EPA
United States
Environmental
Protection Agency
Integrated Review Plan for
the Ozone National Ambient
Air Quality Standards
Review
External Review Draft
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 draft 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 draft plan may
be modified in the final plan to reflect input received during an upcoming consultation with the
Clean Air Scientific Advisory Committee (CASAC) and public comments. Further
modifications to the plan may result from information developed during this review of the Oj
NAAQS and to address advice and comments received from CASAC 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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EPA452/D-09-001
September 2009
Integrated Review Plan for the Ozone
National Ambient Air Quality
Standards Review
External Review Draft
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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i TABLE OF CONTENTS
2 1 INTRODUCTION. 1
3 1.1 LEGISLATIVE REQUIREMENTS 2
4 1.2 OVERVIEW OF THE NAAQS REVIEW PROCESS 4
5 1.3 HISTORY OF O3 NAAQS REVIEWS 6
6 1.4 RECONSIDERATION OF THE 2008 OZONE NAAQS 10
7 2 STATUS AND SCHEDULE FOR NEW REVIEW 13
8 3 KEY POLICY-RELEVANT ISSUES 15
9 3.1 ISSUES RELATED TO THE PRIMARY OZONE NAAQS 15
10 3.2 ISSUES RELATED TO THE SECONDARY OZONE NAAQS 17
11 4 SCIENCE ASSESSMENT 20
12 4.1 SCOPE AND ORGANIZATION 20
13 4.2 ASSESSMENT APPROACH 21
14 4.3 SCIENTIFIC AND PUBLIC REVIEW 34
15 5 HUMAN HEALTH RISK AND EXPOSURE ASSESSMENTS 36
16 5.1 OVERVIEW 36
17 5.2 EXPOSURE AND HEALTH RISK ASSESSMENTS FROM RULEMAKING COMPLETED IN MARCH
18 2008 37
19 5.3 AIR QUALITY CONSIDERATIONS 39
20 5.4 POPULATION EXPOSURE ASSESSMENT APPROACH 41
21 5.5 HUMAN HEALTH RISK ASSESSMENTS 43
22 5.5.1 Approach to Health Risk Assessment Based On Epidemiologic Studies 44
23 5.5.2 Approach to Health Risk Assessment Based on Controlled Human Exposure Studies 45
24 5.5.3 Uncertainty and Variability 46
25 5.5.4 Broader Risk Characterization 46
26 5.6 SCIENTIFIC AND PUBLIC REVIEW 47
27 6 VEGETATION AND OTHER WELFARE-RELATED ASSESSMENTS 49
28 6.1 OVERVIEW 49
29 6.2 EXPOSURE, RISK, AND BENEFITS ASSESSMENTS FROM RULEMAKING COMPLETED IN
30 MARCH 2008 49
31 6.2.1 Exposure Assessment 50
32 6.2.2 Risk Assessment 52
33 6.2.3 Benefits Assessment 54
34 6.3 AIR QUALITY CONSIDERATIONS 54
35 6.4 EXPOSURE ASSESSMENT APPROACH 55
36 6.5 RISK ASSESSMENT APPROACH 56
37 6.6 BENEFIT ASSESSMENT APPROACH 57
38 6.7 UNCERTAINTY AND VARIABILITY 58
39 6.8 SCIENTIFIC AND PUBLIC REVIEW 58
40 7 POLICY ASSESSMENT/RULEMAKING 60
41 8 AMBIENT AIR MONITORING 61
42 8.1 OVERVIEW 61
43 8.2 CURRENT O3 NETWORK STATUS 61
44 8.3 MONITORING ISSUES RELATED TO THE O3 NAAQS 64
45 9 REFERENCES 67
46
11
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Ill
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i 1 INTRODUCTION
2
3 The U.S. Environmental Protection Agency (EPA) last completed a rulemaking on the
4 primary (health-based) and secondary (welfare-based) national ambient air quality standards
5 (NAAQS) for ozone (63) in March 2008 (73 FR 16436), resulting in revisions to both standards.
6 In May 2008, states, environmental groups and industry groups filed petitions with the D.C.
7 Circuit Court of Appeals for review of the 2008 ozone standards. In March 2009, the court
8 granted EPA's request to stay the litigation so the new administration could review the standards
9 and determine whether they should be reconsidered. On September 16, 2009, the Administrator
10 announced her decision to reconsider the 2008 primary and secondary ozone standards to ensure
11 they are scientifically sound and protective of public health and the environment as required by
12 the Clean Air Act (CAA). Prior to the decision to reconsider the 2008 O3 standards, EPA had
13 initiated a new periodic review of the existing air quality criteria and standards for Os in
14 September 2008.
15 This draft Integrative Review Plan (IRP) contains the plans for the new periodic review
16 of the air quality criteria for Os-related effects on public health and public welfare and the
17 current 63 standards or any revised standards that may result from the reconsideration of the
18 2008 63 standards. This draft IRP is being released for the purpose of consulting with the Clean
19 Air Scientific Advisory Committee (CAS AC) of EPA's Science Advisory Board1 and obtaining
20 public comment on the Agency's plans. The final IRP will be informed by comments received
21 from the CAS AC and the public.
22 This draft IRP is organized into eight chapters. Chapter 1 presents the legislative
23 requirements for the review of the NAAQS, an overview of the NAAQS review process, a
24 history of past reviews of the O?, NAAQS, and the Agency's plans to reconsider the 2008 O?,
25 NAAQS. Chapters 2 through 8 outline the Agency's plans for the new periodic review of the
26 existing air quality criteria and the 63 standards that result from the reconsideration of the 2008
27 standards. Chapter 2 presents the status and schedule for the new review. Chapter 3 presents a
28 set of policy-relevant questions that will serve to focus the new review on the critical scientific
1 For purposes of this review, the 7-member CAS AC has been supplemented by additional scientific experts
collectively referred to as the CASAC O3 NAAQS Review Panel.
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1 and policy issues. Chapters 4 through 6 discuss the planned scope and organization of the key
2 assessment documents, the planned approaches for preparing the documents, and plans for
3 scientific and public review of the documents for the new review. Chapter 7 summarizes the
4 policy assessment and rulemaking process for the new Os NAAQS review. Finally, chapter 8
5 discusses the current ambient air monitoring network and monitoring issues related to the 63
6 NAAQS.
7 1.1 LEGISLATIVE REQUIREMENTS
8 Two sections of the Clean Air Act (CAA) govern the establishment and revision of the
9 NAAQS. Section 108 (42 U.S.C. 7408) directs the Administrator to identify and list "air
10 pollutants" that meet three criteria, and to issue air quality criteria for those that are listed. 42
11 U.S.C. § 7408(a),(b). Air quality criteria are intended to "accurately reflect the latest scientific
12 knowledge useful in indicating the kind and extent of identifiable effects on public health or
13 welfare which may be expected from the presence of [a] pollutant in ambient air ... ." 42
14 U.S.C. § 7408(b).
15 Section 109 (42 U.S.C. 7409) directs the Administrator to propose and promulgate
16 "primary" and "secondary" NAAQS for pollutants for which air quality criteria have been
17 issued. 42 U.S.C. § 7409 (a). Section 109(b) (1) defines a primary standard as one "the
18 attainment and maintenance of which in the judgment of the Administrator, based on such
19 criteria and allowing an adequate margin of safety, are requisite to protect the public health."2 42
20 U.S.C. § 7409(b)(l). A secondary standard, as defined in section 109(b)(2), must "specify a
21 level of air quality the attainment and maintenance of which, in the judgment of the
22 Administrator, based on such criteria, is required to protect the public welfare from any known
23 or anticipated adverse effects associated with the presence of [the] pollutant in the ambient air."3
24 42 U.S.C. §7409(b)(2).
2 The legislative history of section 109 indicates that a primary standard is to be set at "the maximum permissible
ambient air level.. . which will protect the health of any [sensitive] group of the population," and that for this
purpose "reference should be made to a representative sample of persons comprising the sensitive group rather than
to a single person in such a group" [S. Rep. No. 91-1196, 91st Cong., 2d Sess. 10 (1970)].
3 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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1 The requirement that primary standards include an adequate margin of safety was
2 intended to address uncertainties associated with inconclusive scientific and technical
3 information available at the time of standard setting. It was also intended to provide a reasonable
4 degree of protection against hazards that research has not yet identified. See Lead Industries
5 Association v. EPA, 647 F.2d 1130, 1154 (D.C. Cir 1980), cert, denied, 449 U.S. 1042 (1980);
6 American Petroleum Institute v. Costle, 665 F.2d 1176, 1186 (D.C. Cir. 1981), cert, denied, 455
7 U.S. 1034(1982). Both kinds of uncertainties are components of the risk associated with
8 pollution at levels below those at which human health effects can be said to occur with
9 reasonable scientific certainty. Thus, in selecting primary standards that include an adequate
10 margin of safety, the Administrator is seeking not only to prevent pollution levels that have been
11 demonstrated to be harmful but also to prevent lower pollutant levels that may pose an
12 unacceptable risk of harm, even if the risk is not precisely identified as to nature or degree.
13 In selecting a margin of safety, the EPA considers such factors as the nature and severity
14 of the health effects involved, the size of the sensitive population(s) at risk, and the kind and
15 degree of the uncertainties that must be addressed. The selection of any particular approach to
16 providing an adequate margin of safety is a policy choice left specifically to the Administrator's
17 judgment. See Lead Industries Association v. EPA, supra, 647 F.2d at 1161-62.
18 In setting standards that are "requisite" to protect public health and welfare, as provided in
19 section 109(b), EPA's task is to establish standards that are neither more nor less stringent than
20 necessary. In so doing, EPA may not consider the costs of implementing the standards. See
21 generally Whitman v. American Trucking Associations, 531 U.S. 457, 465-472, 475-76 (2001).
22 Section 109(d)(l) requires that "not later than December 31, 1980, and at 5-year
23 intervals thereafter, the Administrator shall complete a thorough review of the criteria
24 published under section 108 and the national ambient air quality standards . . . and shall make
25 such revisions in such criteria and standards and promulgate such new standards as may be
26 appropriate . . . ." 42 U.S.C. § 7409(d)(l). Section 109(d)(2) requires that an independent
27 scientific review committee "shall complete a review of the criteria . . . and the national primary
28 and secondary ambient air quality standards . . . and shall recommend to the Administrator any
29 new . . . standards and revisions of existing criteria and standards as may be appropriate
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1 42 U.S.C. § 7409(d)(2). Since the early 1980's, this independent review function has been
2 performed by CAS AC.
3 1.2 OVERVIEW OF THE NAAQS REVIEW PROCESS
4 Since completion of the last O3 NAAQS review, the Agency has made a number of
5 changes to the process for reviewing the NAAQS.4 In making these changes, the Agency
6 considered the advice of CASAC and the public. As described below, this revised process
7 contains four major components: planning, science assessment, risk/exposure assessment, and
8 policy assessment/rulemaking.
9 The planning phase of the review process begins with a "kick-off workshop to get input
10 from CASAC, internal and external experts, and the public regarding policy-relevant science
11 issues that have emerged since the last air quality criteria review. The workshop discussions
12 help inform the preparation of an IRP j ointly by staff from EPA's National Center fro
13 Environmental Assessment, Research Triangle Park, NC (NCEA-RTP) and EPA's Office of Air
14 Quality Planning and Standards (OAQPS). A draft IRP is presented for consultation with
15 CASAC and for public comment. A final IRP reflects CASAC and public comments together
16 with early guidance from Agency management. The IRP includes an outline of the process and
17 schedule that the entire review will follow, the science-policy questions that will frame the
18 review, and more complete descriptions of the purpose, contents, and approach for developing
19 each of the key documents in the review.
20 The science assessment phase involves the preparation of an Integrated Science
21 Assessment (ISA) by NCEA-RTP. The ISA provides a concise evaluation and integration of the
22 policy-relevant science, including key science judgments that are important to inform the design
23 and scope of the risk and exposure assessments. The ISA and its supporting annexes provide a
24 comprehensive assessment of the current scientific literature pertaining to known and anticipated
25 effects on public health and welfare associated with the presence of the pollutant in the ambient
26 air, emphasizing information that has become available since the last air quality criteria review.
27 The process generally includes production of a first and second draft ISA, both of which undergo
28 CASAC and public review prior to completion of the final ISA. Chapter 4 presents a description
4 See http://www.epa.gov/ttn/naaqs/ for more information.
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1 of the planned scope, organization, and assessment approach for the ISA to be prepared for this
2 review.
3 In the risk/exposure assessment phase, OAQPS staff draws upon information and
4 conclusions presented in the ISA to develop quantitative estimates of the risks/exposures for
5 health and/or welfare effects associated with current ambient levels of the pollutant, with levels
6 that just meet the current standards, and with levels that just meet potential alternative standards.
7 The Risk and Exposure Assessments (REAs) provide concise presentations of methods, key
8 results, observations, and related uncertainties. These assessments begin with the preparation of
9 a planning document that discusses the scope and methods planned for use in conducting the
10 quantitative assessments. Such Scope and Methods Plans are generally prepared in conjunction
11 with the first draft ISA and presented for consultation with CASAC and for public comment.
12 Comments received on the Scope and Methods Plans are considered in conducting the
13 assessments to be presented in the REAs. One or more drafts of each REA undergoes CASAC
14 and public review, with the initial draft REAs generally being reviewed in conjunction with
15 review of the second draft ISA, prior to completion of final REAs. Chapters 5 and 6 discuss
16 possible approaches being considered by OAQPS for conducting human health and welfare-
17 related assessments, respectively, for this review.
18 The review process ends with a policy assessment/rulemaking phase. Under recent
19 revisions to the NAAQS review process, the EPA Administrator has reinstated the use of a
20 Policy Assessment (PA), which is, like the previous OAQPS Staff Paper, a document that
21 provides a transparent staff analysis of the scientific basis for alternative policy options for
22 consideration by the Administrator prior to the issuance of proposed and final rules (Jackson,
23 2009). The PA integrates and interprets the information from the ISA and REAs to frame policy
24 options for consideration by the Administrator. One or more drafts of a PA is released for
25 CASAC review and public comment prior to completion of the final PA. The PA is intended to
26 facilitate CAS AC's advice and recommendations to the Administrator on any new standards or
27 revisions to existing standards as may be appropriate, as provided for in the CAA. Following
28 issuance of the final PA, the Agency publishes a proposed rule, followed by a public comment
29 period during which public hearings are held. Taking into account comments received on the
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1 proposed rule, the Agency issues a final rule to complete the rulemaking process. Chapter 7
2 discusses the development of the PA and the rulemaking steps for this review.
3 1.3 HISTORY OF O3 NAAQS REVIEWS
4 Tropospheric (ground-level) O3 is the indicator for the mix of photochemical oxidants
5 formed from biogenic and anthropogenic precursor emissions. Naturally occurring Os in the
6 troposphere can result from biogenic organic precursors reacting with naturally occurring
7 nitrogen oxides (NOX) and by stratospheric Os intrusion into the troposphere. Anthropogenic
8 precursors of C>3; especially NOX and volatile organic compounds (VOCs), originate from a wide
9 variety of stationary and mobile sources. Ambient 63 concentrations produced by these
10 emissions are directly affected by temperature, solar radiation, wind speed, and other
11 meteorological factors.
12 NAAQS are comprised of four basic elements: indicator, averaging time, level, and form.
13 The indicator defines the pollutant to be measured in the ambient air for the purpose of
14 determining compliance with the standard. The averaging time defines the time period over
15 which air quality measurements are to be obtained and averaged or cumulated, considering
16 evidence of effects associated with various time periods of exposure. The level of a standard
17 defines the air quality concentration used (i.e., an ambient concentration of the indicator
18 pollutant) in determining whether the standard is achieved. The form of the standard specifies
19 the air quality measurements that are to be used for compliance purposes (e.g., the annual fourth-
20 highest daily maximum 8-hr concentration, averaged over three years),, and whether the statistic
21 is to be averaged across multiple years. These four elements taken together determine the degree
22 of public health and welfare protection afforded by the NAAQS.
