United States
Environmental
Protection Agency
Integrated Review Plan for the
Ozone National Ambient Air
Quality Standards
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EPA452/R-11-006
April 2011
Integrated Review Plan for the
Ozone National Ambient Air
Quality Standards
U. S. Environmental Protection Agency
National Center for Environmental Assessment
Office of Research and Development
and
Office of Air Quality Planning and Standards
Office of Air and Radiation
Research Triangle Park, North Carolina 27711
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DISCLAIMER
This integrated review plan for the national ambient air quality standards (NAAQS) for
ozone (Os) serves as a public information document and a management tool for the United States
Environmental Protection Agency's National Center for Environmental Assessment and the
Office of Air Quality Planning and Standards. The approach described in this plan may be
modified to reflect information developed during the review of the O?, NAAQS and to address
advice and comments received from the Clean Air Scientific Advisory Committee and the public
throughout this review. Mention of trade names or commercial products does not constitute
endorsement or recommendation for use.
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TABLE OF CONTENTS
LIST OF ACRONYMS/ABBREVIATIONS IV
1 INTRODUCTION. 1-1
1.1 LEGISLATIVE REQUIREMENTS 1-2
1.2 OVERVIEW OF THENAAQS REVIEW PROCESS 1-4
1.3 HISTORY OF O3 NAAQS REVIEWS 1-8
1.4 RECONSIDERATION OF THE 2008 OZONE NAAQS 1-11
2 STATUS AND SCHEDULE FOR NEW REVIEW 2-1
3 KEY POLICY-RELEVANT ISSUES 3-1
3.1 ISSUES RELATED TO THE PRIMARY OZONE NAAQS 3-1
3.2 ISSUES RELATED TO THE SECONDARY OZONE NAAQS 3-3
4 SCIENCE ASSESSMENT 4-1
4.1 SCOPE AND ORGANIZATION 4-1
4.2 ASSESSMENT APPROACH 4-2
4.2.1 Introduction 4-2
4.2.2 Literature Search and Identification of Relevant Studies 4-2
4.2.3 Criteria for Study Selection 4-4
4.2.4 Quality Assurance 4-6
4.3 CONTENT AND ORGANIZATION OF THE ISA 4-6
4.4 CAUSAL DETERMINATIONS 4-13
4.5 SUPPLEMENTARY MATERIALS 4-14
4.6 SCIENTIFIC AND PUBLIC REVIEW 4-14
5 HUMAN HEALTH RISK AND EXPOSURE ASSESSMENTS 5-1
5.1 OVERVIEW 5-1
5.2 EXPOSURE AND HEALTH RISK ASSESSMENTS FROM THE LAST REVIEW ....5-2
5.3 AIR QUALITY CONSIDERATIONS 5-4
5.4 POPULATION EXPOSURE ASSESSMENT APPROACH 5-5
5.5 HUMAN HEALTH RISK ASSESSMENTS 5-6
5.5.1 Approach to Health Risk Assessment Based On Epidemiologic Studies 5-7
5.5.2 Approach to Health Risk Assessment Based on Controlled Human Exposure Studies. 5-8
5.5.3 Uncertainty and Variability 5-9
5.5.4 Broader Risk Characterization 5-9
5.6 SCIENTIFIC AND PUBLIC REVIEW 5-10
6 VEGETATION AND OTHER WELFARE-RELATED ASSESSMENTS 6-1
6.1 OVERVIEW 6-1
6.2 EXPOSURE, RISK, AND BENEFITS ASSESSMENTS FROM THE LAST REVIEW6-1
6.2.1 Exposure Assessment 6-2
6.2.2 Risk Assessment 6-4
6.2.3 Benefits Assessment 6-5
6.3 AIR QUALITY CONSIDERATIONS 6-6
6.4 EXPOSURE ASSESSMENT APPROACH 6-7
6.5 RISK ASSESSMENT APPROACH 6-7
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6.6 BENEFIT ASSESSMENT APPROACH 6-8
6.7 UNCERTAINTY AND VARIABILITY 6-9
6.8 SCIENTIFIC AND PUBLIC REVIEW 6-9
POLICY ASSESSMENT/RULEMAKING 7-1
7.1 POLICY ASSESSMENT 7-1
7.2 RULEMAKING 7-3
AMBIENT AIR MONITORING 8-1
8.1 OVERVIEW 8-1
8.2 CURRENT O3 NETWORK STATUS 8-1
8.3 MONITORING ISSUES RELATED TO THE O3NAAQS 8-3
8.3.1 Monitoring Methods 8-4
8.3.2 Network Design 8-4
8.3.3 Data Reporting and Assessments 5-5
REFERENCES 9-1
in
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LIST OF ACRONYMS/ABBREVIATIONS
A/C
APEX
AQI
AQS
CAA
CASAC
CASTNET
CFR
CHAD
CMAQ
CO
COPD
C-R
CRP
CSA
CV
CVD
ED
EPA
FACE
FEM
FEVi
FIP
FR
FRM
HA
HEI
HRV
fflD
IRP
ISA
Km
ME
MI
MOA
N
NAAQS
NCEA-RTP
NCLAN
NEM
NERL
NOAA
NO2
Air conditioning
EPA's Air Pollutants Exposure model, version 4
Air Quality Index
EPA's Air Quality System
Clean Air Act
Clean Air Scientific Advisory Committee
Clean Air Status and Trends Network
Code of Federal Regulations
EPA's Consolidated Human Activity Database
Community Multiscale Air Quality
Carbon Monoxide
Chronic obstructive pulmonary disease
Concentration-response relationship
C-reactive protein
Consolidated Statistical Area
Cardiovascular
Cardiovascular disease
Emergency department
Environmental Protection Agency
Free-air exposures
Federal Equivalent Method
Change in forced expiratory volume in one second
Federal Implementation Plan
Federal Register
Federal Reference Method
Hospital admissions
Health Effects Institute
Heart rate variability
Ischemic heart disease
Integrated Review Plan
Integrated Science Assessment
Kilometer
Microenvironment
Myocardial infarction
Mode(s) or mechanism(s) of action
Nitrogen
National Ambient Air Quality Standards
National Center for Environmental Assessment in Research Triangle Park
National Crop Loss Assessment Network
NAAQS Exposure Model
National Exposure Research Laboratory
National Oceanic and Atmospheric Administration
Nitrogen dioxide
IV
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NO3"
NOx
NFS
NRC
03
OAQPS
OAR
OMB
ORD
OTC
PA
PAMS
PM
PRB
QA
REA
RR
SAB
SoyFACE
SO2
SO42"
SOX
TB
TREGRO
TSP
UV
VOC
W126
Nitrate
Nitrogen oxides
National Park Service
National Research Council
Ozone
Office of Air Quality Planning and Standards
Office of Air and Radiation
Office of Management and Budget
Office of Research and Development
Open Top Chambers
Policy Assessment
Photochemical Assessment Monitoring Station
Particulate matter
Policy-Relevant Background
Quality assurance
Risk and Exposure Assessment
Relative risk
Science Advisory Board
Free air field based soybean study
Sulfur Dioxide
Sulfate
Sulfur Oxides
Tracheobronchial
Tree growth model
Total suspended particulate
Ultraviolet
Volatile organic compounds
Cumulative, seasonal secondary ozone standard
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VI
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1 INTRODUCTION
The U.S. Environmental Protection Agency (EPA) last completed a review of the primary
(health-based) and secondary (welfare-based) national ambient air quality standards (NAAQS)
for ozone (Cb) in March 2008 (73 FR 16436), resulting in revisions to both standards. In May
2008, states, environmental groups and industry groups filed petitions with the D.C. Circuit
Court of Appeals for review of the 2008 O?, standards. In March 2009, the court granted EPA's
request to stay the litigation so the new administration could review the standards and determine
whether they should be reconsidered. On September 16, 2009, the Administrator announced her
decision to reconsider the 2008 primary and secondary O?, standards to ensure they are
scientifically sound and protective of public health and the environment as required by the Clean
Air Act (CAA). The EPA published a proposed rule on the reconsideration of the 2008 Os
NAAQS on January 19, 2010 (75 FR 2938-2999). Prior to the decision to reconsider the 2008
63 standards, EPA had initiated a new periodic review of the existing air quality criteria and
standards for O^ in September 2008.
This Integrative Review Plan (IRP) contains the plans for the new periodic review of the
air quality criteria for Os-related effects on public health and public welfare and the current Os
standards or any revised standards that may result from the reconsideration of the 2008 O^
standards. This review will provide an integrative assessment of relevant scientific information
for OT, and related photochemical oxidants and will focus on the basic elements of the NAAQS:
the indicator,1 averaging time, form,2 and level. These elements, which together serve to define
each ambient air quality standard, must be considered collectively in evaluating the protection to
public health and public welfare afforded by the standards.
This IRP is organized into eight chapters. Chapter 1 presents the legislative requirements
for the review of the NAAQS, an overview of the NAAQS review process, a history of past
reviews of the 63 NAAQS, and the Agency's plans to reconsider the 2008 63 NAAQS. Chapters
2 through 8 outline the Agency's plans for the new periodic review of the existing air quality
criteria and the Os standards that result from the reconsideration of the 2008 standards. Chapter
2 presents the status and schedule for the new review. Chapter 3 presents a set of policy-relevant
questions that will serve to focus the new review on the critical scientific and policy issues.
Chapters 4 through 6 discuss the planned scope and organization of the key science and
1 The "indicatof of a standard defines the chemical species or mixture that is to be measured in determining
whether an area attains the standard.
2 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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risk/exposure assessment documents, the planned approaches for preparing the documents, and
plans for scientific and public review of the documents for the new review. Chapter 7
summarizes the policy assessment and rulemaking process for the new Os NAAQS review.
Finally, chapter 8 discusses the current ambient air monitoring network and monitoring issues
related to the O3 NAAQS.
1.1 LEGISLATIVE REQUIREMENTS
Two sections of the Clean Air Act (CAA) govern the establishment and revision of the
NAAQS. Section 108 (42 U.S.C. section 7408) directs the Administrator to identify and list
certain air pollutants and then to issue air quality criteria for those pollutants. The Administrator
is to list those air pollutants that in her "judgment, cause or contribute to air pollution which may
reasonably be anticipated to endanger public health or welfare;" "the presence of which in the
ambient air results from numerous or diverse mobile or stationary sources;" and "for which . . .
[the Administrator] plans to issue air quality criteria . . ." Air quality criteria are intended to
"accurately reflect the latest scientific knowledge useful in indicating the kind and extent of all
identifiable effects on public health or welfare which may be expected from the presence of [a]
pollutant in the ambient air . . ." 42 U.S.C. § 7408(b). Section 109 (42 U.S.C. 7409) directs the
Administrator to propose and promulgate "primary" and "secondary" NAAQS for pollutants for
which air quality criteria are issued. 42 U.S.C. § 7409 (a). Section 109(b) (1) defines a primary
standard as one "the attainment and maintenance of which in the judgment of the Administrator,
based on such criteria and allowing an adequate margin of safety, are requisite to protect the
public health"3 42 U.S.C. § 7409(b)(l). A secondary standard, as defined in section 109(b)(2),
must "specify a level of air quality the attainment and maintenance of which, in the judgment of
the Administrator, based on such criteria, is required to protect the public welfare from any
known or anticipated adverse effects associated with the presence of [the] pollutant in the
ambient air."4 42 U.S.C. § 7409(b)(2).
The requirement that primary standards provide an adequate margin of safety was
intended to address uncertainties associated with inconclusive scientific and technical
3 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)].
4 Welfare effects as defined in section 302(h) [42 U.S.C. 7602(h)] include, but are not limited to, "effects on soils,
water, crops, vegetation, man-made materials, animals, wildlife, weather, visibility and climate, damage to and
deterioration of property, and hazards to transportation, as well as effects on economic values and on personal
comfort and well-being."
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information available at the time of standard setting. It was also intended to provide a reasonable
degree of protection against hazards that research has not yet identified. See Lead Industries
Association v. EPA, 647 F.2d 1130, 1154 (D.C. Cir 1980), cert, denied, 449 U.S. 1042 (1980);
American Petroleum Institute v. Costle, 665 F.2d 1176, 1186 (D.C. Cir. 1981), cert, denied, 455
U.S. 1034 (1982); American Farm Bureau Federation v. EPA, 559 F. 3d 512, 533 (D.C. Cir.
2009); Association of Battery Recyclers v. EPA, 604 F. 3d 613, 617-18 (D.C. Cir. 2010). 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. The CAA does not require the Administrator to
establish a primary NAAQS at a zero-risk level or at background concentration levels, see Lead
Industries v. EPA, 647 F.2d at 1156 n.51, but rather at a level that reduces risk sufficiently so as
to protect public health with an adequate margin of safety.
In addressing the requirement for an adequate margin of safety, the EPA considers such
factors as the nature and severity of the health effects involved, the size of sensitive population(s)
at risk, 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. See Lead Industries Association v. EPA, 647 F.2d at 1161-62;
Whitman v. American Trucking Associations, 531 U.S. 457, 495 (2001).
In setting primary and secondary standards that are "requisite" to protect public health and
welfare, respectively, as provided in section 109(b), EPA's task is to establish standards that are
neither more nor less stringent than necessary. In so doing, EPA may not consider the costs of
implementing the standards. See generally Whitman v. American Trucking Associations, 531
U.S. 457, 465-472, 475-76 (2001). Likewise, "[a]ttainability and technological feasibility are not
relevant considerations in the promulgation of national ambient air quality standards." American
Petroleum Institute v. Costle, 665 F. 2d at 1185.
Section 109(d)(l) requires that "not later than December 31, 1980, and at 5-year
intervals thereafter, the Administrator shall complete a thorough review of the criteria
published under section 108 and the national ambient air quality standards . . . and shall make
such revisions in such criteria and standards and promulgate such new standards as may be
appropriate . . . ." Section 109(d)(2) requires that an independent scientific review committee
"shall complete a review of the criteria . . . and the national primary and secondary ambient air
quality standards . . . and shall recommend to the Administrator any new . . . standards and
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revisions of existing criteria and standards as may be appropriate . . . ." Since the early 1980's,
this independent review function has been performed by the Clean Air Scientific Review
Committee (CASAC).5
1.2 OVERVIEW OF THE NAAQS REVIEW PROCESS
Since completion of the last 63 NAAQS review, the Agency has made a number of
changes to the process for reviewing the NAAQS. The current process, which is being applied to
this review of the NAAQS for 63, has four major phases: (1) planning, (2) science assessment,
(3) risk/exposure assessment, and (4) policy assessment and rulemaking. An overview of the
process is illustrated in Figure 1-1 below and each of these phases is described in this section.6
The Agency maintains a web site on which key documents developed for NAAQS reviews are
made available (http://www.epa.gov/ttn/naaqs/).
The planning phase of the NAAQS review process begins with a science policy
workshop, which is intended to identify issues and questions to frame the review. Drawing from
the workshop discussions, a draft IRP is prepared jointly by EPA's National Center for
Environmental Assessment - Research Triangle Park (NCEA-RTP), within the Office of
Research and Development (ORD), and EPA's Office of Air Quality Planning and Standards
(OAQPS), within the Office of Air and Radiation (OAR). The draft IRP is made available for
consultation with CASAC and for public comment. The final IRP is prepared in consideration of
CASAC and public comments. This document presents the current plan and specifies the
schedule for the entire review, the process for conducting the review, and the key policy-relevant
science issues that will guide the review.
The second phase of the review, science assessment, involves the preparation of an
Integrated Science Assessment (ISA) and supplementary materials. The ISA, prepared by
NCEA-RTP, provides a concise review, synthesis, and evaluation of the most policy-relevant
science, including key science judgments that are important to the design and scope of exposure
and risk assessments, as well as other aspects of the NAAQS review. The ISA and its
supplementary materials provide a comprehensive assessment of the current scientific literature
pertaining to known and anticipated effects on public health and welfare associated with the
presence of the pollutant in the ambient air, emphasizing information that has become available
since the last air quality criteria review in order to reflect the current state of knowledge. As
such, the ISA forms the scientific foundation for each NAAQS review and is intended to provide
5 Lists of CASAC members and of members of the CASAC O3 Review Panel are available at:
http://voseniite.epa.gov/sab/sabproduct.nsfAVebCASAC/CommitteesandMembership7OpenDocument.
6 Information on changes to the NAAQS review process since the last O3 NAAQS review is available at:
http://www.epa.gov/ttn/naaqs/review.html.
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information useful in forming judgments about air quality indicator(s), form(s), averaging
time(s) and level(s) for the NAAQS. Hence, the ISA and its associated materials function in the
current NAAQS review process as the Air Quality Criteria Document (AQCD) did in the
previous review process. The current review process generally includes production of a first and
second draft ISA, both of which undergo CAS AC and public review prior to completion of the
final ISA. Section 4 below provides a more detailed description of the planned scope,
organization and assessment approach for the ISA and its supporting materials.
