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Page 1 of 647 EO12866_O3
- NAAQS
- RIN2060
- A P38
- NPR
- Preamble_2014100 6 .docx 6560
- 50
- P

ENVIRONMENTAL PROTECTION AGENCY 40 CFR Parts 50, 51, 52, 53 and 58 [EPA
- HQ
- OAR
- 2008
- 0699; FRL
- ]

RIN 2 060
- AP38 National Ambient Air Quality Standards for Ozone

AGENCY: Environmental Protection Agency (EPA). ACTION: Proposed rule

. SUMMARY: Based on its review of the air quality criteria for ozone (O 3 ) and related photoch emical oxidants and nationa l ambient air quality standards (NAAQS) for O 3 , the EPA proposes to make revisions to the primary and secondary NAAQS for O 3 to provide requisite protection of public health and welfare, respecti vely ; to make corresponding revisions in data handling conventions for O 3 ; to make conforming changes to the Air Quality Index (AQI); to revise regulations for the prevention of significant deterioration (PSD) permitting program to add a grandfathering provision for certain pending p ermit applications from certain requirements with respect to the proposed revisions to the O 3 NAAQS; and to propose schedules and convey information related to implementing any revised standards

. In addition, the EPA is proposing changes to the O 3 monitori ng seasons, the Federal Reference Method (FRM) for monitoring O 3 in the ambient air , Federal Equivalent Method (FEM) procedures for testing, and the Photochemical Assessment Monitoring Stations (PAMS) network.*** E.O. 12866 Review

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Page 2 of 647 The EPA proposes to revise the primary standar d for O 3 by setting the level of that standard to within the range of 0.0 65 to 0.0 70 parts per million (ppm) in order to provide increased public health protection , including for “at

- risk” populations such as
children , older adults, and people with asthma or other lung diseases, against an array of
O 3 - related adverse health effects

. T he Administrator solicits comment on alternative standard levels below 0.065 ppm , and as low as 0.0 60 pp m . The EPA is proposing conforming changes to the AQ I for O 3 , proposing to set an AQI value of 100 equal to the level of the 8

- hour primary standard, and proposing proportional changes to the AQI values of 50, 150, 200 and 300. The EPA also proposes to revise the secondary standard to provide increased protection against vegetation

- related effects on public welfare. The Administrator proposes to conclude that air quality in terms of a three

- year average W126 index value within th e range from 13 ppm

- hours (ppm

- hrs) to 17 ppm

- hrs would provide the requisite protection against known or anticipated adverse effects to the public welfare. The EPA solicits comment on this proposed conclusion. To achieve that level of air quality, the Adm inistrator proposes to revise the level of the current secondary standard to within the range proposed for the primary O 3 standard of 0.065 to 0.070 ppm , which air quality analyses indicate would provide air quality, in terms of three

- year average W126 ind ex values, of a range at or below 13

- 17 ppm

- hrs

. The EPA solicits comments on this proposed revision of the secondary standard. Further, with regard to identification of a W126 index value that would describe air quality providing requisite public welfare protection, the EPA additionally solicits comments on values within the range extending below 13 ppm

- hrs down to 7 ppm

- hrs.*** E.O. 12866 Review

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Page 3 of 647 The EPA also solicits comments on the alternative approach of revising the secondary standard to a cumulative, seasonal, concentrat ion

- weighted form, the W126 index based on the three consecutive month period within the O 3 season with the maximum index value, with daily exposures cumulated for the 12

- hour period from 8:00
am to 8:00 pm and with a form that averages seasonal W126 values across three consecutive years and a level within the range of 1 3 ppm - hrs to 1 7 ppm - hrs. The EPA additionally solicits comments on such a distinct secondary standard with a level within the range extending below 13 ppm

- hrs down to 7 ppm

- hrs. Further , the EPA solicits comments on retaining the current secondary standard, without revision.
I n conjunction with proposing exceptional event schedules related to implementing any revised O 3 standards, the EPA is also proposing to apply this same schedule ap proach to other future revised NAAQS and to remove obsolete regulatory language associated with already expired exceptional event deadlines for historical standards for both O 3 and other NAAQS pollutants. The EPA is also proposing to make minor changes to the procedures and time periods for evaluating potential FRMs and equivalent methods (including making the requirements for nitrogen dioxide consistent with the requirements for O 3 ) and removing an obsolete requirement for the annual submission of document ation by manufacturers of certain particulate matter monitors. DATES: Written comments on this proposed rule must be received by [ INSERT 9 0 DAYS AFTER PUBLICATION IN THE FR ]

. ADDRESSES: Submit your comments, identified by Docket ID No. EPA

- HQ

- OAR

2008

- 0699 , to the EPA by one of the following methods:

 www.regulations.gov : Follow the on

- line instructions for submitting comments.*** E.O. 12866 Review

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Page 4 of 647  Email: a - and

- r - Docket@epa.gov

 Fax: 202

- 566

- 9744

 Mail: Docket No. EPA

- HQ

- OAR

- 2008

- 0699, Environmental Protection Agency, Mail code 6102T, 1200 Pennsylvania Ave., NW, Washington, DC 20460

. Please include a total of two copies

.

 Hand Delivery: Docket No. EPA

- HQ

- OAR

- 2008

- 0699, Environmental Pr otection Agency, EPA West, Room 3334, 1301 Constitution Ave., NW, Washington, DC. Such deliveries are only accepted during the Docket’s normal hours of operation, and special arrangements should be made for deliveries of boxed information. Public Hearings : Three public hearings are scheduled for this proposed rule

. Two of the public hearings will be held on XXX, 2015 in XXX, XXX and XXX, XXX

. The third public hearing will be held on XXX, 2015 in XXX, XXX

. The hearings will be held at the following location s: XXX , XXX

– XXX, 2015 Example location Address Address Address Telephone: XXX, XXX

– XXX, 2015 Example location Address Address Address Telephone: XXX, XXX

– XXX, 2015 Example location Address*** E.O. 12866 Review

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Page 5 of 647 Address Address Telephone: See the SUPPLEMENTARY INFORMATION under “Public Hearings” for
further information.
Instructions : Direct your comments to Docket ID No. EPA

- HQ

- OAR

- 2008

- 0699. The EPA's policy is that all comments received will be included in the public docket without change and may be made available online at www.regulations.gov , including any personal information provided, unless the comment includes information claimed to be Confidential Business Information (CBI) or other information whose disclosure is restricted by statute

. Do not submit information that you consider to be CBI or otherwise protected through www.regulations.gov or e - mail

. The www.regulations.gov website is an “anonymous access” system, which means the EPA will not know your identity or contact information unless you provide it in th e body of your comment

. If you send an e

mail comment directly to the EPA without going through www.regulations.gov your e mail address will be automatically captured and included as part of the comment that is pl aced in the public docket and made available on the Internet

. If you submit an electronic comment, the EPA recommends that you include your name and other contact information in the body of your comment and with any disk or CD

- ROM you submit

. If the EPA ca nnot read your comment due to technical difficulties and cannot contact you for clarification, the EPA may not be able to consider your comment

. Electronic files should avoid the use of special characters, any form of encryption, and be free of any defects or viruses

. For additional information about EPA’s public docket visit the EPA Docket Center homepage at http://www.epa.gov/epahome/dockets.htm

.*** E.O. 12866 Review

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Page 6 of 647 Docket: The EPA has established dockets for these acti ons as discussed above. All documents in the se docket s are listed o n the www.regulations.gov website. This includes documents in the rulemaking docket ( Docket ID No. EPA

- HQ

- OAR

- 2008

- 0699 ) and a separate docket, established for the Integrated Science Assessment (Docket No.
EPA

- HQ

- ORD

- 2011

- 0050 ), that has have been incorporated by reference into the rulemaking docket

. Although listed in the index, some information is not publicly available, e.g., C BI or other information whose disclosure is restricted by statute

. Certain other material, such as copyrighted material, is not placed on the Internet and may be viewed, with prior arrangement, at the EPA Docket Center. Publicly available docket materials are available either electronically in www.regulations.gov or in hard copy at the Air and Radiation Docket and Information Center, EPA/DC, EPA West, Room 3334, 1301 Constitution Ave., NW, Washington, DC

. The Publi c Reading Room is open from 8:30 a.m. to 4:30 p.m., Monday through Friday, excluding legal holidays

. The telephone number for the Public Reading Room is (202) 566

- 1744 and the telephone number for the Air and Radiation Docket and Information Center is (202 ) 566

- 1742. For additional information about EPA’s public docket visit the EPA Docket Center homepage at : http://www.epa.gov/epahome/dockets.htm

. FOR FURTHER INFORMATION CONTACT: Ms. Susan Lyon Stone, Health and Environmental Impacts Division, Office of Air Quality Planning and Standards, U.S. Environmental Protect ion Agency, Mail code C504

- 06, Research Triangle Park, NC 27711; telephone: 919

- 541

- 1146; fax: 919

- 541

- 0237; email: stone.susan@epa.gov

. SUPPLEMENTARY INFORMATION: General Information*** E.O. 12866 Review

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Page 7 of 647 What Should I Consider as I Prepare My Comments for EPA?
1

. Submitting CBI

. Do not submit this information to EPA through www.regulations.gov or email

. Clearly mark the part or all of the information that you claim to be CBI

. For CBI information in a disk or CD ROM that you mail to EPA, mark the outside of the disk or CD ROM as CBI and then identify electronically within the disk or CD ROM the specific information that is claimed as CBI

. In addition to one complete version of the comment that includes information claimed as CBI, a copy of the comment that does not contain the information claimed as CBI must be submitted for in clusion in the public docket

. Information so marked will not be disclosed except in accordance with procedures set forth in 40 CFR part 2.
2

. Tips for Preparing Your Comments

. When submitting comments, remember to:

 Identify the rulemaking by docket number and other identifying information (subject heading, Federal Register date and page number).

 Follow directions

– The Agency may ask you to respond to specific questions or organize comments by referencing a Code of Federal Regulations (CFR) part or section number.

 Explain why you agree or disagree, suggest alternatives, and substitute language for your requested changes.

 Describe any assumptions and provide any technical information and/or data that you used.

 Provide specific examples to illustrate your con cerns, and suggest alternatives.

 Explain your views as clearly as possible, avoiding the use of profanity or personal threats.*** E.O. 12866 Review

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Page 8 of 647  Make sure to submit your comments by the comment period deadline identified. Availability of Related Information A number of docu ments relevant to this rulemaking are available on EPA web sites. The Integrated Science Assessment for Ozone and Related Photochemical Oxidants ( ISA ) ( EPA 600/R

- 10/076F, February 2013 ) is available on EPA’s National Center for Envi ronmental Assessment web site. To obtain this document, go to http://www.epa.gov/ncea , and click on Ozone in the Quick Finder section. This will open a page with a link to the February 2013 Integrated Science Assessment. The 20 14 Policy
Assessment , Health and Welfare Risk and Exposure Assessments , and other related technical documents are available on EPA’s Office of Air Quality Planning and Standards (OAQPS) Technology Transfer Network (TTN) web site. The final 2 014 Policy Assessment is available at: http://www.epa.gov/ttn/naaqs/standards/ozone/s_o3_2008_pa.html and the final 2014 Health and Welfare Risk and Exposure Assessments and other related techn ical docu ments are available at: http://www.epa.gov/ttn/naaqs/standards/ozone/s_o3_2008_rea.html

. These and other related documents are also available for inspection and copying in the EPA docket identified above. Public Hearings The public hearings on XXX, 2015 and XXX, 2015 will provide interested parties the opportunity to present data, views, or arguments concerning the proposed rule

. The EPA may ask clarifying questions during the oral presentations, but will not respond to the presentations at that time

. Written statements and supporting information submitted*** E.O. 12866 Review

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Page 9 of 647 during the comment period will be considered with the same weight as any oral comments and supporting information presented at the public hearing

. Written comments must be received by the last day of the comment period, as specified in this proposed rulemaking. The public hearings will begin at 9:30 a.m. and continue until 7:30 p.m. (local time) or later, if necessary, dependi ng on the number of speakers wishing to participate

. The EPA will make every effort to accommodate all speakers that arrive and register before 7:30 p.m

. A lunch break is scheduled from 12:30 p.m. until 2:00 p.m. If you would like to present oral testimon y at the hearings, please notify Mr/Ms. XXX XXX (Cxxx

- xx), U.S. EPA, Research Triangle Park, NC 27711

. The preferred method for registering is by e

- mail (XXX.XXX@epa.gov)

. Mr/Ms. XXX may be reached by telephone at (919) 541

- xxxx . S/he will arrange a genera l time slot for you to speak

. The EPA will make every effort to follow the schedule as closely as possible on the day of the hearing. Oral testimony will be limited to five (5) minutes for each commenter to address the proposal

. We will not be providing e quipment for commenters to show overhead slides or make computerized slide presentations unless we receive special requests in advance

. Commenters should notify Mr/Ms. XXX if they will need specific audiovisual (AV) equipment

. Commenters should also notify Ms. XXX if they need specific translation services for non

- English speaking commenters

. The EPA encourages commenters to provide written versions of their oral testimonies either electronically on computer disk, CD

- ROM, or in paper copy.*** E.O. 12866 Review

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Page 10 of 647 The hearing sch edules, including lists of speakers, will be posted on EPA’s web site for the proposal at http://www.epa.gov/ttn/naaqs/standards/ozone/s_o3_index.html prior to the hearing. Verbat im transcripts of the hearings and written statements will be included in the rulemaking docket. Table of Contents The following topics are discussed in this preamble: I. Background A. Executive Summary B . Legislative Requirements C . Related Control Programs to Implement O 3 Standards D . Review of Air Quality Criteria and Standards for O 3 E . Ozone Air Quality II. Rationale for Proposed Decision on the Primary Standard A. Approach B. Health Effects Information 1. Overview of Mechanisms 2. Nature of Effects 3. Adversity of O 3 Effects 4. Ozone

- Related Impacts on Public Health C . Human Exposure and Health Risk Assessments 1. Air Quality Adjustment 2. Exposure Assessment 3. Quantitative Health Risk Assessments D . Conclusions on the Adequacy of the Current Primary Standard 1. Evidence

- Based Considerations in the PA 2. Summary of Exposure

- and Risk

- Based Considerations in the PA 3. CASAC Advice 4. Policy Assessment Conclusions on the Current Standard 5 . Administrator’s Proposed Conclusions Concerning the Adequacy of the Current Standard E . Conclusions on the Elements of the Primary Standard 1. Indicator 2. Averaging Time 3. Form 4. Level F . Proposed Decision on the Primary Standard III. Communication of Public Health Information IV. Ration ale for Proposed Decision on the Secondary Standard A. Approach B. Welfare Effects Information 1. Nature of Effects and Biologically Relevant Exposure Metric*** E.O. 12866 Review

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Page 11 of 647 a. Foliar Injury b. Effects on Forest Tree Growth, Productivity and Carbon Storage c. Crop Yield Loss 2. Potential Impacts on Public Welfare C. Exposure and Risk Assessment Information 1. Air Quality Analyses 2. Tree Seedling Growth, Productivity, Carbon Storage and Associated Ecosystem Services a. Overview and Summary of Key R esults b. Key Uncertainties 3. Crop Yield a. Overview and Summary of Key Results b. Key Uncertainties 4. Visible Foliar Injury a. Overview and Summary of Key Results b. Key Uncertainties D. Conclusions on Adequacy of the Current Secondary Standard 1. Evidence

