the NO2 primary NAAQS in a letter to the 
Administrator (Samet, 2008b).
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    \5\ The ``form'' of a standard defines the air quality statistic 
that is to be compared to the level of the standard in determining 
whether an area attains the standard.
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    The schedule for completion of this review is governed by a 
judicial order resolving a lawsuit filed in September 2005, concerning 
the timing of the current review. The order that now governs this 
review, entered by the court in August 2007 and amended in December 
2008, provides that the Administrator will sign, for publication, 
notices of proposed and final rulemaking concerning the review of the 
primary NO2 NAAQS no later than June 26, 2009 and January 
22, 2010, respectively. In accordance with this schedule, the 
Administrator signed a notice of proposed rulemaking on June 26, 2009 
(FR 74 34404). This action presents the Administrator's final decisions 
on the primary NO2 standard.

E. Summary of Proposed Revisions to the NO2 Primary NAAQS

    For the reasons discussed in the preamble of the proposal for the 
NO2 primary NAAQS (74 FR 34404), EPA proposed to make 
revisions to the primary NO2 NAAQS and to make related 
revisions for NO2 data handling conventions in order to 
provide requisite protection of public health. EPA also proposed to 
make corresponding changes to the AQI for NO2. Specifically, 
EPA proposed to supplement the current annual standard by establishing 
a new short-term NO2 standard that would reflect the maximum 
allowable NO2 concentration anywhere in an area. EPA 
proposed that this new short-term standard would be based on the 3-year 
average of the 99th percentile (or 4th highest) of the yearly 
distribution of 1[dash]hour daily maximum NO2 concentrations 
and solicited comment on using the 3-year average of the 98th 
percentile (or 7th or 8th highest) of the yearly distribution of 1-hour 
daily maximum NO2 concentrations. EPA proposed to set the 
level of this new 1-hour standard within the range of 80 to 100 ppb and 
solicited comment on standard levels as low as 65 ppb and as high as 
150 ppb. EPA proposed to specify the level of the standard to the 
nearest ppb. EPA also proposed to establish requirements for an 
NO2 monitoring network at locations where maximum 
NO2 concentrations are expected to occur, including monitors 
within 50 meters of major roadways, as well as area-wide monitors sited 
to measure the NO2 concentrations that can occur more 
broadly across communities. EPA also solicited comment on the 
alternative approach of setting a 1-hour standard that would reflect 
the allowable area-wide NO2 concentration.

F. Organization and Approach to Final NO2 Primary NAAQS Decisions

    This action presents the Administrator's final decisions regarding 
the need to revise the current NO2 primary NAAQS. Revisions 
to the primary NAAQS for NO2, and the rationale supporting 
those revisions, are described below in section II. Requirements for 
the NO2 ambient monitoring network are described in section 
III. Related requirements for data completeness, data handling, data 
reporting, rounding conventions, and exceptional events are described 
in section IV. Implementation of the revised NO2 primary 
NAAQS is discussed in sections V and VI. Communication of public health 
information through the AQI is discussed in section VII and a 
discussion of statutory and executive order reviews is provided in 
section VIII.
    Today's final decisions are based on a thorough review in the ISA 
of scientific information on known and potential human health effects 
associated with exposure to NO2 in the air. These final 
decisions also take into account: (1) Assessments in the REA of the 
most policy-relevant information in the ISA as well as quantitative 
exposure and risk analyses based on that information; (2) CASAC Panel 
advice and recommendations, as reflected in its letters to the 
Administrator and its public discussions of the ISA, the REA, and the 
notice of proposed rulemaking; (3) public comments received during the 
development of ISA and REA; and (4) public comments received on the 
proposed rulemaking.
    Some commenters have referred to and discussed individual 
scientific analyses on the health effects of NO2 that were 
not included in the ISA (EPA, 2008a) (``new studies''). In considering

[[Page 6478]]

and responding to comments for which such ``new studies'' were cited in 
support, EPA has provisionally considered the cited studies in the 
context of the findings of the ISA.
    As in prior NAAQS reviews, EPA is basing its decision in this 
review on studies and related information included in the ISA and 
staff's policy assessment, which have undergone CASAC and public 
review. In this NO2 NAAQS review, staff's policy assessment 
was presented in the form of a policy assessment chapter of the REA 
(EPA, 2008b). The studies assessed in the ISA and REA, and the 
integration of the scientific evidence presented in them, have 
undergone extensive critical review by EPA, CASAC, and the public. The 
rigor of that review makes these studies, and their integrative 
assessment, the most reliable source of scientific information on which 
to base decisions on the NAAQS, decisions that all parties recognize as 
of great import. NAAQS decisions can have profound impacts on public 
health and welfare, and NAAQS decisions should be based on studies that 
have been rigorously assessed in an integrative manner not only by EPA 
but also by the statutorily mandated independent advisory committee, as 
well as the public review that accompanies this process. EPA's 
provisional consideration of ``new studies'' did not and could not 
provide that kind of in-depth critical review.
    This decision is consistent with EPA's practice in prior NAAQS 
reviews and its interpretation of the requirements of the CAA. Since 
the 1970 amendments, the EPA has taken the view that NAAQS decisions 
are to be based on scientific studies and related information that have 
been assessed as a part of the pertinent air quality criteria, and has 
consistently followed this approach. This longstanding interpretation 
was strengthened by new legislative requirements enacted in 1977, which 
added section 109(d)(2) of the Act concerning CASAC review of air 
quality criteria. See 71 FR 61144, 61148 (October 17, 2006) (final 
decision on review of PM NAAQS) for a detailed discussion of this issue 
and EPA's past practice.
    As discussed in EPA's 1993 decision not to revise the NAAQS for 
ozone (O3), ``new studies'' may sometimes be of such 
significance that it is appropriate to delay a decision on revision of 
a NAAQS and to supplement the pertinent air quality criteria so the 
studies can be taken into account (58 FR at 13013-13014, March 9, 
1993). In the present case, EPA's provisional consideration of ``new 
studies'' concludes that, taken in context, the ``new'' information and 
findings do not materially change any of the broad scientific 
conclusions regarding the health effects of NO2 made in the 
air quality criteria. For this reason, reopening the air quality 
criteria review would not be warranted even if there were time to do so 
under the court order governing the schedule for this rulemaking.
    Accordingly, EPA is basing the final decisions in this review on 
the studies and related information included in the NO2 air 
quality criteria that have undergone CASAC and public review. EPA will 
consider the ``new studies'' for purposes of decision-making in the 
next periodic review of the NO2 NAAQS, which will provide 
the opportunity to fully assess these studies through a more rigorous 
review process involving EPA, CASAC, and the public. Further discussion 
of these ``new studies'' can be found below, in section II.E, and in 
the Response to Comments document.

II. Rationale for Final Decisions on the NO2 Primary 
Standard

    This section presents the rationale for the Administrator's 
decision to revise the existing NO2 primary standard by 
supplementing the current annual standard with a new 1-hour standard. 
In developing this rationale, EPA has drawn upon an integrative 
synthesis of the entire body of evidence on human health effects 
associated with the presence of NO2 in the air. As 
summarized below in section II.B, this body of evidence addresses a 
broad range of health endpoints associated with exposure to 
NO2. In considering this entire body of evidence, EPA 
focuses in particular on those health endpoints for which the ISA finds 
associations with NO2 to be causal or likely causal. This 
rationale also draws upon the results of quantitative exposure and risk 
assessments, summarized below in section II.C.
    As discussed below, a substantial amount of new research has been 
conducted since the last review of the NO2 NAAQS, with 
important new information coming from epidemiologic studies in 
particular. The newly available research studies evaluated in the ISA 
have undergone intensive scrutiny through multiple layers of peer 
review and opportunities for public review and comment. While important 
uncertainties remain in the qualitative and quantitative 
characterizations of health effects attributable to exposure to ambient 
NO2, the review of this information has been extensive and 
deliberate.
    The remainder of this section provides background information that 
informed the Administrator's decisions on the primary standard and 
discusses the rationale for those decisions. Section II.A presents a 
discussion of NO2 air quality. Section II.B includes an 
overview of the scientific evidence related to health effects 
associated with NO2 exposure. This overview includes 
discussion of the health endpoints and at-risk populations considered 
in the ISA. Section II.C discusses the approaches taken by EPA to 
assess exposures and health risks associated with NO2, 
including a discussion of key results. Section II.D summarizes the 
approach that was used in the current review of the NO2 
NAAQS with regard to consideration of the scientific evidence and 
exposure-/risk-based results related to the adequacy of the current 
standard and potential alternative standards. Sections II.E-II.G 
discuss the Administrator's decisions regarding the adequacy of the 
current standard, elements of a new 1-hour standard, and retention of 
the current annual standard, respectively, taking into consideration 
public comments on the proposed decisions. Section II.H summarizes the 
Administrator's decisions with regard to the NO2 primary 
NAAQS.

A. Characterization of NO2 Air Quality

1. Current Patterns of NO2 Air Quality
    The size of the State and local NO2 monitoring network 
has remained relatively stable since the early 1980s, and currently has 
approximately 400 monitors reporting data to EPA's Air Quality System 
(AQS) database.\6\ At present, there are no minimum monitoring 
requirements for NO2 in 40 CFR part 58 Appendix D, other 
than a requirement for EPA Regional Administrator approval before 
removing any existing monitors, and that any ongoing NO2 
monitoring must have at least one monitor sited to measure the maximum 
concentration of NO2 in that area (though, as discussed 
below monitors in the current network do not measure peak 
concentrations associated with on-road mobile sources that can occur 
near major roadways because the network was not designed for this 
purpose). EPA removed the specific

[[Page 6479]]

minimum monitoring requirements for NO2 of two monitoring 
sites per area with a population of 1,000,000 or more in the 2006 
monitoring rule revisions (71 FR 61236), based on the fact that there 
were no NO2 nonattainment areas at that time, coupled with 
trends evidence showing an increasing gap between national average 
NO2 concentrations and the current annual standard. 
Additionally, the minimum requirements were removed to provide State, 
local, and Tribal air monitoring agencies flexibility in meeting higher 
priority monitoring needs for pollutants such as O3 and 
PM2.5, or implementing the new multi-pollutant sites (NCore 
network) required by the 2006 rule revisions, by allowing them to 
discontinue lower priority monitoring. There are requirements in 40 CFR 
part 58 Appendix D for NO2 monitoring as part of the 
Photochemical Assessment Monitoring Stations (PAMS) network. However, 
of the approximately 400 NO2 monitors currently in 
operation, only about 10 percent may be due to the PAMS requirements.
---------------------------------------------------------------------------

    \6\ It should be noted that the ISA (section 2.4.1) references a 
different number of active monitors in the NO2 network. 
The discrepancy between the ISA numbers and the number presented 
here is due to differing metrics used in pulling data from AQS. The 
ISA only references SLAMS, NAMS, and PAMS sites with defined 
monitoring objectives, while Watkins and Thompson (2008) considered 
all NO2 sites reporting data at any point during the 
year. Based on this approach, Watkins and Thompson (2008) also noted 
that the size of the NO2 monitoring network has remained 
relatively stable since the early 1980s.
---------------------------------------------------------------------------

    An analysis of the approximately 400 monitors comprising the 
current NO2 monitoring network (Watkins and Thompson, 2008) 
indicates that the current NO2 network has largely remained 
unchanged in terms of size and target monitor objective categories 
since it was introduced in the May 10, 1979 monitoring rule (44 FR 
27571). The review of the current network found that the assessment of 
concentrations for general population exposure and maximum 
concentrations at neighborhood and larger scales were the top 
objectives. A review of the distribution of listed spatial scales of 
representation shows that only approximately 3 monitors are described 
as microscale, representing an area on the order of several meters to 
100 meters, and approximately 23 monitors are described as middle 
scale, which represents an area on the order of 100 to 500 meters. This 
low percentage of smaller spatially representative scale sites within 
the network of approximately 400 monitoring sites indicates that the 
majority of monitors have, in fact, been sited to assess area-wide 
exposures on the neighborhood, urban, and regional scales, as would be 
expected for a network sited to support the current annual 
NO2 standard and PAMS objectives. The current network does 
not include monitors placed near major roadways and, therefore, 
monitors in the current network do not necessarily measure the maximum 
concentrations that can occur on a localized scale near these roadways 
(as discussed in the next section). It should be noted that the network 
not only accommodates NAAQS related monitoring but also serves other 
monitoring objectives, such as support for photochemistry analysis, 
O3 modeling and forecasting, and particulate matter 
precursor tracking.
2. NO2 Air Quality and Gradients Around Roadways
    On-road and non-road mobile sources account for approximately 60% 
of NOX emissions (ISA, table 2.2-1) and traffic-related 
exposures can dominate personal exposures to NO2 (ISA 
section 2.5.4). While driving, personal exposure concentrations in the 
cabin of a vehicle could be substantially higher than ambient 
concentrations measured nearby (ISA, section 2.5.4). For example, 
estimates presented in the REA suggest that on/near roadway 
NO2 concentrations could be approximately 80% (REA, section 
7.3.2) higher on average across locations than concentrations away from 
roadways and that roadway-associated environments could be responsible 
for the majority of 1-hour peak NO2 exposures (REA, Figures 
8-17 and 8-18). Because monitors in the current network are not sited 
to measure peak roadway-associated NO2 concentrations, 
individuals who spend time on and/or near major roadways could 
experience NO2 concentrations that are considerably higher 
than indicated by monitors in the current area-wide NO2 
monitoring network.
    Research suggests that the concentrations of on-road mobile source 
pollutants such as NOX, carbon monoxide (CO), directly 
emitted air toxics, and certain size distributions of particulate 
matter (PM), such as ultrafine PM, typically display peak 
concentrations on or immediately adjacent to roads (ISA, section 2.5). 
This situation typically produces a gradient in pollutant 
concentrations, with concentrations decreasing with increasing distance 
from the road, and concentrations generally decreasing to near area-
wide ambient levels, or typical upwind urban background levels, within 
a few hundred meters downwind. While such a concentration gradient is 
present on almost all roads, the characteristics of the gradient, 
including the distance from the road that a mobile source pollutant 
signature can be differentiated from background concentrations, are 
heavily dependent on factors such as traffic volumes, local topography, 
roadside features, meteorology, and photochemical reactivity conditions 
(Baldauf, et al., 2009; Beckerman et al., 2008; Clements et al., 2008; 
Hagler et al., 2009; Janssen et al., 2001; Rodes and Holland, 1981; 
Roorda-Knape et al., 1998; Singer et al., 2004; Zhou and Levy, 2007).
    Because NO2 in the ambient air is due largely to the 
atmospheric oxidation of NO emitted from combustion sources (ISA, 
section 2.2.1), elevated NO2 concentrations can extend 
farther away from roadways than the primary pollutants also emitted by 
on-road mobile sources. More specifically, review of the technical 
literature suggests that NO2 concentrations may return to 
area-wide or typical urban background concentrations within distances 
up to 500 meters of roads, though the actual distance will vary with 
topography, roadside features, meteorology, and photochemical 
reactivity conditions (Baldauf et al., 2009; Beckerman et al., 2008; 
Clements et al., 2008; Gilbert et al. 2003; Rodes and Holland, 1981; 
Singer et al., 2004; Zhou and Levy, 2007). Efforts to quantify the 
extent and slope of the concentration gradient that may exist from peak 
near-road concentrations to the typical urban background concentrations 
must consider the variability that exists across locations and for a 
given location over time. As a result, we have identified a range of 
concentration gradients in the technical literature which indicate 
that, on average, peak NO2 concentrations on or immediately 
adjacent to roads may typically be between 30 and 100 percent greater 
than concentrations monitored in the same area but farther away from 
the road (ISA, Section 2.5.4; Beckerman et al., 2008; Gilbert et al., 
2003; Rodes and Holland, 1981; Roorda-Knape et al., 1998; Singer et 
al., 2004). This range of concentration gradients has implications for 
revising the NO2 primary standard and for the NO2 
monitoring network (discussed in sections II.F.4 and III).

B. Health Effects Information

    In the last review of the NO2 NAAQS, the 1993 
NOX Air Quality Criteria Document (1993 AQCD) (EPA, 1993) 
concluded that there were two key health effects of greatest concern at 
ambient or near-ambient concentrations of NO2 (ISA, section 
5.3.1). The first was increased airway responsiveness in asthmatic 
individuals after short-term exposures. The second was increased 
respiratory illness among children associated with longer-term 
exposures to NO2. Evidence also was found for increased risk 
of emphysema, but this appeared to be of major concern only with 
exposures to NO2 at levels much higher than then current 
ambient levels (ISA, section 5.3.1). Controlled human

[[Page 6480]]

exposure and animal toxicological studies provided qualitative evidence 
for airway hyperresponsiveness and lung function changes while 
epidemiologic studies provided evidence for increased respiratory 
symptoms with increased indoor NO2 exposures. Animal 
toxicological findings of lung host defense system changes with 
NO2 exposure provided a biologically-plausible basis for the 
epidemiologic results. Subpopulations considered potentially more 
susceptible to the effects of NO2 exposure included persons 
with preexisting respiratory disease, children, and the elderly. The 
epidemiologic evidence for respiratory health effects was limited, and 
no studies had considered endpoints such as hospital admissions, 
emergency department visits, or mortality (ISA, section 5.3.1).
    As summarized below and discussed more fully in section II.B of the 
proposal notice, evidence published since the last review generally has 
confirmed and extended the conclusions articulated in the 1993 AQCD 
(ISA, section 5.3.2). The epidemiologic evidence has grown 
substantially with the addition of field and panel studies, 
intervention studies, time-series studies of endpoints such as hospital 
admissions, and a substantial number of studies evaluating mortality 
risk associated with short-term NO2 exposures. While not as 
marked as the growth in the epidemiologic literature, a number of 
recent toxicological and controlled human exposure studies also provide 
insights into relationships between NO2 exposure and health 
effects. This body of evidence focuses the current review on 
NO2-related respiratory effects at lower ambient and 
exposure concentrations than considered in the previous review.
1. Adverse Respiratory Effects and Short-Term Exposure to 
NO2
    The ISA concluded that the findings of epidemiologic, controlled 
human exposure, and animal toxicological studies provide evidence that 
is sufficient to infer a likely causal relationship for respiratory 
effects following short-term NO2 exposure (ISA, sections 
3.1.7 and 5.3.2.1). The ISA (section 5.4) concluded that the strongest 
evidence for an association between NO2 exposure and adverse 
human health effects comes from epidemiologic studies of respiratory 
symptoms, emergency department visits, and hospital admissions. These 
studies include panel and field studies, studies that control for the 
effects of co-occurring pollutants, and studies conducted in areas 
where the whole distribution of ambient 24-hour average NO2 
concentrations was below the current NAAQS level of 53 ppb (annual 
average). With regard to this evidence, the ISA concluded that 
NO2 epidemiologic studies provide ``little evidence of any 
effect threshold'' (ISA, section 5.3.2.9, p. 5-15). In studies that 
have evaluated concentration-response relationships, they appear linear 
within the observed range of data (ISA, section 5.3.2.9).
    Overall, the epidemiologic evidence for respiratory effects has 
been characterized in the ISA as consistent, in that associations are 
reported in studies conducted in numerous locations with a variety of 
methodological approaches, and coherent, in that the studies report 
associations with respiratory health outcomes that are logically linked 
together. In addition, a number of these associations are statistically 
significant, particularly the more precise effect estimates (ISA, 
section 5.3.2.1). These epidemiologic studies are supported by evidence 
from toxicological and controlled human exposure studies, particularly 
those that evaluated airway hyperresponsiveness in asthmatic 
individuals (ISA, section 5.4). The ISA concluded that together, the 
epidemiologic and experimental data sets form a plausible, consistent, 
and coherent description of a relationship between NO2 
exposures and an array of adverse respiratory health effects that range 
from the onset of respiratory symptoms to hospital admissions.
    In considering the uncertainties associated with the epidemiologic 
evidence, the ISA (section 5.4) noted that it is difficult to determine 
``the extent to which NO2 is independently associated with 
respiratory effects or if NO2 is a marker for the effects of 
another traffic-related pollutant or mix of pollutants.'' On-road 
vehicle exhaust emissions are a widespread source of combustion 
pollutant mixtures that include NOX and are an important 
contributor to NO2 levels in near-road locations. Although 
the presence of other pollutants from vehicle exhaust emissions 
complicates efforts to quantify specific NO2-related health 
effects, a number of epidemiologic studies have evaluated associations 
with NO2 in models that also include co-occurring pollutants 
such as PM, O3, CO, and/or SO2. The evidence 
summarized in the ISA indicates that NO2 associations 
generally remain robust in these multi-pollutant models and supports a 
direct effect of short-term NO2 exposure on respiratory 
morbidity (see ISA Figures 3.1-7, 3.1-10, 3.1-11). The plausibility and 
coherence of these effects are also supported by epidemiologic studies 
of indoor NO2 as well as experimental (i.e., toxicological 
and controlled human exposure) studies that have evaluated host defense 
and immune system changes, airway inflammation, and airway 
responsiveness (see subsequent sections of this proposal and the ISA, 
section 5.3.2.1). The ISA (section 5.4) concluded that the robustness 
of epidemiologic findings to adjustment for co-pollutants, coupled with 
data from animal and human experimental studies, support a 
determination that the relationship between NO2 and 
respiratory morbidity is likely causal, while still recognizing the 
relationship between NO2 and other traffic related 
pollutants.
    The epidemiologic and experimental studies encompass a number of 
respiratory-related health endpoints, including emergency department 
visits and hospitalizations, respiratory symptoms, airway 
hyperresponsiveness, airway inflammation, and lung function. The 
findings relevant to these endpoints, which provide the rationale to 
support the judgment of a likely causal relationship, are described in 
more detail in section II.B.1 of the proposal.
2. Other Effects With Short-Term Exposure to NO2
a. Mortality
    The ISA concluded that the epidemiologic evidence is suggestive, 
but not sufficient, to infer a causal relationship between short-term 
exposure to NO2 and all-cause and cardiopulmonary-related 
mortality (ISA, section 5.3.2.3). Results from several large United 
States and European multicity studies and a meta-analysis study 
indicate positive associations between ambient NO2 
concentrations and the risk of all-cause (nonaccidental) mortality, 
with effect estimates ranging from 0.5 to 3.6% excess risk in mortality 
per standardized increment (20 ppb for 24-hour averaging time, 30 ppb 
for 1-hour averaging time) (ISA, section 3.3.1, Figure 3.3-2, section 
5.3.2.3). In general, the ISA concluded that NO2 effect 
estimates were robust to adjustment for co-pollutants. Both 
cardiovascular and respiratory mortality have been associated with 
increased NO2 concentrations in epidemiologic studies (ISA, 
Figure 3.3-3); however, similar associations were observed for other 
pollutants, including PM and SO2. The range of risk 
estimates for excess mortality is generally smaller than that for other 
pollutants such as PM. In addition, while NO2 exposure, 
alone or in conjunction with other pollutants,

[[Page 6481]]

may contribute to increased mortality, evaluation of the specificity of 
this effect is difficult. Clinical studies showing hematologic effects 
and animal toxicological studies showing biochemical, lung host 
defense, permeability, and inflammation changes with short-term 
exposures to NO2 provide limited evidence of plausible 
pathways by which risks of mortality may be increased, but no coherent 
picture is evident at this time (ISA, section 5.3.2.3).
b. Cardiovascular Effects
    The ISA concluded that the available evidence on cardiovascular 
health effects following short-term exposure to NO2 is 
inadequate to infer the presence or absence of a causal relationship at 
this time (ISA, section 5.3.2.2). Evidence from epidemiologic studies 
of heart rate variability, repolarization changes, and cardiac rhythm 
disorders among heart patients with ischemic cardiac disease are 
inconsistent (ISA, section 5.3.2.2). In most studies, associations with 
PM were found to be similar or stronger than associations with 
NO2. Generally positive associations between ambient 
NO2 concentrations and hospital admissions or emergency 
department visits for cardiovascular disease have been reported in 
single-pollutant models (ISA, section 5.3.2.2); however, most of these 
effect estimate values were diminished in multi-pollutant models that 
also contained CO and PM indices (ISA, section 5.3.2.2). Mechanistic 
evidence of a role for NO2 in the development of 
cardiovascular diseases from studies of biomarkers of inflammation, 
cell adhesion, coagulation, and thrombosis is lacking (ISA, section 
5.3.2.2). Furthermore, the effects of NO2 on various 
hematological parameters in animals are inconsistent and, thus, provide 
little biological plausibility for effects of NO2 on the 
cardiovascular system (ISA, section 5.3.2.2).
3. Health Effects With Long-Term Exposure to NO2
a. Respiratory Morbidity
    The ISA concluded that overall, the epidemiologic and experimental 
evidence is suggestive, but not sufficient, to infer a causal 
relationship between long-term NO2 exposure and respiratory 
morbidity (ISA, section 5.3.2.4). The available database evaluating the 
relationship between respiratory illness in children and long-term 
exposures to NO2 has increased since the 1996 review of the 
NO2 NAAQS (see section II.B.3 of the proposal for a more 
detailed discussion). A number of epidemiologic studies have examined 
the effects of long-term exposure to NO2 and reported 
positive associations with decrements in lung function and partially 
irreversible decrements in lung function growth (ISA, section 3.4.1, 
Figures 3.4-1 and 3.4-2). While animal toxicological studies may 
provide biological plausibility for the chronic effects of 
NO2 that have been observed in epidemiologic studies (ISA, 
sections 3.4.5 and 5.3.2.4), the high correlation among traffic-related 
pollutants in epidemiologic studies makes it difficult to accurately 
estimate independent effects (ISA, section 5.3.2.4).
b. Mortality
    The ISA concluded that the epidemiologic evidence is inadequate to 
infer the presence or absence of a causal relationship between long-
term exposure to NO2 and mortality (ISA, section 5.3.2.6). 
In the United States and European cohort studies examining the 
relationship between long-term exposure to NO2 and 
mortality, results have been inconsistent (ISA, section 5.3.2.6). 
Further, when associations were suggested, they were not specific to 
NO2 but also implicated PM and other traffic indicators. The 
relatively high correlations reported between NO2 and PM 
indices make it difficult to interpret these observed associations at 
this time (ISA, section 5.3.2.6).
c. Carcinogenic, cardiovascular, and reproductive/developmental effects
    The ISA concluded that the available epidemiologic and 
toxicological evidence is inadequate to infer the presence or absence 
of a causal relationship for carcinogenic, cardiovascular, and 
reproductive and developmental effects related to long-term 
NO2 exposure (ISA, section 5.3.2.5). Epidemiologic studies 
conducted in Europe have shown an association between long-term 
NO2 exposure and increased incidence of cancer (ISA, section 
5.3.2.5). However, the animal toxicological studies have provided no 
clear evidence that NO2 acts as a carcinogen (ISA, section 
5.3.2.5). The very limited epidemiologic and toxicological evidence do 
not suggest that long-term exposure to NO2 has 
cardiovascular effects (ISA, section 5.3.2.5). The epidemiologic 
evidence is not consistent for associations between NO2 
exposure and fetal growth retardation; however, some evidence is 
accumulating for effects on preterm delivery (ISA, section 5.3.2.5). 
Scant animal evidence supports a weak association between 
NO2 exposure and adverse birth outcomes and provides little 
mechanistic information or biological plausibility for the 
epidemiologic findings.
4. NO2-related Impacts on Public Health
    Specific groups within the general population are likely at 
increased risk for suffering adverse effects from NO2 
exposure. This could occur because they are affected by lower levels of 
NO2 than the general population or because they experience a 
larger health impact than the general population to a given level of 
exposure (susceptibility) and/or because they are exposed to higher 
levels of NO2 than the general population (vulnerability). 
The term susceptibility generally encompasses innate (e.g., genetic or 
developmental) and/or acquired (e.g., age or disease) factors that make 
individuals more likely to experience effects with exposure to 
pollutants. The severity of health effects experienced by a susceptible 
subgroup may be much greater than that experienced by the population at 
large. Factors that may influence susceptibility to the effects of air 
pollution include age (e.g., infants, children, elderly); gender; race/
ethnicity; genetic factors; and pre-existing disease/condition (e.g., 
obesity, diabetes, respiratory disease, asthma, chronic obstructive 
pulmonary disease (COPD), cardiovascular disease, airway 
hyperresponsiveness, respiratory infection, adverse birth outcome) 
(ISA, sections 4.3.1, 4.3.5, and 5.3.2.8). In addition, certain groups 
may experience relatively high exposure to NO2, thus forming 
a potentially vulnerable population (ISA, section 4.3.6). Factors that 
may influence susceptibility and vulnerability to air pollution include 
socioeconomic status (SES), education level, air conditioning use, 
proximity to roadways, geographic location, level of physical activity, 
and work environment (e.g., indoor versus outdoor) (ISA, section 
4.3.5). The ISA discussed factors that can confer susceptibility and/or 
vulnerability to air pollution with most of the discussion devoted to 
factors for which NO2-specific evidence exists (ISA, section 
4.3). These factors include pre-existing disease (e.g., asthma), age 
(i.e., infants, children, older adults), genetic factors, gender, 
socioeconomic status, and proximity to roadways (see section II.B.4 in 
proposal for more detailed discussion of these factors).
    As discussed in more detail in the proposal (section II.B.4), the 
population potentially affected by NO2 is large. A 
considerable fraction of the population resides, works, or attends 
school near major roadways, and these individuals are likely to have 
increased exposure to NO2 (ISA, section 4.4). Based on data

[[Page 6482]]

from the 2003 American Housing Survey, approximately 36 million 
individuals live within 300 feet (~90 meters) of a four-lane highway, 
railroad, or airport (ISA, section 4.4).\7\ Furthermore, in California, 
2.3% of schools, with a total enrollment of more than 150,000 students 
were located within approximately 500 feet of high-traffic roads, with 
a higher proportion of non-white and economically disadvantaged 
students attending those schools (ISA, section 4.4). Of this 
population, asthmatics and members of other susceptible groups 
discussed above will have even greater risks of experiencing health 
effects related to NO2 exposure. In the United States, 
approximately 10% of adults and 13% of children (approximately 22.2 
million people in 2005) have been diagnosed with asthma, and 6% of 
adults have been diagnosed with COPD (ISA, section 4.4). The prevalence 
and severity of asthma is higher among certain ethnic or racial groups 
such as Puerto Ricans, American Indians, Alaskan Natives, and African 
Americans (ISA, section 4.4). A higher prevalence of asthma among 
persons of lower SES and an excess burden of asthma hospitalizations 
and mortality in minority and inner-city communities have been observed 
(ISA, section 4.4). In addition, based on United States census data 
from 2000, about 72.3 million (26%) of the United States population are 
under 18 years of age, 18.3 million (7.4%) are under 5 years of age, 
and 35 million (12%) are 65 years of age or older. Therefore, large 
portions of the United States population are in age groups that are 
likely at-risk for health effects associated with exposure to ambient 
NO2. The size of the potentially at-risk population suggests 
that exposure to ambient NO2 could have a significant impact 
on public health in the United States.
---------------------------------------------------------------------------

    \7\ The most current American Housing Survey (http://www.census.gov/hhes/www/housing/ahs/ahs.html) is from 2007 and lists 
a higher fraction of housing units within the 300 foot boundary than 
do prior surveys. According to Table 1A-6 from that report (http://www.census.gov/hhes/www/housing/ahs/ahs07/tab1a-6.pdf), out of 
128,203,000 total housing units in the United States, 20,016,000 
were reported by the surveyed occupant or landlord as being within 
300 feet of a 4-or-more lane highway, railroad, or airport. That 
constitutes 15.613% of the total housing units in the U.S. Assuming 
equal distributions, with a current population of 306,330,199, that 
means that there would be 47.8 million people meeting the 300 foot 
criteria.
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C. Human Exposure and Health Risk Characterization

    To put judgments about NO2-associated health effects 
into a broader public health context, EPA has drawn upon the results of 
the quantitative exposure and risk assessments. Judgments reflecting 
the nature of the evidence and the overall weight of the evidence are 
taken into consideration in these quantitative exposure and risk 
assessments, discussed below. These assessments provide estimates of 
the likelihood that asthmatic individuals would experience exposures of 
potential concern and estimates of the incidence of NO2-
associated respiratory emergency department visits under varying air 
quality scenarios (e.g., just meeting the current or alternative 
standards), as well as characterizations of the kind and degree of 
uncertainties inherent in such estimates. As discussed more fully in 
section II.C of the proposal, this section summarizes the approach 
taken in the REA to characterize NO2-related exposures and 
health risks. Goals of the REA included estimating short-term exposures 
and potential human health risks associated with (1) recent levels of 
ambient NO2; (2) NO2 levels adjusted to simulate 
just meeting the current standard; and (3) NO2 levels 
adjusted to simulate just meeting potential alternative standards.
    For purposes of the quantitative characterization of NO2 
health risks, the REA determined that it was appropriate to focus on 
endpoints for which the ISA concluded that the available evidence is 
sufficient to infer either a causal or a likely causal relationship. 
This was generally consistent with judgments made in other recent NAAQS 
reviews (e.g., see EPA, 2005). As noted above in section II.A, the only 
health effect category for which the evidence was judged in the ISA to 
be sufficient to infer either a causal or a likely causal relationship 
is respiratory morbidity following short-term NO2 exposure. 
Therefore, for purposes of characterizing health risks associated with 
NO2, the REA focused on respiratory morbidity endpoints that 
have been associated with short-term NO2 exposures.
    In evaluating the appropriateness of specific endpoints for use in 
the NO2 risk characterization, the REA considered both 
epidemiologic and controlled human exposure studies. As described in 
more detail in the proposal (section II.C.1), the characterization of 
NO2-associated health risks was based on an epidemiology 
study conducted in Atlanta, Georgia by Tolbert et al. (2007) and a 
meta-analysis of controlled human exposure studies of NO2 
and airway responsiveness in asthmatics (ISA, Table 3.1-3).\8\
---------------------------------------------------------------------------

    \8\ The study by Tolbert et al. (2007) reported positive 
associations between 1-hour ambient NO2 concentrations 
and respiratory-related emergency department visits. The meta-
analysis was included in the ISA and reported that short-term 
exposures to NO2 concentrations at or above 100 ppb 
increased airway responsiveness in most asthmatics.
---------------------------------------------------------------------------

    As noted above, the purpose of the assessments described in the REA 
was to characterize air quality, exposures, and health risks associated 
with recent ambient levels of NO2, with NO2 
levels that could be associated with just meeting the current 
NO2 NAAQS, and with NO2 levels that could be 
associated with just meeting potential alternative standards. To 
characterize health risks, the REA employed three approaches. In the 
first approach, for each air quality scenario, NO2 
concentrations at fixed-site monitors and simulated concentrations on/
near roadways were compared to potential health effect benchmark values 
derived from the controlled human exposure literature. In the second 
approach, modeled estimates of exposures in asthmatics were compared to 
potential health effect benchmarks. In the third approach, 
concentration-response relationships from an epidemiologic study were 
used in conjunction with baseline incidence data and recent or 
simulated ambient concentrations to estimate health impacts. An 
overview of the approaches to characterizing health risks is provided 
in the proposal (section II.C.2) and each approach, along with its 
limitations and uncertainties (see proposal, section II.C.3) has been 
described in more detail in the REA (chapters 6 through 9).
    Chapters 7-9 of the REA estimated exposures and health risks 
associated with recent air quality and with air quality, as measured at 
monitors in the current area-wide network, which had been adjusted to 
simulate just meeting the current and potential alternative standards. 
The specific standard levels evaluated, for an area-wide standard based 
on the 3-year average of the 98th and 99th percentile 1-hour daily 
maximum NO2 concentrations, were 50, 100, 150, and 200 ppb. 
In interpreting these results within the context of the current 
revisions to the NO2 primary NAAQS (see below), we note that 
simulation of different standard levels was based on adjusting 
NO2 concentrations at available area-wide monitors. 
Therefore, the standard levels referred to above reflect the allowable 
area-wide NO2 concentrations, not the maximum allowable 
concentrations. As a consequence, the maximum concentrations in an area 
that just meets one of these standard levels would be expected to be 
higher than the standard level. For example, given that near-road

[[Page 6483]]

NO2 concentrations can be 30% to 100% higher than area-wide 
concentrations (see section II.E.2), an area-wide concentration of 50 
ppb could correspond to near-road concentrations from 65 to 100 ppb.
    Key results of the air quality, exposure, and risk analyses were 
presented in the policy assessment chapter of the REA and summarized in 
the proposal (Table 1 in proposal). In considering these results, the 
policy assessment chapter of the REA concluded that the risks estimated 
to be associated with just meeting the current annual standard can be 
judged important from a public health perspective. The results for 
specific 1-hour standard levels estimate that limiting the 98th/99th 
percentile of the distribution of 1-hour daily maximum NO2 
concentrations measured at area-wide monitors to 50 or 100 ppb could 
substantially reduce exposures to ambient NO2 and associated 
health risks (compared to just meeting the current standard). In 
contrast, limiting these area-wide NO2 concentrations to 150 
or 200 ppb is estimated to result in similar, or in some cases higher, 
NO2-associated exposures and health risks than just meeting 
the current standard. The pattern of results was similar for standards 
just meeting either the 98th or the 99th percentile 1-hour daily 
maximum area-wide standards (REA, Chapters 7, 8, and 9).

D. Approach for Reviewing the Need To Retain or Revise the Current 
Standard

    EPA notes that the final decision on retaining or revising the 
current primary NO2 standard is a public health policy 
judgment to be made by the Administrator. This judgment has been 
informed by a recognition that the available health effects evidence 
reflects a continuum consisting of ambient levels of NO2 at 
which scientists generally agree that health effects are likely to 
occur, through lower levels at which the likelihood and magnitude of 
the response become increasingly uncertain. The Administrator's final 
decisions draw upon scientific information and analyses related to 
health effects, population exposures, and risks; judgments about the 
appropriate response to the range of uncertainties that are inherent in 
the scientific evidence and analyses; and comments received from CASAC 
and the public.
    To evaluate whether the current primary NO2 standard is 
requisite or whether consideration of revisions is appropriate, EPA has 
used an approach in this review that was described in the policy 
assessment chapter of the REA. This approach builds upon those used in 
reviews of other criteria pollutants, including the most recent reviews 
of the Pb, O3, and PM NAAQS (EPA, 2007c; EPA, 2007d; EPA, 
2005), and reflects the body of evidence and information that is 
currently available. As in other recent reviews, EPA's considerations 
included the implications of placing more or less weight or emphasis on 
different aspects of the scientific evidence and the exposure/risk-
based information, recognizing that the weight to be given to various 
elements of the evidence and exposure/risk information is part of the 
public health policy judgments that the Administrator will make in 
reaching decisions on the standard.
    A series of general questions framed this approach to considering 
the scientific evidence and exposure-/risk-based information. First, 
EPA's consideration of the scientific evidence and exposure/risk 
information with regard to the adequacy of the current standard has 
been framed by the following questions:

     To what extent does evidence that has become available 
since the last review reinforce or call into question evidence for 
NO2-associated effects that were identified in the last 
review?
     To what extent has evidence for different health 
effects and/or sensitive populations become available since the last 
review?
     To what extent have uncertainties identified in the 
last review been reduced and/or have new uncertainties emerged?
     To what extent does evidence and exposure-/risk-based 
information that has become available since the last review 
reinforce or call into question any of the basic elements of the 
current standard?

    To the extent that the available evidence and exposure-/risk-based 
information suggests it may be appropriate to consider revision of the 
current standard, EPA considers that evidence and information with 
regard to its support for consideration of a standard that is either 
more or less protective than the current standard. This evaluation has 
been framed by the following questions:

     Is there evidence that associations, especially causal 
or likely causal associations, extend to ambient NO2 
concentrations as low as, or lower than, the concentrations that 
have previously been associated with health effects? If so, what are 
the important uncertainties associated with that evidence?
     Are exposures above benchmark levels and/or health 
risks estimated to occur in areas that meet the current standard? If 
so, are the estimated exposures and health risks important from a 
public health perspective? What are the important uncertainties 
associated with the estimated risks?

    To the extent that there is support for consideration of a revised 
standard, EPA then considers the specific elements of the standard 
(indicator, averaging time, form, and level) within the context of the 
currently available information. In so doing, the Agency has addressed 
the following questions:

     Does the evidence provide support for considering a 
different indicator for gaseous NOX?
     Does the evidence provide support for considering 
different averaging times?
     What ranges of levels and forms of alternative 
standards are supported by the evidence, and what are the associated 
uncertainties and limitations?
     To what extent do specific averaging times, levels, and 
forms of alternative standards reduce the estimated exposures above 
benchmark levels and risks attributable to NO2, and what 
are the uncertainties associated with the estimated exposure and 
risk reductions?

The questions outlined above have been addressed in the REA, the 
proposal, and in this final rulemaking. The following sections present 
the rationale for proposed decisions, discussion of public comments, 
and the Administrator's conclusions on the adequacy of the current 
standard and potential alternative standards in terms of indicator, 
averaging time, form, and level.

E. Adequacy of the Current Standard

    This section discusses considerations related to the decision as to 
whether the current NO2 primary NAAQS is requisite to 
protect public health with an adequate margin of safety. Specifically, 
section II.E.1 provides an overview of the rationale supporting the 
Administrator's conclusion in the proposal that the current standard 
alone does not provide adequate public health protection; section 
II.E.2 discusses comments received on the adequacy of the current 
standard; and section II.E.3 discusses the Administrator's final 
decision on whether the current NO2 primary NAAQS is 
requisite to protect public health with an adequate margin of safety.
1. Rationale for Proposed Decision
    In reaching a conclusion regarding the adequacy of the current 
NO2 NAAQS in the proposal (section II.E.5), the 
Administrator considered the scientific evidence assessed in the ISA 
and the conclusions of the ISA, the exposure and risk information 
presented in the REA and the conclusions of the policy assessment 
chapter of the REA, and the views expressed by CASAC. These 
considerations are discussed in detail in the proposal (II.E.) and are 
summarized in this section. In the proposal, the

[[Page 6484]]

Administrator noted the following in considering the adequacy of the 
current standard:
     The ISA concluded that the results of epidemiologic and 
experimental studies form a plausible and coherent data set that 
supports a relationship between NO2 exposures and 
respiratory endpoints, including respiratory symptoms and respiratory-
related hospital admissions and emergency department visits, at ambient 
concentrations that are present in areas that meet the current 
NO2 NAAQS (ISA, section 5.4).
     The policy assessment chapter of the REA concluded that 
risks estimated to be associated with air quality adjusted upward to 
simulate just meeting the current standard can reasonably be judged 
important from a public health perspective (REA, section 10.3.3).
     The policy assessment chapter of the REA concluded that 
exposure- and risk-based results reinforce the scientific evidence in 
supporting the conclusion that consideration should be given to 
revising the current NO2 NAAQS so as to provide increased 
public health protection, especially for at-risk groups, from 
NO2-related adverse health effects associated with short-
term, and potential long-term, exposures (REA, section 10.3.3).
     CASAC agreed that the current annual standard alone is not 
sufficient to protect public health against the types of exposures that 
could lead to these health effects. Specifically, in their letter to 
the Administrator on the final REA, they stated that ``CASAC concurs 
with EPA's judgment that the current NAAQS does not protect the 
public's health and that it should be revised'' (Samet, 2008b).
    Based on these considerations (discussed in more detail in the 
proposal, section II.E), the Administrator concluded in the proposal 
that the current NO2 primary NAAQS is not requisite to 
protect public health with an adequate margin of safety against adverse 
respiratory effects associated with short-term exposures. In 
considering approaches to revising the current standard, the 
Administrator concluded that it is appropriate to consider setting a 
new short-term standard in addition to retaining the current annual 
standard. The Administrator noted that such a short-term standard could 
provide increased public health protection, especially for members of 
at-risk groups, from effects described in both epidemiologic and 
controlled human exposure studies to be associated with short-term 
exposures to NO2.
2. Comments on the Adequacy of the Current Standard
    This section discusses comments received from CASAC and public 
commenters on the proposal that either supported or opposed the 
Administrator's proposed decision to revise the current NO2 
primary NAAQS. Comments on the adequacy of the current standard that 
focused on the scientific and/or the exposure/risk basis for the 
Administrator's proposed conclusions are discussed in sections 
II.E.2.a-II.E.2.c. Comments on the epidemiologic evidence are 
considered in section II.E.2.a. Comments on the controlled human 
exposure evidence are considered in section II.E.2.b. Comments on human 
exposure and health risk assessments are considered in section 
II.E.2.c. To the extent these comments on the evidence and information 
are also used to justify commenters' conclusions on decisions related 
to indicator, averaging time, level, or form, they are noted in the 
appropriate sections below (II.F.1-II.F.4).
    In their comments on the proposal (Samet, 2009), CASAC reiterated 
their support for the need to revise the current annual NO2 
NAAQS in order to increase public health protection. As noted above, in 
its letter to the Administrator on the final REA (Samet, 2008b) CASAC 
stated that it ``concurs with EPA's judgment that the current NAAQS 
does not protect the public's health and that it should be revised.'' 
In supporting adoption of a more stringent NAAQS for NO2, 
CASAC considered the assessment of the scientific evidence presented in 
the ISA, the results of assessments presented in the REA, and the 
conclusions of the policy assessment chapter of the REA. As such, 
CASAC's rationale for revising the current standard was consistent with 
the Administrator's rationale as discussed in the proposal.
    Many public commenters agreed with CASAC that, based on the 
available information, the current NO2 standard is not 
requisite to protect public health with an adequate margin of safety 
and that revisions to the standard are appropriate. Among those calling 
for revisions to the standard were environmental groups (e.g., Clean 
Air Council (CAC), Earth Justice (EJ), Environmental Defense Fund 
(EDF), Natural Resources Defense Council (NRDC), Group Against Smog and 
Pollution (GASP)); medical/public health organizations (e.g., American 
Lung Association (ALA), American Medical Association (AMA), American 
Thoracic Society (ATS), National Association for the Medical Direction 
of Respiratory Care (NAMDRC), National Association of Cardiovascular 
and Pulmonary Rehabilitation (NACPR), American College of Chest 
Physicians (ACCP)); a large number of State agencies and organizations 
(e.g., National Association of Clean Air Agencies (NACAA), Northeast 
States for Coordinated Air Use Management (NESCAUM), and State or local 
agencies in CA, IA, IL, MI, MO, NC, NM, NY, TX, VA, WI); Tribes (e.g., 
National Tribal Air Association (NTAA), Fond du Lac Band of Lake 
Superior Chippewa (Fond du Lac)), and a number of individual 
commenters. These commenters concluded that the current NO2 
standard needs to be revised and that a more stringent standard is 
needed to protect the health of sensitive population groups. In 
supporting the need to adopt a more stringent NAAQS for NO2, 
these commenters often referenced the conclusions of CASAC and relied 
on the evidence and information presented in the proposal. As such, 
similar to CASAC, the rationale offered by these commenters was 
consistent with that presented in the proposal to support the 
Administrator's proposed decision to revise the current NO2 
NAAQS.
    Some industry commenters (e.g., Alliance of Automobile 
Manufacturers (AAM), American Petroleum Institute (API), Interstate 
Natural Gas Association of America (INGAA), Utility Air Regulatory 
Group (UARG)) and one State commenter (IN Department of Environmental 
Management) expressed support for retaining the current annual standard 
alone. In supporting this view, these commenters generally concluded 
that the current standard is requisite to protect public health with an 
adequate margin of safety and that the available evidence is not 
sufficient to support revision of the standard. For example, UARG 
stated that ``EPA has failed to demonstrate that the present 
NO2 NAAQS is no longer at the level requisite to protect 
public health with an adequate margin of safety.'' In addition, INGAA 
stated that
    ``* * * EPA should be compelled to retain the current standard and 
defer a decision on a new short-term standard until the science is more 
clearly defined.''
    In support of their views, these commenters provided specific 
comments on the epidemiologic and controlled human exposure evidence as 
discussed below. In responding to these specific comments, we note that 
the Administrator relied in the proposal on the evidence, information 
and judgments contained in the ISA and the

[[Page 6485]]

REA (including the policy assessment chapter) as well as on the advice 
of CASAC. In considering the evidence, information, and judgments of 
the ISA and the REA, the Agency notes that these documents have been 
reviewed extensively by CASAC and have been discussed by CASAC at 
multiple public meetings (see section I.D). In their letter to the 
Administrator regarding the second draft ISA (Henderson, 2008), CASAC 
noted the following:

    Panel members concur with the primary conclusions reached in the 
ISA with regard to health risks that are associated with 
NO2 exposure. In particular, the Panel agrees with the 
conclusion that the current scientific evidence is ``sufficient to 
infer a likely causal relationship between short-term NO2 
exposure and adverse effects on the respiratory system.'' The 
strongest evidence in support of this conclusion comes from 
epidemiology studies that show generally positive associations 
between NO2 and respiratory symptoms, hospitalizations or 
emergency department visits, as summarized in Figure 5.3.1.''