In the third phase, the risk/exposure assessment phase, OAQPS staff considers
information and conclusions presented in the ISA, with regard to support provided for the
development of quantitative assessments of the risks and/or exposures for health and/or welfare
effects. As an initial step, staff prepares one or more planning documents that consider the
extent to which newly available scientific evidence and tools/methodologies warrant the conduct
of quantitative risk and exposure assessments. To the extent warranted, this document(s)
outlines a general plan, including scope and methods, for conducting the assessments. This
planning document(s) is generally prepared in conjunction with the first draft ISA and presented
for consultation with CASAC and for public comment. As discussed in chapters 5 and 6 below,
these planning documents for the current Os NAAQS review will focus on consideration of the
newly available data, methods and tools in light of areas of uncertainty in the assessments
conducted for the last review and of the potential for new or updated assessments to provide
notably different exposure and risk estimates with lower associated uncertainty. Comments
received on the planning document(s) are considered in the Agency's decision as to whether to
conduct such assessments. When an assessment is performed, one or more drafts of each risk
and exposure assessment document (REA) undergoes CASAC and public review, with the initial
draft REA(s) generally being reviewed in conjunction with review of the second draft ISA, prior
to completion of final REA(s). The REA provides concise presentations of methods, key results,
observations, and related uncertainties. Chapters 5 and 6 discuss possible approaches being
considered with regard to human health- and welfare-related assessments, respectively, for this
review.
The review process ends with a policy assessment and rulemaking phase. Under the
current NAAQS review process (Jackson, 2009), the EPA Administrator has reinstated the use of
a Policy Assessment (PA). The PA, like the previous OAQPS Staff Paper, is a document that
provides a transparent OAQPS staff analysis of the adequacy of the current standards and
potential alternatives that are appropriate to consider prior to the issuance of proposed and final
rules. The PA integrates and interprets the information from the ISA and REA(s) to frame policy
options for consideration by the Administrator. Such an evaluation of policy implications is
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intended to help "bridge the gap" between the Agency's scientific assessments, presented in the
ISA and REA(s), and the judgments required of the EPA Administrator in determining whether it
is appropriate to retain or revise the NAAQS. In so doing, the PA is also intended to facilitate
CASAC's advice to the Agency and recommendations to the Administrator on the adequacy of
the existing standards or revisions that may be appropriate to consider, as provided for in the
CAA. In evaluating the adequacy of the current standards and, as appropriate, a range of
alternative standards, the PA considers the available scientific evidence and, as available,
quantitative risk-based analyses, together with related limitations and uncertainties. The PA
focuses on the information that is most pertinent to evaluating the basic elements of national
ambient air quality standards: indicator, averaging time, form, and level. One or more drafts of
a PA are released for CAS AC review and public comment prior to completion of the final PA.
Following issuance of the final PA and consideration of conclusions presented therein,
the Agency develops and publishes a notice of proposed rulemaking that communicates the
Administrator's proposed decisions regarding the standards review. A draft notice undergoes
interagency review involving other federal agencies prior to publication.7 Materials upon which
this decision is based, including the documents described above, are made available to the public
in the regulatory docket for the review. A public comment period, during which public hearings
are generally held, follows publication of the notice of proposed rulemaking. Taking into
o
account comments received on the proposed rule, the Agency issues a final rule to complete the
rulemaking process. Chapter 7 discusses the development of the PA and the rulemaking steps
for this review.
7 Where implementation of the proposed decision would necessitate the implementation of emissions controls, EPA
develops and releases a draft regulatory impact analysis (RIA) concurrent with the notice of proposed rulemaking.
This activity is conducted under Executive Order 12866. The RIA is conducted completely independent of and, by
statute, is not considered in decisions regarding the NAAQS.
8 In the notice of final rulemaking, and generally also through the use of an accompanying document, the Agency
responds to all significant comments on the proposed rule.
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Peer-reviewed
scientific studies
Integrated Review
Plan: timeline and
key policy-relevant
issues and scientific
questions
Integrated Science Assessment:
concise evaluation and synthesis of most
policy-relevant studies
1
CASAC consultation
and public comment
EPA
proposed
decision on
standards
t
CAS AC review and public
comment
RisWExposure Assessment:
concise quantitative assessment
focused on key results,
observations, and uncertainties
Agency decision-
making and draft
proposal notice
Pol icy Assessment:
staff analysis of
policy options based
on integration and
interpretation of
information in the ISA
and REA
Public hearings
and comments
on proposal
Agency decision-
making and draft
final notice
Interagency
review
EPA final
decision on
standards
Figure 1.1. Overview of NAAQS Review Process
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1.3 HISTORY OF O3 NAAQS REVIEWS
Tropospheric (ground-level) 63 is the indicator for the mix of photochemical oxidants
(e.g., peroxyacetyl nitrate, hydrogen peroxide) formed from biogenic and anthropogenic
precursor emissions. Naturally occurring O?, in the troposphere can result from biogenic organic
precursors reacting with naturally occurring nitrogen oxides (NOX) and by stratospheric 63
intrusion into the troposphere. Anthropogenic precursors of O^ especially NOX and volatile
organic compounds (VOCs), originate from a wide variety of stationary and mobile sources.
Ambient 63 concentrations produced by these emissions are directly affected by temperature,
solar radiation, wind speed, and other meteorological factors.
Table 1-1 summarizes the 63 NAAQS that have been promulgated to date. In each
review, the secondary standard has been set to be identical to the primary standard. These
reviews are briefly described below.
Table 1-1. Summary of Primary and Secondary Os NAAQS Promulgated During the
Period 1971 - 2008.
Final Rule
1971
(36 FR 8 186)
1979
(44 FR 8202)
1993
(58 FR 13008)
1997
(62 FR 3 8856)
2008
(73 FR 16483)
Indicator
Total
photochemical
oxidants
03
Averaging
Time
1-hr
1-hr
Level
(ppm)
0.08
0.12
Form
Not to be exceeded more than one
hr per year
Attainment is defined when the
expected number of days per
calendar year, with maximum
hourly average concentration
greater than 0.12 ppm, is equal to
or less than 1
EPA decided that revisions to the standards were not warranted at the time.
03
03
8-hr
8-hr
0.08
0.075
Annual fourth-highest daily
maximum 8-hr concentration,
averaged over 3 years
Form of the standards remained
unchanged relative to the 1997
standard
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The EPA first established primary and secondary NAAQS for photochemical oxidants in
1971 (36 FR 8186, April 30, 1971). Both primary and secondary standards were set at a level of
0.08 parts per million (ppm), 1-hr average, total photochemical oxidants, not to be exceeded
more than one hour per year. The standards were based on scientific information contained in
the 1970 Air Quality Criteria for Photochemical Oxidants (U.S. DHEW, 1970).
The first periodic review of the NAAQS for photochemical oxidants was initiated in
1977. Based on the 1978 Air Quality Criteria for Ozone and Other Photochemical Oxidants
(U.S. EPA, 1978), EPA published proposed revisions to the original NAAQS in 1978 (43 FR
16962) and final revisions in 1979 (44 FR 8202). The level of the primary and secondary
standards was revised from 0.08 to 0.12 ppm; the indicator was revised from photochemical
oxidants to O^; and the form of the standards was revised from a deterministic to a statistical
form, which defined attainment of the standards as occurring when the expected number of days
per calendar year with maximum hourly average concentration greater than 0.12 ppm is equal to
or less than one.
In 1982, EPA announced plans to revise the 1978 Air Quality Criteria document (47 FR
11561), and in 1983 EPA initiated the second periodic review of the O3 NAAQS (48 FR 38009).
EPA subsequently published the 1986 Air Quality Criteria for Ozone and Other Photochemical
Oxidants (U.S. EPA, 1986) and 1989 Staff Paper (U.S. EPA, 1989). Following publication of
the 1986 Air Quality Criteria,document (AQCD) a number of scientific abstracts and articles
were published that appeared to be of sufficient importance concerning potential health and
welfare effects of Os to warrant preparation of a Supplement (U.S. EPA, 1992). Under the terms
of a court order, on August 10, 1992 EPA published a proposed decision stating that revisions to
the existing primary and secondary standards were not appropriate at the time (57 FR 35542).
The notice explained that the proposed decision would complete EPA's review of information on
health and welfare effects of Os assembled over a 7-year period and contained in the 1986
AQCD and its 1992 Supplement. The proposal also announced EPA's intention to proceed as
rapidly as possible with the next review of the air quality criteria and standards for O?, in light of
emerging evidence of health effects related to 6- to 8-hour Oj, exposures. On March 9, 1993,
EPA concluded the review by deciding that revisions to the standards were not warranted at that
time (58 FR 13008).
In August 1992 EPA announced plans to initiate the third periodic review of the air
quality criteria and Os NAAQS (57 FR 35542). On the basis of the scientific evidence contained
in the 1996 Air Quality Criteria for Ozone and related Photochemical Oxidants (U.S. EPA,
1996a), the 1996 Staff Paper (U.S. EPA, 1996b), and related technical support documents,
linking exposures to ambient O?, to adverse health and welfare effects at levels allowed by the
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then existing standards, EPA proposed to revise the primary and secondary 63 standards on
December 13, 1996 (61 FR 65716). The EPA proposed to replace the then existing 1-hour
primary and secondary standards with 8-hour average O^ standards set at a level of 0.08 ppm
(equivalent to 0.084 ppm using standard rounding conventions). The EPA also proposed, in the
alternative, to establish a new distinct secondary standard using a biologically based cumulative,
seasonal form. The EPA completed the review on July 18, 1997 (62 FR 38856) by setting the
primary standard at a level of 0.08 ppm, based on the annual fourth-highest daily maximum 8-hr
average concentration, averaged over three years, and setting the secondary standard identical to
the revised primary standard.
On May 14, 1999, in response to challenges to EPA's 1997 decision by industry and
others, the U.S. Court of Appeals for the District of Columbia Circuit (D.C. Circuit Court)
remanded the 63 NAAQS to EPA, finding that section 109 of the Act, as interpreted by EPA,
effected an unconstitutional delegation of legislative authority. In addition, the D.C. Circuit
Court directed that, in responding to the remand, EPA should consider the potential beneficial
health effects of 63 pollution in shielding the public from the effects of solar ultraviolet (UV)
radiation, as well as adverse health effects. On January 27, 2000, EPA petitioned the U.S.
Supreme Court for certiorari on the constitutional issue (and two other issues) but did not request
review of the D.C. Circuit Court ruling regarding the potential beneficial health effects of O?,.
On February 27, 2001, the U.S. Supreme Court unanimously reversed the judgment of the D.C.
Circuit Court on the constitutional issue, holding that section 109 of the CAA does not delegate
legislative power to the EPA in contravention of the Constitution, and remanded the case to the
D.C. Circuit Court to consider challenges to the Os NAAQS that had not been addressed by that
Court's earlier decisions. On March 26, 2002, the D.C. Circuit Court issued its final decision,
finding the 1997 03 NAAQS to be "neither arbitrary nor capricious," and denied the remaining
petitions for review. In response to the D.C. Circuit Court remand to consider the potential
beneficial health effects of Os pollution in shielding the public from effects of solar (ultraviolet
or UV) radiation, on November 14, 2001, EPA proposed to leave the 1997 8-hour NAAQS
unchanged (66 FR 52768). After considering public comment on the proposed decision, EPA
published its final response to this remand on January 6, 2003, reaffirming the 8-hour Os
NAAQS set in 1997 (68 FR 614). Finally, on April 30, 2004, EPA announced the decision to
make the 1-hour Oj NAAQS no longer applicable to areas one year after the effective date of the
designation of those areas for the 8-hour NAAQS (69 FR 23966). For most areas, the date that
the 1-hour NAAQS no longer applied was June 15, 2005.
The EPA initiated the next periodic review of the air quality criteria and Oj standards in
September 2000 with a call for information (65 FR 57810). The schedule for completion of that
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rulemaking later became governed by a consent decree resolving a lawsuit filed in March 2003
by a group of plaintiffs representing national environmental and public health organizations.
Based on the Air Quality Criteria for Ozone and Other Photochemical Oxidants (US EPA, 2006)
published in March 2006 and the Staff Paper (U.S EPA, 2007a) and related technical support
documents published in July 2007, the proposed decision was published in the Federal Register
on July 11, 2007 (72 FR 37818). The EPA proposed to revise the level of the primary standard
to a level within the range of 0.075 to 0.070 ppm. Two options were proposed for the secondary
standard: (1) replacing the current standard with a cumulative, seasonal standard, expressed as
an index of the annual sum of weighted hourly concentrations cumulated over 12 daylight hours
during the consecutive 3-month period within the Os season with the maximum index value, set
at a level within the range of 7 to 21 ppm-hrs, and (2) setting the secondary standard identical to
the revised primary standard. The EPA completed the review with publication of a final decision
on March 27, 2008 (73 FR 16436), revising the level of the 8-hour primary Os standard from
0.08 ppm to 0.075 ppm and revising the secondary standard to be identical to the revised primary
standard.
1.4 RECONSIDERATION OF THE 2008 OZONE NAAQS
In May 2008, state, public health, environmental, and industry petitioners filed suit
against EPA regarding the 2008 final decision on the Os NAAQS, and on December 23, 2008,
the Court set a briefing schedule in the consolidated cases. On March 10, 2009, EPA requested
that the Court vacate the briefing schedule and hold the consolidated cases in abeyance. This
request for extension was made to allow time for appropriate EPA officials appointed by the new
Administration to review the Os NAAQS to determine whether the standards established in the
March 2008 Os NAAQS decision should be maintained, modified or otherwise reconsidered. In
granting EPA's request, the Court directed EPA to notify the Court by September 16, 2009 of the
action it will be taking with respect to the 2008 O^ NAAQS rule and the Agency's schedule for
undertaking such action.
The EPA notified the Court on September 16, 2009 of its decision to reconsider the
primary and secondary O^ NAAQS set in March 2008 to ensure they are scientifically sound and
protective of public health and the environment.9 The EPA is basing this reconsideration on the
scientific record from the 2008 review, including public comments and CASAC advice and
recommendations. During the 2008 review, CASAC unanimously recommended a more health
9 The EPA also separately announced that it will move quickly to implement any new standards that might result
from the reconsideration. To reduce the workload for states during the interim period of reconsideration, the
Agency proposed to stay the 2008 standards for the purpose of attainment and nonattainment area designations.
EPA will work with states, local governments and tribes to ensure that air quality is protected during that time.
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protective primary standard than was eventually set in 2008. The CAS AC also recommended a
new cumulative, seasonal secondary standard, distinct from the primary standard, while the 2008
rule made the secondary standard identical to the primary standard. Following the 2008
decision, CASAC offered unsolicited advice that reiterated its previous recommendations and
urged the Agency to reconsider its advice in future action on the Os standards. The EPA's notice
to the Court specifically stated that the Agency had concerns regarding whether the revisions to
the primary and secondary NAAQS adopted in the 2008 63 NAAQS rule satisfy the
requirements of the Clean Air Act.
The EPA is basing the reconsideration of the 2008 Os NAAQS decision on the scientific
and technical information that was assessed during the 2008 review, including information in the
2006 Air Quality Criteria document (U.S. EPA, 2006), the 2007 OAQPS Staff Paper (U.S. EPA,
2007a), and related technical support documents including the 2007 REAs (U.S. EPA, 2007b;
Abt Associates, 2007a,b). Scientific and technical information developed since the 2006 Air
Quality Criteria document is being considered in the new review, not in the reconsideration
rulemaking, allowing the new information to receive careful and comprehensive review by
CASAC and the public before it is used as a basis in a rulemaking that determines whether to
revise the NAAQS. As in prior NAAQS rulemakings, EPA has also conducted a provisional
assessment (U.S. EPA, 2009c) of such "new" scientific information (published since review of
the 2006 Air Quality Criteria document) and has concluded that the scientific literature would
not materially change the conclusions reached in the 2006 Air Quality Criteria document,
providing support for the determination that it was appropriate to proceed with the
reconsideration rulemaking. The provisional assessment was subjected to internal EPA peer
review, and the final provisional assessment (U.S. EPA, 2009c) was made available to CASAC
and the public prior to the proposal (75 FR 2938). Consistent with EPA's approach in other
NAAQS reviews, the Agency has not based its proposed decisions in the reconsideration on the
new science but will instead review and consider the new science in the new review covered by
this IRP.