- and Exposure/Risk

- Based Considerations in Policy Assessment 2. CASAC Advice 3. Administrator’s Proposed Conclusion on Adequacy of the Current Standard E. Consideration of Alternative Secondary Standards 1. Indicator 2. Consi deration of a Cumulative Seasonal Exposure

- based Standard in the Policy Assessment a. Form and Averaging Time b. Level 3. CASAC Advice 4. Air Quality Analyses 5. Administrator’s Proposed Conclusions V. Appendix U: Interpretation of the O 3 NAAQS A. Background B. Data Selection Requirements C. Data Reporting and Data Handling Requirements D. Considerations for the Possibility of a Distinct Secondary Standard E. Exceptional Events Information Submission Schedule VI. Ambient Monitoring Related to Propose d O 3 Standards A. Background B. Revisions to the Length of the Required O 3 Monitoring Seasons C. Revisions to the Photochemical Assessment Monitoring Stations (PAMS) and Network Design D. Addition of a New Federal Reference Method (FRM) for O 3 E. Revisions to the Procedures for Testing Performance Characteristics and Determining Comparability Between Candidate Methods and Reference Methods for Ozone, Nitrogen Dioxide, and Particulate Matter*** E.O. 12866 Review

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Page 12 of 647 VII. Implementation of Proposed O 3 Standards A. NAAQS Implementation Pla ns 1. Background 2. Timing of Rules and Guidance 3. Section 110 State Implementation Plans 4. Nonattainment Area Requirements B. Implementing a Distinct Secondary O 3 NAAQS , i f One is Established C. Designation of Areas D. Prevention of Significant Dete rioration and Nonattainment New Source Review Programs for the Proposed Revised Primary O 3 NAAQS and the Proposed Secondary O 3 NAAQS 1. Prevention of Significant Deterioration (PSD) 2. Nonattainment New Source Review E. Transportation and Gene ral Conformity Programs 1. What are Transportation and General Conformity? 2. Why is the EPA Discussing Transportation and General Conformity in this Proposed Rulemaking? 3. When Would Transportation and General Conformity Apply to Areas Designated Nonatt ainment for a New or Revised O 3 NAAQS, if One is Established? 4. Will Transportation and General Conformity Apply to a Distinct Secondary O 3 NAAQS, if One is Established? 5. What Impact Would the Implementation of a New or Revised O 3 NAAQS Have on a State’s Transportation and/or General Conformity SIP? F. How Background O 3 Is Addressed in CAA Implementation Provisions 1. Introduction 2. Exceptional Event Exclusions 3. Rural Transport Areas 4. International Transport VIII. Statutory and Executive Order Reviews A. National Technology Transfer and Advancement Act B. Paperwork Reduction Act C. Regula tory Flexibility Act D. Unfunded Mandates Reform Act E. EO 12866: Regulatory Planning and Review F. EO 12898: Federal Actions to Ad dress Environmental Ju stice in Minority Populations and Low

- Income Populations G. EO 13045: Protection of Children from Environmental Health & Safety Risks H. EO 13132: Federalism I. EO 13175: Consultation and Coordination with Indian Tribal Governme nts J. EO 13211: Actions that Significantly Affect Energy Supply, Distribution, or Use References I. Background*** E.O. 12866 Review

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Page 13 of 647 A. Executive Summary

– To be added
B

. Legislative Requirements Two sections of the CAA govern the establishment and revision of the NAAQS. Section 108 (42 U.S.C. section 7408) directs the Administrator to identify and list certain air pollutants and then to issue air quality criteria for those pollutants. The Administrator is to list those air pollutants that in her “judgment, cause or contri bute to air pollution which may reasonably be anticipated to endanger public health or welfare;” “the presence of which in the ambient air results from numerous or diverse mobile or stationary sources;” and “for which . . . [the Administrator] plans to iss ue air quality criteria....” Air quality criteria are intended to “accurately reflect the latest scientific knowledge useful in indicating the kind and extent of all identifiable effects on public health or welfare which may be expected from the presence of [a] pollutant in the ambient air . . .” 42 U.S.C. § 7408(b)

. Section 109 (42 U.S.C. 7409) directs the Administrator to propose and promulgate “primary” and “secondary” NAAQS for pollutants for which air quality criteria are issued. Section 109(b)(1) defin es a primary standard as one “the attainment and maintenance of which in the judgment of the Administrator, based on such criteria and allowing an adequate margin of safety, are requisite to protect the public health.” 1 A secondary standard, as defined in section 109(b)(2), must “specify a level of air quality the attainment and maintenance of which, in the judgment of the Administrator, based on

1 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, 91 st Cong., 2d Sess. 10 (1970).*** E.O. 12866 Review

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Page 14 of 647 such criteria, is requisite to protect the public welfare from any known or anticipated adverse effects associa ted with the presence of [the] pollutant in the ambient air.” 2 The requirement that primary standards provide an adequate margin of safety was intended to address uncertainties associated with inconclusive scientific and technical information available at the time of standard setting. It was also intended to provide a reasonable degree of protection against hazards that research has not yet identified. See State of Mississippi v. EPA , 744 F. 3d 1334, 1353 (D.C. Cir. 2012) (“By requiring an ‘adequate margin of safety’, Congress was directing EPA to build a buffer to pro tect against uncertain and unknown dangers to human health”); see also Lead Industries Association v. EPA , 647 F.2d 1130, 1154 (D.C. Cir 1980); American Petroleum Institute v. Costle , 665 F.2d 1176, 1186 (D.C. Cir. 1981); American Farm Bureau Federation v

. EPA , 559 F. 3d 512, 533 (D.C. Cir. 2009); Association of Battery Recyclers v. EPA , 604 F. 3d 613, 617

- 18 (D.C. Cir. 2010). Both kinds of uncertainties are components of the risk associated with pollution at levels below those at which human health effect s can be said to occur with reasonable scientific certainty. Thus, in selecting primary standards that provide an adequate margin of safety, the Administrator is seeking not only to prevent pollution levels that have been demonstrated to be harmful but als o to prevent lower pollutant levels that may pose an unacceptable risk of harm, even if the risk is not precisely identified as to nature or degree. The CAA does not require the Administrator to establish a primary NAAQS at a zero

- risk level or at backgrou nd concentration s , see

2 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.”*** E.O. 12866 Review

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Page 15 of 647 Lead Industries v. EPA , 647 F.2d at 1156 n.51 ; State of Mississippi v. EPA , 744 F. 3d at 1343, 1351, but rather at a level that reduces risk sufficiently so as to protect public health with an adequate margin of safety. In addressin g the requirement for an adequate margin of safety, the EPA considers such factors as the nature and severity of the health effects, the size of sensitive population(s) 3 at risk, and the kind and degree of the uncertainties that must be addressed. The sele ction of any particular approach for providing an adequate margin of safety is a policy choice left specifically to the Administrator’s judgment. See Lead Industries Association v. EPA , 647 F.2d at 1161

- 62; State of Mississippi , 744 F. 3d at 1353. In setti ng primary and secondary standards that are “requisite” to protect public health and welfare, respectively, as provided in section 109(b), EPA’s task is to establish standards that are neither more nor less stringent than necessary for these purposes. In s o doing, the EPA may not consider the costs of implementing the standards. See generally, Whitman v. American Trucking Associations , 531 U.S. 457, 465

- 472, 475

- 76 (2001). Likewise, “[a]ttainability and technological feasibility are not relevant considerati ons in the promulgation of national ambient air quality standards.” American Petroleum Institute v. Costle , 665 F. 2d at 1185. Section 109(d)(1) requires that “not later than December 31, 1980, and at 5

- year intervals thereafter, the Administrator shall co mplete a thorough review of the criteria published under section 108 and the national ambient air quality standards . . . and shall make such revisions in such criteria and standards and promulgate such new standards as

3 As used here and similarly throughout this document, the term population refers to p eople having a quality or characteristic in common, including a specific pre

- existing illness or a specific age or life stage.*** E.O. 12866 Review

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Page 16 of 647 may be appropriate . . . .” Section 109(d)(2) requires that an independent scientific review committee “shall complete a review of the criteria . . . and the national primary and secondary ambient air quality standards . . . and shall recommend to the Administrator any new . . . standards a nd revisions of existing criteria and standards as may be appropriate . . . .” Since the early 1980's, the Clean Air Scientific Advisory Committee (CASAC) has performed this independent review function. 4
C

. Related Control Programs to Implement O 3 Stand ards States are primarily responsible for ensuring attainment and maintenance of ambient air quality standards once the EPA has established them. Under section 110 of the CAA, and related provisions, states are to submit, for the EPA’s approval, state impl ementation plans (SIPs) that provide for the attainment and maintenance of such standards through control programs directed to sources of the pollutants involved. The states, in conjunction with the EPA, also administer the Prevention of Significant Deteri oration (PSD) program (CAA sections 160 to 169). In addition, Federal programs provide for nationwide reductions in emissions of O 3 precursors and other air pollutants through the Federal motor vehicle and motor vehicle fuel control program under title II of the Act (CAA sections 202 to 250) which involves controls for emissions from mobile sources and controls for the fuels used by these sources, and new source performance standards for stationary sources under section 111 of the CAA

. For some stationary

4 Lists of CASAC members and of members of the CASAC Ozone Review Panel are available at: http://yosemite.epa.gov/sab/sabpeople.nsf/WebCommitteesSubCommitt ees/Ozone%20Re view%20Panel.*** E.O. 12866 Review

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Page 17 of 647 s ources, the national emissions standards for hazardous air pollutants under section 112 of the CAA may provide ancillary reductions in O 3 precursors. After the EPA establishes a new or revised NAAQS, the CAA directs the EPA and the states to take steps to ensure that the new or revised NAAQS is met. One of the first steps, known as the initial area designations, involves identifying areas of the country that either are attaining or not attaining the new or revised NAAQS along with the nearby areas that cont ribute to the violations. Upon designation of nonattainment areas, certain states would then be required to develop SIPs to attain the standards. In developing their attainment plans, states would first take into account projected emission reductions from federal and state rules that have been already adopted at the time of plan submittal. A number of significant emission reduction programs that will lead to reductions of O 3 precursors are in place today or are expected to be in place by the time any new SIPs will be due. Examples of such rules include the NO X SIP Call, Clean Air Interstate Rule, and Cross

- State Air Pollution Rule, 5 regulations controlling onroad and nonroad engines and fuels, the utility and industrial boilers hazardous air pollutant rules, and various other programs already adopted by states to reduce emissions from key emissions sources. States would then evaluate the level of additional emission reductions needed for each nonattainment area to attain the O 3 standards “as expeditiously as practicable,” and adopt new state regulations as appropriate. Section VII of this preamble includes additional discussion of designation and implementation issues associate d with any revised O 3 NAAQS.

5 Th e Cross

- State Air Pollution R ule was recently upheld by the Supreme Court in Environmental Protection Agency v. EME Homer City Generation , U.S. (2014).*** E.O. 12866 Review

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Page 18 of 647 D

. Review of Air Quality Criteria and Standards for O 3 The EPA first established primary and secondary NAAQS for photochemical oxidants in 1971 (36 FR 8186, April 30, 1971). The EPA set both primary and secondary standards at a level of 0.08 parts per million (ppm), 1

- hr average, total photochemical oxidants, not to be exceeded more than one hour per year. The EPA based the standards on scientific information contained in the 1970 Air Quality Criteria for Photochemical Oxidants (U.S. DHE W, 1970). The EPA initiated the first periodic review of the NAAQS for photochemical oxidants in 1977. Based on the 1978 Air Quality Criteria for Ozone and Other Photochemical Oxidants (U.S. EPA, 1978), the EPA published proposed revisions to the original NAAQS in 1978 (43 FR 16962) and final revisions in 1979 (44 FR 8202). At that time, the EPA revised the level of the primary and secondary standards from 0.08 to 0.12 ppm and changed the indicator from photochemical oxidants to O 3 , and the form o f the standards from a deterministic (i.e., not to be exceeded more than one hour per year ) to a statistical form. This statistical form defined attainment of the standards as occurring when the expected number of days per calendar year with maximum hourly average concentration greater than 0.12 ppm equaled one or less. Following the final decision in the 1979 review, the City of Houston challenged the Administrator’s decision arguing that the standard was arbitrary and capricious because natural O 3 concen trations and other physical phenomena in the Houston area made the standard unattainable in that area. The U.S. Court of Appeals for the District of Columbia Circuit (D.C. Circuit) rejected this argument, holding (as noted above) that attainability and tec hnological feasibility are not relevant considerations in the promulgation of the NAAQS. The court also noted that the EPA need not tailor the*** E.O. 12866 Review

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Page 19 of 647 NAAQS to fit each region or locale, pointing out that Congress was aware of the difficulty in meeting standards i n some locations and had addressed this difficulty through various compliance related provisions in the Act. See API v. Costle , 665 F.2d 1176, 1184

- 6 (D.C. Cir. 1981). In 1982, the EPA announced plans to revise the 1978 Air Quality Criteria document (47 F R 11561), and in 1983, the EPA initiated the second periodic review of the O 3 NAAQS (48 FR 38009). The EPA subsequently published the 1986 Air Quality Criteria for Ozone and Other Photochemical Oxidants (U.S. EPA, 1986) and the 1989 Staff Paper (U.S. EPA, 1989). Following publication of the 1986 Air Quality Criteria Document (AQCD), a number of scientific abstracts and articles were published that appeared to be of sufficient importance concerning potent ial health and welfare effects of
O 3 to warrant preparation of a Supplement (U.S. EPA, 1992). On August 10, 1992, under the terms of a court order, the EPA published a proposed decision to retain the existing primary and secondary standards (57 FR 35542). The notice explained that the proposed decision would complete the EPA’s review of information on health and welfare effects of O 3 assembled over a 7

- year period and contained in the 1986 AQCD and its 1992 Supplement. The proposal also announced the EPA’s intention to proceed as rapidly as possible with the next review of the air quality criteria and standards for O 3 in light of emerging evidence of health effects related to 6

- to 8

- hour O 3 exposures. On March 9, 1993, the EPA concluded the review by affirm ing its proposed decision to retain the existing primary and secondary standards (58 FR 13008). In August 1992, the EPA announced plans to initiate the third periodic review of the air quality criteria and O 3 NAAQS (57 FR 35542). In December 1996, the E PA*** E.O. 12866 Review

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Page 20 of 647 proposed to replace the then

- existing 1

- hour primary and secondary standards with 8

- hour average O 3 standards set at a level of 0.08 ppm (equivalent to 0.084 ppm using standard rounding conventions) (61 FR 65716). The EPA also proposed to establish a

new distinct secondary standard using a biologically based cumulative, seasonal form. The EPA completed this review on July 18, 1997 (62 FR 38856) by setting the primary standard at a level of 0.08 ppm, based on the annual fourth