    Similarly, in their letter to the Administrator on the final REA 
(Samet, 2008b), CASAC noted the following:

    Overall, CASAC found this version of the REA satisfactory in its 
approach to moving from the scientific foundation developed in the 
Integrated Science Assessment (ISA) to setting out evidence-based 
options for the NAAQS. The REA provides the needed bridge from the 
evidence presented in the ISA to a characterization of the exposures 
and the associated risks with different profiles of exposure. It 
draws on toxicological and epidemiological evidence and addresses 
risk to an identified susceptible population, people with asthmatic 
conditions. EPA has also systematically described uncertainties 
associated with the risk assessments. We commend EPA for developing 
a succinct and thoughtfully developed synthesis in chapter 10. This 
summary chapter represents a long-needed and transparent model for 
linking a substantial body of scientific evidence to the four 
elements of the NAAQS.

Therefore, in discussing comments on the interpretation of the 
scientific evidence and exposure/risk information, we note that CASAC 
has endorsed the approaches and conclusions of the ISA and the REA. 
These approaches and conclusions are discussed below in more detail, 
within the context of specific public comments.
a. Comments on EPA's Interpretation of the Epidemiologic Evidence
    Several industry groups (e.g., API, National Mining Association 
(NMA), American Chemistry Council (ACC), AAM, Annapolis Center for 
Science-Based Public Policy (ACSBPP), Engine Manufacturers Association 
(EMA), ExxonMobil (Exxon), National Association of Manufacturers (NAM)) 
commented that, given the presence of numerous co-pollutants in the 
air, epidemiologic studies do not support the contention that 
NO2 itself is causing health effects.
    While EPA has recognized that multiple factors can contribute to 
the etiology of respiratory disease and that more than one air 
pollutant could independently impact respiratory health, we continue to 
judge, as discussed in the ISA, that the available evidence supports 
the conclusion that there is an independent effect of NO2 on 
respiratory morbidity. In reaching this judgment, we recognize that a 
major methodological issue affecting NO2 epidemiologic 
studies concerns the evaluation of the extent to which other air 
pollutants may confound or modify NO2-related effect 
estimates. The use of multipollutant regression models is the most 
common approach for controlling potential confounding by co-pollutants 
in epidemiologic studies. The issues related to confounding and the 
evidence of potential confounding by co-pollutants has been thoroughly 
reviewed in the ISA (see Figures 3.1-10 and 3.1-11) and in previous 
assessments (e.g., the criteria document for PM) (EPA, 2004). 
NO2 risk estimates for respiratory morbidity endpoints, in 
general, were not sensitive to the inclusion of co-pollutants, 
including particulate and gaseous pollutants. As observed in Figures 
3.1-10 and 3.1-11 in the ISA, relative risks for hospital admissions or 
emergency department visits are generally unchanged, nor is their 
interpretation modified, upon inclusion of PM or gaseous co-pollutants 
in the models. Similarly, associations between short-term 
NO2 exposure and asthma symptoms are generally robust to 
adjustment for co-pollutants in multipollutant models, as shown in 
Figures 3.1-5 and 3.1-7 of the ISA. These results, in conjunction with 
the results of a randomized intervention study evaluating respiratory 
effects of indoor exposure to NO2 (ISA, section 3.1.4.1), 
led to the conclusion that the effect of NO2 on respiratory 
health outcomes is robust and independent of the effects of other 
ambient co-pollutants.
    In addition, experimental studies conducted in animals and humans 
provide support for the plausibility of the associations reported in 
epidemiologic studies. These controlled human exposure and animal 
toxicological studies have reported effects of NO2 on immune 
system function, lung host defense, airway inflammation, and airway 
responsiveness (ISA, section 5.4). These experimental study results 
support an independent contribution of NO2 to the 
respiratory health effects reported in epidemiologic studies (ISA 
Section 5.4).
    In considering the entire body of evidence, including epidemiologic 
and experimental studies, the ISA (section 5.4, p. 5-16) concluded the 
following:

    Although this [presence of co-pollutants] complicates the 
efforts to disentangle specific NO2-related health 
effects, the evidence summarized in this assessment indicates that 
NO2 associations generally remain robust in multi-
pollutant models and supports a direct effect of short-term 
NO2 exposure on respiratory morbidity at ambient 
concentrations below the current NAAQS. The robustness of 
epidemiologic findings to adjustment for co-pollutants, coupled with 
data from animal and human experimental studies, support a 
determination that the relationship between NO2 and 
respiratory morbidity is likely causal, while still recognizing the 
relationship between NO2 and other traffic-related 
pollutants.

Comments on specific epidemiologic studies are discussed below.
    The National Association of Manufacturers (NAM) commented that the 
final REA relied on an epidemiologic study (Delfino et al. 2002) not 
critically reviewed in the final ISA. Contrary to NAM's contention, the 
study by Delfino et al. (2002) was critically reviewed by EPA staff and 
pertinent information was extracted from the study. The respiratory 
health effects of NO2 on asthma reported in this study are 
included in Figure 5.3-1, Table 5.4-1, and Annex Table AX6.3-2 of the 
ISA. While NAM comments on the narrative discussion of this study in 
the final ISA, their contention that EPA scientists did not critically 
analyze the study while preparing the final ISA is incorrect. The 
inclusion of the study in the figures and tables in this ISA, as well 
as inclusion in the 2004 PM AQCD, indicate critical analysis of the 
study that was implemented throughout the review process. The narrative 
discussion in the ISA focused on multicity studies (specifically those 
by Schwartz et al. 1994, Mortimer et al. 2002 and Schildcrout et al. 
2006), which provide substantial epidemiologic evidence for the 
respiratory health effects of NO2 on asthma among children.
    Additional comments from NAM contend that EPA's interpretation of 
three individual epidemiologic studies (e.g. Krewski et al. 2000; 
Schildcrout et al. 2006; Mortimer et al. 2002) is inconsistent across 
different NAAQS reviews. The NAM comments on all three studies are 
discussed below.
    NAM stated the following regarding the study by Krewski et al:

    In the Final ISA, EPA cites the Krewski, et al. (2000) study as 
evidence of a significant

[[Page 6486]]

association between NO2 exposure and mortality. Although 
EPA acknowledges that exposure to NO2 was ``highly 
correlated'' with other pollutants, including PM2.5 and 
SO2, EPA does not consider the analysis of the respective 
contributions of single pollutants in the same study that EPA 
included in its prior Staff Paper for Particulate Matter. In that 
document, EPA stated: ``In single-pollutant models, none of the 
gaseous co-pollutants was significantly associated with mortality 
except SO2.'' If EPA has not altered its scientific views 
concerning this study as expressed in the PM Staff Paper, it is 
entirely inappropriate for EPA to suggest that the Krewski, et al. 
(2000) study provides any evidence of an association between 
NO2 exposure and mortality.

In these comments, NAM fails to recognize that the report from Krewski 
et al. (2000) contains a reanalysis of two cohort studies, the Harvard 
Six Cities and the American Cancer Society (ACS) studies. The 
characterization in the NOX ISA of the study by Krewski et 
al. (2000), referenced by NAM in their comments, refers to the 
reanalysis of the Harvard Six Cities Study. As stated in the 
NOX ISA (p. 3-74):

    Krewski et al. (2000) conducted a sensitivity analysis of the 
Harvard Six Cities study and examined associations between gaseous 
pollutants (i.e., O3, NO2, SO2, CO) 
and mortality. NO2 showed risk estimates similar to those 
for PM2.5 per ``low to high'' range increment with total 
(1.15 [95% CI: 1.04, 1.27] per 10-ppb increase), cardiopulmonary 
(1.17 [95% CI: 1.02, 1.34]), and lung cancer (1.09 [95% CI: 0.76, 
1.57]) deaths; however, in this dataset NO2 was highly 
correlated with PM2.5 (r = 0.78), SO4 2- (r = 
0.78), and SO2 (r = 0.84).

In contrast, the characterization in the PM Staff Paper (EPA, 2005) of 
the study by Krewski et al. (2000), referenced by NAM in their 
comments, refers to the results of the ACS study. Therefore, NAM 
appears to have confused the conclusions on the results of the 
reanalysis of the Harvard Six Cities Study in the NOX ISA 
with the conclusions on the results of the reanalysis of the ACS study 
in the PM Staff Paper.
    Further, in considering the reanalysis of the ACS study by Krewski 
et al. (2000), the NOX ISA observed that ``NO2 
showed no associations with mortality outcomes'' (ISA, p. 3-74). This 
statement is consistent with the interpretation of that reanalysis as 
discussed in the PM Staff Paper. Thus, there is no inconsistency in the 
interpretation of the results of the study by Krewski et al. (2000) in 
the PM Staff Paper (EPA, 2005) and the NOX ISA (EPA, 2008a).
    NAM also commented that EPA has relied on a study by Schildcrout et 
al. (2006) in the NOX ISA but declined to rely on the same 
study for the previous review of the O3 NAAQS. NAM made the 
following comment regarding the study by Schildcrout et al:

    Another example of how EPA has reached different scientific 
conclusions in the Final ISA than in prior NAAQS documents is 
provided by the Schildcrout, et al. (2006) study. In the Final ISA, 
EPA includes an extensive discussion of this study of asthmatic 
children and the relationship purportedly found in this study 
between NO2 and various respiratory symptoms. In 
contrast, as part of the NAAQS review for ozone, EPA expressly 
declined to rely on this same study because of specific limitations 
in the study design. Among the limitations EPA cites were the fact 
that the Schildcrout, et al. (2006) study included ``children in 
which the severity of their asthma was not clearly identified,'' and 
the use of a study population that was ``not comparable to other 
large multi-city studies.'' EPA must explain why it chose to 
discount the value of the Schildcrout, et al. (2006) study when 
evaluating the effects of ozone, but has relied on it extensively in 
the Final ISA for NO2.

The study by Schildcrout et al. (2006) appeared in the peer-review 
literature too late to be considered in the 2006 O3 AQCD; 
however, this study was included in the O3 Provisional 
Assessment. The purpose of the Provisional Assessment was to determine 
if new literature materially changed any of the broad scientific 
conclusions regarding the health effects of O3 exposure as 
stated in the 2006 O3 AQCD. EPA concluded that, taken in 
context, the ``new'' information and findings did not materially change 
any of the broad scientific conclusions regarding the health effects of 
O3 exposure made in the O3 AQCD. Therefore, NAM's 
contention that EPA ``declined'' to rely on the Schildcrout study for 
the O3 review because of limitations in study design is not 
correct.
    The observations NAM draws from the O3 Provisional 
Assessment regarding severity of asthma and the study population do not 
indicate limitations that resulted in EPA ``discounting'' the study 
results. Rather, these observations were intended to put the study in 
perspective for purposes of interpreting the results within the context 
of the larger body of O3 health effects evidence. These 
observations were drawn from comments submitted by Dr. Schildcrout 
regarding the interpretation of the results of his study in the 
decision to revise the ozone standards (see docket ID EPA-HQ-OAR-2005-
0172-6991). The results of this study are being fully considered in the 
ongoing review of the ozone NAAQS.
    Finally, NAM contends that EPA reached differing scientific 
conclusions on the use of self-reported peak expiratory flow (PEF) 
depending on regulatory context, particularly in the large multi-city 
trial by Mortimer et al. (2002). We disagree with this contention. EPA 
consistently examines clinical measurements of lung function, which 
include PEF, forced expiratory flow in 1 second (FEV1), 
forced vital capacity (FVC), maximal midexpiratory flow (MMEF), maximal 
expiratory flow at 50% (MEF50), maximal expiratory flow at 
25% (MEF25), and forced expiratory flow at 25 to 75% of FVC 
(FEF25-75). Evidence for all of these clinical measurements 
is considered before drawing a conclusion related to the association of 
lung function with a criteria pollutant. In different reviews, there 
may be more evidence from one of these clinical measurements than 
another. In the previous review of the O3 NAAQS, EPA 
identified statistically significant associations between increased 
ozone levels and morning PEF, which remained significant even when 
concentrations exceeding 0.08 ppm were excluded from the analysis 
(Mortimer et al. 2002). EPA considered this evidence, along with 
evidence of other clinical measurements of changes in lung function, in 
drawing conclusions on the relationship between ozone and lung 
function. Using a similar approach to weigh the evidence pertinent to 
lung function, including studies that produced no statistically 
significant results for PEF, the NOX ISA (section 3.1.5.3) 
states:

    In summary, epidemiologic studies using data from supervised 
lung function measurements (spirometry or peak flow meters) report 
small decrements in lung function (Hoek and Brunekreef, 1994; Linn 
et al., 1996; Moshammer et al., 2006; Peacock et al., 2003; 
Schindler et al., 2001). No significant associations were reported 
in any studies using unsupervised, self-administered peak flow [PEF] 
measurements with portable devices.

The evaluation of the evidence in the NOX ISA is consistent 
with the way the evidence from multiple clinical measures of lung 
function was used in the review of the O3 NAAQS.
b. Comments on EPA's Interpretation of the Controlled Human Exposure 
Evidence
    A number of industry groups (e.g., AAM, ACC, API, Dow Chemical 
Company (Dow), EMA, NAM, UARG) disagreed with EPA's reliance on a meta-
analysis of controlled human exposure studies of airway responsiveness 
in asthmatics. Based on this meta-analysis (ISA, Table 3.1-3 for 
results), the ISA concluded that ``small but significant increases in 
nonspecific airway hyperresponsiveness were

[[Page 6487]]

observed * * * at 0.1 ppm NO2 for 60-min exposures in 
asthmatics'' (ISA, p. 5-11). Industry groups raised a number of 
objections to this analysis and the way in which it has been used in 
the current review.
    Several of these industry groups concluded that, in relying on this 
analysis, EPA has inappropriately relied on a new unpublished meta-
analysis that has not been peer-reviewed, was not reviewed by CASAC, 
and was not conducted in a transparent manner. For example, as part of 
a Request for Correction submitted under EPA's Information Quality 
Guidelines, NAM stated that ``EPA's substantial reliance on an 
unpublished assessment described as a ``meta-analysis'' of the relation 
between NO2 exposure and changes in airway responsiveness 
violates EPA Guidelines requiring ``transparency about data and 
methods.''
    EPA disagrees with this characterization of the updated meta-
analysis included in the final ISA. As described in the ISA (p. 3-16), 
this meta-analysis is based on an earlier analysis by Folinsbee (1992) 
that has been subject to peer-review, that was published in a 
scientific journal (Toxicol Ind Health. 8:1-11, 1992), and that was 
reviewed by CASAC as part of the previous review of the NO2 
NAAQS (EPA, 1993, Table 15-10). The updates to this earlier analysis 
did not include substantive changes to the approach. As discussed in 
the final ISA (p. 3-16), the changes made to the analysis were to 
remove the results of one allergen study and add results from a non-
specific responsiveness study, which focused the meta-analysis on non-
specific airway responsiveness, and to discuss results for an 
additional exposure concentration (i.e., 100 ppb). The information 
needed to reproduce this meta-analysis is provided in the ISA (Tables 
3.1-2 and 3.1-3, including footnotes).
    While the ISA meta-analysis reports findings on airway 
responsiveness in asthmatics following exposure to 100 ppb 
NO2, a concentration not specifically discussed in the 
findings of the original report by Folinsbee (1992), this does not 
constitute a substantive change to that original analysis. For 
exposures at rest, four of the studies included in the analysis by 
Folinsbee evaluated the effects of exposure to 100 ppb NO2. 
In that original meta-analysis, these studies were grouped with another 
study that evaluated exposures to 140 ppb NO2. When analyzed 
together, exposures to NO2 concentrations of 100 ppb and 140 
ppb (grouped together in the manuscript and described as less than 0.2 
ppm) increased airway responsiveness in 65% of resting asthmatics (p 2 in the 
ISA meta-analysis reflects a change in the way the data are presented 
and does not reflect a substantive change to the study. This change in 
presentation allows specific consideration of the potential for 
exposures to 100 ppb NO2 to increase airway responsiveness, 
rather than grouping results at 100 ppb with results at other exposure 
concentrations.
    In addition, the updated meta-analysis was considered by CASAC 
during their review of the REA (REA, Table 4-5 reports the results of 
the updated meta-analysis), which based part of the assessment of 
NO2-associated health risks on the results of the meta-
analysis. In their letter to the Administrator on the final REA (Samet, 
2008b), CASAC stated that ``[t]he evidence reviewed in the REA 
indicates that adverse health effects have been documented in clinical 
studies of persons with asthma at 100 ppb'' and that ``CASAC firmly 
recommends that the upper end of the range [of standard levels] not 
exceed 100 ppb, given the findings of the REA.'' In addition, in their 
comments on the proposal, CASAC reiterated this advice in their 
statement that ``the level of the one-hour NO2 standard 
should be within the range of 80-100 ppb and not above 100 ppb.'' These 
statements indicate that CASAC did specifically consider the results of 
the updated meta-analysis and that they used those results to inform 
their recommendations on the range of standard levels supported by the 
scientific evidence.
    In summary, we note the following:
     The original meta-analysis was published in a peer-
reviewed journal and was reviewed by CASAC in the previous review of 
the NO2 NAAQS.
     The updated meta-analysis does not include substantive 
changes to the methodology of this original analysis.
     The changes that were made are clearly described in the 
ISA.
     CASAC specifically reviewed and considered the ISA meta-
analysis in making recommendations regarding the range of standard 
levels supported by the science.
    Many of these same industry groups also referred in their comments 
to a recent meta-analysis of controlled human exposure studies 
evaluating the airway response in asthmatics following NO2 
exposure (Goodman et al., 2009). These groups generally recommended 
that EPA rely on this meta-analysis and on the authors' conclusions 
with regard to NO2 and airway responsiveness. Specific 
comments based on the manuscript by Goodman et al., as well as EPA's 
responses, are discussed below in more detail.\9\
---------------------------------------------------------------------------

    \9\ EPA considers the Goodman study to be a ``new study'' on 
which, as discussed above in section 1.B, it would not be 
appropriate to base a standard in the absence of thorough CASAC and 
public review of the study and its methodology. However, as 
discussed below, EPA has considered the study in the context of 
responding to public comments on the proposal and has concluded it 
does not provide a basis to materially change any of the broad 
scientific conclusions regarding the health effects of 
NO2 made in the air quality criteria.
---------------------------------------------------------------------------

    Industry commenters generally claimed that the meta-analysis by 
Goodman et al. supports the conclusion that no adverse effects occur 
following exposures up to 600 ppb NO2. However, Table 4 of 
the Goodman study reports that 64% (95% Confidence Interval: 58%, 71%) 
of resting asthmatics exposed to NO2 experienced an increase 
in airway responsiveness. Furthermore, Figure 2a of this manuscript 
reports that for exposures 2-induced airway 
hyperresponsiveness is not adverse and, therefore, should not be 
considered in setting standards. The basis for this comment appears to 
be the conclusions reached by Goodman et al. that there is no dose-
response relationship for NO2 and that the magnitude of any 
NO2 effect on airway responsiveness is too small to be 
considered adverse.
    Due to differences in study protocols in the NO2-airway 
response literature (ISA, section 3.1.3), EPA disagrees with the 
approach taken in the Goodman study to use existing data to attempt to 
evaluate the presence of a dose-response relationship and to determine 
the magnitude of the NO2 response. Examples of differences 
in the study protocols include the NO2 exposure method 
(i.e., mouthpiece versus chamber), subject activity level (i.e., rest 
versus exercise) during NO2 exposure, choice of airway 
challenge agent, and physiological endpoint used to quantify airway 
responses. Goodman et al. (2009) also recognized heterogeneity among 
studies as a limitation in their analyses.
    As a result of these differences, EPA judged it appropriate in the 
ISA meta-analysis to assess only the fraction of asthmatics 
experiencing increased or decreased airway responsiveness

[[Page 6488]]

following NO2 exposure. We have acknowledged in the REA, the 
proposal, and in this final rulemaking that there is uncertainty with 
regard to the magnitude and the clinical-significance of 
NO2-induced increases in airway responsiveness (see sections 
II.C.3 and II.F.4.a in the proposed rulemaking as well as II.F.3 in 
this final rulemaking). The REA stated the following (p. 302):

    [O]ne of the important uncertainties associated with these 
[NO2-induced airway hyperresponsiveness] results is that, 
because the meta-analysis evaluated only the direction of the change 
in airway responsiveness, it is not possible to discern the 
magnitude of the change from these data. This limitation makes it 
particularly difficult to quantify the public health implications of 
these results.

    While we acknowledge this uncertainty, EPA disagrees with the 
conclusion that the NO2-induced increase in airway 
responsiveness in asthmatics exposed to NO2 concentrations 
up to 600 ppb is not adverse and should not be considered in setting 
standards. Specifically, we note that the ISA concluded that 
``[t]ransient increases in airway responsiveness following 
NO2 exposure have the potential to increase symptoms and 
worsen asthma control'' (ISA, section 5.4). The uncertainty over the 
adversity of the response reported in controlled human exposure studies 
does not mean that the NO2-induced increase in airway 
responsiveness is not adverse. Rather, it means that there is a risk of 
adversity, especially for asthmatics with more than mild asthma, but 
that this risk cannot be fully characterized based on existing studies. 
The studies of NO2 and airway responsiveness included in the 
meta-analysis have generally evaluated mild asthmatics, rather than 
more severely affected asthmatics who could be more susceptible to the 
NO2-induced increase in airway responsiveness (ISA, section 
3.1.3.2). Given that this is the case, and given the large percentage 
of asthmatics that experienced an NO2-induced increase in 
airway responsiveness in the studies and the large size of the 
asthmatic population in the United States, the REA concluded that it is 
appropriate to consider NO2-induced airway 
hyperresponsiveness in characterizing NO2-associated health 
risks (REA, section 10.3.2). As noted above, CASAC endorsed this 
conclusion in their letters to the Administrator on the final REA and 
on the proposal (Samet, 2008b; Samet, 2009).
c. Comments on EPA's Characterization of NO2-Associated 
Exposures and Health Risks
    Several commenters discussed the analyses of NO2-
associated exposures and health risks presented in the REA. As in past 
reviews (EPA 2005, 2007c, 2007d), EPA has estimated allowable risks 
associated with the current standard and potential alternative 
standards to inform judgments on the public health risks that could 
exist under different standard options. Some industry commenters (e.g., 
API, NMA) concluded that the Administrator should consider modeled 
exposures and risks associated with actual NO2 air quality 
rather than with NO2 concentrations adjusted to simulate 
just meeting the current annual standard or potential alternative 1-
hour standards. These commenters pointed out that such simulations 
require large adjustments to air quality and are highly uncertain and 
that NAAQS are intended to address actual, rather than highly 
improbable, risks to health.
    We disagree with these commenters that exposure- and risk-related 
considerations in the NAAQS review should rely only on unadjusted air 
quality. In considering whether the current standard is requisite to 
protect public health with an adequate margin of safety, air quality 
adjustments allow estimates of NO2-related exposures and 
health risks that could exist in areas that just meet that standard. 
That is, these adjustments allow consideration of exposures and risks 
that would be permissible under the current standard. Therefore, such 
adjustments are clearly useful to inform a decision on the issue before 
EPA (i.e., the adequacy of the level of public health protection 
associated with allowable NO2 air quality under the 
standard). Similarly, air quality adjustments to simulate different 
potential alternative standards provide information on exposures and 
risks that would be permissible under these alternatives.\10\ As noted 
above, in their letter to the Administrator on the final REA (Samet, 
2008b), CASAC concluded that ``The REA provides the needed bridge from 
the evidence presented in the ISA to a characterization of the 
exposures and the associated risks with different profiles of 
exposure.''
---------------------------------------------------------------------------

    \10\ Once EPA determines whether to retain or revise the current 
standard, the actual air quality levels in various areas of the 
country are clearly relevant under the NAAQS implementation 
provisions for the Act, such as the provision for designation of 
areas based on whether or not they attain the required NAAQS.
---------------------------------------------------------------------------

    We agree that there are uncertainties inherent in air quality 
adjustments. These uncertainties are discussed thoroughly in the REA 
(sections 7.4, 8.12, 9.6, and 10.3.2.1) and in the proposed rule 
(section II.C.3). For example, the policy assessment chapter of the REA 
(section 10.3.2.1) noted the following regarding adjustment of 
NO2 concentrations:

    In order to simulate just meeting the current annual standard 
and many of the alternative 1-h standards analyzed, an upward 
adjustment of recent ambient NO2 concentrations was 
required. We note that this adjustment does not reflect a judgment 
that levels of NO2 are likely to increase under the 
current standard or any of the potential alternative standards under 
consideration. Rather, these adjustments reflect the fact that the 
current standard, as well as some of the alternatives under 
consideration, could allow for such increases in ambient 
NO2 concentrations. In adjusting air quality to simulate 
just meeting these standards, we have assumed that the overall shape 
of the distribution of NO2 concentrations would not 
change. While we believe this is a reasonable assumption in the 
absence of evidence supporting a different distribution and we note 
that available analyses support this approach (Rizzo, 2008), we 
recognize this as an important uncertainty. It may be an especially 
important uncertainty for those scenarios where considerable upward 
adjustment is required to simulate just meeting one or more of the 
standards.

These air quality adjustments are not meant to imply an expectation 
that NO2 concentrations will increase broadly across the 
United States or in any given area (REA, section 10.3.2.1). Rather, as 
noted above, they are meant to estimate NO2-related 
exposures and health risks that would be permitted under the current 
and potential alternative standards. Such estimates can inform 
decisions on whether the current standard, or particular potential 
alternative standards, provide the requisite protection of public 
health.
3. Conclusions Regarding the Adequacy of the Current Standard
    In considering the adequacy of the current standard, the 
Administrator has considered the scientific evidence assessed in the 
ISA, the exposure and risk results presented in the REA, the 
conclusions of the policy assessment chapter of the REA, and comments 
from CASAC and the public. These considerations are described below.
    In considering the scientific evidence as it relates to the 
adequacy of the current standard, the Administrator notes that the 
epidemiologic evidence has grown substantially since the last review 
with the addition of field and panel studies, intervention studies, and 
time-series studies of effects such as emergency department visits and 
hospital admissions associated with

[[Page 6489]]

short-term NO2 exposures. No epidemiologic studies were 
available in 1993 assessing relationships between NO2 and 
outcomes such as hospital admissions or emergency department visits. In 
contrast, dozens of epidemiologic studies on such outcomes, conducted 
at recent and current ambient NO2 concentrations, are now 
included in this evaluation (ISA, chapter 3).
    As an initial consideration with regard to the adequacy of the 
current standard, the Administrator notes that the evidence relating 
long-term (weeks to years) NO2 exposures at current ambient 
concentrations to adverse health effects was judged in the ISA to be 
either ``suggestive but not sufficient to infer a causal relationship'' 
(respiratory morbidity) or ``inadequate to infer the presence or 
absence of a causal relationship'' (mortality, cancer, cardiovascular 
effects, reproductive/developmental effects) (ISA, sections 5.3.2.4-
5.3.2.6). In contrast, the evidence relating short-term (minutes to 
hours) NO2 exposures to respiratory morbidity was judged to 
be ``sufficient to infer a likely causal relationship'' (ISA, section 
5.3.2.1). This conclusion was supported primarily by a large body of 
recent epidemiologic studies that evaluated associations of short-term 
NO2 concentrations with respiratory symptoms, emergency 
department visits, and hospital admissions. Given these conclusions 
from the ISA, the Administrator judges that, at a minimum, 
consideration of the adequacy of the current annual standard should 
take into account the extent to which that standard provides protection 
against respiratory effects associated with short-term NO2 
exposures.
    In considering the NO2 epidemiologic studies as they 
relate to the adequacy of the current standard, the Administrator notes 
that annual average NO2 concentrations were below the level 
of the current annual NO2 NAAQS in many of the locations 
where positive, and often statistically significant, associations with 
respiratory morbidity endpoints have been reported (ISA, section 5.4). 
As discussed previously, the ISA characterized that evidence for 
respiratory effects as consistent and coherent. The evidence is 
consistent in that associations are reported in studies conducted in 
numerous locations and with a variety of methodological approaches 
(ISA, section 5.3.2.1). It is coherent in the sense that the studies 
report associations with respiratory health outcomes that are logically 
linked together (ISA, section 5.3.2.1). The ISA noted that when the 
epidemiologic literature is considered as a whole, there are generally 
positive associations between NO2 and respiratory symptoms, 
hospital admissions, and emergency department visits. A number of these 
associations are statistically significant, particularly the more 
precise effect estimates (ISA, section 5.3.2.1).
    As discussed in the proposal (II.E.1) and above, the Administrator 
acknowledges that the interpretation of these NO2 
epidemiologic studies is complicated by the fact that on-road vehicle 
exhaust emissions are a nearly ubiquitous source of combustion 
pollutant mixtures that include NO2. She notes that, in 
order to provide some perspective on the uncertainty related to the 
presence of co-pollutants the ISA evaluated epidemiologic studies that 
employed multi-pollutant models, epidemiologic studies of indoor 
NO2 exposure, and experimental studies. Specifically, the 
ISA noted that a number of NO2 epidemiologic studies have 
attempted to disentangle the effects of NO2 from those of 
co-occurring pollutants by employing multi-pollutant models. When 
evaluated as a whole, NO2 effect estimates in these models 
generally remained robust when co-pollutants were included. Therefore, 
despite uncertainties associated with separating the effects of 
NO2 from those of co-occurring pollutants, the ISA (section 
5.4, p. 5-16) concluded that ``the evidence summarized in this 
assessment indicates that NO2 associations generally remain 
robust in multi-pollutant models and supports a direct effect of short-
term NO2 exposure on respiratory morbidity at ambient 
concentrations below the current NAAQS.'' With regard to indoor 
studies, the ISA noted that these studies can test hypotheses related 
to NO2 specifically (ISA, section 3.1.4.1). Although 
confounding by indoor combustion sources is a concern, indoor studies 
are not confounded by the same mix of co-pollutants present in the 
ambient air or by the contribution of NO2 to the formation 
of secondary particles or O3 (ISA, section 3.1.4.1). The ISA 
noted that the findings of indoor NO2 studies are consistent 
with those of studies using ambient concentrations from central site 
monitors and concluded that indoor studies provide evidence of 
coherence for respiratory effects (ISA, section 3.1.4.1). With regard 
to experimental studies, the REA noted that they have the advantage of 
providing information on health effects that are specifically 
associated with exposure to NO2 in the absence of co-
pollutants. The ISA concluded that the NO2 epidemiologic 
literature is supported by (1) evidence from controlled human exposure 
studies of airway hyperresponsiveness in asthmatics, (2) controlled 
human exposure and animal toxicological studies of impaired host-
defense systems and increased risk of susceptibility to viral and 
bacterial infection, and (3) controlled human exposure and animal 
toxicological studies of airway inflammation (ISA, section 5.3.2.1 and 
5.4). Given the above consideration of the evidence, particularly the 
epidemiologic studies reporting NO2-associated health 
effects in locations that meet the current standard, the Administrator 
agrees with the conclusion in the policy assessment chapter of the REA 
that the scientific evidence calls into question the adequacy of the 
current standard to protect public health.
    In addition to the evidence-based considerations described above, 
the Administrator has considered the extent to which exposure- and 
risk-based information can inform decisions regarding the adequacy of 
the current annual NO2 standard. While she acknowledges the 
uncertainties associated with adjusting air quality in these analyses, 
she judges that such analyses are appropriate for consideration in this 
review of the NO2 primary NAAQS. In reaching this conclusion 
she notes the considerations discussed above, particularly the 
endorsement by CASAC of the REA and its characterization of 
NO2-associated exposures and health risks.
    In considering the exposure- and risk-based information with regard 
to the adequacy of the current annual NO2 standard to 
protect the public health, the Administrator notes the conclusion in 
the policy assessment chapter of the REA that risks estimated to be 
associated with air quality adjusted upward to simulate just meeting 
the current standard can reasonably be concluded to be important from a 
public health perspective. In particular, a large percentage (8-9%) of 
respiratory-related ED visits in Atlanta could be associated with 
short-term NO2 exposures, most asthmatics in Atlanta could 
be exposed on multiple days per year to NO2 concentrations 
at or above 300 ppb, and most locations evaluated could experience on-/
near-road NO2 concentrations above 100 ppb on more than half 
of the days in a given year. Therefore, after considering the results 
of the exposure and risk analyses presented in the REA the 
Administrator agrees with the conclusion of the policy assessment 
chapter of the REA that exposure- and risk-based results reinforce the 
scientific evidence in

[[Page 6490]]

supporting the conclusion that consideration should be given to 
revising the current standard so as to provide increased public health 
protection, especially for at-risk groups, from NO2-related 
adverse health effects associated with short-term, and potential long-
term, exposures.
    In reaching a conclusion on the adequacy of the current standard, 
the Administrator has also considered advice received from CASAC. In 
their comments on the final REA, CASAC agreed that the primary concern 
in this review is to protect against health effects that have been 
associated with short-term NO2 exposures. CASAC also agreed 
that the current annual standard is not sufficient to protect public 
health against the types of exposures that could lead to these health 
effects. As noted in their letter to the EPA Administrator, ``CASAC 
concurs with EPA's judgment that the current NAAQS does not protect the 
public's health and that it should be revised'' (Samet, 2008b).
    Based on the considerations discussed above, the Administrator 
concludes that the current NO2 primary NAAQS alone is not 
requisite to protect public health with an adequate margin of safety. 
Accordingly, she concludes that the NO2 primary standard 
should be revised in order to provide increased public health 
protection against respiratory effects associated with short-term 
exposures, particularly for susceptible populations such as asthmatics, 
children, and older adults. In considering approaches to revising the 
current standard, the Administrator concludes that it is appropriate to 
consider setting a new short-term standard (see below). The 
Administrator notes that such a short-term standard could provide 
increased public health protection, especially for members of at-risk 
groups, from effects described in both epidemiologic and controlled 
human exposure studies to be associated with short-term exposures to 
NO2.

F. Elements of a New Short-Term Standard

    In considering a revised NO2 primary NAAQS, the 
Administrator notes the need to protect at-risk individuals from short-
term exposures to NO2 air quality that could cause the types 
of respiratory morbidity effects reported in epidemiologic studies and 
the need to protect at-risk individuals from short-term exposure to 
NO2 concentrations reported in controlled human exposure 
studies to increase airway responsiveness in asthmatics. The 
Administrator's considerations with regard to her decisions are 
discussed in the following sections in terms of indicator (II.F.1), 
averaging time (II.F.2), level (II.F.3), and form (II.F.4).
1. Indicator
a. Rationale for Proposed Decision
    In past reviews, EPA has focused on NO2 as the most 
appropriate indicator for ambient NOX. In making a decision 
in the current review on the most appropriate indicator, the 
Administrator considered the conclusions of the ISA and the policy 
assessment chapter of the REA as well as the view expressed by CASAC. 
The policy assessment chapter of the REA noted that, while the presence 
of NOX species other than NO2 has been 
recognized, no alternative to NO2 has been advanced as being 
a more appropriate surrogate. Controlled human exposure studies and 
animal toxicology studies assessed in the ISA provide specific evidence 
for health effects following exposure to NO2. Epidemiologic 
studies also typically report levels of NO2 though the 
degree to which monitored NO2 reflects actual NO2 
levels, as opposed to NO2 plus other gaseous NOX, 
can vary (REA, section 2.2.3). In addition, because emissions that lead 
to the formation of NO2 generally also lead to the formation 
of other NOX oxidation products, measures leading to 
reductions in population exposures to NO2 can generally be 
expected to lead to reductions in population exposures to other gaseous 
NOX. Therefore, an NO2 standard can also be 
expected to provide some degree of protection against potential health 
effects that may be independently associated with other gaseous 
NOX even though such effects are not discernable from 
currently available studies indexed by NO2 alone. Given 
these key points, the policy assessment chapter of the REA concluded 
that the evidence supports retaining NO2 as the indicator. 
Consistent with this conclusion, the CASAC Panel stated in its letter 
to the EPA Administrator that it ``concurs with retention of 
NO2 as the indicator'' (Samet, 2008b). In light of the above 
considerations, the Administrator proposed to retain NO2 as 
the indicator in the current review.
b. Comments on Indicator
    A relatively small number of comments directly addressed the issue 
of the indicator for the standard (CASAC, Dow, API, AAM, and the 
Missouri Department of Natural Resources Air Pollution Control Program 
(MODNR)). All of these commenters endorsed the proposal to continue to 
use NO2 as the indicator for ambient NOX.
c. Conclusions on Indicator
    Based on the available information discussed above, and consistent 
with the views of CASAC and other commenters, the Administrator 
concludes that it is appropriate to continue to use NO2 as 
the indicator for a standard that is intended to address effects 
associated with exposure to NO2, alone or in combination 
with other gaseous NOX. In so doing, the Administrator 
recognizes that measures leading to reductions in population exposures 
to NO2 will also reduce exposures to other nitrogen oxides.
2. Averaging Time
    This section discusses considerations related to the averaging time 
of the NO2 primary NAAQS. Specifically, this section 
summarizes the rationale for the Administrator's proposed decision 
regarding averaging time (II.F.2.a; see section II.F.2 of the proposal 
for more detail), discusses comments related to averaging time 
(II.F.2.b), and presents the Administrator's final conclusions 
regarding averaging time (II.F.2.c).
a. Rationale for Proposed Decision
    In considering the most appropriate averaging time for the 
NO2 primary NAAQS, the Administrator noted in the proposal 
the conclusions and judgments made in the ISA about available 
scientific evidence, air quality correlations discussed in the REA, 
conclusions of the policy assessment chapter of the REA, and CASAC 
recommendations (section II.F.2 in the proposal). Specifically, she 
noted the following:
     Experimental studies in humans and animals have reported 
respiratory effects following NO2 exposures lasting from 
less than 1-hour up to several hours. Epidemiologic studies have 
reported associations between respiratory effects and both 1 hour and 
24-hour NO2 concentrations. Therefore, the experimental 
evidence provides support for an averaging time of shorter duration 
than 24 hours (e.g., 1 hour) while the epidemiologic evidence provides 
support for both 1-hour and 24-hour averaging times. At a minimum, this 
suggests that a primary concern with regard to averaging time is the 
level of protection provided against 1-hour NO2 
concentrations.
     Air quality correlations presented in the policy 
assessment chapter of the REA illustrated the relatively high degree of 
variability in the ratios of annual average to short-term 
NO2 concentrations (REA, Table 10-2). This

[[Page 6491]]

variability suggests that a standard based on annual average 
NO2 concentrations would not likely be an effective or 
efficient approach to focus protection on short-term exposures.
     These air quality correlations (REA, Table 10-1) suggested 
that a standard based on 1-hour daily maximum NO2 
concentrations could also be effective at protecting against 24-hour 
NO2 concentrations.
     The policy assessment chapter of the REA concluded that 
the scientific evidence, combined with the air quality correlations, 
support the appropriateness of a standard based on 1-hour daily maximum 
NO2 concentrations to protect against health effects 
associated with short-term exposures.
     CASAC concurred ``with having a short-term NAAQS primary 
standard for oxides of nitrogen and using the one-hour maximum 
NO2 value'' (Samet, 2008b).

Based on these considerations, the Administrator proposed to set a new 
standard based on 1-hour daily maximum NO2 concentrations.
b. Comments on averaging time
    As discussed above, CASAC endorsed the establishment of a new 
standard with a 1-hour averaging time. CASAC stated the following in 
their comments on the proposal (Samet, 2009):

    In reviewing the REA, CASAC supported a short-term standard for 
NO2 and in reviewing the proposal, CASAC supports the 
proposed one-hour averaging time in EPA's proposed rule.