Consistent with EPA's notice to the Court, this reconsideration of the 2008 Os NAAQS
rule is being conducted through notice and comment rulemaking, with the notice of proposed
rulemaking signed by the Administrator on January 6, 2010.10 Following publication of the
proposed rule (75 FR 2938) on January 19, 2010, the Agency provided for a 60-day public
comment period, held public hearings in Arlington, Virginia and Houston, Texas on February 2,
2010 and in Sacramento, California on February 4, 2010, and solicited CASAC review of the
10 This reconsideration will include review of the Air Quality Index (AQI) for O3, such that changes to the AQI will
be proposed if the reconsideration results in a proposed change to the 2008 primary O3 standard.
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proposed rule on January 25, 2010. To ensure that the final decision on the reconsideration of
the 2008 Os primary standard would be based on the most appropriate interpretation of the
scientific evidence and exposure/risk information that was available in the 2008 review, in
December 2010 the Administrator decided to ask the CAS AC Ozone Reconsideration Panel to
provide further advice about the strengths and limitations of the scientific evidence and the
results of the exposure and health risk assessments to aid in her interpretation of this information.
Public teleconferences with the CAS AC Ozone Reconsideration Panel were held on February 18,
March 3, and March 23, 2011 to respond to charge questions prepared by EPA. CAS AC
provided its response to the Administrator on March 29, 2011. EPA intends to issue a final
decision on the reconsideration by July 29, 2011.
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2 STATUS AND SCHEDULE FOR NEW REVIEW
On September 29, 2008, the EPA's NCEA-RTP announced the initiation of a new
periodic review of the air quality criteria for Os and related photochemical oxidants and issued a
call for information in the Federal Register (73 FR 56581). A wide range of external experts as
well as EPA staff, representing a variety of areas of expertise (e.g., epidemiology, human and
animal toxicology, statistics, risk/exposure analysis, atmospheric science, ecology, biology, plant
science, benefits analysis) participated in a "kick-off workshop, held by EPA on October 28-29,
2008 in Researach Triangle Park, NC. The proceedings of that workshop have been considered
and the issues discussed at the workshop have been incorporated into this IRP.
The development of this IRP was extended while the Agency reviewed the 2008 Os
NAAQS rule for the purpose of determining whether it would reconsider the 2008 standards, as
discussed above in section 1.4. A draft of this IRP was released on September 30, 2009, for the
purpose of conducting a public teleconference consultation with CAS AC, which was held on
November 16, 2009, in order to discuss the Agency's plans for the continuation of this new
review. This IRP reflects consideration of comments received from CASAC and the public in
presenting plans for the new review of the air quality criteria and standards for Os-related effects
on public health and public welfare. This involved updating the assessments presented in the
2006 Air Quality Criteria document (U.S. EPA, 2006) and the 2007 Staff Paper (U.S. EPA,
2007a) and REAs (U.S. EPA, 2007b; Abt Associates, 2007a,b). Recognizing that the
reconsideration of the 2008 standards will be completed early in this new review, this new
review will involve reviewing any O3 standards that may be set in the July 2011 final rule that
results from the reconsideration of the 2008 O3 standards. While the Agency is reconsidering the
2008 O3 standards, NCEA-RTP will continue the development of the ISA, the first draft of
which was released to CASAC and the public in March 2011.
The schedule for the entire new review of the air quality criteria and standards is shown
below in Table 2-1.
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Table 2-1. Schedule for the New Periodic Os NAAQS Review
Stage of Review
Major Milestone
Target Dates
Integrated Review
Plan (IRP)
Literature Search
Federal Register Call for Information
Workshop on Science/Policy Issues
Draft IRP
CASAC Consultation on Draft IRP
Final IRP
Ongoing
September 29, 2008
October 29-30, 2008
September 30, 2009
November 16, 2009
March 2011
Integrated Science
Assessment (ISA)
First Draft ISA
CASAC/Public Review of First Draft ISA
Second Draft ISA
CASAC/Public Review of Second Draft ISA
Final ISA
March 2011
May 19-20, 2011
September 2011
November 2011
February 2012
Risk/Exposure
Assessments (REAs)
Scope and Methods Plans
CASAC Consultation on Scope and Methods Plans
First Draft REAs
CASAC/Public Review of First Draft REAs
Second Draft REAs
CASAC/Public Review of Second Draft REAs
Final REAs
April 2011
May 19-20, 2011
October 2011
November 2011
May 2012
July 2012
October 2012
Policy Assessment
(PA)/ Rulemaking
First Draft PA for CASAC/Public Review
CASAC/Public Review of First Draft PA
Second Draft PA for CASAC/Public Review
CASAC/Public Review of Second Draft PA
Final PA
Proposed Rulemaking
Final Rulemaking
June 2012
July 2012
November 2012
January 2013
March 2013
September 2013
June 2014
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3 KEY POLICY-RELEVANT ISSUES
The key policy-relevant issues to be addressed in this new review are presented below as a
series of policy-relevant questions that will frame our approach to determining whether the
primary and secondary NAAQS for 63 that result from the Agency's reconsideration of the 2008
63 standards should be retained or revised. The ISA, REAs, and PA to be developed in this new
review will provide the basis for addressing these questions and will inform the Agency's
decisions as to whether to retain or revise those primary and secondary standards for 63.
3.1 ISSUES RELATED TO THE PRIMARY OZONE NAAQS
The first step in reviewing the adequacy of the primary OT, standard is to consider whether
the available body of scientific evidence, assessed in the ISA and used as a basis for the analyses
presented in the public health-related REA, supports or calls into question the scientific
conclusions reached in the last review regarding health effects related to exposure to Os and
other photochemical oxidants (e.g., peroxyacetyl nitrate, hydrogen peroxide) in ambient air, with
a particular emphasis on exposures and health risks in susceptible populations, such as children.
This evaluation of the available scientific evidence will focus on key policy-relevant issues by
addressing a series of questions including the following:
• To what extent has new scientific information become available that alters or
substantiates our understanding of the health effects associated with various time
periods of exposure to ambient 63, including short-term (1 to 3 hrs), prolonged (6 to 8
hrs), and chronic (months to years) exposures?
• To what extent has new scientific information become available that alters or
substantiates our understanding of the health effects of 63 on at-risk populations,
including those with potentially increased susceptibility such as children and
disadvantaged populations? u
• To what extent has new scientific information become available that alters or
substantiates conclusions from previous reviews regarding the plausibility of adverse
health effects caused by 63 exposure?
• At what levels of Os exposure are health effects observed? Is there evidence of
effects at exposure levels lower than those previously observed, and what are the
important uncertainties associated with that evidence? What is the nature of the
exposure-response relationships of 03 for the various health effects evaluated?
11 Susceptibility refers to innate (e.g., genetic or developmental) or acquired (e.g., age, disease, or smoking) factors
that make individuals more likely to experience effects with exposure to O3. Vulnerability refers to O3-related
effects due to factors including socioeconomic status (e.g., reduced access to health care) or particularly elevated
exposure levels.
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• To what extent has new scientific information become available that alters or
substantiates our understanding of non-Os-exposure factors that might influence the
associations between 63 levels and health effects being considered (e.g., weather-
related factors; behavioral factors such as heating/air conditioning use; driving
patterns; and time-activity patterns)?
• To what extent do risk and/or exposure analyses suggest that exposures of concern for
Os-related health effects are likely to occur with current ambient levels of Os or with
levels that just meet the Os standard? Are these risks/exposures of sufficient
magnitude such that the health effects might reasonably be judged to be important
from a public health perspective? What are the important uncertainties associated
with these risk/exposure estimates?
• To what extent have important uncertainties identified in the last review been
addressed and/or have new uncertainties emerged?
• To what extent does newly available information reinforce or call into question any of
the basic elements of the current O?, standard?
Drawing upon the evidence and analyses presented in the ISA and REA, EPA will
evaluate whether revisions to the primary 63 standard might be appropriate, and, if so, how this
standard might be revised. Specifically, we will evaluate how the scientific information and
assessments inform decisions regarding the basic elements of the NAAQS: indicator, averaging
time, level, and form. These elements will be considered collectively in evaluating the health
protection afforded by the current standard or any alternative standards considered. Specific
policy-relevant questions that will be addressed include:
• To what extent is there any new information that would support consideration of a
different indicator for photochemical oxidants?
• To what extent does the health effects evidence evaluated in the ISA, air quality
analyses, and the REA provide support for considering different averaging times?
• To what extent do air quality analyses and other information provide support for
consideration of alternative forms?
• What range of alternative standard levels should be considered based on the scientific
evidence evaluated in the ISA, air quality analyses, and the REA?
• In considering alternative standards, to what extent do alternative levels, averaging
times and forms reduce estimated exposures and risks of concern attributable to Os
and other photochemical oxidants, and what are the uncertainties associated with the
estimated exposure and risk reductions? What conclusions can be drawn regarding
the health protection afforded susceptible populations?
• What are the important uncertainties and limitations in the evidence and assessments
and how might those uncertainties and limitations be taken into consideration in
identifying alternative standards for consideration?
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3.2 ISSUES RELATED TO THE SECONDARY OZONE NAAQS
As with the review of the primary NAAQS, the first step in reviewing the adequacy of the
secondary Os standard is to consider whether the available body of scientific evidence, assessed
in the ISA and used as a basis for the analyses presented in the public welfare-related REA,
supports or calls into question the scientific conclusions reached in the last review regarding
welfare effects related to exposure to Os and other photochemical oxidants (e.g., peroxyacetyl
nitrate, hydrogen peroxide) in ambient air. This evaluation of the available scientific evidence
will focus on key policy-relevant issues by addressing a series of questions including the
following:
• To what extent has new scientific information become available that alters or
substantiates our understanding of the effects on vegetation and other welfare effects
following exposures to levels of Os found in the ambient air?
• To what extent has new scientific information become available to inform our
understanding of the nature of the exposures that are associated with such effects in
terms of biologically relevant cumulative, seasonal exposure indices?
• To what extent has new scientific information become available that alters or
substantiates our understanding of the effects of Os on sensitive plant species,
ecological receptors, or ecosystem processes?
• To what extent has new scientific information become available that alters or
substantiates our understanding of exposure factors other than 63 that might influence
the associations between 63 levels and welfare effects being considered (e.g., site
specific features such as elevation, soil moisture level, presence of co-occurring
competitors, pests, pathogens, other pollutant stressors, weather-related factors)?
• To what extent has new scientific information become available that alters or
substantiates conclusions regarding the occurrence of adverse welfare effects at levels
of 63 as low as or lower than those observed previously? What is the nature of the
exposure-response relationships of 63 for the various welfare effects evaluated?
• Given recognition in the last review that the significance of (^-induced effects to the
public welfare depends in part on the intended use of the plants or ecosystems on
which those effects occurred, to what extent has new scientific evidence become
available to suggest additional locations where the vulnerability of sensitive species
or ecosystems would have special significance to the public welfare and should be
given increased focus in this review?
• To what extent do risk and/or exposure analyses suggest that exposures of concern for
(Vrelated welfare effects are likely to occur with current ambient levels of 63 or with
levels that just meet the 03 standard? Are these risks/exposures of sufficient
magnitude such that the welfare effects might reasonably be judged to be important
from a public welfare perspective? What are the important uncertainties associated
with these risk/exposure estimates?
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To what extent have important uncertainties identified in the last review been
addressed and/or have new uncertainties emerged?
To what extent does newly available information reinforce or call into question any of
the basic elements of the current Os standard?
Drawing upon the information and assessments presented in the ISA and REA, EPA
will evaluate whether revisions to the secondary 63 standard might be appropriate, and, if
so, how this standard might be revised. Specifically, EPA will evaluate how the scientific
information and assessments inform decisions regarding the basic elements of the NAAQS:
indicator, averaging time, level, and form. These elements will be considered collectively in
evaluating the welfare protection afforded by the current or any alternative standards
considered. Specific policy-relevant questions that will be addressed include:
• To what extent is there any new information that would support consideration of a
different indicator for photochemical oxidants?
• To what extent do the welfare effects evidence evaluated in the ISA, air quality
analyses, and the REA provide support for considering different averaging times and
forms that reflect biologically relevant exposure indices?
• What range of alternative standard levels should be considered based on the scientific
information evaluated in the ISA, air quality analyses, and the REA?
• In considering alternative standards, to what extent do alternative levels, averaging
times, and forms reduce estimated exposures and risks of concern attributable to 63
and other photochemical oxidants, and what are the uncertainties associated with the
estimated exposure and risk reductions?
• What are the important uncertainties and limitations in the evidence and assessments
and how might those uncertainties and limitations be taken into consideration in
identifying alternative standards for consideration?
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4 SCIENCE ASSESSMENT
4.1 SCOPE AND ORGANIZATION
As noted in chapter 1, the Integrated Science Assessment (ISA) is a concise review,
synthesis, and evaluation of the most policy-relevant science that communicates critical science
judgments relevant to the NAAQS review. The current ISA serves to update and revise the
scientific information available at the time of the last review of the air quality criteria. As such,
the ISA forms the scientific foundation for the new review of the primary (health-based) and
secondary (welfare-based) NAAQS. The judgments and conclusions drawn in the ISA are
intended to support risk, exposure and policy analyses as well as decisions to retain or revise the
NAAQS.
The science assessment will consist of an ISA and supplementary materials which are
discussed in more detail in subsequent sections. In brief, the ISA critically evaluates and
integrates the scientific information on the health and welfare effects associated with exposure to
63 and related photochemical oxidants in ambient air. This document and its supplementary
materials will not provide a detailed literature review; but, rather, will discuss the current state of
knowledge on the most relevant scientific literature on issues pertinent to the review of the
NAAQS for Os. Discussions in the ISA will primarily focus on scientific evaluations that can
inform the key policy questions described in chapter 3 of this document. Although emphasis is
placed on discussion of health and welfare effects information, other scientific data are presented
and evaluated in order to provide a better understanding of the nature, sources, measurement, and
concentration distribution of 63 and related photochemical oxidants in ambient air, as well as the
measurement of population exposure to these pollutants.
The ISA will build on the conclusions of the 2006 Air Quality Criteria document (U.S.
EPA, 2006) and focus on peer reviewed literature published since the previous review of the air
quality criteria for O?,. The 2006 Air Qyality Criteria document primarily evaluated literature
published through December 2004. Major legal and historical aspects of prior review documents
as well as key milestones and procedures for document preparation will be briefly summarized at
the beginning of the ISA. In subsequent chapters the results of recent scientific studies will be
integrated with previous findings. Important older studies may be more specifically discussed in
detail to reinforce key concepts and conclusions and/or if they are open to reinterpretation in
light of newer data. Older studies also may be the primary focus in some areas of the document
where research efforts have subsided and these older studies remain the definitive works
available in the literature. Emphasis will be placed on studies conducted at or near Os
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concentrations found in ambient air. Other studies are included if they contain unique data, such
as a previously unreported effect or mechanism for an observed effect, or examine multiple
concentrations to elucidate exposure-response relationships.
4.2 ASSESSMENT APPROACH
4.2.1 Introduction
The EPA's NCEA-RTP is responsible for preparing the ISA and its supplementary
materials for 03. Expert authors include EPA staff with extensive knowledge in their respective
fields and extramural scientists solicited by EPA for their expertise in specific fields. A diagram
showing the standard protocol for development of an ISA is shown in Figure 4.1. A description
of the NAAQS review process is addressed in section 1.2.
4.2.2 Literature Search and Identification of Relevant Studies
The NCEA-RTP will use a systematic approach to identify relevant studies for
consideration. The EPA has already published a Federal Register notice (73 FR 56581,
September 29, 2008) to announce the initiation of this review and request information from the
public. In addition to the call for information, publications will be identified through an ongoing
literature search process that includes extensive computer database mining on specific topics.
Additional publications will be identified by EPA scientists in a variety of disciplines by
combing through relevant, peer reviewed scientific literature obtained through these ongoing
literature searches, reviewing previous EPA reports, and a review of reference lists from key
publications; studies are also identified in the course of CASAC and public review.
Relevant epidemiologic, human clinical, and animal toxicological studies, including those
related to exposure response relationships, mode(s) of action (MOA), susceptible populations,
and ecological or welfare effects studies published since the last air quality criteria review will
be considered. Additionally, air quality and emissions data, studies on atmospheric chemistry,
transport, and fate of these emissions, as well as issues related to Os exposure are considered.
Further information will be acquired from consultation with content and area experts and the
public. The studies identified will include research published or accepted for publication
approximately a month prior to the release of the second external review draft of the ISA (see
Table 2-1). Some additional studies, published after that date, may also be included if they
provide new information that impacts one or more key scientific issues. The combination of
these approaches should produce the comprehensive collection of pertinent studies needed to
form the basis of the ISA.