- highest daily maximum 8

- hr

ave rage concentration, averaged over three years, and setting the secondary standard identical to the revised primary standard. In reaching this decision, the EPA identified several reasons supporting its decision to reject a poten tial alternate standard set at 0.07 ppm. Most importantly, the EPA pointed out the scientific uncertainty at lower concentrations and placed significant weight on the fact that no CASAC panel member supported a standard level set lower than 0.08 ppm (62 FR 38868). In addition to noti ng the uncertainties in the health evidence for exposure concentrations below 0.08 ppm and the advice of CASAC, the EPA noted that a standard set at a level of 0.07 ppm would be closer to peak background concentrations that infrequently occur in some areas due to nonanthropogenic sources of O 3 precursors (62 FR 38856, 38868; July 18, 1997). On May 14, 1999, in response to challenges by industry and others to EPA’s 1997 decision, the U.S. Court of Appeals for the District of Columbia Circuit remanded the O 3 NAAQS to the EPA, finding that section 109 of the Act, as interpreted by the EPA, effected an unconstitutional delegation of legislative authority. American Trucking
Assoc. vs. EPA , 175 F.3d 1027, 1034

- 1040 (D.C. Cir. 1999) (“ ATA I ”). In addition, the

cou rt directed that, in responding to the remand, the EPA should consider the potential beneficial health effects of O 3 pollution in shielding the public from the effects of solar*** E.O. 12866 Review

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Page 21 of 647 ultraviolet (UV) radiation, as well as adverse health effects. Id. at 1051

- 53. In 1999, the EPA petitioned for rehearing en banc on several issues related to that decision. The court granted the request for rehearing in part and denied it in part, but declined to review its ruling with regard to the potential beneficial effects of O 3 pollution. 195 F3d 4, 10 (D.C Cir., 1999) (“ ATA II ”). On January 27, 2000, the EPA petitioned the U.S. Supreme Court for certiorari on the constitutional issue (and two other issues), but did not request review of the ruling regarding the potential benefi cial health effects of O 3 . On February 27, 2001, the U.S. Supreme Court unanimously reversed the judgment of the D.C. Circuit on the constitutional issue. Whitman v. American Trucking Assoc ., 531 U. S. 457, 472

- 74 (2001) (holding that section 109 of the CA A does not delegate legislative power to the EPA in contravention of the Constitution). The Court remanded the case to the D.C. Circuit to consider challenges to the O 3 NAAQS that had not been addressed by that court’s earlier decisions. On March 26, 2002, the D.C. Circuit issued its final decision on remand, finding the 1997 O 3 NAAQS to be “neither arbitrary nor capricious,” and so denying the remaining petitions for review. American Trucking Associations, Inc. v EPA , 283 F.3d 355, 379 (D.C Cir., 2002)(“ AT A III ”). Specifically, in ATA III , the D.C. Circuit upheld the EPA’s decision on the 1997
O 3 standard as the product of reasoned decision

- making. The Court made clear that the most important support for EPA’s decision was the health evidence and the concer ns it raised about setting a standard level below 0.08 ppm (“the record is replete with references to studies demonstrating the inadequacies of the old one

- hour standard ”), as well as extensive information supporting the change to an 8

- hour averaging time

. 283 F 3d at 378. The Court also pointed to the significant weight that the EPA properly placed*** E.O. 12866 Review

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Page 22 of 647 on the advice it received from CASAC. Id. at 379. The court further noted that “although relative pr oximity to peak background O 3 concentrations did not, in its elf, necessitate a level of 0.08, EPA could consider that factor when choosing among the three alternative levels.” Id. Independently of the litigation, the EPA also responded to the Court’s remand to consider the potential beneficial health effects of O 3 pollution in shielding the public from effects of UV radiation. The EPA provisionally determined that the information linking changes in patterns of ground

- level O 3 concentrations to changes in relevant patterns of exposures to UV radiation of concern to public health was too uncertain, at that time, to warrant any relaxation in 1997 O 3 NAAQS. The EPA also expressed the view that any plausible changes in UV

- B radiation exposures from changes in patterns of ground

- level O 3 concentrations would likely be ver y small from a public health perspective. In view of these findings, the EPA proposed to leave the 1997 8

- hour NAAQS unchanged (66 FR 57268, Nov. 14, 2001). After considering public comment on the proposed decision, the EPA published its final response to this remand on January 6, 2003, re

- affirming the 8

- hour O 3 NAAQS set in 1997 (68 FR 614). The EPA initiated the fourth periodic review of the air quality criteria and O 3 standards in September 2000 with a call for information (65 FR 57810). The schedule f or completion of that review was ultimately governed by a consent decree resolving a lawsuit filed in March 2003 by plaintiffs representing national environmental and public health organizations, who maintained that the EPA was in breach of a mandatory leg al duty to complete review of the O 3 NAAQS within a statutorily mandated deadline. On July 11, 2007, the EPA proposed to revise the level of the primary standard withi n a*** E.O. 12866 Review

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Page 23 of 647 range of 0.075 to 0.070 ppm (72 FR 37818). Documents supporting this proposed decisio n included the Air Quality Criteria for Ozone and Other Photochemical Oxidants ( U.S. EPA, 2006a ) and the Staff Paper (U.S EPA, 2007) and related technical support documents. The EPA also proposed two options for revising the secondary standard: (1) replace the current standard with a cumulative, seasonal standard, expressed as an index of the annual sum of weighted hourly concentrations cumulated over 12 daylight hours during the consecutive 3

- month period within the O 3 season with the maximum index value, set at a level within the range of 7 to 21 ppm

- hrs, or (2) set the secondary standard identical to the proposed primary standard. The EPA completed the review with publication of a final decision on March 27, 2008 (73 FR 16436). In that final rule, the
EPA revised the NAAQS by lowering the level of the 8

- hour primary O 3 standard from 0.08 ppm to 0.075 ppm, not otherwise revising the primary standard, and adopting a secondary standard identical to the revised primary standard. In May 2008, state, public heal th, environmental, and industry petitioners filed suit challenging EPA’s final decision on the 2008 O 3 standards. On September 16, 2009, the EPA announced its intention to reconsider the 2008 O 3 standards, and initiated a rulemaking to do so

. At EPA’s requ est, the Court held the consolidated cases in abeyance pending EPA’s reconsideration of the 2008 decision. On January 19, 2010 (75 FR 2938), the EPA issued a notice of proposed rulemaking to reconsider the 2008 final decision. In that notice, the EPA prop osed that further revisions of the primary and secondary standards were necessary to provide a requisite level of protection to public health and welfare. The EPA proposed to decrease the level of the 2008 8

- hour primary standard from 0.075 ppm to a level within the range*** E.O. 12866 Review

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Page 2 4 of 647 of 0.060 to 0.070 ppm, and to change the secondary standard to a new cumulative, seasonal standard expressed as an annual index of the sum of weighted hourly concentrations, cumulated over 12 hours per day (8 am to 8 pm), during the consec utive
3

- month period within the O 3 season with a maximum index value , set at a level within the range of 7 to 15 ppm

- hours. The Agency also solicited CASAC review of the proposed rule on January 25, 2010 and solicited additional CASAC advice on January 26, 2011. After considering comments from CASAC and the public, the EPA prepared a draft final rule, which was submitted for interagency review pursuant to Executive Order 12866. On September 2, 2011, consistent with the direction of the President, the Admini strator of the Office of Infor mation and Regulatory Affairs (OIRA ), Office of Management and Budget (OMB ), returned the draft final rule to the EPA for further consideration. In view of this return and the fact that the Agency’s next periodic review of the O 3 NAAQS required under Clean Air Act section 109 had already begun (as announced on September 29, 2008), the EPA decided to defer the decisions involved in the reconsideration until it complete d its statutori ly required periodic review. In light of EPA’ s decision to consolidate the reconsideration with the current review, the D.C. Circuit Court of Appeals proceeded with the litigation on the 2008 final decision. On July 23, 2013, the Court upheld EPA’s 2008 primary O 3 standard, but remanded the 2008 secondary standard to the EPA. State of Mississippi v. EPA , 744 F. 3d 1334 . With respect to the primary standard, the court first held that the EPA reasonably determined that the existing standard was not requisite to prote ct public health with an adequate margin of safety, and consequently required revision. Specifically, the court noted that there were “numerous epidemiologic studies linking health effects to*** E.O. 12866 Review

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Page 25 of 647 exposure to ozone levels below 0.08 ppm and clinical human expos ure studies finding a causal relationship between health effects and exposure to ozone levels at and below 0.08
ppm . ” 744 F. 3d at 1345 . The court also specifically endorsed the weight of evidence approach utilized by the EPA in its deliberations. Id. at 1 344 The court went on to reject arguments that the EPA should have adopted a more stringent primary standard. Dismissing arguments that a clinical study (as properly interpreted by the EPA) showing effects at 0.06 ppm necessitated a standard level lower
t han that selected, the court noted that this was a single, limited study. Id. at 1350 . With respect to the epidemiologic evidence, the court accepted EPA’s argument that there could be legitimate uncertainty that a causal relationship between O 3 and 8

- hour exposures less than 0.075 ppm exists, so that associations at lower levels reported in epidemiologic studies did not necessitate a more stringent standard. Id. at 1351

- 52

. 6 The court also rejected arguments that an 8

- hour primary standard of 0.075 ppm fai led to provide an adequate margin of safety, noting that margin of safety considerations involved policy judgments by the agency, and that by setting a standard “appreciably below” the level of the current standard (0.08 ppm), the agency had made a

reason able policy choice. Id. Finally, the court rejected arguments that the EPA’s decision was inconsistent with CASAC’s scientific recommendations because CASAC had been insufficiently clear in its recommendations whether it was providing scientific

6 The court cautioned, however, that “perhaps more [clinical] studies li ke the Adams studies will yet reveal that the 0.060 ppm level produces significant adverse decrements that simply cannot be attributed to normal variation in lung function”, and further cautioned that “agencies may not merely recite the terms ‘substantial uncertainty’ as a justification for their actions’”. Id. at 1350, 1357 (internal citations omitted).*** E.O. 12866 Review

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Page 26 of 647 or policy recommendations, and the EPA had reasonably addressed CASAC’s policy
recommendations. Id. at 1357

- 58

. With respect to the secondary standard, the court held that because the EPA had failed to identify a level of air quality requisite to protect public wel fare, the EPA’s comparison between the primary and secondary standards for determining if requisite protection for public welfare was afforded by the primary standard did not comply with the Act . The court thus rejected the EPA’s explanation for setting th e secondary standard identical to the revised 8

- hour primary standard, and remanded the secondary standard to
EPA. Id. at 1360

- 62

. At the time of the court’s decision, the EPA had already completed significant portions of its next statutorily required periodic review of the O 3 NAAQS. On September 29, 2008, the EPA announced the initiation of a new periodic review of the air quality criteria for O 3 and related photochemical oxidants and issued a call for information in the Federal Register (73 FR 56581, Sept. 29, 2008). A wide range of external experts, as well as the EPA staff, representing a variety of areas of expertise (e.g., epidemiology, human and animal toxicology, statistics, risk/exposure analysis, atmospheric science, ecology, biology, plant sci ence, ecosystem services) participated in a workshop. This workshop was held on October 28

- 29, 2008 in Research Triangle Park, NC. The workshop provided an opportunity for a public discussion of the key policy

- relevant issues around which the EPA would str ucture this O 3 NAAQS review and the most meaningful new science that would be available to inform our understanding of these issues.*** E.O. 12866 Review

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Page 27 of 647 Based in part on the workshop discussions, the EPA developed a draft Integrated Review Plan (IRP) outlining the schedule, process, and key policy

- relevant questions that would guide the evaluation of the air quality criteria for O 3 and the review of the primary and secondary O 3 NAAQS. A draft of the IRP was released for public review and comment in September 2009. This IRP wa s the subject of a consultation with the CASAC on November 13, 2009 (74 FR 54562; October 22, 2009). 7 The EPA considered comments received from that consultation and from the public in finalizing the plan and in beginning the review of the air quality cri teria. The EPA’s overall plan and schedule for this review is presented in the Integrated Review Plan for the Ozone National Ambient Air Quality Standards

. 8 As part of the process of preparing the O 3 Integrated Science Assessment ( ISA ) , the EPA’s National Center for Environmental Assessment ( NCEA ) hosted a workshop to review and discuss preliminary drafts of key ISA on August 6, 2010 (75 FR 42085, July 20, 2010) . The CASAC and the public reviewed the first external r eview draft ISA (U.S. EPA, 2011a ; 76 FR 10893, February 28, 2011) at a meeting held in May 19

- 20, 2011 (76 FR 23809; April 28, 2011). Based on CASAC and public comments, NCEA prepared a second draft ISA (U.S. EPA, 2011 b ; 76 FR 60820, September 30, 2011)

. CASAC and the public reviewed this draft at a January 9

- 10, 2012 (76 FR 236, December 8, 2011) meeting. Based on CASAC and public comments, NCEA prepared a third draft ISA (U.S.

7 See http://yosemite.epa.gov/sab/sabproduct.nsf/WebProjectsbyTopicCASAC!OpenView for more information on CASAC activities related to the current O 3 NAAQS review. 8 EPA 452/R

- 11

- 006; April 2011; Available: http://www.epa.gov/ttn/naaqs/standards/ozone/data/2011_04_OzoneIRP.pdf*** E.O. 12866 Review

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Page 28 of 647 EPA 2012a; 77 FR 36534; June 19, 2012), which was reviewed at a CASAC meeting in September 2012. EPA released the final ISA in February 2013. The EPA presented its plans for conducting the Risk and Exposure Assessments (REAs) that build on the scientific evidence presented in the ISA, in two planning documents titled Ozone National Ambient Air Quality Standards: Scope and Methods Plan for Health Risk and Exposure Assessment and Ozone National Ambient Air Quality Standards: Scope and Methods Plan for Welfare Risk and Exposure Assessment (henceforth, Scope and Methods Plans). 9 These planning documents outlined the scope

a nd approaches that staff planned to use in conducting quantitative assessments, as well as key issues that would be addresse d as part of the assessments. The EPA released these documents for public comment in April 2011, and consulted with CASAC on May 19

- 20, 2011 (76 FR 23809; April 28, 2011). In designing and conducting the initial health risk and welfare risk assessments, the EPA considered CASAC comments (Samet , 2011) on the Scope and Methods Plans and also considered public comments. In May 2012, the
EPA issued a memo titled Updates to Information Presented in the Scope and Methods Plans for the Ozone NAAQS Health and Welfare Risk and Exposure Assessments that described changes to elements of the scope and methods plans and provided a brief explana tion of each change and the reason for it. In July 2012, the EPA made the first drafts of the Health and Welfare REAs available for CASAC review and public comment (77 FR 42495, July 19, 2012). The first

9 EPA

- 452/P

- 11

- 001 and

- 002; April 2011; Available: http://www.epa.gov/tt n/naaqs/standards/ozone/s_o3_2008_pd.html*** E.O. 12866 Review

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Page 29 of 647 draft Policy Assessment 10 ( PA ) was made available fo r CASAC review and public comment in August 2012. These documents were reviewed by the CASAC O 3 Panel at a public meeting in September 2012. The second draft REAs and PA , made available by the EPA in January 2014 (79 FR 4694, January 29, 2014), were prepar ed with consideration of advice from CASAC (Frey and Samet, 2012a, 2012b) and comments from the public. These drafts were reviewed by the CASAC O 3 Panel at a public meeting on March 25

- 27, 2014. The CASAC issued final reports on the second drafts HRE A on
J uly 1, 2014 (Frey, 2014a), the WREA on June 18, 2 014 (Frey, 2014b), respectively. The CASAC issued a final report on the second draft PA on June 26, 2014 (Frey, 2014c). Th e final versions of the Health REA ( HREA ) (U.S. EPA 2014a), Welfare REA ( WREA ) (U.S. EPA, 2014b), and PA (U.S. EPA, 2014c) were made available by the EPA in August , 2014