The supporting rationale offered by CASAC in support of a new 1-hour 
standard was generally the same as that put forward in the final REA 
and the proposal. Specifically, that rationale considered the available 
scientific evidence, which supports a link between 1-hour 
NO2 concentrations and adverse respiratory effects, and air 
quality information presented in the REA, which suggests that a 1-hour 
standard can protect against effects linked to short-term 
NO2 exposures while an annual standard would not be an 
effective or efficient approach to protecting against these effects.
    A large number of public commenters also endorsed the establishment 
of a new standard with a 1-hour averaging time. These included a number 
of State agencies and organizations (e.g., NACAA, NESCAUM and agencies 
in CA, IL, NM, TX, VA); environmental, medical, and public health 
organizations (e.g., ACCP, ALA, AMA, ATS, CAC, EDF, EJ, GASP, NACPR, 
NAMDRC, NRDC); and most individual commenters. The supporting 
rationales offered by these commenters often acknowledged the 
recommendations of CASAC and the Administrator's rationale as discussed 
in the proposal.
    Though many industry commenters recommended not revising the 
current annual standard (as discussed above in section II.E.2), several 
of these groups did conclude that if a short-term standard were to be 
set, a 1-hour averaging time would be appropriate (e.g., Colorado 
Petroleum Association (CPA), Dow, NAM, Petroleum Association of Wyoming 
(PAW), Utah Petroleum Association (UPA)). As discussed above, industry 
commenters who disagreed with setting a new 1-hour standard generally 
based this conclusion on their interpretation of the scientific 
evidence and their conclusion that this evidence does not support the 
need to revise the current annual standard. These comments, and EPA's 
responses, are discussed in more detail above (section II.E) and in the 
Response to Comments document.
c. Conclusions on Averaging Time
    In considering the most appropriate averaging time for the 
NO2 primary NAAQS, the Administrator notes the available 
scientific evidence as assessed in the ISA, the air quality analyses 
presented in the REA, the conclusions of the policy assessment chapter 
of the REA, CASAC recommendations, and public comments received. These 
considerations are described below.
    When considering averaging time, the Administrator notes that the 
evidence relating short-term (minutes to hours) NO2 
exposures to respiratory morbidity was judged in the ISA to be 
``sufficient to infer a likely causal relationship'' (ISA, section 
5.3.2.1) while the evidence relating long-term (weeks to years) 
NO2 exposures to adverse health effects was judged to be 
either ``suggestive but not sufficient to infer a causal relationship'' 
(respiratory morbidity) or ``inadequate to infer the presence or 
absence of a causal relationship'' (mortality, cancer, cardiovascular 
effects, reproductive/developmental effects) (ISA, sections 5.3.2.4-
5.3.2.6). Thus, the Administrator concludes that these judgments most 
directly support an averaging time that focuses protection on short-
term exposures to NO2.
    As in past reviews of the NO2 NAAQS, the Administrator 
notes that it is instructive to evaluate the potential for a standard 
based on annual average NO2 concentrations, as is the 
current standard, to provide protection against short-term 
NO2 exposures. To this end, the Administrator notes that 
Table 10-1 in the REA reported the ratios of short-term to annual 
average NO2 concentrations. Ratios of 1-hour daily maximum 
concentrations (98th and 99th percentile \11\) to annual average 
concentrations across 14 locations ranged from 2.5 to 8.7 while ratios 
of 24-hour average concentrations to annual average concentrations 
ranged from 1.6 to 3.8 (see Thompson, 2008 for more details). The 
policy assessment chapter of the REA concluded that the variability in 
these ratios across locations, particularly those for 1-hour 
concentrations, suggested that a standard based on annual average 
NO2 concentrations would not likely be an effective or 
efficient approach to focus protection on short-term NO2 
exposures. For example, in an area with a relatively high ratio (e.g., 
8), the current annual standard (53 ppb) would be expected to allow 1-
hour daily maximum NO2 concentrations of about 400 ppb. In 
contrast, in an area with a relatively low ratio (e.g., 3), the current 
standard would be expected to allow 1-hour daily maximum NO2 
concentrations of about 150 ppb. Thus, for purposes of protecting 
against the range of 1-hour NO2 exposures, the REA noted 
that a standard based on annual average concentrations would likely 
require more control than necessary in some areas and less control than 
necessary in others, depending on the standard level selected.
---------------------------------------------------------------------------

    \11\ As discussed below, 98th and 99th percentile forms were 
evaluated in the REA. A 99th percentile form corresponds 
approximately to the 4th highest 1-hour concentration in a year 
while a 98th percentile form corresponds approximately to the 7th or 
8th highest 1-hour concentration in a year. A 4th highest 
concentration form has been used previously in the O3 
NAAQS while a 98th percentile form has been used previously in the 
PM2.5 NAAQS.
---------------------------------------------------------------------------

    In considering the level of support available for specific short-
term averaging times, the Administrator notes that the policy 
assessment chapter of the REA considered evidence from both 
experimental and epidemiologic studies. Controlled human exposure 
studies and animal toxicological studies provide evidence that 
NO2 exposures from less than 1-hour up to 3-hours can result 
in respiratory effects such as increased airway responsiveness and 
inflammation (ISA, section 5.3.2.7). Specifically, the ISA concluded 
that NO2 exposures of 100 ppb for 1-hour (or 200 ppb to 300 
ppb for 30-min) can result in small but significant increases in 
nonspecific airway responsiveness (ISA, section 5.3.2.1). In contrast, 
the epidemiologic literature provides support for short-term averaging 
times ranging from approximately 1-hour up to 24-hours (ISA, section 
5.3.2.7). A

[[Page 6492]]

number of epidemiologic studies have detected positive associations 
between respiratory morbidity and 1-hour (daily maximum) and/or 24-hour 
NO2 concentrations. A few epidemiologic studies have 
considered both 1-hour and 24-hour averaging times, allowing 
comparisons to be made. The ISA reported that such comparisons in 
studies that evaluate asthma emergency department visits failed to 
reveal differences between effect estimates based on a 1-hour averaging 
time and those based on a 24-hour averaging time (ISA, section 
5.3.2.7). Therefore, the ISA concluded that it is not possible, from 
the available epidemiologic evidence, to discern whether effects 
observed are attributable to average daily (or multi-day) 
concentrations (24-hour average) or high, peak exposures (1-hour 
maximum) (ISA, section 5.3.2.7).
    As noted in the policy assessment chapter of the REA, given the 
above conclusions, the experimental evidence provides support for an 
averaging time of shorter duration than 24 hours (e.g., 1-h) while the 
epidemiologic evidence provides support for both 1-hour and 24-hour 
averaging times. The Administrator concludes that, at a minimum, this 
suggests that a primary concern with regard to averaging time is the 
level of protection provided against 1-hour NO2 
concentrations. However, she also notes that it is important to 
consider the ability of a 1-hour averaging time to protect against 24-
hour average NO2 concentrations. To this end, the 
Administrator notes that Table 10-2 in the REA presented correlations 
between 1-hour daily maximum NO2 concentrations and 24-hour 
average NO2 concentrations (98th and 99th percentile) across 
14 locations (see Thompson, 2008 for more detail). Typical ratios 
ranged from 1.5 to 2.0, though one ratio (Las Vegas) was 3.1. These 
ratios were far less variable than those discussed above for annual 
average concentrations, suggesting that a standard based on 1-hour 
daily maximum NO2 concentrations could also be effective at 
protecting against 24-hour NO2 concentrations. The REA 
concluded that the scientific evidence, combined with the air quality 
correlations described above, support the appropriateness of a standard 
based on 1-hour daily maximum NO2 concentrations to protect 
against health effects associated with short-term exposures.
    Based on these considerations, the Administrator concludes that a 
standard with a 1-hour averaging time can effectively limit short-term 
(i.e., 1- to 24-hours) exposures that have been linked to adverse 
respiratory effects. This conclusion is based on the observations 
summarized above and in more detail in the proposal, particularly that: 
(1) The 1-hour averaging time has been directly associated with 
respiratory effects in both epidemiologic and experimental studies and 
that (2) results from air quality analyses suggest that a 1-hour 
standard could also effectively control 24-hour NO2 
concentrations. In addition, the Administrator notes the support 
provided for a 1-hour averaging time in comments from CASAC, States, 
environmental groups, and medical/public health groups. The 
Administrator notes that arguments offered by some industry groups 
against setting a 1-hour NO2 standard generally focus on 
commenters' conclusions regarding uncertainties in the scientific 
evidence. As discussed in more detail above (section II.E.2), the 
Administrator disagrees with the conclusions of these commenters 
regarding the appropriate interpretation of the scientific evidence and 
associated uncertainties. Given these considerations, the Administrator 
judges that it is appropriate to set a new NO2 standard with 
a 1-hour averaging time.
3. Form
    This section discusses considerations related to the form of the 1-
hour NO2 primary NAAQS. Specifically, this section 
summarizes the rationale for the Administrator's proposed decision 
regarding form (II.F.4.a; see section II.F.3 of the proposal for more 
detail), discusses comments related to form (II.F.4.b), and presents 
the Administrator's final conclusions regarding form (II.F.4.c).
a. Rationale For Proposed Decision
    When considering alternative forms in the proposal, the 
Administrator noted the conclusions in the policy assessment chapter of 
the REA. Specifically, she noted the conclusion that the adequacy of 
the public health protection provided by the combination of standard 
level and form should be the foremost consideration. With regard to 
this, she noted that concentration-based forms can better reflect 
pollutant-associated health risks than forms based on expected 
exceedances. This is the case because concentration-based forms give 
proportionally greater weight to years when pollutant concentrations 
are well above the level of the standard than to years when the 
concentrations are just above the standard, while an expected 
exceedance form would give the same weight to years with concentrations 
that just exceed the standard as to years when concentrations greatly 
exceed the standard. The Administrator also recognized the conclusion 
in the policy assessment chapter of the REA that it is desirable from a 
public health perspective to have a form that is reasonably stable and 
insulated from the impacts of extreme meteorological events. With 
regard to this, she noted that a form that calls for averaging 
concentrations over three years would provide greater regulatory 
stability than a form based on a single year of concentrations. 
Therefore, consistent with recent reviews of the O3 and PM 
NAAQS, the proposal focused on concentration-based forms averaged over 
3 years, as evaluated in the REA.
    In considering specific concentration-based forms, the REA focused 
on 98th and 99th percentile concentrations averaged over 3 years. This 
focus on the upper percentiles of the distribution is appropriate given 
the reliance, in part, on NO2 health evidence from 
experimental studies, which provide information on specific exposure 
concentrations that are linked to specific health effects. The REA 
noted that a 99th percentile form for a 1-hour daily maximum standard 
would correspond approximately to the 4th highest daily maximum 
concentration in a year (which is the form of the current O3 
NAAQS) while a 98th percentile form (which is the form of the current 
short-term PM2.5 NAAQS) would correspond approximately to 
the 7th or 8th highest daily maximum concentration in a year (REA, 
Table 10-4; see Thompson, 2008 for methods).
    Consideration in the REA of an appropriate form for a 1-hour 
standard was based on analyses of standard levels that reflected the 
allowable area-wide NO2 concentration, not the maximum 
allowable concentration. Therefore, in their review of the final REA, 
CASAC did not have the opportunity to comment on the appropriateness of 
specific forms in conjunction with a standard level that reflects the 
maximum allowable NO2 concentration anywhere in an area. 
Given this, when considering alternative forms for the 1-hour standard 
in the proposal, the Administrator judged that it was appropriate to 
consider both forms evaluated in the REA (i.e., 98th and 99th 
percentiles). Therefore, she proposed to adopt either a 99th percentile 
or a 4th highest form, averaged over 3 years, and she solicited comment 
on both 98th percentile and 7th or 8th highest forms.
b. CASAC and Public Comments on Form
    In their letter to the Administrator, CASAC discussed the issue of 
form within the context of the proposed

[[Page 6493]]

approach of setting a 1-hour standard level that reflects the maximum 
allowable NO2 concentration anywhere in an area. CASAC 
recommended that, for such a standard, EPA adopt a form based on the 3-
year average of the 98th percentile of the distribution of 1-hour daily 
maximum NO2 concentrations. Specifically, they stated the 
following in their comments on the proposal (Samet, 2009):

    The 98th percentile is preferred by CASAC for the form, given 
the likely instability of measurements at the upper range and the 
absence of data from the proposed two-tier approach.

As indicated in their letter, CASAC concluded that the potential 
instability in higher percentile NO2 concentrations near 
major roads argues for a 98th, rather than a 99th, percentile form. 
Several State organizations and agencies (e.g., NESCAUM and agencies in 
IN, NC, SD, VA) and industry groups (e.g., AAM, ACC, API, AirQuality 
Research and Logistics (AQRL), CPA, Dow, ExxonMobil, IPAMS, PAW, UPA) 
also recommended a 98th percentile form in order to provide regulatory 
stability. In contrast, a small number of State and local agencies 
(e.g., in MO and TX), several environmental organizations (e.g., EDF, 
EJ, GASP, NRDC), and medical/public health organizations (e.g., ALA, 
ATS) recommended either a 99th percentile form or a more stringent form 
(e.g., no exceedance) to further limit the occurrence of NO2 
concentrations that exceed the standard level in locations that attain 
the standard.
c. Conclusions On Form
    The Administrator recognizes that there is not a clear health basis 
for selecting one specific form over another. She also recognizes that 
the analyses of different forms in the REA are most directly relevant 
to a standard that reflects NO2 concentrations permitted to 
occur broadly across a community, rather than the maximum concentration 
that can occur anywhere in the area. In contrast, as discussed below 
(section II.F.4.c), the Administrator has judged it appropriate to set 
a new 1-hour standard that reflects the maximum allowable 
NO2 concentration anywhere in an area. In light of this, the 
Administrator places particular emphasis on the comments received on 
form from CASAC relating to a 1-hour standard level that reflects the 
maximum allowable NO2 concentration anywhere in an area. In 
particular, the Administrator notes that CASAC recommended a 98th 
percentile form averaged over 3 years for such a standard, given the 
potential for instability in the higher percentile concentrations 
around major roadways.
    In considering this recommendation, the Administrator recognizes 
that the public health protection provided by the 1-hour NO2 
standard is based on the approach used to set the standard and the 
level of the standard (see below), in conjunction with the form of the 
standard. Given that the Administrator is setting a standard that 
reflects the maximum allowable NO2 concentration anywhere in 
an area, rather than a standard that reflects the allowable area-wide 
NO2 concentration, she agrees with CASAC that an appropriate 
consideration with regard to form is the extent to which specific 
statistics could be unstable at locations where maximum NO2 
concentrations are expected, such as near major roads. When considering 
alternative forms for the standard, the Administrator notes that an 
unstable form could result in areas shifting in and out of attainment, 
potentially disrupting ongoing air quality planning without achieving 
public health goals. Given the limited available information on the 
variability in peak NO2 concentrations near important 
sources of NO2 such as major roadways, and given the 
recommendation from CASAC that the potential for instability in the 
99th percentile concentration is cause for supporting a 98th percentile 
form, the Administrator judges it appropriate to set the form based on 
the 3-year average of the 98th percentile of the annual distribution of 
1-hour daily maximum NO2 concentrations.
4. Level
    As discussed below and in more detail in the proposal (section 
II.F.4), the Administrator has considered two different approaches to 
setting the 1-hour NO2 primary NAAQS. In the proposal, each 
of these approaches was linked with a different range of standard 
levels. Specifically, the Administrator proposed to set a 1-hour 
standard reflecting the maximum allowable NO2 concentration 
anywhere in an area and to set the level of such a standard from 80 to 
100 ppb. The Administrator also solicited comment on the alternative 
approach of setting a standard that reflects the allowable area-wide 
NO2 concentration and setting the standard level from 50 to 
75 ppb. This section summarizes the rationale for the Administrator's 
proposed approach and range of standard levels (II.F.3.a), describes 
the alternative approach and range of standard levels (II.F.3.b), 
discusses comments related to each approach and range of standard 
levels (II.F.3.c), and presents the Administrator's final conclusions 
regarding the approach and level (II.F.3.d).
a. Rationale For Proposed Decisions on Approach and Level
    In assessing the most appropriate approach to setting the 1-hour 
standard and the most appropriate range of standard levels to propose, 
the Administrator considered the broad body of scientific evidence 
assessed in the ISA, including epidemiologic and controlled human 
exposure studies, as well as the results of exposure/risk analyses 
presented in the REA. In light of the body of available evidence and 
analyses, as described above, the Administrator concluded in the 
proposal that it is necessary to provide increased public health 
protection for at-risk individuals against an array of adverse 
respiratory health effects linked with short-term (i.e., 30 minutes to 
24 hours) exposures to NO2. Such health effects have been 
associated with exposure to the distribution of short-term ambient 
NO2 concentrations across an area, including higher short-
term (i.e., peak) exposure concentrations, such as those that can occur 
on or near major roadways and near other sources of NO2, as 
well as the lower short-term exposure concentrations that can occur in 
areas not near major roadways or other sources of NO2. The 
Administrator's proposed decisions on approach and level, as discussed 
in detail in the proposal (section II.F.4), are outlined below.
    In considering a standard-setting approach, the Administrator was 
mindful in the proposal that the available evidence and analyses from 
the ISA and REA support the public health importance of roadway-
associated NO2 exposures. The exposure assessment described 
in the REA estimated that roadway-associated exposures account for the 
majority of exposures to peak NO2 concentrations (REA, 
Figures 8-17, 8-18). The ISA concluded (section 4.3.6) that 
NO2 concentrations in heavy traffic or on freeways ``can be 
twice the residential outdoor or residential/arterial road level.'' In 
considering the potential variability in the NO2 
concentration gradient, the proposal noted that available monitoring 
studies suggest that NO2 concentrations could be 30 to 100% 
higher than those in the same area but away from the road.\12\
---------------------------------------------------------------------------

    \12\ In addition, the air quality analyses presented in the REA 
estimated that on-road NO2 concentrations are about 80% 
higher on average than concentrations away from the road (REA, 
section 7.3.2) and that NO2 monitors within 20 m of roads 
measure NO2 concentrations that are, on average across 
locations, 40% higher than concentrations measured by monitors at 
least 100 m from the road (REA, compare Tables 7-11 and 7-13).

---------------------------------------------------------------------------

[[Page 6494]]

    The Administrator also considered that millions of people in the 
United States live, work, and/or attend school near important sources 
of NO2 such as major roadways (ISA, section 4.4), and that 
ambient NO2 concentrations in these locations vary depending 
on the distance from major roads (i.e., the closer to a major road, the 
higher the NO2 concentration) (ISA, section 2.5.4). 
Therefore, these populations, which likely include a disproportionate 
number of individuals in groups with higher prevalence of asthma and 
higher hospitalization rates for asthma (e.g. ethnic or racial 
minorities and individuals of low socioeconomic status) (ISA, section 
4.4), are likely exposed to NO2 concentrations that are 
higher than those occurring away from major roadways.
    Given the above considerations, the Administrator proposed an 
approach to setting the 1-hour NO2 primary NAAQS whereby the 
standard would reflect the maximum allowable NO2 
concentration anywhere in an area. In many locations, this 
concentration is likely to occur on or near a major roadway. EPA 
proposed to set the level of the standard such that, when available 
information regarding the concentration gradient around roads is 
considered, appropriate public health protection would be provided by 
limiting the higher short-term peak exposure concentrations expected to 
occur on and near major roadways, as well as the lower short-term 
exposure concentrations expected to occur away from those roadways. The 
Administrator concluded that this approach to setting the 1-hour 
NO2 NAAQS would be expected to protect public health against 
exposure to the distribution of short-term NO2 
concentrations across an area and would provide a relatively high 
degree of confidence regarding the protection provided against peak 
exposures to higher NO2 concentrations, such as those that 
can occur around major roadways. The remainder of this section 
discusses the proposed range of standard levels.
    In considering the appropriate range of levels to propose for a 
standard that reflects the maximum allowable NO2 
concentration anywhere in an area, the Administrator considered the 
broad body of scientific evidence and exposure/risk information as well 
as available information on the relationship between NO2 
concentrations near roads and those away from roads. Specifically, she 
considered the extent to which a variety of levels would be expected to 
protect at-risk individuals against increased airway responsiveness, 
respiratory symptoms, and respiratory-related emergency department 
visits and hospital admissions.
    After considering the scientific evidence and the exposure/risk 
information (see sections II.B, II.C, and II.F.4.a.1 through II.F.4.a.3 
in the proposal), as well as the available information on the 
NO2 concentration gradient around roadways (section II.A.2 
above and in the proposal), the Administrator concluded that the 
strongest support is for a standard level at or somewhat below 100 ppb. 
The Administrator's rationale in reaching this proposed conclusion is 
provided below.
    The Administrator noted that a standard level at or somewhat below 
100 ppb in conjunction with the proposed approach would be expected to 
limit short-term NO2 exposures to concentrations that have 
been reported to increase airway responsiveness in asthmatics (i.e., at 
or above 100 ppb). While she acknowledged that exposure to 
NO2 concentrations below 100 ppb could potentially increase 
airway responsiveness in some asthmatics, the Administrator also noted 
uncertainties regarding the magnitude and the clinical significance of 
the NO2-induced increase in airway responsiveness, as 
discussed in the policy assessment chapter of the REA (section 
10.3.2.1, discussed in section II.F.4.e in the proposal). Given these 
uncertainties, the Administrator concluded in the proposal that 
controlled human exposure studies provide support for limiting 
exposures at or somewhat below 100 ppb NO2.
    The Administrator also noted that a standard level at or somewhat 
below 100 ppb in conjunction with the proposed approach would be 
expected to maintain peak area-wide NO2 concentrations 
considerably below those measured in locations where key U.S. 
epidemiologic studies have reported associations with more serious 
respiratory effects, as indicated by increased emergency department 
visits and hospital admissions. Specifically, the Administrator noted 
that 5 key U.S. studies provide evidence for such associations in 
locations where the 99th percentile of the distribution of 1-hour daily 
maximum NO2 concentrations measured at area-wide monitors 
ranged from 93 to 112 ppb (Ito et al., 2007; Jaffe et al., 2003; Peel 
et al., 2005; Tolbert et al., 2007; and a study by the New York State 
Department of Health, 2006).\13\ The Administrator concluded that these 
studies provide support for a 1-hour standard that limits the 99th 
percentile of the distribution of 1-hour daily maximum area-wide 
NO2 concentrations to below 90 ppb (corresponds to a 98th 
percentile concentration of 85 ppb), and that limiting area-wide 
concentrations to considerably below 90 ppb would be appropriate in 
order to provide an adequate margin of safety. The Administrator noted 
that, based on available information about the NO2 
concentration gradient around roads, a standard level at or somewhat 
below 100 ppb set in conjunction with the proposed approach would be 
expected to accomplish this. Specifically, she noted that given 
available information regarding NO2 concentration gradients 
around roads (see section II.A.2), a standard level at or below 100 ppb 
(with either a 99th or 98th percentile form) would be expected to limit 
peak area-wide NO2 concentrations to approximately 75 ppb or 
below.\14\ Therefore, the Administrator concluded that a standard level 
at or somewhat below 100 ppb under the proposed approach would be 
expected to maintain peak area-wide NO2 concentrations well 
below 90 ppb across locations despite the expected variation in the 
NO2 concentration gradient that can exist around roadways in 
different locations and over time.
---------------------------------------------------------------------------

    \13\ The 98th percentile concentrations in these study locations 
ranged from 85 to 94 ppb.
    \14\ For a standard of 100 ppb, area-wide concentrations would 
be expected to range from approximately 50 ppb (assuming near-road 
concentrations are 100% higher than area-wide concentrations) to 75 
ppb (assuming near-road concentrations are 30% higher than area-wide 
concentrations).
---------------------------------------------------------------------------

    The Administrator also noted that a study by Delfino provides mixed 
evidence for effects in a location with area-wide 98th and 99th 
percentile 1-hour daily maximum NO2 concentrations of 50 and 
53 ppb, respectively. In that study, NO2 effect estimates 
were positive, but some reported 95% confidence limits for the odds 
ratio (OR) that included values less than 1.00. Given the mixed results 
of the Delfino study, the Administrator concluded that it may not be 
necessary to maintain area-wide NO2 concentrations at or 
below 50 ppb to provide protection against the effects reported in 
epidemiologic studies.
    In addition to these evidence-based considerations, the 
Administrator noted that a standard level at or somewhat below 100 ppb 
under the proposed approach would be consistent with the

[[Page 6495]]

results of the exposure and risk analyses presented in the REA. As 
discussed in section II.C of the proposal, the results of these 
analyses provide support for setting a standard that limits 1-hour 
area-wide NO2 concentrations to between 50 and 100 ppb. As 
described above, a standard level of 100 ppb that reflects the maximum 
allowable NO2 concentration would be expected to maintain 
area-wide NO2 concentrations at or below approximately 75 
ppb. Given all of these considerations, the Administrator concluded in 
the proposal that a standard level at or somewhat below 100 ppb (with a 
99th percentile form), in conjunction with the proposed approach, would 
be requisite to protect public health with an adequate margin of safety 
against the array of NO2-associated health effects.
    In addition to the considerations discussed above, which support 
setting a standard level at or somewhat below 100 ppb, the 
Administrator also considered the extent to which available evidence 
could support standard levels below 100 ppb. The Administrator 
concluded that the evidence could support setting the standard level 
below 100 ppb to the extent the following were emphasized:
     The possibility that an NO2-induced increase in 
airway responsiveness could occur in asthmatics following exposures to 
concentrations below 100 ppb and/or the possibility that such an 
increase could be clinically significant.
     The mixed results reported in the study by Delfino et al. 
(2002) of an association between respiratory symptoms and the 
relatively low ambient NO2 concentrations measured in the 
study area.
    Specifically, she noted that a standard level of 80 ppb (99th 
percentile form), in conjunction with the proposed approach, could 
limit area-wide NO2 concentrations to 50 ppb \15\ and would 
be expected to limit exposure concentrations to below those that have 
been reported to increase airway responsiveness in asthmatics. For the 
reasons stated above, the Administrator proposed to set the level of a 
new 1-hour standard between 80 ppb and 100 ppb.
---------------------------------------------------------------------------

    \15\ This conclusion assumes that near-road NO2 
concentrations are 65% higher than area-wide concentrations, 
reflecting the mid-point in the range of 30 to 100%. Based on 
available information suggesting that near-road concentrations can 
be 30 to 100% higher than area-wide concentrations, a standard level 
of 80 ppb could limit area-wide concentrations to between 40 and 60 
ppb.
---------------------------------------------------------------------------

b. Rationale for the Alternative Approach and Range of Levels
    As described above, the Administrator proposed to set a 1-hour 
NO2 NAAQS reflecting the maximum allowable NO2 
concentration anywhere in an area and to set the level of such a 
standard from 80 to 100 ppb. However, prior to the proposal, the 
approach of setting a 1-hour NO2 NAAQS that reflects the 
maximum allowable NO2 concentration anywhere in an area had 
not been discussed by EPA in the REA or considered by CASAC. Rather, 
the potential alternative standards discussed in the REA, and reviewed 
by CASAC, reflected allowable area-wide NO2 concentrations 
(i.e., concentrations that occur broadly across communities).
    Given this, the Administrator noted in the proposal that comments 
received on the approach to setting the 1-hour standard (i.e., from 
CASAC and from members of the public) could provide important new 
information for consideration. Therefore, the Administrator also 
solicited comment on the alternative approach of setting a 1-hour 
NO2 primary NAAQS that would reflect the allowable area-wide 
NO2 concentration, analogous to the standards evaluated in 
the REA, and with a level set within the range of 50 to 75 ppb. In 
discussing this alternative approach with a standard level from 50 to 
75 ppb, the Administrator noted the following in the proposal:
     Such a standard would be expected to maintain area-wide 
NO2 concentrations below peak 1-hour area-wide 
concentrations measured in locations where key U.S. epidemiologic 
studies have reported associations with respiratory-related emergency 
department visits and hospital admissions.
     Standard levels from the lower end of the range would be 
expected to limit roadway-associated exposures to NO2 
concentrations that have been reported in controlled human exposure 
studies to increase airway responsiveness in asthmatics. Specifically, 
a standard level of 50 ppb under this approach could limit near-road 
concentrations to between approximately 65 and 100 ppb, depending on 
the relationship between near-road NO2 concentrations and 
area-wide concentrations.
     This alternative approach would provide relatively more 
confidence regarding the degree to which a specific standard level 
would limit area-wide NO2 concentrations and less confidence 
regarding the degree to which a specific standard level would limit the 
peak NO2 concentrations likely to occur near major roadways.
c. Comments on Approach and Level
    In the proposal, each approach to setting the 1-hour standard, and 
each range of standard levels, was linked to different requirements for 
the design of the NO2 monitoring network. Specifically, in 
conjunction with the proposed approach (i.e., standard reflects the 
maximum allowable NO2 concentration anywhere in an area and 
the level is set within the range of 80 to 100 ppb), the Administrator 
proposed to establish a 2-tiered monitoring network that would include 
monitors sited to measure the maximum NO2 concentrations 
anywhere in an area, including near major roadways, and monitors sited 
to measure maximum area-wide NO2 concentrations. In 
conjunction with the alternative approach (i.e., standard reflects the 
allowable area-wide NO2 concentration and the level is set 
within the range of 50 to 75 ppb), the Administrator solicited comment 
on a monitoring network that would only include area-wide 
NO2 monitors. Because of these linkages in the proposal, 
most commenters combined their comments on the approach to setting a 1-
hour standard and on the standard level with their comments on the 
monitoring requirements. In this section, we discuss comments from 
CASAC and public commenters on the approach to setting a 1-hour 
standard and on the standard level. Comments on the monitoring network 
are also discussed in this section to the extent they indicate a 
preference for either the proposed or alternative approach to setting 
the 1-hour standard. More specific comments on monitor placement and 
network design are discussed below in section III.B.2 and in the 
Response to Comments document. EPA responses to technical comments on 
the scientific evidence and the exposure/response information are 
discussed above in section II.E.2 and in the Response to Comments 
document. The Administrator's response to commenters' views on the 
approach to setting the 1-hour standard and on the standard level is 
embodied in the discussed in section II.F.4.d.
i. CASAC Comments on the Approach to Setting the Standard
    A majority of CASAC and CASAC Panel members \16\ favored the 
proposed approach of setting a 1-hour standard that reflects the 
maximum allowable

[[Page 6496]]

NO2 concentration anywhere in an area and linking such a 
standard with a 2-tiered monitoring network that would include both 
near-road and area-wide monitors, though CASAC did not reach consensus 
on this approach. Specifically, in their letter to the Administrator 
(Samet, 2009), CASAC stated the following:
---------------------------------------------------------------------------

    \16\ CASAC members were also part of the CASAC Panel for the 
NO2 NAAQS review (i.e., the Oxides of Nitrogen Primary 
National Ambient Air Quality Standards Panel). Therefore, references 
to the CASAC Panel include both CASAC members and Panel members.

    There was a split view on the two approaches among both CASAC 
and CASAC panel members with a majority of each favoring the 
Agency's proposed two-tiered monitoring network because they thought 
this approach would be more effective in limiting near-roadway 
exposures that may reach levels in the range at which some 
individuals with asthma may be adversely affected. Other members 
acknowledged the need for research and development of near-road 
monitoring data for criteria pollutants in general but favored 
retention of EPA's current area-wide monitoring for NO2 
regulatory purposes, due to the lack of epidemiological data based 
on near-roadway exposure measurements and issues related to 
---------------------------------------------------------------------------
implementing a near-road monitoring system for NO2.

Thus, the recommendation of the majority of CASAC Panel members was 
based on their conclusion that the proposed approach would be more 
effective than the alternative at limiting near-roadway exposures to 
NO2 concentrations that could adversely affect asthmatics. 
In addition, these CASAC Panel members noted important uncertainties 
with the alternative approach. Specifically, they stated the following 
(Samet, 2009):

    Panel members also supported the proposed two-tiered approach 
because basing regulations on area-wide monitoring alone was 
problematic. Such an approach would require EPA to embed 
uncertainties and assumptions about the relationship between area-
wide and road-side monitoring into the area-wide standard.

    A minority of CASAC Panel members expressed support for the 
alternative approach of setting a 1-hour standard that reflects the 
allowable area-wide NO2 concentration. These CASAC Panel 
members concluded that there would be important uncertainties 
associated with the proposed approach. Specifically, they noted that 
the key U.S. NO2 epidemiologic studies relied upon area-wide 
NO2 concentrations. In their view, the use of area-wide 
concentrations in these studies introduces uncertainty into the 
selection of a standard level for a standard that reflects the maximum 
allowable NO2 concentration anywhere in an area and that is 
linked with a requirement to place monitors near major roads. As a 
result of this uncertainty, CASAC Panel members who favored the 
alternative approach noted that ``it would be better to set the 
standard on the same area-wide monitoring basis as employed in the 
epidemiologic studies upon which it [the standard] now relies'' (Samet, 
2009). These CASAC Panel members also strongly supported obtaining 
monitoring data near major roads, while recognizing uncertainties 
associated with identifying appropriate monitoring sites near roads 
(see section III.B.2 and the Response to Comments document for more 
discussion of CASAC's monitoring comments).
ii. Public Comments on the Approach to Setting the Standard
    Consistent with the views expressed by the majority of CASAC 
members, a number of commenters concluded that the most appropriate 
approach would be to set a 1-hour standard that reflects the maximum 
allowable NO2 concentration anywhere in an area and to 
couple that standard with a requirement that monitors be placed in 
locations where maximum concentrations are expected, including near 
major roads. This view was expressed by some State and local agencies 
(e.g., in CA, IA, NY, TX, WA, WI), by a number of environmental 
organizations (e.g., CAC, EDF, EJ, GASP, NRDC), by the ALA, and 
individual commenters. Several additional medical and public health 
organizations (ACCP, AMA, ATS, NADRC, NACPR) did not explicitly express 
a recommendation regarding the approach though these organizations did 
recommend that, in setting a 1-hour standard, particular attention 
should be paid to NOX concentrations around major roadways. 
In support of their recommendation to adopt the proposed approach and 
to focus monitoring around major roads, these commenters generally 
concluded that a primary consideration should be the extent to which 
the NO2 NAAQS protects at-risk populations that live and/or 
attend school near important sources of NO2 such as major 
roads. As such, these comments supported the rationale in the proposal 
for setting a 1-hour standard that reflects the maximum allowable 
NO2 concentration anywhere in an area.
    A number of State commenters expressed the view that area-wide 
monitors should be used for attainment/non-attainment determinations 
(e.g., NACAA, NESCAUM and agencies in IL, IN, MI, MS, NC, NM, SC). One 
State commenter (NESCAUM) agreed with EPA concerns about near-road 
exposures but concluded that it is premature to establish a large near-
road monitoring network at this time due to uncertainty regarding the 
relationship between near-road and area-wide NO2 
concentrations and the variability in that relationship. NESCAUM 
recommended that EPA work with States to establish a targeted 
monitoring program in select urban areas to gather data that would 
inform future modifications to the monitoring network, but that ``[t]he 
existing area-wide monitoring network should be used to identify 
initial nonattainment areas.'' Other State commenters also concluded 
that the most appropriate approach would be to base non-attainment 
determinations only on area-wide monitors. Based on their monitoring 
comments, many of these commenters appeared to support setting a 1-hour 
standard that reflects the allowable area-wide NO2 
concentration. State concerns with the proposed approach often included 
uncertainties associated with identifying and accessing appropriate 
monitor sites near major roads, as well as concerns related to 
implementation and cost to States (as discussed further in the Response 
to Comments document, the Administrator may not consider cost of 
implementation in decisions on a NAAQS).
    One commenter (AAM) concluded that the focus of the proposed 
approach on NO2 concentrations around major roadways is not 
justified because the REA and the proposal overstate the extent to 
which NO2 concentrations near roads are higher than 
NO2 concentrations farther away from the road. This 
conclusion is based on an analysis of 42 existing NO2 
monitors in 6 locations. Comparing NO2 concentrations 
measured by these monitors, some of which are closer to roads and 
others of which are farther from roads, AAM concluded that ``roadside 
monitors are not measuring high NO2 concentrations.''
    We agree that there is uncertainty associated with estimates of 
roadway-associated NO2 concentrations (see REA, sections 
7.4.6 and 8.4.8.3 for detailed discussion of these uncertainties) and 
in identifying locations where maximum concentrations are expected to 
occur. However, we note that the Administrator's conclusions regarding 
the relationship between NO2 concentrations near roads and 
those away from roads rely on multiple lines of scientific evidence and 
information. Specifically, the Administrator relied in the proposal on 
the following in drawing conclusions regarding the distribution of 
NO2 concentrations across areas:
     Monitoring studies discussed in the ISA and REA that were 
designed to characterize the NO2 concentration gradient 
around roads, which indicated that NO2 concentrations near 
roads can

[[Page 6497]]

be approximately 30 to 100% higher than concentrations away from the 
road in the same area.
     Air quality and exposure analyses presented in the REA 
which estimate that, on average across locations, NO2 
concentrations on roads could be 80% higher than those away from roads 
and that roadway-associated exposures account for the majority of 
exposures to NO2 concentrations at or above 100 ppb.
    In contrast, the existing NO2 monitoring network, which 
was the basis for the analysis submitted by AAM, was not designed to 
characterize the spatial gradients in NO2 concentrations 
surrounding roadways. Rather, concentrations of NO2 measured 
by existing monitors are likely to reflect contributions from a 
combination of mobile and stationary sources, with one or the other 
dominating depending on the proximity of these sources to the monitors. 
Therefore, we conclude that the analysis submitted by AAM, which does 
not consider other relevant lines of evidence and information, does not 
appropriately characterize the relationship between NO2 
concentrations near roads and those away from roads. (See the Response 
to Comments document for a more detailed discussion of AAM comments.)
    In addition, we note that, although the Administrator concluded in 
the proposal that maximum NO2 concentrations in many areas 
are likely to occur around major roads, she also recognized that 
maximum concentrations can occur elsewhere in an area. For this reason, 
she proposed to set a 1-hour NO2 standard that reflects the 
maximum allowable NO2 concentration anywhere in an area, 
regardless of where that maximum concentration occurs.\17\ Therefore, 
the proposed approach to setting the standard would be expected to 
limit the maximum NO2 concentrations anywhere in an area 
even if in some areas, as is contended by AAM, those maximum 
NO2 concentrations do not occur near roads.
---------------------------------------------------------------------------

    \17\ To measure maximum concentrations, the Administrator 
proposed monitoring provisions that would require monitors within 50 
meters of major roads and to allow the Regional Administrator to 
require additional monitors in situations where maximum 
concentrations would be expected to occur in locations other than 
near major roads (e.g., due to the influence of multiple smaller 
roads and/or stationary sources).
---------------------------------------------------------------------------

iii. CASAC Comments on Standard Level
    In commenting on the proposal, CASAC discussed both the proposed 
range of standard levels (i.e., 80-100 ppb) and the alternative range 
of standard levels (i.e., 50-75 ppb). CASAC did express the consensus 
conclusion that if the Agency finalizes a 1-hour standard in accordance 
with the proposed approach (i.e., standard level reflects the maximum 
allowable NO2 concentration anywhere in an area), then it is 
appropriate to consider the proposed range of standard levels from 80 
to 100 ppb. Specifically, the CASAC letter to the Administrator on the 
proposal (Samet, 2009) stated the following with regard to the proposed 
approach:

    [T]he level of the one-hour NO2 standard should be 
within the range of 80-100 ppb and not above 100 ppb. In its letter 
of December 2, 2008, CASAC strongly voiced a consensus view that the 
upper end of the range should not exceed 100 ppb, based on evidence 
of risk at that concentration. The lower limit of 80 ppb was viewed 
as reasonable by CASAC; selection of a value lower than 80 ppb would 
represent a policy judgment based on uncertainty and the degree of 
public health protection sought, given the limited health-based 
evidence at concentrations below 100 ppb.

CASAC also recommended that this level be employed with a 98th 
percentile form, in order to promote the stability of the standard (see 
above for discussion of form).
iv. Public Comments on Standard Level
    A number of State and local agencies and organizations expressed 
support for setting the level of the 1-hour NO2 standard 
within the proposed range of 80 to 100 ppb. While some State and local 
agencies (e.g., in CA, IA, MI, NY, TX) made this recommendation in 
conjunction with a recommendation to focus monitoring near major roads 
and other important sources of NO2, a number of State 
commenters (e.g., NACAA, NESCAUM and agencies in IL, NC, NM, TX, VA) 
recommended a standard level from 80 to 100 ppb in conjunction with a 
recommendation that only area-wide monitors be deployed for purposes of 
determining attainment with the standard. Based on these monitoring 
comments, these State commenters appear to favor an approach where a 
standard level from 80 to 100 ppb would reflect the allowable area-wide 
NO2 concentration. As discussed above (and in more detail in 
section III.B.2 and the Response to Comments document), State 
commenters often based these recommendations on uncertainties 
associated with designing an appropriate national near-road monitoring 
network.
    A number of environmental organizations (e.g., CAC, EDF, EJ, GASP, 
NRDC) and medical/public health organizations (e.g., ACCP, ALA, AMA, 
ATS, NACPR, NAMDRC) supported setting a standard level below 80 ppb for 
a standard that reflects the maximum allowable NO2 
concentration anywhere in an area. Several of these groups recommended 
a standard level of 50 ppb. This recommendation was typically based on 
the commenters' interpretation of the epidemiologic and controlled 
human exposure evidence, as described below.
    Some of these commenters noted that the 98th percentile area-wide 
NO2 concentration was below 80 ppb in the location of a 
single key U.S. epidemiologic study (i.e., 50 ppb in study by Delfino). 
Given this, commenters concluded that the standard level should be set 
at 50 ppb. Their comments on the monitoring network generally favored a 
requirement to place monitors near major roads and, therefore, these 
commenters appeared to favor a standard level as low as 50 ppb and to 
recommend that such a standard level reflect the maximum allowable 
NO2 concentration anywhere in an area. In their comments, 
the ALA, EDF, EJ, and NRDC stated the following:

    Considering the Delfino study alone on EPA's terms, that is, 
focusing on the 98th percentile of the 1-hour daily maximum 
concentrations, EPA reports a concentration of 50 ppb where asthma 
symptoms were observed. Based primarily on this study, EPA concluded 
in the REA that it was appropriate to set the lower end of the range 
at 50 ppb, which corresponded to the lowest-observed effects level 
of airway hyperresponsiveness in asthmatics. To provide the 
strongest public health protection, we therefore urge the level of 
the standard be set at 50 ppb.

In some cases, the same commenters also appeared to recommend setting a 
standard level below 50 ppb because mean area-wide NO2 
concentrations reported in locations of key U.S. epidemiologic studies 
are below this concentration. Specifically, with regard to the key U.S. 
epidemiologic studies, these commenters (e.g., ALA, EDF, EJ, NRDC) 
stated the following:

    These studies clearly identify adverse health effects such as 
emergency room visits and hospital admissions for respiratory causes 
at concentrations currently occurring in the United States. Mean 
concentrations for all but two of these studies are about or below 
50 ppb, suggesting that the standard must be set below this level to 
allow for a margin of safety.

The Administrator's consideration of the Delfino study as it relates to 
a decision on standard level is discussed below (section II.F.4.d). 
Regarding the recommendation to set the level below 50 ppb based on 
mean area-wide NO2 concentrations in epidemiologic study

[[Page 6498]]

locations, we note that the Administrator proposed to set a standard 
that reflects the maximum allowable NO2 concentration 
anywhere in an area and to set the form of that standard at the upper 
end of the distribution of 1-hour daily maximum NO2 
concentrations.\18\ As described in the proposal, such a standard, with 
a level from the proposed range of 80 to 100 ppb, would be expected to 
maintain peak area-wide NO2 concentrations below the peak 
area-wide concentrations measured in locations where key U.S. 
epidemiologic studies have reported associations with respiratory-
related emergency department visits and hospital admissions. Because 
reducing NOX emissions to meet a 98th percentile 
NO2 standard should lower the distribution of NO2 
concentrations, including the mean, a standard that limits the 98th 
percentile of the distribution of 1-hour daily maximum concentrations 
would also be expected to limit mean concentrations. Therefore, 
although we acknowledge that the relationship between peak and mean 
NO2 concentrations will likely vary across locations and 
over time, if peak area-wide NO2 concentrations are 
maintained below those in key epidemiologic study locations, mean area-
wide NO2 concentrations would also be expected to be 
maintained below the mean area-wide concentrations in those locations 
(see ISA, figure 2.4-13 for information on the relationship between 
peak and mean NO2 concentrations).
---------------------------------------------------------------------------

    \18\ As discussed above, the Administrator has selected the 98th 
percentile as the form for the new 1-hour NO2 standard.
---------------------------------------------------------------------------

    As discussed above (section, II.E.2), a number of industry groups 
did not support setting a new 1-hour NO2 standard. However, 
several of these groups (e.g., AAM, Dow, NAM, NPRA) also concluded 
that, if EPA does choose to set a new 1-hour standard, the level of 
that standard should be above 100 ppb. As a basis for this 
recommendation, these groups emphasized uncertainties in the scientific 
evidence. Specifically, as discussed in more detail above (section 
II.E.2), these commenters typically concluded that available 
epidemiologic studies do not support the conclusion that NO2 
causes reported health effects. This was based on their assertion that 
the presence of co-pollutants in the ambient air precludes the 
identification of a specific NO2 contribution to reported 
effects. As a result, these commenters recommended that a 1-hour 
standard should be based on the controlled human exposure evidence and 
that, in considering that evidence, EPA should rely on the meta-
analysis of NO2 airway responsiveness studies conducted by 
Goodman et al., (2009) rather than the meta-analysis included in the 
final ISA. As described above, they concluded that in relying on the 
ISA meta-analysis, EPA has inappropriately relied on a new unpublished 
meta-analysis that has not been peer-reviewed, was not reviewed by 
CASAC, and was not conducted in a transparent manner. EPA recognizes 
the uncertainties in the scientific evidence that are discussed by 
these industry commenters; however, we strongly disagree with their 
conclusions regarding the implications of these uncertainties for 
decisions on the NO2 NAAQS. These comments, and EPA's 
responses, are discussed in detail above (section II.E.2) and in the 
Response to Comments document and are summarized briefly below.
    As noted in section II.E.2, we agree that the presence of co-
pollutants in the ambient air complicates the interpretation of 
epidemiologic studies; however, our conclusions regarding causality are 
based on consideration of the broad body of epidemiologic studies 
(including those employing multi-pollutant models) as well as animal 
toxicological and controlled human exposure studies. The ISA concluded 
that this body of evidence ``supports a direct effect of short-term 
NO2 exposure on respiratory morbidity at ambient 
concentrations below the current NAAQS level'' (ISA, p. 5-16). In 
addition, the ISA (p. 5-15) concluded the following:

    [T]he strongest evidence for an association between 
NO2 exposure and adverse human health effects comes from 
epidemiologic studies of respiratory symptoms and ED visits and 
hospital admissions. These new findings were based on numerous 
studies, including panel and field studies, multipollutant studies 
that control for the effects of other pollutants, and studies 
conducted in areas where the whole distribution of ambient 24-h avg 
NO2 concentrations was below the current NAAQS level of 
0.053 ppm (53 ppb) (annual average).