23 Table 1-1 summarizes the Os NAAQS that have been promulgated to date. In each
24 review, the secondary standard has been set to be identical to the primary standard. These
25 reviews are briefly described below.
26
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Table 1-1. Summary of Primary and Secondary National Ambient Air Quality
Standards Promulgated for Ozone During the Period 1971-2008
Final Rule
1971
(36 FR 8 186)
1979
(44 FR 8202)
1993
(58 FR 13008)
1997
(62 FR 38856)
2008
(73 FR 16483)
Indicator
Total
photochemical
oxidants
03
Ave. Time
1-hr
1-hr
Level (ppm)
0.08
0.12
Form
Mot to be exceeded more than
one hr per year
Attainment is defined when the
expected number of days per
calendar year, with maximum
lourly average concentration
greater than 0.12 ppm, is equal
o or less than 1
EPA decided that revisions to the standards were not warranted at the time.
03
03
8-hr
8-hr
L
0.08 i
i
I
0.075 i
c
\nnual fourth-highest daily
naximum 8-hr concentration,
iveraged over 3 years
"orm of the standards remained
unchanged relative to the 1997
>tandard
3 EPA first established primary and secondary NAAQS for photochemical oxidants in 1971
4 (36 FR 8186, April 30, 1971). Both primary and secondary standards were set at a level of 0.08
5 parts per million (ppm), 1-hr average, total photochemical oxidants, not to be exceeded more
6 than one hr per year. The standards were based on scientific information contained in the 1970
7 CD (U.S. DHEW, 1970).
8 In 1977, EPA announced the first periodic review of the 1970 CD (U.S DHEW, 1970) in
9 accordance with section 109(d)(l) of the Act. In 1978, EPA published a 1978 CD (U.S. EPA,
10 1978). Based on the 1978 CD, EPA published proposed revisions to the original NAAQS in
11 1978 (43 FR 16962) and final revisions in 1979 (44 FR 8202). The level of the primary and
12 secondary standards was revised from 0.08 to 0.12 ppm; the indicator was revised from
13 photochemical oxidants to O3; and the form of the standards was revised from a deterministic to
14 a statistical form, which defined attainment of the standards as occurring when the expected
15 number of days per calendar year with maximum hourly average concentration greater than 0.12
16 ppm is equal to or less than one.
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1 In 1982 (47 FR 11561), EPA announced plans to revise the 1978 CD (U.S. EPA, 1978).
2 In 1983, EPA announced (48 FR 38009) that the second periodic review of the primary and
3 secondary standards for Os had been initiated. EPA subsequently published the!986 CD (U.S.
4 EPA, 1986) and 1989 Staff Paper (U.S. EPA, 1989). Following publication of the 1986 CD
5 (U.S. EPA, 1986), a number of scientific abstracts and articles were published that appeared to
6 be of sufficient importance concerning potential health and welfare effects of 63 to warrant
7 preparation of a Supplement to the 1986 CD (U.S. EPA, 1992). Under the terms of a court order,
8 on August 10, 1992 (57 FR 35542) EPA published a proposed decision stating that revisions to
9 the existing primary and secondary standards were not appropriate at the time. The notice
10 explained (57 FR 35546 ) that the proposed decision would complete EPA's review of
11 information on health and welfare effects of Os assembled over a 7 year period and contained in
12 the 1986 CD (U.S. EPA, 1986) and its Supplement to the 1986 CD (U.S. EPA, 1992). The
13 proposal also announced EPA's intention to proceed as rapidly as possible with the next review
14 of the air quality criteria and standards for 63 in light of emerging evidence of health effects
15 related to 6- to 8-hr 63 exposures. On March 9, 1993, EPA concluded the review by deciding
16 that revisions to the standards were not warranted at that time (58 FR 13008).
17 In August 1992 (57 FR 35542), EPA announced plans to initiate the third periodic review
18 of the air quality criteria and Os NAAQS. On the basis of the scientific evidence contained in
19 the 1996 CD (U.S. EPA 1996a) and the 1996 Staff Paper (U.S. EPA, 1996b), and related
20 technical support documents, linking exposures to ambient Os to adverse health and welfare
21 effects at levels allowed by the then existing standards, EPA proposed to revise the primary and
22 secondary Os standards on December 13, 1996 (61 FR 65716). The EPA proposed to replace the
23 then existing 1-hr primary and secondary standards with 8-hr average Os standards set at a level
24 of 0.08 ppm (equivalent to 0.084 ppm using standard rounding conventions). The EPA also
25 proposed, in the alternative, to establish a new distinct secondary standard using a biologically
26 based cumulative seasonal form. The EPA completed the review on July 18, 1997 (62 FR
27 38856) by setting the primary standard at a level of 0.08 ppm, based on the annual fourth-highest
28 daily maximum 8-hr average concentration, averaged over three years, and setting the secondary
29 standard identical to the revised primary standard.
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1 On May 14, 1999, in response to challenges to EPA's 1997 decision by industry and
2 others, the U.S. Court of Appeals for the District of Columbia Circuit (D.C. Circuit Court)
3 remanded the 63 NAAQS to EPA, finding that section 109 of the Act, as interpreted by EPA,
4 effected an unconstitutional delegation of legislative authority. In addition, the D.C. Circuit
5 Court directed that, in responding to the remand, EPA should consider the potential beneficial
6 health effects of 63 pollution in shielding the public from the effects of solar ultraviolet (UV)
7 radiation, as well as adverse health effects. On January 27, 2000, EPA petitioned the U.S.
8 Supreme Court for certiorari on the constitutional issue (and two other issues) but did not request
9 review of the D.C. Circuit Court ruling regarding the potential beneficial health effects of O3.
10 On February 27, 2001, the U.S. Supreme Court unanimously reversed the judgment of the D.C.
11 Circuit Court on the constitutional issue, holding that section 109 of the CAA does not delegate
12 legislative power to the EPA in contravention of the Constitution, and remanded the case to the
13 D.C. Circuit Court to consider challenges to the O3 NAAQS that had not been addressed by that
14 Court's earlier decisions. On March 26, 2002, the D.C. Circuit Court issued its final decision,
15 finding the 1997 O3 NAAQS to be "neither arbitrary nor capricious," and denied the remaining
16 petitions for review. In response to the D.C. Circuit Court remand to consider the potential
17 beneficial health effects of O3 pollution in shielding the public from effects of solar (UV)
18 radiation, on November 14, 2001, EPA proposed to leave the 1997 8-hr NAAQS unchanged (66
19 FR 52768). After considering public comment on the proposed decision, EPA published its final
20 response to this remand on January 6, 2003, reaffirming the 8-hr O3 NAAQS set in 1997 (68 FR
21 614). Finally, on April 30, 2004, EPA announced the decision to make the 1-hr O3 NAAQS no
22 longer applicable to areas one year after the effective date of the designation of those areas for
23 the 8-hr NAAQS (69 FR 23966). For most areas, the date that the 1-hr NAAQS no longer
24 applied was June 15, 2005.
25 EPA initiated the next periodic review if the air quality criteria and O3 standards in
26 September 2000 with a call for information (65 FR 57810). The schedule for completion of that
27 rulemaking later became governed by a consent decree resolving a lawsuit filed in March 2003
28 by a group of plaintiffs representing national environmental and public health organizations.
29 Based on the CD (US EPA, 2006) published in March 2006 and the Staff Paper (U.S EPA, 2007)
30 and related technical support documents published in July 2007, the proposed decision was
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1 published in the Federal Register on July 11, 2007 (72 FR 37818). The EPA proposed to revise
2 the level of the primary standard to a level within the range of 0.075 to 0.070 ppm. Two options
3 were proposed for the secondary standard: (1) replacing the current standard with a cumulative,
4 seasonal standard, expressed as an index of the annual sum of weighted hourly concentrations
5 cumulated over 12 daylight hours during the consecutive 3-month period within the O3 season
6 with the maximum index value, set at a level within the range of 7 to 21 ppm-hrs, and (2) setting
7 the secondary standard identical to the revised primary standard. The EPA completed the
8 rulemaking with publication of a final decision on March 27, 2008 (73 FR 16436), revising the
9 level of the 8-hr primary O3 standard from 0.08 ppm to 0.075 ppm and revising the secondary
10 standard to be identical to the primary standard.
11 As discussed in the next section, on September 16, 2009 the EPA Administrator
12 announced her decision to reconsider the March 2008 decisions on revisions to the primary and
13 secondary O3 NAAQ S.
14 1.4 RECONSIDERATION OF THE 2008 OZONE NAAQS
15 In May 2008, state, public health, environmental, and industry petitioners filed suit
16 against EPA regarding that final decision, and on December 23, 2008, the Court set a briefing
17 schedule in the consolidated cases. On March 10, 2009, EPA requested that the Court vacate the
18 briefing schedule and hold the consolidated cases in abeyance. This request for extension was
19 made to allow time for appropriate EPA officials appointed by the new Administration to review
20 the O3 NAAQS to determine whether the standards established in the March 2008 O3 NAAQS
21 decision should be maintained, modified or otherwise reconsidered. In granting EPA's request,
22 the Court directed EPA to notify the Court by September 16, 2009 of the action it will be taking
23 with respect to the 2008 O3 NAAQS rule and the Agency's schedule for undertaking such action.
24 The EPA notified the Court on September 16, 2009 of its decision to reconsider the
25 primary and secondary O3 NAAQS set in March 2008 to ensure they are scientifically sound and
26 protective of public health and the environment.5 The EPA will base this reconsideration on the
27 scientific record from the 2008 rulemaking, including public comments and CASAC advice and
5 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 will propose 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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1 recommendations. During the 2008 review, CASAC unanimously recommended a more health
2 protective primary standard than was eventually set in 2008. The CASAC also recommended a
3 new cumulative, seasonal secondary standard, distinct from the primary standard, while the 2008
4 rule made the secondary standard identical to the primary standard. Following the 2008
5 decision, CASAC offered unsolicited advice that reiterated its previous recommendations and
6 urged the Agency to reconsider its advice in future action on the 63 standards. The EPA's notice
7 to the Court specifically stated that the Agency had concerns regarding whether the revisions to
8 the primary and secondary NAAQS adopted in the 2008 63 NAAQS rule satisfy the
9 requirements of the Clean Air Act.
10 The EPA plans to base the reconsideration of the 2008 Os NAAQS decision on the
11 scientific and technical information that was assessed during the 2008 rulemaking, including
12 information in the 2006 Air Quality Criteria Document (AQCD, U. S. EPA, 2006), the 2007
13 Policy Assessment of Scientific and Technical Information, referred to as the OAQPS Staff
14 Paper (U.S. EPA, 2007a), and related technical support documents including the 2007 REAs
15 (U.S. EPA, 2007b; Abt Associates, 2007a,b). Scientific and technical information developed
16 since the 2006 AQCD will be considered in the new review, not in the reconsideration
17 rulemaking, allowing the new information to receive careful and comprehensive review by
18 CASAC and the public before it is used as a basis in a rulemaking that determines whether to
19 revise the NAAQS. As in prior NAAQS rulemaking, EPA is also conducting a provisional
20 assessment of such "new" scientific information (published since review of the 2006 AQCD) to
21 consider whether that scientific literature would materially change the conclusions reached in the
22 2006 AQCD in conjunction with determining the appropriateness of proceeding with the
23 reconsideration rulemaking. The provisional assessment is subject to internal EPA peer review,
24 and the final provisional assessment will be made available to CASAC and the public at the time
25 of proposal. Consistent with EPA's approach in other NAAQS reviews, the Agency will not
26 base its decisions in the reconsideration on the new science but will instead review and consider
27 the new science in the new review covered by this integrated review plan.
28 Consistent with EPA's notice to the Court, this reconsideration of the 2008 63 NAAQS
29 rule will be conducted through notice and comment rulemaking, with a notice of proposed
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1 rulemaking to be signed by December 21, 2009. Following the issuance of a proposed rule, the
2 Agency will provide for a 60-day public comment period, hold public hearings, and solicit
3 CAS AC review of the proposed rule. Taking into consideration CAS AC and public comments
4 on the proposed rule, the final rule will be signed by August 31, 2010.
6 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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i 2 STATUS AND SCHEDULE FOR NEW REVIEW
2 . On September 29, 2008, the EPA's NCEA-RTP announced the initiation of a new
3 periodic review of the air quality criteria for Os and issued a call for information in the Federal
4 Register (73 FR 56581). A wide range of external experts as well as EPA staff, representing a
5 variety of areas of expertise (e.g., epidemiology, human and animal toxicology, statistics,
6 risk/exposure analysis, atmospheric science, ecology, biology, plant science, benefits analysis)
7 participated in a "kick-off workshop, held by EPA on October 28-29, 2008 in RTF, NC. The
8 proceedings of that workshop have been considered and the issues discussed at the workshop
9 have been incorporated into this draft IRP.
10 The development of this draft IRP was extended while the Agency reviewed the 2008 Os
11 NAAQS rule for the purpose of determining whether it would reconsider the 2008 standards, as
12 discussed above in section 1.4. We are releasing this draft IRP for the purpose of conducting a
13 public teleconference consultation with CAS AC, planned for November 2009, on the Agency's
14 plans for the continuation of this new review. The final IRP will reflect consideration of
15 comments received from CAS AC and the public in presenting plans for the new review of the air
16 quality criteria and standards for Os-related effects on public health and public welfare. This will
17 involve updating the assessments presented in the 2006 AQCD (U.S. EPA, 2006) and the 2007
18 Staff Paper (U.S. EPA, 2007a) and REAs (U.S. EPA, 2007b; Abt Associates, 2007a,b).
19 Recognizing that the reconsideration of the 2008 standards will be completed early in this new
20 review, before any draft assessment documents are released, this new review will involve
21 reviewing any O?, standards that may be set in the August 2010 final rule that results from the
22 reconsideration of the 2008 Os standards. While the Agency is reconsidering the 2008 Os
23 standards, NCEA-RTP will continue the development of the first draft ISA, planned for release
24 to CAS AC and the public in November 2010.
25 The schedule for the entire new review of the air quality criteria and standards is shown
26 below in Table 2-1. The scope of this review and of the key documents to be prepared during
27 this review, are discussed throughout the rest of this document.
28
29
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Table 2-1. Proposed Schedule for the New Periodic O3 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 2009
November 2009
December 2009
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
November 2010
February 2011
June 2011
September 2011
December 2011
Risk/Exposure
Assessments (REAs)
Prepare Draft Scope and Methods Plans
CASAC Consultation on Draft 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
January 2011
February 2011
July 2011
September 2011
March 2012
May 2012
September 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
August 2011
September 2011
April 2012
May 2012
October 2012
May 2013
February 2014
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i 3 KEY POLICY-RELEVANT ISSUES
2 The key policy-relevant issues to be addressed in this new review are presented below as a
3 series of policy-relevant questions that will frame our approach to determining whether the
4 primary and secondary NAAQS for Os that result from the Agency's reconsideration of the 2008
5 63 standards should be retained or revised. The ISA, REAs, and PA to be developed in this new
6 review will provide the basis for addressing these questions and will inform the Agency's
7 decisions as to whether to retain or revise those primary and secondary standards for 63.
8 3.1 ISSUES RELATED TO THE PRIMARY OZONE NAAQS
9 The first step in reviewing the adequacy of the primary Os standard is to consider whether
10 the available body of scientific evidence, assessed in the ISA and used as a basis for the analyses
11 presented in the public health-related REA, supports or calls into question the scientific
12 conclusions reached in the last rulemaking regarding health effects related to exposure to 63 in
13 ambient air. This evaluation of the available scientific evidence will focus on key policy -
14 relevant issues by addressing a series of questions including the following:
15 "To what extent has new scientific information become available that alters or
16 substantiates our understanding of the health effects associated with various time
17 periods of exposure to ambient 63, including short-term (1 to 3 hrs), prolonged (6 to 8
18 hrs), and chronic (months to years) exposures?