. These documents reflect staff’s consideration of the comments and recommendations made by CASAC, as well as comments made by members of the public, in their review of the draft versions of these documents

. E

. Ozone Air Quality Ozone is formed near the Earth’s surface due to chemical interactions involving solar radiation and precursor pollutants including volatile organic compounds (VOCs), nitrogen oxides (NO X ), methane (CH 4 ) and carbon monoxide (CO). The precursor

10 The PA is prepared by the staff in the EPA’s Office of Air Quality Planning and Standards (OAQPS). It presents a staff evaluation of the policy implications of the key scientific and technical information in the ISA and REAs for the EPA’s consideration. The PA provides a transparent evaluation, and staff conclusions, regarding policy considerations related to reaching judgments about the adequacy of the current standards, and if revision is considered, what revis ions may be appropriate to consider. The PA is intended to help “bridge the gap” between the Agency’s scientific assessments presented in the ISA and REAs, and the judgments required of the EPA Administrator in determining whether it is appropriate to reta in or revise the NAAQS.*** E.O. 12866 Review

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Page 30 of 647 emissions leading to O 3 formation can result from both man

- made sources (e.g., motor vehicles and electric power generation) and natural sources (e.g., vegetation and wildfires). Occasionally, O 3 that is create d naturally in the stratosphere can also contribute to O 3 levels near the surface. Once formed, O 3 can be transported by wind s before eventually being removed from the atmosphere via chemical reactions or deposition to surfaces. In sum, O 3 concentrations a re influenced by complex interactions between precursor emissions, meteorological conditions, and surface characteristics. In order to continuously assess O 3 air pollution levels, state and local environmental agencies operate O 3 monitors at various locati ons and subsequently submit the data to the EPA. At present, there are approximately 1,400 monitors across the U.S. reporting hourly O 3 averages during the time of the year when local O 3 pollution can be important. Much of this monitoring is focused on O 3 measurements in urban areas where precursor emissions tend to be largest, as well as locations directly downwind of these areas, but there are also over 100 sites in rural areas where high levels of O 3 can periodically exist due to transport from upwind so urces. Based on data from this national network, the EPA estimates that approximately 133 million Americans live in counties where O 3 concentrations were above the level of the existing health

- based NAAQS of 0.075 ppm at least 4 days in 2012. High O 3 value s can occur almost anywhere within the contiguous 48 states, although locations in California, Texas, and the Northeast Corridor are especially subject to poor O 3 air quality. From a temporal perspective, the highest daily peak O 3 concentrations generally tend to occur during the afternoon within the

warm er months due to higher solar radiation and other conducive meteorological conditions during these times. The exceptions to this general rule include : 1) some rural*** E.O. 12866 Review

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Page 31 of 647 sites where transport of O 3 from upwind a reas of regional production can occasionally result in high nighttime levels of O 3 , 2) high

- elevation sites periodically influenced by stratospheric intrusions, and 3) certain locations in the western U.S. where large quantities of O 3 precursors emissions associated with oil and gas development c an be trapped by strong inversions associated with snow cover during the colder months and efficiently converted to O 3 . One of the challenging aspects of developing plans to reduce emissions leading to
h igh O 3 concentrations is that the response of O 3 to precursor reductions is nonlinear

. In particular, NO X causes both the formation and destruction of O 3 . The net impact of NO X emissions on ozone concentrations depend s on the local quantities of NO X , VOC, and sunlight which interact in a set of complex chemical reactions

. In some areas, such as urban centers where NO X emissions typically are high, NO X leads to the net destruction of ozone - making ozone levels lower in the immediate vicinity. This phenomeno n is particularly pronounced under conditions that lead to low ozone concentrations (i.e. during cool, cloudy weather and at night when photochemical activity is limited or nonexistent)

. However, while NO X can initially destroy ozone near the emission sources, these same NO X emissions eventually do react to form more ozone downwind. Photochemical m odel simulations suggest that the additional expected reductions in NO X emissions will slightly increase O 3 concentrations on days wi th lower O 3 concentrations in areas in close proximity to NO X sources, while at the same time decreasing the highest
O 3 concentrations in outlying areas. At present, both the primary and secondary NAAQS use the annual fourth

- highest daily maximum 8

- hour c oncentration, averaged over three years, as the form of the*** E.O. 12866 Review

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Page 32 of 647 standard. An additional air quality metric, referred to as W126, is often used to assess cumulative impact of O 3 exposure on ecosystems and vegetation. W126 is a seasonal aggregate of weighted hou rly O 3 values observed between 8 am and 8 pm. As O 3 precursor emissions have decreased across the U.S., O 3 design values have concurrently shown a modest downward trend

. Ozone design values decreased by approximately 9 percent o n average between 2000 and 2 012 . Air quality model simulations estimate that peak O 3 levels will continue to improve over the next decade as additional reductions in
O 3 precursors from power plants, motor vehicles, and other sources are realized. In addition to being affected by cha nging emissions, future O 3 concentrations will also be affected by climate change. Modeling studies in EPA’s Interim Assessment (U.S. EPA, 2009b ) and cited in support of the 2009 Endangerment Finding (74 FR 66,496; Dec. 15, 2009) show that, while the impac t is not uniform, simulated climate change causes increases in summertime O 3 concentrations over substantial regions of the country, with increases tending to occur during higher peak pollution episodes in the summer. These increases in O 3 pollution over b road areas of the U.S., including in the largest metropolitan areas with the worst O 3 problems, increase the risk of morbidity and mortality. Children, older adults, and people with asthma or other lung diseases are among the most vulnerable to these O 3 - related health effects. If unchecked, climate change has the potential to offset some of the improvements in O 3 air quality, and therefore some of the improvements in public health, that are expected from reductions in emissions of O 3 precursors. Another challenging aspect of the O 3 issue is the involvement of sources of O 3 and O 3 precursors beyond those from domestic, anthropogenic sources. Modeling*** E.O. 12866 Review

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Page 33 of 647 analyses have suggested that nationally the majority of O 3 exceedances are predominantly caused by anthropo genic emissions from within the U.S. However, observational and modeling analyses have concluded that O 3 concentrations in some locations in the U.S. can be substantially influenced by sources that may not be suited to domestic control measures. In particu lar, certain high

- elevation sites in the western U.S. are impacted by a combination of non

- local sources like international transport, stratospheric O 3 , and O 3 originating from wildfire emissions. Ambient O 3 from these non

local sources is collectively ref erred to as background O 3 . See generally section 2.4 of the Policy Assessment ( U.S. EPA , 2014c). The analyses suggest that, at these locations, there can be episodic events with substantial background contributions where O 3 concentrations approach or excee d the level of the current NAAQS (i.e., 75 ppb)

. These events are relatively infrequent and the EPA has policies that allow for the exclusion of air quality monitoring data from design value calculations when they are substantially affected by certain back ground influences

. However, t he CAA requires the EPA to set the NAAQS at level s requisite to protect public health and welfare without regard to the source of the pollutant. API, 665 F. 2d at 1185

- 86

. The EPA may co nsider proximity to bac kground levels as a factor in the decis ion whether and how to revise the NAAQS when considering levels within the range of reasonable values supported by the air quality criteria and judgments of the Administrator. ATA III, 283 F. 3d at 279. It is in the implementation process that states and the EPA can address how to develop effective public policy in locations in which background sources contribute substantially to high ozone levels

. Section VII.F provides more detail about how background o zone can be addressed via CAA implementation provisions.*** E.O. 12866 Review

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Page 34 of 647 II. Rationale for Proposed Decision on the Primary Standard This section presents the Administrator’s rationale for her proposed decision to revise the existing primary O 3 standard by lowering the l evel of the standard to within the
range of 0.065 to 0.0 70 ppm. As discussed more fully below, this rationale draws from the thorough review in the ISA of the available scientific evidence , published through July 2011, on human health effects associated wi th the presence of O 3 in the ambient air. This rationale also takes into account : (1) analyses of O 3 air quality, human exposure s to O 3 , and O 3 - associated health risks, as presented and assessed in the HREA; (2) the EPA staff assessment of the most policy

- relevant scientific evidence and exposure/risk information in the PA ; (3) CASAC advice and recommendations, as reflected in discussions of drafts of the ISA, REA , and PA at public meetings, in separate written comments, and in CASAC’s l e tters to the Administrator; and (4) public input received during the development of these documents, either in connection with CASAC meetings or separately

. Section II.A below provides an overview of the approach es used to consider the scientific evi den ce and exposure/risk information as it relates to the primary O 3 standard

. This includes summaries of the approach adopted by the Administrator in the 2008 review of the O 3 NAAQS and of the approach adopted in the PA in the current review. Section II.B summarizes the body of evidence for health effects attributable to short

- or long

- term O 3 exposures, with a focus on effects for which the ISA judges that there is a “causal” or a “likely to be causal ” relationship with O 3 exposure s . S ection II.C summarize s the HREA ’s quantitative estimates of O 3 exposures and health risks, including key results and uncertainties

. Section s II.D and II.E present the Administrator’s*** E.O. 12866 Review

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Page 35 of 647 proposed conclusions on the adequacy of the current primary O 3 standard and alternative primary standards, respectively.
A. Approach In the 2008 review of the O 3 NAAQS, Administrator Stephen L. Johnson revised the level of the 8

- hour primary O 3 standard from 0.08 ppm 11 to 0.075 ppm (75 ppb 12 ). This decision was based on his co nsideration of the available scientific evidence and exposure/risk information, the advice and recommendations of CASAC, and comments from the public. The Administrator placed primary emphasis on the body of available scientific evidence, while viewing the results of exposure and risk assessments as providing supporting information. Specifically, he judged that a standard set at 75 ppb would be appreciably below the concentration in controlled human exposure studies at which adverse effects had been demonst rated at the time (i.e., 80 ppb) , and would provide a significant increase in protection compared to the then

- current standard. T he Administrator further concluded that the body of evidence did not support setting a lower standard level, given the increasi ng uncertainty in the evidence at lower O 3 concentrations (U.S. EPA, 2014c, Chapter 1).
I n the current review, the EPA’s approach to informing decisions on the primary
O 3 standard builds upon th e general approach used in the last review and reflects the broader body of scientific evidence, updated exposure/risk information, and advances in

11 Due to rounding convention, the 1997 standard level of 0.08 ppm corresponded to 0.084 ppm (84 ppb). 12 The level of the O 3 standard is specified as 0.075 ppm rather than 75 ppb. However, in the PA we refer to ppb, which is most oft en used in the scientific literature and in the ISA, in order to avoid the confusion that could result from switching units when discussing the evidence in relation to the standard level. Similarly, in the preamble to this notice we refer to ppb.*** E.O. 12866 Review

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Page 36 of 647 O 3 air quality modeling now available. This approach, described in detail in the PA (U.S. EPA, 2014c, section 1.3.1), is based most fundamentally on using the EPA’s assessment of the available scientific evidence and associated quantitative analyses to inform the Administrator’s judgments regarding a primary standard for O 3 that is “requisite” (i.e.,
neither more nor less stringent than necessary) to protect public health wit h an adequate margin of safety. Specifically, it is based on consideration of the available body of scientific evidence assessed in the ISA (U.S. EPA, 2013) , exposure and risk analyses present ed in the HREA (U.S. EPA, 2014a) , advice and recommendations from CASAC (Frey, 2014 a, c ), and public comments. Based on the application of this approach, t he PA assesses and integrates the evidence and information, and reaches conclusions for the Administr ator’s consideration about the range of policy options that could be supported

. The remainder of this section describes the PA’s approach to reviewing the primary O 3 standard, and to informing the Administrator’s proposed decisions on the current and alter native standards

. As an initial matter, t he PA recognizes that the final decision to retain or revise the current primary O 3 standard is a public health policy judgment to be made by the Administrator and will draw upon the available scientific evidence f or O 3 - attributable health effects and on analyses of population exposures and health risks, including judgments about the appropriate weight to assign the range of uncertainties inherent in the evidence and analyses. The PA’s general approach t o informing these public health policy judgments recognizes that the available health effects evidence reflects a continuum from relatively higher O 3 concentrations, at which scientists generally agree that health effects are likely to occur, through lower concentrati ons, at which the*** E.O. 12866 Review

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Page 37 of 647 likelihood and magnitude of a response become increasingly uncertain. Therefore, the conclusions in the PA reflect an interpretation of the available scientific evidence and exposure/risk information that neither overstates nor understate s the strengths and limitations of that evidence and information. This approach is consistent with the requirements of sections 108 and 109 of the CAA , as well as with how the EPA and the courts have historically interpreted the CAA

. The PA draws upon an integrative synthesis of the entire body of available scientific evidence for O 3 - related health effects, including the evidence newly available in the current review and the evidence from previous reviews, as presented in the ISA (U.S. EPA, 2013). C onsider ation of the scientific evidence is based fundamentally on information from controlled human exposure and epidemiologic studies, supplemented by information from animal toxicology studies. Such evidence informs the PA’s
consideration of the health e ndpoints and at

- risk populations 13 on which to focus the current review, and the PA’s consideration of the O 3 concentrations at which various health effects can occur.

13 I n this review , the term “at

- risk population” is used to encompass populations or lifestages that have a greater likelihood of experiencing health effects related to exposure to an air pollutant due to a variety of factors; other terms used in the literature include susceptible, vulnerable, and sensitive. These factors may be intrinsic, such as genetic factors, lifestage, or the presence of preexisting diseases, or they may be extrinsic, such as socioeconomic status (SES), activity pattern and exercise level, or increased pollutant exposures (U.S. EPA 2013, p. lxx, 8

- 1, 8

- 2). The courts and the CAA ’s legislative history refer to these at

- risk subpopulations as “susceptible” or “sensitive” populations. See, e.g., American Lung Ass’n v. EPA , 134 F. 3d 388, 389 (D .C. Cir. 1998) (“NAAQS must protect not only average health individuals, but also ‘sensitive citizens’

– children, for example, or people with asthma, emphysema, or other conditions rendering them particularly vulnerable to air pollution” (quoting S. Rep. No. 91

- 1196 at 10).*** E.O. 12866 Review

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Page 38 of 647 Since the 2008 review of the O 3 NAAQS, the EPA has developed formal frameworks for char acterizing the strength of the scientific evidence with regard to health effects associated with exposures to O 3 in ambient air and factors that may increase risk in some populations or lifestages. These frameworks provide the basis for robust, consistent, and transparent processes for evaluating the scientific evidence, including uncertainties in the evidence, and for drawing weight

- of

- evidence conclusions on air pollution

- related health effects and at

- risk populations. These frameworks for characterizing the strength of the scientific evidence are discussed in detail in the ISA (U.S. EPA, 2013, Preamble; Chapter 8)

. With regard to characterization of health effects, the ISA uses a five

- level hierarchy to classify the overall weight of evidence into one o f the following categories: causal relationship, likely to be a causal relationship, suggestive of a causal relationship, inadequate to infer a causal relationship, and not likely to be a causal relationship (U.S. EPA, 2013, Preamble Table II). In using th e weight

- of

- evidence approach to inform judgments about the degree of confidence that various health effects are likely to be caused by exposure to O 3 , confidence increases as the number of studies consistently reporting a particular health endpoint grows and as other factors, such as biological plausibility and the strength, consistency , and coherence of evidence , increase. Conclusions about biological plausibility and about the consistency and coherence of O 3 - related health effects are drawn from the inte gration of epidemiologic studies with mechanistic information from controlled human exposure and animal toxicological studies, as discussed in the ISA (U.S. EPA, 2013, EPA Framework for Causal Determination, p. 1viii). The PA place s the greatest weight on the health effects for*** E.O. 12866 Review

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Page 39 of 647 which the evidence has been judged in the ISA to support a “causal” or a “likely to be
causal ” relationship with O 3 exposures. The PA further consider s the evidence base assessed in the ISA with regard to the types and levels of ex posure at which health effects are indicated. This consideration of the evidence , which directly informs conclusions regarding the adequacy of current or alternative standards , differs from consideration of the evidence in the ISA with regard to overarchin g determinations of causality. Therefore, studies that inform determinations of causality may or may not be concluded to be informative with regard to the adequacy of the current or alternative standards

. 14 As with health endpoints, the ISA’s characterization of the weight of evidence for potential at

- risk populations is based on the evaluation and synthesis of evidence from across scientific disciplines. The ISA characterizes the evidence for a number of “factors” that have the potential to p lace populations at increased risk for O 3 - related effects. The categories considered in evaluating the evidence for these potential at

- risk factors are “adequate evidence,” “suggestive evidence,” “inadequate evidence,” and “evidence of no effect.” These c ategories are discussed in more detail in the ISA (U.S. EPA, 2013, chapter 8, Table 8

- 1). In this review, the PA focus es on those factors for which the ISA judges there is “adequate” evidence of increased risk (U.S. EPA, 2013, Table 8

- 5). At

risk populatio ns are discussed in more detail in section 3.1.5 of the PA (U.S. EPA, 2014 c ).