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Standard Protocol for ISA Development
Database
Outside experts:
Atmospheric science
Exposure
Dosimetry
Animal Toxicology
Clinical Studies
Epidemiology
Ecology
Environmental Effects
Peer Review
Draft/Author Workshop
NCEA staff review
ofliterature (ongoing)
Draft Integrated
Review Plan
CASAC consultation
and public review
I
Final Integrated
Review Plan
First External
Review Draft ISA
i
CASAC and public review
I
I
Second External
Review Draft ISA
Federal Register
Call for Information
Workshop on
science/policy issues
Science and policy
issues from previous
NAAQS review
CASAC and public review
,
Final ISA
Figure 4.1. Standard steps in the development of Integrated Science Assessments (ISAs)
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4.2.3 Criteria for Study Selection
In selecting epidemiologic studies for the present assessment, EPA will consider studies
containing information on (1) short- or long-term exposures at or near ambient levels of Cb; (2)
health endpoints that repeat or extend findings from earlier assessments as well as those not
previously extensively researched; (3) populations that are susceptible to 63 exposures; (4)
issues related to potential confounding, and modification of effects; and/or (5) important
methodological issues (e.g., lag of effects, model specifications, thresholds, mortality
displacement) related to 63 exposure effects. Among the epidemiologic studies, emphasis will
be focused on those relevant to standard setting in the United States. Specifically, studies
conducted in the U.S. or Canada will be generally accorded more emphasis than those from other
geographic regions, as the potential impacts of different health care systems and the underlying
health status of populations need to be accounted for in the assessment. However, informative
studies conducted in other countries will be included, as appropriate. In addition, emphasis will
be placed on discussion of (1) new, multi-city studies that employ standardized methodological
analyses for evaluating 63 effects, provide overall estimates for effects based on combined
analyses of information pooled across cities, and examine results for consistency across cities;
(2) new studies that provide quantitative effect estimates for populations of interest; and (3)
studies that evaluate 63 as a component of a complex mixture of air pollutants and thus give
consideration to the levels of other co-pollutants.
The selection of research evaluating controlled exposures of laboratory animals will focus
primarily on those studies conducted at or near ambient 63 concentrations and those studies that
approximate expected human dose conditions in terms of concentration and duration, which will
depend on the toxicokinetics and biological sensitivity of the particular laboratory animals
examined. Studies will be sought that reveal site-specific effects of 63 exposure within the
respiratory tract. Consideration will be given mainly to animal studies conducted at less than 1
ppm 63. The necessity of such upper concentrations limits may be illustrated by rats, a key
species used in Os toxicological studies, but a species having both behavioral and physiological
mechanisms that can lower core temperature in response to acute exposures, thus limiting
extrapolation of data to human responses. However, in recognition of the fact that toxicological
studies using near ambient concentrations of Os or other pollutants do not necessarily reflect
effects in the most susceptible populations, studies at higher exposure levels may be included
when they provide information relevant to previously unreported effects, evidence of potential
mechanisms for an observed effect, information on exposure-response relationships, or otherwise
improve our understanding of interspecies differences or susceptible populations. Additionally,
in vitro studies may provide information on related to mechanisms of Os uptake and effect or the
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influence of photochemical oxidation processes that would otherwise be unavailable through in
vivo studies. The appropriateness of Os concentrations will be evaluated as necessary.
For research evaluating controlled human exposures to Os, emphasis will be placed on
studies that: (1) investigate effects in healthy populations and/or potentially susceptible
populations such as those with preexisting respiratory diseases; (2) include appropriate control
(or sham) exposures such as filtered air so that subjects serve as their own control as well as the
use of age-matched healthy controls in studies of susceptible individuals; (3) address issues such
as dose-response or time-course of responses; (4) investigate exposure to O^ separately and in
combination with other pollutants such as PM and NC>2; and (5) have sufficient sample size and
statistical power to assess findings adequately. Due to the limited amount of recently published
controlled human exposure studies, much of the available scientific information is expected to
come from literature that has been included in prior reviews. This older literature will be
reevaluated and discussed in light of more recent epidemiologic findings and mechanistic
toxicological data, as well as new controlled human exposure studies.
For research evaluating welfare effects, emphasis will be placed on recent studies that: (1)
evaluate effects at realistic ambient levels and (2) investigate effects on cultivated and non-
cultivated vegetation and ecosystems that occur in the U.S. Studies conducted in other
geographical areas will be included in the assessment when they contribute to the general
knowledge of the effects of Os irrespective of species or locality. As in the evaluation of health-
related scientific studies, the evaluation of welfare-related studies will assess advances in our
understanding of mechanisms of direct Os effects on vegetation and the resulting consequences
on growth and yield. These mechanisms will inform our considerations of Os effects on larger
scale ecosystem structure, function and services. These and other welfare effects will be
addressed in the ISA for both short- and long-term O^ exposures. Evaluations of research
methodologies will be integrated into the discussion to allow for comparisons between
methodologies and to allow characterization of the uncertainties associated with estimating
exposure of vegetation using different types of experimental systems.
These criteria provide generalized benchmarks for evaluating various studies and for
focusing on the highest quality studies in assessing the body of health and welfare effects
evidence. Detailed critical analysis of all Os health and welfare effects studies, especially in
relation to the above considerations, is beyond the scope of this document. Of most relevance
for evaluation of studies is whether they provide useful qualitative or quantitative information on
exposure-effect or exposure-response relationships for effects associated with current ambient air
concentrations of 63 likely to be encountered in the United States. Since the last scientific
review was completed relatively recently, i.e., within the past four years, it is expected that a
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considerable portion of the current ISA could reasonably be devoted to reiterating the basis for
scientific conclusions reached in last review.
4.2.4 Quality Assurance
NCEA participates in the Agency-wide Quality Management System, which requires the
development of a Quality Management Plan (QMP). Implementation of the NCEA QMP
ensures that all data generated or used by NCEA scientists are "of the type and quality needed
and expected for their intended use" and that all information disseminated by NCEA adheres to a
high standard for quality including objectivity, utility and integrity.
The NCEA QA staff is responsible for the review and approval of quality-related
documentation. NCEA scientists are responsible for the evaluation of all inputs to the ISA,
including primary (new) and secondary (existing) data, to ensure their quality is appropriate for
their intended purpose. NCEA follows the Data Quality Objectives, which identify the most
appropriate inputs to the science assessment, and provides QA instruction for researchers citing
secondary information. The approaches utilized to search the literature and criteria for study
selection were detailed in the two preceding subsections. Generally, NCEA scientists rely on
scientific information found in peer-reviewed journal articles, books, and government reports.
Where information is integrated or reduced from multiple sources to create new figures, tables,
or summation, the data generated are considered to be new and subject to rigorous quality
assurance measures to ensure their accuracy.
4.3 CONTENT AND ORGANIZATION OF THE ISA
The organization of the ISA for Oi will be consistent with that used in the ISA for
paniculate matter completed in December 2009 (U.S. EPA, 2009a). The ISA will contain
information relevant to considering whether it is appropriate to retain or revise the current
standards. Taking into consideration the broad policy-relevant questions outlined in chapter 3,
the policy-relevant questions that will guide development of the ISA are related to two
overarching issues. The first issue is the extent to which new scientific evidence has become
available that alters or substantiates the scientific evidence presented and evaluated in the last Os
NAAQS review. The second issue is whether uncertainties from the last air quality criteria
review have been addressed and/or whether new uncertainties have emerged. Specific questions
related to the review of the scientific literature for 03 that stem from these issues will guide the
content of the ISA. These questions were derived from the last Os NAAQS review, as well as
from discussions of new scientific evidence that occurred at the EPA kickoff workshop (October
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29-30, 2008) for this review of 63 and related photochemical oxidants. These questions are
listed below by topic area.
Source to Exposure
Air Quality and Atmospheric Science: The ISA will present and evaluate data related to:
ambient concentration distributions of Os, and its potential associations with other photochemical
oxidants and with other relevant atmospheric pollutants. New information concerning the
mechanisms of formation of 63 and other photochemical oxidants, such as peroxyacyl nitrates,
and hydrogen peroxide and organic peroxides, and the physical properties governing their
transport and lifetimes in the atmosphere will be considered. The ISA will evaluate relevant data
concerning the origin, transformation and transport, and fate of atmospheric oxidants in addition
toO3.
The assessment will also include information about the distribution of monitors in the
regulatory 63 network relevant for the interpretation of health and ecosystem effects and new
studies dealing with the precision and accuracy of the Federal Reference and Federal Equivalent
Methods (FRM and FEM, respectively) for 03. New information on the distribution of ambient
63 concentrations from in situ instruments, satellites, and other remote sensing tools will also be
considered.
Since a key component of quantitative risk assessments has been the distribution of the
1 9
policy-relevant background (PRB) concentration of Oj, in the U.S., the ISA will evaluate
methods for producing these concentrations and characterize 63 PRB concentrations. In the last
review, OT, PRB concentrations were generated using the global scale, three dimensional,
chemical transport model GEOS-CHEM, based on contributions from natural sources
everywhere in the world and from anthropogenic sources outside continental North America.
The ISA will evaluate relevant new studies and information on background concentrations. The
assessment will include estimation of Oi PRB concentrations based on the definition of PRB
used in previous reviews, and it will also evaluate additional approaches to estimation of Os PRB
concentrations, including consideration of alternative definitions of PRB. This may include
evaluation of the use of models such as MOZART or CMAQ and approaches to the use of these
models.
12 "Policy-relevant background" has been defined by EPA historically as the O3 concentrations that would be
observed in the U.S. in the absence of anthropogenic emissions of O3 precursors (e.g., VOC and NOx) in the U.S.,
Canada, and Mexico. Under this definition, PRB concentrations include contributions from natural sources
everywhere in the world and from anthropogenic sources outside continental North America (U.S. EPA, 2006).
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The ISA will include evaluation of data on the effects of tropospheric 63 on climate,
including its role as a constituent greenhouse gas, i.e., in its role as a radiative forcing agent and
its effects as an absorber of UV-B radiation in the troposphere. The potential effects of climate
change on regional air quality are being assessed elsewhere by the Agency
(http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=203459).
Exposure: The ISA will compile and evaluate information new since the last assessment that
helps characterize the variability and uncertainty in the relationships between ambient O^
concentrations and exposures to 63 of humans and ecosystems relevant to the primary and
secondary standards. Regarding the primary standard for human health, this means assessing
data concerning the range of measured Os concentrations in various human microenvironments
including indoors, outdoors near roadways, in vehicles, etc. and its relationship with
concentrations measured by ambient monitors. EPA will also assess data concerning errors in
measurement or estimation of human exposures as well as the possibly differential exposures of
some populations.
Human Health Effects
The ISA will evaluate the literature related to respiratory, cardiovascular, and other health
effects associated with short and/or long term exposures to O?,. Building upon the last air quality
criteria review, EPA plans to continue to review the available scientific evidence related to these
health endpoints and to integrate the previous findings with the results of new studies on these
health endpoints and, to the extent data are available, on additional endpoints of concern (e.g.,
developmental, inflammatory, carcinogenic/mutagenic, and cellular outcomes). Health effects
that occur following short- (including sub-daily) and/or long-term exposures to Os will be
evaluated in epidemiologic, human clinical, and toxicological studies. The ISA will also
integrate previous information on susceptible populations (e.g., asthmatics, children, outdoor
workers) with new evidence for these and possibly other susceptible populations (e.g., fetuses,
neonates, genetically susceptible populations).
For a given type of health outcome, the ISA will evaluate the strength, robustness and
consistency of the findings from the different disciplines. The health findings will be further
integrated, using the toxicological and human clinical studies to assess biological plausibility and
mechanistic evidence for the epidemiologic findings. Efforts will be directed at identifying the
lower levels at which effects are observed and at determining concentration-response
relationships. Concentration-response relationships among these studies will be evaluated for
coherence. The ISA will evaluate the scientific evidence on the occurrence of health effects
from short-term or long-term exposure to O^ at ambient levels. The ISA will also assess the
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evidence for uncertainties related to these associations and information on the public health
implications related to ambient Os exposure. The evaluation will also focus on which exposure
durations and developmental time periods of exposure are most strongly associated with effects,
for both short-term and long-term exposures. Grouped by topic area, some of the scientific
questions that EPA will seek to address in the ISA follow.
Health Effects from Exposure: The ISA will evaluate health effects evidence for a multitude of
outcomes from epidemiologic, lexicological, and human clinical studies.
• How do results of recent studies expand our understanding of the relationship
between short-term exposure to Os and respiratory effects, such as lung function
changes, airways hyperresponsiveness, lung inflammation, and host defense against
infectious disease? What new evidence is available on the potential clinical relevance
of these effects? Do recent studies expand the current understanding of adaptation to
repeated short-term 03 exposures?
• Do long-term exposures to 63 result in chronic effects manifested as permanent lung
tissue damage, altered lung development, or accelerated decline in lung function with
age? To what extent does long-term OT, exposure promote development of asthma or
chronic lung or cardiovascular disease?
• Does new evidence from studies of hospital admissions or emergency department
visits support previous findings regarding respiratory or cardiovascular effects of 63?
Is there evidence of coherence and plausibility for such effects?
• What new evidence is available on associations between 63 and mortality (total,
respiratory or cardiovascular)?
• To what extent is key evidence becoming available that could inform the
understanding of populations and life stages that are particularly susceptible to 63
exposures? What is known about genetic traits, metabolic syndrome, or other factors
that affect susceptibility? What is known about susceptibility at various ages and
developmental stages, including critical windows of exposure that result in different
effects and/or effects at lower exposures? Are new animal models becoming available
to better characterize susceptible populations?
• What Os-induced health effects are sufficiently characterized to be quantitatively
compared across species?
• To what extent does exposure to 03 contribute to health effects in other organ
systems?
• What new evidence has become available to help discern health effects of
multipollutant exposures (containing Os) versus Os alone (e.g., additive, synergistic,
or antagonistic effects)?
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Uncertainties: The ISA will evaluate uncertainty in the scientific data, particularly in relation to
observed epidemiologic findings and their consistency with toxicological and controlled human
exposure studies in terms of observed effects and biological pathways.
• How do meteorological factors and co-exposure to other criteria pollutants (e.g., PM,
NC>2, SC>2, and CO) influence the uncertainty of the evidence base for both short- and
long-term 63 exposures?
• To what extent are the observed health effects attributable to 63 versus other oxidants
that are associated with 63?
• What are the uncertainties due to other factors in epidemiologic studies (e.g.,
demographic and lifestyle attributes, socioeconomic status, genetic susceptibility
factors, occupational exposure, and medical care)?
• What is the nature and shape of the concentration-response models (e.g., linear, non-
linear, threshold models) based on 03 studies?
• What uncertainties surround the evidence for long-term effects such as life shortening
and development/progression of disease?
• How do the findings of the available studies improve our understanding of exposure
error? What evidence is newly available on the uncertainties related to statistical
model specification and how can it be used to assess the influence of these
uncertainties on the outcome of epidemiologic studies?
Biological Mechanism(s) or Modes of Action: The ISA will evaluate the data examining
mechanisms for the health outcomes associated with exposure to 63.
• Is there new information related to the pathways and underlying biological
mechanism(s) or modes of action for Os?
• What are the inherent interspecies differences in sensitivity to 63 and in 63 dosimetry
in different regions of the respiratory tract? Are these likely to vary across age
groups? Are there site-specific responses to OT, in the respiratory tract that would
better explain local and systemic effects of 63 exposure?
• What are the interspecies differences in basic mechanisms of lung injury and repair
and cardiovascular responses? What are the implications of interspecies differences
for extrapolation of results to humans?
• What are the mechanisms and time-courses of (Vinduced cellular and tissue injury,
repair, and remodeling?
Susceptible Populations: The ISA will examine health outcome data to identify specific groups
that have a greater likelihood of experiencing health effects related to 63 exposure due to a
variety of factors including, but not limited to: genetic or developmental factors, race, gender,
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lifestage (e.g., children), lifestyle (e.g., smoking status, nutrition, outdoor work) or preexisting
disease; as well as, population-level factors that can affect an individual's exposure to Os such as
socioeconomic status (SES), which encompasses reduced access to health care, low educational
attainment, residential location, and other factors. The host and environmental factors that are
responsible for differential susceptibility to Os will be investigated.
• What do controlled human exposure, animal lexicological, and epidemiologic studies
indicate regarding the relationship between acute exposures to 63 and health effects
of concern in healthy individuals and those with preexisting diseases (e.g., asthma,
COPD, cardiovascular diseases)? What other medical conditions (e.g., diabetes,
metabolic syndrome) are identified as increasing susceptibility to 63 effects? What
are the pathways and mechanisms through which 63 may be acting for these groups?
What is the nature and time-course of the development of effects in healthy persons
and in persons with pre-existing disease (e.g., asthma, heart disease)?