19 "To what extent has new scientific information become available that alters or
20 substantiates our understanding of the health effects of 63 on at-risk populations,
21 including those with increased susceptible and/or vulnerability? 7
22 • To what extent has new scientific information become available that alters or
23 substantiates conclusions from previous reviews regarding the plausibility of adverse
24 health effects caused by 63 exposure?
7 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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1 BAt what levels of Os exposure are health effects observed? Is there evidence of
2 effects at exposure levels lower than those previously observed, and what are the
3 important uncertainties associated with that evidence? What is the nature of the
4 exposure-response relationships of Os for the various health effects evaluated?
5 "To what extent has new scientific information become available that alters or
6 substantiates our understanding of non-Os-exposure factors that might influence the
7 associations between Os levels and health effects being considered (e.g., weather-
8 related factors; behavioral factors such as heating/air conditioning use; driving
9 patterns; and time-activity patterns)?
10 "To what extent do risk and/or exposure analyses suggest that exposures of concern for
11 Os-related health effects are likely to occur with current ambient levels of Os or with
12 levels that just meet the Os standard? Are these risks/exposures of sufficient
13 magnitude such that the health effects might reasonably be judged to be important
14 from a public health perspective? What are the important uncertainties associated
15 with these risk/exposure estimates?
16 "To what extent have important uncertainties identified in the last rulemaking been
17 addressed and/or have new uncertainties emerged?
18
19 Drawing upon the evidence and analyses presented in the ISA and REA, EPA will
20 evaluate whether revisions to the primary 63 standard might be appropriate, and, if so, how this
21 standard might be revised. Specifically, EPA will evaluate how the scientific information and
22 assessments inform decisions regarding the basic elements of the NAAQS: indicator, averaging
23 time, level, and form. These elements will be considered collectively in evaluating the health
24 protection afforded by the current or any alternative standards considered. Specific policy-
25 relevant questions that will be addressed include:
26 • To what extent is there any new information that would support consideration of a
27 different indicator for photochemical oxidants?
28 • To what extent do the health effects evidence evaluated in the ISA, air quality
29 analyses, and the REA provide support for considering different averaging times?
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1 'To what extent do air quality analyses and other information provide support for
2 consideration of alternative forms?
3 • What range of alternative standard levels should be considered based on the scientific
4 evidence evaluated in the ISA, air quality analyses, and the REA?
5 "In considering alternative standards, to what extent do alternative levels, averaging
6 times and forms reduce estimated exposures and risks of concern attributable to 63
7 and other photochemical oxidants, and what are the uncertainties associated with the
8 estimated exposure and risk reductions?
9 • What are the important uncertainties and limitations in the evidence and assessments
10 and how might those uncertainties and limitations be taken into consideration in
11 identifying alternative standards for consideration?
12
13 3.2 ISSUES RELATED TO THE SECONDARY OZONE NAAQS
14 The first step in reviewing the adequacy of the secondary Os standard is to consider
15 whether the available body of scientific evidence, assessed in the ISA and used as a basis for the
16 analyses presented in the public welfare-related REA, supports or calls into question the
17 scientific conclusions reached in the last rulemaking regarding welfare effects related to
18 exposure to O3 in ambient air. This evaluation of the available scientific evidence will focus on
19 key policy-relevant issues by addressing a series of questions including the following::
20 • To what extent has new scientific information become available that alters or
21 substantiates our understanding of the effects on vegetation and other welfare effects
22 following exposures to levels of Oj found in the ambient air?
23 • To what extent has new scientific information become available to inform our
24 understanding of the nature of the exposures that are associated with such effects in
25 terms of biologically relevant cumulative, seasonal exposure indices?
26 • To what extent has new scientific information become available that alters or
27 substantiates our understanding of the effects of 63 on sensitive plant species,
28 ecological receptors, or ecosystem processes?
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1 'To what extent has new scientific information become available that alters or
2 substantiates our understanding of exposure factors other than Os that might influence
3 the associations between Os levels and welfare effects being considered (e.g., site
4 specific features such as elevation, soil moisture level, presence of co-occurring
5 competitors, pests, pathogens, other pollutant stressors, weather-related factors)?
6 "To what extent has new scientific information become available that alters or
7 substantiates conclusions regarding the occurrence of adverse welfare effects at levels
8 of Os as low as or lower than those observed previously? What is the nature of the
9 exposure-response relationships of Os for the various welfare effects evaluated?
10 • Given recognition in the last rulemaking that the significance of Os-induced effects to
11 the public welfare depends in part on the intended use of the plants or ecosystems on
12 which those effects occurred, to what extent has new scientific evidence become
13 available to suggest additional locations where the vulnerability of sensitive species
14 or ecosystems would have special significance to the public welfare and should be
15 given increased focus in this review?
16 "To what extent do risk and/or exposure analyses suggest that exposures of concern for
17 Os-related welfare effects are likely to occur with current ambient levels of Os or with
18 levels that just meet the 63 standard? Are these risks/exposures of sufficient
19 magnitude such that the welfare effects might reasonably be judged to be important
20 from a public welfare perspective? What are the important uncertainties associated
21 with these risk/exposure estimates?
22 • To what extent have important uncertainties identified in the last rulemaking been
23 addressed and/or have new uncertainties emerged?
24
25 Drawing upon the information and assessments presented in the ISA and REA, EPA
26 will evaluate whether revisions to the secondary Os standard might be appropriate, and, if
27 so, how this standard might be revised. Specifically, EPA will evaluate how the scientific
28 information and assessments inform decisions regarding the basic elements of the NAAQS:
29 indicator, averaging time, level, and form. These elements will be considered collectively in
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1 evaluating the welfare protection afforded by the current or any alternative standards
2 considered. Specific policy-relevant questions that will be addressed include:
3 "To what extent is there any new information that would support consideration of a
4 different indicator for photochemical oxidants?
5 "To what extent do the welfare effects evidence evaluated in the ISA, air quality
6 analyses, and the REA provide support for considering different averaging times and
7 forms that reflect biologically relevant exposure indices?
8 • What range of alternative standard levels should be considered based on the scientific
9 information evaluated in the ISA, air quality analyses, and the REA?
10 "In considering alternative standards, to what extent do alternative levels, averaging
11 times, and forms reduce estimated exposures and risks of concern attributable to Os
12 and other photochemical oxidants, and what are the uncertainties associated with the
13 estimated exposure and risk reductions?
14 • What are the important uncertainties and limitations in the evidence and assessments
15 and how might those uncertainties and limitations be taken into consideration in
16 identifying alternative standards for consideration?
17
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4 SCIENCE ASSESSMENT
2 4.1 SCOPE AND ORGANIZATION
3 As noted in chapter 1, the Integrated Science Assessment (ISA) is a concise review,
4 synthesis, and evaluation of the most policy-relevant science that communicates critical science
5 judgments relevant to the NAAQS review. The current ISA serves to update and revise the
6 scientific information available at the time of the last review of the air quality criteria. As such,
7 the ISA forms the scientific foundation for the new review of the primary (health-based) and
8 secondary (welfare-based) NAAQS. A general outline of the types of information that are
9 considered is provided in the illustration below. The judgments and conclusions drawn in the
10 ISA are intended to support risk, exposure and policy analyses as well as decisions to retain or
11 revise the NAAQS.
12
13
14
15
16
17
18
19
HEALTH EFFECTS
Effects on the health of the general
population, or identifiable groups
within the population, who are exposed
to pollutants in ambient air
Effects on mortality
Effects on morbidity
Effects on other health outcomes
WELFARE EFFECTS
Effects on the environment, including:
• animals
• climate
• crops
• materials
• soils
• vegetation
• visibility
• water
• weather
• wildlife
Effects on economic values
Effects on personal comfort
Deterioration of property
Source: Adapted from U.S. EPA (2001)
The science assessment will consist of an ISA and supporting annexes 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
Os and related photochemical oxidants in ambient air. The annexes are intended to provide
additional technical details of pertinent studies that may or may not otherwise be noted within
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1 the ISA. These documents will not provide a detailed literature review; but, rather, will discuss
2 the current state of knowledge on the most relevant scientific literature on issues pertinent to the
3 review of the NAAQS for Os. Discussions in the ISA will primarily focus on scientific
4 evaluations that can inform the key policy questions described in chapter 3 of this document.
5 Although emphasis is placed on discussion of health and welfare effects information, other
6 scientific data are presented and evaluated in order to provide a better understanding of the
7 nature, sources, measurement, and concentration distribution of 63 and related photochemical
8 oxidants in ambient air, as well as the measurement of population exposure to these pollutants.
9 The ISA will build on the conclusions of the 2006 CD (U.S. EPA, 2006) and focus on
10 peer reviewed literature published since the previous review of the air quality criteria for Os.
11 The 2006 CD (U.S. EPA, 2006) primarily evaluated literature published through December
12 2004. Major legal and historical aspects of prior review documents as well as key milestones
13 and procedures for document preparation will be briefly summarized at the beginning of the ISA.
14 In subsequent chapters the results of recent scientific studies will be integrated with previous
15 findings. Important older studies will be more specifically discussed if they are open to
16 reinterpretation in light of newer data and/or to reinforce key concepts and conclusions.
17 Emphasis will be placed on studies conducted at or near O3 concentrations found in ambient air.
18 Other studies are included if they contain unique data, such as a previously unreported effect or
19 mechanism for an observed effect, or examine multiple concentrations to elucidate exposure-
20 response relationships.
21 4.2 ASSESSMENT APPROACH
22 Introduction
23 The EPA's National Center for Environmental Assessment in Research Triangle Park
24 (NCEA-RTP) is responsible for preparing the ISA and its annexes for Os. Expert authors include
25 EPA staff with extensive knowledge in their respective fields and extramural scientists solicited
26 by EPA for their expertise in specific fields. A diagram showing the standard protocol for
27 development of an ISA is shown in Figure 4.1. A description of the recently revised NAAQS
28 process is addressed in section 1.2.
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1 Literature Search
2 The NCEA-RTP will use a systematic approach to identify relevant studies for
3 consideration. The EPA has already published a Federal Register notice (73 FR 56581,
4 September 29, 2008) to announce the initiation of this review and request information from the
5 public. In addition to the call for information, publications will be identified through an ongoing
6 literature search process that includes extensive computer database mining on specific topics.
7 Additional publications will be identified by EPA scientists in a variety of disciplines by
8 combing through relevant, peer reviewed scientific literature obtained through these ongoing
9 literature searches, reviewing previous EPA reports, and a review of reference lists from key
10 publications; studies are also identified in the course of CASAC and public review.
11 Relevant epidemiologic, human clinical, and animal toxicological studies, including those
12 related to exposure response relationships, mode(s) of action (MOA), susceptible or vulnerable
13 subpopulations, and ecological or welfare effects studies published since the last air quality
14 criteria review will be considered. Additionally, air quality and emissions data, studies on
15 atmospheric chemistry, transport, and fate of these emissions, as well as issues related to Os
16 exposure are considered. Further information will be acquired from consultation with content
17 and area experts and the public. The studies identified will include research published or
18 accepted for publication by a date determined to be as inclusive as possible given the relevant
19 target dates in the 63 NAAQS review schedule. Some additional studies, published after that
20 date, may also be included if they provide new information that impacts one or more key
21 scientific issues. The combination of these approaches should produce the comprehensive
22 collection of pertinent studies needed to form the basis of the ISA.
23
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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
of literature (ongoing)
Draft Integrated
Review Plan
CAS AC consultation
and public re view
I
Final Integrated
Review Plan
First External
Review Draft ISA
CASAC and public review
Second External
Review Draft ISA
CASAC and public review
Y
Final ISA
Federal Register
Call for Information
Workshop on
science/policy issues
Science and policy
issues from previous
NAAQSreview
Figure 4.1 Standard steps in the development of Integrated Science Assessments (ISAs)
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1 Criteria for Study Selection
2 In selecting epidemiologic studies for the present assessment, EPA will consider studies
3 containing information on (1) short- or long-term exposures at or near ambient levels of O3; (2)
4 health endpoints that repeat or extend findings from earlier assessments as well as those not
5 previously extensively researched; (3) populations that are susceptible and/or vulnerable to Os
6 exposures; (4) issues related to potential confounding, and modification of effects; and/or (5)
7 important methodological issues (e.g., lag of effects, model specifications, thresholds, mortality
8 displacement) related to 63 exposure effects. Among the epidemiologic studies, emphasis will
9 be focused on those relevant to standard setting in the United States. Specifically, studies
10 conducted in the U.S. or Canada will be generally accorded more emphasis than those from other
11 geographic regions, as the potential impacts of different health care systems and the underlying
12 health status of populations need to be accounted for in the assessment. However, informative
13 studies conducted in other countries will be included, as appropriate. In addition, emphasis will
14 be placed on discussion of (1) new, multi-city studies that employ standardized methodological
15 analyses for evaluating Os effects, provide overall estimates for effects based on combined
16 analyses of information pooled across cities, and examine results for consistency across cities;
17 (2) new studies that provide quantitative effect estimates for populations of interest; and (3)
18 studies that evaluate 63 as a component of a complex mixture of air pollutants and thus give
19 consideration to the levels of other co-pollutants.
20 The selection of research evaluating controlled exposures of laboratory animals will focus
21 primarily on those studies conducted at or near ambient Os concentrations and those studies that
22 approximate expected human dose conditions in terms of concentration and duration, which will
23 depend on the toxicokinetics and biological sensitivity of the particular laboratory animals
24 examined. Studies will be sought that reveal site-specific effects of Os exposure within the
25 respiratory tract. Consideration will be given mainly to animal studies conducted at less than 1
26 ppm 63. The necessity of such upper concentrations limits may be illustrated by rats, a key
27 species used in 63 toxicological studies, but a species having both behavioral and physiological
28 mechanisms that can lower core temperature in response to acute exposures, thus limiting
29 extrapolation of data to human responses. However, in recognition of the fact that toxicological
30 studies using near ambient concentrations of Os or other pollutants do not necessarily reflect
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1 effects in the most sensitive populations, studies at higher exposure levels may be included when
2 they provide information relevant to previously unreported effects, evidence of potential
3 mechanisms for an observed effect, information on exposure-response relationships, or otherwise
4 improve our understanding of interspecies differences or susceptible populations. Additionally,
5 in vitro studies may provide information on related to mechanisms of 63 uptake and effect or the
6 influence of photochemical oxidation processes that would otherwise be unavailable through in
7 vivo studies. The appropriateness of 63 concentrations will be evaluated as necessary.
8 For research evaluating controlled human exposures to 63, emphasis will be placed on
9 studies that: (1) investigate effects in healthy populations and/or potentially susceptible
10 populations such as those with preexisting respiratory diseases; (2) include appropriate control
11 (or sham) exposures such as filtered air so that subjects serve as their own control as well as the
12 use of age-matched healthy controls in studies of susceptible individuals; (3) address issues such
13 as dose-response or time-course of responses; (4) investigate exposure to Os separately and in
14 combination with other pollutants such as PM and NO2; and (5) have sufficient sample size and
15 statistical power to assess findings adequately. Due to the limited amount of recently published
16 controlled human exposure studies, much of the available scientific information is expected to
17 come from literature that has been included in prior reviews. This older literature will be
18 reevaluated and discussed in light of more recent epidemiologic findings and mechanistic
19 toxicological data, as well as new controlled human exposure studies.