Given that epidemiologic studies provide the strongest support for an 
association between NO2 and respiratory morbidity, and that 
a number of these studies controlled for the presence of other 
pollutants with multi-pollutant models (in which NO2 effect 
estimates remained robust), we disagree that NO2 
epidemiologic studies should not be used to inform a decision on the 
level of the 1-hour NO2 standard.
    In addition, we agree that uncertainty exists regarding the extent 
to which the NO2-induced increase in airway responsiveness 
is adverse (REA, section 10.3.2.1); however, as discussed in detail 
above (section II.E.2), we disagree with the conclusion by many 
industry commenters that this effect is not adverse in asthmatics 
following exposures from 100 to 600 ppb NO2. Specifically, 
we do not agree that the approach taken in the study by Goodman et al. 
(2009), which was used by many industry commenters to support their 
conclusions, was appropriate. The authors of the Goodman study used 
data from existing NO2 studies to characterize the dose-
response relationship of NO2 and airway responsiveness and 
to calculate the magnitude of the NO2 effect. Given the 
protocol differences in existing studies of NO2 and airway 
responsiveness, we do not agree that it is appropriate to base such an 
analysis on these studies.
    The Administrator's consideration of these uncertainties, within 
the context of setting a standard level, is discussed in the next 
section.
d. Conclusions on Approach and Standard Level
    Having carefully considered the public comments on the appropriate 
approach and level for a 1-hour NO2 standard, as discussed 
above, the Administrator believes the fundamental conclusions reached 
in the ISA and REA remain valid. In considering the approach, the 
Administrator continues to place primary emphasis on the conclusions of 
the ISA and the analyses of the REA, both of which focus attention on 
the importance of roadways in contributing to peak NO2 
exposures, given that roadway-associated exposures can dominate 
personal exposures to NO2. In considering the level at which 
the 1-hour primary NO2 standard should be set, the 
Administrator continues to place primary emphasis on the body of 
scientific evidence assessed in the ISA, as summarized above in section 
II.B, while viewing the results of exposure and risk analyses, 
discussed above in section II.C, as providing information in support of 
her decision.
    With regard to her decision on the approach to setting the 1-hour 
standard, the Administrator continues to judge it appropriate to 
provide increased public health protection for at-risk individuals 
against an array of adverse respiratory health effects linked with 
short-term exposures to NO2, where such health effects have 
been associated with exposure to the distribution of short-term ambient 
NO2 concentrations across

[[Page 6499]]

an area. In protecting public health against exposure to the 
distribution of short-term NO2 concentrations across an 
area, the Administrator is placing emphasis on providing a relatively 
high degree of confidence regarding the protection provided against 
exposures to peak concentrations of NO2, such as those that 
can occur around major roadways. Available evidence and information 
suggest that roadways account for the majority of exposures to peak 
NO2 concentrations and, therefore, are important 
contributors to NO2-associated public health risks. In 
reaching this conclusion, the Administrator notes the following:
     Mobile sources account for the majority of NOX 
emissions (ISA, Table 2.2-1).
     The ISA stated that NO2 concentrations in heavy 
traffic or on freeways ``can be twice the residential outdoor or 
residential/arterial road level,'' that ``exposure in traffic can 
dominate personal exposure to NO2,'' and that 
``NO2 levels are strongly associated with distance from 
major roads (i.e., the closer to a major road, the higher the 
NO2 concentration)'' (ISA, sections 2.5.4, 4.3.6).
     The exposure assessment presented in the REA estimated 
that roadway-associated exposures account for the majority of exposures 
to peak NO2 concentrations (REA, Figures 8-17, 8-18).
     Monitoring studies suggest that NO2 
concentrations near roads can be considerably higher than those in the 
same area but away from roads (e.g., by 30-100%, see section II.A.2).
     In their comments on the approach to setting the 1-hour 
NO2 standard, the majority of CASAC Panel members emphasized 
the importance of setting a standard that limits roadway-associated 
exposures to NO2 concentrations that could adversely affect 
asthmatics. These CASAC Panel members favored the proposed approach, 
including its focus on roads.
    In addition, the Administrator notes that a considerable fraction 
of the population resides, works, or attends school near major roadways 
or other sources of NO2 and that these populations are 
likely to have increased exposure to NO2 (ISA, section 4.4). 
Based on data from the 2003 American Housing Survey, approximately 36 
million individuals live within 300 feet (~90 meters) of a four-lane 
highway, railroad, or airport (ISA, section 4.4).\19\ Furthermore, in 
California, 2.3% of schools with a total enrollment of more than 
150,000 students were located within approximately 500 feet of high-
traffic roads (ISA, section 4.4). Of this population, which likely 
includes a disproportionate number of individuals in groups with a 
higher prevalence of asthma and higher hospitalization rates for asthma 
(e.g., ethnic or racial minorities and individuals of low socioeconomic 
status) (ISA, section 4.4), asthmatics and members of other susceptible 
groups (e.g., children, elderly) will have the greatest risks of 
experiencing health effects related to NO2 exposure. In the 
United States, approximately 10% of adults and 13% of children have 
been diagnosed with asthma, and 6% of adults have been diagnosed with 
COPD (ISA, section 4.4).
---------------------------------------------------------------------------

    \19\ The most current American Housing Survey (http://www.census.gov/hhes/www/housing/ahs/ahs.html) is from 2007 and lists 
a higher fraction of housing units within the 300 foot boundary. 
According to Table 1A-6 from that report (http://www.census.gov/hhes/www/housing/ahs/ahs07/tab1a-6.pdf), out of 128.2 million total 
housing units in the United States, about 20 million were reported 
by the surveyed occupant or landlord as being within 300 feet of a 
4-or-more lane highway, railroad, or airport. That constitutes 15.6% 
of the total housing units in the U.S. Assuming equal distributions, 
with a current population of 306.3 million, that means that there 
would be 47.8 million people meeting the 300 foot criteria.
---------------------------------------------------------------------------

    In considering the approach to setting the 1-hour standard, the 
Administrator also notes that concerns with the proposed approach 
expressed by the minority of CASAC Panel members included concern with 
the uncertainty in the relationship between near-road and area-wide 
NO2 concentrations, given that U.S. epidemiologic studies 
have been based on concentrations measured at area-wide monitors. 
However, as discussed by the majority of CASAC Panel members, a similar 
uncertainty would be involved in setting a standard with the 
alternative approach (Samet, 2009). The Administrator agrees with the 
majority of CASAC Panel members and concludes that uncertainty in the 
relationship between near-road and area-wide NO2 
concentrations should be considered regardless of the approach selected 
to set the standard. She recognizes that this uncertainty can and 
should be taken into consideration when considering the level of the 
standard.
    In drawing conclusions on the approach, the Administrator has 
considered the extent to which each approach, in conjunction with the 
ranges of standard levels discussed in the proposal, would be expected 
to limit the distribution of NO2 concentrations across an 
area and, therefore, would be expected to protect against risks 
associated with NO2 exposures. Specifically, she has 
considered the extent to which a standard set with each approach would 
be expected to limit maximum NO2 concentrations and area-
wide NO2 concentrations.
    With regard to expected maximum concentrations, the Administrator 
notes the following:
     A standard reflecting the maximum allowable NO2 
concentration anywhere in an area would provide a relatively high 
degree of confidence regarding the level of protection provided against 
peak exposures, such as those that can occur on or near major roadways. 
A standard level from anywhere within the proposed range (i.e., 80 to 
100 ppb) would be expected to limit exposures to NO2 
concentrations reported to increase airway responsiveness in 
asthmatics.
     A standard reflecting the allowable area-wide 
NO2 concentration would not provide a high degree of 
confidence regarding the extent to which maximum NO2 
concentrations would be limited. Maximum NO2 concentrations 
would be expected to be controlled to varying degrees across locations 
and over time depending on the NO2 concentration gradient 
around roads. Given the expected variability in gradients across 
locations and over time, most standard levels within the range 
considered in the proposal with this option (i.e., 50 to 75 ppb) would 
not be expected to consistently limit the occurrence of NO2 
concentrations that have been reported to increase airway 
responsiveness in asthmatics.
    With regard to expected area-wide concentrations, the Administrator 
notes the following:
     The extent to which a standard reflecting the maximum 
allowable NO2 concentration anywhere in an area would be 
expected to limit area-wide NO2 concentrations would vary 
across locations, e.g., depending on the NO2 concentration 
gradient around roads. However, in conjunction with a standard level 
from anywhere within the proposed range (i.e., 80-100 ppb), such an 
approach would be expected to maintain area-wide NO2 
concentrations below those measured in locations where key U.S. 
epidemiologic studies have reported associations between ambient 
NO2 and respiratory-related hospital admissions and 
emergency department visits (based on available information regarding 
the NO2 concentration gradient around roads as discussed 
below).
     A standard reflecting the maximum allowable area-wide 
NO2 concentration would provide a relatively high degree of 
certainty regarding the extent to which area-wide NO2 
concentrations are limited. In conjunction with a standard level from 
anywhere within the range of

[[Page 6500]]

levels discussed in the proposal (i.e., 50-75 ppb) with this 
alternative approach, such a standard would be expected to maintain 
area-wide NO2 concentrations below those measured in 
locations where key U.S. epidemiologic studies have reported 
associations between ambient NO2 and respiratory-related 
hospital admissions and emergency department visits.
    Given the above considerations, the Administrator concludes that 
both approaches, in conjunction with appropriate standard levels, would 
be expected to maintain area-wide NO2 concentrations below 
those measured in locations where key U.S. epidemiologic studies have 
reported associations between ambient NO2 and respiratory-
related hospital admissions and emergency department visits. In 
contrast, the Administrator concludes that only a standard reflecting 
the maximum allowable NO2 concentration anywhere in an area, 
in conjunction with an appropriate standard level, would be expected to 
consistently limit exposures, across locations and over time, to 
NO2 concentrations reported to increase airway 
responsiveness in asthmatics. After considering the evidence and 
uncertainties, and the advice of the CASAC Panel, the Administrator 
judges that the most appropriate approach to setting a 1-hour standard 
to protect against the distribution of short-term NO2 
concentrations across an area, including the higher concentrations that 
can occur around roads and result in elevated exposure concentrations, 
is to set a standard that reflects the maximum allowable NO2 
concentration anywhere in an area.
    In considering the level of a 1-hour NO2 standard that 
reflects the maximum allowable NO2 concentration anywhere in 
an area, the Administrator notes that there is no bright line clearly 
directing the choice of level. Rather, the choice of what is 
appropriate is a public health policy judgment entrusted to the 
Administrator. This judgment must include consideration of the 
strengths and limitations of the evidence and the appropriate 
inferences to be drawn from the evidence and the exposure and risk 
assessments. Specifically, the Administrator notes the following:
     Controlled human exposure studies have reported that 
various NO2 exposure concentrations increased airway 
responsiveness in mostly mild asthmatics (section II above and II.B.1.d 
in proposal). These studies can inform an evaluation of the risks 
associated with exposure to specific NO2 concentrations, 
regardless of where those exposures occur in an area. Because 
concentrations evaluated in controlled human exposure studies are at 
the high end of the distribution of ambient NO2 
concentrations (ISA, section 5.3.2.1), these studies most directly 
inform consideration of the risks associated with exposure to peak 
short-term NO2 concentrations.
     Epidemiologic studies (section II.B.1.a and b) conducted 
in the United States have reported associations between ambient 
NO2 concentrations measured at area-wide monitors in the 
current network and increased respiratory symptoms, emergency 
department visits, and hospital admissions. Area-wide monitors in the 
urban areas in which these epidemiologic studies were conducted are not 
sited in locations where localized peak concentrations are likely to 
occur. Thus, they do not measure the full range of ambient 
NO2 concentrations across the area. Rather, the area-wide 
NO2 concentrations measured by these monitors are used as 
surrogates for the distribution of ambient NO2 
concentrations across the area, a distribution that includes 
NO2 concentrations both higher than (e.g., around major 
roadways) and lower than the area-wide concentrations measured in study 
locations. Epidemiologic studies evaluate whether area-wide 
NO2 concentrations are associated with the risk of 
respiratory morbidity. Available information on NO2 
concentration gradients around roadways can inform estimates of the 
relationship between the area-wide NO2 concentrations 
measured in epidemiologic study locations and the higher NO2 
concentrations likely to have occurred around roads in those locations, 
which can then inform the decision on the level of a standard 
reflecting the maximum allowable NO2 concentration anywhere 
in an area.
     The risk and exposure analyses presented in the REA 
provide information on the potential public health implications of 
setting standards that limit area-wide NO2 concentrations to 
specific levels. While the Administrator acknowledges the uncertainties 
associated with these analyses which, as discussed in the REA, could 
result in either over- or underestimates of NO2-associated 
health risks, she judges that these analyses are informative for 
considering the relative levels of public health protection that could 
be provided by different standards.
    The Administrator's consideration of the controlled human exposure 
evidence, epidemiologic evidence, and exposure/risk information are 
discussed below specifically with regard to a decision on the level of 
a standard that reflects the maximum allowable NO2 
concentration anywhere in an area.
    In considering the potential for controlled human exposure studies 
of NO2 and airway responsiveness to inform a decision on 
standard level, the Administrator notes the following:
     NO2-induced increases in airway responsiveness, 
as reported in controlled human exposure studies, are logically linked 
to the adverse respiratory effects that have been reported in 
NO2 epidemiologic studies.
     The meta-analysis of controlled human exposure data in the 
ISA reported increased airway responsiveness in a large percentage of 
asthmatics at rest following exposures at and above 100 ppb 
NO2, the lowest NO2 concentration for which 
airway responsiveness data are available in humans.
     This meta-analysis does not provide any evidence of a 
threshold below which effects do not occur. The studies included in the 
meta-analysis evaluated primarily mild asthmatics while more severely 
affected individuals could respond to lower concentrations. Therefore, 
it is possible that exposure to NO2 concentrations below 100 
ppb could increase airway responsiveness in some asthmatics.
    In considering the evidence, the Administrator recognizes that the 
NO2-induced increases in airway responsiveness reported for 
exposures to NO2 concentrations at or above 100 ppb could be 
adverse for some asthmatics. However, she also notes that important 
uncertainties exist with regard to the extent to which NO2-
induced increases in airway responsiveness are adverse. Specifically, 
she notes the following with regard to these uncertainties:
     The magnitude of the NO2-induced increase in 
airway responsiveness, and the extent to which it is adverse, cannot be 
quantified from the ISA meta-analysis (REA, section 10.3.2.1).
     The NO2-induced increase in airway 
responsiveness in resting asthmatics was typically not accompanied by 
increased respiratory symptoms, even following exposures to 
NO2 concentrations well above 100 ppb (ISA, section 
3.1.3.3).
     The increase in airway responsiveness that was reported 
for resting asthmatics was not present in exercising asthmatics (ISA, 
Table 3.1-3).
    Taking into consideration all of the above, the Administrator 
concludes that existing evidence supports the conclusion that the 
NO2-induced increase in airway responsiveness at or above 
100 ppb presents a risk of adverse

[[Page 6501]]

effects for some asthmatics, especially those with more serious (i.e., 
more than mild) asthma. The Administrator notes that the risks 
associated with increased airway responsiveness cannot be fully 
characterized by these studies, and thus she is not able to determine 
whether the increased airway responsiveness experienced by asthmatics 
in these studies is an adverse health effect. However, based on these 
studies the Administrator concludes that asthmatics, particularly those 
suffering from more severe asthma, warrant protection from the risk of 
adverse effects associated with the NO2-induced increase in 
airway responsiveness. Therefore, the Administrator concludes that the 
controlled human exposure evidence supports setting a standard level no 
higher than 100 ppb to reflect a cautious approach to the uncertainty 
regarding the adversity of the effect. However, those uncertainties 
lead her to also conclude that this evidence does not support setting a 
standard level lower than 100 ppb.
    In considering the more serious health effects reported in 
NO2 epidemiologic studies, as they relate to the level of a 
standard that reflects the maximum allowable NO2 
concentration anywhere in an area, the Administrator notes the 
following:
     A cluster of 5 key U.S. epidemiologic studies (Ito et al., 
2007; Jaffe et al., 2003; Peel et al., 2005; Tolbert et al., 2007; and 
a study by the New York State Department of Health, 2006) provide 
evidence for associations between NO2 and respiratory-
related emergency department visits and hospital admissions in 
locations where 98th percentile 1-hour daily maximum NO2 
concentrations measured at area-wide monitors ranged from 85 to 94 ppb. 
The Administrator judges it appropriate to place substantial weight on 
this cluster of key U.S. epidemiologic studies in selecting a standard 
level, as they are a group of studies that reported positive, and often 
statistically significant, associations between NO2 and 
respiratory morbidity in multiple cities across the United States.\20\
---------------------------------------------------------------------------

    \20\ Some of these studies also included susceptible and 
vulnerable populations (e.g., children in Peel et al. (2005); poor 
and minority populations in Ito et al., 2007).
---------------------------------------------------------------------------

     A single study (Delfino et al., 2002) provides mixed 
evidence for NO2 effects (i.e., respiratory symptoms) in a 
location with a 98th percentile 1-hour daily maximum NO2 
concentration, as measured by an area-wide monitor, of 50 ppb. In that 
study, most of the reported NO2 effect estimates were 
positive, but not statistically significant. Given the variability in 
the NO2 effect estimates in this study, as well as the lack 
of studies in other locations with similarly low NO2 
concentrations, the Administrator judges it appropriate to place 
limited weight on this study, compared to the cluster of 5 studies as 
noted above.
    Given these considerations, the Administrator concludes that the 
epidemiologic evidence provides strong support for setting a standard 
that limits the 98th percentile of the distribution of 1-hour daily 
maximum area-wide NO2 concentrations to below 85 ppb. This 
judgment takes into account the determinations in the ISA, based on a 
much broader body of evidence, that there is a likely causal 
association between exposure to NO2 and the types of 
respiratory morbidity effects reported in these studies. Given the 
considerations discussed above, the Administrator judges that it is not 
necessary, based on existing evidence, to set a standard that maintains 
peak area-wide NO2 concentrations to below 50 ppb.
    In considering specific standard levels supported by the 
epidemiologic evidence, the Administrator notes that a level of 100 
ppb, for a standard reflecting the maximum allowable NO2 
concentration anywhere in the area, would be expected to maintain area-
wide NO2 concentrations well below 85 ppb, which is the 
lowest 98th percentile concentration in the cluster of 5 studies. With 
regard to this, she specifically notes the following:
     If NO2 concentrations near roads are 100% 
higher than concentrations away from roads, a standard level of 100 ppb 
would limit area-wide concentrations to approximately 50 ppb.
     If NO2 concentrations near roads are 30% higher 
than concentrations away from roads, a standard level of 100 ppb would 
limit area-wide concentrations to approximately 75 ppb.
    The Administrator has also considered the NO2 exposure 
and risk information within the context of the above conclusions on 
standard level. Specifically, she notes that the results of exposure 
and risk analyses were interpreted as providing support for limiting 
area-wide NO2 concentrations to no higher than 100 ppb. 
Specifically, these analyses estimated that a standard that limits 
area-wide NO2 concentrations to approximately 100 ppb or 
below would be expected to result in important reductions in 
respiratory risks, relative to the level of risk permitted by the 
current annual standard alone. As discussed above, a standard 
reflecting the maximum allowable NO2 concentration with a 
level of 100 ppb would be expected to maintain area-wide NO2 
concentrations to within a range of approximately 50 to 75 ppb. Given 
this, the Administrator concludes that a standard level of 100 ppb is 
consistent with conclusions based on the NO2 exposure and 
risk information.
    Finally, the Administrator notes that a standard level of 100 ppb 
is consistent with the consensus recommendation of CASAC.
    Given the above considerations and the comments received on the 
proposal, the Administrator determines that the appropriate judgment, 
based on the entire body of evidence and information available in this 
review, and the related uncertainties, is a standard level of 100 ppb 
(for a standard that reflects the maximum allowable NO2 
concentration anywhere in an area). She concludes that such a standard, 
with the averaging time and form discussed above, will provide a 
significant increase in public health protection compared to that 
provided by the current annual standard alone and would be expected to 
protect against the respiratory effects that have been linked with 
NO2 exposures in both controlled human exposure and 
epidemiologic studies. Specifically, she concludes that such a standard 
will limit exposures at and above 100 ppb for the vast majority of 
people, including those in at-risk groups, and will maintain maximum 
area-wide NO2 concentrations well below those in locations 
where key U.S. epidemiologic studies have reported that ambient 
NO2 is associated with clearly adverse respiratory health 
effects, as indicated by increased hospital admissions and emergency 
department visits.
    In setting the standard level at 100 ppb rather than a lower level, 
the Administrator notes that a 1-hour standard with a level lower than 
100 ppb would only result in significant further public health 
protection if, in fact, there is a continuum of serious, adverse health 
risks caused by exposure to NO2 concentrations below 100 ppb 
and/or associated with area-wide NO2 concentrations well-
below those in locations where key U.S. epidemiologic studies have 
reported associations with respiratory-related emergency department 
visits and hospital admissions. Based on the available evidence, the 
Administrator does not believe that such assumptions are warranted. 
Taking into account the uncertainties that remain in interpreting the 
evidence from available controlled human exposure and epidemiologic 
studies, the Administrator notes that the likelihood of obtaining 
benefits to public health with a standard set below

[[Page 6502]]

100 ppb decreases, while the likelihood of requiring reductions in 
ambient concentrations that go beyond those that are needed to protect 
public health increases.
    Therefore, the Administrator judges that a standard reflecting the 
maximum allowable NO2 concentration anywhere in an area set 
at 100 ppb is sufficient to protect public health with an adequate 
margin of safety, including the health of at-risk populations, from 
adverse respiratory effects that have been linked to short-term 
exposures to NO2 and for which the evidence supports a 
likely causal relationship with NO2 exposures. The 
Administrator does not believe that a lower standard level is needed to 
provide this degree of protection. These conclusions by the 
Administrator appropriately consider the requirement for a standard 
that is neither more nor less stringent than necessary for this purpose 
and recognizes that the CAA does not require that primary standards be 
set at a zero-risk level or to protect the most sensitive individual, 
but rather at a level that reduces risk sufficiently so as to protect 
the public health with an adequate margin of safety.

G. Annual Standard

    In the proposal, the Administrator noted that some evidence 
supports a link between long-term exposures to NO2 and 
adverse respiratory effects and that CASAC recommended in their 
comments prior to the proposal that, in addition to setting a new 1-
hour standard to increase public health protection, the current annual 
standard be retained. CASAC's recommendation was based on the 
scientific evidence and on their conclusion that a 1-hour standard 
might not provide adequate protection against exposure to long-term 
NO2 concentrations (Samet, 2008b).
    With regard to an annual standard, CASAC and a large number of 
public commenters (e.g., NACAA, NESCAUM; agencies from States including 
CA, IN, MO, NC, NY, SC, TX, VA; Tribal organizations including Fon du 
Lac and the National Tribal Air Organization; environmental/medical/
public health groups including ACCP, ALA, AMA, ATS, CAC, EDF, EJ, GASP, 
NACPR, NAMDRC, NRDC) agreed with the proposed decision to maintain an 
annual standard, though their recommendations with regard to the level 
of that annual standard differed (see below).
    As noted above, CASAC recommended ``retaining the current standard 
based on the annual average'' based on the ``limited evidence related 
to potential long-term effects of NO2 exposure and the lack 
of strong evidence of no effect'' and that ``the findings of the REA do 
not provide assurance that a short-term standard based on the one-hour 
maximum will necessarily protect the population from long-term 
exposures at levels potentially leading to adverse health effects'' 
(Samet, 2008b). A number of State agencies and organizations also 
recommended maintaining the current level of the annual standard (i.e., 
53 ppb). This recommendation was based on the conclusion that, while 
some evidence supports a link between long-term NO2 
exposures and adverse respiratory effects, that evidence is not 
sufficient to support a standard level either higher or lower than the 
current level. In addition, a number of industry groups (e.g., AAM, 
API, Dow, INGAA, UARG) recommended retaining the level of the current 
annual standard but, as described above, did so within the context of a 
recommendation that EPA should not set a new 1-hour standard.
    In contrast, some environmental organizations and medical/public 
health organizations as well as a small number of States (e.g., ALA, 
EDF, EJ, NRDC, and organizations in CA) recommended setting a lower 
level for the annual standard. These commenters generally supported 
their recommendation by pointing to the State of California's annual 
standard of 30 ppb and to studies where long-term ambient 
NO2 concentrations have been associated with adverse 
respiratory effects such as impairments in lung function growth.
    As discussed above (II.B.3), the evidence relating long-term 
NO2 exposures to adverse health effects was judged in the 
ISA to be either ``suggestive but not sufficient to infer a causal 
relationship'' (respiratory morbidity) or ``inadequate to infer the 
presence or absence of a causal relationship'' (mortality, cancer, 
cardiovascular effects, reproductive/developmental effects) (ISA, 
sections 5.3.2.4-5.3.2.6). In the case of respiratory morbidity, the 
ISA (section 5.3.2.4) concluded that ``The high correlation among 
traffic-related pollutants made it difficult to accurately estimate the 
independent effects in these long-term exposure studies.'' Given these 
uncertainties associated with the role of long-term NO2 
exposures in causing the reported effects, the Administrator concluded 
in the proposal that, consistent with the CASAC recommendation, 
existing evidence is not sufficient to justify setting an annual 
standard with either a higher or lower level than the current standard. 
Commenters have not submitted any new analyses or information that 
would change this conclusion. Therefore, the Administrator does not 
agree with the commenters who recommended a lower level for the annual 
standard.
    The Administrator judges that her conclusions in the proposal 
regarding the annual standard remain appropriate. Specifically, she 
continues to agree with the conclusion that, though some evidence does 
support the need to limit long-term exposures to NO2, the 
existing evidence for adverse health effects following long-term 
NO2 exposures does not support either increasing or 
decreasing the level of the annual standard. In light of this and 
considering the recommendation from CASAC to retain the current level 
of the annual standard, the Administrator judges it appropriate to 
maintain the level of the annual standard at 53 ppb.

H. Summary of Final Decisions on the Primary NO2 Standard

    For the reasons discussed above, and taking into account 
information and assessments presented in the ISA and REA, the advice 
and recommendations of the CASAC, and public comments, the 
Administrator has decided to revise the existing primary NO2 
standard. Specifically, the Administrator has determined that the 
current annual standard by itself is not requisite to protect public 
health with an adequate margin of safety. In order to provide 
protection for asthmatics and other at-risk populations against an 
array of adverse respiratory health effects related to short-term 
NO2 exposure, the Administrator is establishing a short-term 
NO2 standard defined by the 3-year average of the 98th 
percentile of the yearly distribution of 1-hour daily maximum 
NO2 concentrations. She is setting the level of this 
standard at 100 ppb, which is to reflect the maximum allowable 
NO2 concentration anywhere in an area. In addition to 
setting a new 1-hour standard, the Administrator retains the current 
annual standard with a level of 53 ppb. The new 1-hour standard, in 
combination with the annual standard, will provide protection for 
susceptible groups against adverse respiratory health effects 
associated with short-term exposures to NO2 and effects 
potentially associated with long-term exposures to NO2.

III. Amendments to Ambient Monitoring and Reporting Requirements

    The EPA is finalizing several changes to the ambient air 
monitoring, reporting, and network design requirements for the 
NO2 NAAQS. This section discusses the changes we are 
finalizing which are intended to support the proposed 1-

[[Page 6503]]

hour NAAQS and retention of the current annual NAAQS as discussed in 
Section II. Ambient NO2 monitoring data are used to 
determine whether an area is in violation of the NO2 NAAQS. 
Ambient NO2 monitoring data are collected by State, local, 
and Tribal monitoring agencies (``monitoring agencies'') in accordance 
with the monitoring requirements contained in 40 CFR parts 50, 53, and 
58.

A. Monitoring Methods

    We are finalizing the proposed changes regarding the NO2 
Federal Reference Method (FRM) or Federal Equivalent Method (FEM) 
analyzers. Specifically, we are continuing to use the NO2 
chemiluminescence FRM and are finalizing the requirement that any 
NO2 FRM or FEM used for making primary NAAQS decisions must 
be capable of providing hourly averaged concentration data. The 
following paragraphs provide background and rationale for the continued 
use of the chemiluminescence FRM and the decision to finalize the 
proposed changes.
1. Chemiluminescence FRM and Alternative Methods
    The current monitoring method in use by most State and local 
monitoring agencies is the gas-phase chemiluminescence FRM (40 CFR Part 
50, Appendix F), which was implemented into the NO2 
monitoring network in the early 1980s. EPA did not propose to 
discontinue using the chemiluminescence FRM, although we received some 
comments from industry (Alliance of Automobile Manufacturers, Edison 
Electric, and the National Petrochemical and Refiners Association) 
raising concerns about using a method that is subject to known 
interferences from certain species of oxides of nitrogen known as 
NOZ. Important components of ambient NOZ include 
nitrous acid (HNO2), nitric acid (HNO3), and the 
peroxyacetyl nitrates (PANs).
    The issue of concern in public comments is that the reduction of 
NO2 to NO on the MoOX converter substrate used in 
chemiluminescence FRMs is not specific to NO2; hence, 
chemiluminescence method analyzers are subject to varying interferences 
produced by the presence in the air sample of the NOZ 
species listed above and others occurring in trace amounts in ambient 
air. This interference is often termed a ``positive artifact'' in the 
reported NO2 concentration since the presence of 
NOZ results in an over-estimate in the reported measurement 
of the actual ambient NO2 concentration. This interference 
by NOZ compounds has long been known and evaluated 
(Fehsenfeld et al., 1987; Nunnermacker et al., 1998; Parrish and 
Fehsenfeld, 2000; McClenny et al., 2002; U.S. Environmental Protection 
Agency, 1993, 2006a). Further, as noted in the ISA (ISA Section 2.3), 
it appears that interference by NOZ on chemiluminescence 
FRMs is not more than 10 percent of the reported NO2 
concentration during most or all of the day during winter (cold 
temperatures), but larger interference ranging up to 70 percent can be 
found during summer (warm temperatures) in the afternoon at sites away 
and downwind from strong emission sources.
    The EPA acknowledges that the NOZ interference in the 
reported NO2 concentrations collected well downwind of 
NOX source areas and in relatively remote areas away from 
concentrated point, area, or mobile sources is significantly larger 
than the NOZ interference in NO2 measurements 
taken in urban cores or other areas with fresh NOX 
emissions. To meet the primary objective of monitoring maximum 
NO2 concentrations in an area, the EPA is requiring 
NO2 monitors to be placed in locations of the expected 
highest concentrations, not in relatively remote areas away from 
NOX sources. The required monitors resulting from the 
network design discussed below in Section III.B will require monitors 
to be placed near fresh NOX sources or in areas of dense 
NOX emissions, where NO2 concentrations are 
expected to be at a maximum, and interference from NOZ 
species is at a minimum. Therefore, EPA believes that the positive 
artifact issue, although present, is small, relative to the actual 
NO2 being measured. As a result EPA believes the 
chemiluminescence FRM is suitable for continued use in the ambient 
NO2 monitoring network, as the potential positive bias from 
NOZ species is not significant enough to discontinue using 
the chemiluminescence FRM.
    EPA also received support from some industry groups (e.g. Savannah 
River Nuclear Solutions, Teledyne API, and the Utility Air Regulatory 
Groups) and States (e.g., MODEQ and NCDENR) to further the development 
of alternative methods in determining NO2 concentrations. 
Such alternative methods include the photolytic- chemiluminescence 
method and cavity ring-down spectroscopy. As a result, EPA will 
continue working with commercial and industrial vendors, to identify 
and evaluate such new technologies. These efforts may include field 
testing instruments and further characterizing methods in a laboratory 
setting to assess their potential as future reference or equivalent 
methods, and their role in more directly measuring NO2.
2. Allowable FRM and FEMs for Comparison to the NAAQS
    The current CFR language does not prohibit the use of any 
particular NO2 FRM or FEM to be used in comparison to the 
standard.\21\ There are designated wet chemical methods that are only 
able to report ambient concentration values averaged across multiple 
hours. With the establishment of a 1-hour NAAQS, any FRM or FEM which 
is a wet chemical based method would not be appropriate for use in 
determining compliance of the 1-hour NAAQS because they are unable to 
report hourly data. EPA addressed this issue by proposing and 
finalizing that only those methods capable of providing 1-hour 
measurements will be comparable to the NAAQS.
---------------------------------------------------------------------------

    \21\ A list of approved FRM and FEMs is maintained by EPA's 
Office of Research and Development, and can be found at: http://www.epa.gov/ttn/amtic/files/ambient/criteria/reference-equivalent-methods-list.pdf.
---------------------------------------------------------------------------

a. Proposed Changes to FRM and FEMs That May Be Compared to the NAAQS
    EPA proposed that only those FRMs or FEMs that are capable of 
providing hourly averaged concentration data may be used for comparison 
to the NAAQS.
b. Comments
    EPA received comments from some State and industry groups (e.g. 
Missouri, North Carolina, and Air Quality Research and Logistics) 
supporting the proposed approach to only allowing those FRMs or FEMs 
that are capable of providing hourly averaged concentration data may be 
used for comparison to both the annual and 1-hour NAAQS, and did not 
receive any public comments that objected to the proposed approach.
c. Decisions on Allowable FRM and FEMs for Comparison to the NAAQS
    Accordingly, EPA is finalizing the proposed changes to 40 CFR Part 
58 Appendix C to allow only data from FRM or FEMs that are capable of 
providing hourly data to be used for comparison to both the annual and 
1-hour NAAQS.

B. Network Design

    With the establishment of a 1-hour NO2 NAAQS intended to 
limit exposure to maximum concentrations that may occur anywhere in an 
area, EPA recognizes that the data from the current NO2 
network is inadequate to fully assess compliance with the revised

[[Page 6504]]

NAAQS. As a result, EPA is promulgating new NO2 network 
design requirements. The following sections provide background, 
rationale, and details for the final changes to the NO2 
network design requirements.
1. Two-Tiered Network Design
    A two-tiered monitoring network is appropriate for the 
NO2 NAAQS because one tier (the near-road network) reflects 
the much higher NO2 concentrations that occur near-road and 
the second-tier (area-wide) characterizes the NO2 
concentrations that occur in a larger area such as neighborhood or 
urban areas. The ISA (Section 2.5.4 and 4.3.6) stated that 
NO2 concentrations in heavy traffic or on freeways ``can be 
twice the residential outdoor or residential/arterial road level,'' 
that ``exposure in traffic can dominate personal exposure to 
NO2,'' and that ``NO2 levels are strongly 
associated with distance from major roads (i.e., the closer to a major 
road, the higher the NO2 concentration).'' The exposure 
assessment presented in the REA estimated that roadway-associated 
exposures account for the majority of exposures to peak NO2 
concentrations (REA, Figures 8-17, 8-18). Monitoring studies suggest 
that NO2 concentrations near roads can be considerably 
higher than those in the same area but away from the road (e.g., by 30-
100%, see section II.A.2), where pollutants typically display peak 
concentrations on or immediately adjacent to roads, producing a 
gradient in pollutant concentrations where concentrations decrease with 
increasing distance from roads. Since the intent of the revised NAAQS 
is to limit exposure to peak NO2 concentrations that occur 
anywhere in an area, monitors intended to measure the maximum allowable 
NO2 concentration in an area should include measurements of 
the peak concentrations that occur on and near roads due to on-road 
mobile sources. The first tier of the network design, which focuses 
monitoring near highly trafficked roads in urban areas where peak 
NO2 concentrations are likely to occur, is intended to 
measure maximum concentrations anywhere in an area, particularly those 
due to on-road mobile sources since roadway-associated exposures 
account for the majority of exposures to peak NO2 
concentrations. The basis for the second tier of the network design is 
to measure the highest area-wide concentrations to characterize the 
wider area impact of a variety of NO2 sources on urban 
populations. Area-wide monitoring of NO2 also serves to 
maintain continuity in collecting data to inform long-term pollutant 
concentration trends analysis and support ongoing health and scientific 
research.
    This section discusses the two-tier network design approach 
compared to the alternative network design which was also presented for 
comment in conjunction with a solicitation for comment on an 
alternative NAAQS. The alternative network design concept was based 
entirely on requiring only monitors that would be considered area-wide, 
while not requiring any near-road monitoring sites. The details of the 
two-tier network design, including how many monitors are required, 
where they are to be located, and the related siting criteria are 
discussed in subsequent sections.
a. Proposed Two-Tier Network Design
    EPA proposed a two-tier network design composed of (1) near-road 
monitors which would be placed in locations of expected maximum 1-hour 
NO2 concentrations near heavily trafficked roads in urban 
areas and (2) monitors located to characterize areas with the highest 
expected NO2 concentrations at the neighborhood and larger 
spatial scales (also referred to as ``area-wide'' monitors). As an 
alternative, and in conjunction with a solicitation for comment on an 
alternative NAAQS, EPA solicited comment on a network comprised of only 
area-wide monitors.
b. Comments
    EPA received many comments on the overall two-tier network design, 
with those who made statements with a relatively clear position on the 
issue generally falling into four categories: (1) Those who support the 
adoption of the proposed two-tier design approach, (2) those who 
support the adoption of the two-tier concept, but with modifications, 
(3) those who only supported the adoption of the alternative network 
design, and (4) those who encourage EPA to commit to further research 
of the near-road environment by monitoring near-roads, but not to use 
near-road data for regulatory purposes, and therefore support the 
alternative network design in which EPA solicited comment on a network 
design composed only of area-wide monitors.
    Those commenters who generally supported the proposed two-tier 
network, included CASAC (while there was not a consensus, a majority 
were in support of the proposed network design), public health 
organizations (e.g., AACPR, ACCP, AMA, ATA, and NAMDRC), several State 
groups (e.g., the New York City Law Department and the Metropolitan 
Washington Air Quality Committee), and some industry commenters (e.g., 
American Chemistry Council, The Clean Energy Group, and Dow Chemical).
    Those commenters who supported the adoption of the two-tier network 
design concept, but suggested modifications to the actual design 
included some health and environmental organizations (e.g., ALA, EDF, 
EJ, and the NRDC), some States (e.g., California, the Central 
Pennsylvania Clean Air Board, Harris County (Texas), Iowa, New York, 
San Joaquin Air Pollution Control District, Spokane Regional Clean Air 
Agency (SRCAA), the Texas Commission on Environmental Quality, and 
Wisconsin), and some industry commenters, including the American 
Petroleum Institute and the Utility Air Regulatory Group, who are cited 
by other industry commenters. We believe that although these commenters 
made suggestions to modify the proposed two-tier network design, they 
are indicating that it is an acceptable approach. Their comments and 
suggestions are discussed in greater detail in the following sections.
    Those commenters who only supported the adoption of the alternative 
network design included State and industry groups (e.g., Indiana 
Department of Environmental Management, the New York Department of 
Transportation (NYSDOT), Alliance of Automobile Manufacturers, and the 
Engine Manufacturers Association). These commenters typically made 
comments on the two-tier network design, but did not do so in a way 
that clearly supported near-road research.
    EPA received comments from some States or State organizations 
(e.g., National Association of Clean Air Agencies (NACAA), the 
Northeast States for Coordinated Air Use Management (NESCAUM), and 10 
other individual States or State groups) and industry commenters (e.g., 
Consumers Energy, Edison Electric, and the National Association of 
Manufacturers) that encouraged EPA to further research the near-road 
environment, opposing use of near-road monitoring data for regulatory 
purposes, and supported the adoption of the alternative network design 
for regulatory purposes. For example, with regard to implementing the 
two-tier network design that includes near-road regulatory monitoring, 
NACAA stated that ``* * *a major new network--particularly one that is 
inherently complicated and untried--should not be rolled out without 
the benefit of an effective near-road monitoring research program that 
can address many of the relevant data questions, and inform the 
specific siting requirements of the rule.'' The NAM stated that 
``conducting such

[[Page 6505]]

a near road [research] monitoring program would allow EPA to collect 
necessary data that can be used to better understand the health impacts 
associated with short term NO2 exposures.''
    The EPA notes that the existing scientific research referenced in 
the proposal and throughout this final rule show that there are on- and 
near-road peaks of NO2 concentrations, relative to upwind or 
background levels, which exist due to on-road mobile source emissions. 
This research, as a body of evidence, also identifies the multiple 
local factors that affect how, where, and when peak NO2 
concentrations occur on or near a particular road segment. These 
factors include traffic volume, fleet mix, roadway design, congestion 
patterns, terrain, and meteorology. The EPA and States have access to 
such data typically through Federal, State, and/or local departments of 
transportation or other government organizations, and, as a result, are 
in a position to implement a near-roar monitoring network that is 
intended to measure maximum expected NO2 concentrations 
resulting from on-road mobile source emissions. Further, EPA notes that 
near-road monitoring is not a new objective for the ambient air 
monitoring community as near-road carbon monoxide monitoring has been a 
part of ongoing, long-term, routine networks for nearly three decades. 
As a result, there is experience within EPA (both OAR and ORD) and 
State and local agencies on conducting ambient monitoring near-roads. 
In addition, EPA intends to develop guidance with input from all 
stakeholders to assist with implementation of the monitoring 
requirements, which is discussed in section III.B.5. EPA believes that 
the existing science and research provide a sufficient base of 
information to require a near-road monitoring network and that the 
collective experience that exists in the ambient monitoring community 
will allow for successful implementation of that network. EPA also 
believes that through adherence of requirements for near-road site 
selection and siting criteria discussed in sections III.B.6 and 
III.B.7, respectively, that the two-tier network design will provide a 
network that has a reasonable degree of similarity across the country 
where the required near-road monitors are targeting the maximum 
NO2 concentrations in an area attributable to on-road mobile 
sources.
    Some industry commenters (e.g., Engine Manufacturers Association, 
the South Carolina Chamber of Commerce, and the South Carolina 
Manufacturers Alliance) who supported the adoption of the alternative 
network design suggested that monitoring in the near-road environment 
would not be indicative of exposure for general populations, and that 
EPA should not focus on the near-road environment when requiring 
monitoring. For example, the South Carolina Chamber of Commerce and the 
South Carolina Manufacturers Alliance both state that ``it appears the 
proposed monitoring network will result in a collection of microscale 
data, which is not at all representative of air quality relevant to 
population exposure.''
    The EPA notes that the intent of a near-road monitoring is to 
support the revised NAAQS by assessing peak NO2 
concentrations that may occur anywhere in an area. EPA recognizes that 
there is variability in the properties (such as traffic counts, fleet 
mix, and localized features) among the road segments that may exist in 
an area, but on the whole, roads are ubiquitous, particularly in urban 
environments. Consequently, a substantial fraction of the population is 
potentially exposed to relatively higher concentrations of 
NO2 that can occur in the near-road environment. The 2007 
American Housing Survey (http://www.census.gov/hhes/www/housing/ahs/ahs07/ahs07.html) estimates that over 20 million housing units are 
within 300 feet (91 meters) of a 4-lane highway, airport, or railroad. 
Using the same survey, and considering that the average number of 
residential occupants in a housing unit is approximately 2.25, it is 
estimated that at least 45 million American citizens live near 4-lane 
highways, airports, or railroads. Although that survey includes 
airports and railroads, roads are the most pervasive of the three, 
indicating that a significant amount of the general population live 
near roads. Furthermore, the 2008 American Time Use Survey (http://www.bls.gov/tus/) reported that the average U.S. civilian spent over 70 
minutes traveling per day. Accordingly, EPA concludes that monitors 
near major roads will address a component of exposure for a significant 
portion of the general population that would otherwise not be 
addressed.
    The majority of State commenters, regardless of their position on 
the proposed network design, along with some industry commenters, 
observed that there was a need for funding the monitoring network. 
These comments urged EPA to provide the resources needed to implement 
and operate the required monitoring network. EPA notes that it has 
historically funded part of the cost of the installation and operation 
of monitors used to satisfy Federal monitoring requirements. EPA 
understands these concerns, although the CAA requirements from which 
this final rule derives (CAA sections 110, 310(a) and 319) are not 
contingent on EPA providing funding to States to assist in meeting 
monitoring requirements. However, EPA intends to work with NACAA and 
the State and local air agencies in identifying available State and 
Tribal Air Grant (STAG) funds and consider the increased resource needs 
that may be needed to plan, implement, and operate this revised set of 
minimum requirements.
c. Conclusions Regarding the Two-Tier Network Design
    The EPA believes that requiring near-road monitors in urban areas 
as part of the network design are necessary to protect against risks 
associated with exposures to peak concentrations of NO2 
anywhere in an area. The combination of increased mobile source 
emissions and increased urban population densities can lead to 
increased exposures and associated risks, therefore urban areas are the 
appropriate areas to concentrate required near-road monitoring efforts. 
The EPA also recognizes the need to have monitors in neighborhood and 
larger spatial scale locations away from roads that represent area-wide 
concentrations. These types of monitors serve multiple important 
monitoring objectives including comparison to the NAAQS, photochemical 
pollutant assessment, ozone forecasting, characterization of point and 
area source impacts, and by providing historical trends data for 
current and future epidemiological health research. In some situations, 
when coupled with data from near-road monitors, area-wide monitors may 
also assist in the determination of spatial variation of NO2 
concentrations across a given area and provide insight to the gradients 
that exist between near-road or stationary source oriented 
concentrations and area-wide concentration levels.
    After considering the scientific data and the public comments 
regarding the proposed network design, the Administrator concludes that 
a two-tier network design composed of (1) near-road monitors which 
would be placed in locations of expected maximum 1-hour NO2 
concentrations near heavily trafficked roads in urban areas and (2) 
monitors located to characterize areas with the maximum expected 
NO2 concentrations at the neighborhood and larger spatial 
scales (also referred to as ``area-wide'' monitors) are needed to 
implement the 1-hour NO2 NAAQS and

[[Page 6506]]

support the annual NAAQS. The details of this two-tier network design 
are discussed in the following eight sections.
2. First Tier (Near-Road Monitoring Component) of the NO2 
Network Design
    This section provides background, rationale, and details for the 
final changes to the first tier of the two-tier NO2 network 
design. In particular, this section will focus on the thresholds that 
trigger monitoring requirements. Near-road site selection and siting 
criteria details will be discussed in subsequent sections.
a. Proposed First Tier (Near-Road Monitoring Component) of the Network 
Design
    EPA proposed that the first tier of the two-tier NO2 
monitoring network design focus monitors in locations of expected 
maximum 1-hour concentrations near major roads in urban areas. As noted 
in the previous section, the exposure assessment presented in the REA 
estimated that roadway-associated exposures account for the majority of 
exposures to peak NO2 concentrations (REA, Figures 8-17, 8-
18). Since the combination of increased mobile source emissions and 
increased urban population densities leads to increased exposures and 
associated risks, the Administrator judges that urban areas are the 
appropriate areas in which to concentrate required near-road monitoring 
efforts. Therefore, we proposed that a minimum of one near-road 
NO2 monitor be required in Core Based Statistical Areas 
(CBSAs) with a population greater than or equal to 350,000 persons. 
Based on 2008 Census Bureau statistics, EPA estimated this would result 
in approximately 143 monitoring sites in as many CBSAs.
    We also proposed that a second near-road monitor be required in 
CBSAs with a population greater than or equal to 2,500,000 persons, or 
in any CBSAs with one or more road segments with an Annual Average 
Daily Traffic (AADT) count greater than or equal to 250,000. Based on 
2008 Census Bureau statistics and data from the 2007 Highway 
Performance Monitoring System (HPMS) maintained by the U.S. Department 
of Transportation (DOT) Federal Highway Administration (FHWA), this 
particular element of the minimum monitoring requirements would have 
added approximately 24 \22\ sites to the approximate 143 near-road 
sites in CBSAs that already would have had one near-road monitor 
required due to the 350,000 population threshold. Overall, the first 
tier of the proposed network design was estimated to require 167 near-
road sites in 143 CBSAs.
---------------------------------------------------------------------------

    \22\ Of the 24 additional sites, 22 are estimated to be 
triggered due to a population of 2,500,000 while 2 (Las Vegas, NV 
and Sacramento, CA) are estimated to be triggered by the presence of 
one or more road segments with 250,000 AADT since they do not have a 
population of 2,500,000 people.
---------------------------------------------------------------------------

b. Comments
    The EPA received comments from some industry and public health 
organizations (e.g. Dow Chemical, ATS, and the AMA) supporting the 
proposed approach to use population thresholds for triggering minimum 
near-road monitoring requirements. For example, Dow Chemical Company 
stated that ``Dow comments that the proposed population thresholds are 
reasonable for implementation of the new network design and that we 
don't see a need to establish a threshold lower than 350,000 people for 
the lower bound.''
    The EPA received comments from some States and State groups 
suggesting that a combination of population and AADT counts or just 
AADT counts should be used to trigger minimum near-road monitoring 
requirements. For example, the San Joaquin Air Pollution Control 
District in California suggested that we modify minimum monitoring 
requirements so that one near-road NO2 monitor is required 
for any CBSA with a population of 350,000 people which also had one or 
more road segments with AADT counts of 125,000 or more. In another 
example, Harris County Public Health and Environmental Services 
(HCPHES) suggested that ``* * * rather than specifying population 
limits for the monitoring, HCPHES supports a metric like the Annual 
Average Daily Traffic (AADT) as a threshold for requiring a near-road 
monitor. An initial focus on an AADT in excess of 250,000 is acceptable 
as a starting point but EPA should revisit that level and consider 
lowering it to 100,000 in five years.'' AASHTO \23\ and NYDOT \23\ 
suggested that EPA could set a threshold at 140,000 AADT for requiring 
near-road monitors rather than using population thresholds.
---------------------------------------------------------------------------

    \23\ AASHTO, NESCAUM, and NYDOT did not support the two-tier 
network design; however they provided suggestions on how the network 
design might be modified if the EPA were to finalize requirements 
for near-road monitors. In the case of AASHTO and NYDOT, their 
suggestions were made with the suggestion that EPA use a separate 
rulemaking process to require monitors.
---------------------------------------------------------------------------