• How has new evidence increased our understanding of the potential susceptibility of
children and older adults to effects from Os exposure? With regard to the
interpretation of epidemiologic results and exposure-response characteristics of
populations, to what extent are these findings driven by effects in susceptible
populations?
• What evidence is available regarding susceptibility to Cb-induced responses in
population groups due to age, race, gender, or genetic makeup? How do the nature of
the effects and exposure-response relationships differ between groups? Is there
evidence of differing biological modes of action related to observed susceptibility?
• To what extent is susceptibility to the effects of short-term Os exposure is associated
with long-term 63 susceptibility?
• What factors (e.g., demographic and socioeconomic) affect susceptibility to short-
and long-term 63 exposures? Are there new data regarding population groups, such
as disadvantaged populations with potentially greater susceptibility to effects of 63?
Public Health Implications: The ISA will present concepts to define potential health outcomes
and their implications on public health. This will include estimates of the numbers of people in
specific at-risk populations groups (e.g., asthmatics, diabetics, older adults, and children).
Vegetation, Ecosystems and other Welfare Effects
The ISA will evaluate the literature related to 63 exposures on the growth of vegetation,
visible foliar injury, ecosystem services and other welfare effects. This will include evaluation
of Os exposures on productivity of ecosystems and crops systems and potential effects on
ecosystem services. Other effects that will be evaluated include 63 effects on materials and
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climate. Grouped by topic area, some scientific questions that EPA will seek to address in the
ISA follow.
Vegetation: Scientific studies have previously reported concentration response functions for the
relationship between O?, exposure and plant response for a range of endpoints. The ISA will
consider key uncertainties identified in the last air quality criteria review and the extent to which
new scientific evidence may be available to substantially inform our ability to characterize
and/or reduce these uncertainties.
• Past reviews have highlighted evidence from Os exposure experiments performed in
open-top chambers (OTCs). More recent studies have also utilized other techniques
such as Free-air exposures (FACE) and gradient studies. In what ways does the more
recent literature inform our understanding of O^ exposure on vegetation? For
example, topics may include: comparing OTC results to other studies and differences
between small and large trees.
• Though there is a large, historic body of research on Os effects on vegetation, there
has been no common metric used across studies to describe the relationship between
63 exposures and plant response. How can 63 studies which use various 63 metrics,
plant species and methodologies be appropriately quantitatively synthesized and
assessed?
Ecosystem Services: Some recent research has examined further how 63 effects are potentially
linked to ecosystem services and processes related to these services. Such linked ecosystem
services and processes identified in recent studies include water supply and quality, N-cycling,
bee pollination, and CC>2 sequestration.
• What is the nature of the information linking 63 pollution and ecosystem services?
What are the existing studies that make direct or indirect linkages between 03
exposure and ecosystem services? How can studies at smaller scales be used to
address ecosystem services issues?
• Can information available in the older literature be re-examined in light of these
broader linkages?
• What new information is available on potential effects of OT, on CO2 sequestration in
ecosystems?
• How does 63 influence the biodiversity of ecological systems?
• Has Os altered nutritional content of forage for domestic animals or wildlife
populations?
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Materials Damage: Ozone and other photochemical oxidants react with many economically
important man-made materials, decreasing their useful life and aesthetic appearance. Materials
damaged by O^ include elastomers; textiles and fibers; dyes, pigments, and inks; and paints and
other surface coatings. The new scientific literature will be evaluated in this area to determine
the extent to which new scientific evidence may inform the standard.
Climate: The ISA will include evaluation of data relevant to the issue of tropospheric 63
as a constituent greenhouse gas, i.e., in its role as a radiative forcing agent and its effects as an
absorber of UV-B radiation in the troposphere. The potential effects of climate change on
regional air quality are being assessed elsewhere by the Agency
(http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=203459).
4.4 CAUSAL DETERMINATIONS
Since the last Os NAAQS review, EPA has developed a framework that is intended to
provide a consistent and transparent basis for drawing conclusions on causal relationships
between pollutant exposures and health or environmental effects. Use of this framework in the
recent science assessment for particulate matter is described in chapter 1 of that ISA (EPA,
2009a). Briefly, the framework includes the following considerations for drawing conclusions of
causality for specific endpoints: consistency of findings for an endpoint across studies in which it
was examined, coherence of the results related to a specific endpoint among different study types
or disciplines, the coherence of results with characterized mechanisms of action (biological
plausibility), and evidence of a concentration- or dose-response relationship for an endpoint. in
drawing judgments regarding causality for the criteria air pollutants, EPA focuses on evidence of
effects at relevant pollutant exposures.
In the current ISA for Os, EPA will assess the results of recent relevant publications,
building upon evidence available during the previous O^ NAAQS review, to draw conclusions
regarding the strength of the evidence for causal relationships between health and environmental
effects associated with short- and long-term exposure periods. Evaluations of causality for
ecological and welfare effects generally consider the probability of quantitative changes in
response to exposure. Exposure-response relationships are often determined for a specific
ecological system and scale, rather than at the national or even regional scale. In making
determinations of causality for human health effects, evidence will be evaluated for broad health
outcome categories, such as respiratory effects, and then conclusions drawn based upon the
integration of evidence from across disciplines (e.g., epidemiology, clinical studies and
toxicology) and also across the suite of related individual health outcomes. EPA will focus on
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health outcome categories, rather than very specific endpoints, since the coherence of evidence
across a spectrum of related endpoints (e.g., effects ranging from inflammatory effects to
respiratory mortality) is an important aspect for drawing conclusions regarding causality.
4.5 SUPPLEMENTARY MATERIALS
Previous science assessments conducted to support NAAQS reviews included
supplementary materials, which were designed to provide detailed supporting information and
more comprehensive coverage of the research areas summarized in the ISA. NCEA intends to
change the form, while maintaining the relevant content, of the materials that were formerly
contained within the Annexes to the ISA.
As discussed previously, studies included in the text of the ISA will be those deemed
informative to the NAAQS review process (e.g. policy-relevant) and of adequate quality. The
ISA text, tables and figures will highlight and summarize key study details that are needed to
understand and interpret the results of a study. This information, which was described in the text
as well as reiterated in the annex tables of previous documents, includes: (1) the chemistry,
physics, sources, emissions, and measurement of 63; (2) environmental concentrations and
human exposure to 63; (3) dosimetry; (4) toxicological studies of 63 health effects in laboratory
animals and in vitro systems; (5) human clinical studies examining health effects following
controlled exposure to 63; (6) epidemiologic studies of health effects from short- and long-term
exposure to Cb; (7) environmental studies on vegetation and ecosystem effects; and (8) materials
damage and climate change related to 03. In addition, supplementary materials will be provided
in the form of output from the Health and Environmental Research Online (HERO) database. A
key function of the HERO output will be to document the base of evidence containing
publications evaluated for the Os review, including any publications considered but not included
in the ISA. This information will be presented as links to lists of references in the HERO
database, which include bibliographic information and abstracts.
4.6 SCIENTIFIC AND PUBLIC REVIEW
Drafts of the ISA will be reviewed by the CAS AC Os Review Panel and made available
for public comment. The CASAC Os Review Panel will review the first draft ISA and discuss
their comments in a public meeting announced in the Federal Register. Based on CASAC's past
practice, EPA anticipates that key CASAC advice and recommendations for revision of the first
draft ISA will be summarized by the CASAC Chair in a letter to the EPA Administrator. In
revising the first draft ISA, EPA will take into account any such recommendations. EPA will
also consider comments received from CASAC or from the public at the meeting itself and any
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written public comments. EPA will prepare a second draft ISA for CASAC review and public
comment. The CASAC Os Review Panel will review the second draft ISA and discuss their
comments in a public meeting announced in the Federal Register. Again, based on CASAC's
past practice, EPA anticipates that key CASAC advice and recommendations for revision of the
second draft ISA will be summarized by the CASAC Chair in a letter to the EPA Administrator.
In finalizing the ISA, EPA will take into account any such recommendations. EPA will also
consider comments received from CASAC or from the public at the meeting itself and any
written public comments. After appropriate revision, the final document will be made publicly
available on an EPA website and in hard copy. A notice announcing the availability of the final
ISA will be published in the Federal Register. In addition, the final ISA will be placed in the
ozone ISA docket (Docket ID: EPA-HQ-ORD-2011-0050).
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5 HUMAN HEALTH RISK AND EXPOSURE
ASSESSMENTS
5.1 OVERVIEW
Characterizing health risks for the new periodic review of the primary NAAQS for Os will
include conducting air quality analyses to support quantitative exposure and risk assessments in
specific locations to the extent warranted by new information, taking into consideration available
resources. The results of such assessments will be put into a broader public health perspective,
with a particular emphasis on exposures and health risks in susceptible populations, such as
children. These assessments will be designed to estimate human exposures and to characterize
the potential health risks that are associated with current ambient levels, with ambient levels
simulated to just meet the current standard, and with ambient levels simulated to just meet
alternative standards that may be considered. The EPA is planning to focus the quantitative
exposure/risk assessments on Os, but recognizes that Os serves as an indicator of the broader
photochemical oxidant mix. Therefore, health effects reported to be associated with exposure to
63 may not be due to 63 only, but to the broader mix of photochemical oxidants.
An important issue associated with conducting exposure and human health risk
assessments is the treatment of variability and the characterization of uncertainty. Variability
refers to the inherent heterogeneity in a population or variable of interest (e.g., residential air
exchange rates) and cannot be reduced through further research, only better characterized with
additional measurement. Uncertainty refers to the lack of knowledge regarding both the actual
values of model input variables (i.e., parameter uncertainty) and the physical systems or
relationships (i.e., model uncertainty - e.g., the shapes of concentration-response relationships).
As part of such analyses, variability and uncertainty will be explicitly addressed, where feasible,
in the planned air quality, exposure, and health risk assessments.
The major components of the risk characterization (e.g., air quality analyses, quantitative
exposure assessment, quantitative health risk assessment, broad health risk characterization) are
outlined below and will be described in more detail in a Scope and Methods Plan. Preparation of
this plan will coincide with the development of the first draft ISA to facilitate the integration of
policy-relevant science into both documents. In particular, the availability of air quality,
exposure-response, concentration-response, and baseline incidence data will impact the type of
risk and exposure assessments that will be developed.
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5.2 EXPOSURE AND HEALTH RISK ASSESSMENTS FROM THE LAST
REVIEW
The exposure and health risk assessments conducted in the last review developed
exposure and health risk estimates for 12 urban areas across the U.S. which were chosen based
on the location of Os epidemiologic studies and to represent a range of geographic areas,
population demographics, and O^ climatology. These analysies were in part based upon the
exposure and health risk assessments done as part of the review completed in 1997. The
exposure and risk assessment incorporated air quality data (i.e., 2002 through 2004) and
estimated annual or 63 season-specific exposure and risk estimates for these recent years of air
quality and for air quality scenarios simulating just meeting the existing 8-hr 63 standard and
several alternative 8-hr 03 standards. Exposure estimates were used as an input to the risk
assessment for lung function responses (i.e., a health endpoint for which exposure-response
functions were available from controlled human exposure studies). Exposures were estimated
for the general population and identified populations, including school age children with asthma
as well as all school age children. The modeled exposures were also used to estimate the number
of persons having exposures above potential health effect benchmark levels. Staff identified the
benchmark levels using the occurrence of observed health effect endpoints (e.g., lung
inflammation, increased airway responsiveness, and decreased resistance to infection) that were
associated with 6-8 hour exposures to Os while engaged in moderate exertion that were observed
in several controlled human exposure studies.
The exposure analysis took into account several important factors including the
magnitude and duration of exposures, frequency of repeated high exposures, and breathing rate
of individuals at the time of exposure. Estimates were developed for several indicators of
exposure to various levels of Os air quality, including counts of people exposed one or more
times to a given O?, concentration while at a specified breathing rate, and counts of person-
occurrences which accumulate occurrences of specific exposure conditions over all people in the
population groups of interest over an Os season.
As discussed in the Staff Paper and in section II. A of the 2008 Os NAAQS final rule (73
FR 16440 to 16442), of the uncertainties identified and evaluated, the most important
uncertainties affecting the exposure estimates were related to modeling human activity patterns
over an 63 season, modeling of variations in ambient concentrations near roadways, and
modeling of air exchange rates that affect the amount of Os that penetrates indoors. Another
important uncertainty, discussed in more detail in the Staff Paper (section 4.3.4.7), was the
uncertainty in energy expenditure values which directly affect the modeled breathing rates.
These were important since they were used to classify exposures occurring when children were
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engaged in moderate or greater exertion and health effects observed in the controlled human
exposure studies generally occurred under these exertion levels for 6 to 8-hr exposures to Os
concentrations at or near 0.08 ppm.
The human health risk assessment conducted in the last review was designed to estimate
population risks in a number of urban areas across the U.S., consistent with the scope of the
exposure analysis described above. The risk assessment included risk estimates based on both
controlled human exposure studies and epidemiologic and field studies. Ozone-related risk
estimates for lung function decrements were generated based on probabilistic exposure-response
relationships developed based on data from controlled human exposure studies, together with
probabilistic exposure estimates from the exposure analysis. For several other health endpoints,
Os-related risk estimates were generated based on concentration-response relationships reported
in epidemiologic or field studies, together with ambient air quality concentrations, baseline
health incidence rates, and population data for the various locations included in the assessment.
Health endpoints included in the assessment based on epidemiologic or field studies included:
hospital admissions for respiratory illness in 4 urban areas, premature mortality in 12 urban
areas, and respiratory symptoms in asthmatic children in 1 urban area.
In the previous health risk assessment, EPA recognized that there were many sources of
uncertainty and variability in the inputs to the assessment and that there was a high degree of
uncertainty in the resulting risk estimates. The statistical uncertainty surrounding the estimated
63 coefficients in concentration-response functions as well as the shape of the exposure-response
relationship chosen were addressed quantitatively. Additional uncertainties were addressed
through sensitivity analyses and/or qualitatively. The previous risk assessment incorporated
some of the variability in key inputs to the assessment by using location-specific inputs (e.g.,
location-specific concentration-response function, baseline incidence rates and population data,
and air quality data for epidemiologic -based endpoints, location specific air quality data and
exposure estimates for the lung function risk assessment). In the previous health risk assessment,
twelve urban areas were included to provide some sense of the variability in the risk estimates
across the U.S. Sensitivity analysis was carried out for two sources of uncertainties. The first
analysis investigated the impact of alternative estimates for policy-relevant background (PRB)
levels in 3 of the 12 urban areas. The second sensitivity analysis looked at the impact of
different assumptions around the shape of the exposure-response function.
Key observations and insight from the Os risk assessment, in addition to important caveats
and limitations, were addressed in section II.B of the 2008 Os NAAQS final rule notice (73 FR
16440 to 16443). In general, estimated risk reductions associated with going from current 63
levels to just meeting the current and alternative 8-hr standards showed patterns of increasing
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estimated risk reductions associated with just meeting the lower alternative 8-hr standards
considered. Furthermore, the estimated percentage reductions in risk were strongly influenced
by the baseline air quality year used in the analysis, which was due to significant year-to-year
variability in 63 concentrations. There was also noticeable city-to-city variability in estimated
Os-related incidence of morbidity and mortality across the 12 urban areas. Uncertainties
associated with estimated PRB concentrations were also addressed and revealed differential
impacts on the risk estimates depending on the health effect considered as well as the location.
The EPA also acknowledged that there were considerable uncertainties surrounding estimates of
63 coefficients and the shape for concentration-response relationships and whether or not a
population threshold or non-linear relationship exists within the range of concentrations
examined in the epidemiologic studies.
5.3 AIR QUALITY CONSIDERATIONS
Air quality analyses are required to conduct both exposure and health risk assessments for
NAAQS reviews. Air quality inputs to the exposure and/or health risk assessment include: (1)
provision of ambient air quality data from the fixed-site ambient monitoring network for the
period 2008-2010 for the urban areas included in the exposure and risk assessments, (2)
estimates of PRB concentrations for the specific urban areas included in the risk assessment, and
(3) ambient air quality scenario data sets that are obtained from simulation procedures that adjust
recent air quality data to reflect changes in the distribution of air quality estimated to occur at
some unspecified time in the future when an area just meets a given set of NAAQS. Broader
national scale air quality analyses may also be conducted to place the results of the quantitative
risk and exposure assessments into a broader public health context.
While incremental risk reductions may not require estimates of PRB, estimates of the
risks in excess of PRB remaining upon meeting the current or potential alternative standards, do
require EPA to estimate PRB. Both types of risk estimates are considered relevant to inform the
EPA Administrator's decision on the adequacy of a given standard.