20 For evaluation of welfare effects research, emphasis shall be placed on recent studies that:
21 (1) evaluate effects at realistic ambient levels and (2) investigate effects on cultivated and non-
22 cultivated vegetation and ecosystems that occur in the U.S. Studies conducted in other
23 geographical areas will be included in the assessment when they contribute to the general
24 knowledge of the effects of 63 irrespective of species or locality. As in the evaluation of health-
25 related scientific studies, the evaluation of welfare-related studies will assess advances in our
26 understanding of mechanisms of direct Os effects on vegetation and the resulting consequences
27 on growth and yield, principally. Effects on larger scale ecosystem structure, function and
28 services will also be considered. These and other welfare effects will be addressed in the ISA for
29 both short- and long-term O?, exposures. Evaluations of research methodologies will be
30 integrated into the discussion to allow for comparisons between methodologies and to allow
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1 characterization of the uncertainties associated with estimating exposure of vegetation using
2 different types of experimental systems.
3 These criteria provide generalized benchmarks for evaluating various studies and for
4 focusing on the highest quality studies in assessing the body of health and welfare effects
5 evidence. Detailed critical analysis of all 63 health and welfare effects studies, especially in
6 relation to the above considerations, is beyond the scope of this document. Of most relevance
7 for evaluation of studies is whether they provide useful qualitative or quantitative information on
8 exposure-effect or exposure-response relationships for effects associated with current ambient air
9 concentrations of O3 likely to be encountered in the United States. Since the last scientific
10 review was completed relatively recently, i.e., within the past four years, it is expected that a
11 considerable portion of the current ISA could reasonably be devoted to reiterating the basis for
12 scientific conclusions reached in last rulemaking.
13 Quality Assurance
14 Important quality assurance measures will be incorporated from the start of the current 63
15 review. EPA uses scientific information found in peer-reviewed journal articles, books, and
16 government reports. The approaches utilized to search the literature and criteria for study
17 selection were detailed in the two preceding subsections. Additionally, NCEA has Data Quality
18 Objectives which identify inputs to the science assessment and provide quality assurance (QA)
19 instruction for researchers citing secondary information.
20 Content and Organization of the ISA
21 The organization of the ISA for Os will be consistent with that used in the second external
22 review draft ISA for particulate matter (U.S. EPA, 2009a). The ISA will contain information
23 relevant to considering whether it is appropriate to retain or revise the current standards. Taking
24 into consideration the broad policy-relevant questions outlined in chapter 3, the policy-relevant
25 questions that will guide development of the ISA are related to two overarching issues. The first
26 issue is the extent to which new scientific evidence has become available that alters or
27 substantiates the scientific evidence presented and evaluated in the last 63 NAAQS review. The
28 second issue is whether uncertainties from the last air quality criteria review have been addressed
29 and/or whether new uncertainties have emerged. Specific questions related to the review of the
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1 scientific literature for Os that stem from these issues will guide the content of the ISA. These
2 questions were derived from the last Os NAAQS rulemaking, as well as from discussions of new
3 scientific evidence that occurred at the EPA kickoff workshop (October 29-30, 2008) for this
4 review of Os and related photochemical oxidants. These questions are listed below by topic area.
5 Source to Exposure
6 Air Quality and Atmospheric Science: The ISA will present and evaluate data related to:
7 ambient concentration distributions of O3, and its potential associations with other photochemical
8 oxidants and with other relevant atmospheric pollutants. New information concerning the
9 mechanisms of formation Os and other photochemical oxidants and the physical properties
10 governing their transport and lifetimes in the atmosphere will be considered. The ISA will assess
11 the appropriateness and utility of using Os as the chemical indicator of the broad range of
12 atmospheric oxidants for which this NAAQS is defined by evaluating relevant data concerning
13 the origin, transformation and transport, and fate of atmospheric oxidants in addition to 63. The
14 assessment will also include information about the distribution of monitors in the regulatory 63
15 network relevant for the interpretation of health and ecosystem effects and new studies dealing
16 with the precision and accuracy of the Federal Reference and Federal Equivalent Methods (FRM
17 and FEM, respectively) for Os. New information on the distribution of ambient Os
18 concentrations from in situ instruments, satellites, and other remote sensing tools will also be
19 considered. Since a key issue for the Risk and Exposure Assessments (REAs) will be the
20 distribution of the policy-relevant background (PRB)8 concentration of Oj, in the U.S., the ISA
21 will include an assessment of methods for producing these concentrations and will provide
22 estimates of 63 PRB concentrations for possible use in the REAs. Because the secondary
23 standard includes treatment of 63 effects on climate, the ISA will include evaluation of data
24 relevant to the issue of tropospheric O3 as a constituent greenhouse gas and its effects as an
25 absorber of UV-B radiation in the troposphere.
8 "Policy-relevant background" has been defined 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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1 Exposure: The ISA will compile and evaluate information new since the last assessment that
2 helps characterize the variability and uncertainty in the relationships between ambient Os
3 concentrations and exposures to Os of humans and ecosystems relevant to the primary and
4 secondary standards. Regarding the primary standard for human health, this means assessing
5 data concerning the range of measured Os concentrations in various human microenvironments
6 including indoors, outdoors near roadways, in vehicles, etc. and its relationship with
7 concentrations measured by ambient monitors. EPA will also assess data concerning errors in
8 measurement or estimation of human exposures as well as the possibly differential exposures of
9 some subpopulations.
10 Human Health Effects
11 The ISA will evaluate the literature related to respiratory, cardiovascular, and other health
12 effects associated with short and/or long term exposures to Os. Building upon the last air quality
13 criteria review, EPA plans to continue to review the available scientific evidence related to these
14 health endpoints and to integrate the previous findings with the results of new studies on these
15 health endpoints and, to the extent data are available, on additional endpoints of concern (e.g.,
16 developmental, inflammatory, carcinogenic/mutagenic, and cellular outcomes). Health effects
17 that occur following short- (including sub-daily) and/or long-term exposures to O3 will be
18 evaluated in epidemiologic, human clinical, and toxicological studies. The ISA will also
19 integrate previous information on sensitive subpopulations (e.g., asthmatics, children, outdoor
20 workers) with new evidence for these and possibly other sensitive subpopulations (e.g., fetuses,
21 neonates, genetically susceptible populations).
22 For a given type of health outcome, the ISA will evaluate the strength, robustness and
23 consistency of the findings from the different disciplines. The health findings will be further
24 integrated, using the toxicological and human clinical studies to assess biological plausibility and
25 mechanistic evidence for the epidemiologic findings. Efforts will be directed at identifying the
26 lower levels at which effects are observed and at determining concentration-response
27 relationships. Concentration-response relationships among these studies will be evaluated for
28 coherence. The ISA will evaluate the scientific evidence on the occurrence of health effects
29 from short-term or long-term exposure to O3 at ambient levels. The ISA will also assess the
30 evidence for uncertainties related to these associations and information on the public health
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1 implications related to ambient Os exposure. The evaluation will also focus on which exposure
2 durations and developmental time periods of exposure are most strongly associated with effects,
3 for both short-term and long-term exposures. Grouped by topic area, some of the scientific
4 questions that EPA will seek to address in the ISA follow.
5 Health Effects from Exposure: The ISA will evaluate health effects evidence for a multitude of
6 outcomes from epidemiologic, lexicological, and human clinical studies.
7 • How do results of recent studies expand our understanding of the relationship
8 between short-term exposure to Os and respiratory effects, such as lung function
9 changes, airways hyperresponsiveness, lung inflammation, and host defense against
10 infectious disease? What new evidence is available on the potential clinical relevance
11 of these effects? Do recent studies expand the current understanding of adaptation to
12 repeated short-term 63 exposures?
13 • Do long-term exposures to Os result in chronic effects manifested as permanent lung
14 tissue damage, altered lung development, or accelerated decline in lung function with
15 age? To what extent does long-term 63 exposure promote development of asthma or
16 chronic lung or cardiovascular disease?
17 • Does new evidence from studies of hospital admissions or emergency department
18 visits support previous findings regarding respiratory or cardiovascular effects of 63?
19 Is there evidence of coherence and plausibility for such effects?
20 • What new evidence is available on associations between Os and mortality (total,
21 respiratory or cardiovascular)?
22 • To what extent is key evidence becoming available that could inform the
23 understanding of subpopulations that are particularly susceptible to Os exposures?
24 What is known about genetic traits that underlie susceptibility? Are new animal
25 models becoming available to better characterize sensitive subpopulations?
26 • What Os-induced health effects are sufficiently characterized to be quantitatively
27 compared across species?
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1 'To what extent does exposure to Os contribute to health effects in other organ
2 systems?
3 • What new evidence has become available to help discern health effects of
4 multipollutant exposures (containing O3) versus O3 alone (e.g., additive, synergistic,
5 or antagonistic effects)?
6 Uncertainties: The ISA will evaluate uncertainty in the scientific data, particularly in relation to
7 observed epidemiologic findings and their consistency with toxicological and controlled human
8 exposure studies in terms of observed effects and biological pathways.
9 • How do meteorological factors and co-exposure to other criteria pollutants (e.g., PM,
10 NC>2, SC>2, and CO) influence the uncertainty of the evidence base for both short- and
11 long-term 63 exposures?
12 • To what extent are the observed health effects attributable to Os versus other oxidants
13 that are associated with Os?
14 • What are the uncertainties due to other factors in epidemiologic studies (e.g.,
15 demographic and lifestyle attributes, socioeconomic status, genetic susceptibility
16 factors, occupational exposure, and medical care)?
17 • What is the nature and shape of the concentration-response models (e.g., linear, non-
18 linear, threshold models) based on Os studies?
19 • What uncertainties surround the evidence for long-term effects such as life shortening
20 and development/progression of disease?
21 • How do the findings of the available studies improve our understanding of exposure
22 error? What evidence is newly available on the uncertainties related to statistical
23 model specification and how can it be used to assess the influence of these
24 uncertainties on the outcome of epidemiologic studies?
25 Biological Mechanism(s) or Modes of Action: The ISA will evaluate the data examining
26 mechanisms for the health outcomes associated with exposure to 63.
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1 'Is there new information related to the pathways and underlying biological
2 mechanism(s) or modes of action for Os?
3 • What are the inherent interspecies differences in sensitivity to 63 and in 63 dosimetry
4 in different regions of the respiratory tract? Are there site-specific responses to O3 in
5 the respiratory tract that would better explain local and systemic effects of Os
6 exposure?
7 • What are the interspecies differences in basic mechanisms of lung injury and repair
8 and cardiovascular responses? What are the implications of interspecies differences
9 for extrapolation of results to humans?
10 • What are the mechanisms and time-courses of (Vinduced cellular and tissue injury,
11 repair, and remodeling?
12 Susceptible and Vulnerable Populations: The ISA will examine health outcome data to identify
13 specific groups that are more susceptible and/or vulnerable to the adverse effects of Os exposure
14 than normal healthy adults (e.g., patients with COPD, children, and asthmatics). The host and
15 environmental factors that are responsible for differential susceptibility to 63 will be
16 investigated.
17 • What do controlled human exposure, animal lexicological, and epidemiologic studies
18 indicate regarding the relationship between acute exposures to 63 and health effects
19 of concern in healthy individuals and those with preexisting diseases (e.g., asthma,
20 COPD, cardiovascular diseases)? What other medical conditions (e.g., diabetes,
21 metabolic syndrome) are identified as increasing susceptibility to O3 effects? What
22 are the pathways and mechanisms through which Os may be acting for these groups?
23 What is the nature and time-course of the development of effects in healthy persons
24 and in persons with pre-existing disease (e.g., asthma, heart disease)?
25 • Are children and older adults are more sensitive than the general population to effects
26 from Os exposure? With regard to the interpretation of epidemiologic results and
27 exposure-response characteristics of populations, to what extent are these findings
28 driven by effects in sensitive subpopulations?
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1 • What evidence is available regarding susceptibility to Os-induced responses in
2 subgroups due to age, race, gender, or genetic makeup? To what extent is
3 susceptibility to the effects of short-term Os exposure is associated with long-term Os
4 susceptibility?
5 • What factors (e.g., demographic and socioeconomic) affect vulnerability to short- and
6 long-term Os exposures? Are there new data regarding population groups with
7 potentially greater vulnerability to effects of Os?
8 Public Health Implications: The ISA will present concepts to define potential health outcomes
9 and their implications on public health. This will include estimates of the numbers of people in
10 specific at-risk populations groups (e.g., asthmatics, diabetics, older adults, and children).
11 Causality: EPA will assess the results of recent relevant publications, building upon evidence
12 available during the previous NAAQS review, to draw conclusions on the causal relationships
13 between health effects and O3 exposures. The EPA has developed a framework that provides a
14 consistent and transparent basis to evaluate the causal nature of air pollution-induced health or
15 environmental effects (for a detailed discussion see chapter 1 of U.S. EPA, 2009a).
16 Considerations that are expected to play a larger role in determination of causality are
17 consistency of results across studies, coherence of effects observed in different study types or
18 disciplines, biological plausibility, and exposure-response relationships. The ISA will place
19 emphasis on health studies conducted at or near typical ambient levels, except those providing
20 evidence of biological plausibility and mechanisms, as these may only be observable in animal
21 or human exposure study populations at higher levels than they might be observed in susceptible
22 human populations.
23 Vegetation, Ecosystems and other Welfare Effects
24 The ISA will evaluate the literature related to O3 exposures on the growth of vegetation,
25 visible foliar injury, ecosystem services and other welfare effects. This will include evaluation
26 of O3 exposures on productivity of ecosystems and crops systems and potential effects on
27 services such as CC>2 sequestration. Other effects that will be evaluated include 63 effects on
28 materials. Grouped by topic area, some scientific questions that EPA will seek to address in the
29 ISA follow.
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1 Vegetation: Scientific studies have previously reported concentration response functions for the
2 relationship between Os exposure and plant response for a range of endpoints. The ISA will
3 consider key uncertainties identified in the last air quality criteria review and the extent to which
4 new scientific evidence may be available to substantially inform our ability to characterize
5 and/or reduce these uncertainties.
6 • Past reviews have highlighted evidence from Os exposure experiments performed in
7 open-top chambers (OTCs). More recent studies have also utilized other techniques
8 such as Free-air exposures (FACE) and gradient studies. In what ways does the more
9 recent literature inform our understanding of Os exposure on vegetation? For
10 example, topics may include: comparing OTC results to other studies and differences
11 between small and large trees.
12 • Though there is a large, historic body of research on Os effects on vegetation, there
13 has been no common metric used across studies to describe the relationship between
14 63 exposures and plant response. How can 63 studies which use various 63 metrics,
15 plant species and methodologies be appropriately quantitatively synthesized and
16 assessed?
17 Ecosystem Services: Some recent research has examined further how Os effects are potentially
18 linked to ecosystem services. Such linked ecosystem services identified in recent studies include
19 water supply and quality, N-cycling, bee pollination, and CC>2 sequestration.
20 • What is the nature of the information linking Os pollution and ecosystem services?
21 What are the existing studies that make direct or indirect linkages between Os
22 exposure and ecosystem services? How can studies at smaller scales be used to
23 address ecosystem services issues?
24 • Can information available in the older literature be re-examined in light of these
25 broader linkages?
26 • What new information is available on potential effects of Os on CC>2 sequestration in
27 ecosystems?
28 • How does 63 influence the biodiversity of ecological systems?
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1 • Has Os altered nutritional content of forage for domestic animals or wildlife
2 populations?
3 Materials Damage: Ozone and other photochemical oxidants react with many economically
4 important man-made materials, decreasing their useful life and aesthetic appearance. Materials
5 damaged by Os include elastomers; textiles and fibers; dyes, pigments, and inks; and paints and
6 other surface coatings. The new scientific literature will be evaluated in this area to determine the
7 extent to which new scientific evidence may inform the standard.