    EPA is finalizing the population-only threshold approach to trigger 
near-road monitoring, as the first step in the process of establishing 
the first-tier of near-road monitors, and for identifying the 
appropriate number and locations for siting these monitors. EPA 
believes that the uncertainty in defining specific national AADT counts 
is too great to support use in this first step of the alternative 
approaches suggested by the commenters. EPA notes that, in general, 
roads with higher AADT counts have relatively higher amounts of mobile 
source emissions, leading to an increased potential for relatively 
higher on-road and roadside NO2 concentrations. This concept 
is supported, for example, by Gilbert et al., 2007, who state that the 
NO2 concentrations analyzed in their study are significantly 
associated with traffic counts. In part, these suggestions by 
commenters to include AADT counts as part of, or independently as, a 
threshold for requiring monitors appears to be aimed at increasing the 
focus of the near-road network to locations where NO2 
concentrations are expected to be highest. However these suggestions 
would also, in effect, reduce the size of the required network compared 
to the network that EPA had proposed. The differences in fleet mix, 
roadway design, congestion patterns, terrain, and local meteorology 
amongst road segments that may have identical AADTs are quite variable 
and affect the NO2 concentrations on and near those 
segments. The available data and related technical and scientific 
quantification of what particular AADT count might be expected to 
contribute to some specific NO2 concentration is 
insufficient to establish a specific, nationally applicable AADT count 
threshold that could be used as part of a population-AADT combination, 
or a distinct AADT count, to require all near-road monitors. Therefore, 
EPA chose not to utilize a population-AADT or an AADT-only threshold to 
trigger all minimally required near-road monitoring because of the lack 
of a quantitative, nationally applicable relationship between a certain 
AADT threshold and an expected NO2 concentration. Instead, 
EPA is finalizing the proposed population-only threshold approach to 
trigger a minimum of one monitor in a CBSA. In larger CBSAs, EPA does 
require, at a minimum, a second monitor based on either an AADT count 
of 250,000 or a population threshold of 2,500,00 or more persons in a 
CBSA as described more fully below. EPA believes this approach for 
siting near-road monitoring provides a greater degree of certainty in 
covering a large segment of the total population (66%, which is 
explained below) and will provide data on exposure from geographically 
and spatially diverse areas where a larger number of people

[[Page 6507]]

are likely to be exposed to peak NO2 concentrations.
    Some commenters (e.g., AASHTO,\23\ NESCAUM,\23\ NYDEC, NYDOT \23\) 
suggested focusing multiple near-road monitors only in relatively 
larger CBSAs than those which were proposed. For example, NYDEC 
suggested that EPA require, at minimum, two near-road monitors in any 
CBSA of 2,500,000 people or more, but not in CBSAs below that 
population threshold. In their comments, they point out the variety of 
near-road environments that exist in the larger CBSAs such as New York 
City.
    EPA notes that the larger CBSAs, such as those with a population of 
2,500,000 or more persons, are more likely to have a greater number of 
major roads across a potentially larger geographic area, and a 
corresponding increase in potential for exposure in different settings 
(evidenced in the U.S. Department of Transportation (U.S. DOT) Federal 
Highway Administration (FHWA) ``Status of the Nation's Highways, 
Bridges, and Transit: 2006 Conditions and Performance'' document which 
is discussed below). This is the primary reasoning behind the 
requirement for two monitors in CBSAs with more than 2,500,000 people. 
EPA also believes that having multiple monitors in the largest CBSAs 
will allow better understanding of the differences that may exist 
between roads in the same CBSA due to fleet mix, congestion patterns, 
terrain, or geographic locations. However, EPA believes that a network 
with substantially fewer monitors in correspondingly fewer CBSAs, as 
the commenters suggested, would lead to an insufficient monitoring 
network lacking a balanced approach needed for a regulatory network 
intended to support the revised NAAQS on a national basis.
    On a related note to those comments that suggested focusing more 
near-road monitors only in the larger CBSAs, EPA proposed that any 
CBSAs with one or more road segments with an Annual Average Daily 
Traffic (AADT) count greater than or equal to 250,000 must have a 
second monitor if they do not already have two near-road monitors 
because of the population threshold. Such an AADT-triggered monitor 
would account for situations where a relatively less populated area has 
a very highly trafficked road. In this case, EPA notes that because 
those road segments with 250,000 AADT have been identified by U.S. DOT 
FHWA (http://www.fhwa.dot.gov/policyinformation/tables/02.cfm) as being 
the top 0.03 percent of the most traveled public road segments, that 
they are the most heavily trafficked roads in the country. Again noting 
that NO2 concentrations are significantly associated with 
traffic counts (Gilbert et al. 2007), these roads segments likely have 
the greatest potential for high exposures directly connected to motor 
vehicle emissions in the entire country. Typically, these very highly 
trafficked roads are in the largest populated CBSAs, such as those with 
2,500,000 people or more, and are somewhat atypical for CBSAs with less 
than 2,500,000 people. As a result, EPA believes it is appropriate to 
require a second monitor in a CBSA that has one or more road segments 
with 250,000 AADT counts or more if they do not already have two near-
road monitors required due their population.
    EPA received comments requesting that EPA explain the rationale for 
the selection of the population thresholds that trigger minimum 
monitoring requirements and also to reconsider the size of the network. 
For example, NYDOT suggested that this final rule explain the basis for 
the 350,000 and 2,500,000 population thresholds that will establish 
near-road monitors. In another comment, the Clean Air Council (CAC) 
questioned the selected population thresholds, noting that they believe 
that the population thresholds that were proposed were too high. 
Specifically, CAC stated that ``at 350,000 persons, numerous metro 
areas in the mid-Atlantic and Northeastern States with urban cores and 
highways running through will likely be exempted from the new 
monitors.'' The Spokane Regional Clean Air Agency stated that they ``do 
not believe it is necessary to require air quality monitoring for 
NO2 near major roadways in every metropolitan area. It is 
our [SRCAA's] view that EPA could establish a statistically significant 
number of air quality monitoring stations near roadways and develop a 
correlation between traffic density and ambient NO2 
levels.'' Further, the EPA received many State comments suggesting 
reductions to the overall size of the near-road network; however the 
commenters did not provide very specific suggestions on how EPA should 
accomplish that reduction in size. For example, the Regional Air 
Pollution Control Agency, which represents a portion of Ohio, stated 
``given the fairly standard fleet of vehicles on the nation's major 
highways, we urge EPA to consider the need for 142 near-roadway 
monitors. Perhaps a limited number of monitors across the country would 
suffice to sufficiently characterize near-roadway NO2 
levels.'' These State commenters provided various reasons which are 
discussed throughout this document suggesting that the network be 
reduced in size, including funding concerns (section III.B.1.b), the 
perceived need to implement a smaller near-road research network in 
lieu of a regulatory network (section III.B.1.b), safety issues 
(section III.B.7.b), and problems with State implementation plans 
(section VI. D) and designation issues (section V).
    EPA notes that the intent of the first tier of the network design 
is to support the revised NAAQS in measuring peak NO2 
exposures in an area by including a minimum number of monitors 
resulting in a sufficiently sized national near-road monitoring network 
that will provide data from a geographically and spatially diverse 
array of areas, in terms of population, potential fleet mixes, 
geographic extent, and geographic setting, from across the country. The 
U.S. Department of Transportation (U.S. DOT) Federal Highway 
Administration (FHWA) ``Status of the Nation's Highways, Bridges, and 
Transit: 2006 Conditions and Performance'' document (http://www.fhwa.dot.gov/policy/2006cpr/es02h.htm) states that ``while urban 
mileage constitutes only 24.9 percent of total (U.S.) mileage, these 
roads carried 64.1 percent of the 3 trillion vehicles miles (VMT) 
travelled in the United States in 2004.'' The document also states that 
``urban interstate highways made up only 0.4 percent of total (U.S.) 
mileage but carried 15.5 percent of total VMT.'' These statements 
indicate how much more traffic volume exists on roads in urban areas 
versus the more rural areas that have significant amounts mileage of 
the total public road inventory. The basis for the selection of the 
proposed CBSA population level of 350,000 to trigger the requirement of 
one near-road monitor was chosen in an attempt to provide near-road 
monitoring data from a diverse array of areas, as noted above. However, 
in response to the significant number of comments discussed above, 
which in various ways encouraged at least a reduction of the size of 
the required near-road network or the implementation of a relatively 
smaller research network, EPA reconsidered the population threshold 
that will require one near-road NO2 monitor in a CBSA.
    EPA reviewed the data, such as population, geographic, and spatial 
distribution, associated with particular CBSA areas that would and 
would not be included in particular CBSA population thresholds. 
According to the 2008 U.S. Census Bureau estimates (http://www.census.gov) there are 143 CBSAs with 350,000 or more persons 
(including territories) which contain approximately 71% of the total 
population (excluding territories). These

[[Page 6508]]

CBSAs collectively represent territory in 44 States, the District of 
Columbia, and Puerto Rico. For comparison, there are 391 CBSAs with 
100,000 or more persons, which contain approximately 86% of the total 
population (excluding territories). These particular CBSAs collectively 
represent territory in 49 States, the District of Columbia, and Puerto 
Rico. Further, there are 102 CBSAs with 500,000 or more persons, which 
contain approximately 66% of the total population (excluding 
territories). These 102 CBSAs collectively represent territory in 43 
States, the District of Columbia, and Puerto Rico. Finally, there are 
22 CBSAs with 2,500,000 or more persons, which contain approximately 
39% of the total population, collectively representing territory in 19 
States, the District of Columbia, and Puerto Rico. In comparison to the 
CBSA population threshold of 350,000, the 500,000 population threshold 
has 41 less CBSAs. However, the percentage of the total U.S. population 
residing in these two sets of CBSAs differs by only approximately 5 
percent of the total population (e.g., 71% in CBSAs of 350,000 or more 
versus 66% in CBSAs of 500,000 or more persons). Also, when comparing 
the number of States that have some amount of their territory included 
in these CBSAs, the difference between the two sets of CBSAs differs by 
only 1 State (Alaska).
    Further, EPA notes that the REA Air Quality Analysis, (REA, section 
7.3.2) estimated the exceedences of health benchmark levels across the 
United States, including explicit consideration of on- or near- roadway 
exceedances in 17 urban areas associated with CBSA populations ranging 
from approximately 19,000,000 to 540,000. The analysis indicated that 
all 17 of the areas under explicit consideration were estimated to 
experience NO2 concentrations on or near roads that exceeded 
health benchmark levels.
c. Conclusions Regarding the First Tier (Near-Road Monitoring 
Component) of the Network Design
    After consideration of public comments, and in light of the 
information discussed above, the Administrator has chosen to finalize 
the CBSA population threshold for requiring a minimum of one near-road 
monitor in CBSAs with a population of 500,000 or more persons. The 
Administrator is finalizing the other thresholds that will trigger a 
second near-road monitor as proposed. Accordingly, one near-road 
NO2 monitor is required in CBSAs with a population greater 
than or equal to 500,000 persons and a second near-road monitor is 
required in CBSAs with a population greater than or equal to 2,500,000 
persons, or in any CBSAs with one or more road segments with an Annual 
Average Daily Traffic (AADT) count greater than or equal to 250,000.
    The Administrator has concluded that using a population threshold 
of 500,000 to require a minimum of one near-road monitor in a CBSA 
provides a sufficiently sized, national network of near-road monitors 
that will provide data from a geographically and spatially diverse set 
of CBSAs that supports the intent of the revised NAAQS and continues to 
meet the monitoring objectives of the network. Combined with the forty 
additional monitors that the Regional Administrators are required to 
site, discussed below, the monitoring network would cover an additional 
percentage of the total population.
    EPA believes that selecting a lower population threshold, such as 
100,000 or, to a lesser degree, 350,000, as discussed in the above 
examples, would create a much larger network of required near-road 
monitors but would provide diminished population coverage per monitor, 
compared to that provided by the 500,000 threshold. EPA notes that if a 
particular area, such as one with a population less than 500,000 
people, might warrant a near-road monitor, the Regional Administrator 
has the authority to require additional monitors. The Regional 
Administrators' authority is discussed in section III.B.4. Further, 
States have the right to conduct additional monitoring above the 
minimum requirements on their own initiative. In the Administrator's 
judgment, selecting a higher threshold, such as 2,500,000, as was 
suggested by some commenters, does not provide a sufficient 
geographical and spatially diverse near-road network, compared to that 
provided by the 500,000 threshold. The selection of the 2,500,000 
population threshold to trigger a second near-road monitor, as noted 
earlier in this section, is based on the fact that the larger urban 
areas in the country are likely to have a greater number of major roads 
across a potentially larger geographic area, and have a corresponding 
increase in potential for population exposure to elevated levels in 
different settings.
    Changing the CBSA population threshold 350,000 to 500,000 results 
in a near-road monitoring network requiring approximately 126 monitors 
distributed within 102 CBSAs. Compared to the total number of required 
near-road monitors that would have resulted from the proposed CBSA 
population threshold of 350,000 (167 monitors), an estimated 41 fewer 
monitors are required. EPA has also recognized that susceptible and 
vulnerable populations, which include asthmatics and disproportionately 
exposed groups, (as discussed in sections II.B.4 and II.F.4.d) are at 
particular risk of NO2-related health effects. The 
Administrator is therefore requiring the Regional Administrators, 
working in collaboration with States, to site forty monitors in 
appropriate locations, focusing primarily on protecting such 
susceptible and vulnerable communities. This decision is discussed in 
detail in section III.B.4.
3. Second Tier (Area-Wide Monitoring Component) of the Network Design
    The following paragraphs provide background, rationale, and details 
for the final changes to the second tier of the two-tier NO2 
network design. In particular, this section will focus on the threshold 
that triggers area-wide monitoring requirements. Area-wide site 
selection and siting criteria details will be discussed in a subsequent 
section.
a. Proposed Second Tier (Area-Wide Monitoring Component) of the Network 
Design
    As the second tier of the proposed two-tier network design, EPA 
proposed to require monitors to characterize the expected maximum 
NO2 concentrations at the neighborhood and larger (area-
wide) spatial scales in an area. This component of the two-tier network 
design provides information on area-wide exposures that may occur due 
to an individual or a group of point, area, on-road, and/or non-road 
sources. Further, area-wide sites serve multiple monitoring objectives 
aside from NAAQS comparison to both the 1-hour and the annual NAAQS, 
including photochemical pollutant assessment, aiding in ozone 
forecasting, aiding in particulate matter precursor analysis and 
particulate matter forecasting. We proposed to require one area-wide 
monitoring site in each CBSA with a population greater than or equal to 
1,000,000. We proposed that these area-wide sites were to be sited to 
represent an area of highest concentration at the neighborhood or 
larger spatial scales. Based on 2008 Census Bureau statistics, there 
are 52 CBSAs with 1,000,000 people or more, which would result in an 
estimated 52 area-wide monitors in as many CBSAs being minimally 
required. EPA also proposed to allow any current photochemical 
assessment monitoring station (PAMS) sites that are sited where the 
highest NO2 concentrations occur in an urban area

[[Page 6509]]

and represent a neighborhood or urban scale to satisfy the area-wide 
monitoring requirement.
b. Comments
    Most commenters who commented on area-wide monitoring supported the 
adoption of the alternative area-wide network design and did not 
specifically comment on the area-wide monitoring component of the 
proposed two-tier network design. However, EPA did receive comments 
from public health organizations on area-wide monitoring in the context 
of the proposed network design. The public health group commenters, 
including the ALA, EJ, EDF, and the NRDC, stated they ``oppose the 
proposed requirement to retain only 52 air monitors to measure area-
wide concentrations of NO2.''
    EPA understands the perceived concern to be that with this 
provision, EPA is actively reducing the number of required area-wide 
monitors. Prior to this rulemaking, the Ambient Air Monitoring 
Regulations, 71 FR 61236 (Oct. 17, 2006) (2006 monitoring rule) removed 
minimum monitoring requirements for NO2, and the rationale 
for that action is explained in that rule; however, the 2006 Monitoring 
rule has had a limited impact to date, evidenced by the fact that the 
size of the NO2 network has remained relatively steady at 
around 400 monitors, a majority of which are area-wide monitors, that 
were operating in 2008 (Watkins and Thompson, 2008). The stability of 
the NO2 network is due in large part to the fact that area-
wide monitors serve multiple monitoring objectives, including 
photochemical pollutant assessment, pollutant forecasting, and in some 
cases, support to ongoing health research. However, considering the 
objective of this two-tier network design, particularly the first tier, 
of supporting the revised NAAQS to protect against peak NO2 
exposures, some shrinkage in the area-wide network is appropriate and 
likely. EPA believes that the actual number of area-wide monitors that 
will operate in the NO2 network will be greater than the 
minimally required 52 sites, but likely less than the current number. 
States and Regional Administrators will work together on which area-
wide sites may warrant retention above the minimum required if States 
request existing area-wide sites to be shut down or relocated.
c. Conclusions on the Second Tier (Area-Wide Monitoring Component) of 
the Network Design
    Area-wide monitoring sites serve multiple monitoring objectives 
aside from NAAQS comparison to both the 1-hour and the annual NAAQS, 
including photochemical pollutant assessment, ozone forecasting, 
particulate matter precursor analysis and particulate matter 
forecasting. EPA recognizes that a significant portion of the existing 
NO2 monitoring network can be characterized as area-wide 
monitors and that these monitoring sites serve multiple monitoring 
objectives, as noted above. In order to ensure that a minimum number of 
area-wide monitors continue operating into the future, we are 
finalizing the proposed minimum monitoring requirements for area-wide 
monitors, where one area-wide monitor is required in any CBSA with 
1,000,000 people or more. Since there were no adverse comments received 
with regard to allowing PAMS stations that meet siting criteria to 
satisfy minimum monitoring requirements for area-wide monitors, we are 
finalizing that allowance as proposed. EPA encourages States to use the 
upcoming 2010 network assessment process to review existing area-wide 
NO2 sites to help determine what monitors might meet minimum 
monitoring requirements and whether or not other existing monitors 
warrant continued operation.
4. Regional Administrator Authority
    The following paragraphs provide background, rationale, and details 
for the final changes to Regional Administrator authority to use 
discretion in requiring additional NO2 monitors beyond the 
minimum network requirements. The proposed rule estimated that 
approximately 167 near-road monitors would be required within CBSAs 
having populations of 350,000 or more persons. As discussed above in 
section III.B.2, in response to public comments, particularly from 
States, EPA is changing the population threshold for siting a minimum 
of one near-road NO2 monitor from CBSAs with 350,000 or more 
persons to CBSAs with 500,000 or more persons. EPA estimates that this 
change in the population threshold will result in a reduction in the 
number of minimally required near-road NO2 monitors by 
approximately forty monitors. EPA has also recognized that susceptible 
and vulnerable populations, which include asthmatics and 
disproportionately exposed groups (as discussed in sections II.B.4 and 
II.F.4.d) are at particular risk of NO2-related health 
effects. The Administrator is therefore requiring the Regional 
Administrators, working in collaboration with States, to site these 
forty monitors in appropriate locations, focusing primarily on 
protecting susceptible and vulnerable communities. In addition, the 
Regional Administrators, working with States, may take into account 
other considerations described below in using their discretion to 
require additional monitors.
a. Proposed Regional Administrator Authority
    EPA proposed that Regional Administrators have the authority to 
require monitoring at their discretion in particular instances. First, 
EPA proposed that the Regional Administrator have discretion to require 
monitoring above the minimum requirements as necessary to address 
situations where the required near-road monitors do not represent a 
location or locations where the expected maximum hourly NO2 
concentrations exist in a CBSA. Second, EPA proposed to allow Regional 
Administrators the discretion to require additional near-road 
monitoring sites to address circumstances where minimum monitoring 
requirements are not sufficient to meet monitoring objectives, such as 
where exposures to NO2 concentrations vary across an area 
because of varied fleet mixes, congestion patterns, terrain, or 
geographic areas within a CBSA. And third, EPA proposed that Regional 
Administrators have the discretion to require additional area-wide 
NO2 monitoring sites above the minimum requirements for 
area-wide monitors where the minimum requirements are not sufficient to 
meet monitoring objectives.
b. Comments
    EPA received comments from the Center on Race, Poverty and 
Environment expressing concern that the proposed monitoring provisions 
fail to consider ``disproportionately impacted communities'' which 
include people of color and of lower socioeconomic status. The 
commenter argues that this is ``a gaping hole'' in the proposed 
monitoring system and disproportionately impacts minority and low 
income populations in rural communities. In addition, the National 
Tribal Air Association stated that ``Indian Tribes and Alaska Natives 
are highly susceptible to health impacts as a result of NO2 
exposure'' and ``the prevalence and severity of asthma is higher among 
certain ethnic or racial groups such as Indian Tribes and Alaska 
Natives,'' which is also discussed in section II.B.4 and the ISA (ISA, 
section 4.4).
    The proposed rule provided the Regional Administrators with the 
authority to use their discretion and

[[Page 6510]]

consider certain factors to require monitors above the minimum number 
in a CBSA. The proposal described one example where a Regional 
Administrator might require an additional near-road monitor where ``a 
particular community or neighborhood is significantly or uniquely 
affected by road emissions.'' EPA recognizes that susceptible and 
vulnerable populations, which include asthmatics and disproportionately 
exposed groups, as noted in section II.F.4.d, are at particular risk of 
NO2-related health effects, both because of increased 
exposure and because these groups have a higher prevalence of asthma 
and higher hospitalization rates for asthma. As noted above, in 
conjunction with raising the threshold for requiring one near-road 
NO2 monitor in CBSAs with 500,000 persons or more, EPA is 
requiring the Regional Administrators, under their discretionary 
authority, to work with States to site an additional forty monitors, 
nationally, focusing primarily on communities where susceptible and 
vulnerable populations are located. To address the risks of increased 
exposure to these populations, the Administrator has determined that it 
is appropriate and necessary, under this provision, to ensure these 
additional forty monitors are sited primarily in communities where 
susceptible and vulnerable populations are exposed to NO2 
concentrations that have the potential to exceed the NAAQS (due to 
emissions from motor vehicles, point sources, or area sources). As a 
result of this action, the total number of monitors required through 
this rulemaking is generally equivalent to the proposed number of 
minimally required monitors.
    EPA received comments from public health groups (e.g., ALA, Center 
on Race, Poverty, and the Environment, EDF, EJ, NRDC) and the Swinomish 
Tribe, who suggested that EPA expand monitoring coverage to address 
impacts from stationary sources outside of urban areas. For example, 
ALA, EDF, EJ, and NRDC, stated that ``EPA should require States and 
local offices to review inventory data to identify any potential 
NO2 hotspots outside of those large metropolitan areas. For 
instance, if a large power plant or any other source is creating 
elevated NO2 levels in proximity to homes, schools or other 
sensitive sites, in an area of less than one million people, EPA should 
consider requiring a monitor.''
    EPA recognizes that there are major NO2 sources outside 
of CBSAs that have the potential to contribute to NO2 
concentrations approaching or exceeding the NAAQS. The issue is whether 
such monitoring should be addressed through a more extensive set of 
minimum requirements that might include monitoring near all large 
stationary sources such as airports, seaports, and power plants, which 
could lead to deploying a large number of monitors. EPA believes that a 
more reasonable approach to address monitoring needs related to the 
diverse set of point, area, and non-road mobile NO2 sources, 
whether inside or outside of CBSAs, is to provide Regional 
Administrators the authority to require additional monitoring in areas 
where these impacts could occur. While the proposal did not 
specifically state that Regional Administrators could require non-area-
wide monitors outside of CBSAs, EPA believes that it is important that 
Regional Administrators have the authority to require NO2 
monitoring in locations where NO2 concentrations may be 
approaching or exceeding the NAAQS, whether located inside or outside 
of CBSAs. Therefore, in the final rule, EPA is not limiting the 
Regional Administrators' discretionary authority to require 
NO2 monitoring only inside CBSAs; instead, the EPA is 
providing Regional Administrators the authority to site monitors in 
locations where NO2 concentrations may be approaching or 
exceeding the NAAQS, both inside or outside of CBSAs.
    The EPA also received comments from some State groups (e.g. the New 
York Department of Environmental Conservation (NYSDEC), New York 
Department of Transportation (NYSDOT), and the New York City Law 
Department) and an industry group (the Council of Industrial Boiler 
Operators) requesting greater clarification on the way in which 
Regional Administrators may use their authority to require additional 
monitors above the minimum requirements. For example, the Council of 
Industrial Boiler Operators stated that ``this [Regional Administrator 
authority] unreasonably vests an unbounded amount of discretion in EPA 
to determine when ``minimum monitoring requirements are not 
sufficient'' and which neighborhoods are ``uniquely affected,'' and 
impose additional monitoring requirements where all applicable 
monitoring requirements are already met by the State and local 
agency.''
    The authority of Regional Administrators to require additional 
monitoring above the minimum required is not unique to NO2. 
For example, Regional Administrators have or are proposed to have the 
authority to use their discretion to require additional Pb monitors (40 
CFR Part 58 Appendix D section 4.5), and have the discretion to work 
with States or local agencies in designing and/or maintaining an 
appropriate ozone network, per 40 CFR Part 58 Appendix D section 4.1. 
EPA believes that while the NO2 monitoring network is 
sufficiently sized and focused, a nationally applicable network design 
may not account for all locations in which potentially high 
concentrations approaching or exceeding the NAAQS exist. Therefore, EPA 
believes it is important for Regional Administrators to have the 
ability to address possible gaps in the minimally required monitoring 
network, by granting them authority to require monitoring above the 
minimum requirements.
    One case in which the Regional Administrator may exercise 
discretion in requiring a monitor might be a location or community 
affected by a stationary source where the required near-road 
NO2 monitor site is not the location of the maximum hourly 
concentration in a CBSA. For any given CBSA, there is the possibility 
that the maximum NO2 concentrations could be attributed to 
impacts from one, or a combination of, multiple sources that could 
include point, area, and non-road source emissions in addition to on-
road mobile source emissions. As a result, the Regional Administrator 
may choose to require monitoring in such a location. In addition, there 
is the possibility that a single source or group of sources exists 
which may contribute to concentrations approaching or exceeding the 
NAAQS at locations inside or outside CBSAs, including rural 
communities. In such cases, Regional Administrators, working with 
States, may require a monitor in these locations. Further, if there are 
NO2 sources responsible for producing more widespread 
impacts on a community or relatively larger area, Regional 
Administrators may require an area-wide monitor to assess wider 
population exposures, or to support other monitor objectives served by 
area-wide monitors such as photochemical pollutant assessment or 
pollutant forecasting.
    Regional Administrators may also require additional monitoring 
where a State or local agency is fulfilling its minimum monitoring 
requirements with an appropriate number of near-road monitors, but an 
additional location is identified where near-road population exposure 
exists at concentrations approaching or exceeding the NAAQS. In this 
case, the exposure may be due to differences in fleet mix, congestion 
patterns, terrain, or geographic area, relative to any minimally 
required monitoring site(s) in that area. We note

[[Page 6511]]

that such areas might exist in CBSAs with populations less than 500,000 
persons.
    EPA recognizes that high concentrations of NO2 that 
approach or exceed the NAAQS could potentially occur in a variety of 
locations in an area, and we believe that Regional Administrators 
should have the discretion to require additional monitoring when a 
location is identified based on the factors discussed in the paragraph 
above. In such situations, State or EPA Regional staff is likely to 
have identified these locations through data analysis, such as the 
evaluation of existing ambient data and/or emissions data, or through 
air quality modeling. Such information may indicate that an area has 
NO2 concentrations that may approach or exceed the NAAQS, 
and that there is potential for population exposure to those high 
concentrations.
    The Regional Administrator would use this authority in 
collaboration with State agencies. We expect Regional Administrators to 
work with State and local agencies to design and/or maintain the most 
appropriate NO2 network to meet the needs of a given area. 
For all the situations where a Regional Administrator may require 
additional monitoring, including the forty additional monitors the 
Regional Administrators are required to site, EPA expects Regional 
Administrators to work on a case-by-case basis with States. Further, 
for the forty additional monitors that will focus primarily on 
protecting susceptible and vulnerable communities, EPA intends to work 
with States to develop criteria to guide site selection for those 
monitors.
c. Conclusions on Regional Administrator Authority
    EPA is requiring Regional Administrators to work with States to 
site forty NO2 monitors, above the minimum number required 
in the two-tier network design, focused primarily in susceptible and 
vulnerable communities exposed to NO2 concentrations that 
have the potential to approach or exceed NAAQS. In addition, 
recognizing that a nationally applicable monitoring network design will 
not include all sites with potentially high concentrations due to 
variations across locations, and in response to public comments, the 
Administrator is providing Regional Administrators with the discretion 
to require additional monitors above the minimum requirements.
    Regional Administrators may also use their discretionary authority 
to require monitoring above the minimum requirements as necessary to 
address situations inside or outside of CBSAs in which (1) The required 
near-road monitors do not represent all locations of expected maximum 
hourly NO2 concentrations in an area and NO2 
concentrations may be approaching or exceeding the NAAQS in that area; 
(2) areas that are not required to have a monitor in accordance with 
the monitoring requirements and NO2 concentrations may be 
approaching or exceeding the NAAQS; or (3) the minimum monitoring 
requirements for area-wide monitors are not sufficient to meet 
monitoring objectives. In all cases in which a Regional Administrator 
may consider the need for additional monitoring, EPA expects that 
Regional Administrators will work with the State or local agencies to 
evaluate evidence that suggests an area may warrant additional 
monitoring. EPA also notes that if additional monitoring should be 
required, as negotiated between the Regional Administrator and the 
State, the State will modify the information in its Annual Monitoring 
Network Plan to include any potential new sites prior to approval by 
the EPA Regional Administrator.
5. Monitoring Network Implementation
    The following paragraphs provide background, rationale, and details 
for the final changes to the approach for the monitoring network 
implementation.
a. Proposed Monitoring Network Implementation Approach
    EPA proposed that State and, when appropriate, local air monitoring 
agencies provide a plan for deploying monitors in accordance with the 
proposed network design by July 1, 2011. EPA also proposed that the 
proposed NO2 network be physically established no later than 
January 1, 2013.
b. Comments
    Most environmental and public health group commenters suggested 
that EPA change the implementation date from the proposed January 1, 
2013 to a date that would require the minimum required NO2 
network to be deployed sooner than proposed. Most States and State 
group commenters, along with industry group commenters, recommended 
that EPA keep the network implementation date as January 1, 2013, or 
move it later than proposed. Those commenters who suggested moving it 
later noted that issues with monitoring site identification, site 
development, and overall lack of experience working in the near-road 
environment would make implementation difficult under the proposed 
implementation deadline.
    EPA recognizes the challenges involved with deploying the two-tier 
network design by the January 1, 2013 date. We recognize the need for 
additional information and plan to aid State agencies in the network 
implementation process, particularly by developing guidance in 
partnership with affected stakeholders, ideally including at a minimum 
NACAA and the States. EPA agrees with NACAA's suggestion that the CASAC 
Ambient Air Monitoring and Methods subcommittee should be consulted as 
part of developing any guidance developed for near-road monitoring, and 
has already begun the process by scheduling meetings with them 
regarding near-road monitoring. Further, EPA believes that 
collaboration with the States and State groups in developing guidance 
will be highly beneficial to the implementation process. This would 
allow for those States that do have increased experience in near-road 
monitoring to support the guidance development process and provide a 
conduit for sharing experiences amongst all stakeholders.
    In perspective, EPA believes that the approximate 2 years and 11 
months between promulgation of this rulemaking and the mandated January 
1, 2013 network implementation date includes extra time relative to 
what is traditionally allowed for network implementation following 
rulemakings. We are also cognizant of the time needed to collect 
complete data that would allow data from the two-tier network to be 
considered for designations and for use in the next NO2 
NAAQS review data from the 2013, 2014, and 2015 years would provide 
critical information in the next NAAQS review, intended to occur on a 
5-year cycle, and for use in subsequent designations. Even with 
complete data from 2013, 2014, and 2015 years designations would not 
occur until 2017, at the earliest.
c. Conclusions on Monitoring Network Implementation
    EPA is finalizing the date by which State and, when appropriate, 
local air monitoring agencies shall establish the required 
NO2 monitoring network as January 1, 2013, as was proposed. 
We believe that the allotted time for implementation will allow for the 
development of guidance documentation, particularly allowing for 
interactions with CASAC and NACAA/States, and for the processes that 
will be involved in deploying this network. However, EPA recognizes 
that the network implementation process,

[[Page 6512]]

particularly for near-road monitors, will include the assessment of 
road segments in CBSAs to identify locations of maximum expected hourly 
NO2 concentrations, identifying and working with other State 
and local agencies, such as transportation officials, as needed on 
issues regarding access and safety, and the exchange of information and 
feedback on potential sites with EPA, prior to any commitment to 
selecting and presenting new sites in an annual monitoring plan. As a 
result, based on feedback received through public comments, and to 
allow for more time to process guidance information, to carry out the 
deployment processes, and to allow for information exchanges to occur, 
we are changing the date by which State and, when appropriate, local 
air monitoring agencies shall provide a plan for deploying monitors in 
accordance with required network design, including the monitors 
required under the Regional Administrators' discretional authority 
which are to be primarily focused on providing protection to 
susceptible and vulnerable populations, as discussed in section 
III.B.4, from July 1, 2011 to July 1, 2012. EPA strongly encourages 
State and local air agencies to supply as much information as possible 
on the NO2 sites they may be considering, including possible 
site coordinates if available, or have possibly selected, to satisfy 
the minimum NO2 network monitoring requirements in their 
Annual Monitoring Network Plan submitted July 1, 2011.
6. Near-Road Site Selection
    The following paragraphs provide background, rationale, and details 
for the final changes to the approach and criteria by which required 
near-road sites shall be selected.
a. Proposed Near-Road Site Selection Criterion
    EPA proposed that the required near-road NO2 monitoring 
stations shall be selected by ranking all road segments within a CBSA 
by AADT and then identifying a location or locations adjacent to those 
highest ranked road segments where maximum hourly NO2 
concentrations are expected to be highest and siting criteria can be 
met in accordance with that proposed for 40 CFR Part 58 Appendix E 
(discussed in III.B.7). Where a State or local air monitoring agency 
identifies multiple acceptable candidate sites where maximum hourly 
NO2 concentrations are expected to occur, the monitoring 
agency should consider taking into account the potential for population 
exposure in the criteria utilized to select the final site location. 
Where one CBSA is required to have two near-road NO2 
monitoring stations, we proposed that the sites shall be differentiated 
from each other by one or more of the following factors: Fleet mix; 
congestion patterns; terrain; geographic area within the CBSA; or 
different route, interstate, or freeway designation.
b. Comments
    EPA received many comments from CASAC, public health groups, States 
and State groups, and industry groups on the proposed process by which 
States will select near-road sites. CASAC, along with some health group 
and State commenters questioned how States should select a site near 
the road with the highest ranked AADT possible, noting that EPA did not 
appear to require States to account for other factors. For example, one 
CASAC panel member noted that siting monitors based on traffic counts 
alone might miss locations where maximum NO2 concentrations 
would occur. They proceeded to recommend the use of modeling to assist 
in the site selection process. In another example, the ALA, EDJ, EJ, 
and NRDC, stated that ``Near-road monitor placement should be 
determined not only by the highest AADT volumes in a given CBSA, but 
also by the highest heavy-duty truck volumes.'' NACAA also expressed 
concerns on ``* * * basing monitor locations on the annual average 
daily traffic (AADT) without regard to vehicle mix or dispersion 
characteristics * * *''.
    EPA does not intend for AADT counts to be the sole basis for 
choosing a near-road site. As noted earlier in section III.B.2, there 
is a general relationship between AADT and mobile source pollution, 
where higher traffic counts correspond to higher mobile source 
emissions. The use of AADT counts is intended to be a mechanism for 
focusing on identifying the locations of expected maximum 
NO2 concentrations due to mobile sources. There are other 
factors that can influence which road segment in a CBSA may be the 
actual location where the maximum NO2 concentrations could 
occur. These factors include vehicle fleet mix, roadway design, 
congestion patterns, terrain, and meteorology. When States identify 
their top-ranked road segments by AADT, EPA intends for States to 
evaluate all of the factors listed above in their site selection 
process, due to their influence on where the location of expected 
maximum NO2 concentration may occur. As a result of the 
comments indicating a need for clarification, EPA will specifically 
list the factors that must be considered by States in their site 
selection process once a State has identified the most heavily 
trafficked roads in a CBSA based on AADT counts. In addition, EPA 
proposed that States consider these factors when they are required to 
place two near-road monitors in a CBSA, i.e., CBSAs with a population 
of 2,500,000 persons or more. EPA notes that these factors will be used 
in differentiating the two monitoring sites from each other, providing 
further characterization of near-road environments in larger urban 
areas that are more likely to have a greater number of major roads 
across a potentially larger geographic area, and a corresponding 
increase in potential for exposure in different settings. Finally, EPA 
notes that air quality models, which were noted by the CASAC panel 
member to be considered for use in near-road site selection, are tools 
that EPA believes will be useful, and likely used by some States to 
inform where near-road sites need to be placed.
    EPA received comments from some State and industry commenters (e.g. 
Iowa, NY DEC, Edison Electric Institute, and Savannah River Nuclear 
Solutions) who suggested that potential population exposure should be a 
first-level metric in the near-road monitoring site selection process, 
instead of a second-level metric as EPA had proposed.
    EPA notes that the intent of the revised primary NO2 
NAAQS is to protect against the maximum allowable NO2 
concentration anywhere in an area, which includes ambient air on and 
around roads. This would limit exposures to peak NO2 
concentrations, including those due to mobile source emissions, across 
locations (including those locations where population exposure near 
roads is greatest) in a given CBSA or area, with a relatively high 
degree of confidence. We also note the agency's historical practice has 
been to site ambient air monitors in locations of maximum 
concentration, at the appropriate spatial scale. If EPA were to allow 
population, population density, or another population weighted metric 
to be a primary factor in the decision on where required near-road 
NO2 monitors are to be located, it is possible that the 
required near-road monitors in a CBSA would not be located at a site of 
expected maximum hourly near-road NO2 concentration. By 
monitoring in the location of expected maximum 1-hour concentrations, 
near-road monitoring sites will likely represent the highest 
NO2 concentrations in an area directly attributable to 
mobile sources or a group of sources that includes mobile sources. The 
proposed rule did permit, and the final rule states, that States are to

[[Page 6513]]

consider population in the site selection process in situations when a 
State identifies multiple candidate sites where maximum hourly 
NO2 concentrations are expected to occur.
    EPA received a comment from HCPHES suggesting that required 
monitoring should take into consideration the location of other major 
mobile sources for NO2 emissions such as airports and 
seaports. EPA also received a comment from the South Carolina 
Department of Health and Environmental Control stating that a near-road 
network does not address ``widespread pollutants from numerous and 
diverse sources.''
    EPA recognizes that there are major NO2 sources outside 
of CBSAs that have the potential to contribute to NO2 
concentrations approaching or exceeding the NAAQS. The issue is whether 
such monitoring should be addressed through a more extensive set of 
minimum requirements that might include monitoring near all large 
stationary sources such as airports, seaports, and power plants, which 
could lead to deploying a large number of monitors. EPA believes that a 
more reasonable approach to address monitoring needs related to the 
diverse set of point, area, and non-road mobile NO2 sources, 
whether inside or outside of CBSAs, is to provide Regional 
Administrators the authority to require additional monitoring in areas 
where these impacts could occur. Providing the Regional Administrators 
with the discretion to require additional monitors allows them to 
effectively address such situations, even if that area is satisfying 
minimum monitoring requirements. This Regional Administrator authority 
is discussed above in section III.B.4. EPA also notes that State and 
local agencies may also monitor such locations on their own initiative.
    One State commenter, the Wisconsin Department of Natural Resources, 
requested that the term ``major road'' be defined and also requested 
clarification on what ``top-ranked'' means with regard to AADT counts 
on road segments. While the term ``major road'' is widely used in 
literature and can be found to be defined differently from one 
scientific study to another, here, EPA is using it in its commonly 
understood meaning as a road that is relatively heavily trafficked. EPA 
also does not believe it is appropriate to provide a bright-line 
definition for ``top-ranked''. Each CBSA will have a different 
distribution of total road segments and corresponding AADT counts on 
those segments. Further, since required near-road monitors are to be 
sited in locations of expected maximum concentrations, a percentile 
restriction on ``top ranked'' roads is unnecessary. The intent of the 
requirement to rank all road segments by AADT counts and select a site, 
considering the other local factors noted above, near a ``top-ranked'' 
road segment is to focus attention on the most heavily trafficked 
roads, around which there is higher potential for maximum 
NO2 concentrations to occur.
c. Conclusions on Near-Road Site Selection
    We are finalizing the near-road site selection criteria as 
proposed, and are clarifying that the proposal intended the selection 
criteria to include consideration of localized factors when identifying 
locations of expected maximum concentrations. As a result, required 
near-road NO2 monitoring stations shall be selected by 
ranking all road segments within a CBSA by AADT and then identifying a 
location or locations adjacent to those highest ranked road segments, 
considering fleet mix, roadway design, congestion patterns, terrain, 
and meteorology, where maximum hourly NO2 concentrations are 
expected to occur and siting criteria can be met in accordance with 40 
CFR Part 58 Appendix E. As was noted in section III.B.5 above, EPA will 
work with States to assist with the near-road site selection process 
through the development of guidance material and through information 
exchanges amongst the air monitoring community.
    We are also finalizing the requirement, as proposed, that when one 
CBSA is required to have two near-road NO2 monitoring 
stations, the sites shall be differentiated from each other by one or 
more of the following factors: fleet mix; congestion patterns; terrain; 
geographic area within the CBSA; or different route, interstate, or 
freeway designation, as was proposed.
7. Near-Road Siting Criteria
    The following paragraphs provide background, rationale, and details 
for the final changes to the siting criteria for required near-road 
monitoring sites.
a. Proposed Near-Road Siting Criteria
    EPA proposed that near-road NO2 monitoring stations must 
be sited so that the NO2 monitor probe is no greater than 50 
meters away, horizontally, from the outside nearest edge of the traffic 
lanes of the target road segment, and shall have no obstructions in the 
fetch between the monitor probe and roadway traffic such as noise 
barriers or vegetation higher than the monitor probe height. We 
solicited comment on, but did not propose, having near-road sites 
located on the predominantly downwind side of the target roadways. EPA 
proposed that the monitor probe shall be located within 2 to 7 meters 
above the ground, as is required for microscale PM2.5 and 
PM10 sites. We also proposed that monitor probe placement on 
noise barriers or buildings, where the inlet probe height is no less 
than 2 meters and no more than 7 meters above the target road, will be 
acceptable, so long as the inlet probe is at least 1 meter vertically 
or horizontally away (in the direction of the target road) from any 
supporting wall or structure, and the subsequent residence time of the 
pollutant in the sample line between the inlet probe and the analyzer 
does not exceed 20 seconds.
b. Comments
    EPA received comments from a number of States (e.g. Michigan, 
Mississippi, and Tennessee) indicating that the near-road network poses 
significant safety issues and a related need for increased logistical 
flexibility for installing a monitoring site. For example, the 
Mississippi Department of Environmental Quality states that ``Given the 
fact that these NO2 sites will be required to be housed in 
shelters that are within 50 meters of the road, we believe that these 
buildings could be large and pose a serious risk to drivers on the 
road.''
    EPA notes that in all instances of field work, safety is a top 
priority. In this instance of near-road monitoring, we are dealing with 
the safety of the public driving on roads and the monitoring staff who 
may operate the near-road monitoring station as well. There are various 
ways to install near-road sites while ensuring worker and traffic 
safety, and safety is an important part of the logistical 
considerations that States should consider when selecting and 
installing near-road sites. In many cases, State and local monitoring 
agencies may be able to work with their State or local transportation 
officials during the site selection process to deal with access and 
safety issues. In public comments, AASHTO recommended that ``* * * 
State and local air monitoring agencies be required to coordinate with 
State and local DOTs for near-road monitoring during the establishment 
of the monitoring plan.'' Although EPA cannot require States to 
coordinate with other State or local entities, EPA believes that 
transportation officials would likely be able to assist in finding 
solutions to ensure safety while working with monitoring agencies in 
accommodating a new near-road monitoring station. An

[[Page 6514]]

example of a step that could be taken to alleviate safety concerns 
might be purposefully placing a monitoring site behind existing 
barriers like guardrails and fencing, or possibly by installing a short 
distance of such barriers to protect the site workers, site 
infrastructure, and nearby traffic. In addition, EPA notes that the 50m 
distance proposed is wide enough to accommodate a site that would 
satisfy many setback provisions that exist for private or commercial 
building permits near roads, and may be viewed as a confirmation that 
our proposed siting criteria are safely attainable.
    Some State commenters (e.g. AASHTO, NYSDOT, and Wisconsin) 
suggested that the allowable maximum distance a near-road monitoring 
probe can be from the target road be increased from 50 meters to 
something wider, such as 200 meters. Conversely, there were some State, 
environmental, and industry commenters (e.g. NESCAUM,\24\ Group Against 
Smog and Pollution, and Air Quality Research and Logistics) who 
suggested that the proposed range was appropriate, or, as suggested by 
both NESCAUM and the Group Against Smog and Pollution, the allowable 
distance should be reduced to as close as 30 or 20 meters to the 
nearest edge of the traffic lanes of the target road segment, 
respectively.
---------------------------------------------------------------------------

    \24\ NESCAUM officially supported the alternative network 
design; however, they made suggestions regarding the near-road 
network in the event EPA finalized the proposed two-tier network 
design.
---------------------------------------------------------------------------