14 For example, the PA judge s that health studies evaluating exposure concentrations near or below the level of the current standard and epidemiologic studies conducted in locations meeting the current standard are particularly informati ve when considering the adequacy of the public health protection provided by the current standard (U.S. EPA, 2014c, Chapters 3 and 4)

.*** E.O. 12866 Review

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Page 40 of 647 Using the available scientific evidence to inform conclusions on the current and alternative standards is complicated by the recognition that a population

- level th reshold has n ot been identified below which it can be concluded with confidence that O 3 - attributable effects do not occur (U.S. EPA, 2013, section 2.5.4.4). In the absence of a discernible threshold, the PA’s general approach to considering the available O 3 health evid ence involves characterizing confidence in the extent to which O 3 - attributable effects occur, and the extent to which such effects are adverse, over the ranges of O 3 exposure concentrations evaluated in controlled human exposure studies and over the distri butions of ambient O 3 concentrations in locations where epidemiologic studies have been conducted. As noted above, the PA recognizes that the available health effects evidence reflects a continuum from relatively high O 3 concentrations, at which scientists generally agree that adverse health effects are likely to occur, through lower concentrations, at which the likelihood and magnitude of a response become increasingly uncertain. Aspects of the approach used in this review to evaluate evidence from control led human exposure and epidemiologic studies, respectively, are discussed below. Controlled human exposure studies provide direct evidence of relationships between pollutant exposures and human health effects (U.S. EPA, 2013, p.lx). Controlled human expo sure studies provide data with the highest level of confidence since they provide human effects data under closely monitored conditions and can provide exposure response relationships. Such studies are particularly useful in defining the specific condition s under which pollutant exposures can result in health impacts, including the exposure concentrations, durations, and ventilation rates under which effects can occur. As discussed in the ISA, controlled human exposure studies provide clear and compelling*** E.O. 12866 Review

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Page 41 of 647 e vidence for an array of human health effects that are directly attributable to acute exposures to O 3 per se (i.e., as opposed to O 3 and other photochemical oxidants, for which O 3 is an indicator, or other co

- occurring pollutants) (U.S. EPA, 2013, Chapter 6 ). Together with animal toxicological studies, which can provide information about more serious health outcomes as well as the effects of long

- term exposures and mode of action, controlled human exposure studies also help to provide biological plausibility for health effects observed in epidemiologic studies. The PA consider s the evidence from controlled human exposure studies in two ways. First, the PA consider s the extent to which controlled human exposure studies provide evidence for health effects fol lowing exposures to different O 3 concentrations, down to the lowest

- observed

- effects levels in those studies. Second, the PA use s these studies to help e valuat e the extent to which there is confidence in health effect associations reported in epidemiologic studies down through lower ambient O 3 concentrations, where the likelihood and magnitude of O 3 - attributable effects become increasingly uncertain. The PA con sider s the range of O 3 exposure concentrations evaluated in controlled human exposure studies, including concentrations near or below the level of the current standard. The PA consider s both group mean responses, which provide insight into the extent to wh ich observed changes are due to O 3 exposures rather than to chance alone, and interindividual variability in responses, which provides insight into the fraction of the population that might be affected by such O 3 exposures ( U.S. EPA, 2013, section
6.2.1.1 ) . When considering the relative weight to place on various controlled human exposure studies, the discussion in the PA focuses on the exposure conditions evaluated*** E.O. 12866 Review

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Page 42 of 647 (e.g., exercising versus resting, exposure duration); the nature, magnitude, and likely adve rsity of effects over the range of reported O 3 exposure concentrations; the statistical precision of reported effects; and the consistency of results across studies for a given health endpoint and exposure concentration. In addition, because controlled hum an exposure studies typically involve healthy individuals and do not evaluate the most sensitive individuals in the population (U.S. EPA, 2013, Preamble p. lx), when considering the implications of these studies for evaluation of the current and alternativ e standards , the PA also consider s the extent to which reported effects are likely to reflect the magnitude and/or severity of effects in at

- risk groups. The PA also consider s epidemiologic studies of short

- and long

- term O 3 concentrations in ambient air . Epidemiologic studies provide information on associations between variability in ambient O 3 concentrations and variability in various health outcomes, including lung function decrements, respiratory symptoms, school absences, hospital admissions, emergen cy department visits, and premature mortality (U.S. EPA, 2013, Chapters 6 and 7). Epidemiologic studies can inform understanding of the effects in the study population (which may include at

- risk groups) of real

- world exposures to the range of O 3 concentrat ions in ambient air, as well as provide evidence of associations between ambient O 3 levels and more serious acute and chronic health effects that cannot be assessed in controlled human exposure studies. For these studies, the degree of uncertainty introduc ed by confounding variables (e.g., other pollutants, temperature) and other factors affects the level of confidence that the health effects being investigated are attributable to O 3 exposures, alone and in combination with copollutants.*** E.O. 12866 Review

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Page 43 of 647 Available epidemio logic studies have generally not indicated a d iscernible population threshold below which O 3 is no longer associated with health effects (U.S. EPA, 2013, section 2.5.4.4). However, the currently available epidemiologic evidence indicates decreased confiden ce in reported concentration

- response relationships for O 3 concentrations at the lower ends of ambient distributions due to the low density of data in this range (U.S. EPA, 2013, section 2.5.4.4). As discussed more fully in Chapter 1 of the
PA (U.S. EPA, 2014c), the general approach to considering the results of epidemiologic studies within the context of the current and alternative standards focuses on characterizing the range of ambient O 3 concentrations over which studies indicate the
most c onfidence in O 3 - associated health effects, and the concentrations below which confidence in such health effect associations becomes appreciably lower. In placing emphasis on specific epidemiologic studies, as in past reviews, the discussion in the PA foc uses on the epidemiologic studies conducted in the U.S. and Canada. Such studies reflect air quality and exposure patterns that are likely more typical of the U.S. population , since studies conducted outside the U.S. and Canada may well reflect different d emographic and air pollution characteristics

. 15 The PA also focuses on studies reporting associations with effects judged in the ISA (U.S. EPA, 2013) to be robust to confounding by other factors, including co

- occurring air pollutants. To put judgments abo ut O 3 - related health effects into a broader public health
context, the PA also consider s exposure and risk estimates from the HREA, which develops and applies models to estimate human exposures to O 3 and O 3 - related health

15 Though the PA recognizes that a broader body of studies, including international studies, inform the causal determinat ions in the ISA.*** E.O. 12866 Review

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Page 44 of 647 risks in urban study areas across the United States (U.S. EPA, 2014a). The HREA estimates exposures of concern, based on interpreting quantitative exposure estimates within the context of controlled human exposure study results; lung function risks, based on applying exposure

- response rela tionships from controlled human exposure studies to quantitative estimates of exposures; and epidemiologic

- based risk estimates, based on applying concentration

- response relationships drawn from epidemiologic studies to adjusted air quality. Each of these types of assessments is discussed briefly below. As in the 2008 review, the HREA estimates exposures at or above benchmark concentrations of 60, 70, and 80 ppb, reflecting exposure concentrations of concern based on the available health evidence. 16 Estima tes of exposures of concern, defined as personal exposures while at moderate or greater exertion to 8

- hour average ambient O 3 levels, at or above these discrete benchmark concentrations provide perspective on the public health risks of O 3 - related health ef fects that have been demonstrated in controlled human exposure and toxicological studies . However, because of a lack of exposure

- response information across a range of exposure concentrations in these studies, these risks cannot be assessed using a quantit ative risk assessment. Though this analysis is conducted using discrete benchmark concentrations, information from the broad body of evidence indicates that health

- relevant exposures are more appropriately viewed as a continuum with greater confidence and certainty about the existence of health effects at higher O 3 exposure concentrations and less confidence and certainty at lower exposure concentrations. This approach recognizes that there is no sharp breakpoint within the

16 For example, see 75 FR 2945

- 2946 (January 19, 2010) and 73 FR 16441

- 16442 (March 27, 2008) discussing “exposures of concern

. ”*** E.O. 12866 Review

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Page 45 of 647 exposure - response relationship fo r exposure concentrations at and above 80 ppb down to 60 ppb. Within the context of this continuum, estimates of exposures of concern at these discrete benchmark concentrations provide some perspective on the public health impacts of O 3 - related health effects, such as pulmonary inflammation, that are plausibly linked to the more serious effects seen in epidemiologic studies but cannot be evaluated in quantitative risk assessments. They also help elucidate the extent to which such impacts may be reduced by meeting the current and alternative standards. Estimates of the number of people likely to experience exposures of concern cannot be directly translated into quantitative estimates of the number of people likely to experience specific health effects due to individual variability in responsiveness. Only a subset of individuals can be expected to experience such adverse health effects, and at

- risk populations or lifestages, such as people with asthma or children, are expected to be affected more by such

ex posures than healthy adults. The HREA also generates quantitative estimates of O 3 health risks for air quality adjusted to just meet the current and alternative standards

. O ne approach to estimating O 3 health risks is to combine modeled exposure estimates with exposure

- response relationships derived from controlled human exposure studies of O 3 - induced health effects. The HREA uses this approach to estimate the occurrence of O 3 - induced lung function decrements in at

- risk populations, including school

- age ch ildren, school

- age children with asthma, adults with asthma, and older adults. The available exposure

response information does not support this approach for other endpoints evaluated in controlled human exposure studies (U.S. EPA, 2014a, section 2.3).*** E.O. 12866 Review

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Page 46 of 647 T he other approach used in this review to estimat e O 3 - associated health risks is to apply concentration

- response relationships derived from short

- and/or long

- term epidemiologic studies to air quality adjusted to just meet current and alternative standards

. The concentration

- response relationships drawn from epidemiologic studies are based on population exposure surrogates, such as 8

- hour concentrations averaged across monitors and over more than one day (U.S. EPA, 2013, Chapter 6). The HREA presents epidemi ologic

- based risk estimates for O 3 - associated mortality, hospital admissions, emergency department visits, and respiratory symptoms (U.S. EPA, 2014a, section 2.3). These estimates are derived from the full distributions of ambient O 3 concentrations estimat ed for the study locations. 17 In addition, the HREA estimates mortality risks associated with various portions of distributions of short

- term O 3 concentrations (U.S. EPA, 2014a). The PA considers risk estimates based on the full distributions of ambient O 3 concentrations and, when available, estimates of the risk associated with various portions of those ambient distributions. 18 In doing so, the PA takes note of the ISA conclusions regarding confidence in linear concentration

- response relationships over distr ibutions of ambient concentrations (see above) , and of the extent

17 In previous reviews, including the 2008 review and reconsideration, such risks were separately estimated for O 3 concentrations characterized as above policy

- relevant background concentrations. Policy

- relevant background concentrations were defined as the distribution of ozone concentrations attributable to sources other than anthropogenic emissions of ozone prec ursor emissions (e.g., VOC, CO, NO X ) in the U.S., Canada, and Mexico. The decision in this review to estimate total risk across the full range of O 3 concentrations reflects consideration of advice from CASAC (Frey and Samet, 2012b). 18 In a series of sensit ivity analyses, the HREA also evaluates a series of threshold models for respiratory mortality associated with long

- term O 3 concentrations. The PA considers these risk estimates based on threshold models, in addition to HREA core estimates based on the lin ear model (sections 3.2.3.2, 4.4.2.3).*** E.O. 12866 Review

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Page 47 of 647 to which health effect associations at various ambient O 3 concentrations are supported by the evidence from experimental studies for effects following specific O 3 exposures . B

. Health Effects Information This section outlines key information contained in the ISA (U.S. EPA, 2013, Chapters 4 to 8) and in the PA (U.S. EPA, 2014c, Chapters 3 and 4) on the known or potential effects on public health which may be expected from the presence of O 3 in the ambient air. The information highlighted here summarizes: (1) New information available on potential mechanisms for health effects associated with exposure to O 3 (II.B.1); (2) the nature of effects that have been associated directly with both sh ort

- and long

- term exposure to O 3 and indirectly with the presence of O 3 in ambient air (II.B.2) ; (3) considerations related to the adversity of O 3 - attributable health effects (II.B.3) ; and (4) considerations in characterizing the public health impact of O 3 , including the identification of “at risk” populations (II.B.4)

. The decision in the 2008 rulemaking emphasize d the large number of epidemiologic studies published since the 1997 review that continued to report associations with respiratory hospital admi ssions and emergency department visits, as well as additional health endpoints, including the effects of acute (short

- term and prolonged) and chronic exposures to O 3 on lung function decrements and enhanced respiratory symptoms in asthmatic individuals, sc hool absences , and premature mortality

. It also emphasized controlled human exposure studies showing respiratory effects with prolonged O 3 exposures at levels below 80 ppb, changes in lung host defenses, and increased airway responsiveness, and animal toxicology studies that provided information about mechanisms of action

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Page 48 of 647 The ISA (U.S. EPA, 2013) prepared for this review emphasizes a lar ge number of new epidemiologic studies published since the last review on effects associated with both short

- and long

- term exposures, including new epidemiologic studies about risk factors. I t also emphasize s important new information from controlled huma n exposure, dosimetry and toxicology studies

. Highlights of the new evidence included: (1) Two new controlled human exposure studies are now available that examine respiratory effects associated with prolonged, 6.6

- hour, O 3 exposures to levels of
72 ppb 19 and 60 ppb. These studies observed effects in healthy adults, including lung function decrements combined with respiratory symptoms at 72 ppb, and lung function decrements and pulmonary inflammation at 60 ppb. These studies expand on evidence of lung func tion decrements with O 3 exposure at 60 ppb available in the last review, and provide new evidence of airway inflammation, a mechanism by which O 3 may cause other more serious respiratory effects (e.g., asthma exacerbations)

. (2) Recent multicity and sing le city epidemiologic studies continue to report associations between short

- term O 3 exposures and respiratory hospital admissions and respiratory emergency department visits. R ecent multicity studies and a multi

- continent study have reported consistent pos itive associations between short

- term O 3 exposure and total (nonaccidental) mortality, expanding upon evidence available in the last review. They also observed associations between O 3 exposure and cardiovascular and respiratory mortality.