8 Annex Materials
9 The ISA will be supplemented by a series of annexes. The annexes are intended to
10 provide additional technical details of pertinent studies that may or may not otherwise be noted
11 within the ISA. These materials will not provide a detailed literature review; but, rather,
12 summarize the most relevant scientific literature on issues pertinent to the review of the NAAQS
13 for Os. The annexes will provide supplementary information on (1) the chemistry, physics,
14 sources, emissions, and measurement of Os; (2) environmental concentrations and human
15 exposure to Os; (3) dosimetry; (4) toxicological studies of Os health effects in laboratory animals
16 and in vitro systems; (5) human clinical studies examining health effects following controlled
17 exposure to Os; (6) epidemiologic studies of health effects from short- and long-term exposure to
18 Os; (7) environmental studies on material damage and ecosystem stress; and (8) climate change
19 related to Os. More detailed information on various methods and results for the health and
20 environmental studies will be summarized in tabular form in the annexes. These tables will
21 generally be organized to include information about (1) concentrations of Os and related
22 averaging times; (2) description of study methods used; (3) results and comments; and (4)
23 quantitative outcomes for Os measures. Additionally, the annexes may contain background
24 material on legislative requirements, the NAAQS review process, and the history of earlier Os
25 reviews.
26 4.3 SCIENTIFIC AND PUBLIC REVIEW
27 Drafts of the ISA will be reviewed by the CAS AC Os Review Panel and made available
28 for public comment. The annexes to the ISA will also be made available to CASAC in order to
29 assist with their review; however, the panel will not be specifically charged with reviewing the
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1 annexes. The CASAC O?, Review Panel will review the first draft ISA and discuss their
2 comments in a public meeting announced in the Federal Register. Based on CASAC's past
3 practice, EPA anticipates that key CASAC advice and recommendations for revision of the first
4 draft ISA will be summarized by the CASAC Chair in a letter to the EPA Administrator. In
5 revising the first draft ISA, EPA will take into account any such recommendations. EPA will
6 also consider comments received from CASAC or from the public at the meeting itself and any
7 written public comments. EPA will prepare a second draft ISA for CASAC review and public
8 comment. The CASAC Os Review Panel will review the second draft ISA and discuss their
9 comments in a public meeting announced in the Federal Register. Again, based on CASAC's
10 past practice, EPA anticipates that key CASAC advice and recommendations for revision of the
11 second draft ISA will be summarized by the CASAC Chair in a letter to the EPA Administrator.
12 In finalizing the ISA, EPA will take into account any such recommendations. EPA will also
13 consider comments received from CASAC or from the public at the meeting itself and any
14 written public comments. After appropriate revision, the final document will be made publicly
15 available on an EPA website and in hard copy. A notice announcing the availability of the final
16 ISA will be published in the Federal Register. In addition, the final ISA will be placed in the
17 rulemaking docket.
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1
2 5 HUMAN HEALTH RISK AND EXPOSURE
3 ASSESSMENTS
4 5.1 OVERVIEW
5 Characterizing health risks for the new periodic review of the primary NAAQS for Os will
6 include conducting air quality analyses to support quantitative exposure and risk assessments in
7 specific locations as well as putting the results into a broader public health perspective. These
8 assessments will be designed to estimate human exposures and to characterize the potential
9 health risks that are associated with current ambient levels, with ambient levels simulated to just
10 meet the current standard, and with ambient levels simulated to just meet alternative standards
11 that may be considered. The EPA is planning to focus the quantitative exposure/risk assessments
12 on Os, but recognizes that Os serves as an indicator of the broader photochemical oxidant mix.
13 Therefore, health effects reported to be associated with exposure to Os may not be due to Os
14 only, but to the broader mix of photochemical oxidants.
15 An important issue associated with conducting exposure and human health risk
16 assessments is the treatment of variability and the characterization of uncertainty. Variability
17 refers to the inherent heterogeneity in a population or variable of interest (e.g., residential air
18 exchange rates) and cannot be reduced through further research, only better characterized with
19 additional measurement. Uncertainty refers to the lack of knowledge regarding both the actual
20 values of model input variables (i.e., parameter uncertainty) and the physical systems or
21 relationships (i.e., model uncertainty - e.g., the shapes of concentration-response relationships).
22 As part of such analyses, variability and uncertainty will be explicitly addressed, where feasible,
23 in the planned air quality, exposure, and health risk assessments.
24 The major components of the risk characterization (e.g., air quality analyses, quantitative
25 exposure assessment, quantitative health risk assessment, broad health risk characterization) are
26 outlined below and will be described in more detail in a draft Scope and Methods Plan.
27 Preparation of this draft plan will coincide with the development of the first draft ISA to
28 facilitate the integration of policy-relevant science into both documents. In particular, the
29 availability of air quality, exposure-response, concentration-response, and baseline incidence
30 data will impact the type of risk and exposure assessments that will be developed.
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1 5.2 EXPOSURE AND HEALTH RISK ASSESSMENTS FROM
2 RULEMAKING COMPLETED IN MARCH 2008
3 The exposure and health risk assessment conducted in the rulemaking completed in
4 March 2008 developed exposure and health risk estimates for 12 urban areas across the U.S.
5 which were chosen based on the location of Os epidemiologic studies and to represent a range of
6 geographic areas, population demographics, and Os climatology. This analysis was in part based
7 upon the exposure and health risk assessments done as part of the review completed in 1997.
8 The exposure and risk assessment incorporated air quality data (i.e., 2002 through 2004) and
9 estimated annual or Os season-specific exposure and risk estimates for these recent years of air
10 quality and for air quality scenarios simulating just meeting the existing 8-hr 63 standard and
11 several alternative 8-hr 63 standards. Exposure estimates were used as an input to the risk
12 assessment for lung function responses (i.e., a health endpoint for which exposure-response
13 functions were available from controlled human exposure studies). Exposures were estimated
14 for the general population and identified subpopulations, including school age children with
15 asthma as well as all school age children. The modeled exposures were also used to estimate the
16 number of persons having exposures above potential health effect benchmark levels. Staff
17 identified the benchmark levels using the occurrence of observed health effect endpoints (e.g.,
18 lung inflammation, increased airway responsiveness, and decreased resistance to infection) that
19 were associated with 6-8 hour exposures to 63 while engaged in moderate exertion that were
20 observed in several controlled human exposure studies.
21 The exposure analysis took into account several important factors including the
22 magnitude and duration of exposures, frequency of repeated high exposures, and breathing rate
23 of individuals at the time of exposure. Estimates were developed for several indicators of
24 exposure to various levels of Os air quality, including counts of people exposed one or more
25 times to a given O?, concentration while at a specified breathing rate, and counts of person-
26 occurrences which accumulate occurrences of specific exposure conditions over all people in the
27 population groups of interest over an 63 season.
28 As discussed in the Staff Paper and in section II. A of the O3 Final Rule (73 FR 16440 to
29 16442, March 27, 2008), of the uncertainties identified and evaluated, the most important
30 uncertainties affecting the exposure estimates were related to modeling human activity patterns
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1 over an Os season, modeling of variations in ambient concentrations near roadways, and
2 modeling of air exchange rates that affect the amount of Os that penetrates indoors. Another
3 important uncertainty, discussed in more detail in the Staff Paper (section 4.3.4.7), was the
4 uncertainty in energy expenditure values which directly affect the modeled breathing rates.
5 These were important since they were used to classify exposures occurring when children were
6 engaged in moderate or greater exertion and health effects observed in the controlled human
7 exposure studies generally occurred under these exertion levels for 6 to 8-hr exposures to 63
8 concentrations at or near 0.08 ppm.
9 The human health risk assessment presented in the 2008 rulemaking was designed to
10 estimate population risks in a number of urban areas across the U.S., consistent with the scope of
11 the exposure analysis described above. The risk assessment included risk estimates based on
12 both controlled human exposure studies and epidemiologic and field studies. Ozone-related risk
13 estimates for lung function decrements were generated based on probabilistic exposure-response
14 relationships developed based on data from controlled human exposure studies, together with
15 probabilistic exposure estimates from the exposure analysis. For several other health endpoints,
16 (Vrelated risk estimates were generated based on concentration-response relationships reported
17 in epidemiologic or field studies, together with ambient air quality concentrations, baseline
18 health incidence rates, and population data for the various locations included in the assessment.
19 Health endpoints included in the assessment based on epidemiologic or field studies included:
20 hospital admissions for respiratory illness in 4 urban areas, premature mortality in 12 urban
21 areas, and respiratory symptoms in asthmatic children in 1 urban area.
22 In the previous health risk assessment, EPA recognized that there were many sources of
23 uncertainty and variability in the inputs to the assessment and that there was a high degree of
24 uncertainty in the resulting risk estimates. The statistical uncertainty surrounding the estimated Os
25 coefficients in concentration-response functions as well as the shape of the exposure-response
26 relationship chosen were addressed quantitatively. Additional uncertainties were addressed through
27 sensitivity analyses and/or qualitatively. The previous risk assessment incorporated some of the
28 variability in key inputs to the assessment by using location-specific inputs (e.g., location-
29 specific concentration-response function, baseline incidence rates and population data, and air
30 quality data for epidemiologic -based endpoints, location specific air quality data and exposure
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1 estimates for the lung function risk assessment). In the previous health risk assessment, twelve
2 urban areas were included to provide some sense of the variability in the risk estimates across the
3 U.S. Sensitivity analysis was carried out for two sources of uncertainties. The first analysis
4 investigated the impact of alternative estimates for policy-relevant background (PRB) levels in 3
5 of the 12 urban areas. The second sensitivity analysis looked at the impact of different
6 assumptions around the shape of the exposure-response function.
7 Key observations and insight from the Os risk assessment, in addition to important caveats
8 and limitations, were addressed in section II.B of the Final Rule notice (73 FR 16440 to 16443,
9 March 27, 2008). In general, estimated risk reductions associated with going from current Os levels
10 to just meeting the current and alternative 8-hr standards showed patterns of increasing estimated risk
11 reductions associated with just meeting the lower alternative 8-hr standards considered.
12 Furthermore, the estimated percentage reductions in risk were strongly influenced by the baseline air
13 quality year used in the analysis, which was due to significant year-to-year variability in Os
14 concentrations. There was also noticeable city-to-city variability in estimated Os-related incidence of
15 morbidity and mortality across the 12 urban areas. Uncertainties associated with estimated PRB
16 concentrations were also addressed and revealed differential impacts on the risk estimates depending
17 on the health effect considered as well as the location. The EPA also acknowledged that there were
18 considerable uncertainties surrounding estimates of O3 coefficients and the shape for concentration-
19 response relationships and whether or not a population threshold or non-linear relationship exists
20 within the range of concentrations examined in the epidemiologic studies.
21 5.3 AIR QUALITY CONSIDERATIONS
22 Air quality analyses are required to conduct both exposure and health risk assessments for
23 NAAQS reviews. Air quality inputs to the exposure and/or health risk assessment include: (1)
24 provision of ambient air quality data from the fixed-site ambient monitoring network for the
25 period 2006-2008 for the urban areas included in the exposure and risk assessments, (2)
26 estimates of PRB concentrations for the specific urban areas included in the risk assessment, and
27 (3) ambient air quality scenario data sets that are obtained from simulation procedures that adjust
28 recent air quality data to reflect changes in the distribution of air quality estimated to occur at
29 some unspecified time in the future when an area just meets a given set of NAAQS. Broader
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1 national scale air quality analyses also will be conducted to place the results of the quantitative
2 risk and exposure assessments into a broader public health context.
3 While incremental risk reductions do not require estimates of PRB, estimates of the risks
4 in excess of PRB remaining upon meeting the current or potential alternative standards, do
5 require EPA to estimate PRB. Both types of risk estimates are considered relevant to inform the
6 EPA Administrator's decision on the adequacy of a given standard.
7 Historically, PRB has been defined as the "the distribution of 63 concentrations that
8 would be observed in the U.S. in the absence of anthropogenic (man-made) emissions of
9 precursor emissions (e.g., VOC, NOX, and CO) in the U.S., Canada, and Mexico" (US EPA,
10 2007, p.2-48). This has been referred to as PRB, since this definition of background facilitates
11 separating pollution levels that can be controlled by U.S. regulations (or through international
12 agreements with neighboring countries) from levels that are not generally controllable in this
13 manner. Thus, PRB includes: (1) Os generated in the U.S. that arises from natural (biogenic)
14 sources of emissions in the U.S., Canada, and Mexico and (2) 63 in the U.S. from the transport
15 of 63 or the transport of precursor emissions from both natural and man-made sources, from
16 outside of the U.S. and its neighboring countries. As discussed in chapter 4, the ISA will include
17 an assessment of methods for estimating PRB concentrations and will produce O3 PRB
18 concentrations for use in the risk assessment. In this new review, EPA plans to place greater
19 emphasis on understanding the contribution of the different components that contribute to PRB
20 (e.g., what portion of PRB is due to natural emissions alone and what is the contribution of
21 transport from outside the North American continent, as well as the contribution of Canadian and
22 Mexican anthropogenic emissions to Os levels observed in the U.S. This additional information
23 will help inform policy considerations for this review of the Os NAAQS as well as more broadly
24 inform efforts related to international efforts to reduce trans-boundary 63 air pollution.
25 As part of the exposure and risk assessments, it will be necessary to adjust recent O3 air
26 quality data to simulate just meeting the current standard and any alternative Os standards that
27 might be considered. In the last rulemaking, EPA used a quadratic air quality rollback approach
28 (U.S. EPA, 2007a, section 4.5.8). EPA will consider this approach and alternative air quality
29 simulation procedures for use in this current review. Staff will evaluate candidate procedures to
30 adjust air quality by analyzing historical changes in measured 63 levels and by analyzing
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1 changes in O? levels predicted by air quality models. In this new review, EPA also will examine
2 techniques that may be used to assess the variability and uncertainty of the simulated change in
3 concentrations likely to result from just meeting the current or alternative standards.
4 5.4 POPULATION EXPOSURE ASSESSMENT APPROACH
5 Population exposure to Os will be evaluated using EPA's Air Pollutants Exposure model
6 (APEX), a model that simulates microenvironmental personal exposures using temporally and
7 spatially variable ambient concentrations and personal time-location-activity patterns. One
8 objective is to provide exposure estimates as an input to the portion of the health risk assessment
9 that uses exposure-response relationships from controlled human exposure studies. The
10 exposure analysis will also provide estimates of population exposure exceeding potential health
11 effect benchmarks, values identified based on 63 exposure concentrations and associated health
12 effects observed in controlled human exposure studies.
13 The approach to the current exposure assessment will build upon the methods developed
14 and insights gained from the exposure assessment conducted for the 2008 rulemaking. Staff
15 anticipates performing the exposure assessment, at a minimum, for the same 12 urban areas (i.e.,
16 Atlanta, Boston, Chicago, Cleveland, Detroit, Houston, Los Angeles, New York, Philadelphia,
17 Sacramento, St. Louis, and Washington D.C). Several key considerations in planning for the
18 exposure assessment are discussed below.
19 The most current version of the APEX model (also referred to as the Total Risk
20 Integrated Methodology/Exposure (TREVI.Expo) model) will be used to estimate population
21 exposures for the various air quality scenarios of interest. APEX simulates the movement of
22 individuals through time and space and their exposure to Os in indoor, outdoor, and in-vehicle
23 microenvironments. APEX is a probabilistic model that will be used to simulate a large number
24 of randomly sampled individuals within each urban area (e.g., 200,000) to represent area-wide
25 population exposures.
26 As in the previous exposure assessment, human activity data needed for the analysis will
27 be drawn from the Consolidated Human Activity Database (CHAD) developed and maintained
28 by ORD' s National Exposure Research Laboratory (NERL). A number of additional activity
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1 diaries have been added to the database (i.e., the CHAD-Master file)9 and will be used in this
2 exposure assessment. This expanded database will likely improve the representation of the
3 simulated exposure population of interest because there are increases in the numbers of data
4 diaries available, in particular for children, and much of the added data are from studies
5 conducted within the past decade. One key issue in this analysis regarding time-location activity
6 patterns is the further evaluation and possible modification of the approach used for creating (V
7 season or year-long activity sequences for individuals from primarily cross-sectional activity
8 data diaries. The CHAD-Master file contains additional longitudinal diaries from numerous
9 individuals ranging from 2 days in duration to 369 days that may be informative in the method
10 evaluation and development.