Historically, PRB has been defined as the "the distribution of Os concentrations that
would be observed in the U.S. in the absence of anthropogenic (man-made) emissions of
precursor emissions (e.g., VOC, NOX, and CO) in the U.S., Canada, and Mexico" (US EPA,
2007, p.2-48). This has been referred to as PRB, since this definition of background facilitates
separating pollution levels that can be controlled by U.S. regulations (or through international
agreements with neighboring countries) from levels that are not generally controllable in this
manner. Thus, PRB in past reviews included: (1) O?, generated in the U.S. that arises from
natural (biogenic) sources of emissions in the U.S., Canada, and Mexico and (2) 63 in the U.S.
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from the transport of 63 or the transport of precursor emissions from both natural and man-made
sources, from outside of the U.S. and its neighboring countries. As discussed in chapter 4, the
ISA will include an assessment of methods for estimating PRB concentrations, including
alternative approaches for defining PRB, and will produce 63 PRB concentrations for use in the
risk assessment. In this new review, EPA plans to place greater emphasis on understanding the
contribution of the different components that contribute to PRB (e.g., what portion of PRB is due
to natural emissions alone and what is the contribution of transport from outside the North
American continent, as well as the contribution of Canadian and Mexican anthropogenic
emissions to 63 levels observed in the U.S.) and to the extent warranted, evaluate alternative
definitions of PRB and their implications on exposures and risk. This additional information will
help inform policy considerations for this review of the O?, NAAQS as well as more broadly
inform efforts related to international efforts to reduce trans-boundary 63 air pollution.
As part of the exposure and risk assessments, it will be necessary to adjust recent OT, air
quality data to simulate just meeting the current standard and any alternative 63 standards that
might be considered. In the last review, EPA used a quadratic air quality rollback approach
(U.S. EPA, 2007a, section 4.5.8). EPA will consider this approach and alternative air quality
simulation procedures for use in this current review. Staff will evaluate candidate procedures to
adjust air quality by analyzing historical changes in measured OT, levels and by analyzing
changes in 03 levels predicted by air quality models. In this new review, EPA also will examine
techniques that may be used to assess the variability and uncertainty of the simulated change in
concentrations likely to result from just meeting the current or alternative standards.
5.4 POPULATION EXPOSURE ASSESSMENT APPROACH
Population exposure to Os will be evaluated using EPA's Air Pollutants Exposure model
(APEX), a model that simulates microenvironmental personal exposures using temporally and
spatially variable ambient concentrations and personal time-location-activity patterns. One
objective is to provide exposure estimates as an input to the portion of the health risk assessment
that uses exposure-response relationships from controlled human exposure studies. The
exposure analysis will also provide estimates of population exposure exceeding potential health
effect benchmarks, values identified based on 03 exposure concentrations and associated health
effects observed in controlled human exposure studies.
The approach to the current exposure assessment will build upon the methods developed
and insights gained from the exposure assessment conducted for the last review. Staff will
consider performing the exposure assessment for the same 12 urban areas (i.e., Atlanta, Boston,
Chicago, Cleveland, Detroit, Houston, Los Angeles, New York, Philadelphia, Sacramento, St.
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Louis, and Washington D.C). Several key considerations in planning for the exposure
assessment are discussed below.
The most current version of the APEX model (also referred to as the Total Risk
Integrated Methodology/Exposure (TREVI.Expo) model) will be used to estimate population
exposures for the various air quality scenarios of interest. APEX simulates the movement of
individuals through time and space and their exposure to 63 in indoor, outdoor, and in-vehicle
microenvironments. APEX is a probabilistic model that will be used to simulate a large number
of randomly sampled individuals within each urban area (e.g., 200,000) to represent area-wide
population exposures.
As in the previous exposure assessment, human activity data needed for the analysis will
be drawn from the Consolidated Human Activity Database (CHAD) developed and maintained
by ORD's National Exposure Research Laboratory (NERL). A number of additional activity
diaries have been added to the database and will be used in this exposure assessment. This
expanded database will likely improve the representation of the simulated exposure population of
interest because there are increases in the numbers of data diaries available, in particular for
children, and much of the added data are from studies conducted within the past decade. One
key issue in this analysis regarding time-location activity patterns is the further evaluation and
possible modification of the approach used for creating Os-season or year-long activity
sequences for individuals from primarily cross-sectional activity data diaries.
As done in the last Os NAAQS review and other recent NAAQS reviews (e.g., US EPA,
2007a,b; US EPA, 2008; US EPA, 2009b) and where possible, staff will identify, incorporate,
and describe any observed variability in input data sets and estimated parameters within the
analyses performed. In addition, consistent with other NAAQS reviews, the exposure
assessment will include an uncertainty characterization of the model inputs and model
formulation.
5.5 HUMAN HEALTH RISK ASSESSMENTS
The goals of the Os health risk assessment are: (1) to provide estimates of the potential
magnitude of selected morbidity and mortality health effects in the population associated with
recent ambient 63 levels and with just meeting the current 63 standard and any alternative
standards that might be considered in specific urban areas, (2) to develop a better understanding
of the influence of various inputs and assumptions on the risk estimates; and (3) to gain insights
into the distribution of risks and patterns of risk reduction and uncertainties in those risk
estimates. The approach to the current health risk assessment will build upon the methods
developed and insights gained from the risk assessment conducted in the last review. Staff will
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consider performing the assessment for the same 12 urban areas (i.e., Atlanta, Boston, Chicago,
Cleveland, Detroit, Houston, Los Angeles, New York, Philadelphia, Sacramento, St. Louis, and
Washington D.C). Several key considerations in planning for the health risk assessment are
discussed below.
Staff is planning to focus the quantitative risk assessments on the most important health
effect categories and endpoints from the standpoint of public health significance and for which
the weight of the evidence supports the judgment that the effect category and specific health
effects endpoints are judged sufficiently causal with respect to Os either alone and/or in
combination with other pollutants to be included in the quantitative risk assessment. An
important additional consideration in deciding which health effect endpoints to include in the
risk assessment is the availability of sufficient information to conduct a quantitative assessment
(e.g., characterization of exposure- or concentration-response relationship, information on
baseline incidence).
The risk and exposure assessments will draw upon the information presented in the ISA
and its supplementary materials. This includes information on atmospheric chemistry, air
quality, human exposure, and health effects of concern. In particular, the availability of air
quality, concentration- and exposure-response relationships, and baseline incidence rate data will
impact the type of risk assessments that will be performed.
As described in section 5.3 above, air quality inputs required to conduct the health risk
assessment include: (1) recent 63 air quality data from suitable monitors for each selected
location, (2) estimates of PRB concentrations for each location, and (3) simulated air quality that
reflects changes in the distribution of 63 air quality estimated to occur when an area just meets a
given 63 standard.
5.5.1 Approach to Health Risk Assessment Based On Epidemiologic Studies
As noted above, the health risk assessment conducted in this review will build on the
approach developed and applied in the last review. Staff plans to rely on a weight-of-evidence
approach, as provided in the ISA, based on evaluation of new and prior epidemiologic studies
including identification of relevant concentration-response functions that characterize the
relationships between Os exposures and health outcomes, particularly those conducted at or near
current ambient concentrations. Quantitative relationships provided in the specific studies or
derived from the data presented in the epidemiologic studies describe the change in
concentration (generally based on ambient fixed-site monitors) associated with a change in
health response. These concentration-response relationships will be combined with air quality
data, baseline incidence data, and population data to develop population health risk estimates.
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Epidemiologic studies typically provide estimated concentration-response relationships
based on data collected in real-world settings. Ambient Os concentrations are typically measured
as the area-wide average of monitor-specific measurements, although personal exposures are
occasionally measured. Health responses for 63 included in the prior risk assessment were:
respiratory symptoms in asthmatic children, asthma and other respiratory-related hospital
admissions, and premature mortality. Staff will consider the type of health response function(s)
available and the availability of ambient 63 concentration data to characterize public health risks.
We consider that these analyses are most appropriately applied in areas where the specific
epidemiologic studies were performed. It should be noted that a risk characterization based on
epidemiologic studies also requires baseline incidence rates and population data for the specific
locations evaluated in the risk assessment.
The inclusion of any particular health endpoint depends in part on the extent to which the
Os ISA infers the likelihood of a causal relationship between Os exposure and a given health
effect category and the weight of the evidence for concluding that 63 exposures are related to the
specific health effect endpoint. A number of issues related to the selection and application of
appropriate concentration-response functions for use in the assessment will be addressed in the
Scope and Methods Plan. For example, consideration will be given to the appropriate use of
functions based on single- and multi-city studies, single- and multi-pollutant concentration-
response models, and alternative lags.
5.5.2 Approach to Health Risk Assessment Based on Controlled Human
Exposure Studies
As noted above, the health risk assessment conducted in this new review will build on the
approach developed and applied in the last review. In that previous assessment, risk estimates for
lung function responses associated with 8-hr exposures while engaged in moderate exertion were
developed. These estimates were based in part on exposure-response relationships estimated from
the combined data sets from multiple Os controlled human exposure studies. Data from the studies
by Folinsbee et al. (1988), Horstman et al. (1990), and McDonnell et al. (1991) in addition to more
recent data from Adam (2002, 2003, 2006) were used to estimate exposure-response relationships for
>10, 15, and 20% decrements in FEVi. In this new review, staff intends to investigate the possibility
of using a model (McDonnell et al., 2007) that estimates FEVi responses associated with Os short-
term exposures. This model is based on the controlled human exposure data included in the prior
lung function risk assessment as well as additional data sets for different averaging times and
breathing rates. We will also consider whether there is sufficient evidence to consider adding other
health endpoints observed in controlled human exposure studies to the quantitative risk assessment
based on the information contained in the draft ISA.
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5.5.3 Uncertainty and Variability
For the health risk assessment to be conducted for the new review, we will include both a
qualitative characterization of uncertainty and variability, and where feasible, a quantitative
characterization of uncertainty and/or sensitivity analyses for those aspects of the assessment judged
most influential. Following the same general approach described above in section 5.4, and
adapted from WHO (2008), staff plans to perform a succinct qualitative characterization of the
components contributing to uncertainty in estimated health risks. This qualitative
characterization will be performed early in the process of developing the risk assessment to
inform and prioritize potential health risk model development activities and to identify additional
uncertainties that were not previously evaluated.
5.5.4 Broader Risk Characterization
For this new review, staff is considering extending the risk assessment to a broader range
of urban areas, beyond the 12 urban areas included in the previous assessment, in light of newly
available data to provide greater coverage of additional regions of the country where significant
63 exposures are likely to occur. We also will consider the feasibility of developing
concentration-response relationships that can be applied on a regional basis. It is very likely that
the geographic (and population) coverage will vary for different health endpoint categories due
to data limitations (e.g., the availability of emergency department and hospital admission
baseline incidence data is more limited than mortality baseline incidence data). However, we
recognize that there have been noticeable improvements in the availability of baseline incidence
data for emergency department and hospital admissions since the last review.
Beyond the quantitative risk and exposure assessments conducted for this review, staff will
consider ways to put the results of those assessments into a broader context. Specifically, we
will explore analyses that would complement quantitative risk and exposure assessments
conducted for a limited number of locations and selected health endpoints to better characterize
the nature, magnitude, extent, variability, and uncertainty of the public health impacts associated
with Os exposures on a broader scale. We will consider how additional analyses can be used to
inform our understanding of:
• Additional health endpoints not considered in the quantitative risk assessment;
• Additional locations not evaluated in the quantitative risk/exposure assessment to inform
a broader understanding of public health impacts including non-urban environments;
• Regional differences in 63 risks taking into consideration the following factors:
variations in individual and/or population susceptibility;
- population demographics;
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- variations in exposures; and
impacts of potential effect modifiers (e.g., weather, co-pollutants).
5.6 SCIENTIFIC AND PUBLIC REVIEW
A Scope and Methods Plan for the risk/exposure assessment will be submitted to CASAC
for consultation and will be provided to the public for comment subsequent to the release of the
1st draft ISA. The CASAC Os Review Panel will discuss its comments on the Scope and
Methods Plan in a public meeting that will be announced in the Federal Register. In conducting
the risk/exposure assessment, staff will take into account comments received from CASAC and
from the public at the meeting itself and in any written comments. Staff plans to prepare two
drafts of the risk/exposure assessment for CASAC review and public comment. The CASAC 63
Review Panel will review each draft risk/exposure assessment and discuss their comments in two
public meetings to be announced in the Federal Register. Based on CASAC's past practice, staff
anticipates that key CASAC advice and recommendations for revision of the draft risk/exposure
assessment will be presented in letters to the EPA Administrator. Staff will also consider
comments received from CASAC and from the public at the meetings themselves and any
written public comments. In finalizing the risk/exposure assessment, we will take into account
any such comments and recommendations. After appropriate revision, the final risk/exposure
assessment document will be made publicly available on an EPA website and in hard copies. A
notice announcing the availability of the final document will be published in the Federal
Register. In addition, the final risk/exposure assessment document will be placed in the
rulemaking docket.
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6 VEGETATION AND OTHER WELFARE-RELATED
ASSESSMENTS
6.1 OVERVIEW
Assessments being considered for this new review of the secondary Oi NAAQS would
focus on new information that has become available since the review completed in 2008. Key-
policy relevant findings from the ISA integrated with information from previous reviews will
inform policy judgments in regard to the adequacy of the current indicators, averaging times,
levels and forms of the Os standard. New information and methods available in this review have
the potential to improve characterization of 63 exposures and associated impacts, especially in
non-urban areas, forests, and Class I protected lands. Recent information regarding direct Os
effects on plants, including emerging evidence that 63 alters the chemical signature and
longevity of scents released by plants to attract pollinators, and the indirect impacts that can
occur in associated ecological processes that can lead to ecosystem level effects and shifts in or
loss of ecosystem services (e.g., carbon sequestration, water balance, pollination and/or
biodiversity) will be considered and evaluated using qualitative and/or quantitative exposure, risk
and benefits assessments, where feasible.
As in the last review, information regarding the interaction between 63, local
meteorological conditions, and climate will be reviewed, although we do not anticipate sufficient
information being available for quantitative analyses of this complex relationship in this review.
Ozone-related damage to certain manmade materials (e.g., elastomers, textile fibers, dyes, paints
and pigments) will not be re-assessed, as the scientific literature contains very little new
information to adequately quantify these effects.
A more detailed description of assessment methods and approaches being considered for
the exposure, risk and benefits assessments will be provided in a subsequent Scope and Methods
Plan. Preparation of this plan will coincide with the development of the first draft ISA to
facilitate the integration of policy-relevant science.
6.2 EXPOSURE, RISK, AND BENEFITS ASSESSMENTS FROM THE
LAST REVIEW
The exposure, risk and benefits assessments conducted as part of the last review focused
on Os-related impacts to sensitive vegetation and their associated ecosystems. The vegetation
exposure assessment was performed using an interpolation approach that included information
from ambient monitoring networks and results from air quality modeling. The vegetation risk
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assessment included both tree and crop analyses. The tree risk analysis included three distinct
lines of evidence: (1) observations of visible foliar injury in the field linked to monitored Os air
quality for the years 2001 - 2004; (2) estimates of seedling growth loss under then current and
alternative 63 exposure conditions; and (3) simulated mature tree growth reductions using the
TREGRO model to simulate the effect of meeting alternative air quality standards on the
predicted annual growth of mature trees from three different species. The crop risk analysis
included estimates of crop yields under current and alternative 63 exposure conditions. The
associated change in economic benefits expected to accrue to the agriculture sector upon meeting
the levels of various alternative standards were analyzed using an agricultural benefits model.
Key elements and observations from these exposure and risk assessments are outlined in the
following sections.
6.2.1 Exposure Assessment
In many rural and remote areas where sensitive species of vegetation can occur,
monitoring coverage remained limited. Thus, the Staff Paper concluded that it was necessary to
use an interpolation method in order to better characterize Os air quality over broad geographic
areas and at the national scale. Based on the significant difference in monitor network density
between the eastern and western U.S., the Staff Paper further concluded that it was appropriate to
use separate interpolation techniques in these two regions: The Air Quality System (AQS;
http://www.epa.gov/ttn/airs/airsaqs) and Clean Air Status and Trends Network (CASTNET;
http://www.epa.gov/castnet/) monitoring data were solely used for the eastern interpolation, and
in the western U.S., where rural monitoring is more sparse, O^ outputs from the EPA/NOAA
Community Multi-scale Air Quality (CMAQ)13 model system
(http://www.epa.gov/asmdnerl/CMAQ, Byun and Ching, 1999) were used to develop scaling
factors to augment the monitor interpolation. In order to characterize uncertainty associated with
the exposure estimates generated using the interpolation method, monitored 63 concentrations
were systematically compared to interpolated OT, concentrations in areas where monitors were
located. In general, the interpolation method performed well in many areas in the U.S. This
approach was used to develop a national vegetation 63 exposure surface.