19 As noted below, for the 70 ppb exposure concentration Schelegle et al. (2009) reported that the actual mean exposure concentration was 72 ppb.*** E.O. 12866 Review

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Page 49 of 647 (3) Recent controlled human exposure studies reporting systemic inflammation and cardiac changes provide support for the expanded body of epidemiologic evidence for cardiovascular mortality, although l ack of coherence with epidemiologic studies of cardiova scular morbidity remains an important uncertainty

. (4) New epidemiologic studies provide e xpanded evidence for respiratory effects associated with long

- term or repeated O 3 concentrations (e.g., seasonal average of
1

- or 8

- hour daily max concentrations). Re cent studies demonstrate interactions between exercise or different genetic variants and both new

- onset asthma in children and increased respiratory symptom effects in individuals with asthma ;

a dditional studies of respiratory morbidity and mortality suppo rt the association between long

- term exposure to O 3 and a range of respiratory health effects

. (5) New evidence of risk factors (i.e., people with certain genetic variants related to antioxidant status or inflammation, and people with reduced intake of

an tioxidant nutrients) strengthens our understanding of the modes of action from
O 3 - induced effects

. 1. Overview of Mechanisms The purpose of this section is to describe the key events and pathways that contribute to health effects resulting from both shor t

- term and long

- term exposures to O 3 . The information in this section draws from section 5.3 of the ISA (U.S. EPA, 2013). Mode of action refers to a sequence of key events and processes that result in a given toxic effect. Elucidation of mechanisms provide s a more detailed understanding of these key events and processes. E xperimental e vidence elucidating modes of action and/or*** E.O. 12866 Review

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Page 50 of 647 mechanisms contribute s to our understanding of the biological plausibility of adverse O 3 - related health effects, including respiratory effects and effects outside the respiratory system (U.S. EPA, 2013, Chapters 6 and 7). Figure 3.1 in the PA (U.S. EPA, 2014c) shows key events in the toxicity pathway of O 3 that are described briefly here and in more detail in section 3.1.1 of the PA. The initial key event is the formation of secondary oxidation products in the respiratory tract (U.S. EPA, 2013, section 5.3). This mainly involves direct reactions with components of the extracellular lining flu id ( ELF ). Although the ELF has inherent capacity to quench (based on individual antioxidant capacity), this capacity can be overwhelmed, especially with exposure to elevated concentrations of O 3 . The resulting secondary oxidation products transmit signals to the epithelium, pain receptive nerve fibers and, if present, immune cells (i.e., eosinophils, dendritic cells and mast cells) involved in allergic responses . Thus, the effects of O 3 are mediated by components of ELF and by the mul tiple cell types found in the respiratory tract . Further, oxidative stress is an implicit part of this initial key event. It is well understood that secondary oxidation products initiate numerous responses at the cellular, tissue, and whole organ level of the respiratory syste m. These responses include the activation of neural reflexes leading to lung function decrements, airway obstruction, and extrapulmonary effects such as slow resting heart rate; initiation of inflammation; alteration of barrier epithelial function; sensiti zation of bronchial smooth muscle; modification of lung host defenses; and airways remodeling (U.S. EPA, 2013, section 5.3.10, Figure 5

- 8). Each of these effects is discussed in more detail in section 3.1.1 of the PA (U.S. EPA, 2014c).*** E.O. 12866 Review

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Page 51 of 647 Persistent inflamm ation and injury, which are observed in animal models of chronic and intermittent exposure to O 3 , are associated with airways remodeling ( see Section 7.2.3 of the ISA, U.S. EPA 2013 ). Chronic intermittent exposure to O 3 has also been shown to result in eff ects on the developing lung and immune system. Systemic inflammation and vascular oxidative/nitrosative stress are also key events in the toxicity pathway of O 3 . Extrapulmonary effects of O 3 occur in numerous organ systems, including the cardiovascular, ce ntral nervous, reproductive, and hepatic systems (see Sections 6.3 to 6.5 and Sections 7.3 to 7.5 of the ISA, U.S. EPA, 2013 ). Responses to O 3 exposure are variable within the population. S tudies have shown a large range of pulmonary function (i.e., spirometric) responses to O 3 among healthy young adults , while responses within an individual are relatively consistent over time. Other responses to O 3 have also been characterized by a large degree of interindividual variability. For example, a 3

- to 20

- fold difference among subjects in their studies in airways inflammation (i.e., neutrophilia influx) following O 3 exposure has been reported (Schelegle et al., 1991 and Devlin et al., 1991, respectively)

. R eproducibility of an individual’s inflammato ry response to O 3 exposure in humans , measured as sputum neutrophilia, was demonstrated by Holz et al (1999) . Since individual inflammatory responses were relatively consistent across time, it was thought that inflammatory responsiveness reflected an intri nsic characteristic of the subject (Mudway and Kelly, 2000) . While the basis for the observed interindividual variability in responsiveness to O 3 is not clear, section 5.4.2 of the ISA discusses mechanisms that may underlie the variability in responses see n among individuals. Certain functional genetic polymorphisms, pre

- existing conditions or diseases, nutritional status, lifestages, and co

-*** E.O. 12866 Review

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Page 52 of 647 exposures contribute to altered risk of O 3 - induced effects. Experimental evidence for such O 3 - induced changes contrib utes to our understanding of the biological plausibility of adverse O 3 - related health effects, including a range of respiratory effects as well as effects outside the respiratory system (e.g., cardiovascular effects ) (U.S. EPA, 2013, Chapters 6 and 7).
2. Nature of Effects The health effects of O 3 are described in detail and assessed in the ISA (U.S. EPA, 2013). Based on this assessment, the ISA determine d that a “ causal ” relationship exists between short

- term exposure to O 3 in ambient air 20 and effects on the respiratory system and that a “likely to be causal” relationship 21 exists between long

- term exposure to O 3 in ambient air and respiratory effects (U.S. EPA 2013 , pp. 1

- 6 to 1

- 7 ). As stated in the ISA, “[c]ollectively, a very large amount of evidence spanning several decades supports a relationsh i p between exposure to O 3 and a broad range of respiratory effects” (ISA, p. 1

- 6). The ISA summarizes the longstanding body of evidence for O 3 respiratory effects as follows (U.S. EPA, 2013, p. 1

- 5 ). The clearest evidence for health effects associated with exposure to O 3 is provided by studies of respiratory effects. Collectively, a very large amount of evidence spanning several decades supports a relationship between exposure to O 3 and a broad rang e of respiratory effects (see Section 6.2.9 and Section 7.2.8). The majority of this evidence is derived from studies investigating short

- term exposures (i.e., hours to weeks) to O 3 , although animal toxicological studies and recent epidemiologic

20 In determining that a causal relationship exists for O 3 with specific health effects, EPA has concluded that “[e]vidence is sufficient to conclude that there is a causal relationship with relevant pollutant exposures” (ISA, p. lxiv). 21 In determining a likely to be a causal relationship exists for O 3 with spec ific health effects, the EPA has concluded that “[e]vidence is sufficient to conclude that a causal relationship is likely to exist with relevant pollutant exposures, but important uncertainties remain” (ISA, p. lxiv).*** E.O. 12866 Review

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Page 53 of 647 evidence d emonstrate that long

- term exposure (i.e., months to years) may also harm the respiratory system

. Additionally, the ISA determine d that the relationships between short

- term exposures to O 3 in ambient air and both total mortali t y and cardiovascular effects are likely to be causal , based on expanded evidence bases in the current review (U.S. EPA, 2013 , pp. 1

- 7 to 1

- 8). In the ISA, the EPA additionally determined that the currently available evidence for additional endpoints is “suggestive” of causal relation ships between short

- term (central nervous system effects) and long

- term exposure (cardiovascular effects, reproductive and developmental effects, central nervous system effects and total mortality) to ambient O 3

. Consistent with emphasis in past reviews on O 3 health effects for which the evidence is strongest, in this review the EPA places the greatest emphasis on studies of health effects that have been judged in the ISA to be caused by, or likely to be caused by,
O 3 exposures (U.S. EPA, 2013 , section 2. 5.2). This section discusses the evidence for health effects attributable to O 3 exposures, with a focus on respiratory morbidity and mortality effects attributable to short

- and long

- term exposures, and cardiovascular system effects (including mortality) a nd total mortality attributable to short

- term exposures. This section focuses particularly on considering the extent to which the scientific evidence available in the current review has been strengthened since the last review, and the extent to which impor tant uncertainties and limitations in the evidence from the last review have been addressed. a. Respiratory effects

– short

- term The 2006 O 3 AQCD concluded that there was clear, consistent evidence of a causal relationship between short

- term O 3 exposure and respiratory effects ( U.S. EPA,*** E.O. 12866 Review

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Page 54 of 647 2006a ) . This co nclusion was substantiated by evidence from controlled h uman exposure and toxicological studies indicating a range of respiratory effects in response to short

term O 3 exposure s , including pulmonary function decrements and increases in respiratory symptoms, lung inflammation, lung permeability, and airway hyperresponsiveness. Toxicological studies provided additional evidence for O 3 - induced impairment of host defenses. Combined, these findings from experimental studies provided support for epidemiologic evidence, in which short

- term increases in ambient O 3 concentration were consistently associated with decreases in lung function in populations with increased outdoor exposures, especially children with asthma and healthy children; increases in respiratory symptoms and asthma medication use in children with asthma; and increases in respiratory

- related hospital admissions and asthma

- related ED visits (U.S. EPA, 2013, pp. 6

- 1 to 6

- 2)

. As discussed in detail in the ISA (U.S. EPA, 2013, section 6.2.9), studies evaluated since the completion of the 2006 O 3 AQCD support and expand upon the strong body of evidence that , in the last review, indicated a causal relationship between short

- term O 3 exposure s a nd respiratory health effects. Recent c ontrolled human
exposu re studies conducted in young, healthy adults with moderate exertion have reported FEV 1 decrements and pulmonary inflammation following prolonged exposures
to O 3 concentrations as low as 60 ppb , and respiratory symptoms following exposures to concentration s as low as 72 ppb

. 22 Epidemiologic studies provide evidence that increases

22 Schelegle et al. (2009) reported a s tatistically significant increase in respiratory symptoms in healthy adults at a target O 3 exposure concentration of 70 ppb , averaged over the study period. For this 70 ppb target exposure concentration , Schelegle et al. (2009) reported that the actual mea n exposure concentration was 72 ppb.*** E.O. 12866 Review

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Page 55 of 647 in ambient O 3 exposure s can result in lung function decrements, increases in respiratory symptoms, and pulmonary inflammation in children with asthma; increases in respiratory

- relat ed hospital admissions and emergency department visits; and increases in respiratory mortality. Some of these studies report such associations even for O 3 concentrations at the low end of the distribution of daily concentrations. R ecent epidemiologic studi es report that associations with respiratory morbidity and mortality are stronger during the warm/sum mer months and remain robust after adjustment for copollutants. Recent toxicological studies reporting O 3 - induced inflammation, airway hyperresponsiveness, and impaired lung host defense continue to support the biological plausibility and modes of action for the O 3 - induced respiratory effects observed in the controlled human exposure and epidemiologic studies. Further support is provided by recent studies th at found O 3 - associated increases in indicators of airway inflammation and oxidative stress in children with asthma (U.S. EPA, 2013, section 6.2.9)

. Together, epidemiologic and experimental studies support a continuum of respiratory effects associated with O 3 exposure that c an result in respiratory

- related emergency department visits, hospital admissions, and/or mortality (U.S. EPA, 2013, section 6.2.9). Across respiratory endpoints, evidence indicates antioxidant capacity may modify the risk of respirator y morbidity associated with O 3 exposure (U.S. EPA, 2013, section 6.2.9, p. 6

- 161) (section 3.1.1, above) . The potentially elevated risk of populations with diminished antioxidant capacity and the reduced risk of populations with sufficient antioxidant capa city is supported by epidemiologic studies and from controlled human exposure studies . Additional evidence characterizes O 3 - induced decreases in antioxidant levels as a key event in the mode of action for downstream effects

.*** E.O. 12866 Review

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Page 56 of 647 Key aspects of this evidence are discussed below with regard to lung function decrements; pulmonary inflammation, injury, and oxidative stress; airway hyperresponsiveness; respiratory symptoms and medication use ; lung host defense; allergic and asthma

- related responses; hospital admis sions and emergency department visits; and respiratory mortality

. i. Lung function decrements
In the 2008 review, a large number of controlled human exposure studies 23 reported O 3 - induced lung function decrements in young, healthy adults engaged in intermittent, moderate exertion following 6.6 hour exposures to O 3 concentrations at or above 80 ppb. Although two studies also reported effects following exposures to lower concentrations, an important uncertainty in the last review was the extent to which
expo sures to O 3 concentrations below 80 ppb result in lung function decrements. In addition, in the last review epidemiologic panel studies had reported O 3 - associated lung function decrements in a variety of different populations (e.g., children, outdoor worke rs) likely to experience increased exposures. In the current review, additional controlled human exposure studies are available that have evaluated exposures to O 3 concentrations of 60 or 72 ppb . The available evidence from controlled human exposure and pa nel

23 The controlled human exposure studies emphasized in the PA utilize only healthy adult subjects. In the near absence of controlled human exposure data for children, HREA estimates of lung function decrements are based on the assumption that children exhibit the same lung function responses following O 3 exposures as healthy 18 year olds (U.S. EPA, 2014, section 6.2.4 and 6.5). This assumption is justified in part by the findings of McDonnell et al. (1985), who reported t hat children 8

- 11 year old experienced FEV 1 responses similar to those observed in adults 18

- 35 years old. Thus, the conclusions about the occurrence of lung function decrements that follow generally apply to children as well as to adults.*** E.O. 12866 Review

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Page 57 of 647 studies is assessed in detail in the ISA (U.S. EPA, section 6.2.1) and is summarized below. Controlled exposures to O 3 concentrations that can be found in the ambient air can result in a number of lung function effects, including decreased inspirator y capacity , mild bronchoconstriction , and rapid, shallow breathing patterns during exercise. Reflex inhibition of inspiration results in a decrease in forced vital capacity (FVC) and total lung capacity (TLC) and, in combination with mild bronchoconstriction, contributes to a decrease in the forced expiratory volume in 1 second (FEV 1 ) (U.S. EPA, 2013, section 6.2.1.1). Accumulating evidence indicates that such effects are mediated by activation of sensory nerves, resulting in the involuntary truncation of inspiration and a mild increase in air way obstruction due to bronchoconstriction (U.S. EPA, 2013, section 5.3.10). Data from controlled human exposure studies show that increasing the duration of
O 3 exposures and increasing ventilation rates decreases the O 3 exposure concentrations required to impair lung function. Ozone exposure concentrations well above those typically found in ambient air are required to impair lung function in healthy resting adults, while exposure to O 3 concentrations at or below those in the ambient air have been report ed to impair lung function in healthy adults exposed for longer durations while undergoing intermittent, moderate exertion (U.S. EPA, 201 3 , section 6.2.1.1). With repeated O 3 exposures over several days, FEV 1 responses become attenuated in both healthy adu lts and adults with mild asthma, though this attenuation of response is lost after about a week without exposure (U.S. EPA, 2013, section 6.2.1.1; page 6