    EPA believes that increasing the allowable distance above 50 meters 
would compromise the intent of near-road monitoring. As was noted in 
the proposal and this document, the ISA (2.5.4 and 4.3.6) and REA 
(7.3.2) indicate that on-road, mobile source derived NO2 
exhibits a peak concentration on or very near the source road, and 
those concentrations decay over a variable but relatively short 
distance back to near area-wide or background (upwind of the target 
road) concentrations. Literature values indicate that the distance 
required for NO2 concentrations to return to near area-wide 
or background concentrations away from major roadways can range up to 
500 meters, but the peak concentrations are occurring on or very near 
the source roadway. The behavior of NO2 concentrations and 
the actual distance over which concentrations return to near area-wide 
or background levels is variable, and highly dependent on topography, 
roadside features, meteorology, and the related photochemical 
reactivity conditions (Baldauf et al., 2008; Beckerman et al., 2007; 
Clements et al., 2008; Gilbert et al., 2003; Hagler et al., 2009; Rodes 
and Holland, 1980; Singer et al., 2003; Zhou and Levy, 2007). 
Therefore, monitor probe placement at increasing distances from a road, 
such as 200 meters, will correspondingly decrease the potential for 
sampling maximum concentrations of NO2 due to the traffic on 
the target road. Baldauf et al. (2009) indicate that monitoring probes 
would ideally be situated between 10 and 20 meters from the nearest 
traffic lane for near-road pollutant monitoring.
    Regarding the comments suggesting required monitor probes be closer 
than 50 meters, EPA believes the allowable distance of 50 meters that a 
near-road NO2 probe can be from the target road provides 
enough flexibility for the logistical issues that can occur on a case-
by-case basis, which is inherent in monitoring site placement, while 
not sacrificing the potential to monitor the peak NO2 
concentrations. However, in light of the information provided here on 
how NO2 peak concentrations can decay over relatively short 
distances away from roads, EPA strongly encourages States to place 
near-road sites, or at least monitor probes, as close as safely 
possible to target roads to increase the probability of measuring the 
peak NO2 concentrations that occur in the near-road 
environment, again noting that Baldauf et al. (2009) indicate that 
monitor probes would ideally be situated between 10 and 20 meters from 
the nearest traffic lane for near-road pollutant monitoring.
    EPA also proposed that required near-road NO2 monitor 
probes shall have no obstructions in the fetch between the monitor 
probe and roadway traffic such as noise barriers or vegetation higher 
than the monitor probe height. EPA expects that when a State makes a 
measurement in determining whether an NO2 inlet probe is no 
greater than 50 meters away, horizontally, from the outside nearest 
edge of the traffic lanes of the target road segment, that the 
measurement would likely represent a path to the monitor probe that is 
normal to the target road. However, EPA notes that the monitor probe 
will likely be influenced by various parts of the target road segment 
that are at a relative angle compared to the normal transect between 
the road and the monitor probe. EPA is not adjusting the wording of 
this requirement, but does intend for States to consider more than one 
linear pathway between the target road and the monitor probe being 
clear of obstructions when considering candidate site locations.
    EPA received comments on the solicitation for comment on requiring 
near-road monitoring sites to be placed on the downwind side of the 
target road where the commenters (e.g. NACAA,\25\ NESCAUM, and the 
Clean Air Council) encouraged such a requirement. Conversely, other 
commenters (e.g., Air Quality and Logistics and NYSDEC suggested that 
such a requirement may be overly restrictive and not necessary. For 
example, NYSDEC stated that ``It is important to avoid making the 
monitor siting criteria too restrictive. It is very likely that in some 
CBSAs, finding suitable locations near the busiest road segments will 
not be possible. It is also important to remember that the 
NO2 monitoring instrumentation provides data continuously. 
Sites located downwind of sources will likely be impacted more 
frequently than the sites located upwind particularly when the sites 
are more than 50 meters from the source, and are preferred, but either 
side of the road will be downwind some of the time. Many of the highest 
NO2 concentrations are also likely to occur during inversion 
periods and during calm meteorological conditions when the upwind-
downwind designations have little meaning.''
---------------------------------------------------------------------------

    \25\ NACAA made a statement containing many concerns about the 
near-road monitoring component proposal which included a passage 
regarding the lack of requiring sites to be downwind. They expressed 
concern in ``* * * allowing upwind siting of monitors over a wide 
range of horizontal and vertical distances from the road * * *''.
---------------------------------------------------------------------------

    EPA noted in its proposal that research literature indicates that 
in certain cases, mobile source derived pollutant concentrations, 
including NO2, can be detected upwind of roads, above 
background levels, due to a phenomenon called upwind meandering. 
Kalthoff et al. (2007) indicates that mobile source derived pollutants 
can meander upwind on the order of tens of meters, mainly due to 
vehicle induced turbulence. Further, Beckerman et al. (2008) note that 
near-road pollutant concentrations on the predominantly upwind side of 
their study sites dropped off to near background levels within the 
first 50 meters, but were above background in this short and variable 
upwind range, which could be due, at least in part, to vehicle induced 
turbulence. This upwind meandering characteristic of pollutants in the 
near-road environment provides an additional basis for locating near-
road sites within 50 meters of target road segments, but also reduces 
the absolute need to be downwind of the road. EPA believes that very 
few, if any, near-road sites would be able to be situated in a location 
that was always downwind. For example, a hypothetical

[[Page 6515]]

site may have winds routinely out of several different cardinal 
directions throughout the year, without one being a dominant direction. 
As a result, given variable meteorology, for some period of a year, a 
given near-road site may not be downwind of the target road, no matter 
which side of the road it is on. Therefore, EPA is not finalizing a 
requirement that near-road sites must be climatologically downwind of 
the target road segment because of the additional limitations this 
introduces to finding potential site candidates in exchange for what 
may be a small increase in the opportunity to monitor peak 
NO2 concentrations. However, EPA encourages States to place 
monitors in the climatologically downwind direction whenever possible, 
in an attempt to measure the peak NO2 concentrations more 
often than not. One way States may identify where the predominantly 
downwind location might be for candidate sites could be to use portable 
meteorological devices to characterize meteorological tendencies, in 
addition to evaluating other available meteorological data sources.
    EPA proposed that required near-road NO2 monitor probes 
be located within 2 to 7 meters above the ground, as is required for 
microscale PM2.5 and PM10 sites. EPA also 
proposed that monitor probe placement on noise barriers or buildings, 
where the inlet probe height is no less than 2 meters and no more than 
7 meters above the target road, will be acceptable, so long as the 
inlet probe is at least 1 meter vertically or horizontally away (in the 
direction of the target road) from any supporting wall or structure. 
NESCAUM commented that ``EPA needs to reconcile near-roadway 
NO2 probe height requirements with the existing micro-scale 
near-roadway CO probe height requirement of 2.5 to 3.5 meters above 
prevailing terrain. NESCAUM supports using this existing height for all 
near-roadway pollution monitors, as it minimizes probe height effects 
on measurements, and allows for proper measurement of collocated 
particle number concentration (which requires a very short inlet, i.e., 
on the order of inches) and CO.'' NYSDEC commented that ``The height 
requirement may not be practical for road segments in dense urban areas 
where existing buildings heights may exceed 7 meters. The requirement 
to maintain a 1 meter clearance from a supporting wall or structure may 
not be adequate for taller walls often found in urban areas. These 
walls can create down washing and street canyon effects which will make 
the resulting data less representative of nearby areas and will make 
interpretation of the resulting data difficult. However, there will 
need to be consistency between similar site settings.'' Finally, EPA 
received comments from some health groups (e.g., ALA, EJ, EDF, and 
NRDC) who commented that ``the lower end of the proposed height of 2 to 
7 meters appears to capture the highest NO2 concentrations, 
and more accurately represents human exposure at the breathing zone.''
    In the proposal, EPA noted that near-road monitoring sites will be 
adjacent to a variety of road types, where some target roads will be on 
an even plane with the monitoring station, while others may be cut 
roads (i.e., below the plane of the monitoring station) or fill and 
open elevated roads (i.e., where the road plane is above the monitoring 
station). EPA recognizes that consistency across sites with regard to 
probe height is desirable, and consistency with microscale, urban 
canyon CO sites might also be desirable. However, as was noted in the 
earlier discussion on ``downwind'' site placements, it is important to 
avoid making the monitor siting criteria too restrictive. An allowable 
range between 2 and 7 meters provides more flexibility in site 
installation, which EPA considers important because of the variety of 
siting situations each State may have to deal with for each individual 
site. While EPA agrees that a tighter allowable range such as 2.5 to 
3.5 meters would reduce site to site variability and keep probes nearer 
the microscale siting requirements of CO, the wider range of 2 to 7 
meters still provides an adequate amount of site to site consistency. 
EPA may also address this issue through forthcoming guidance, where an 
increased consistency for probe heights in similar situations such as 
urban canyons may be a site implementation goal, within the required 2 
to 7 meter probe height range. Further, EPA believes that although 
certain situations, as noted by NYSDEC, may exist where the 1 meter 
clearance from walls or structures may be problematic near taller 
buildings or walls, this requirement is consistent with similar such 
clearance requirements for microscale CO sites in similar such 
situations that exist in urban canyons.
    In the proposed rule, EPA proposed in the siting criteria language 
that the subsequent residence time of the pollutant in the sample line 
between the inlet probe and the analyzer cannot exceed 20 seconds. EPA 
received comments from Air Quality Research and Logistics regarding 
guidelines for maximum allowable inlet length and sample residence 
time, where they stated that ``* * * the fast photodynamic 
O3-NOX equilibrium may occur in darkened sample 
lines at residence times of 10-20 seconds (Butcher et al. 1971; Ridley 
et al. 1988; Parrish et al. 1990). EPA should correct this apparent 
error by specifying much lower maximum residence times (e.g., 1-2 
seconds) or accounting for this effect by reporting `corrected' values 
in error by no more than the allowed rounding convention (e.g., 1 ppb).''
    EPA notes that in 40 CFR Part 58 Appendix E, paragraph (9)(c), 
states that sample probes for reactive gas analyzers, particularly 
NOY monitors, at NCore monitoring sites must have a sample 
residence time less than 20 seconds. EPA believes this rule is also 
appropriate for NO2 monitors, particularly if a monitor 
inlet manifold is extended away from the main monitoring shelter. EPA 
does agree that shorter sample residence time in the inlet manifold is 
desirable. Although we do not believe it appropriate to require 
residence times on the order of 1 to 2 seconds, and do not believe 
correcting values is appropriate (which was not a concept which was 
proposed), we do encourage States to use best practices in selecting 
non-reactive manifold materials, and to install sampling manifolds in 
an efficient manner that minimizes sample residence time. While EPA 
proposed this concept in the preamble to the proposed rule, we did not 
include it in the proposed regulatory text. The final rule includes 
regulatory text on this subject at 40 CFR Part 58 Appendix E, paragraph 
(9)(c).
c. Conclusions on Near-Road Siting Criteria
    We are finalizing the near-road NO2 monitor siting 
criteria, as proposed, where (1) required near-road NO2 
monitor probes shall be as near as practicable to the outside nearest 
edge of the traffic lanes of the target road segment; but shall not be 
located at a distance greater than 50 meters, in the horizontal, from 
the outside nearest edge of the traffic lanes of the target road 
segment, (2) required near-road NO2 monitor probes shall 
have an unobstructed air flow, where no obstacles exist at or above the 
height of the monitor probe, between the monitor probe and the outside 
nearest edge of the traffic lanes of the target road segment, (3) 
required near-road NO2 monitors are required to have sampler 
inlets between 2 and 7 meters above ground level, and (4) residence 
time of NO2 in the sample line between the

[[Page 6516]]

inlet probe and the analyzer does not exceed 20 seconds.
8. Area-Wide Monitor Site Selection and Siting Criteria
    The following paragraphs provide background, rationale, and details 
for the final changes to the site selection and monitor siting criteria 
for required area-wide monitoring sites.
a. Proposed Area-Wide Monitor Site Selection and Siting Criteria
    EPA proposed that sites required as part of the second tier of the 
NO2 monitoring network design, known as the area-wide 
monitoring component, be sited to characterize the highest expected 
NO2 concentrations at the neighborhood and larger (area-
wide) spatial scales in a CBSA.
b. Comments
    While most commenters who supported area-wide monitoring did so 
with regard to the adoption of the alternative area-wide network design 
rather than as part of the proposed approach, only a few commented on 
the actual sites and siting criteria. The Dow Chemical Company 
suggested that area-wide sites should be located at least 1,000 meters 
away from any major roads or intersections to ensure that the 
concentration of NO2 measured is representative of an area-
wide concentration instead of peak near-road concentrations.
    EPA notes that in order for an NO2 monitoring site to be 
classified as a neighborhood (or larger) spatial scale site, it must 
meet the roadway set-back requirements in Table E-1 of 40 CFR Part 58 
Appendix E. EPA believes that this existing set-back table is 
appropriate to use to ensure that any NO2 site that may be 
intended as an area-wide site will be sufficiently distanced from any 
major road. For example, an NO2 monitoring site may be 
considered neighborhood scale if it is 10 or more meters from the edge 
of the nearest traffic lane of a road with 10,000 or less AADT counts.
c. Conclusions on Area-Wide Monitor Site Selection and Siting Criteria
    We are finalizing the requirement that any sites required as part 
of the second tier of the NO2 monitoring network design, 
known as the area-wide monitoring component, be sited to characterize 
the highest expected NO2 concentrations at the neighborhood 
and larger (area-wide) spatial scales in a CBSA.
9. Meteorological Measurements
    The following paragraphs provide background, rationale, and details 
for the final changes to the requirement of meteorological monitoring 
at near-road monitoring sites.
a. Proposed Meteorological Measurements
    In further support of characterizing the peak NO2 
concentrations occurring in the near-road environment, EPA proposed to 
require three-dimensional anemometry, providing wind vector data in the 
horizontal and vertical planes, along with temperature and relative 
humidity measurements, at all required near-road monitoring sites.
b. Comments
    EPA received comments from the South Carolina Department of Health 
and Environmental Control commented that the recording of air 
turbulence data at near-road monitoring stations should be encouraged 
but not required. Other States (e.g., Alaska, North Carolina, and 
Wisconsin) provided comments that did not support the proposed 
meteorological measurement requirements, noting issues with costs, 
problems siting the probe nearer to structures and to the ground than 
is typically done, and that the averaging period required to better 
understand turbulence (through anemometry data) in the near-road 
environment requires a much higher frequency than what is typically 
reported.
    EPA is removing the proposed requirements that would have required 
meteorological monitoring at near-road NO2 monitoring 
stations. However, EPA strongly encourages States to do some 
meteorological monitoring to better characterize the conditions under 
which they are acquiring NO2 data. The near-road microscale 
environment is complex, and understanding the turbulent dispersion that 
may be affecting NO2 measurements, along with having a basic 
understanding of from which direction the measured NO2 
concentrations are coming from, which are very informative in the 
effort to fully understand the data being collected. At a minimum, 
basic anemometry data would be useful in identifying whether the site 
is upwind, downwind, or otherwise oriented, relative to the target 
road.
c. Conclusions on Meteorological Measurements
    We are not finalizing the proposal to require three-dimensional 
anemometry, providing wind vector data in the horizontal and vertical 
planes, along with temperature and relative humidity measurements, at 
all required near-road monitoring sites.

C. Data Reporting

    The following paragraphs provide background, rationale, and details 
for the final changes to the data reporting requirements, data quality 
objectives, and measurement uncertainty.
1. Proposed Data Quality Objectives and Measurement Uncertainty
    In the proposal, EPA noted that State and local monitoring agencies 
are required to report hourly NO, NO2, and NOX 
data to AQS within 90 days of the end of each calendar quarter. We also 
noted that many agencies also voluntarily report their pre-validated 
data on an hourly basis to EPA's real time AIRNow data system, where 
the data may be used by air quality forecasters to assist in ozone 
forecasting. We believe these data reporting procedures are appropriate 
to support the revised primary NO2 NAAQS.
    EPA proposed to develop data quality objectives (DQOs) for the 
proposed NO2 network. We proposed a goal for acceptable 
measurement uncertainty for NO2 methods to be defined for 
precision as an upper 90 percent confidence limit for the coefficient 
of variation (CV) of 15 percent and for bias as an upper 95 percent 
confidence limit for the absolute bias of 15 percent.
2. Comments
    EPA received comments from the State of Missouri, supporting the 
proposed DQOs and goals for measurement uncertainty, and from North 
Carolina, suggesting that measurement uncertainty goals match those of 
the NCore multi-pollutant network.
    EPA agrees that it is desirable to have measurement uncertainty 
goals that match that of other pollutants. EPA originally proposed the 
goals for precision and bias under consideration that there may be a 
need to account for potential increased uncertainty in 1-hour near-road 
NO2 data. However, we agree with the suggestion from the 
State of North Carolina, and are changing the goals for acceptable 
measurement uncertainty for NO2 methods to be defined for 
precision as an upper 90 percent confidence limit for the coefficient 
of variation (CV) of 10 percent and for bias as an upper 95 percent 
confidence limit for the absolute bias of 15 percent. These goals match 
the existing goals for NO2 and are consistent with 
historical measurement uncertainty goals.

[[Page 6517]]

3. Conclusions on Data Quality Objectives and Measurement Uncertainty
    We are finalizing the approach to develop data quality objectives, 
and are changing the proposed goal for measurement uncertainty, where 
the goals for acceptable measurement uncertainty for NO2 
methods to be defined for precision as an upper 90 percent confidence 
limit for the coefficient of variation (CV) of 10 percent and for bias 
as an upper 95 percent confidence limit for the absolute bias of 15 
percent.

IV. Appendix S--Interpretation of the Primary NAAQS for Oxides of 
Nitrogen and Revisions to the Exceptional Events Rule

    The EPA proposed to add Appendix S, Interpretation of the Primary 
National Ambient Air Quality Standards for Oxides of Nitrogen, to 40 
CFR part 50 in order to provide data handling procedures for the 
proposed NO2 1-hour primary standard and for the existing 
NO2 annual primary standard. The proposed Appendix S 
detailed the computations necessary for determining when the proposed 
1-hour and existing annual primary NO2 NAAQS are met. The 
proposed Appendix S also addressed data reporting, data completeness 
considerations, and rounding conventions.
    Two versions of Appendix S were proposed. The first applied to a 1-
hour primary standard based on the annual 4th high value form, while 
the second applied to a 1-hour primary standard based on the 99th 
percentile daily value form.
    The final version of Appendix S is printed at the end of this 
notice and applies to an annual primary standard and a 1-hour primary 
standard based on the 98th percentile daily value form. Appendix S is 
based on the near-roadway approach to the setting the level of the 1-
hour standard and to siting monitors. As such, these versions place no 
geographical restrictions on which monitoring sites' concentration data 
can and will be compared to the 1-hour standard when making 
nonattainment determinations and other findings related to attainment 
or violation of the standard.
    The EPA is amending and moving the provisions of 40 CFR 50.11 
related to data completeness for the existing annual primary standard 
to the new Appendix S, and adding provisions for the proposed 1-hour 
primary standard. Substantively, the data handling procedures for the 
annual primary standard in Appendix S are the same as the existing 
provisions in 40 CFR 50.11 for that standard, except for an addition of 
a cross-reference to the Exceptional Events Rule, the addition of 
Administrator discretion to consider otherwise incomplete data 
complete, and the addition of a provision addressing the possibility of 
there being multiple NO2 monitors at one site. The 
procedures for the 1-hour primary standard are entirely new.
    The EPA is also making NO2-specific changes to the 
deadlines, in 40 CFR 50.14, by which States must flag ambient air data 
that they believe have been affected by exceptional events and submit 
initial descriptions of those events, and the deadlines by which States 
must submit detailed justifications to support the exclusion of that 
data from EPA determinations of attainment or nonattainment with the 
NAAQS. The deadlines now contained in 40 CFR 50.14 are generic, and are 
not always appropriate for NO2 given the anticipated 
schedule for the designations of areas under the final NO2 
NAAQS.
    The purpose of a data interpretation appendix in general is to 
provide the practical details on how to make a comparison between 
multi-day and possibly multi-monitor ambient air concentration data and 
the level of the NAAQS, so that determinations of compliance and 
violation are as objective as possible. Data interpretation guidelines 
also provide criteria for determining whether there are sufficient data 
to make a NAAQS level comparison at all. The regulatory language for 
the pre-existing annual NO2 NAAQS, originally adopted in 
1977, contained data interpretation instructions only for the issue of 
data completeness. This situation contrasts with the situations for 
ozone, PM2.5, PM10, and most recently Pb for 
which there are detailed data interpretation appendices in 40 CFR part 
50 addressing more issues that can arise in comparing monitoring data 
to the NAAQS.

A. Interpretation of the Primary NAAQS for Oxides of Nitrogen for the 
Annual Primary Standard

    The purpose of a data interpretation rule for the NO2 
NAAQS is to give effect to the form, level, averaging time, and 
indicator specified in the regulatory text at 40 CFR 50.11, 
anticipating and resolving in advance various future situations that 
could occur. Appendix S provides common definitions and requirements 
that apply to both the annual and the 1-hour primary standards for 
NO2. The common requirements concern how ambient data are to 
be reported, what ambient data are to be considered (including the 
issue of which of multiple monitors' data sets will be used when more 
than one monitor has operated at a site), and the applicability of the 
Exceptional Events Rule to the primary NO2 NAAQS.
    The proposed Appendix S also addressed several issues in ways which 
are specific to the individual primary NO2 standards, as 
described below.
1. Proposed Interpretation of the Annual Standard
    The proposed data interpretation provisions for the annual standard 
are consistent with the pre-existing instructions included along with 
the statement of the level and form of the standard in 40 CFR 50.11. 
These are the following: (1) At least 75% of the hours in the year must 
have reported concentration data. (2) The available hourly data are 
arithmetically averaged, and then rounded (not truncated) to whole 
parts per billion. (3) The design value is this rounded annual average 
concentration. (4) The design value is compared with the level of the 
annual primary standard (expressed in parts per billion).
    In the proposal, EPA noted that it would be possible to introduce 
additional steps for the annual primary standard which in principle 
could make the design value a more reliable indicator of actual annual 
average concentration in cases where some monitoring data have been 
lost. For example, averaging within a calendar quarter first and then 
averaging across quarters could help compensate for uneven data capture 
across the year. For some aspects of the data interpretation procedures 
for some other pollutants, the current data interpretation appendices 
do contain such additional steps. The proposed provisions for the 
proposed 1-hour NO2 standard also incorporated some such 
features.
2. Comments on Interpretation of the Annual Standard
    We received four comments, all from State agencies, on data 
interpretation for the annual NO2 standard. Of the four 
commenters, two recommended the use of a weighted annual mean to 
appropriately implement the annual primary standard. Two other 
commenters asserted that there is no strong seasonality in 
NO2 concentrations, and that therefore there is no need to 
use a weighted annual mean or to require data completeness quarter-by-
quarter.

[[Page 6518]]

3. Conclusions on Interpretation of the Annual Standard
    Upon investigating the issue of NO2 seasonality using 
data from AQS as part of considering the comments, we have found that 
there are notable variations in quarterly mean NO2 
concentrations. It is therefore quite possible that an unweighted 
annual mean calculated without a quarter-by-quarter data completeness 
requirement might not represent the true annual mean as well as a 
weighted annual mean calculated with a quarter-by-quarter completeness 
requirement. However, the current practice of requiring 75% 
completeness of all of the hours in the year and calculating the annual 
mean without weighting has been retained in the final rule, because of 
its simplicity and because we believe it will not interfere with 
effective implementation of the annual NAAQS. No area presently is 
nonattainment for or comes close to violating the annual standard. 
Therefore, the choice between the two approaches can only have a 
practical effect, if any, on whether at some time in the future an area 
is determined to be newly violating the annual standard. If a monitor 
has a complete and valid design value below the standard using the 
unweighted mean approach (with only an annual data completeness 
requirement) but the design value would be considered incomplete and 
invalid under a hypothetical weighted mean approach (with a quarterly 
completeness requirement), the monitor would in either case be 
considered not to be violating and its data would not be the basis for 
a nonattainment designation. If a monitor has a design value above the 
standard using the unweighted annual mean approach but is incomplete 
with respect to a hypothetical quarterly completeness requirement, then 
the two approaches would have different implications for the 
determination of a violation. A quarterly completeness requirement 
would make a finding of violation impossible, unless the Administrator 
chose to treat the data as if complete under another provision of the 
final rule. The unweighted annual mean approach would allow but not 
force a finding of violation, because the Administrator will have 
discretion to make any such findings because there will be no mandatory 
round of designations for the annual standard given that the annual 
standard has not been revised in this review. The Administrator will be 
able to consider the representativeness of the unweighted annual mean 
when deciding whether to make a discretionary nonattainment 
redesignation. Given that the annual standard requires only one year of 
monitoring data for the calculation of a design value, little time will 
be lost if the Administrator chooses to work with a State to obtain a 
new design value based on more complete and/or seasonally balanced 
monitoring data.

B. Interpretation of the Primary NAAQS for Oxides of Nitrogen 1-Hour 
Primary Standard

1. Proposed Interpretation of the 1-Hour Standard
    With regard to data completeness for the 1-hour primary standard 
with a 4th highest daily value form, the proposed Appendix followed 
past EPA practice for other NAAQS pollutants by requiring that in 
general at least 75% of the monitoring data that should have resulted 
from following the planned monitoring schedule in a period must be 
available for the key air quality statistic from that period to be 
considered valid. For the 1-hour primary NO2 NAAQS, the key 
air quality statistics are the daily maximum 1-hour concentrations in 
three successive years. It is important that sampling within a day 
encompass the period when concentrations are likely to be highest and 
that all seasons of the year are well represented. Hence, the 75% 
requirement was proposed to be applied at the daily and quarterly 
levels.
    Recognizing that there may be years with incomplete data, the 
proposed text provided that a design value derived from incomplete data 
would nevertheless be considered valid in either of two situations.
    First, if the design value calculated from at least four days of 
monitoring observations in each of these years exceeds the level of the 
1-hour primary standard, it would be valid. This situation could arise 
if monitoring was intermittent but high NO2 levels were 
measured on enough hours and days for the mean of the three annual 4th 
high values to exceed the standard. In this situation, more complete 
monitoring could not possibly have indicated that the standard was 
actually met.
    Second, we proposed a diagnostic data substitution test which was 
intended to identify those cases with incomplete data in which it 
nevertheless is very likely, if not virtually certain, that the daily 
1-hour design value would have been observed to be below the level of 
the NAAQS if monitoring data had been minimally complete.
    It should be noted that one possible outcome of applying the 
proposed substitution test is that a year with incomplete data may 
nevertheless be determined to not have a valid design value and thus to 
be unusable in making 1-hour primary NAAQS compliance determinations 
for that 3-year period.
    Also, we proposed that the Administrator have general discretion to 
use incomplete data based on case-specific factors, either at the 
request of a State or at her own initiative. Similar provisions exist 
already for some other NAAQS.
    The second version of the proposed Appendix S contained proposed 
interpretation procedures for a 1-hour primary standard based on the 
99th percentile daily value form. The 4th high daily value form and the 
99th percentile daily value form would yield the same design value in a 
situation in which every hour and day of the year has reported 
monitoring data, since the 99th percentile of 365 daily values is the 
4th highest value. However, the two forms diverge if data completeness 
is 82% or less, because in that case the 99th percentile value is the 
3rd highest (or higher) value, to compensate for the lack of monitoring 
data on days when concentrations could also have been high.
    Logically, provisions to address possible data incompleteness under 
the 99th percentile daily value form should be somewhat different from 
those for the 4th highest form. With a 4th highest form, incompleteness 
should not invalidate a design value that exceeds the standard, for 
reasons explained above. With the 99th percentile form, however, a 
design value exceeding the standard stemming from incomplete data 
should not automatically be considered valid, because concentrations on 
the unmonitored days could have been relatively low, such that the 
actual 99th percentile value for the year could have been lower, and 
the design value could have been below the standard. The second 
proposed version of Appendix S accordingly had somewhat different 
provisions for dealing with data incompleteness. One difference was the 
addition of another diagnostic test based on data substitution, which 
in some cases can validate a design value based on incomplete data that 
exceeds the standard.
    The second version of the proposed Appendix S provided a table for 
determining which day's maximum 1-hour concentration will be used as 
the 99th percentile concentration for the year. The proposed table is 
similar to one used now for the 24-hour PM2.5 NAAQS, which 
is based on a 98th percentile form, but adjusted to reflect

[[Page 6519]]

a 99th percentile form for the 1-hour primary NO2 standard. 
The proposed Appendix S also provided instructions for rounding (not 
truncating) the average of three annual 99th percentile hourly 
concentrations before comparison to the level of the primary NAAQS.
2. Comments on Interpretation of the 1-Hour Standard
    Three commenters expressed the view that the 75% completion per 
quarter requirement should apply with respect to the 1-hour standard. A 
fourth commenter recommended that the requirement be increased to 82%. 
Another person commented that the requirement of 75% of the hours in a 
day is too stringent. The commenter noted that it would be 
inappropriate not to count the day if the maximum concentration 
observed in the hours measured is sufficiently high to make a 
difference with regard to compliance with the NAAQS. A comment was 
received that the substitution test should not be included, on the 
grounds that nonattainment should not be declared without irrefutable 
proof. This commenter also said that the same completeness requirement 
as used for nonattainment should be used for attainment. We received 
one comment that the computation of design values where multiple 
monitors are present at a site should be averaged and not taken from a 
designated primary monitor.
3. Conclusions on Interpretation of the 1-Hour Standard
    Consistent with the Administrator's decision to adopt a 98th 
percentile form for the 1-hour NAAQS, the final version of Appendix S 
is based on that form. Table 1 has been revised from the version that 
was proposed, so that it results in the selection of the 98th 
percentile value rather than the 99th percentile value.
    We agree with the three comments expressing the view that the 
requirement for 75% data completeness per quarter should apply with 
respect to the 1-hour standard. A fourth comment recommended that the 
requirement be increased to 82%. We believe 82% is too stringent 
because of the number of monitors that would not achieve such a 
requirement and we believe that 75% captures the season. We agree that 
an incomplete day should be counted if the maximum concentration 
observed in the hours measured is sufficiently high to make a 
difference with regard to compliance with the NAAQS, and we have 
accounted for that in section 3.2.c.i by validating the design value if 
it is above the level of the primary 1-hour standard when at least 75 
percent of the days in each quarter have at least one reported hourly 
value. We agree that substitution should not be used for the 
establishment of attainment/nonattainment. The commenter who remarked 
on this issue appears not to have understood that the specific proposed 
substitution tests have essentially zero probability of making a clean 
area fail the NAAQS, or vice versa, because the substituted values are 
chosen to be conservative against such an outcome. As noted in section 
3.2(c)(i), when substitution is used, the 3-year design value based on 
the data actually reported, not the ``test design value'', shall be 
used as the valid design value.
    In the course of considering the above comment regarding data 
substitution tests to be used in cases of data incompleteness, EPA has 
realized that there could be some cases of data incompleteness in which 
the proposed procedure for calculating the 1-hour design value might 
result in an in appropriately low design value. As proposed, only days 
with measurements for at least 75% of the hours in the day would be 
considered in any way when identifying the 99th percentile value (99th 
for purposes of the adopted NAAQS). However, there could be individual 
hours in other, incompletely monitored days that had measured 
concentrations higher than the identified 98th percentile value from 
the complete days. It would be inappropriate not to consider those 
hours and days in some way. However, if all days with at least one 
hourly concentration were used to identify the 99th percentile value 
without any regard to their incompleteness, this could also result in a 
design value that is biased low because the extra days could increase 
the number of ``annual number of days with valid data'' enough to 
affect which row of Table 1 of Appendix S is used. It could, for 
example, result in the 8th highest ranked daily maximum concentration 
being identified as the 98th percentile value (based on Table 1 of 
Appendix S) rather than a higher ranked concentration; this would also 
be inappropriate because days which were not monitored intensively 
enough to give a reasonable likelihood of catching the maximum hourly 
concentration would in effect be treated as if they had such a 
likelihood. For example, 50 days with only one hourly measurement 
during a time of day with lower concentrations would ``earn'' the State 
the right to drop one notch lower in the ranking of days when 
identifying the 98th percentile day, inappropriately. The final version 
of Appendix S solves this problem by providing that two procedures be 
used to identifying the 98th percentile value, the first based only on 
days with 75% data completeness and the second based on all days with 
at least one hourly measurement. The final design value is the higher 
of the two values that result from these two procedures.
    With regard to situations with multiple monitors operating at one 
site, we think as discussed in the proposal, that designation of a 
primary monitor is preferable to averaging the data from multiple 
monitors based on administrative simplicity and transparency for the 
public, and is unbiased with respect to compliance outcome provided the 
State is able to make the designation only before any data has been 
collected.
    Finally, as proposed, the final version of Appendix S has a cross 
reference to the Exceptional Events Rule (40 CFR 50.14) with regard to 
the exclusion of data affected by exceptional events. In addition, the 
specific steps for including such data in completeness calculations 
while excluding such data from actual design value calculations is 
clarified in Appendix S.

C. Exceptional Events Information Submission Schedule

    The Exceptional Events Rule at 40 CFR 50.14 contains generic 
deadlines for a State to submit to EPA specified information about 
exceptional events and associated air pollutant concentration data. A 
State must initially notify EPA that data has been affected by an event 
by July 1 of the year after the data are collected; this is done by 
flagging the data in AQS and providing an initial event description. 
The State must also, after notice and opportunity for public comment, 
submit a demonstration to justify any claim within 3 years after the 
quarter in which the data were collected. However, if a regulatory 
decision based on the data (for example, a designation action) is 
anticipated, the schedule to flag data in AQS and submit complete 
documentation to EPA for review is foreshortened, and all information 
must be submitted to EPA no later than one year before the decision is 
to be made.
    These generic deadlines are suitable for the period after initial 
designations have been made under a NAAQS, when the decision that may 
depend on data exclusion is a redesignation from attainment to 
nonattainment or from nonattainment to attainment. However, these 
deadlines present problems with respect to initial designations under a 
newly revised NAAQS. One problem is

[[Page 6520]]

that some of the deadlines, especially the deadlines for flagging some 
relevant data, may have already passed by the time the revised NAAQS is 
promulgated. Until the level and form of the NAAQS have been 
promulgated a State does not know whether the criteria for excluding 
data (which are tied to the level and form of the NAAQS) were met on a 
given day. The only way a State could guard against this possibility is 
to flag all data that could possibly be eligible for exclusion under a 
future NAAQS. This could result in flagging far more data than will 
eventually be eligible for exclusion. EPA believes this is an 
inefficient use of State and EPA resources, and is potentially 
confusing and misleading to the public and regulated entities. Another 
problem is that it may not be feasible for information on some 
exceptional events that may affect final designations to be collected 
and submitted to EPA at least one year in advance of the final 
designation decision. This could have the unintended consequence of EPA 
designating an area nonattainment as a result of uncontrollable natural 
or other qualified exceptional events.
    When Section 50.14 was revised in March 2007, EPA was mindful that 
designations were needed under the recently revised PM2.5 
NAAQS, so exceptions to the generic deadline were included for 
PM2.5. The EPA was also mindful that similar issues would 
arise for subsequent new or revised NAAQS. The Exceptional Events Rule 
at section 50.14(c)(2)(v) indicates ``when EPA sets a NAAQS for a new 
pollutant, or revises the NAAQS for an existing pollutant, it may 
revise or set a new schedule for flagging data for initial designation 
of areas for those NAAQS.''
    EPA proposed revised exceptional event data flagging and 
documentation deadlines in FR 34404 [Federal Register/Vol. 74, No. 134/
Wednesday, July 15, 2009/Proposed Rules] and invited comments from the 
public. The Agency received no comments related to the revised proposed 
schedule for NO2 exceptional event data flagging and 
documentation deadlines.
    For the specific case of NO2, EPA anticipates that 
initial designations under the revised NAAQS may be made by January 22, 
2012 based on air quality data from the years 2008-2010. (See Section 
VI below for more detailed discussion of the designation schedule and 
what data EPA intends to use.) If final designations are made by 
January 22, 2012, all events to be considered during the designations 
process must be flagged and fully documented by States one year prior 
to designations, by January 22, 2011. This date also coincides with the 
Clean Air Act deadline for Governors to submit to EPA their 
recommendations for designating all areas of their States.
    The final rule text at the end of this notice shows the changes 
that will apply if a revised NO2 NAAQS is promulgated by 
January 22, 2010, and designations are made two years after 
promulgation of a NO2 NAAQS revision.
    Table 1 below summarizes the data flagging and documentation 
deadlines corresponding to the two year designation schedule discussed 
in this section. If the promulgation date for a revised NO2 
NAAQS occurs on a different date than January 22, 2010, EPA will revise 
the final NO2 exceptional event flagging and documentation 
submission deadlines accordingly to provide States with reasonably 
adequate opportunity to review, identify, and document exceptional 
events that may affect an area designation under a revised NAAQS.

      Table 1--Schedule for Exceptional Event Flagging and Documentation Submission for Data To Be Used in
                                 Designations Decisions for New or Revised NAAQS
----------------------------------------------------------------------------------------------------------------
                                         Air quality
  NAAQS pollutant/standard/(level)/    data collected  Event flagging & initial       Detailed documentation
          promulgation date             for calendar     description deadline          submission deadline
                                            year
----------------------------------------------------------------------------------------------------------------
NO2/1-Hour Standard (100 PPB)........            2008  July 1, 2010 \a\........  January 22, 2011.
                                                 2009  July 1, 2010............  January 22, 2011.
                                                 2010  April 1, 2011\a\........  July 1, 2011.\a\
----------------------------------------------------------------------------------------------------------------
\a\ 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 or revised NAAQS. The general schedule applies for all other purposes, most
  notably, for data used by EPA for redesignations to attainment.

V. Designation of Areas

A. Proposed Process

    The CAA requires EPA and the States to take steps to ensure that 
the new or revised NAAQS are met following promulgation. The first step 
is to identify areas of the country that do not meet the new or revised 
NAAQS. Section 107(d)(1) provides that, ``By such date as the 
Administrator may reasonably require, but not later than 1 year after 
promulgation of a new or revised NAAQS for any pollutant under section 
109, the Governor of each State shall * * * submit to the Administrator 
a list of all areas (or portions thereof) in the State'' that should be 
designated as nonattainment, attainment, or unclassifiable for the new 
NAAQS. Section 107(d)(1)(B)(i) further provides, ``Upon promulgation or 
revision of a NAAQS, the Administrator shall promulgate the 
designations of all areas (or portions thereof) * * * as expeditiously 
as practicable, but in no case later than 2 years from the date of 
promulgation.''
    No later than 120 days prior to promulgating designations, EPA is 
required to notify States of any intended modifications to their 
designations as EPA may deem necessary. States then have an opportunity 
to comment on EPA's tentative decision. Whether or not a State provides 
a recommendation, the EPA must promulgate the designation that it deems 
appropriate.
    Accordingly, Governors must submit their initial NO2 
designation recommendations to EPA no later than January 2011. If the 
Administrator intends to modify any State's recommendation, the EPA 
will notify the Governor no later than 120 days prior to designations 
in January 2012. States that believe the Administrator's modification 
is inappropriate will have an opportunity to demonstrate why they 
believe their recommendation is more appropriate before designations 
are finalized.

B. Public Comments

    Several industry commenters requested that EPA slow the timeline 
for implementing a near-roadway monitoring network and designating 
roadway areas because they believe EPA lacks significant information 
about the implementation and performance of a national, near-roadway 
monitoring network. Two commenters also requested that if a near-
roadway monitoring network is deployed, that 1-hour NO2 
standards be made more

[[Page 6521]]

lenient until the next review period so that more information will be 
available about near-roadway NO2 concentrations before a 
stringent standard is selected.
    A response to commenters' requests that EPA slow the monitoring 
implementation schedule and the request that EPA make the 1-hour 
NO2 standard more lenient until the next review period are 
addressed in sections III.B.5 and II.F.4.D, respectively.
    Section 110(d)(1)(B) requires the EPA to designate areas no later 
than 2 years following promulgation of a new or revised NAAQS (i.e., by 
January 2012). While the CAA provides the Agency an additional third 
year from promulgation of a NAAQS to complete designations in the event 
that there is insufficient information to make NAAQS compliance 
determinations, we anticipate that delaying designations for an 
additional year would not result in significant new data to inform the 
initial designations. A near-roadway monitoring network is not expected 
to be fully deployed until January 2013 therefore, EPA must proceed 
with initial designations using air quality data from the existing 
NO2 monitoring network. Because none of the current 
NO2 monitors are sited to measure near-roadway ambient air, 
we expect that most areas in the country with current NO2 
monitors will not violate the new NO2 NAAQS. In the event 
that a current NO2 monitor indicates a violation of the 
revised standards, EPA intends to designate such areas 
``nonattainment'' no later than 2 years following promulgation of the 
revised standards. We intend to designate the rest of the country as 
``unclassifiable'' for the revised NO2 NAAQS until 
sufficient air quality data is collected from a near-roadway monitoring 
network. Once the near-roadway network is fully deployed and 3 years of 
air quality data are available, the EPA has authority under the CAA to 
redesignate areas as appropriate from ``unclassifiable'' to 
``attainment'' or ``nonattainment.'' We anticipate that sufficient data 
to conduct designations would be available after 2015.
    A number of commenters, largely from industry groups, focused on 
the concern that a near-roadway monitoring network would lead to 
regional nonattainment on the basis of high NO2 
concentrations found near roadways. These commenters requested that any 
future nonattainment areas be limited to the area directly surrounding 
roadways found to have above-standard NO2 concentrations.
    The CAA requires that any area that does not meet a NAAQS or that 
contributes to a violation in a nearby area that does not meet the 
NAAQS be designated ``nonattainment.'' States and EPA will need to 
determine which sources and activities contribute to a NAAQS violation 
in each area. Depending on the circumstances in each area this may 
include sources and activities in areas beyond the area directly 
surrounding a major roadway. EPA intends to issue nonattainment area 
boundary guidance after additional information is gathered on the 
probable contributors to violating near-roadway NO2 
monitors.

C. Final Designations Process

    The EPA intends to promulgate initial NO2 designations 
by January 2012 (2 years after promulgation of the revised NAAQS). 
Along with today's action EPA is also promulgating new monitoring rules 
that focus on roadways. As noted in section III, States must site 
required NO2 near-roadway monitors and have them operational 
by January 1, 2013. States will need an additional 3 years thereafter 
to collect air quality data in order to determine compliance with the 
revised NAAQS. This means that a full set of air quality data from the 
new network will not be available until after 2015. Since we anticipate 
that data from the new network will not be available prior to the CAA 
designation deadlines discussed above, the EPA intends to complete 
initial NO2 designations by January 2012 using the 3 most 
recent years of quality-assured air quality data from the current 
monitoring network, which would be for the years 2008-2010. The EPA 
will designate as ``nonattainment'' any areas with NO2 
monitors recording violations of the revised NO2 NAAQS. We 
intend to designate all other areas of the country as 
``unclassifiable'' to indicate that there is insufficient data to 
determine whether or not they are attaining the revised NO2 
NAAQS.
    Once the NO2 monitors are positioned in locations 
meeting the near-roadway siting requirements and monitoring data become 
available, the Agency has authority under section 107(d)(3) of the CAA 
to redesignate areas as appropriate from ``unclassifiable'' to 
``attainment'' or ``nonattainment.'' The EPA intends to issue guidance 
on the factors that States should consider when determining 
nonattainment boundaries after additional information is gathered on 
the probable contributors to violating near-roadway NO2 
monitors.

VI. Clean Air Act Implementation Requirements

    This section of the preamble discusses the Clean Air Act (CAA) 
requirements that States and emissions sources must address when 
implementing new or revised NO2 NAAQS based on the structure 
outlined in the CAA and existing rules.\26\ EPA may provide additional 
guidance in the future, as necessary, to assist States and emissions 
sources to comply with the CAA requirements for implementing new or 
revised NO2 NAAQS.
---------------------------------------------------------------------------

    \26\ Since EPA is retaining the annual standard without 
revision, the discussion in this section relates to implementation 
of the proposed 1-hour standard, rather than the annual standard.
---------------------------------------------------------------------------

    The CAA assigns important roles to EPA, States, and, in specified 
circumstances, Tribal governments to achieve the NAAQS. States have the 
primary responsibility for developing and implementing State 
Implementation Plans (SIPs) that contain State measures necessary to 
achieve the air quality standards in each area. EPA provides assistance 
to States by providing technical tools, assistance, and guidance, 
including information on the potential control measures that may help 
areas meet the standards.
    States are primarily responsible for ensuring attainment and 
maintenance of ambient air quality standards once they have been 
established by EPA. Under section 110 of the CAA, 42 U.S.C. 7410, and 
related provisions, States are required to submit, for EPA approval, 
SIPs that provide for the attainment and maintenance of such standards 
through control programs directed at sources of NO2 
emissions. If a State fails to adopt and implement the required SIPs by 
the time periods provided in the CAA, the EPA has responsibility under 
the CAA to adopt a Federal Implementation Plan (FIP) to assure that 
areas attain the NAAQS in an expeditious manner.
    The States, in conjunction with EPA, also administer the prevention 
of significant deterioration (PSD) program for NO2 and 
nonattainment new source review (NSR). See sections 160-169 of the CAA. 
In addition, Federal programs provide for nationwide reductions in 
emissions of NO2 and other air pollutants under Title II of 
the Act, 42 U.S.C. 7521-7574, which involves controls for automobiles, 
trucks, buses, motorcycles, nonroad engines, and aircraft emissions; 
the new source performance standards (NSPS) for stationary sources 
under section 111 of the CAA, 42 U.S.C. 7411.
    CAA Section 301(d) authorizes EPA to treat eligible Indian Tribes 
in the same manner as States (TAS) under the CAA and requires EPA to 
promulgate regulations specifying the provisions of the statute for 
which such treatment is appropriate. EPA has promulgated these

[[Page 6522]]

regulations--known as the Tribal Authority Rule or TAR--at 40 CFR Part 
49. See 63 FR 7254 (February 12, 1998). The TAR establishes the process 
for Indian Tribes to seek TAS eligibility and sets forth the CAA 
functions for which TAS will be available. Under the TAR, eligible 
Tribes may seek approval for all CAA and regulatory purposes other than 
a small number of functions enumerated at section 49.4. Implementation 
plans under section 110 are included within the scope of CAA functions 
for which eligible Tribes may obtain approval. Section 110(o) also 
specifically describes Tribal roles in submitting implementation plans. 
Eligible Indian Tribes may thus submit implementation plans covering 
their reservations and other areas under their jurisdiction.
    Under the CAA and TAR, Tribes are not, however, required to apply 
for TAS or implement any CAA program. In promulgating the TAR EPA 
explicitly determined that it was not appropriate to treat Tribes 
similarly to States for purposes of, among other things, specific plan 
submittal and implementation deadlines for NAAQS-related requirements. 
40 CFR 49.4(a). In addition, where Tribes do seek approval of CAA 
programs, including section 110 implementation plans, the TAR provides 
flexibility and allows them to submit partial program elements, so long 
as such elements are reasonably severable--i.e., ``not integrally 
related to program elements that are not included in the plan 
submittal, and are consistent with applicable statutory and regulatory 
requirements.'' 40 CFR 49.7.
    To date, very few Tribes have sought TAS for purposes of section 
110 implementation plans. However, some Tribes may be interested in 
pursuing such plans to implement today's proposed standard. As noted 
above, such Tribes may seek approval of partial, reasonably severable 
plan elements, or they may seek to implement all relevant components of 
an air quality program for purposes of meeting the requirements of the 
Act. In several sections of this preamble, EPA describes the various 
roles and requirements States will address in implementing today's 
proposed standard. Such references to States are generally intended to 
include eligible Indian Tribes to the extent consistent with the 
flexibility provided to Tribes under the TAR. Where Tribes do not seek 
TAS for section 110 implementation plans, EPA will promulgate Federal 
implementation plans as ``necessary or appropriate to protect air 
quality.'' 40 CFR 49.11(a). EPA also notes that some Tribes operate air 
quality monitoring networks in their areas. For such monitors to be 
used to measure attainment with this primary NAAQS for NO2, 
the criteria and procedures identified in this rule would apply.