11 As done in the last Os NAAQS rulemaking and other ongoing NAAQS reviews (e.g., US
12 EPA, 2007a,b; US EPA, 2008; US EPA, 2009b) and where possible, staff will identify,
13 incorporate, and describe any observed variability in input data sets and estimated parameters
14 within the analyses performed. In addition, consistent with other NAAQS reviews, the exposure
15 assessment will include an uncertainty characterization of the model inputs and model
16 formulation.
17 Following the same general approach described in US EPA (2009b) and adapted from
18 WHO (2008), staff will first perform a succinct qualitative characterization of the components
19 contributing to uncertainty in estimated exposures in large part informed by the results of the
20 prior uncertainty characterization conducted for the Os exposure assessment (Langstaff, 2007).
21 This qualitative characterization will be performed early in the process of developing the
22 exposure assessment to inform and prioritize potential exposure model development activities
23 and to identify additional uncertainties that were not previously evaluated.
24 Briefly, staff will qualitatively characterize the potential magnitude10 (low., medium., and
25 high) and direction of influence (over, under, both, and unknown) for each major source of
26 uncertainty; that is, qualitatively rate how the source of uncertainty, in the presence of alternative
27 information, may affect the estimated exposures. In addition and consistent with the WHO
28 (2008) guidance, staff will discuss the uncertainty in the knowledge-base (e.g., the accuracy of
9 Approximately 18,000 diaries have been added to the previous 17,000 diaries used in the 2007 O3 exposure
assessment. The data are currently available through EPA at mccurdy.tom@epa.gov.
10 This is synonymous with the "level of uncertainty" discussed in WHO (2008), section 5.1.2.2.
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1 the data used, acknowledgement of data gaps) and decisions made (e.g., selection of particular
2 model forms), though qualitative ratings will be assigned only to uncertainty regarding the
3 knowledge-base.
4 A qualitative uncertainty characterization will be part of a tiered approach characterizing
5 uncertainty. Qualitative rankings, along with available data and information, will be used to
6 identify potential uncertainties to be propagated as part of a broader quantitative uncertainty
7 characterization. Note that in performing exposure assessments, we often have information
8 regarding the variability of model inputs, and sometimes the variability and uncertainty
9 combined, but for most inputs it is difficult to estimate the uncertainty separately from the
10 variability. There may be adequate information on APEX Os exposure modeling inputs and
11 algorithms for staff to define reasonable bounds or ranges for the uncertainties of many of the
12 model inputs. Thus, as part of a higher tier quantitative uncertainty characterization, staff may
13 assess the combined impacts of the uncertainties of the model inputs across these ranges, and use
14 these results to inform a discussion of model uncertainties.
15 Following the approach previously used (Langstaff, (2007), we may employ a 2-
16 dimensional Monte Carlo/Latin hypercube sampling approach to generate a combined variability
17 and uncertainty analysis for APEX. The 2-dimensional Monte Carlo method allows for the
18 separate characterization of the variability and uncertainty in the model results (Morgan and
19 Henri on, 1990). In addition, the sensitivity of the modeling procedure to selected model
20 parameters, data, and algorithms may be assessed to identify the factors having the greatest
21 impact on current exposure estimations. This may include uncertainties identified in the
22 previous review such as the longitudinal activity algorithm, the activity pattern data base, the
23 decay rate, and microenvironmental proximity factors, among other inputs potentially identified
24 in the qualitative uncertainty characterization.
25 5.5 HUMAN HEALTH RISK ASSESSMENTS
26 The goals of the Os health risk assessment are: (1) to provide estimates of the potential
27 magnitude of selected morbidity and mortality health effects in the population associated with
28 recent ambient Os levels and with just meeting the current O?, standard and any alternative
29 standards that might be considered in specific urban areas, (2) to develop a better understanding
30 of the influence of various inputs and assumptions on the risk estimates; and (3) to gain insights
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1 into the distribution of risks and patterns of risk reduction and uncertainties in those risk
2 estimates. The approach to the current health risk assessment will build upon the methods
3 developed and insights gained from the risk assessment conducted for the 2008 rulemaking.
4 Staff anticipates performing the assessment, at a minimum, for the same 12 urban areas (i.e.,
5 Atlanta, Boston, Chicago, Cleveland, Detroit, Houston, Los Angeles, New York, Philadelphia,
6 Sacramento, St. Louis, and Washington D.C). Several key considerations in planning for the
7 health risk assessment are discussed below.
8 Staff is planning to focus the quantitative risk assessments on the most important health
9 effect categories and endpoints from the standpoint of public health significance and for which
10 the weight of the evidence supports the judgment that the effect category and specific health
11 effects endpoints are judged sufficiently causal with respect to Os either alone and/or in
12 combination with other pollutants to be included in the quantitative risk assessment. An
13 important additional consideration in deciding which health effect endpoints to include in the
14 risk assessment is the availability of sufficient information to conduct a quantitative assessment
15 (e.g., characterization of exposure- or concentration-response relationship, information on
16 baseline incidence).
17 The risk and exposure assessments will draw upon the information presented in the ISA
18 and its annexes. This includes information on atmospheric chemistry, air quality, human
19 exposure, and health effects of concern. In particular, the availability of air quality,
20 concentration- and exposure-response relationships, and baseline incidence rate data will impact
21 the type of risk assessments that will be performed.
22 As described in section 5.3 above, air quality inputs required to conduct the health risk
23 assessment include: (1) recent 63 air quality data from suitable monitors for each selected
24 location, (2) estimates of PRB concentrations for each location, and (3) simulated air quality that
25 reflects changes in the distribution of O3 air quality estimated to occur when an area just meets a
26 given Os standard.
27 5.5.1 Approach to Health Risk Assessment Based On Epidemiologic Studies
28 As noted above, the health risk assessment conducted in this review will build on the
29 approach developed and applied in the 2008 rulemaking. Staff plans to rely on a weight-of-
30 evidence approach, as provided in the ISA, based on evaluation of new and prior epidemiologic
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1 studies including identification of relevant concentration-response functions that characterize the
2 relationships between Os exposures and health outcomes, particularly those conducted at or near
3 current ambient concentrations. Quantitative relationships provided in the specific studies or
4 derived from the data presented in the epidemiologic studies describe the change in
5 concentration (generally based on ambient fixed-site monitors) associated with a change in
6 health response. These concentration-response relationships will be combined with air quality
7 data, baseline incidence data, and population data to develop population health risk estimates.
8 Epidemiologic studies typically provide estimated concentration-response relationships
9 based on data collected in real-world settings. Ambient O3 concentrations are typically measured
10 as the area-wide average of monitor-specific measurements, although personal exposures are
11 occasionally measured. Health responses for Os included in the prior risk assessment were:
12 respiratory symptoms in asthmatic children, asthma and other respiratory-related hospital
13 admissions, and premature mortality. Staff will consider the type of health response function(s)
14 available and the availability of ambient 63 concentration data to characterize public health risks.
15 We consider that these analyses are most appropriately applied in areas where the specific
16 epidemiologic studies were performed. It should be noted that a risk characterization based on
17 epidemiologic studies also requires baseline incidence rates and population data for the specific
18 locations evaluated in the risk assessment.
19 The inclusion of any particular health endpoint depends in part on the extent to which the
20 Os ISA infers the likelihood of a causal relationship between Os exposure and a given health
21 effect category and the weight of the evidence for concluding that Os exposures are related to the
22 specific health effect endpoint. A number of issues related to the selection and application of
23 appropriate concentration-response functions for use in the assessment will be addressed in the
24 Scope and Methods Plan. For example, consideration will be given to the appropriate use of
25 functions based on single- and multi-city studies, single- and multi-pollutant concentration-
26 response models, and alternative lags.
27 5.5.2 Approach to Health Risk Assessment Based on Controlled Human Exposure Studies
28 As noted above, the health risk assessment conducted in this new review will build on the
29 approach developed and applied in the 2008 rulemaking. In that previous assessment, risk estimates
30 for lung function responses associated with 8-hr exposures while engaged in moderate exertion were
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1 developed. These estimates were based in part on exposure-response relationships estimated from
2 the combined data sets from multiple O3 controlled human exposure studies. Data from the studies
3 by Folinsbee et al. (1988), Horstman et al. (1990), and McDonnell et al. (1991) in addition to more
4 recent data from Adam (2002, 2003, 2006) were used to estimate exposure-response relationships for
5 >10, 15, and 20% decrements in FEVi. In this new review, staff intends to investigate the possibility
6 of using a model (McDonnell et al., 2007) that estimates FEVi responses associated with Os short-
7 term exposures. This model is based on the controlled human exposure data included in the prior
8 lung function risk assessment as well as additional data sets for different averaging times and
9 breathing rates. We will also consider whether there is sufficient evidence to consider adding other
10 health endpoints observed in controlled human exposure studies to the quantitative risk assessment
11 based on the information contained in the draft ISA.
12 5.5.3 Uncertainty and Variability
13 A persistent issue raised in CAS AC and public comments on the quantitative risk assessment
14 conducted for the 2008 rulemaking was the desire to provide a more comprehensive characterization
15 of the most significant uncertainties impacting the health risk estimates. For the health risk
16 assessment to be conducted for the new review, we will include both a qualitative characterization of
17 uncertainty and variability, and where feasible, a quantitative characterization of uncertainty and/or
18 sensitivity analyses for those aspects of the assessment judged most influential.
19 Following the same general approach described above in section 5.4, and adapted from
20 WHO (2008), staff will first perform a succinct qualitative characterization of the components
21 contributing to uncertainty in estimated health risks. This qualitative characterization will be
22 performed early in the process of developing the risk assessment to inform and prioritize
23 potential health risk model development activities and to identify additional uncertainties that
24 were not previously evaluated.
25 5.5.4 Broader Risk Characterization
26 For this new review, staff is considering extending the risk assessment to a broader range
27 of urban areas, beyond the 12 urban areas included in the previous assessment, in light of newly
28 available data to provide greater coverage of additional regions of the country where significant
29 63 exposures are likely to occur. We also will consider the feasibility of developing
30 concentration-response relationships that can be applied on a regional basis. It is very likely that
31 the geographic (and population) coverage will vary for different health endpoint categories due
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1 to data limitations (e.g., the availability of emergency department and hospital admission
2 baseline incidence data is more limited than mortality baseline incidence data). However, we
3 recognize that there have been noticeable improvements in the availability of baseline incidence
4 data for emergency department and hospital admissions since the last rulemaking.
5 Beyond the quantitative risk and exposure assessments conducted for this review, staff will
6 consider ways to put the results of those assessments into a broader context. Specifically, we
7 will explore analyses that would complement quantitative risk and exposure assessments
8 conducted for a limited number of locations and selected health endpoints to better characterize
9 the nature, magnitude, extent, variability, and uncertainty of the public health impacts associated
10 with Os exposures on a broader scale. We will consider how additional analyses can be used to
11 inform our understanding of:
12 • Additional health endpoints not considered in the quantitative risk assessment;
13 • Additional locations not evaluated in the quantitative risk/exposure assessment to inform
14 a broader understanding of public health impacts including non-urban environments;
15 • Regional differences in Os risks taking into consideration the following factors:
16 - variations in individual and/or population susceptibility;
17 - population demographics;
18 - variations in exposures; and
19 - impacts of potential effect modifiers (e.g., weather, co-pollutants).
20 5.6 SCIENTIFIC AND PUBLIC REVIEW
21 A draft of the Scope and Methods Plan for the risk/exposure assessment will be submitted
22 to CASAC for consultation and will be provided to the public for comment subsequent to the
23 release of the 1st draft ISA. The CASAC Os Review Panel will discuss its comments on the
24 draft Scope and Methods Plan in a public meeting that will be announced in the Federal Register.
25 In conducting the risk/exposure assessment, staff will take into account comments received from
26 CASAC and from the public at the meeting itself and in any written comments. Staff plans to
27 prepare two drafts of the risk/exposure assessment for CASAC review and public comment. The
28 CASAC Os Review Panel will review each draft risk/exposure assessment and discuss their
29 comments in two public meetings to be announced in the Federal Register. Based on CAS AC's
30 past practice, staff anticipates that key CASAC advice and recommendations for revision of the
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1 draft risk/exposure assessment will be presented in letters to the EPA Administrator. Staff will
2 also consider comments received from CASAC and from the public at the meetings themselves
3 and any written public comments. In finalizing the risk/exposure assessment, we will take into
4 account any such comments and recommendations. After appropriate revision, the final
5 risk/exposure assessment document will be made publicly available on an EPA website and in
6 hard copies. A notice announcing the availability of the final document will be published in the
7 Federal Register. In addition, the final risk/exposure assessment document will be placed in the
8 rulemaking docket.
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1
2 6 VEGETATION AND OTHER WELFARE-RELATED
3 ASSESSMENTS
4 6.1 OVERVIEW
5 The assessments conducted in this new review of the secondary Os NAAQS will focus on
6 new information that has become available since the 2008 rulemaking. Key-policy relevant
7 findings from the ISA integrated with information from previous reviews will inform policy
8 judgments in regard to the adequacy of the current indicators, averaging times, levels and forms
9 of the 63 standard. New information and methods available in this review are expected to
10 improve characterization of 63 exposures and associated impacts, especially in non-urban areas,
11 forests, and Class I protected lands. Recent information regarding direct O3 effects on plants,
12 including emerging evidence that Os alters the chemical signature and longevity of scents
13 released by plants to attract pollinators, and the indirect impacts that can occur in associated
14 ecological processes that can lead to ecosystem level effects and shifts in or loss of ecosystem
15 services (e.g., carbon sequestration, water balance, pollination and/or biodiversity) will be
16 considered and evaluated using qualitative and/or quantitative exposure, risk and benefits
17 assessments, where feasible. As in the last rulemaking, information regarding the interaction
18 between 63, local meteorological conditions, and climate will be reviewed, although we do not
19 anticipate sufficient information being available for quantitative analyses of this complex
20 relationship in this review. Ozone-related damage to certain manmade materials (e.g.,
21 elastomers, textile fibers, dyes, paints and pigments) will not be re-assessed, as the scientific
22 literature contains very little new information to adequately quantify these effects. A more
23 detailed description of assessment methods and approaches being considered for the exposure,
24 risk and benefits assessments will be provided in a subsequent Scope and Methods Plan.
25 Preparation of this plan will coincide with the development of the first draft ISA to facilitate the
26 integration of policy-relevant science.
27 6.2 EXPOSURE, RISK, AND BENEFITS ASSESSMENTS FROM
28 RULEMAKING COMPLETED IN MARCH 2008
29 The exposure, risk and benefits assessments conducted as part of the 2008 rulemaking
30 focused on Os-related impacts to sensitive vegetation and their associated ecosystems. The
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1 vegetation exposure assessment was performed using an interpolation approach that included
2 information from ambient monitoring networks and results from air quality modeling. The
3 vegetation risk assessment included both tree and crop analyses. The tree risk analysis included
4 three distinct lines of evidence: (1) observations of visible foliar injury in the field linked to
5 monitored 63 air quality for the years 2001 - 2004; (2) estimates of seedling growth loss under
6 then current and alternative 63 exposure conditions; and (3) simulated mature tree growth
7 reductions using the TREGRO model to simulate the effect of meeting alternative air quality
8 standards on the predicted annual growth of mature trees from three different species. The crop
9 risk analysis included estimates of crop yields under current and alternative O3 exposure
10 conditions. The associated change in economic benefits expected to accrue to the agriculture
11 sector upon meeting the levels of various alternative standards were analyzed using an
12 agricultural benefits model. Key elements and observations from these exposure and risk
13 assessments are outlined in the following sections.