The CMAQ model is a multi-pollutant, multi-scale air quality model that contains state-of-the-science techniques
for simulating all atmospheric and land processes that affect the transport, transformation, and deposition of
atmospheric pollutants and/or their precursors on both regional and urban scales. It is designed as a science-based
modeling tool for handling many major pollutants (including photochemical oxidants/O3, paniculate matter, and
nutrient deposition) holistically. The CMAQ model can generate estimates of hourly O3 concentrations for the
contiguous U.S., making it possible to express model outputs in terms of a variety of exposure indices (e.g., W126,
8-hr average).
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To evaluate changing vegetation exposures under selected air quality scenarios, a number
of analyses were conducted. One analysis adjusted 2001 base year Os air quality distributions
using a rollback method (Horst and Duff, 1995; Rizzo, 2005, 2006) to reflect meeting the current
and alternative secondary standard options. For "just meet" and alternative 8-hr average
standard scenarios, the associated maps of estimated 12-hr, W126 exposures were generated.
Based on these comparisons, the following observations were drawn: (1) current 63 air quality
levels could result in significant 63 exposures to vegetation in some areas; (2) overall 3-month
12-hr W126 O^ levels were somewhat but not substantially improved under the "just meet"
current scenario; (3) exposures generated for just meeting a 0.070 ppm, 4th-highest maximum 8-
hr average alternative standard (the lower end of the then proposed range for the primary Os
standard) showed substantially improved O^ air quality when compared to just meeting the
current 0.08 ppm, 8-hr standard.
A second analysis described in the Staff Paper was performed to evaluate the extent to
which county-level 63 air quality measured in terms of various levels of the current 8-
hr average form overlapped with that measured in terms of various levels of the 12-
hr W126 cumulative, seasonal form.14 While these results also suggested that meeting a
proposed 0.070 ppm, 8-hr secondary standard would provide substantially improved vegetation
protection in some areas, the Staff Paper recognized that this analysis had several important
limitations. In particular, the lack of monitoring in rural areas where sensitive vegetation and
ecosystems are located, especially at higher elevation sites could have resulted in an inaccurate
characterization of the degree of potential overlap at sites which have air quality patterns that can
result in relatively low 8-hr averages while still experiencing relatively high cumulative
exposures (72 FR 37892). Thus, the Staff Paper concluded that it is reasonable to anticipate that
additional unmonitored rural high elevation areas with sensitive vegetation may not be
adequately protected even with a lower level of the 8-hr form. The Staff Paper further indicated
that it remained uncertain as to the extent to which air quality improvements designed to reduce
8-hr 03 average concentrations would reduce 03 exposures measured by a seasonal, cumulative
W126 index. The Staff Paper indicated this to be an important consideration because: (1) the
biological database stresses the importance of cumulative, seasonal exposures in determining
plant response; (2) plants have not been specifically tested for the importance of daily maximum
8-hr 63 concentrations in relation to plant response; and (3) the effects of attainment of a 8-hr
14
The Staff Paper presented this analysis using then recent (2002-2004) county-level O3 air quality data (using 3-
year average data as well as data from each individual year) from AQS sites and the subset of CASTNET sites
having the highest O3 levels for the counties in which they are located.
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standard in upwind urban areas on rural air quality distributions cannot be characterized with
confidence due to the lack of monitoring data in rural and remote areas.
6.2.2 Risk Assessment
The risk assessments in the last review reflected the availability of several additional
lines of evidence that provided a basis for a more complete and coherent picture of the scope of
Os-related vegetation risks, especially those faced by seedling, sapling and mature tree species
growing in field settings, and indirectly, forested ecosystems. Specifically, new research
available at the time reflected an increased emphasis on field-based exposure methods (e.g., free
air exposure and ambient gradient), improved field survey biomonitoring techniques, and
mechanistic tree process models. Highlights from the analyses that addressed visible foliar
injury, seedling and mature tree biomass loss, and effects on crops are summarized below.
With regard to visible foliar injury, the Staff Paper presented an assessment that
combined recent U.S. Forest Service Forest Inventory and Analysis (FIA) biomonitoring site
data with the county level air quality data for those counties containing the FIA biomonitoring
sites. This assessment showed that incidence of visible foliar injury ranged from 21 to 39
percent of the counties during the four-year period (2001-2004) across all counties with air
quality levels at or below that of the then current 0.08 ppm 8-hr standard. Of the counties that
met an 8-hr level of 0.07 ppm in those years, 11 to 30 percent of the counties still had incidence
of visible foliar injury.
With respect to tree seedling biomass loss, concentration-response (C-R) functions
developed from OTC data for biomass loss for available seedling tree species and information on
tree growing regions derived from the U.S. Department of Agriculture's Atlas of United States
Trees were combined with projections of air quality based on 2001 interpolated exposures, to
produce estimated biomass loss for each individual seedling tree species. These analyses
predicted that biomass loss could still occur in many tree species when 63 air quality was
adjusted to meet the current 8-hr standard. Though this type of analysis was not new to this
review, the context for understanding these results had changed due to recent field work at the
AspenFACE site in Wisconsin on quaking aspen (Karnosky et al., 2005) and a gradient study
performed in the New York City area (Gregg et al., 2003), which confirmed the detrimental
effects of 63 exposure on tree growth in field studies without chambers and beyond the seedling
stage (King et al., 2005).
With respect to risk of mature tree growth reductions, a tree growth model (TREGRO)
was used to evaluate the effect of changing 63 air quality scenarios from just meeting alternative
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C>3 standards on the growth of mature trees.15 The model was run for a single western species
(ponderosa pine) and two eastern species (red maple and tulip poplar). Staff Paper analyses
found that just meeting the current standard would likely continue to allow Os-related reductions
in annual net biomass gain in these species. Though there was uncertainty associated with the
above analyses, it was important to note that new evidence from experimental studies that go
beyond the seedling growth stage continued to show decreased growth under elevated 63 (King
et al., 2005); some mature trees such as red oak have shown an even greater sensitivity of
photosynthesis to O^ than seedlings of the same species (Hanson et al., 1994); and the potential
for cumulative "carry over" effects as well as compounding should be considered (Andersen, et
al, 1997).
With respect to risks of yield loss in agricultural crops and fruit and vegetable species,
little new information was available beyond that of the previous review. However, limited
information from a free air field based soybean study (SoyFACE) and information on then
current cultivar sensitivities, led to the conclusion that C-R functions developed in OTCs under
the National Crop Loss Assessment Network (NCLAN) program could still be usefully applied.
The crop risk assessment, like the tree seedling assessment, combined NCLAN C-R information
on commodity crops, fruits and vegetables, crop growing regions, and interpolated exposures
during each crop growing season. The risk assessment estimated that just meeting the 0.08 ppm,
8-hr standard would still allow Os-related yield loss to occur in some sensitive commodity crops
and fruit and vegetable species growing at that time in the U.S.
6.2.3 Benefits Assessment
The Staff Paper also presented estimates of monetized benefits for crops associated with
the then current and alternative standards. The Agriculture Simulation Model (AGSEVI) (Taylor,
1994; Taylor, 1993) was used to calculate annual average changes in total undiscounted
economic surplus for commodity crops and fruits and vegetables when then current and
alternative standard levels were met. Meeting the various alternative standards did show some
significant benefits beyond the 0.08 ppm, 8-hr standard. However, the Staff Paper recognized
that the modeled economic benefits from AGSEVI had many associated uncertainties which
limited the usefulness of these estimates.
TREGRO is a process-based, individual tree growth simulation model (Weinstein et al, 1991) that is linked with
concurrent climate data to account for Os and climate/meteorology interactions on tree growth. TREGRO has been
used to evaluate the effects of a variety of O^ scenarios on several species of trees in different regions of the U.S.
(Tingey et al., 2001; Weinstein et al., 1991; Retzlaff et al., 2000; Laurence et al., 1993; Laurence et al., 2001;
Weinstein et al., 2005).
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6.3 AIR QUALITY CONSIDERATIONS
Air quality analyses are necessary to inform and support welfare-related exposure, risk,
and benefits assessments. The air quality analyses being considered for this review would build
upon those of the ISA and would include consideration of: (1) summaries of recent ambient air
quality data, (2) estimation approaches to extrapolate air quality values for rural areas without
monitors as well as federally designated Class I natural areas important to welfare effects
assessment, (3) estimates of PRB concentrations, (4) air quality simulation procedures that
modify recent air quality data to reflect changes in the distribution of air quality estimated to
occur at some unspecified time in the future when an area just meets a given set of NAAQS. In
this review, air quality analyses would support quantitative exposure and risk assessments that
may be considered in light of the new scientific information available for specific locations, as
well as at regional and national scales.
In addition to updating air quality summaries since the last review, these air quality
analyses may include summaries of the most currently available ambient measurements for the
current 8-hr average standard form, the cumulative concentration-weighted W126 form, and
comparisons of these two types of forms. Such air quality analyses would use monitor data from
the AQS data base (which includes National Park Service monitors) and the CASTNET network.
In addition, staff may explore the suitability of using other sources of 63 concentration
information that might be available, such as from portable monitors or satellites.
In the last review, the vegetation exposure analysis used a spatial interpolation technique
to create an interpolated air quality surface to fill in the gaps in ambient monitoring data,
especially those left by a sparse rural monitoring network in the western United States. In this
review, additional approaches that potentially could be used to fill in the gaps in the rural
monitoring network, as well as opportunities for enhancing the fusion of monitoring and
modeled O^ data, may be explored.
Estimates of the risks in excess of PRB remaining upon meeting the current or potential
alternative standards require EPA to estimate PRB. As noted above in sections 4.2 and 5.3, EPA
will be evaluating alternative definitions of PRB and the implications of those definitions for
estimates of risk. This type of risk estimate is considered relevant to inform the EPA
Administrator's decision on the adequacy of a given standard. The current approach to
estimating 63 PRB for use in conducting the welfare risk assessment is the same as that outlined
in section 5.3 above.
As part of the air quality analyses that would support any exposure, risk and benefits
assessments that may be conducted, it would be necessary to adjust recent 63 air quality data to
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simulate just meeting the current standard and any alternative Os standards. In the last review,
EPA used a quadratic air quality rollback approach (U.S. EPA, 2007a, section 4.5.8). Staff may
consider alternative air quality simulation procedures for use in this current review as previously
characterized in section 5.3.
6.4 EXPOSURE ASSESSMENT APPROACH
Since the last review, little has changed in terms of the extent of monitoring coverage in
non-urban areas. We are planning to consider both past and alternative approaches for
generating estimates of national Os exposures in an effort to continue enhancing our ability to
characterize exposures in these non-monitored areas. It is expected that any vegetation exposure
assessments that may be conducted will again include assessments of recent air quality, air
quality associated with just meeting the current standard and any alternative standards that might
be considered.
In addition, given the importance of providing protection for sensitive vegetation in areas
afforded special protections, such as in federally designated Class I natural areas, we may also
consider alternative sources of 63 exposure information for those types of sites. For example,
portable 63 monitors are being deployed in some national parks and a current exploratory study
is underway to measure Os concentration variations with gradients in elevation. Information
from these monitors could potentially inform our understanding of uncertainties associated with
assessing Os distribution patterns in complex terrain and high elevations.
6.5 RISK ASSESSMENT APPROACH
Since the last review, new scientific information on the direct and indirect effects of Os on
vegetation and ecosystems, respectively, has become available. With respect to mature trees and
forests, the information regarding Os impacts to forest ecosystems has continued to expand,
including limited new evidence that implicates Os as an indirect contributor to decreases in
stream flow through direct impacts on whole tree level water use. Long-term FACE (Free Air
CO2 enrichment) studies are continuing to provide additional evidence regarding chronic Os
exposures in closed forest canopy scenarios including interspecies interactions such as decreased
growth of branches and root mass in sensitive species. Also, lichen and moss communities on
trees monitored in FACE sites have been shown to undergo species shifts when exposed to Os.
In addition, it is expected that as in the previous review, recent available data from annual field
surveys conducted by the USFS to assess foliar damage to selected tree species will again be
available. In light of this new scientific information, we will consider whether additional
analyses are warranted, such as combining the USFS data with recent county level air quality
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data to determine the incidence of visible 63 damage occurring across the U.S. at air quality
levels that meet or are below the current standard, as was done in the last review. To the extent
warranted, based on new information regarding O^ effects on forest trees, both qualitative and
quantitative assessments may be considered in an effort to place both the estimates of risk from
more recent long-term studies and historic shorter-term studies in the context of Essential
Services.
Additional information relevant to both tree and crop risk assessments expected to be
available includes that regarding the interactions between elevated O^ and CC>2 with respect to
plant growth and how these interactions might be expected to be modified under different
climatic conditions, and potential reactions of Os with chemicals released by plants to attract
pollinators that could decrease the distance the floral "scent trail" travels and potentially
changing the distance pollinators have to travel to find flowers. To the extent warranted, staff
also plans to consider any available information regarding potential risks to threatened or
endangered species.
6.6 BENEFIT ASSESSMENT APPROACH
To the extent warranted, qualitative and/or quantitative benefits assessments of ecosystem
services impacted by O^ will be considered to inform the current review. For example, benefits
assessments in this review may include tree biomass and crop analyses, and when possible, may
include impacts on ecosystem services such as impacts on biodiversity, biological community
composition, health of forest ecosystems, aesthetic values of trees and plants and the nutritive
quality of forage crops. The impact of 63 on limiting potential CC>2 sequestration is another
important ecosystem services. New preliminary evidence of Os effects on the ability of
pollinators to find their target is also of special interest with respect to the possible implication
for benefits assessment of ecosystem service. Impairment of the ability of pollinators to locate
flowers could have broad implications for agriculture, horticulture and forestry.
A new benefits model, the Forest and Agricultural Sector Optimization Model (FASOM),
is being considered for this assessment. This model jointly assesses the economic impacts of Os
damage to forests and agricultural crops. FASOM is a dynamic, non-linear programming model
designed for use by the EPA to evaluate welfare and market effects of carbon sequestration in
trees, understory, forest floor, wood products and landfills that would occur under different
agricultural and forestry scenarios. It may be possible to use FASOM to model damage by Os to
the agriculture and forestry sectors and quantify how Os-exposed vegetation impacts the
ecosystem service of carbon sequestration.
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A conclusion in the last review was that the science continued to support the use of an
exposure index that reflects the effects of cumulative, seasonal Os exposures on plants. In light
of new information on exposures, risks, non-plant effects, and ecosystem services, we will
consider whether additional analyses are warranted to evaluate the relative risks associated with
alternative cumulative, seasonal forms. In addition, we plan to consider the impact of using
different length diurnal windows (e.g., 12, 16 or 24 hrs), different seasonal periods (e.g., 3, 5, or
7 months), and annual vs. three-year averages.
6.7 UNCERTAINTY AND VARIABILITY
For exposure, risk and benefits assessments that are being considered for this review, staff is
considering a similar approach to that used in the previous review to characterize uncertainty and
variability associated with these assessments. In addition, we are considering the feasibility of
conducting additional analyses to better characterize the uncertainties and variability associated with
these assessments.
Many of the sources of uncertainty and variability that were present in the last assessments are
expected to remain in this review. In particular, uncertainties associated with the use of various
models such as CMAQ and FASOM would be characterized and where possible, sensitivity analyses
performed to test the impact of various assumptions imbedded in the models. The uncertainty
associated with the monitor probe height is expected to remain due to lack of definitive information
becoming available. Where information exists, staff plans to consider the impact of using different
adjustment factors. As in the last review, every effort will be made to provide information on the
uncertainties and variability associated with whatever exposure and risk assessments may be
conducted. Uncertainties associated with empirical evidence due to exposure or research methods
would be described.
6.8 SCIENTIFIC AND PUBLIC REVIEW
A Scope and Methods Plan for the vegetation and other welfare-related assessments will
be submitted to CASAC for consultation and will be provided to the public for comment. The
CASAC Os Review Panel will discuss their comments on the Scope and Methods Plan in a
public meeting that will be announced in the Federal Register. In conducting the welfare-related
assessments, staff will take into account comments received from CASAC and from the public at
the meeting itself and in any written comments. Staff plans to prepare two drafts of the
vegetation and other welfare-related assessments for CASAC review and public comment. The
CASAC Os Review Panel will review each draft welfare-related assessment and discuss their
comments in two public meetings to be announced in the Federal Register. Based on CASAC's
past practice, we anticipate that key CASAC advice and recommendations for revision of the
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draft risk/exposure assessment will be presented in letters to the EPA Administrator. Staff will
also consider comments received from CASAC or from the public at the meetings themselves
and any written public comments. In finalizing the vegetation and welfare-related assessments,
we will take into account any such comments and recommendations. After appropriate revision,
the final welfare-related assessment document will be made publicly available on an EPA
website and in hard copy. A notice announcing the availability of the final document will be
published in the Federal Register. In addition, the final welfare-related assessment document
will be placed in the rulemaking docket.