A. Classifications

1. Proposal
    Section 172(a)(1)(A) of the CAA authorizes EPA to classify areas 
designated as nonattainment for the purpose of applying an attainment 
date pursuant to section 172(a)(2), or for other reasons. In 
determining the appropriate classification, EPA may consider such 
factors as the severity of the nonattainment problem and the 
availability and feasibility of pollution control measures (see section 
172(a)(1)(A) of the CAA). The EPA may classify NO2 
nonattainment areas, but is not required to do so. The primary reason 
to establish classifications is to set different deadlines for each 
class of nonattainment area to complete the planning process and to 
provide for different attainment dates based upon the severity of the 
nonattainment problem for the affected area. However, the CAA 
separately establishes specific planning and attainment deadlines for 
certain pollutants including NO2 in sections 191 and 192: 18 
months from nonattainment designation for the submittal of an 
attainment plan, and as expeditiously as possible, but no later than 5 
years from nonattainment designation for areas to attain the standard. 
In the proposal, EPA stated its belief that classifications are 
unnecessary in light of these relatively short deadlines.
2. Public Comments
    One commenter stated that they disagree with EPA's decision not to 
impose non-attainment classifications on areas with measured near-road 
NO2 concentrations in excess of the new NO2 
standard, and urged EPA to provide a graduated non-attainment 
classification system for the new standard. According to the commenter, 
``a classification system defining higher levels of non-attainment with 
increasingly stringent requirements at those levels is one that allows 
for finer calibration of air quality regulatory response defined at the 
Federal level.''
    As stated in the proposed rule, Section 192(a), of part D, of the 
CAA specifically provides an attainment date for areas designated as 
nonattainment for the NO2 NAAQS. Therefore, EPA has legal 
authority to classify NO2 nonattainment areas, but the 5-
year attainment date addressed under section 192(a) cannot be extended 
pursuant to section 172(a)(2)(D). Based on this limitation, EPA 
proposed not to establish classifications within the 5- year interval 
for attaining any new or revised NO2 NAAQS. It is also EPA's 
belief that given the short deadlines that States have to develop and 
submit SIP's and for areas to achieve emissions reductions in order to 
attain the standard within the 5 year attainment period, a graduated 
classifications system would not be appropriate. Therefore, EPA is 
using it's discretion under the CAA not to establish classifications.
3. Final
    EPA is not making any changes to the discussion on classifications 
in the proposed rule. Therefore, there will be no classifications for 
the revised NO2 NAAQS.

B. Attainment Dates

    The maximum deadline by which an area is required to attain the 
NO2 NAAQS is determined from the effective date of the 
nonattainment designation for the affected area. For areas designated 
nonattainment for the revised NO2 NAAQS, SIPs must provide 
for attainment of the NAAQS as expeditiously as practicable, but no 
later than 5 years from the date of the nonattainment designation for 
the area (see section 192(a) of the CAA). The EPA will determine 
whether an area has demonstrated attainment of the NO2 NAAQS 
by evaluating air quality monitoring data consistent with the form of 
the NAAQS for NO2 if revised, which will be codified at 40 
CFR part 50, Appendix F.
1. Attaining the NAAQS
a. Proposal
    In order for an area to be redesignated as attainment, the State 
must comply with the five requirements as provided under section 
107(d)(3)(E) of the CAA. This section requires that:

--EPA must have determined that the area has met the NO2 
NAAQS;
--EPA has fully approved the State's implementation plan;
--The improvement in air quality in the affected area is due to 
permanent and enforceable reductions in emissions;
--EPA has fully approved a maintenance plan for the area; and
--The State(s) containing the area have met all applicable requirements 
under section 110 and part D.
b. Final
    EPA did not receive any comments on this aspect of the proposed 
rule and is not making any changes to the

[[Page 6523]]

discussion on attaining the NAAQS in the proposed rule.
2. Consequences of Failing To Attain by the Statutory Attainment Date
a. Proposal
    Any NO2 nonattainment area that fails to attain by its 
statutory attainment date would be subject to the requirements of 
sections 179(c) and (d) of the CAA. EPA is required to make a finding 
of failure to attain no later than 6 months after the specified 
attainment date and publish a notice in the Federal Register. The State 
would be required to submit an implementation plan revision, no later 
than one year following the effective date of the Federal Register 
notice making the determination of the area's failure to attain, which 
demonstrates that the standard will be attained as expeditiously as 
practicable, but no later than 5 years from the effective date of EPA's 
finding that the area failed to attain. In addition, section 179(d)(2) 
provides that the SIP revision must include any specific additional 
measures as may be reasonably prescribed by EPA, including ``all 
measures that can be feasibly implemented in the area in light of 
technological achievability, costs, and any nonair quality and other 
air quality-related health and environmental impacts.''
b. Final
    EPA did not receive any comments on this aspect of the proposed 
rule and is not making any changes to the discussion on consequences of 
failing to attain by the statutory attainment date in the proposed 
rule.

C. Section 110(a)(2) NAAQS Infrastructure Requirements

1. Proposal
    Section 110(a)(2) of the CAA requires all States to develop and 
maintain a solid air quality management infrastructure, including 
enforceable emission limitations, an ambient monitoring program, an 
enforcement program, air quality modeling, and adequate personnel, 
resources, and legal authority. Section 110(a)(2)(D) also requires 
State plans to prohibit emissions from within the State which 
contribute significantly to nonattainment or maintenance areas in any 
other State, or which interfere with programs under part C to prevent 
significant deterioration of air quality or to achieve reasonable 
progress toward the national visibility goal for Federal class I areas 
(national parks and wilderness areas).
    Under section 110(a)(1) and (2) of the CAA, all States are required 
to submit SIPs to EPA which demonstrate that basic program elements 
have been addressed within 3 years of the promulgation of any new or 
revised NAAQS. Subsections (A) through (M) of section 110(a)(2) listed 
below, set forth the elements that a State's program must contain in 
the SIP.\27\ The list of section 110(a)(2) NAAQS implementation 
requirements are the following:
---------------------------------------------------------------------------

    \27\ Two elements identified in section 110(a)(2) are not listed 
below because, as EPA interprets the CAA, SIPs incorporating any 
necessary local nonattainment area controls would not be due within 
3 years, but rather are due at the time the nonattainment area 
planning requirements are due. These elements are: (1) Emission 
limits and other control measures, section 110(a)(2)(A), and (2) 
Provisions for meeting part D, section 110(a)(2)(I), which requires 
areas designated as nonattainment to meet the applicable 
nonattainment planning requirements of part D, title I of the CAA.
---------------------------------------------------------------------------

     Ambient air quality monitoring/data system: Section 
110(a)(2)(B) requires SIPs to provide for setting up and operating 
ambient air quality monitors, collecting and analyzing data and making 
these data available to EPA upon request.
     Program for enforcement of control measures: Section 
110(a)(2)(C) requires SIPs to include a program providing for 
enforcement of measures and regulation and permitting of new/modified 
sources.
     Interstate transport: Section 110(a)(2)(D) requires SIPs 
to include provisions prohibiting any source or other type of emissions 
activity in the State from contributing significantly to nonattainment 
in another State or from interfering with measures required to prevent 
significant deterioration of air quality or to protect visibility.
     Adequate resources: Section 110(a)(2)(E) requires States 
to provide assurances of adequate funding, personnel and legal 
authority for implementation of their SIPs.
     Stationary source monitoring system: Section 110(a)(2)(F) 
requires States to establish a system to monitor emissions from 
stationary sources and to submit periodic emissions reports to EPA.
     Emergency power: Section 110(a)(2)(G) requires States to 
include contingency plans, and adequate authority to implement them, 
for emergency episodes in their SIPs.
     Provisions for SIP revision due to NAAQS changes or 
findings of inadequacies: Section 110(a)(2)(H) requires States to 
provide for revisions of their SIPs in response to changes in the 
NAAQS, availability of improved methods for attaining the NAAQS, or in 
response to an EPA finding that the SIP is inadequate.
     Consultation with local and Federal government officials: 
Section 110(a)(2)(J) requires States to meet applicable local and 
Federal government consultation requirements when developing SIP and 
reviewing preconstruction permits.
     Public notification of NAAQS exceedances: Section 
110(a)(2)(J) requires States to adopt measures to notify the public of 
instances or areas in which a NAAQS is exceeded.
     PSD and visibility protection: Section 110(a)(2)(J) also 
requires States to adopt emissions limitations, and such other 
measures, as may be necessary to prevent significant deterioration of 
air quality in attainment areas and protect visibility in Federal Class 
I areas in accordance with the requirements of CAA Title I, part C.
     Air quality modeling/data: Section 110(a)(2)(K) requires 
that SIPs provide for performing air quality modeling for predicting 
effects on air quality of emissions of any NAAQS pollutant and 
submission of data to EPA upon request.
     Permitting fees: Section 110(a)(2)(L) requires the SIP to 
include requirements for each major stationary source to pay permitting 
fees to cover the cost of reviewing, approving, implementing and 
enforcing a permit.
     Consultation and participation by affected local 
government: Section 110(a)(2)(M) requires States to provide for 
consultation and participation by local political subdivisions affected 
by the SIP.
2. Final
    EPA did not receive any comments on this aspect of the proposed 
rule and is not making any changes to the discussion on section 
110(a)(2) NAAQS infrastructure requirements in the proposed rule.

D. Attainment Planning Requirements

1. Nonattainment Area SIPs
a. Proposal
    Any State containing an area designated as nonattainment with 
respect to the NO2 NAAQS must develop for submission a SIP 
meeting the requirements of part D, Title I, of the CAA, providing for 
attainment by the applicable statutory attainment date (see sections 
191(a) and 192(a) of the CAA). As indicated in section 191(a) all 
components of the NO2 part D SIP must be submitted within 18 
months of the effective date of an area's designation as nonattainment.
    Section 172 of the CAA includes general requirements for all 
designated nonattainment areas. Section 172(c)(1)

[[Page 6524]]

requires that each nonattainment area plan ``provide for the 
implementation of all reasonably available control measures (RACM) as 
expeditiously as practicable (including such reductions in emissions 
from existing sources in the area as may be obtained through the 
adoption, at a minimum, of Reasonably Available Control Technology 
(RACT)), and shall provide for attainment of the national primary 
ambient air quality standards.'' States are required to implement RACM 
and RACT in order to attain ``as expeditiously as practicable''.
    Section 172(c) requires States with nonattainment areas to submit a 
SIP for these areas which contains an attainment demonstration that 
shows that the affected area will attain the standard by the applicable 
statutory attainment date. The State must also show that the area will 
attain the standards as expeditiously as practicable, and it must 
include an analysis of whether implementation of reasonably available 
measures will advance the attainment date for the area.
    Part D SIPs must also provide for reasonable further progress (RFP) 
(see section 172(c)(2) of the CAA). The CAA defines RFP as ``such 
annual incremental reductions in emissions of the relevant air 
pollution as are required by part D, or may reasonably be required by 
the Administrator for the purpose of ensuring attainment of the 
applicable NAAQS by the applicable attainment date.'' (See section 171 
of the CAA.) Historically, for some pollutants, RFP has been met by 
showing annual incremental emission reductions sufficient to maintain 
generally linear progress toward attainment by the applicable 
attainment date.
    All NO2 nonattainment area SIPs must include contingency 
measures which must be implemented in the event that an area fails to 
meet RFP or fails to attain the standards by its attainment date. (See 
section 172(c)(9).) These contingency measures must be fully adopted 
rules or control measures that take effect without further action by 
the State or the Administrator. The EPA interprets this requirement to 
mean that the contingency measures must be implemented with only 
minimal further action by the State or the affected sources with no 
additional rulemaking actions such as public hearings or legislative 
review.
    Emission inventories are also critical for the efforts of State, 
local, and Federal agencies to attain and maintain the NAAQS that EPA 
has established for criteria pollutants including NO2. 
Section 191(a) in conjunction with section 172(c) requires that areas 
designated as nonattainment for NO2 submit an emission 
inventory to EPA no later than 18 months after designation as 
nonattainment. In the case of NO2, sections 191(a) and 
172(c) also require that States submit periodic emission inventories 
for nonattainment areas. The periodic inventory must include emissions 
of NO2 for point, nonpoint, mobile (on-road and non-road), 
and area sources.
b. Public Comments
    Several commenters indicated that EPA should take steps to ensure 
that States actually require mobile source emissions reductions in 
order to attain the NO2 NAAQS as opposed to controlling 
point sources. Another commenter went further and stated that States be 
required to control on-road emissions as opposed to emissions from 
stationary sources and in particular EGUs. This commenter also 
indicated that EPA should delay nonattainment designations until States 
had a cost effective means of reducing on-road emissions of 
NO2.
    EPA cannot require States to develop a SIP that only addresses one 
type of source, in this case on-road mobile sources. States may select 
appropriate control measures to attain the NAAQS and EPA must approve 
them if they otherwise meet all applicable requirements of the Act. See 
CAA 116. EPA expects that States will evaluate a range of control 
measures that will reduce NO2 emissions within the time 
allowed to attain the standard. This would include the emissions 
reductions attributable to Federal controls on on-road and non-road 
mobile sources, and controls that they have put in place to reduce 
NOX emissions in order to attain the 8-hour ozone NAAQS and/
or the PM2.5 NAAQS. If these existing controls are not 
sufficient for an area to reach attainment with the NO2 
NAAQS, EPA would expect the State to implement additional control 
measures that would bring the area into attainment by the deadline. For 
a designation based on data from a near roadway monitor EPA would 
expect the States to give primary consideration to controlling 
emissions from on-road sources; however, it is likely that other types 
of sources contribute to the concentrations that are measured at a near 
roadway monitor and a State may decide to implement controls on these 
other contributing sources.
    The Clean Air Act requires that EPA finalize designations within 
two years after a NAAQS is revised unless the available air quality 
data is insufficient to make designations by that time. In that case, 
EPA must finalize designations within three years after the NAAQS is 
revised. As discussed elsewhere in today's final rule, EPA believes 
that it has sufficient data to make designations within two years and 
that most areas will be designated as unclassifiable at that time. 
Taking the additional year provided by the CAA would not allow 
additional data from the new near roadway monitors to be factored into 
the designations process in any event. Therefore, it is EPA's intention 
to designate areas within two years as required by the Act. EPA intends 
to redesignate areas once it has sufficient data from the new 
monitoring network to designate areas as clearly attaining or not 
attaining the standard.
c. Final
    The EPA is not making any changes to the discussion on 
nonattainment area SIPs in the proposed rule.
2. New Source Review and Prevention of Significant Deterioration 
Requirements
a. Proposal
    The Prevention of Significant Deterioration (PSD) and nonattainment 
New Source Review (NSR) programs contained in parts C and D of Title I 
of the CAA govern preconstruction review of any new or modified major 
stationary sources of air pollutants regulated under the CAA as well as 
any precursors to the formation of that pollutant when identified for 
regulation by the Administrator.\28\ The EPA rules addressing these 
programs can be found at 40 CFR 51.165, 51.166, 52.21, 52.24, and part 
51, appendix S. States which have areas designated as nonattainment for 
the NO2 NAAQS must submit, as a part of the SIP due 18 
months after an area is designated as nonattainment, provisions 
requiring permits for the construction and operation of new or modified 
stationary sources anywhere in the nonattainment area. SIPs that 
address the PSD requirements related to attainment areas are due no 
later than 3 years after the promulgation of a revised NAAQS for 
NO2.
---------------------------------------------------------------------------

    \28\ The terms ``major'' and ``minor'' define the size of a 
stationary source, for applicability purposes, in terms of an annual 
emissions rate (tons per year, tpy) for a pollutant. Generally, a 
minor source is any source that is not ``major.'' ``Major'' is 
defined by the applicable regulations--PSD or nonattainment NSR.
---------------------------------------------------------------------------

    The NSR program is composed of three different permit programs:
     Prevention of Significant Deterioration (PSD).
     Nonattainment NSR (NA NSR).
     Minor NSR.
    The PSD program applies when a major source, that is located in an 
area that is designated as attainment or

[[Page 6525]]

unclassifiable for any criteria pollutant, is constructed, or undergoes 
a major modification.\29\ The nonattainment NSR program applies on a 
pollutant-specific basis when a major source constructs or modifies in 
an area that is designated as nonattainment for that pollutant. The 
minor source NSR program addresses both major and minor sources which 
undergo construction or modification activities that do not qualify as 
major, and it applies, as necessary to assure attainment, regardless of 
the designation of the area in which a source is located.
---------------------------------------------------------------------------

    \29\ In addition, the PSD program applies to non-criteria 
pollutants subject to regulation under the Act, except those 
pollutants regulated under section 112 and pollutants subject to 
regulation only under section 211(o).
---------------------------------------------------------------------------

    The PSD requirements include but are not limited to the following:
     Installation of Best Available Control Technology (BACT);
     Air quality monitoring and modeling analyses to ensure 
that a project's emissions will not cause or contribute to a violation 
of any NAAQS or maximum allowable pollutant increase (PSD increment);
     Notification of Federal Land Manager of nearby Class I 
areas; and
     Public comment on permit.
    Nonattainment NSR requirements include but are not limited to:
     Installation of Lowest Achievable Emissions Rate (LAER) 
control technology;
     Offsetting new emissions with creditable emissions 
reductions;
     A certification that all major sources owned and operated 
in the State by the same owner are in compliance with all applicable 
requirements under the CAA;
     An alternative siting analysis demonstrating that the 
benefits of a proposed source significantly outweigh the environmental 
and social costs imposed as a result of its location, construction, or 
modification; and
     Public comment on the permit.
    Minor NSR programs must meet the statutory requirements in section 
110(a)(2)(C) of the CAA which requires ``* * * regulation of the 
modification and construction of any stationary source * * * as 
necessary to assure that the [NAAQS] are achieved.'' Areas which are 
newly designated as nonattainment for the NO2 NAAQS as a 
result of any changes made to the NAAQS will be required to adopt a 
nonattainment NSR program to address major sources of NO2 
where the program does not currently exist for the NO2 NAAQS 
and may need to amend their minor source program as well. Prior to 
adoption of the SIP revision addressing major source nonattainment NSR 
for NO2 nonattainment areas, the requirements of 40 CFR part 
51, appendix S may apply.
b. Public Comments
    One commenter claimed that EPA's setting of a more stringent 
standard, i.e., short-term NO2 NAAQS, could have important 
implications for NSR and PSD and title V permits. Another commenter 
indicated that the promulgation of a new 1-hr NO2 short-term 
standard could create the need for a short-term PSD increment. Another 
commenter stated that a 1-hr NO2 Significant Impact Level 
(SIL) should be developed.
    The EPA acknowledges that a decision to promulgate a new short-term 
NO2 NAAQS will clearly have implications for the air 
permitting process. The full extent of how a new short-term 
NO2 NAAAQS will affect the NSR process will need to be 
carefully evaluated. First, major new and modified sources applying for 
NSR/PSD permits will initially be required to demonstrate that their 
proposed emissions increases of NOX will not cause or 
contribute to a violation of either the annual or 1-hour NO2 
NAAQS and the annual PSD increment. In addition, we believe that 
section 166 of the CAA authorizes us to consider the need to promulgate 
a new 1-hour increment. Historically, EPA has developed increments for 
each applicable averaging period for which a NAAQS has been 
promulgated. However, increments for a particular pollutant do not 
necessarily need to match the averaging periods that have been 
established for NAAQS for the same pollutant. Environmental Defense 
Fund, Inc. v. EPA, 898 F.2d 183, 189-190 (DC Cir. 1990) (`` * * * the 
`goals and purposes' of the PSD program, set forth in 160, are not 
identical to the criteria on which the ambient standards are based.'') 
Thus, we would need to evaluate the need for a new 1-hour 
NO2 increment in association with the goals and purposes of 
the statutory PSD program requirements.
    We also believe that there may be a need to revise the screening 
tools currently used under the NSR/PSD program for completing 
NO2 analyses. These screening tools include the significant 
impact levels (SILs), as mentioned by one commenter, but also include 
the significant emissions rate for emissions of NOX and the 
significant monitoring concentration (SMC) for NO2. EPA 
intends to evaluate the need for possible changes or additions to each 
of these important screening tools for NOX/NO2 
due to the addition of a 1-hour NO2 NAAQS. If changes or 
additions are deemed necessary, EPA will propose any such changes for 
public notice and comment in a separate action.
c. Final
    The EPA is not making any changes to the discussion concerning the 
requirements for NSR and PSD as stated in the proposed rule.
3. General Conformity
a. Proposal
    Section 176(c) of the CAA, as amended (42 U.S.C. 7401 et seq.), 
requires that all Federal actions conform to an applicable 
implementation plan developed pursuant to section 110 and part D of the 
CAA. The EPA rules, developed under the authority of section 176(c) of 
the CAA, prescribe the criteria and procedures for demonstrating and 
assuring conformity of Federal actions to a SIP. Each Federal agency 
must determine that any actions covered by the general conformity rule 
conform to the applicable SIP before the action is taken. The criteria 
and procedures for conformity apply only in nonattainment areas and 
those areas redesignated attainment since 1990 (``maintenance areas'') 
with respect to the criteria pollutants under the CAA: \30\ carbon 
monoxide (CO), lead (Pb), nitrogen dioxide (NO2), ozone 
(O3), particulate matter (PM2.5 and 
PM10), and sulfur dioxide (SO2). The general 
conformity rules apply one year following the effective date of 
designations for any new or revised NAAQS.
---------------------------------------------------------------------------

    \30\ Criteria pollutants are those pollutants for which EPA has 
established a NAAQS under section 109 of the CAA.
---------------------------------------------------------------------------

    The general conformity determination examines the impacts of direct 
and indirect emissions related to Federal actions. The general 
conformity rule provides several options to satisfy air quality 
criteria, such as modeling or offsets, and requires the Federal action 
to also meet any applicable SIP requirements and emissions milestones. 
The general conformity rule also requires that notices of draft and 
final general conformity determinations be provided directly to air 
quality regulatory agencies and to the public by publication in a local 
newspaper.
b. Final
    EPA did not receive any comments on this aspect of the proposed 
rule and is not making any changes to the discussion concerning general 
conformity stated in the proposed rule.

[[Page 6526]]

4. Transportation Conformity
a. Proposal
    Transportation conformity is required under CAA section 176(c) (42 
U.S.C. 7506(c)) to ensure that transportation plans, transportation 
improvement programs (TIPs) and Federally supported highway and transit 
projects will not cause new air quality violations, worsen existing 
violations, or delay timely attainment of the relevant NAAQS or interim 
reductions and milestones. Transportation conformity applies to areas 
that are designated nonattainment and maintenance for transportation-
related criteria pollutants: Carbon monoxide (CO), ozone 
(O3), nitrogen dioxide (NO2), and particulate 
matter (PM2.5 and PM10). Transportation 
conformity for a revised NO2 NAAQS does not apply until one 
year after the effective date of a nonattainment designation. (See CAA 
section 176(c)(6) and 40 CFR 93.102(d)).
    EPA's Transportation Conformity Rule (40 CFR 51.390, and Part 93, 
Subpart A establishes the criteria and procedures for determining 
whether transportation activities conform to the SIP. The EPA is not 
making changes to the Transportation Conformity rule in this 
rulemaking. However, in the future, EPA will review the need to conduct 
a rulemaking to establish any new or revised transportation conformity 
tests that would apply under a revision to the NO2 NAAQS for 
transportation plans, TIPs, and applicable highway and transit 
projects.
b. Public Comments
    Several commenters stated that transportation conformity could stop 
the funding of highway and transit projects in NO2 
nonattainment areas. These commenters stated that if an area fails to 
demonstrate conformity, it enters a conformity lapse and only certain 
types of projects can be funded during a lapse. The commenters further 
stated that the NO2 NAAQS will require more areas to 
determine conformity for the first time. The commenters also expressed 
concern that the NO2 NAAQS proposal did not contain 
sufficient information to understand to what extent revisions to the 
NAAQS, and the NO2 monitoring requirements, will result in 
transportation conformity requirements for individual transportation 
projects such as the need for a hot-spot analysis. The commenters 
further stated that hot-spot analyses could result in needless delays 
for transportation improvement projects.
    With regard to the comment that more areas will have to demonstrate 
conformity for the first time due to the revisions to the 
NO2 NAAQS, given that today's final rule is requiring that 
near roadway monitoring be carried out in urban areas with populations 
greater than 350K, EPA believes that most areas with such populations 
that would be designated nonattainment for NO2 are already 
designated nonattainment or maintenance for one or more of the other 
transportation-related criteria pollutants (ozone, PM2.5, 
PM10 and carbon monoxide). As such, these areas would have 
experience in making transportation conformity determinations. If areas 
with no conformity experience are designated nonattainment for the 
NO2 NAAQS, EPA and U.S. DOT would be available to assist 
areas in implementing the transportation conformity requirements.
    The commenter expressed concern that transportation conformity 
could stop highway and transit funding because areas could experience a 
conformity lapse and in such cases only certain types of projects could 
be funded. A conformity lapse occurs when an area misses a deadline for 
a required conformity determination. A new nonattainment area must 
demonstrate conformity within one year after the effective date of its 
designation. For any areas designated nonattainment for the revised 
NO2 NAAQS in early-2012, they would have to determine 
conformity within one year of the effective date of that designation 
which would be in early-2013. If that date was missed, a lapse would 
occur and only projects exempt from conformity such as safety projects, 
transportation control measures in an approved SIP for the area and 
projects or project phases that were approved by U.S. DOT before the 
lapse began can proceed during the lapse. EPA's experience in 
implementing the 1997 ozone and PM2.5 NAAQS shows that 
nearly all areas make their initial conformity determinations within 
the one-year grace period. Areas can also lapse if they fail to 
determine conformity by an applicable deadline such as determining 
conformity within two years after motor vehicle emissions budgets are 
found adequate. However, areas that miss one of these conformity 
deadlines have a one-year grace period before the lapse goes into 
effect. During the grace period, the area can continue to advance 
projects from the transportation plan and transportation improvement 
program. EPA's experience is that areas generally are able to make a 
conformity determination before the end of the grace period.
    The commenter expressed concern that the NO2 NAAQS 
proposal did not contain sufficient detail concerning possible project-
level requirements for transportation projects and that any 
requirements for hot-spot analyses could needlessly delay 
transportation projects. As EPA indicated in the NPRM, EPA is 
considering whether to revise the transportation conformity rule to 
establish requirements that would apply to transportation plans, 
transportation improvement programs and/or transportation projects in 
NO2 nonattainment and maintenance areas. If EPA concludes 
that the conformity rule must be revised in light of the final 
NO2 NAAQS, we will conduct notice and comment rulemaking to 
accomplish the revisions. At that time interested parties will have the 
opportunity to comment on any transportation conformity NPRM. This is 
the same course of action that EPA has taken with respect to revising 
the transportation conformity rule for the ozone and PM2.5 
NAAQS.
    With regard to the commenter's assertion that a requirement for 
hot-spot analyses for individual projects would needlessly delay 
transportation projects, EPA disagrees. First, CAA section 176(c)(1)(B) 
requires that transportation projects not cause new violations or make 
existing violations worse, or delay timely attainment or cause an 
interim milestone to be missed. EPA would only impose a hot-spot 
requirement for projects in NO2 nonattainment and 
maintenance areas if they are necessary to comply with CAA conformity 
requirements and therefore are needed to protect public health by 
reducing exposures to unhealthy levels of NO2 that could be 
created by the implementation of a proposed highway or transit project. 
The public would be exposed to unhealthy levels of NO2 if a 
highway or transit project caused a new violation of the NO2 
NAAQS, made an existing violation worse, or delayed timely attainment 
or delayed achieving an interim emissions milestone. If any delay in 
the project did occur, it would not be viewed as needless as it 
occurred for the important purpose of protecting the exposed public's 
health. Second, EPA does not agree that requiring a hot-spot analysis 
would needlessly delay projects in NO2 nonattainment areas. 
Such hot-spot analyses, if they are eventually required, generally 
would be done as part of the NEPA process, which these projects are 
already subject to; therefore, conducting an NO2 hot-spot 
analysis would not be introducing a new step to a project's approval 
process, but rather would add one additional analysis which must be 
completed as part of an existing project approval process.

[[Page 6527]]

c. Final
    EPA is not making any changes to the discussion concerning 
transportation conformity as stated in the proposed rule.

VII. Communication of Public Health Information

    Information on the public health implications of ambient 
concentrations of criteria pollutants is currently made available 
primarily through EPA's Air Quality Index (AQI) program. This section 
describes the conforming changes that were proposed, major comments 
received on these changes, EPA's responses to these comments and final 
decisions on the AQI breakpoints. Recognizing the importance of 
revising the AQI in a timely manner to be consistent with any revisions 
to the NAAQS, EPA proposed conforming changes to the AQI in connection 
with the final decision on the NO2 NAAQS if revisions to the 
primary standard were promulgated. Conforming changes would include 
setting the 100 level of the AQI at the same level as the revised 
primary NO2 NAAQS and also setting the other AQI breakpoints 
at the lower end of the AQI scale (i.e., AQI values of 50 and 150). EPA 
did not propose to change breakpoints at the higher end of the AQI 
scale (from 200 to 500), which would apply to State contingency plans 
or the Significant Harm Level (40 CFR 51.16), because the information 
from this review does not inform decisions about breakpoints at those 
higher levels.
    With regard to an AQI value of 50, the breakpoint between the good 
and moderate categories, EPA proposed to set this value to be between 
0.040 and 0.053 ppm NO2, 1-hour average. EPA proposed that 
the figure towards the lower end of this range would be appropriate if 
the standard is set towards the lower end of the proposed range for the 
standard (e.g. 80 ppb), while figures towards the higher end of the 
range would be more appropriate for standards set at the higher end of 
the range for the standard (e.g., 100 ppb). EPA noted that historically 
this value is set at the level of the annual NAAQS, if there is one, or 
one-half the level of the short-term NAAQS in the absence of an annual 
NAAQS, and solicited comments on this range for an AQI of 50 and the 
appropriate basis for selecting an AQI of 50 within this range.
    With regard to an AQI value of 150, the breakpoint between the 
unhealthy for sensitive groups and unhealthy categories, the range of 
0.360 to 0.370 ppm NO2, 1-hour average, represents the 
midpoint between the proposed range for the short-term standard and the 
level of an AQI value of 200 (0.64 ppm NO2, 1-hour average). 
Therefore, EPA proposed to set the AQI value of 150 to be between 0.360 
and 0.370 ppm NO2, 1-hour average.
    EPA received comments from several State environmental agencies and 
organizations of State and local agencies that generally expressed the 
view that the AQI was designed to provide the public with information 
about regional air quality and therefore it should be based on 
community-wide monitors. These commenters went on to state that using 
near-road NO2 monitors for the AQI would present problems 
because they would not represent regional NO2 concentrations 
and it would be difficult to communicate this type of information to 
the public using the AQI. Some expressed concern that NO2 
measured at near-roadway monitors could be the critical pollutant and 
could drive the AQI even though it may not represent air quality across 
the area. Other agencies expressed concern that there is currently no 
way to forecast ambient NO2 levels near roadways. One State 
agency commented that the AQI is intended to represent air quality 
where people live, work and play.
    EPA agrees with commenters that the AQI should represent regional 
air quality, and that measurements that apply to a limited area should 
not be used to characterize air quality across the region. Community-
wide NO2 monitors should be used to characterize air quality 
across the region. However, the AQI reporting requirements encourage, 
but do not require, the reporting of index values of sub-areas of an 
MSA. We agree with the commenter that stated the view that the AQI is 
intended to represent air quality where people live, work and play. To 
the extent that near-roadway monitoring occurs in areas where people 
live, work or play, EPA encourages reporting of the AQI for that 
specific sub-area of the MSA (64 FR 42548, August 4, 1999). We also 
agree that it may be difficult to communicate this type of information 
and we plan to work with State and local air agencies to figure out the 
best way to present this information to the public using the AQI. Air 
quality forecasting is recommended but not required (64 FR 42548, 
August 4, 1999). EPA will work with State agencies that want to develop 
a forecasting program.
    With regard to the proposed breakpoints, EPA received few comments. 
The National Association of Clean Air Agencies commented that it would 
be confusing to the public to have an AQI value of 50 set below the 
level of the annual NO2 standard. We agree with this 
comment, and therefore have decided that it is appropriate to set the 
AQI value of 50, the breakpoint between the good and moderate ranges, 
set at the numerical level of the annual standard, 53 ppb 
NO2, 1-hour average. The AQI value of 100, the breakpoint 
between the moderate and unhealthy for sensitive groups category, is 
set at 100 ppb, 1-hour average, the level of the primary NO2 
NAAQS. EPA is setting an AQI value of 150, the breakpoint between the 
unhealthy for sensitive groups and unhealthy categories, at 0.360 ppm 
NO2, 1-hour average.

VIII. Statutory and Executive Order Reviews

A. Executive Order 12866: Regulatory Planning and Review

    Under Executive Order 12866 (58 FR 51735, October 4, 1993), this 
action is a ``significant regulatory action'' because it was deemed to 
``raise novel legal or policy issues.'' Accordingly, EPA submitted this 
action to the Office of Management and Budget (OMB) for review under 
Executive Order 12866 and any changes made in response to OMB 
recommendations have been documented in the docket for this action. In 
addition, EPA prepared a Regulatory Impact Analysis (RIA) of the 
potential costs and benefits associated with this action. However, the 
CAA and judicial decisions make clear that the economic and technical 
feasibility of attaining ambient standards are not to be considered in 
setting or revising NAAQS, although such factors may be considered in 
the development of State plans to implement the standards. Accordingly, 
although an RIA has been prepared, the results of the RIA have not been 
considered in developing this final rule.

B. Paperwork Reduction Act

    The information collection requirements in this final rule have 
been submitted for approval to the Office of Management and Budget 
(OMB) under the Paperwork Reduction Act, 44 U.S.C. 3501 et seq. The 
information collection requirements are not enforceable until OMB 
approves them.
    The Information Collection Request (ICR) document prepared by EPA 
for these revisions to part 58 has been assigned EPA ICR number 
2358.02.
    The information collected under 40 CFR part 53 (e.g., test results, 
monitoring records, instruction manual, and other associated 
information) is needed to determine whether a candidate method intended 
for use in determining attainment of the National Ambient Air Quality 
Standards (NAAQS) in 40 CFR part 50 will meet

[[Page 6528]]

the design, performance, and/or comparability requirements for 
designation as a Federal reference method (FRM) or Federal equivalent 
method (FEM). We do not expect the number of FRM or FEM determinations 
to increase over the number that is currently used to estimate burden 
associated with NO2 FRM/FEM determinations provided in the 
current ICR for 40 CFR part 53 (EPA ICR numbers 2358.01). As such, no 
change in the burden estimate for 40 CFR part 53 has been made as part 
of this rulemaking.
    The information collected and reported under 40 CFR part 58 is 
needed to determine compliance with the NAAQS, to characterize air 
quality and associated health impacts, to develop emissions control 
strategies, and to measure progress for the air pollution program. The 
amendments would revise the technical requirements for NO2 
monitoring sites, require the siting and operation of additional 
NO2 ambient air monitors, and the reporting of the collected 
ambient NO2 monitoring data to EPA's Air Quality System 
(AQS). The annual average reporting burden for the collection under 40 
CFR part 58 (averaged over the first 3 years of this ICR) is 
$3,261,007. Burden is defined at 5 CFR 1320.3(b). State, local, and 
Tribal entities are eligible for State assistance grants provided by 
the Federal government under the CAA which can be used for monitors and 
related activities.
    An agency may not conduct or sponsor, and a person is not required 
to respond to, a collection of information unless it displays a 
currently valid OMB control number. The OMB control numbers for EPA's 
regulations in 40 CFR are listed in 40 CFR part 9.

C. Regulatory Flexibility Act

    The Regulatory Flexibility Act (RFA) generally requires an agency 
to prepare a regulatory flexibility analysis of any rule subject to 
notice and comment rulemaking requirements under the Administrative 
Procedure Act or any other statute unless the agency certifies that the 
rule will not have a significant economic impact on a substantial 
number of small entities. Small entities include small businesses, 
small organizations, and small governmental jurisdictions.
    For purposes of assessing the impacts of this rule on small 
entities, small entity is defined as: (1) A small business that is a 
small industrial entity as defined by the Small Business 
Administration's (SBA) regulations at 13 CFR 121.201; (2) a small 
governmental jurisdiction that is a government of a city, county, town, 
school district or special district with a population of less than 
50,000; and (3) a small organization that is any not-for-profit 
enterprise which is independently owned and operated and is not 
dominant in its field.
    After considering the economic impacts of this final rule on small 
entities, I certify that this action will not have a significant 
economic impact on a substantial number of small entities. This final 
rule will not impose any requirements on small entities. Rather, this 
rule establishes national standards for allowable concentrations of 
NO2 in ambient air as required by section 109 of the CAA. 
American Trucking Ass'ns v. EPA, 175 F.3d 1027, 1044-45 (DC cir. 1999) 
(NAAQS do not have significant impacts upon small entities because 
NAAQS themselves impose no regulations upon small entities). Similarly, 
the amendments to 40 CFR part 58 address the requirements for States to 
collect information and report compliance with the NAAQS and will not 
impose any requirements on small entities.

D. Unfunded Mandates Reform Act

    This rule does not contain a Federal mandate that may result in 
expenditures of $100 million or more for State, local, and Tribal 
governments, in the aggregate, or the private sector in any one year. 
The revisions to the NO2 NAAQS impose no enforceable duty on 
any State, local or Tribal governments or the private sector. The 
expected costs associated with the monitoring requirements are 
described in EPA's ICR document, but those costs are not expected to 
exceed $100 million in the aggregate for any year. Furthermore, as 
indicated previously, in setting a NAAQS EPA cannot consider the 
economic or technological feasibility of attaining ambient air quality 
standards. Because the Clean Air Act prohibits EPA from considering the 
types of estimates and assessments described in section 202 when 
setting the NAAQS, the UMRA does not require EPA to prepare a written 
statement under section 202 for the revisions to the NO2 
NAAQS. Thus, this rule is not subject to the requirements of sections 
202 or 205 of UMRA.
    With regard to implementation guidance, the CAA imposes the 
obligation for States to submit SIPs to implement the NO2 
NAAQS. In this final rule, EPA is merely providing an interpretation of 
those requirements. However, even if this rule did establish an 
independent obligation for States to submit SIPs, it is questionable 
whether an obligation to submit a SIP revision would constitute a 
Federal mandate in any case. The obligation for a State to submit a SIP 
that arises out of section 110 and section 191 of the CAA is not 
legally enforceable by a court of law, and at most is a condition for 
continued receipt of highway funds. Therefore, it is possible to view 
an action requiring such a submittal as not creating any enforceable 
duty within the meaning of 2 U.S.C. 658 for purposes of the UMRA. Even 
if it did, the duty could be viewed as falling within the exception for 
a condition of Federal assistance under 2 U.S.C. 658.
    This rule is also not subject to the requirements of section 203 of 
UMRA because it contains no regulatory requirements that might 
significantly or uniquely affect small governments because it imposes 
no enforceable duty on any small governments.

E. Executive Order 13132: Federalism

    This action does not have federalism implications. It will not have 
substantial direct effects on the States, on the relationship between 
the national government and the States, or on the distribution of power 
and responsibilities among the various levels of government, as 
specified in Executive Order 13132. The rule does not alter the 
relationship between the Federal government and the States regarding 
the establishment and implementation of air quality improvement 
programs as codified in the CAA. Under section 109 of the CAA, EPA is 
mandated to establish NAAQS; however, CAA section 116 preserves the 
rights of States to establish more stringent requirements if deemed 
necessary by a State. Furthermore, this rule does not impact CAA 
section 107 which establishes that the States have primary 
responsibility for implementation of the NAAQS. Finally, as noted in 
section E (above) on UMRA, this rule does not impose significant costs 
on State, local, or Tribal governments or the private sector. Thus, 
Executive Order 13132 does not apply to this rule.

F. Executive Order 13175: Consultation and Coordination With Indian 
Tribal Governments

    This action does not have Tribal implications, as specified in 
Executive Order 13175 (65 FR 67249, November 9, 2000). It does not have 
a substantial direct effect on one or more Indian Tribes, on the 
relationship between the Federal government and Indian Tribes, or on 
the distribution of power and responsibilities between the Federal 
government and Tribes. The rule does not alter the relationship between 
the

[[Page 6529]]

Federal government and Tribes as established in the CAA and the TAR. 
Under section 109 of the CAA, EPA is mandated to establish NAAQS; 
however, this rule does not infringe existing Tribal authorities to 
regulate air quality under their own programs or under programs 
submitted to EPA for approval. Furthermore, this rule does not affect 
the flexibility afforded to Tribes in seeking to implement CAA programs 
consistent with the TAR, nor does it impose any new obligation on 
Tribes to adopt or implement any NAAQS. Finally, as noted in section E 
(above) on UMRA, this rule does not impose significant costs on Tribal 
governments. Thus, Executive Order 13175 does not apply to this action.

G. Executive Order 13045: Protection of Children From Environmental 
Health Risks and Safety Risks

    This action is subject to Executive Order 13045 (62 FR 19885, April 
23, 1997) because it is an economically significant regulatory action 
as defined by Executive Order 12866, and EPA believes that the 
environmental health or safety risk addressed by this action has a 
disproportionate effect on children. The final rule will establish 
uniform national ambient air quality standards for NO2; 
these standards are designed to protect public health with an adequate 
margin of safety, as required by CAA section 109. The protection 
offered by these standards may be especially important for asthmatics, 
including asthmatic children, because respiratory effects in asthmatics 
are among the most sensitive health endpoints for NO2 
exposure. Because asthmatic children are considered a sensitive 
population, we have evaluated the potential health effects of exposure 
to NO2 pollution among asthmatic children. These effects and 
the size of the population affected are discussed in chapters 3 and 4 
of the ISA; chapters 3, 4, and 8 of the REA, and sections II.A through 
II.E of this preamble.

H. Executive Order 13211: Actions Concerning Regulations That 
Significantly Affect Energy Supply, Distribution or Use

    This action is not a ``significant energy action'' as defined in 
Executive Order 13211, ``Actions Concerning Regulations That 
Significantly Affect Energy Supply, Distribution, or Use'' (66 FR 28355 
(May 22, 2001)) because it is not likely to have a significant adverse 
effect on the supply, distribution, or use of energy. The purpose of 
this rule is to establish revised NAAQS for NO2. The rule 
does not prescribe specific control strategies by which these ambient 
standards will be met. Such strategies will be developed by States on a 
case-by-case basis, and EPA cannot predict whether the control options 
selected by States will include regulations on energy suppliers, 
distributors, or users. Thus, EPA concludes that this rule is not 
likely to have any adverse energy effects.

I. National Technology Transfer and Advancement Act

    Section 12(d) of the National Technology Transfer and Advancement 
Act of 1995 (NTTAA), Public Law 104-113, section 12(d) (15 U.S.C. 
272 note) directs EPA to use voluntary consensus standards 
in its regulatory activities unless to do so would be inconsistent with 
applicable law or otherwise impractical. Voluntary consensus standards 
are technical standards (e.g., materials specifications, test methods, 
sampling procedures, and business practices) that are developed or 
adopted by voluntary consensus standards bodies. The NTTAA directs EPA 
to provide Congress, through OMB, explanations when the Agency decides 
not to use available and applicable voluntary consensus standards.
    This final rulemaking involves technical standards. Therefore the 
Agency conducted a search to identify potential applicable voluntary 
consensus standards. However, we identified no such standards, and none 
were brought to our attention in comments. Therefore, EPA has decided 
to use the technical standard described in Section III.A of the 
preamble.

J. Executive Order 12898: Federal Actions To Address Environmental 
Justice in Minority Populations and Low-Income Populations

    Executive Order 12898 (59 FR 7629; Feb. 16, 1994) establishes 
Federal executive policy on environmental justice. Its main provision 
directs Federal agencies, to the greatest extent practicable and 
permitted by law, to make environmental justice part of their mission 
by identifying and addressing, as appropriate, disproportionately high 
and adverse human health or environmental effects of their programs, 
policies, and activities on minority populations and low-income 
populations in the United States.
    EPA has determined that this final rule will not have 
disproportionately high and adverse human health or environmental 
effects on minority or low-income populations because it increases the 
level of environmental protection for all affected populations without 
having any disproportionately high and adverse human health effects on 
any population, including any minority or low-income population. The 
final rule will establish uniform national standards for NO2 
in ambient air.

K. Congressional Review Act

    The Congressional Review Act, 5 U.S.C. 801 et seq., as added by the 
Small Business Regulatory Enforcement Fairness Act of 1996, generally 
provides that before a rule may take effect, the agency promulgating 
the rule must submit a rule report, which includes a copy of the rule, 
to each House of the Congress and to the Comptroller General of the 
United States. EPA will submit a report containing this rule and other 
required information to the U.S. Senate, the U.S. House of 
Representatives, and the Comptroller General of the United States prior 
to publication of the rule in the Federal Register. A Major rule cannot 
take effect until 60 days after it is published in the Federal 
Register. This action is a ``major rule'' as defined by 5 U.S.C. 
804(2). This rule will be effective on April 12, 2010.