14 6.2.1 Exposure Assessment
15 In many rural and remote areas where sensitive species of vegetation can occur,
16 monitoring coverage remained limited. Thus, the Staff Paper concluded that it was necessary to
17 use an interpolation method in order to better characterize Os air quality over broad geographic
18 areas and at the national scale. Based on the significant difference in monitor network density
19 between the eastern and western U.S., the Staff Paper further concluded that it was appropriate to
20 use separate interpolation techniques in these two regions: The Air Quality System (AQS;
21 http://www.epa.gov/ttn/airs/airsaqs) and Clean Air Status and Trends Network (CASTNET;
22 http://www.epa.gov/castnet/) monitoring data were solely used for the eastern interpolation, and
23 in the western U.S., where rural monitoring is more sparse, Os outputs from the EPA/NOAA
24 Community Multi-scale Air Quality (CMAQ)11 model system
25 (http://www.epa.gov/asmdnerl/CMAQ, Byun and Ching, 1999) were used to develop scaling
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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1 factors to augment the monitor interpolation. In order to characterize uncertainty associated with
2 the exposure estimates generated using the interpolation method, monitored Os concentrations
3 were systematically compared to interpolated Os concentrations in areas where monitors were
4 located. In general, the interpolation method performed well in many areas in the U.S., although
5 it under-predicted higher 12-hr W126 exposures in rural areas. This approach was used to
6 develop a national vegetation 63 exposure surface.
7 To evaluate changing vegetation exposures under selected air quality scenarios, a number
8 of analyses were conducted. One analysis adjusted 2001 base year 63 air quality distributions
9 using a rollback method (Horst and Duff, 1995; Rizzo, 2005, 2006) to reflect meeting the current
10 and alternative secondary standard options. For "just meet" and alternative 8-hr average
11 standard scenarios, the associated maps of estimated 12-hr, W126 exposures were generated.
12 Based on these comparisons, the following observations were drawn: (1) current Os air quality
13 levels could result in significant Os exposures to vegetation in some areas; (2) overall 3-month
14 12-hr W126 63 levels were somewhat but not substantially improved under the "just meet"
15 current scenario; (3) exposures generated for just meeting a 0.070 ppm, 4th-highest maximum 8-
16 hr average alternative standard (the lower end of the proposed range for the primary 63 standard)
17 showed substantially improved O3 air quality when compared to just meeting the current 0.08
18 ppm, 8-hr standard.
19 A second analysis described in the Staff Paper was performed to evaluate the extent to
20 which county-level Os air quality measured in terms of various levels of the current 8-
21 hr average form overlapped with that measured in terms of various levels of the 12-
22 hr W126 cumulative, seasonal form.12 While these results also suggested that meeting a
23 proposed 0.070 ppm, 8-hr secondary standard would provide substantially improved vegetation
24 protection in some areas, the Staff Paper recognized that this analysis had several important
25 limitations. In particular, the lack of monitoring in rural areas where sensitive vegetation and
26 ecosystems are located, especially at higher elevation sites could have resulted in an inaccurate
27 characterization of the degree of potential overlap at sites which have air quality patterns that can
28 result in relatively low 8-hr averages while still experiencing relatively high cumulative
The Staff Paper presented this analysis using 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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1 exposures (72 FR 37892). Thus, the Staff Paper concluded that it is reasonable to anticipate that
2 additional unmonitored rural high elevation areas with sensitive vegetation may not be
3 adequately protected even with a lower level of the 8-hr form. The Staff Paper further indicated
4 that it remained uncertain as to the extent to which air quality improvements designed to reduce
5 8-hr 63 average concentrations would reduce 63 exposures measured by a seasonal, cumulative
6 W126 index. The Staff Paper indicated this to be an important consideration because: (1) the
7 biological database stresses the importance of cumulative, seasonal exposures in determining
8 plant response; (2) plants have not been specifically tested for the importance of daily maximum
9 8-hr O3 concentrations in relation to plant response; and (3) the effects of attainment of a 8-hr
10 standard in upwind urban areas on rural air quality distributions cannot be characterized with
11 confidence due to the lack of monitoring data in rural and remote areas.
12 6.2.2 Risk Assessment
13 The risk assessments in the last rulemaking reflected the availability of several additional
14 lines of evidence that provided a basis for a more complete and coherent picture of the scope of
15 Os-related vegetation risks, especially those faced by seedling, sapling and mature tree species
16 growing in field settings, and indirectly, forested ecosystems. Specifically, new research
17 available at the time reflected an increased emphasis on field-based exposure methods (e.g., free
18 air exposure and ambient gradient), improved field survey biomonitoring techniques, and
19 mechanistic tree process models. Highlights from the analyses that addressed visible foliar
20 injury, seedling and mature tree biomass loss, and effects on crops are summarized below.
21 With regard to visible foliar injury, the Staff Paper presented an assessment that
22 combined recent U.S. Forest Service Forest Inventory and Analysis (FIA) biomonitoring
23 site data with the county level air quality data for those counties containing the FIA
24 biomonitoring sites. This assessment showed that incidence of visible foliar injury
25 ranged from 21 to 39 percent of the counties during the four-year period (2001-2004)
26 across all counties with air quality levels at or below that of the then current 0.08 ppm 8-hr
27 standard. Of the counties that met an 8-hr level of 0.07 ppm in those years, 11 to 30
28 percent of the counties still had incidence of visible foliar injury.
29 With respect to tree seedling biomass loss, concentration-response (C-R) functions
30 developed from OTC data for biomass loss for available seedling tree species and information on
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1 tree growing regions derived from the U.S. Department of Agriculture's Atlas of United States
2 Trees were combined with projections of air quality based on 2001 interpolated exposures, to
3 produce estimated biomass loss for each individual seedling tree species. These analyses
4 predicted that biomass loss could still occur in many tree species when Os air quality was
5 adjusted to meet the current 8-hr standard. Though this type of analysis was not new to this
6 review, the context for understanding these results had changed due to recent field work at the
7 AspenFACE site in Wisconsin on quaking aspen (Karnosky et al., 2005) and a gradient study
8 performed in the New York City area (Gregg et al., 2003) which confirmed the detrimental
9 effects of O3 exposure on tree growth in field studies without chambers and beyond the seedling
10 stage (King et al., 2005).
11 With respect to risk of mature tree growth reductions, a tree growth model (TREGRO)
12 was used to evaluate the effect of changing Os air quality scenarios from just meeting alternative
13 Os standards on the growth of mature trees.13 The model was run for a single western species
14 (ponderosa pine) and two eastern species (red maple and tulip poplar). Staff Paper analyses
15 found that just meeting the current standard would likely continue to allow (Vrelated reductions
16 in annual net biomass gain in these species. Though there was uncertainty associated with the
17 above analyses, it was important to note that new evidence from experimental studies that go
18 beyond the seedling growth stage continued to show decreased growth under elevated Os (King
19 et al., 2005); some mature trees such as red oak have shown an even greater sensitivity of
20 photosynthesis to Os than seedlings of the same species (Hanson et al., 1994); and the potential
21 for cumulative "carry over" effects as well as compounding should be considered.
22 With respect to risks of yield loss in agricultural crops and fruit and vegetable species,
23 little new information was available beyond that of the previous review. However, limited
24 information from a free air field based soybean study (SoyFACE) and information on then
25 current cultivar sensitivities, led to the conclusion that C-R functions developed in OTCs under
26 the National Crop Loss Assessment Network (NCLAN) program could still be usefully applied.
TREGRO is a process-based, individual tree growth simulation model (Weinstein et al, 1991) that is linked with
concurrent climate data to account for Oj, and climate/meteorology interactions on tree growth. TREGRO has been
used to evaluate the effects of a variety of Oj, 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 etal., 2005).
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1 The crop risk assessment, like the tree seedling assessment, combined C-R information on
2 commodity crops, fruits and vegetables, crop growing regions, and interpolated exposures during
3 each crop growing season. The risk assessment estimated that just meeting the 0.08 ppm, 8-hr
4 standard would still allow Os-related yield loss to occur in some sensitive commodity crops and
5 fruit and vegetable species growing at that time in the U. S.
6 6.2.3 Benefits Assessment
7 The Staff Paper also presented estimates of monetized benefits for crops associated with
8 the then current and alternative standards. The Agriculture Simulation Model (AGSIM) (Taylor,
9 1994; Taylor, 1993) was used to calculate annual average changes in total undiscounted
10 economic surplus for commodity crops and fruits and vegetables when then current and
11 alternative standard levels were met. Meeting the various alternative standards did show some
12 significant benefits beyond the 0.08 ppm, 8-hr standard. However, the Staff Paper recognized
13 that the modeled economic benefits from AGSIM had many associated uncertainties which
14 limited the usefulness of these estimates.
15 6.3 AIR QUALITY CONSIDERATIONS
16 As in the last rulemaking, air quality analyses will be necessary to inform and support
17 welfare-related exposure, risk, and benefits assessments in this new review. The required air
18 quality analyses for this review will build upon those of the ISA and will include consideration
19 of: (1) summaries of recent ambient air quality data, (2) estimation approaches to extrapolate air
20 quality values for rural areas without monitors as well as Class I Federally designated natural
21 areas important to welfare effects assessment, (3) estimates of policy-relevant background (PRB)
22 concentrations, (4) air quality simulation procedures that modify recent air quality data to reflect
23 changes in the distribution of air quality estimated to occur at some unspecified time in the future
24 when an area just meets a given set of NAAQS. In this review, air quality analyses will be
25 conducted to support quantitative exposure and risk assessments for specific locations, as well as
26 at regional and national scales.
27 In addition to updating air quality summaries since the last rulemaking, these air quality
28 analyses will include summaries of the most currently available ambient measurements for the
29 current 8-hr average standard form, the cumulative concentration-weighted W126 form, and
30 comparisons of these two types of forms. These air quality analyses will use monitor data from
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1 the AQS data base (which includes National Park Service monitors) and the CASTNET network.
2 In addition, staff will explore the suitability of using other sources of Os concentration
3 information that might be available, such as from portable monitors or satellites.
4 In the last rulemaking, the vegetation exposure analysis used a spatial interpolation
5 technique, to create an interpolated air quality surface to fill in the gaps in ambient monitoring
6 data, especially those left by a sparse rural monitoring network in the western United States. In
7 this current review, additional approaches that potentially could be used to fill in the gaps in the
8 rural monitoring network, as well as opportunities for enhancing the fusion of monitoring and
9 modeled O3 data will be explored.
10 While incremental risk reductions do not require estimates of PRB, estimates of the risks
11 in excess of PRB remaining upon meeting the current or potential alternative standards, do
12 require EPA to estimate PRB. Both types of risk estimates are considered relevant to inform the
13 EPA Administrator's decision on the adequacy of a given standard. The current approach to
14 estimating 63 PRB for use in conducting the welfare risk assessment is the same as that outlined
15 in section 5.3 above.
16 As part of the air quality analyses supporting the exposure, risk and benefits assessments,
17 it will be necessary to adjust recent O3 air quality data to simulate just meeting the current
18 standard and any alternative Os standards. In the last rulemaking, EPA used a quadratic air
19 quality rollback approach (U.S. EPA, 2007a, section 4.5.8). Staff will consider alternative air
20 quality simulation procedures for use in this current review as previously characterized in section
21 5.3.
22 6.4 EXPOSURE ASSESSMENT APPROACH
23 Since the last rulemaking, little has changed in terms of the extent of monitoring coverage
24 in non-urban areas. We will consider both past and alternative approaches for generating
25 estimates of national Os exposures in an effort to continue enhancing our ability to characterize
26 exposures in these non-monitored areas. It is expected that vegetation exposure assessments will
27 again include assessments of recent air quality, air quality associated with just meet scenarios
28 both for the current and alternative standards.
29 In addition, given the stated importance in the Final Os Rule (73 FR 16436) on providing
30 protection for sensitive vegetation in areas afforded special protections such as in federally
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1 designated Class I natural areas, we will also consider alternative sources of Os exposure
2 information for those types of sites. For example, portable Os monitors are being deployed in
3 some national parks and a current exploratory study is underway to measure Os concentration
4 variations with gradients in elevation. Though these monitors are not FRM or reported in AQS,
5 information from these monitors could potentially decrease uncertainties associated with
6 assessing 63 distribution patterns in complex terrain and high elevations. New exposure data
7 that informs the 63 review will be considered where appropriate.
8 As described in 6.5 below, staff will conduct an analysis of associated exposure
9 assessment uncertainties.
10 6.5 RISK ASSESSMENT APPROACH
11 Since the last rulemaking, new scientific information on the direct and indirect effects of
12 Os on vegetation and ecosystems, respectively, has become available. With respect to mature
13 trees and forests, the information regarding 63 impacts to forest ecosystems has continued to
14 expand, including limited new evidence that implicates 63 as an indirect contributor to decreases
15 in stream flow through direct impacts on whole tree level water use efficiencies. Long-term
16 FACE (Free Air CO2 enrichment) studies are continuing to provide additional evidence
17 regarding chronic Os exposures in closed forest canopy scenarios including interspecies
18 interactions such as decreased growth of branches and root mass in sensitive species. Also,
19 lichen and moss communities on trees monitored in FACE sites have been shown to undergo
20 species shifts when exposed to 03. In addition, it is expected that as in the previous review,
21 recent available data from annual field surveys conducted by the USFS to assess foliar damage to
22 selected tree species will again be combined with recent county level air quality data to
23 determine the incidence of visible 63 damage occurring across the U.S. at air quality levels that
24 meet or are below the current standard. To the extent possible, new information regarding O3
25 effects on forest trees will be both qualitatively and quantitatively assessed and an effort made to
26 place both the estimates of risk from more recent long-term studies and historic shorter-term
27 studies in the appropriate context.
28 Additional information relevant to both tree and crop risk assessments expected to be
29 available includes that regarding the interactions between elevated Os and CO2 with respect to
30 plant growth and how these interactions might be expected to be modified under different
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1 climatic conditions, and potential reactions of Os with chemicals released by plants to attract
2 pollinators that could decrease the distance the floral "scent trail" travels and potentially
3 changing the distance pollinators have to travel to find flowers. Staff also plans to consider any
4 available information regarding potential risks to threatened or endangered species.
5 6.6 BENEFIT ASSESSMENT APPROACH
6 Qualitative and/or quantitative benefits assessments of ecosystem services impacted by Os
7 will be conducted to inform the current review. In particular, the benefits assessments in this
8 review will focus more broadly than the crop yield analyses conducted in the last rulemaking, to
9 include impacts on ecosystem services such as impacts on biodiversity, biological community
10 composition, health of forest ecosystems, aesthetic values of trees and plants and the nutritive
11 quality of forage and other crops. The impact of 63 on limiting potential CC>2 sequestration is
12 another important ecosystem services. New preliminary evidence of Oj effects on the ability of
13 pollinators to find their target is also of special interest with respect to the possible implication
14 for benefits assessment of ecosystem service. Impairment of the ability of pollinators to locate
15 flowers could have broad implications for agriculture, horticulture and forestry.
16 A new benefits model, the Forest and Agricultural Sector Optimization Model (FASOM),
17 is being considered in this review. This model jointly assesses the economic impacts of 63
18 damage to forests and agricultural crops. FASOM is a dynamic, non-linear programming model
19 designed for use by the EPA to evaluate welfare and market effects of carbon sequestration in
20 trees, understory, forest floor, wood products and landfills that would occur under different
21 agricultural and forestry scenarios. It may be possible to model damage by Os to the agriculture
22 and forestry sectors and quantify how Os-exposed vegetation impacts the ecosystem service of
23 carbon sequestration.