- 27)

. When considering controlled human exp osure studies of O 3 - induced lung function decrements , the ISA and PA evaluate both group mean changes in lung function and the*** E.O. 12866 Review

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Page 58 of 647 interindividual variability in the magnitude of responses. An advantage of O 3 controlled human exposure studies (i.e., compared t o the epidemiologic panel studies discussed below) is that reported effects necessarily result from exposures to O 3 itself. 24 To the extent studies report statistically significant decrements in mean lung function following
O 3 exposures after controlling fo r other factors, these studies provide greater confidence that measured decrements are due to the O 3 exposure itself, rather than to chance alone. As discussed below, group mean changes in lung function are often small, especially following exposures to re latively low O 3 concentrations (e.g., 60 ppb). However, even when group mean decrements in lung function are small, some individuals could experience decrements that are “clinically meaningful” ( Pellegrino et al., 2005 ; ATS, 1991 ) with respect to criteria for spirometric testing, and/or th at could be considered adverse with respect to public health policy decisions. See section 3.1.3 below

. At the time of the last review, a number of controlled human exposure studies had reported lung function d ecrements in young, healthy adults following prolonged (6.6

- hour) exposures while at moderate exertion to O 3 concentrations at and above 80 ppb. In addition, there were two controlled human exposure studies by Adams (2002, 2006) that examined lung function effects following exposures to 60 ppb O 3 . The EPA’s analysis of the data from the Adams (2006) study reported a small but statistically significant O 3 - induced decrement in group mean FEV 1 following exposures of young, healthy adults to 60 ppb O 3 while at moderate exertion, when compared with filtered air controls (Brown,

24 The ISA notes that the use of filtered air responses as a control for the assessment of responses following O 3 exposure in controlled human exposure studies serves to eliminate alternative explanations other than O 3 itself in causing the measured responses (U.S. EPA, 2013, section 6.2.1.1).*** E.O. 12866 Review

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Page 59 of 647 200 8 ). 25 Further examination of the post

- exposure FEV 1 data, and mean data for other time points and other concentrations, indicated that the temporal pattern of the response to 60 ppb O 3 was generally consistent with the temporal patterns of responses to higher
O 3 concentra tions in this and other studies (75 FR 2950, January 19, 2010). This suggested a pattern of response following exposures to 60 ppb O 3 that was consistent with a dose

- res ponse relationship, rather than random variability. See also State of Mississippi v. EPA , F. 3d 2013 U.S. App. LEXIS 24596 at * 28

- 29 (upholding EPA’s interpretation of the Adams studies)

. Figure 6

- 1 in the ISA summarizes the currently available evidence from multiple controlled human exposure studies evaluating group mean changes in FEV 1 following prolonged O 3 exposures (i.e., 6.6 hours) in young, healthy adults engaged in moderate levels of physical activity (U.S. EPA, 201 3 , section 6.2.1.1)

. With regard to the group mean changes reported in these studies, the ISA specifically notes the following (U.S. EPA, 201 3 , section 6.2.1.1, Figure 6

- 1):
1. Prolonged exposure to 40 ppb O 3 results in a small decrease in group mean FEV 1 that is not statistically di fferent from responses following exposure to filtered air (Adams, 2002; Adams, 2006)

. 2. Prolonged exposure to an average O 3 concentration of 60 ppb results in group
mean FEV 1 decrements ranging from 1.8% to 3.6% (Adams 2002; Adams,

25 Adams (2006 ) did not find effects on FEV 1 at 60 ppb to be statistically significant. In an a nalysis of the Adams (2006 ) data, Brown (2008) showed that even after removal of potential outliers, the average effect on FEV 1 at 60 ppb was small, but highly statistical ly significant (p < 0.002) using several common statistical tests.*** E.O. 12866 Review

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Page 60 of 647 2006; 26 Schelegle et al., 2009; 27 Kim et al., 2011). Based on data from multiple studies, the weighted average group mean decrement was 2.7%. In some analyses, these group mean decrements in lung function were statistically significant (Brown et al., 2008; Kim et al., 2011), while i n other analyses they were not (Adams, 2006; Schelegle et al., 2009). 28

3. Prolonged exposure to an average O 3 concentration of 7 2 ppb results in a statistically significant group mean decrement in FEV 1 of about 6% (Schelegle et al., 2009). 29

4. Prolonged square

- wave exposure to average O 3 concentrations of 80 ppb, 100 ppb, or 120 ppb O 3 results in statistically significant group mean decrements in
FEV 1 ranging from 6 to 8%, 8 to 14%, and 13 to 16%, respectively (Folinsbee et al., 1988; Horstman et al., 1990; McD onnell et al., 1991; Adams, 2002; Adams, 2003; Adams, 2006)

.

26 Adams (2006); (2002) both provide data for an additional group of 30 healthy subjects that were exposed via facemask to 60 ppb (square

- wave) O 3 for 6.6 hours with moderate exercise ( V

̇ E = 23 L/min per m 2 BSA). These subjects are described on page 133 of Adams (2006) and pages 747 and 761 of Adams (2002). The FEV 1 decrement may be somewhat increased due to a target V ̇ E of 23 L/min per m 2 BSA relative to other studies having the target V

̇ E of 20 L/min per m 2 BSA. The facemask exposure is not expected to affect the FEV 1 responses relative to a chamber exposure. 27 For the 60 ppb target exposure concentration , Schelegle et al. (2009) reported that the actual mean exposure concentration was 63 ppb. 28 Adams (2006) did not find effects on FEV 1 at 60 ppb to be statistically significant

. In an analysis of the Adams (2006) data, Brown et al. (2008) addressed the mo re fundamental question of whether there were statistically significant differences in responses before and after the 6.6 hour exposure period and found the average effect on FEV 1 at 60 ppb to be small, but highly statistically significant using several co mmon statistical tests, even after removal of potential outliers. 29 For the 70 ppb exposure group, Schelegle et al. (2009) reported that the actual mean exposure concentration was 72 ppb.*** E.O. 12866 Review

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Page 61 of 647 As illustrated in Figure 6

- 1 of the ISA, there is a smooth dose

- response curve without evidence of a threshold for exposures between 40 and 120 ppb O 3 (U.S. EPA, 201 3 , Figure 6

- 1)

. When these data are taken together, the ISA concludes that “mean
FEV 1 is clearly decreased by 6.6

- h exposures to 60 ppb O 3 and higher concentrations in [healthy, young adult] subjects performing moderate exercise” (U.S. EPA, 201 3 , p. 6

- 9). With respect to interindiv idual variability in lung function, in an individual with relatively “normal” lung function, with recognition of the technical and biological variability in measurements, within

- day changes in FEV 1 of ≥ 5% are clinically meaningful ( Pellegrino et al., 2005 ; ATS, 1991 ) . The ISA (U.S. EPA, 2013, section 6.1.) focuses on individuals with >10% decrements in FEV 1 for two reasons. A 10% FEV 1 decrement is accepted by the American Thoracic Society (ATS) as an abnormal response and a reasonable criterion for assessing exercise

- induced bronchoc onstriction ( Dryden et al., 2010 ; ATS, 2000a ) . (U.S. EPA, 2013, section 6.2.1.1). Also, some individuals in the Schelegle et al. (2009 ) study experienced 5

- 10% FEV 1 decrements following exposure to filtered air. In previous NAAQS reviews , the EPA has made judgments regarding the
p otential implications for individuals experiencing FEV 1 decrements of varying degrees of severity. 30 For people with lung disease, the EPA judged that moderate functional decrements (e.g., FEV 1 decrements > 10 percent but < 20 percent, lasting up to 24 hours) would likely interfere with normal activity for many individuals, and would likely result

30 Such judgments have been made for decrements in FEV 1 as well as f or increased airway responsiveness and symptomatic responses (e.g., cough, chest pain, wheeze). Ranges of pulmonary responses and their associated potential impacts are presented in Tables 3

- 2 and 3

- 3 of the 2007 Staff Paper (U.S. EPA, 2007).*** E.O. 12866 Review

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Page 62 of 647 in more frequent use of medication (75 FR 2973, January 19, 2010). In previous reviews CASAC has endorsed these conclusions. In t he context of standard setting, in the last review of the O 3 NAAQS CASAC indicated that it i s appropriate to focus on the lower end of the range of moderate functional responses (e.g., FEV 1 decrements  10 percent) when estimating potentially adverse lung function decrements in people with lung disease, especially children with asthma (Henderson, 2006c; transcript of CASAC meeting, day 8/24/06, page 149 ). More specifically, CASAC stated that “[a] 10%
decrement in FEV 1 can lead to respiratory symptoms, espec ially in individuals with pre

existing pulmonary or cardiac disease. For example, people with chronic obstructive pulmonary disease have decreased ventilatory reserve (i.e., decreased baseline FEV 1 ) such that a ≥ 10% decrement could lead to moderate to sev ere respiratory symptoms” (Samet, 2011). In this review, CASAC reiterated its support for this conclusion, stating that “[a] n FEV 1 decrement of ≥10% is a scientifically relevant surrogate for adverse health outcomes for people with asthma and lung disease” (Frey, 2014c p. 3). Therefore, in considering interindividual variability in O 3 - induced lung function decrements in the current review, the EPA also focus es on the extent to which individuals were reported to experience FEV 1 decrements of 10% or greater. New studies (Schelegle et al., 2009; Kim et al., 2011) add to the previously available evidence for interindividual variability in the responses of healthy adults following exposures to O 3 . Following prolonged exposures to 80 ppb O 3 while at moderate exer tion, the proportion of healthy adults experiencing FEV 1 decrements greater than 10% was 17% by Adams (2006 ) , 26% by McDonnell (1996 ) , and 29% by Schelegle et al. (2009 ) . Following exposures to 60 ppb O 3 , that proportion was 20% by*** E.O. 12866 Review

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Page 63 of 647 Adams (2002 ) , 3% by Adams (2006 ) , 16% by Schelegle et al. (2009 ) , and 5% by Kim et al. (2011 ) . Based on these studies, the weighted average proportion (i.e., based on numbers of subjects in each study) of young, healthy adults with >10% FEV 1 decrements is 25% following exposure to 80 ppb O 3 and 10% following exposure to 60 ppb O 3 (U.S. EPA, 2013, page 6

- 19). 31 The ISA notes that responses within an individual tend to be reproducible over a period of several months, indicating that interindividual differences reflect diff

erences in intrinsic responsiveness. Given this, the ISA concludes that “a considerable fraction” of healthy individuals experience clinically meaningful decrements in lung function when exposed for 6.6 hours to 60 ppb O 3 during quasi continuous, moderate exertion (U.S. EPA, 2013, section 6.2.1.1, p. 6

- 20). As discussed above and in the ISA (U.S EPA, 2013, Section 5.3.2), secondary oxidation products formed following O 3 exposures can activate neural reflexes leading to decreased lung function. Two new quant itative models ( McDonnell et al., 2012 ; Schelegle et al., 2012 ), discussed in section 6.2.1.1 of the ISA (U.S. EPA, 2013, p. 6

- 15), included mathematical approaches to simulate the protective effect of antioxidants in the ELF at lower ambient O 3 concentrations, and include a threshold below which changes in lung function do not occu r . McDonnell et al. (2012 ) and Schelegle et al. (2012 ) developed models using data
on O 3 exposure concentrations, ventilation rates, duration of exposures, and lung function

31 The ISA als o notes that by considering responses uncorrected for filtered air exposures, during which lung function typically improves (which would increase the size of the change, pre

- and post

- exposure), 10% is an underestimate of the proportion of healthy individua ls that are likely to experience clinically meaningful changes in lung function following exposure for 6.6 hours to 60 ppb O 3 during intermittent moderate exertion (U.S. EPA, 2012, section 6.2.1.1).*** E.O. 12866 Review

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Page 64 of 647 responses from a number of controlled human exposure studies. The McDonnell et al. (2012 ) and Schelegle et al. (2 012 ) studies analyzed large datasets to fit compartmental models that included the concept of a dose of onset in lung function response or a response threshold based upon the inhaled O 3 dose. The McDonnell et al. (2012 ) model was fit to a dataset consisting of the FEV 1 responses of 741 young, healthy adul ts (18

- 35 years of age) from 23 individual controlled exposure studies. Concentrations across individual studies ranged from 40 ppb to 400 ppb, 32 activity level ranged from rest to heavy exercise, duration of exposure was from 2 to 7.6 hours. The extension of the McDonnell et al. (2012 ) model to children and older adults is discussed in section 6.2.4 of the HREA (U.S. EPA a , 201 4 ). Schelegle et al. (2012 ) also a nalyzed a large dataset with substantial overlap to that used by McDonnell et al. (2012 ) . The Schelegle et al. (2012 ) model was fit to the FEV 1 responses of 220 young healthy adults (taken from a dataset of 704 individuals) from 21 individual controlled exposure studies. The resulting empirical models can estimate the frequency distribution of individual responses for any exposure scenario as wel l as summary measures of the distribution such as the mean or median response and the proportions of individuals with FEV 1 decrements > 10%, 15%, and 20%. The predictions of the McDonnell and Schelegle models are consistent with the observed results from the individual studies of O 3 - induced FEV 1 decrements. Specifically, the model developed by McDonnell et al. (2012) predicts that 9% of healthy exercising adults would experience FEV 1 decrements greater than 10% following 6.6

32 Responses to O 3 in these studies were adjusted for res ponses observed following exposure to filtered air.*** E.O. 12866 Review

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Page 65 of 647 hour exposure to 60 ppb O 3 , and that 22% would experience such decrements following exposure to 80 ppb O 3 (U.S. EPA, 2013, p. 6

- 18 and Figure 6

- 3). The model developed by Schelegle et al. (2012) predicts that, for a prolonged (6.6 hours) O 3 exposure with moderate, quasi

- continuous exerc ise, the average dose of onset for FEV 1 decrement would be reached following 4 to 5 hours of exposure to 60 ppb, and following 3 to 4 hours of exposure to 80 ppb. However, 14% of the individuals had a dose of onset that was less than 40% of the average. Th ose individuals would reach their dose of onset following 1 to 2 hours of exposure to 50 to 80 ppb O 3 (U.S. EPA, 2013, p. 6

- 16), which is consistent with the threshold FEV 1 responses reported by McDonnell et al. (2012). Epidemiologic studies 33 have consist ently linked short

- term increases in ambient
O 3 concentrations with lung function decrements in diverse populations and lifestages, including children attending summer camps, adults exercising or working outdoors, and groups with pre

- existing respiratory d iseases such as asthmatic children (U.S. EPA, 2013, section 6.2.1.2). Some of these studies reported O 3 - associated lung function decrements accompanied by respiratory symptoms 34 in asthmatic children ( Just et al., 2002 ; Mortimer et al., 2002 ; Ross et al., 2002 ; Gielen et al., 1997 ; Romieu et al., 1997 ; Thur ston et al., 1997 ; Romieu et al., 1996 ) . In contrast, studies of children in the general population have reported similar O 3 - associated lung function decrements but without accompanying respiratory symptoms ( Ward et al., 2002 ; Gold et al., 1999 ; Linn et al., 1996 ) (U.S. EPA, 2013, section 6.2.1.2).