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and Manhattan. Prepared for: The U.S. Department of Health and Human 
Services, Agency for Toxic Substance and Disease Registry.
Nunnermacker, LJ, Imre D, Daum PH, Kleinman L, Lee YN, Lee JH, 
Springston SR, Newman L, Weinstein-Lloyd J, Luke WT, Banta R, 
Alvarez R, Senff C, Sillman S, Holdren M, Keigley GW, Zhou X. 
(1998). Characterization of the Nashville urban plume on July 3 and 
July 18, 1995. J. Geophys. Res. [Atmos.] 103:28,129-28,148.
Parrish, DD, Hahn CH, Fahey DW, Williams EJ, Bollinger MJ, Hubler G, 
Buhr MP, Murphy PC, Trainer M, Hsie EY, Liu SC, Fehsenfeld FC. 
(1990). Systematic variations in the concentration of NOX 
(NO plus NO2) at Niwot Ridge, Colorado. J. Geophys. Res. 
95:1817-1836.
Parrish, DD, Fehsenfeld FC. (2000). Methods for gas-phase 
measurements of ozone, ozone precursors and aerosol precursors. 
Atmos. Environ. 34:1921-1957.
Peacock, M. (2008). Letter to CASAC chair Rogene Henderson. 
September 8.
Peacock, JL, Symonds P, Jackson P, Bremner SA, Scarlett JF, Strachan 
DP, Anderson HR. (2003). Acute effects of winter air pollution on 
respiratory function in schoolchildren in southern England. Occup. 
Environ. Med. 60:82-89.
Peel, JL, Tolbert PE, Klein M, Metzger KB, Flanders WD, Knox T, 
Mulholland JA, Ryan PB, Frumkin H. (2005). Ambient air pollution and 
respiratory emergency department visits. Epidemiology. 16:164-174.
Ridley, BA, Carroll MA, Torres AL, Condon EP, Sachse GW, Hill GF, 
Gregory GL. (1988). An intercomparison of results from ferrous 
sulphate and photolytic converter techniques for measurements of 
NOX made during the NASA GTE/CITE 1 aircraft program. J. 
Geophys. Res. 93:15,803-15,811.
Rizzo (2008). Investigation of how distributions of hourly nitrogen 
dioxide concentrations have changed over time in six cities. 
Nitrogen Dioxide NAAQS Review Docket (EPA-HQ-OAR-2006-
0922). Available at http://www.epa.gov/ttn/naaqs/standards/nox/s_nox_cr_rea.html.
Rodes, CE and Holland DM. (1981). Variations of NO, NO2, 
and O3 concentrations downwind of a Los Angeles Freeway. 
Atmos. Environ. 15:243-250.
Roorda-Knape, MC, Janssen NAH, De Hartog JJ, Van Vliet PHN, Harssema 
H, Brunekreef B. (1998). Air pollution from traffic in city 
districts near major motorways. Atmos. Environ. 32:1921-1930.
Samet, J. (2008a). Letter to EPA Administrator Stephen Johnson: 
``Clean Air Scientific Advisory Committee's (CASAC) Peer Review of 
Draft Chapter 8 of EPA's Risk and Exposure Assessment to Support the 
Review of the NO2 Primary National Ambient Air Quality 
Standard.'' EPA-CASAC-09-001, October 2008.
Samet, J. (2008b). Letter to EPA Administrator Stephen Johnson: 
``Clean Air Scientific Advisory Committee's (CASAC) Review Comments 
on EPA's Risk and Exposure Assessment to Support the Review of the 
NO2 Primary National Ambient Air Quality Standard.'' EPA-
CASAC-09-003, December 16.
Samet, J. (2009). Letter to EPA Administrator Lisa P. Jackson: 
``Comments and

[[Page 6531]]

Recommendations Concerning EPA's Proposed Rule for the Revision of 
the National Ambient Air Quality Standards (NAAQS) for Nitrogen 
Dioxide.'' EPA-CASAC-09-014, September 9.
Schildcrout, JS, Sheppard L, Lumley T, Slaughter JC, Koenig JQ, 
Shapiro GG. (2006). Ambient air pollution and asthma exacerbations 
in children: an eight-city analysis. Am J Epidemiol. 164:505-517.
Schindler, C, K[uuml]nzli N, Bongard JP, Leuenberger P, Karrer W, 
Rapp R, Monn C, Ackermann-Liebrich U. (2001). Short-term variation 
in air pollution and in average lung function among never-smokers. 
Am. J. Respir. Crit. Care Med. 163: 356-361.
Schwartz, J, Dockery DW, Neas LM, Wypij D, Ware JH, Spengler JD, 
Koutrakis P, Speizer FE, Ferris BG, Jr. (1994). Acute effects of 
summer air pollution on respiratory symptom reporting in children. 
Am J Respir Crit Care Med. 150:1234-1242.
Singer, B, Hodgson A, Hotchi T, Kim J. (2004). Passive measurement 
of nitrogen oxides to assess traffic-related pollutant exposure for 
the East Bay Children's Respiratory Health Study. Atmos Environ. 
38:393-403.
Thompson, R. (2008). Nitrogen Dioxide (NO2) Descriptive 
Statistics Tables. Memo to the NO2 NAAQS docket. 
Available at http://www.epa.gov/ttn/naaqs/standards/nox/s_nox_cr_rea.html.
Tolbert, PE, Klein M, Peel JL, Sarnat SE, Sarnat JA. (2007). 
Multipollutant modeling issues in a study of ambient air quality and 
emergency department visits in Atlanta. J. Exposure Sci. Environ. 
Epidemiol. 17(Suppl. 2s): S29-S35.
Watkins, N. and Thompson, R. (2008). NOX Network Review 
and Background. Memo to the NO2 NAAQS docket.
Zhou, Y and Levy JI. (2007). Factors influencing the spatial extent 
of mobile source air pollution impacts: a meta-analysis. BMC Public 
Health. 7:89.

List of Subjects

40 CFR Part 50

    Environmental protection, Air pollution control, Carbon monoxide, 
Lead, Nitrogen dioxide, Ozone, Particulate matter, Sulfur oxides.

40 CFR Part 58

    Environmental protection, Administrative practice and procedure, 
Air pollution control, Intergovernmental relations, Reporting and 
recordkeeping requirements.

    Dated: January 22, 2010.
Lisa P. Jackson,
Administrator.

0
For the reasons stated in the preamble, title 40, chapter I of the Code 
of Federal Regulations is amended as follows:

PART 50--NATIONAL PRIMARY AND SECONDARY AMBIENT AIR QUALITY 
STANDARDS

0
1. The authority citation for part 50 continues to read as follows:

    Authority: 42 U.S.C. 7401, et seq.


0
2. Section 50.11 is revised to read as follows:


Sec.  50.11  National primary and secondary ambient air quality 
standards for oxides of nitrogen (with nitrogen dioxide as the 
indicator).

    (a) The level of the national primary annual ambient air quality 
standard for oxides of nitrogen is 53 parts per billion (ppb, which is 
1 part in 1,000,000,000), annual average concentration, measured in the 
ambient air as nitrogen dioxide.
    (b) The level of the national primary 1-hour ambient air quality 
standard for oxides of nitrogen is 100 ppb, 1-hour average 
concentration, measured in the ambient air as nitrogen dioxide.
    (c) The level of the national secondary ambient air quality 
standard for nitrogen dioxide is 0.053 parts per million (100 
micrograms per cubic meter), annual arithmetic mean concentration.
    (d) The levels of the standards shall be measured by:
    (1) A reference method based on appendix F to this part; or
    (2) By a Federal equivalent method (FEM) designated in accordance 
with part 53 of this chapter.
    (e) The annual primary standard is met when the annual average 
concentration in a calendar year is less than or equal to 53 ppb, as 
determined in accordance with Appendix S of this part for the annual 
standard.
    (f) The 1-hour primary standard is met when the three-year average 
of the annual 98th percentile of the daily maximum 1-hour average 
concentration is less than or equal to 100 ppb, as determined in 
accordance with Appendix S of this part for the 1-hour standard.
    (g) The secondary standard is attained when the annual arithmetic 
mean concentration in a calendar year is less than or equal to 0.053 
ppm, rounded to three decimal places (fractional parts equal to or 
greater than 0.0005 ppm must be rounded up). To demonstrate attainment, 
an annual mean must be based upon hourly data that are at least 75 
percent complete or upon data derived from manual methods that are at 
least 75 percent complete for the scheduled sampling days in each 
calendar quarter.

0
3. Section 50.14 is amended by adding an entry to the end of table in 
paragraph (c)(2)(vi) to read as follows:


Sec.  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 or Revised NAAQS
----------------------------------------------------------------------------------------------------------------
                                         Air quality
 NAAQS pollutant/ standard/ (level)/   data collected  Event flagging & initial       Detailed documentation
          promulgation date             for calendar     description deadline          submission deadline
                                            year
----------------------------------------------------------------------------------------------------------------

                                                  * * * * * * *
NO2/1-Hour Standard (100 PPB)........            2008  July 1, 2010 \a\........  January 22, 2011.
                                                 2009  July 1, 2010............  January 22, 2011.
                                                 2010  April 1, 2011 \a\.......  July 1, 2011 \a\.
----------------------------------------------------------------------------------------------------------------
\a\ 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 or revised NAAQS. The general schedule applies for all other purposes, most
  notably, for data used by EPA for redesignations to attainment.


[[Page 6532]]

* * * * *

0
4. Appendix S to Part 50 is added to read as follows:

Appendix S to Part 50--Interpretation of the Primary National Ambient 
Air Quality Standards for Oxides of Nitrogen (Nitrogen Dioxide)

1. General

    (a) This appendix explains the data handling conventions and 
computations necessary for determining when the primary national 
ambient air quality standards for oxides of nitrogen as measured by 
nitrogen dioxide (``NO2 NAAQS'') specified in 50.11 are 
met. Nitrogen dioxide (NO2) is measured in the ambient 
air by a Federal reference method (FRM) based on appendix F to this 
part or by a Federal equivalent method (FEM) designated in 
accordance with part 53 of this chapter. Data handling and 
computation procedures to be used in making comparisons between 
reported NO2 concentrations and the levels of the 
NO2 NAAQS are specified in the following sections.
    (b) Whether to exclude, retain, or make adjustments to the data 
affected by exceptional events, including natural events, is 
determined by the requirements and process deadlines specified in 
50.1, 50.14 and 51.930 of this chapter.
    (c) The terms used in this appendix are defined as follows:
    Annual mean refers to the annual average of all of the 1-hour 
concentration values as defined in section 5.1 of this appendix.
    Daily maximum 1-hour values for NO2 refers to the 
maximum 1-hour NO2 concentration values measured from 
midnight to midnight (local standard time) that are used in NAAQS 
computations.
    Design values are the metrics (i.e., statistics) that are 
compared to the NAAQS levels to determine compliance, calculated as 
specified in section 5 of this appendix. The design values for the 
primary NAAQS are:
    (1) The annual mean value for a monitoring site for one year 
(referred to as the ``annual primary standard design value'').
    (2) The 3-year average of annual 98th percentile daily maximum 
1-hour values for a monitoring site (referred to as the ``1-hour 
primary standard design value'').
    98th percentile daily maximum 1-hour value is the value below 
which nominally 98 percent of all daily maximum 1-hour concentration 
values fall, using the ranking and selection method specified in 
section 5.2 of this appendix.
    Quarter refers to a calendar quarter.
    Year refers to a calendar year.

2. Requirements for Data Used for Comparisons With the NO2 
NAAQS and Data Reporting Considerations

    (a) All valid FRM/FEM NO2 hourly data required to be 
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. Multi-hour average concentration values collected by 
wet chemistry methods shall not be used.
    (b) When two or more NO2 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 1-
hour primary 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 NO2 measurement data shall be reported to 
AQS in units of parts per billion (ppb), to at most one place after 
the decimal, with additional digits to the right being truncated 
with no further rounding.

3. Comparisons With the NO2 NAAQS

3.1 The Annual Primary NO2 NAAQS

    (a) The annual primary NO2 NAAQS is met at a site 
when the valid annual primary standard design value is less than or 
equal to 53 parts per billion (ppb).
    (b) An annual primary standard design value is valid when at 
least 75 percent of the hours in the year are reported.
    (c) An annual primary standard design value based on data that 
do not meet the completeness criteria stated in section 3.1(b) may 
also be considered 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.
    (d) The procedures for calculating the annual primary standard 
design values are given in section 5.1 of this appendix.

3.2 The 1-hour Primary NO2 NAAQS

    (a) The 1-hour primary NO2 NAAQS is met at a site 
when the valid 1-hour primary standard design value is less than or 
equal to 100 parts per billion (ppb).
    (b) An NO2 1-hour primary standard design value is 
valid if it encompasses three consecutive calendar years of complete 
data. A year meets data completeness requirements when all 4 
quarters are complete. A quarter is complete when at least 75 
percent of the sampling days for each quarter have complete data. A 
sampling day has complete data if 75 percent of the hourly 
concentration values, including State-flagged data affected by 
exceptional events which have been approved for exclusion by the 
Administrator, are reported.
    (c) In the case of one, two, or three years that do not meet the 
completeness requirements of section 3.2(b) of this appendix and 
thus would normally not be useable for the calculation of a valid 3-
year 1-hour primary standard design value, the 3-year 1-hour primary 
standard design value shall nevertheless be considered valid if one 
of the following conditions is true.
    (i) At least 75 percent of the days in each quarter of each of 
three consecutive years have at least one reported hourly value, and 
the design value calculated according to the procedures specified in 
section 5.2 is above the level of the primary 1-hour standard.
    (ii)(A) A 1-hour primary standard design value that is below the 
level of the NAAQS can be validated if the substitution test in 
section 3.2(c)(ii)(B) results in a ``test design value'' that is 
below the level of the NAAQS. The test substitutes actual ``high'' 
reported daily maximum 1-hour values from the same site at about the 
same time of the year (specifically, in the same calendar quarter) 
for unknown values that were not successfully measured. Note that 
the test is merely diagnostic in nature, intended to confirm that 
there is a very high likelihood that the original design value (the 
one with less than 75 percent data capture of hours by day and of 
days by quarter) reflects the true under-NAAQS-level status for that 
3-year period; the result of this data substitution test (the ``test 
design value'', as defined in section 3.2(c)(ii)(B)) is not 
considered the actual design value. For this test, substitution is 
permitted only if there are at least 200 days across the three 
matching quarters of the three years under consideration (which is 
about 75 percent of all possible daily values in those three 
quarters) for which 75 percent of the hours in the day, including 
State-flagged data affected by exceptional events which have been 
approved for exclusion by the Administrator, have reported 
concentrations. However, maximum 1-hour values from days with less 
than 75 percent of the hours reported shall also be considered in 
identifying the high value to be used for substitution.
    (B) The substitution test is as follows: Data substitution will 
be performed in all quarter periods that have less than 75 percent 
data capture but at least 50 percent data capture, including State-
flagged data affected by exceptional events which have been approved 
for exclusion by the Administrator; if any quarter has less than 50 
percent data capture then this substitution test cannot be used. 
Identify for each quarter (e.g., January-March) the highest reported 
daily maximum 1-hour value for that quarter, excluding State-flagged 
data affected by exceptional events which have been approved for 
exclusion by the Administrator, looking across those three months of 
all three years under consideration. All daily maximum 1-hour values 
from all days in the quarter period shall be considered when 
identifying this highest value, including days with less than

[[Page 6533]]

75 percent data capture. If after substituting the highest non-
excluded reported daily maximum 1-hour value for a quarter for as 
much of the missing daily data in the matching deficient quarter(s) 
as is needed to make them 100 percent complete, the procedure in 
section 5.2 yields a recalculated 3-year 1-hour standard ``test 
design value'' below the level of the standard, then the 1-hour 
primary standard design value is deemed to have passed the 
diagnostic test and is valid, and the level of the standard is 
deemed to have been met in that 3-year period. As noted in section 
3.2(c)(i), in such a case, the 3-year design value based on the data 
actually reported, not the ``test design value'', shall be used as 
the valid design value.
    (iii)(A) A 1-hour primary standard design value that is above 
the level of the NAAQS can be validated if the substitution test in 
section 3.2(c)(iii)(B) results in a ``test design value'' that is 
above the level of the NAAQS. The test substitutes actual ``low'' 
reported daily maximum 1-hour values from the same site at about the 
same time of the year (specifically, in the same three months of the 
calendar) for unknown values that were not successfully measured. 
Note that the test is merely diagnostic in nature, intended to 
confirm that there is a very high likelihood that the original 
design value (the one with less than 75 percent data capture of 
hours by day and of days by quarter) reflects the true above-NAAQS-
level status for that 3-year period; the result of this data 
substitution test (the ``test design value'', as defined in section 
3.2(c)(iii)(B)) is not considered the actual design value. For this 
test, substitution is permitted only if there are a minimum number 
of available daily data points from which to identify the low 
quarter-specific daily maximum 1-hour values, specifically if there 
are at least 200 days across the three matching quarters of the 
three years under consideration (which is about 75 percent of all 
possible daily values in those three quarters) for which 75 percent 
of the hours in the day have reported concentrations. Only days with 
at least 75 percent of the hours reported shall be considered in 
identifying the low value to be used for substitution.
    (B) The substitution test is as follows: Data substitution will 
be performed in all quarter periods that have less than 75 percent 
data capture. Identify for each quarter (e.g., January-March) the 
lowest reported daily maximum 1-hour value for that quarter, looking 
across those three months of all three years under consideration. 
All daily maximum 1-hour values from all days with at least 75 
percent capture in the quarter period shall be considered when 
identifying this lowest value. If after substituting the lowest 
reported daily maximum 1-hour value for a quarter for as much of the 
missing daily data in the matching deficient quarter(s) as is needed 
to make them 75 percent complete, the procedure in section 5.2 
yields a recalculated 3-year 1-hour standard ``test design value'' 
above the level of the standard, then the 1-hour primary standard 
design value is deemed to have passed the diagnostic test and is 
valid, and the level of the standard is deemed to have been exceeded 
in that 3-year period. As noted in section 3.2(c)(i), in such a 
case, the 3-year design value based on the data actually reported, 
not the ``test design value'', shall be used as the valid design 
value.
    (d) A 1-hour primary standard design value based on data that do 
not meet the completeness criteria stated in 3.2(b) and also do not 
satisfy section 3.2(c), may also be considered 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) The procedures for calculating the 1-hour primary standard 
design values are given in section 5.2 of this appendix.

4. Rounding Conventions

4.1 Rounding Conventions for the Annual Primary NO2 
NAAQS

    (a) Hourly NO2 measurement data shall be reported to 
AQS in units of parts per billion (ppb), to at most one place after 
the decimal, with additional digits to the right being truncated 
with no further rounding.
    (b) The annual primary standard design value is calculated 
pursuant to section 5.1 and then rounded to the nearest whole number 
or 1 ppb (decimals 0.5 and greater are rounded up to the nearest 
whole number, and any decimal lower than 0.5 is rounded down to the 
nearest whole number).

4.2 Rounding Conventions for the 1-hour Primary NO2 NAAQS

    (a) Hourly NO2 measurement data shall be reported to 
AQS in units of parts per billion (ppb), to at most one place after 
the decimal, with additional digits to the right being truncated 
with no further rounding.
    (b) Daily maximum 1-hour values are not rounded.
    (c) The 1-hour primary standard design value is calculated 
pursuant to section 5.2 and then rounded to the nearest whole number 
or 1 ppb (decimals 0.5 and greater are rounded up to the nearest 
whole number, and any decimal lower than 0.5 is rounded down to the 
nearest whole number).

5. Calculation Procedures for the Primary NO2 NAAQS

5.1 Procedures for the Annual Primary NO2 NAAQS

    (a) When the data for a site and year meet the data completeness 
requirements in section 3.1(b) of this appendix, or if the 
Administrator exercises the discretionary authority in section 
3.1(c), the annual mean is simply the arithmetic average of all of 
the reported 1-hour values.
    (b) The annual primary standard design value for a site is the 
valid annual mean rounded according to the conventions in section 
4.1.

5.2 Calculation Procedures for the 1-hour Primary NO2 NAAQS

    (a) Procedure for identifying annual 98th percentile values. 
When the data for a particular site and year meet the data 
completeness requirements in section 3.2(b), or if one of the 
conditions of section 3.2(c) is met, or if the Administrator 
exercises the discretionary authority in section 3.2(d), 
identification of annual 98th percentile value is accomplished as 
follows.
    (i) The annual 98th percentile value for a year is the higher of 
the two values resulting from the following two procedures.
    (1) Procedure 1.
    (A) For the year, determine the number of days with at least 75 
percent of the hourly values reported including State-flagged data 
affected by exceptional events which have been approved for 
exclusion by the Administrator.
    (B) For the year, from only the days with at least 75 percent of 
the hourly values reported, select from each day the maximum hourly 
value excluding State-flagged data affected by exceptional events 
which have been approved for exclusion by the Administrator.
    (C) Sort all these daily maximum hourly values from a particular 
site and year by descending value. (For example: (x[1], x[2], x[3], 
* * *, x[n]). In this case, x[1] is the largest number and x[n] is 
the smallest value.) The 98th percentile is determined from this 
sorted series of daily values which is ordered from the highest to 
the lowest number. Using the left column of Table 1, determine the 
appropriate range (i.e., row) for the annual number of days with 
valid data for year y (cny) as determined from step (A). 
The corresponding ``n'' value in the right column identifies the 
rank of the annual 98th percentile value in the descending sorted 
list of daily site values for year y. Thus, P0.98, y = 
the nth largest value.
    (2) Procedure 2.
    (A) For the year, determine the number of days with at least one 
hourly value reported including State-flagged data affected by 
exceptional events which have been approved for exclusion by the 
Administrator.
    (B) For the year, from all the days with at least one hourly 
value reported, select from each day the maximum hourly value 
excluding State-flagged data affected by exceptional events which 
have been approved for exclusion by the Administrator.
    (C) Sort all these daily maximum values from a particular site 
and year by descending value. (For example: (x[1], x[2], x[3], * * 
*, x[n]). In this case, x[1] is the largest number and x[n] is the 
smallest value.) The 98th percentile is determined from this sorted 
series of daily values which is ordered from the highest to the 
lowest number. Using the left column of Table 1, determine the 
appropriate range (i.e., row) for the annual number of days with 
valid data for year y (cny) as determined from step (A). 
The corresponding ``n'' value in the right column identifies the 
rank of the annual 98th percentile value in the descending sorted 
list of daily site values for year y. Thus, P0.98, y = 
the nth largest value.
    (b) The 1-hour primary standard design value for a site is mean 
of the three annual 98th percentile values, rounded according to the 
conventions in section 4.

[[Page 6534]]



                                 Table 1
------------------------------------------------------------------------
                                                        P0.98, y is the
                                                      nth maximum  value
  Annual number  of days with  valid data for  year      of the  year,
                     ``y'' (cny)                        where n  is the
                                                        listed  number
------------------------------------------------------------------------
1-50................................................                  1
51-100..............................................                  2
101-150.............................................                  3
151-200.............................................                  4
201-250.............................................                  5
251-300.............................................                  6
301-350.............................................                  7
351-366.............................................                  8
------------------------------------------------------------------------

PART 58--AMBIENT AIR QUALITY SURVEILLANCE

0
5. The authority citation for part 58 continues to read as follows:

    Authority: 42 U.S.C. 7403, 7410, 7601(a), 7611, and 7619.

Subpart A--[Amended]

0
6. Section 58.1, is amended by adding the definitions for ``AADT'' and 
``Near-road NO2 Monitor'' in alphabetical order to read as 
follows:


Sec.  58.1  Definitions

* * * * *
    AADT means the annual average daily traffic.
    * * *
    Near-road NO2 Monitor means any NO2 monitor meeting the 
specifications in 4.3.2 of Appendix D and paragraphs 2, 4(d), 6.1, and 
6.4 of Appendix E of this part.
* * * * *

Subpart B [Amended]

0
7. Section 58.10, is amended by adding paragraphs (a)(5) and (b)(12) to 
read as follows:


Sec.  58.10  Annual monitoring network plan and periodic network 
assessment.

    (a) * * *
    (5) A plan for establishing NO2 monitoring sites in 
accordance with the requirements of appendix D to this part shall be 
submitted to the Administrator by July 1, 2012. The plan shall provide 
for all required monitoring stations to be operational by January 1, 
2013.
* * * * *
    (b) * * *
    (12) The identification of required NO2 monitors as 
either near-road or area-wide sites in accordance with Appendix D, 
Section 4.3 of this part.
* * * * *

0
8. Section 58.13 is amended by adding paragraph (c) to read as follows:


Sec.  58.13  Monitoring network completion.

* * * * *
    (c) The network of NO2 monitors must be physically 
established no later than January 1, 2013, and at that time, must be 
operating under all of the requirements of this part, including the 
requirements of appendices A, C, D, and E to this part.

0
9. Section 58.16 is amended by revising paragraph (a) to read as 
follows:


Sec.  58.16  Data submittal and archiving requirements.

* * * * *
    (a) The State, or where appropriate, local agency, shall report to 
the Administrator, via AQS all ambient air quality data and associated 
quality assurance data for SO2; CO; O3; 
NO2; NO; NOY; NOX; Pb-TSP mass 
concentration; Pb-PM10 mass concentration; PM10 
mass concentration; PM2.5mass concentration; for filter-
based PM2.5FRM/FEM the field blank mass, sampler-generated 
average daily temperature, and sampler-generated average daily 
pressure; chemically speciated PM2.5 mass concentration 
data; PM10-2.5 mass concentration; chemically speciated 
PM10-2.5 mass concentration data; meteorological data from 
NCore and PAMS sites; average daily temperature and average daily 
pressure for Pb sites if not already reported from sampler generated 
records; and metadata records and information specified by the AQS Data 
Coding Manual (http://www.epa.gov/ttn/airs/airsaqs/manuals/manuals.htm). The State, or where appropriate, local agency, may report 
site specific meteorological measurements generated by onsite equipment 
(meteorological instruments, or sampler generated) or measurements from 
the nearest airport reporting ambient pressure and temperature. Such 
air quality data and information must be submitted directly to the AQS 
via electronic transmission on the specified quarterly schedule 
described in paragraph (b) of this section.
* * * * *

0
10. Appendix A to Part 58 is amended by adding paragraph 2.3.1.5 to 
read as follows:

Appendix A to Part 58--Quality Assurance Requirements for SLAMS, SPMs 
and PSD Air Monitoring

* * * * *
    2.3.1.5 Measurement Uncertainty for NO2. The goal for 
acceptable measurement uncertainty is defined for precision as an 
upper 90 percent confidence limit for the coefficient of variation 
(CV) of 15 percent and for bias as an upper 95 percent confidence 
limit for the absolute bias of 15 percent.
* * * * *

0
11. Appendix C to Part 58 is amended by adding paragraph 2.1.1 to read 
as follows:

Appendix C to Part 58--Ambient Air Quality Monitoring Methodology

* * * * *
    2.1.1 Any NO2 FRM or FEM used for making primary 
NAAQS decisions must be capable of providing hourly averaged 
concentration data.
* * * * *

0
12. Appendix D to Part 58 is amended by revising paragraph 4.3 to read 
as follows:

Appendix D to Part 58--Network Design Criteria for Ambient Air Quality 
Monitoring

* * * * *

4.3 Nitrogen Dioxide (NO2) Design Criteria

4.3.1 General Requirements

    (a) State and, where appropriate, local agencies must operate a 
minimum number of required NO2 monitoring sites as 
described below.

4.3.2 Requirement for Near-road NO2 Monitors

    (a) Within the NO2 network, there must be one 
microscale near-road NO2 monitoring station in each CBSA 
with a population of 500,000 or more persons to monitor a location 
of expected maximum hourly concentrations sited near a major road 
with high AADT counts as specified in paragraph 4.3.2(a)(1) of this 
appendix. An additional near-road NO2 monitoring station 
is required for any CBSA with a population of 2,500,000 persons or 
more, or in any CBSA with a population of 500,000 or more persons 
that has one or more roadway segments with 250,000 or greater AADT 
counts to monitor a second location of expected maximum hourly 
concentrations. CBSA populations shall be based on the latest 
available census figures.
    (1) The near-road NO2 monitoring stations shall be 
selected by ranking all road segments within a CBSA by AADT and then 
identifying a location or locations adjacent to those highest ranked 
road segments, considering fleet mix, roadway design, congestion 
patterns, terrain, and meteorology, where maximum hourly 
NO2 concentrations are expected to occur and siting 
criteria can be met in accordance with appendix E of this part. 
Where a State or local air monitoring agency identifies multiple 
acceptable candidate sites where maximum hourly NO2 
concentrations are expected to occur, the monitoring agency shall 
consider the potential for population exposure in the criteria 
utilized to select the final site location. Where one CBSA is 
required to have two near-road NO2 monitoring stations, 
the sites shall be differentiated from each other by one or more of 
the following factors: fleet mix; congestion patterns; terrain; 
geographic area within the

[[Page 6535]]

CBSA; or different route, interstate, or freeway designation.
    (b) Measurements at required near-road NO2 monitor 
sites utilizing chemiluminescence FRMs must include at a minimum: 
NO, NO2, and NOX.

4.3.3 Requirement for Area-wide NO2 Monitoring

    (a) Within the NO2 network, there must be one 
monitoring station in each CBSA with a population of 1,000,000 or 
more persons to monitor a location of expected highest 
NO2 concentrations representing the neighborhood or 
larger spatial scales. PAMS sites collecting NO2 data 
that are situated in an area of expected high NO2 
concentrations at the neighborhood or larger spatial scale may be 
used to satisfy this minimum monitoring requirement when the 
NO2 monitor is operated year round. Emission inventories 
and meteorological analysis should be used to identify the 
appropriate locations within a CBSA for locating required area-wide 
NO2 monitoring stations. CBSA populations shall be based 
on the latest available census figures.

4.3.4 Regional Administrator Required Monitoring

    (a) The Regional Administrators, in collaboration with States, 
must require a minimum of forty additional NO2 monitoring 
stations nationwide in any area, inside or outside of CBSAs, above 
the minimum monitoring requirements, with a primary focus on siting 
these monitors in locations to protect susceptible and vulnerable 
populations. The Regional Administrators, working with States, may 
also consider additional factors described in paragraph (b) below to 
require monitors beyond the minimum network requirement.
    (b) The Regional Administrators may require monitors to be sited 
inside or outside of CBSAs in which:
    (i) The required near-road monitors do not represent all 
locations of expected maximum hourly NO2 concentrations 
in an area and NO2 concentrations may be approaching or 
exceeding the NAAQS in that area;
    (ii) Areas that are not required to have a monitor in accordance 
with the monitoring requirements and NO2 concentrations 
may be approaching or exceeding the NAAQS; or
    (iii) The minimum monitoring requirements for area-wide monitors 
are not sufficient to meet monitoring objectives.
    (c) The Regional Administrator and the responsible State or 
local air monitoring agency should work together to design and/or 
maintain the most appropriate NO2 network to address the 
data needs for an area, and include all monitors under this 
provision in the annual monitoring network plan.

4.3.5 NO2 Monitoring Spatial Scales

    (a) The most important spatial scale for near-road 
NO2 monitoring stations to effectively characterize the 
maximum expected hourly NO2 concentration due to mobile 
source emissions on major roadways is the microscale. The most 
important spatial scales for other monitoring stations 
characterizing maximum expected hourly NO2 concentrations 
are the microscale and middle scale. The most important spatial 
scale for area-wide monitoring of high NO2 concentrations 
is the neighborhood scale.
    (1) Microscale--This scale represents areas in close proximity 
to major roadways or point and area sources. Emissions from roadways 
result in high ground level NO2 concentrations at the 
microscale, where concentration gradients generally exhibit a marked 
decrease with increasing downwind distance from major roads. As 
noted in appendix E of this part, near-road NO2 
monitoring stations are required to be within 50 meters of target 
road segments in order to measure expected peak concentrations. 
Emissions from stationary point and area sources, and non-road 
sources may, under certain plume conditions, result in high ground 
level concentrations at the microscale. The microscale typically 
represents an area impacted by the plume with dimensions extending 
up to approximately 100 meters.
    (2) Middle scale--This scale generally represents air quality 
levels in areas up to several city blocks in size with dimensions on 
the order of approximately 100 meters to 500 meters. The middle 
scale may include locations of expected maximum hourly 
concentrations due to proximity to major NO2 point, area, 
and/or non-road sources.
    (3) Neighborhood scale--The neighborhood scale represents air 
quality conditions throughout some relatively uniform land use areas 
with dimensions in the 0.5 to 4.0 kilometer range. Emissions from 
stationary point and area sources may, under certain plume 
conditions, result in high NO2 concentrations at the 
neighborhood scale. Where a neighborhood site is located away from 
immediate NO2 sources, the site may be useful in 
representing typical air quality values for a larger residential 
area, and therefore suitable for population exposure and trends 
analyses.
    (4) Urban scale--Measurements in this scale would be used to 
estimate concentrations over large portions of an urban area with 
dimensions from 4 to 50 kilometers. Such measurements would be 
useful for assessing trends in area-wide air quality, and hence, the 
effectiveness of large scale air pollution control strategies. Urban 
scale sites may also support other monitoring objectives of the 
NO2 monitoring network identified in paragraph 4.3.4 
above.

4.3.6 NOy Monitoring

    (a) NO/NOy measurements are included within the NCore 
multi-pollutant site requirements and the PAMS program. These NO/
NOy measurements will produce conservative estimates for 
NO2 that can be used to ensure tracking continued 
compliance with the NO2 NAAQS. NO/NOy monitors 
are used at these sites because it is important to collect data on 
total reactive nitrogen species for understanding O3 
photochemistry.
* * * * *

0
13. Appendix E to Part 58 is amended as follows:
0
a. By revising paragraphs 2, and 6.1.
0
b. By adding paragraphs 4(d) and 6.4.
0
c. By revising paragraphs 9(c), 11 and Table E-4.

Appendix E to Part 58--Probe and Monitoring Path Siting Criteria for 
Ambient Air Quality Monitoring

* * * * *

2. Horizontal and Vertical Placement

    The probe or at least 80 percent of the monitoring path must be 
located between 2 and 15 meters above ground level for all ozone and 
sulfur dioxide monitoring sites, and for neighborhood or larger 
spatial scale Pb, PM10, PM10-2.5, 
PM2.5, NO2 and carbon monoxide sites. Middle 
scale PM10-2.5 sites are required to have sampler inlets 
between 2 and 7 meters above ground level. Microscale Pb, 
PM10, PM10-2.5 and PM2.5 sites are 
required to have sampler inlets between 2 and 7 meters above ground 
level. Microscale near-road NO2 monitoring sites are 
required to have sampler inlets between 2 and 7 meters above ground 
level. The inlet probes for microscale carbon monoxide monitors that 
are being used to measure concentrations near roadways must be 
3\1/2\ meters above ground level. The probe or at least 
90 percent of the monitoring path must be at least 1 meter 
vertically or horizontally away from any supporting structure, 
walls, parapets, penthouses, etc., and away from dusty or dirty 
areas. If the probe or a significant portion of the monitoring path 
is located near the side of a building or wall, then it should be 
located on the windward side of the building relative to the 
prevailing wind direction during the season of highest concentration 
potential for the pollutant being measured.
* * * * *

4. * * *

    (d) For near-road NO2 monitoring stations, the 
monitor probe shall have an unobstructed air flow, where no 
obstacles exist at or above the height of the monitor probe, between 
the monitor probe and the outside nearest edge of the traffic lanes 
of the target road segment.
* * * * *

6. * * *

6.1 Spacing for Ozone Probes and Monitoring Paths

    In siting an O3 analyzer, it is important to minimize 
destructive interferences form sources of NO, since NO readily 
reacts with O3. Table E-1 of this appendix provides the 
required minimum separation distances between a roadway and a probe 
or, where applicable, at least 90 percent of a monitoring path for 
various ranges of daily roadway traffic. A sampling site having a 
point analyzer probe located closer to a roadway than allowed by the 
Table E-1 requirements should be classified as microscale or middle 
scale, rather than neighborhood or urban scale, since the 
measurements from such a site would more closely represent the 
middle scale. If an open path analyzer is used at a site, the 
monitoring path(s) must not cross over a roadway with an average 
daily traffic count of 10,000 vehicles per day or more. For those 
situations where a monitoring path crosses a roadway with fewer than 
10,000 vehicles per day, monitoring agencies must consider the 
entire segment of the monitoring

[[Page 6536]]

path in the area of potential atmospheric interference from 
automobile emissions. Therefore, this calculation must include the 
length of the monitoring path over the roadway plus any segments of 
the monitoring path that lie in the area between the roadway and 
minimum separation distance, as determined from the Table E-1 of 
this appendix. The sum of these distances must not be greater than 
10 percent of the total monitoring path length.
* * * * *

6.4 Spacing for Nitrogen Dioxide (NO2) Probes and 
Monitoring Paths

    (a) In siting near-road NO2 monitors as required in 
paragraph 4.3.2 of appendix D of this part, the monitor probe shall 
be as near as practicable to the outside nearest edge of the traffic 
lanes of the target road segment; but shall not be located at a 
distance greater than 50 meters, in the horizontal, from the outside 
nearest edge of the traffic lanes of the target road segment.
    (b) In siting NO2 monitors for neighborhood and 
larger scale monitoring, it is important to minimize near-road 
influences. Table E-1 of this appendix provides the required minimum 
separation distances between a roadway and a probe or, where 
applicable, at least 90 percent of a monitoring path for various 
ranges of daily roadway traffic. A sampling site having a point 
analyzer probe located closer to a roadway than allowed by the Table 
E-1 requirements should be classified as microscale or middle scale 
rather than neighborhood or urban scale. If an open path analyzer is 
used at a site, the monitoring path(s) must not cross over a roadway 
with an average daily traffic count of 10,000 vehicles per day or 
more. For those situations where a monitoring path crosses a roadway 
with fewer than 10,000 vehicles per day, monitoring agencies must 
consider the entire segment of the monitoring path in the area of 
potential atmospheric interference form automobile emissions. 
Therefore, this calculation must include the length of the 
monitoring path over the roadway plus any segments of the monitoring 
path that lie in the area between the roadway and minimum separation 
distance, as determined form the Table E-1 of this appendix. The sum 
of these distances must not be greater than 10 percent of the total 
monitoring path length.
* * * * *

9. * * *

    (c) No matter how nonreactive the sampling probe material is 
initially, after a period of use reactive particulate matter is 
deposited on the probe walls. Therefore, the time it takes the gas 
to transfer from the probe inlet to the sampling device is also 
critical. Ozone in the presence of nitrogen oxide (NO) will show 
significant losses even in the most inert probe material when the 
residence time exceeds 20 seconds.\26\ Other studies \27-28\ 
indicate that a 10 second or less residence time is easily 
achievable. Therefore, sampling probes for reactive gas monitors at 
NCore and at NO2 sites must have a sample residence time 
less than 20 seconds.
* * * * *

11. Summary

    Table E-4 of this appendix presents a summary of the general 
requirements for probe and monitoring path siting criteria with 
respect to distances and heights. It is apparent from Table E-4 that 
different elevation distances above the ground are shown for the 
various pollutants. The discussion in this appendix for each of the 
pollutants describes reasons for elevating the monitor, probe, or 
monitoring path. The differences in the specified range of heights 
are based on the vertical concentration gradients. For CO and near-
road NO2 monitors, the gradients in the vertical 
direction are very large for the microscale, so a small range of 
heights are used. The upper limit of 15 meters is specified for the 
consistency between pollutants and to allow the use of a single 
manifold or monitoring path for monitoring more than one pollutant.

                                Table E-4 of Appendix E to Part 58. Summary of Probe and Monitoring Path Siting Criteria
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                         Horizontal and
                                                                                       vertical distance
                                         Scale (maximum       Height from ground to     from supporting      Distance from trees       Distance from
             Pollutant                   monitoring path     probe, inlet or 80% of     structures\2\ to      to probe, inlet or     roadways to probe,
                                         length, meters)       monitoring path \1\    probe, inlet or 90%     90% of monitoring     inlet or monitoring
                                                                                     of monitoring path\1\     path\1\ (meters)       path\1\ (meters)
                                                                                            (meters)
--------------------------------------------------------------------------------------------------------------------------------------------------------
SO2 3,4,5,6........................  Middle (300 m)          2-15..................  >1...................  >10..................  N/A
                                      Neighborhood Urban,
                                      and Regional (1 km).
CO 4,5,7...........................  Micro, middle (300 m),  3\1/2\: 2-15..........  >1...................  >10..................  2-10; see Table E-2
                                      Neighborhood (1 km).                                                                          of this appendix for
                                                                                                                                    middle and
                                                                                                                                    neighborhood scales.
O3 3,4,5...........................  Middle (300 m)          2-15..................  >1...................  >10..................  See Table E-1 of this
                                      Neighborhood, Urban,                                                                          appendix for all
                                      and Regional (1 km).                                                                          scales.
NO2 3,4,5..........................  Micro (Near-road [50-   2-7 (micro);..........  >1...................  >10..................  1...................  >10..................  See Table E-4 of this
                                      (1 km).                                                                                       appendix for all
                                                                                                                                    scales.
PM, Pb 3,4,5,6,8...................  Micro: Middle,          2-7 (micro); 2-7        >2 (all scales,        >10 (all scales).....  2-10 (micro); see
                                      Neighborhood, Urban     (middle PM10	2.5); 2-   horizontal distance                           Figure E-1 of this
                                      and Regional.           15 (all other scales).  only).                                        appendix for all
                                                                                                                                    other scales.
--------------------------------------------------------------------------------------------------------------------------------------------------------
N/A--Not applicable.
\1\ Monitoring path for open path analyzers is applicable only to middle or neighborhood scale CO monitoring, middle, neighborhood, urban, and regional
  scale NO2 monitoring, and all applicable scales for monitoring SO2,O3, and O3 precursors.
\2\ When probe is located on a rooftop, this separation distance is in reference to walls, parapets, or penthouses located on roof.
\3\ Should be >20 meters from the dripline of tree(s) and must be 10 meters from the dripline when the tree(s) act as an obstruction.
\4\ Distance from sampler, probe, or 90% of monitoring path to obstacle, such as a building, must be at least twice the height the obstacle protrudes
  above the sampler, probe, or monitoring path. Sites not meeting this criterion may be classified as middle scale (see text).
\5\ Must have unrestricted airflow 270 degrees around the probe or sampler; 180 degrees if the probe is on the side of a building or a wall.

[[Page 6537]]


\6\ The probe, sampler, or monitoring path should be away from minor sources, such as furnace or incineration flues. The separation distance is
  dependent on the height of the minor source's emission point (such as a flue), the type of fuel or waste burned, and the quality of the fuel (sulfur,
  ash, or lead content). This criterion is designed to avoid undue influences from minor sources.
\7\ For microscale CO monitoring sites, the probe must be >10 meters from a street intersection and preferably at a midblock location.
\8\ Collocated monitors must be within 4 meters of each other and at least 2 meters apart for flow rates greater than 200 liters/min or at least 1 meter
  apart for samplers having flow rates less than 200 liters/min to preclude airflow interference.

* * * * *
    14. Appendix G to Part 58 is amended as by revising paragraph 9 and 
Table 2 to read as follows:

Appendix G to Part 58--Uniform Air Quality Index (AQI) and Daily 
Reporting

* * * * *

9. How Does the AQI Relate to Air Pollution Levels?

    For each pollutant, the AQI transforms ambient concentrations to 
a scale from 0 to 500. The AQI is keyed as appropriate to the 
national ambient air quality standards (NAAQS) for each pollutant. 
In most cases, the index value of 100 is associated with the 
numerical level of the short-term (i.e., averaging time of 24-hours 
or less) standard for each pollutant. The index value of 50 is 
associated with one of the following: the numerical level of the 
annual standard for a pollutant, if there is one; one-half the level 
of the short-term standard for the pollutant; or the level at which 
it is appropriate to begin to provide guidance on cautionary 
language. Higher categories of the index are based on increasingly 
serious health effects that affect increasing proportions of the 
population. An index value is calculated each day for each pollutant 
(as described in section 12 of this appendix), unless that pollutant 
is specifically excluded (see section 8 of this appendix). The 
pollutant with the highest index value for the day is the 
``critical'' pollutant, and must be included in the daily AQI 
report. As a result, the AQI for any given day is equal to the index 
value of the critical pollutant for that day. For the purposes of 
reporting the AQI, the indexes for PM10 and 
PM2.5 are to be considered separately.
* * * * *

                                                            Table 2--Breakpoints for the AQI
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                      These breakpoints                                                            Equal these AQIs
--------------------------------------------------------------------------------------------------------------------------------------------------------
                               PM2.5          PM10
O3 (ppm) 8-  O3 (ppm) 1-    ([micro]g/     ([micro]g/    CO (ppm)    SO2 (ppm)   NO2 (ppm) 1-     AQI                         Category
    hour       hour\1\         m\3\)         m\3\)                                   hour
--------------------------------------------------------------------------------------------------------------------------------------------------------
0.000-0.059  ...........        0.0-15.4         0-54      0.0-4.4  0.000-0.034      0-0.053         0-50  Good.
0.060-0.075  ...........       15.5-40.4       55-154      4.5-9.4  0.035-0.144  0.054-0.100       51-100  Moderate.
0.076-0.095  0.125-0.164       40.5-65.4      155-254     9.5-12.4  0.145-0.224  0.101-0.360      101-150  Unhealthy for Sensitive Groups.
0.096-0.115  0.165-0.204  \3\ 65.5-150.4      255-354    12.5-15.4  0.225-0.304   0.361-0.64      151-200  Unhealthy.
0.116-0.374  0.205-0.404      \3\ 150.5-      355-424    15.5-30.4  0.305-0.604    0.65-1.24      201-300  Very Unhealthy.
                                   250.4
      (\2\)  0.405-0.504      \3\ 250.5-      425-504    30.5-40.4  0.605-0.804    1.25-1.64      301-400  Hazardous.
                                   350.4
      (\2\)  0.505-0.604      \3\ 350.5-      505-604    40.5-50.4  0.805-1.004    1.65-2.04      401-500  Hazardous.
                                   500.4
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ Areas are generally required to report the AQI based on 8-hour ozone values. However, there are a small number of areas where an AQI based on 1-hour
  ozone values would be more precautionary. In these cases, in addition to calculating the 8-hour ozone index value, the 1-hour ozone index value may be
  calculated, and the maximum of the two values reported.
\2\ 8-hours O3 values do not define higher AQI values (>=301). AQI values of 301 or greater are calculated with 1-hour O3 concentrations.
\3\ If a different SHL for PM2.5 is promulgated, these numbers will change accordingly.


[FR Doc. 2010-1990 Filed 2-8-10; 8:45 am]
BILLING CODE 6560-50-P
```