24 A conclusion in the last rulemaking was that the science continued to support a change in
25 the form of the secondary standard for 63 to better reflect the effects of cumulative 63 exposures
26 on plants and crops. The current form of the secondary standard may not protect sensitive
27 species that are chronically exposed to elevated 63 concentrations. The risk assessment
28 conducted in this review will once more evaluate the relative risks associated with both the
29 current and potentially alternative cumulative seasonal forms, in light of new information on
30 exposures, risks, non-plant effects, and ecosystem services. In addition, we plan to consider the
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1 impact of using different length diurnal windows (e.g., 12, 16 or 24 hrs), different seasonal
2 periods (e.g., 3, 5, or 7 months), and annual vs. three-year averages.
3 6.7 UNCERTAINTY AND VARIABILITY
4 For the exposure, risk and benefits assessments planned for this review, staff is considering, at
5 a minimum, a similar approach to that used in the previous review to characterize uncertainty and
6 variability associated with these estimates. In addition, we are considering the feasibility of
7 conducting additional analyses to better characterize the uncertainties and variability associated with
8 these assessments.
9 Many of the sources of uncertainty and variability that were present in the last assessments are
10 expected to remain in this review. In particular, uncertainties associated with the use of various
11 models such as the CMAQ and FASOM models would be characterized and where possible,
12 sensitivity analyses performed to test the impact of various assumptions imbedded in the models.
13 The uncertainty associated with the monitor probe height is expected to remain due to lack of
14 definitive information becoming available. Where information exists, staff plans to conduct an
15 assessment of the impact of using different adjustment factors. As in the last rulemaking, every
16 effort will be made to provide information on the uncertainties and variability associated with the
17 exposure surface approach selected and risk assessments conducted. Uncertainties associated with
18 empirical evidence due to exposure or research methods will be described.
19 6.8 SCIENTIFIC AND PUBLIC REVIEW
20 A draft of the Scope and Methods Plan for the vegetation and other welfare-related
21 assessments will be submitted to CAS AC for consultation and will be provided to the public for
22 comment. The CASAC Os Review Panel will discuss their comments on the draft Scope and
23 Methods Plan in a public meeting that will be announced in the Federal Register. In conducting
24 the welfare-related assessments, staff will take into account comments received from CASAC
25 and from the public at the meeting itself and in any written comments. Staff plans to prepare two
26 drafts of the vegetation and other welfare-related assessments for CASAC review and public
27 comment. The CASAC O?, Review Panel will review each draft welfare-related assessment and
28 discuss their comments in two public meetings to be announced in the Federal Register. Based
29 on CASAC's past practice, we anticipate that key CASAC advice and recommendations for
30 revision of the draft risk/exposure assessment will be presented in letters to the EPA
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1 Administrator. Staff will also consider comments received from CAS AC or from the public at
2 the meetings themselves and any written public comments. In finalizing the vegetation and
3 welfare-related assessments, we will take into account any such comments and
4 recommendations. After appropriate revision, the final welfare-related assessment document
5 will be made publicly available on an EPA website and in hard copy. A notice announcing the
6 availability of the final document will be published in the Federal Register. In addition, the final
7 welfare-related assessment document will be placed in the rulemaking docket.
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i 7 POLICY ASSESSMENT/RULEMAKING
2 Based on the information in the ISA, the human health REA, and the vegetation REA, the
3 Agency will develop a Policy Assessment (PA) that reflects EPA staffs initial views regarding
4 the need to retain or revise the NAAQS for 03. In doing so, the PA will consider the policy-
5 relevant questions outlined in chapter 3, including the fundamental questions associated with the
6 adequacy of the current standards and consideration of alternative standards in terms of the
7 specific elements of the standards: indicator, averaging time, level, and form.
8 The PA will identify conceptual evidence-based and risk/exposure-based approaches for
9 reaching public health and welfare policy judgments. It will discuss the implications of the
10 science and risk/exposure assessments for the adequacy of the current standards, and for
11 alternative standards under consideration. The PA will also describe a range of policy options
12 for standard setting including a description of the underlying interpretations of the scientific
13 evidence and risk/exposure information that might support such alternative standards and that
14 could be considered by the Administrator in making decisions for the 63 standards.
15 Use of the PA will provide an opportunity for CAS AC and the public to evaluate the
16 policy options under consideration and to offer comments and recommendations to inform the
17 development of a proposed rule. Taking into account CAS AC advice and recommendations and
18 public comment on the PA, the Agency will publish a proposed rule. This proposal will be
19 followed by a public comment period. Taking into account comments received on the proposed
20 rule, the Agency will then issue a final rule to complete the rulemaking process.
21 Monitoring rule changes associated with review of the Os standards, as outlined below in
22 chapter 8, will be developed, if necessary, in conjunction with this NAAQS rulemaking.
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i 8 AMBIENT AIR MONITORING
2 8.1 OVERVIEW
3 The Os monitoring network provides data to meet a wide variety of objectives. They
4 include ensuring the public has access to clean air by comparing data to the NAAQS, providing
5 the public with reports and forecasts of their exposure to 63 through the Air Quality Index,
6 providing input to health and welfare studies utilized as part of the NAAQS review process,
7 evaluating the performance of regional air quality models used in developing emission strategies,
8 tracking trends in air pollution abatement control measures impact on improving air quality, and
9 supporting research studies on atmospheric chemistry and transport or Os.
10 To meet these multiple objectives, national Os sites are deployed in variety of locations to
11 determine the following information: highest concentrations in an area, typical concentrations in
12 areas of high population density, the impacts of significant sources or source categories on Os
13 precursors and formation processes, general background concentration levels, the extent of
14 regional pollutant transport among populated areas, assessment impacts on visibility, vegetation
15 damage, or other welfare-based effects.
16 Federal rules that regulate ambient air monitoring programs are found in 40 CFR Parts 50,
17 53 and 58. During the last rulemaking completed in 2008, EPA followed a complementary
18 process in which changes to monitoring regulations that were required to support the revised
19 NAAQS were proposed in a separate rulemaking.14 During this review, EPA intends to include
20 any proposed monitoring rule changes as part of the NAAQS rule, potentially reducing the time
21 necessary to institute monitoring changes that might be required by a decision to revise the
22 NAAQS.
23 8.2 CURRENT O3 NETWORK STATUS
24 Presently, states and local air quality management agencies operate minimum numbers of
25 EPA-approved 63 monitors based on the population of each of their Metropolitan Statistical
26 Area (MSA) and the most recently measured 63 levels for each area. Currently, there are 369
27 MS As in the U.S. subject to minimum 63 monitoring requirements. In these areas, a total of
14
The proposed rule, Ambient Ozone Monitoring Regulations: Revisions to Network Design Requirements, was
published on July 16, 2009 (74 FR 34525). A final rule is expected to be completed during the spring of 2010.
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1 392 monitors are required to meet the minimum requirements. In actuality, 992 monitors were in
2 operation during 2005 to 2007 representing these MSAs. This monitor count indicates the
3 typical practice of operating more than the minimum required number of monitors to support the
4 basic monitoring objectives described above. In addition, state and local agencies operated 55
5 monitors during 2005 to 2007 in MSAs that were not required to have monitors.
6 Many of these Os monitors that were operated in excess of minimum requirements were
7 sited to characterize the 63 concentrations in metropolitan areas and in downwind areas that were
8 potentially impacted by transport from MSAs. As noted in the current monitoring regulations
9 described in Part 58, O3 minimum requirements do not account for the full breadth of additional
10 factors that would be considered in designing a complete Os monitoring program for an area.
11 Some of these additional factors include geographic size, population density, complexity of
12 terrain and meteorology, presence of nearby Os monitoring sites operated by adjacent State
13 programs, air pollution transport from neighboring areas, and measured air quality in comparison
14 to all forms of the O3 NAAQS (i.e., 8-hr and 1-hr forms). States and EPA Regional
15 Administrators work together to design and/or maintain the most appropriate 63 network to
16 service the variety of data needs in an area. The results of these negotiations are documented in
17 annual monitoring network plans that are made available for public inspection and then approved
18 by the EPA Regional Administrator, and the Os monitoring requirements in approved plans
19 become the basis for state Os monitoring requirements for the 1-year period following plan
20 approval.
21 Although there are currently no EPA requirements for Os monitoring other than in or
22 adjacent to MSAs , there are at present about 200 state-operated 63 monitors in counties that are
23 not part of MSAs, and these monitors can be categorized in several ways. States commonly
24 locate 63 monitors both upwind and downwind of major urban areas to evaluate the spatial
25 gradient or extent of transported O3 pollution and the lag time typically associated with
26 photochemical production. In some cases, these Os monitors are located in non-urban or rural
27 areas within MSAs or physically outside the MSA boundary if the expected location of
28 maximum downwind Os concentration is outside the MSA.
29 As part of the Clean Air Status and Trends Network (C ASTNET), the EPA operates 57
30 63 monitors, and the National Park Service (NFS) operates 23 monitors across the eastern and
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1 western U.S. The NFS also operates additional Os monitors independent of CASTNET stations.
2 CASTNET Os monitors operate year-round and are primarily located in rural areas; siting
3 criteria require distances of at least 40 kilometers from cities of greater than 50,000 population as
4 well as other separation requirements from air pollution sources.
5 Taking into account both state and EPA/NPS-operated non-urban 63 monitors, an
6 analysis of the distribution of these monitors indicates a relatively uniform spatial density in the
7 eastern one-third of the U.S. and in California, with significant gaps in coverage elsewhere
8 across the country. Virtually all states east of the Mississippi River have at least two to four non-
9 urban Oj monitors, while many large mid-western and western states have one or no non-urban
10 monitors.
11 Section 182(c)(l) of the Clean Air Act required EPA to promulgate rules requiring
12 enhanced monitoring of Os, NO, and VOC in Os nonattainment areas classified as serious,
13 severe, or extreme. On February 12, 1993, EPA promulgated requirements for State and local
14 monitoring agencies to establish Photochemical Assessment Monitoring Stations (PAMS) as part
15 of their SIP monitoring networks in Os nonattainment areas classified as serious, severe, or
16 extreme. Design criteria for the PAMS network are based on locations relative to Os precursor
17 source areas and predominant wind directions associated with high O3 events. Specific
18 monitoring objectives are associated with each location. The overall design supports the
19 characterization of precursor emission sources within an area, transport of Os and its precursors,
20 and the photochemical processes related to Os nonattainment. EPA reduced PAMS requirements
21 as part of the October 17, 2006 rulemaking. Current requirements include site-specific
22 measurements for speciated VOC, carbonyls, NOx, NOy, CO, Os, surface meteorology, and
23 upper air meteorology.
24 Unlike the ambient monitoring requirements for other criteria pollutants that mandate
25 year-round monitoring, O3 monitoring is currently only required during the seasons of the year
26 that are conducive to Os formation. These seasons vary in length from place to place as the
27 conditions that determine the likely Os formation (i.e., seasonally-dependent factors such as
28 ambient temperature, strength of solar insolation, and length of day) differ by location. In some
29 locations, conditions conducive to Os formation are limited to a few summer months of the year.
30 For example, in states with colder climates such as Montana and South Dakota, the currently
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1 required Os monitoring season has a length of 4 months. However, in other states with warmer
2 climates such as California, Nevada, and Arizona, the currently required Os monitoring season
3 for most sites continues all 12 months of the year.
4 8.3 MONITORING ISSUES RELATED TO THE O3 NAAQS
5 This new review of the Os NAAQS will explore a number of policy-relevant issues
6 associated with measuring and characterizing Os levels in ambient air. The EPA will draw upon
7 the information presented in the ISA to inform the evaluation of appropriate ambient monitoring
8 methods and network design for Os, including consideration of the available information on
9 probe and siting criteria that could best support the current or alternative standards.
10 Monitoring Methods
11 The nation's O3 monitoring data currently being reported to AQS are obtained
12 exclusively with ultraviolet (UV) absorption spectrometry based methods. These methods are
13 approved Federal Equivalent Methods (FEMs) per 40 CFR Part 53; a number of commercial
14 manufacturers supply such FEM instruments for use in the national network. The use of the
15 Federal Reference Method (FRM) in ambient monitoring (a chemiluminescence-based method)
16 has become basically non-existent with the adoption of FEMs. States utilize calibration and
17 quality assurance procedures that relate their own calibrators to a network of Standard Reference
18 Photometers (SRPs) that are maintained and operated by EPA.
19 Previous reviews of the Os NAAQS have considered the implications of interferences in
20 the response of UV and chemiluminescence-based instruments due the effects of water vapor,
21 VOC's, aromatic compounds and their oxidation products, and other organic and inorganic
22 compounds.
23 Policy-relevant issues that will be considered in this review to inform the selection of
24 monitoring methods are reflected in the following questions:
25 • To what extent is new information available to judge the adequacy of the current
26 methodologies that are approved by EPA for use in judging compliance with the 63
27 NAAQS and meeting other objectives?
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1 • Has new information become available that supports the need for alternative
2 methodologies to supplement the currently approved FRM and FEM's?
3 • What other technologies (e.g., portable monitors, passive or personal sampling) might
4 be appropriate to consider where methods do not have to be EPA-approved, such as
5 in the support of ecosystem or epidemiologic studies?
6 Network Design
7 Monitoring sites must represent ambient air (i.e., that portion of the atmosphere, external
8 to buildings, to which the general public has access). The minimum number of required monitors
9 for Os is stated in 40 CFR Part 58, Appendix D, Network Design Criteria for Ambient Air
10 Quality Monitoring. The EPA negotiates with States to determine the total number of monitors
11 needed to represent an area's air quality. It should be noted that although monitors are often
12 sited with the intention to represent an area of a certain geographic scale, in general, a monitor
13 need not be representative of the ambient air quality across an area of any specific size to be
14 eligible for comparison to most NAAQS.
15 Network design issues that will be considered in this review are reflected in the following
16 questions:
17 • Are further revisions to urban Os monitoring requirements necessary to improve
18 characterization of Os concentrations in metropolitan areas? If so, what specific
19 changes are needed?
20 • Are there situations where fewer monitors could be utilized in urban areas without
21 increasing the uncertainty surrounding data analysis? If so, what criteria should be
22 considered when monitors are evaluated for potential termination or relocation?
23 • Are further revisions to non-urban Os monitoring requirements necessary to improve
24 characterization of O3 concentrations outside of metropolitan areas? If so, what
25 specific objectives should considered in any proposed changes to these requirements?
26 • What new information is available to inform network design options and technologies
27 that are utilized in the PAMS network? What specific changes, if any, should be
28 considered in PAMS requirements?
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1 • Os monitoring sites are typically located to meet very specific probe and monitor
2 siting criteria described in 40 CFR Part 58, Appendix E (e.g., acceptable probe
3 height). Are there situations where a different set of monitor placement criteria
4 would be appropriate to consider depending on the specific objective being
5 characterized? For example, would a different set of probe height criteria be
6 appropriate for monitors deployed in ecosystems with (Vsensitive vegetation versus
7 monitors deployed in cities for NAAQS compliance objectives? What changes, if
8 any, should be considered?
9 "Is the length of the currently required O?, monitoring seasons adequate to characterize
10 concentrations in urban and non-urban areas? What changes, if any, should be
11 considered?
12 Data Reporting and Assessments
13 The data interpretation of the primary and secondary NAAQS appendix describes the
14 computations necessary for determining when the primary and secondary standards are met. The
15 appendix addresses in detail, data completeness requirements, data reporting and handling
16 conventions, the form of the standard, averaging times, and provides examples. As part of this
17 review, the data interpretation appendix may need further revisions to ensure that EPA is
18 providing the best protection of public health and welfare. This review will provide the
19 opportunity to take advantage of the insights and newer concepts that have arisen in the recent
20 review of other NAAQS pollutants.
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United States Office of Air Quality Planning and Publication No. EPA-
Environmental Standards 452/D-09-001
Protection Health & Environmental Impacts September 2009
Agency Division
Research Triangle Park, NC
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