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7 POLICY ASSESSMENT/RULEMAKING
7.1 POLICY ASSESSMENT
The Policy Assessment (PA), like the previous OAQPS Staff Paper, is a document that
provides a transparent OAQPS staff analysis and staff conclusions regarding the adequacy of the
current standards and potential alternatives that are appropriate to consider prior to the issuance
of proposed and final rules. The PA integrates and interprets the information from the ISA and
REA(s) to frame policy options for consideration by the Administrator. The PA is also intended
to facilitate CASAC's advice to the Agency and recommendations to the Administrator on the
adequacy of the existing standards or revisions that may be appropriate to consider, as provided
for in the Clean Air Act. Staff conclusions will be based on the information contained in the
ISA, and, as available, the REAs, and any additional staff evaluations and assessments discussed
in the PA. In so doing, the discussion in the PA will be framed by consideration of a series of
the policy-relevant questions drawn from those outlined in chapter 3, including the fundamental
questions associated with the adequacy of the current standards and, as appropriate,
consideration of alternative standards in terms of the specific elements of the standards:
indicator, averaging time, level, and form.
The PA will identify conceptual evidence-based and risk/exposure-based approaches for
reaching public health and welfare policy judgments. It will discuss the implications of the
science and quantitative assessments for the adequacy of the current standards, and for any
alternative standards under consideration. The PA will also describe a broad range of policy
options for standard setting, identifying the broadest range for which the staff identifies support
within the available information. In so doing, the PA will describe the underlying interpretations
of the scientific evidence and risk/exposure information that might support such alternative
policy options that could be considered by the Administrator in making decisions for the Os
standards.
In identifying a range of primary standard options for the Administrator to consider, it is
recognized that the final decision will be largely a public health policy judgment. A final
decision must draw upon scientific information and analyses about health effects and risks, as
well as judgments about how to deal with the range of uncertainties that are inherent in the
scientific evidence and analyses. Staffs approach to informing these judgments is based on a
recognition that the available health effects evidence generally reflects a continuum consisting of
ambient levels 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
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uncertain. This approach is consistent with the requirements of the NAAQS provisions of the
Act and with how EPA and the courts have historically interpreted the Act. These provisions
require the Administrator to establish primary standards that are requisite to protect public health
and are neither more nor less stringent than necessary for this purpose. The provisions do not
require that primary standards be set at a zero-risk level, but rather at a level that avoids
unacceptable risks to public health, including the health of susceptible populations.16
In identifying a range of secondary standard options for the Administrator to consider,
staff recognizes that the final decision will be largely a public policy judgment. A final decision
must draw upon scientific evidence and analyses about effects on public welfare, as well as
judgments about how to deal with the range of uncertainties that are inherent in the relevant
information. This approach is consistent with the requirements of the NAAQS provisions of the
Act and with how EPA and the courts have historically interpreted the Act. These provisions
require the Administrator to establish secondary standards that are requisite to protect public
welfare from any known or anticipated adverse effects associated with the presence of the
pollutant in the ambient air. In so doing, the Administrator seeks to establish standards that are
neither more nor less stringent than necessary for this purpose. The provisions do not require
that secondary standards be set to eliminate all welfare effects, but rather at a level that protects
public welfare from those effects that are judged to be adverse.
Staff will prepare at least one draft of the PA document for CAS AC review and public
comment. The draft PA document will be distributed to the CASAC Oi Review Panel for their
consideration and provided to the public for review and comment. Review by the CASAC Os
Review Panel will be discussed at public meetings that will be announced in the Federal
Register. Based on past practice by CASAC, EPA expects that key advice and recommendations
for revision of the document would be summarized by the CASAC in a letter to the EPA
Administrator. In revising the draft PA document, OAQPS will take into account any such
recommendations, and also consider comments received, from CASAC and from the public, at
the meeting itself, and any written comments received. The final document will be made
available on an EPA website, with its public availability announced in the Federal Register.
16 The susceptible populations identified in a NAAQS review may be comprised of low income or minority groups.
Where low income/minority groups are among the susceptible populations, the rulemaking decision will be based on
providing protection for these and other susceptible populations. To the extent that low income/minority groups are
not among the susceptible populations, a decision based on providing protection of the susceptible populations
would be expected to provide protection for the low income/minority groups (as well as any other less sensitive
population groups).
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7.2 RULEMAKING
Following issuance of the final PA and EPA management consideration of staff analyses
and conclusions presented therein, and taking into consideration CASAC advice and
recommendations, the Agency will develop a notice of proposed rulemaking. The proposed
rulemaking notice conveys the Administrator's proposed conclusions regarding the adequacy of
the current standards and any revision that may be appropriate. A draft notice of proposed
rulemaking will be submitted to the Office of Management and Budget (OMB) for interagency
review, in which OMB and other federal agencies are provided the opportunity for review and
comment. After the completion of interagency review, EPA will publish the notice of proposed
rulemaking in the Federal Register. Monitoring rule changes associated with review of the Os
standards, and drawing from considerations outlined in chapter 8 below, will be developed and
proposed, as appropriate, in conjunction with this NAAQS rulemaking.
At the time of publication of the notice of proposed rulemaking, all materials on which the
proposal is based are made available in the public docket for the rulemaking.1? Publication of
the proposal notice is followed by a public comment period, generally lasting 60 to 90 days,
during which the public is invited to submit comments on the proposal to the rulemaking docket.
Taking into account comments received on the proposed rule, the Agency will then develop a
notice of final rulemaking, which again undergoes OMB-coordinated interagency review prior to
issuance by EPA of the final rule. In the notice of final rulemaking, and generally also through
the use of an accompanying document, the Agency responds to all significant comments on the
proposed rule. Publication of the final rule in the Federal Register completes the rulemaking
process.
17 The rulemaking docket for the current Oj review is identified as EPA-HQ-OAR-2008-0699. This docket has
incorporated the ISA docket (EPA-HQ-ORD-2011-0050) by reference. Both dockets are publicly accessible at
www.regulations. gov.
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8 AMBIENT AIR MONITORING
8.1 OVERVIEW
The 63 monitoring network provides data to meet a wide variety of objectives. They
include ensuring the public has access to clean air by comparing data to the NAAQS, providing
the public with reports and forecasts of their exposure to 63 through the Air Quality Index,
providing input to health and welfare studies utilized as part of the NAAQS review process,
evaluating the performance of regional air quality models used in developing emission strategies,
tracking trends in air pollution abatement control measures impact on improving air quality, and
supporting research studies on atmospheric chemistry and transport or O?,.
To meet these multiple objectives, national 03 sites are deployed in a variety of locations
to determine the following information: highest concentrations in an area, typical concentrations
in areas of high population density, the impacts of significant sources or source categories on Os
precursors and formation processes, general background concentration levels, the extent of
regional pollutant transport among populated areas, assessment impacts on visibility, vegetation
damage, or other welfare-based effects.
Federal rules that regulate ambient air monitoring programs are found in 40 CFR Parts 50,
53 and 58. During the last review completed in 2008, EPA followed a complementary process in
which changes to monitoring regulations that were required to support the revised NAAQS were
proposed in a separate rulemaking.18 During this review, EPA intends to include any monitoring
rule changes as part of the NAAQS rule, potentially reducing the time necessary to institute
monitoring changes that might be required by a decision to revise the NAAQS.
8.2 CURRENT O3 NETWORK STATUS
Presently, states and local air quality management agencies operate minimum numbers of
EPA-approved 03 monitors based on the population of each of their Metropolitan Statistical
Area (MSA) and the most recently measured 63 levels for each area. Currently, there are 369
MS As in the U.S. subject to minimum Os monitoring requirements. In these areas, a total of
392 monitors are required to meet the minimum requirements. In actuality, 992 monitors were in
operation during 2005 to 2007 representing these MSAs. This monitor count indicates the
typical practice of operating more than the minimum required number of monitors to support the
1 8
The proposed rule, Ambient Ozone Monitoring Regulations: Revisions to Network Design Requirements, was
published on July 16, 2009 (74 FR 34525).
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basic monitoring objectives described above. In addition, state and local agencies operated 55
monitors during 2005 to 2007 in MSAs that were not required to have monitors.
Many of these Os monitors that were operated in excess of minimum requirements were
sited to characterize the Os concentrations in metropolitan areas and in downwind areas that were
potentially impacted by transport from MSAs. As noted in the current monitoring regulations
described in Part 58, Os minimum requirements do not account for the full breadth of additional
factors that would be considered in designing a complete 63 monitoring program for an area.
Some of these additional factors include geographic size, population density, complexity of
terrain and meteorology, presence of nearby 63 monitoring sites operated by adjacent State
programs, air pollution transport from neighboring areas, and measured air quality in comparison
to all forms of the 63 NAAQS (i.e., 8-hr and 1-hr forms). States and EPA Regional
Administrators work together to design and/or maintain the most appropriate 63 network to
service the variety of data needs in an area. The results of these negotiations are documented in
annual monitoring network plans that are made available for public inspection and then approved
by the EPA Regional Administrator, and the 63 monitoring requirements in approved plans
become the basis for state Os monitoring requirements for the 1-year period following plan
approval.
Although there are currently no EPA requirements for Os monitoring other than in or
adjacent to MSAs , there are at present about 200 state-operated 03 monitors in counties that are
not part of MSAs, and these monitors can be categorized in several ways. States commonly
locate Os monitors both upwind and downwind of major urban areas to evaluate the spatial
gradient or extent of transported 63 pollution and the lag time typically associated with
photochemical production. In some cases, these 63 monitors are located in non-urban or rural
areas within MSAs or physically outside the MSA boundary if the expected location of
maximum downwind Os concentration is outside the MSA.
As part of the Clean Air Status and Trends Network (CASTNET), the EPA operates 57
Os monitors, and the National Park Service (NPS) operates 23 monitors across the eastern and
western U.S. The NPS also operates additional Os monitors independent of CASTNET stations.
CASTNET Os monitors operate year-round and are primarily located in rural areas; siting
criteria require distances of at least 40 kilometers from cities of greater than 50,000 population as
well as other separation requirements from air pollution sources.
Taking into account both state and EPA/NPS-operated non-urban Os monitors, an
analysis of the distribution of these monitors indicates a relatively uniform spatial density in the
eastern one-third of the U.S. and in California, with significant gaps in coverage elsewhere
across the country. Virtually all states east of the Mississippi River have at least two to four non-
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urban Os monitors, while many large mid-western and western states have one or no non-urban
monitors.
Section 182(c)(l) of the Clean Air Act required EPA to promulgate rules requiring
enhanced monitoring of 63, NO, and VOC in 63 nonattainment areas classified as serious,
severe, or extreme. On February 12, 1993, EPA promulgated requirements for State and local
monitoring agencies to establish Photochemical Assessment Monitoring Stations (PAMS) as part
of their SIP monitoring networks in 63 nonattainment areas classified as serious, severe, or
extreme. Design criteria for the PAMS network are based on locations relative to 03 precursor
source areas and predominant wind directions associated with high 63 events. Specific
monitoring objectives are associated with each location. The overall design supports the
characterization of precursor emission sources within an area, transport of O^ and its precursors,
and the photochemical processes related to 63 nonattainment. EPA reduced PAMS requirements
as part of the October 17, 2006 rulemaking. Current requirements include site-specific
measurements for speciated VOC, carbonyls, NOx, NOy, CO, Os, surface meteorology, and
upper air meteorology.
Unlike the ambient monitoring requirements for other criteria pollutants that mandate
year-round monitoring, Oj, monitoring is currently only required during the seasons of the year
that are conducive to Os formation. These seasons vary in length from place to place as the
conditions that determine the likely O?, formation (i.e., seasonally-dependent factors such as
ambient temperature, strength of solar insolation, and length of day) differ by location. In some
locations, conditions conducive to Os formation are limited to a few summer months of the year.
For example, in states with colder climates such as Montana and South Dakota, the currently
required Oj monitoring season has a length of 4 months. However, in other states with warmer
climates such as California, Nevada, and Arizona, the currently required Os monitoring season
for most sites continues all 12 months of the year.
8.3 MONITORING ISSUES RELATED TO THE O3 NAAQS
This new review of the Os NAAQS will explore a number of policy-relevant issues
associated with measuring and characterizing O?, levels in ambient air. The EPA will draw upon
the information presented in the ISA to inform the evaluation of appropriate ambient monitoring
methods and network design for Os, including consideration of the available information on
probe and siting criteria that could best support the current or alternative standards.
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8.3.1 Monitoring Methods
The nation's 63 monitoring data currently being reported to AQS are obtained
exclusively with ultraviolet (UV) absorption spectrometry based methods. These methods are
approved Federal Equivalent Methods (FEMs) per 40 CFR Part 53; a number of commercial
manufacturers supply such FEM instruments for use in the national network. The use of the
Federal Reference Method (FRM) in ambient monitoring (a chemiluminescence-based method)
has become basically non-existent with the adoption of FEMs. States utilize calibration and
quality assurance procedures that relate their own calibrators to a network of Standard Reference
Photometers (SRPs) that are maintained and operated by EPA.
Previous reviews of the Os NAAQS have considered the implications of interferences in
the response of UV and chemiluminescence-based instruments due the effects of water vapor,
VOC's, aromatic compounds and their oxidation products, and other organic and inorganic
compounds.
Issues that will be considered in this review to inform the selection of monitoring
methods are reflected in the following questions:
• To what extent is new information available to judge the adequacy of the current
methodologies that are approved by EPA for use in judging compliance with the 63
NAAQS and meeting other objectives?
• Has new information become available that supports the need for alternative
methodologies to supplement the currently approved FRM and FEM's?
• What other technologies (e.g., portable monitors, passive or personal sampling) might
be appropriate to consider where methods do not have to be EPA-approved, such as
in the support of ecosystem or epidemiologic studies?
8.3.2 Network Design
Monitoring sites must represent ambient air (i.e., that portion of the atmosphere, external
to buildings, to which the general public has access). The minimum number of required
monitors for Os is stated in 40 CFR Part 58, Appendix D, Network Design Criteria for Ambient
Air Quality Monitoring. The EPA negotiates with States to determine the total number of
monitors needed to represent an area's air quality. It should be noted that although monitors are
often sited with the intention to represent an area of a certain geographic scale, in general, a
monitor need not be representative of the ambient air quality across an area of any specific size
to be eligible for comparison to most NAAQS.
Network design issues that will be considered in this review are reflected in the following
questions:
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• Are revisions to urban Os monitoring requirements necessary to improve
characterization of Os concentrations in metropolitan areas? If so, what specific
changes are needed?
• Are there situations where fewer monitors could be utilized in urban areas without
increasing the uncertainty surrounding data analysis? If so, what criteria should be
considered when monitors are evaluated for potential termination or relocation?
• Are revisions to non-urban Oi monitoring requirements necessary to improve
characterization of 63 concentrations outside of metropolitan areas? If so, what
specific objectives should be considered in any proposed changes to these
requirements?
• What new information is available to inform network design options and technologies
that are utilized in the P AMS network? What specific changes, if any, should be
considered in PAMS requirements?
• OT, monitoring sites are typically located to meet very specific probe and monitor
siting criteria described in 40 CFR Part 58, Appendix E (e.g., acceptable probe
height). Are there situations where a different set of monitor placement criteria
would be appropriate to consider depending on the specific objective being
characterized? For example, would a different set of probe height criteria be
appropriate for monitors deployed in ecosystems with Os-sensitive vegetation versus
monitors deployed in cities forNAAQS compliance objectives? What changes, if
any, should be considered?
• Is the length of the currently required 63 monitoring seasons adequate to characterize
concentrations in urban and non-urban areas? What changes, if any, should be
considered?
8.3.3 Data Reporting and Assessments
The data interpretation of the primary and secondary NAAQS appendix describes the
computations necessary for determining when the primary and secondary standards are met. The
appendix addresses in detail, data completeness requirements, data reporting and handling
conventions, the form of the standard, averaging times, and provides examples. As part of this
review, the data interpretation appendix may need further revisions to ensure that EPA is
providing the best protection of public health and welfare. This review will provide the
opportunity to take advantage of the insights and newer concepts that have arisen in the recent
review of other NAAQS pollutants.
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United States Office of Air Quality Planning and Standards Publication No. EP A-452/R-11 -006
Environmental Protection Health & Environmental Impacts Division April 2011
Agency Research Triangle Park, NC
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