33 Unless otherwise specified, the epidemiologic studies discussed in the PA evaluate only adults. 34 Reversible loss of lung function in combination with the presence of symptoms meets the ATS definition o f adversity (ATS, 2000).*** E.O. 12866 Review

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Page 66 of 647 Several epidemiologic panel studies reported that associations with lung function decrements persisted at relatively low ambient O 3 concentrations. For outdoor recreation or exercise, associations were reported in analyses restricted to 1

- hour average O 3 concentrations less than 80 ppb ( Spektor et al., 1988a ; Spektor et al., 1988b ) , 60 ppb ( Brunekreef et al., 1994 ; Spektor et al., 1988a ) , and 50 ppb ( Brunekreef et al., 1994 )

. Among outdoo r workers, Brauer et al. (1996 ) found a robust association with daily
1

- hour max O 3 concentrations less than 40 ppb. Ulmer et al. (1997 ) found a robust association in schoolchildren with 30

- minute maximum O 3 concentrations less than
60 ppb. For 8

- hour average O 3 concentrations, associations with lung function decrements in children with asthma were found to pe rsist at concentrations less than
80 ppb in a U.S. multicity study ( Mortimer et al., 2002 ) and l ess than 51 ppb in a study conducted in the Netherlands ( Gielen et al., 1997 )

. Epidemiologic panel studies investigating the effects of short

- term exposure to O 3 provided information on potential confounding by copollutants such as PM 2.5 , PM 10 , NO 2 , or SO 2 . These studies varied in how they evaluated confounding. Some studi es of subjects exercising outdoors indicated that ambient concentrations of copollutants such as
NO 2 , SO 2 , or acid aerosol were low, and thus not likely to confound associations observed for O 3 ( Hoppe et al., 2003 ; Brunekreef et al., 1994 ; Hoek et al., 1993 ) . In other studies of children with increased outdoor exposures, O 3 was consistently associated with decreases in lung function, whereas other pollutants such as PM 2.5 , sulf ate, and acid aerosol individually showed variable associations across studies ( Thurston et al., 1997 ; Castillejos et al., 1995 ; Berry et al., 1991 ; Avol et al., 1990 ; Spektor et al., 1988a )

. Studies that conducted copollutant modeling generally found O 3 - associated lung function*** E.O. 12866 Review

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Page 67 of 647 decrements to be robust (i.e., most copollutant

- adjusted effect estimates fell within the 95% CI of the single

- pollutant effect estimates) (U.S. EPA, 2013, Figure 6

- 10 and Table
6

- 14). Most O 3 effect est imates for lung function were robust to adjustment for temperature, humidity, and copollutants such as PM 2.5 , PM 10 , NO 2 , or SO 2 . Although examined in only a few epidemiologic studies, O 3 also remained associated with decreases in lung function with adjustm ent for pollen or acid aerosols (U.S. EPA, 2013, section 6.2.1.2). Several epidemiologic studies demonstrated the protective effects of vitamin E and vitamin C supplementation, and increased dietary antioxidant intake, on O 3 - induced lung function decremen ts ( Romieu et al., 2002 ) (U.S. EPA, 2013, Figure 6

- 7 and Table 6

- 8). 35 Th ese results provide support for the n ew, quantitative models ( McDonnell et al.,
2012 ; Schelegle et al., 2012 ) , discussed above, which make use of the concept of oxidant stress to estimate the occurrence of lung function decrements following exposures to relatively low O 3 concentrations. In conclusion, new information from controlled human exposure studies considerably strengthens the evidence an d reduces the uncertainties, relative to the evidence that was available at the time of the 2008 review, regarding the presence and magnitude of lung function decrements in healthy adults following prolonged exposures
to O 3 concentrations below 80 ppb. As discussed in Section 6.2.1.1 in the ISA (U.S. EPA , 2013, p. 6

- 12), there is information available from four separate studies that evaluated exposures to 60 ppb O 3 ( Kim et al., 2011 ; Schelegle et al., 2009 ; Adams 2002 ; 2006 )

.

35 Eviden ce from controlled human exposure studies is mixed, suggesting that supplementation may be ineffective in the absence of antioxidant deficiency (U.S. EPA, 2013, p. 5

- 63).*** E.O. 12866 Review

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Page 68 of 647 Although not consistently statistically significant, group mean FEV 1 decrements following exposures to 60 ppb O 3 are consistent among these studies. Moreover, as is illustrated in Figure 6

- 1 of the ISA (U.S. EPA, 2013) , the group mean FEV 1 responses at 60 ppb fall on a smooth intake dose

- response curve for exposures betwe en 40 and
120 ppb O 3 . These studies also indicate that, on average, 10% of young, healthy adults experience clinically meaningful decrements in lung function when exposed for 6.6 hours to 60 ppb O 3 during intermittent, moderate exertion. One recent study h as also reported statistically significant decrements following exposures to 72 ppb O 3 (Schelegle et al., 2009). Predictions from newly developed quantitative models are consistent with these experimental results. Additionally, as discussed in more detail in section 3.1.4 below, epidemiologic studies continue to provide evidence of lung function decrements in people who are active outdoors, including people engaged in outdoor recreation or exercise, children, and outdoor workers, at low ambient O 3 concentra tions. While few new epidemiologic studies of O 3 - associated lung function decrements are available in this review, previously available studies have reported associations with decrements, including at relatively low ambient O 3 concentrations. ii. Pulmonary inflammation, injury, and oxidative stress Ozone exposures result in increased respiratory tract inflammation and epithelial permeability. Inflammation is a host response to injury, and the induction of inflammation is evidence that injury has oc curred. Oxidative stress has been shown to play a key role in initiating and sustaining O 3 - induced inflammation. Secondary oxidation products formed as a result of reactions between O 3 and components of the ELF can increase the expression of molecules (i.e ., cytokines, chemokines, and adhesion*** E.O. 12866 Review

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Page 69 of 647 molecules) that can enhance airway epithelium permeability (U.S. EPA, 2013, Sections 5.3.3 and 5.3.4). As discussed in detail in the ISA (U.S. EPA, 2013, section 6.2.3), O 3 exposures can initiate an acute inflammatory response throughout the respiratory tract that has been reported to persist for at least 18

- 24 hours after exposure. Inflammation induced by exposure of humans to O 3 can have several potential outcomes: (1) inflammation induced by a single exposure (or s everal exposures over the course of a summer) can resolve entirely; (2) continued acute inflammation can evolve into a chronic inflammatory state; (3) continued inflammation can alter the structure and function of other pulmonary tissue, leading to disease s such as asthma; (4) inflammation can alter the body’s host defense response to inhaled microorganisms, particularly in potentially at

- risk populations or lifestages such as the very young and old; and (5) inflammation can alter the lung’s response to oth er agents such as allergens or toxins (U.S. EPA, 2013, Section 6.2.3). Thus, lung injury and the resulting inflammation provide a mechanism by which O 3 may cause other more serious morbidity effects (e.g., asthma exacerbations). In the last review, contro lled human exposure studies reported O 3 - induced airway inflammation following exposures at or above 80 ppb and a nimal toxicological studies
prov ided evidence for increases in inflammation and permeability in rabbits at levels as low as 100 ppb O 3 . In the c urrent review, the link between O 3 exposures and airway inflammation and injury has been evaluated in additional controlled human exposure studies, as well as in recent epidemiologic studies. Controlled human exposure studies have generally been conducted in young, healthy adults or in adults with asthma using lavage (proximal airway and bronchoalveolar), bronchial biopsy, and more recently,*** E.O. 12866 Review

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Page 70 of 647 induced sputum. These studies have evaluated one or more indicators of inflammation, including neutrophil 36 (PMN) infl ux, markers of eosinophilic inflammation, increased permeability of the respiratory epithelium, and/or prevalence of proinflammatory molecules (U.S. EPA, 2013, section 6.2.3.1). Epidemiologic studies have generally evaluated associations between ambient O 3 and markers of inflammation and/or oxidative stress, which plays a key role in initiating and sustaining inflammation (U.S. EPA, 2013, section 6.2.3.2). There is an extensive body of evidence from controlled human exposure studies indicating that short

- t erm exposures to O 3 can cause pulmonary inflammation. A single acute exposure (1

- 4 hours) of humans to moderate concentrations of O 3 (200

- 600 ppb) while exercising at moderate to heavy intensities resulted in a number of cellular and biochemical changes in the lung, including inflammation characterized by increased numbers of PMNs, increased permeability of the epithelial lining of the respiratory tract, cell damage, and production of proinflammatory molecules (i.e., cytokines and prostaglandins, U.S. EPA, 2006a b ) . A meta

- analysis of 21 controlled human exposure studies ( Mudway and Kelly, 2004 ) using varied experimental protocols (80

- 600 ppb O 3 exposures; 1

- 6.6 hours exposure duration; light to heavy exercise; bronchoscopy at 0

- 24

36 Referred to as either neutrophils or polymorphonuclear neutrophils (or PMNs), these are the most abundant type of white blood cells in mammals. PMNs are recruited to the site of injury following trauma and are the hallmark of acute inflammation. The prese nce of PMNs in the lung has long been accepted as a hallmark of inflammation and is an important indicator that O 3 causes inflammation in the lungs. Neutrophilic inflammation of tissues indicates activation of the innate immune system and requires a comple x series of events, that then are normally followed by processes that clear the evidence of acute inflammation.*** E.O. 12866 Review

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Page 71 of 647 hours post

- O 3 exposure) reported that PMN influx in healthy subjects is linearly associated with total O 3 dose. Several studies, including one published since the last review (Alexis et al. , 2010), have reported O 3 - induced increases in PMN influx and permeability following exposures at or above 80 ppb ( Alexis et al., 2010 ; Peden et al., 1997 ; Devlin et al., 1991 ), and eosinophilic inflammation following exposures at or above 160 ppb ( Scannell et al., 1996 ; Peden et al., 1997 ; Hiltermann et al., 1999 ; Vagaggini et al., 2002 ). In addition, one recent controlled human exposure study has reported O 3 - induced PMN influx following exposures of healthy adu lts to 60 ppb O 3 (Kim et al., 2011), the lowest concentration at which inflammatory responses have b een evaluated in human studies.
As with FEV 1 responses to O 3 , inflammatory responses to O 3 are generally reproducible within individuals, with some individuals experiencing more severe O 3 - induced airway inflammation than indicated by group averages ( Holz et al., 2005 ; Holz et al., 1999 )

. Unlike O 3 - induced decrements in lung function, which are attenuated following repeated exposures over several days (U. S. EPA, 2013, section 6.2.1.1), some markers of O 3 - induced inflammation and tissue damage remain elevated during repeated exposures, indicating ongoing damage to the respiratory system (U.S. EPA, 2013, section 6.2.3.1). Most controlled human exposure stud ies have reported that asthmatics experience larger O 3 - induced inflammatory responses than non

- asthmatics. Specifically, asthmatics exposed to 200 ppb O 3 for 4

- 6 hours with exercise show significantly more neutrophils in bronchoalveolar lavage fluid (BALF) than similarly exposed healthy individuals ( Scannell et al., 1996 ; Basha et al., 1994 )

. Bosson et al. (2003 ) reported significantly*** E.O. 12866 Review

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Page 72 of 647 greater expression of a variety of pro

- inflammatory cytokines in asthmatics, compared to healthy subjects, following exposure to 200 ppb O 3 for 2 hours. In addition, research available in the last review, combined with a recent study newly available in this review, indicates that pretreatment of asthmatics with corticosteroids can prevent the O 3 - induced inflammatory response in induced sputum , though pretreatment did not prevent FEV 1 decrements ( Vagaggini et al., 2001; 2007 ) . In contrast, Stenfors et al. (2002 ) did not detect a difference in the O 3 - induced increases in neutrophil numbers between 15 subjects with mild asthma and 15 healthy subjects by bronchial wash at the 6 hours postexposure time point, although the neutrophil increase in the asthmatic group was on top of an elevated baseline. In people with allergic airway disease, including people with rhinitis and asthma, evidence available in the last review indicated that proinflammatory mediators also cause accumulation of eosinophils in the airways (Jorres et al., 1996; Peden et al., 1995 and 1997; Frampton et a l., 1997; Hiltermann et al., 1999; Holz et al., 2002; Vagaggini et al., 2002). The eosinophil, which increases inflammation and allergic responses, is the cell most frequently associated with exacerbations of asthma (75 CFR 2969, January 19, 2010). Studie s reporting inflammatory responses and markers of lung injury have clearly demonstrated that there is important variation in the responses of exposed subjects (75 FR 2953, January 19, 2010). Some individuals also appear to be intrinsically more susceptible to increased inflammatory responses from O 3 exposure (Holz et al., 2005). In healthy adults exposed to each 80 and 100 ppb O 3 , Devlin et al. (1991) observed group average increases in neutrophilic inflammation of 2.1

- and 3.8

- fold, respectively.*** E.O. 12866 Review

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Page 73 of 647 However, there was a 20

- fold range in inflammatory responses between individuals at both concentrations. Relative to an earlier, similar study conducted at 400 ppb (Koren et al., 1989), Devlin et al. (1991) noted that although some of the study population showed
li ttle or no increase in inflammatory and cellular injury indicators analyzed after exposures to lower levels of O 3 (i.e., 80 and 100 ppb), others had changes that were as large as those seen when subjects were exposed to 400 ppb O 3 . The data suggest that as a whole the healthy population, on average, may have small inflammatory responses following exposure to near

- ambient levels of O 3 , though there may be a sizable subpopulation that is very sensitive to low levels of O 3 . A number of studies report that O 3 exposures increase epithelial permeability. Increased BALF protein, suggesting O 3 - induced changes in epithelial permeability, has been reported at 1 hour and 18 hours postexposure ( Devlin et al., 1997 ; Balmes et al., 1996 ) . A meta

- analysis of results from 21 publications ( Mudw ay and Kelly, 2004 ) for varied experimental protocols (80

- 600 ppb O 3 ; 1

- 6.6 hours duration; light to heavy exercise; bronchoscopy at 0

- 24 hours post

- O 3 exposure; healthy subjects), showed that increased BALF protein is associated with total inhaled O 3 d ose. As noted in the 2009 PM ISA (U.S. EPA, 2009a ), it has been postulated that changes in permeability associated with acute inflammation may provide increased access of inhaled antigens, particles, and other inhaled substances deposited on lung surfaces to the smooth muscle, interstitial cells, immune cells underlying the epithelium, and the blood (U.S. EPA, 2013, sections 5.3.4, 5.3.5)

. As has been observed with FEV 1 responses, within individual changes in permeability a re correlated with changes followi ng sequential O 3 exposures ( Que et al. , 2011) . C hanges in permeability and AHR apear to be mediated by different*** E.O. 12866 Review

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Page 74 of 647 pathways. Animal toxicology studies have provided some support for this hypothesis (Adamson and Prieditis, 1995; Chen et al 2006), though these studies did not specifically evaluate O 3 exposures (U.S. EPA, 2009a ). The limited epidemiologic evidence reviewed in the 2006 O 3 AQCD ( U.S. EPA, 2006a ) demonstrated an association between short

- term increases in ambient O 3 concentrations and airways infl ammation in children (1

- hour max O 3 of approximately
100 ppb). In the 2006 O 3 AQCD ( U.S. EPA, 2006a ), there was limited evidence for increases in nasal lavage levels of inflammatory cell counts and molecules released by inflammatory cells (i.e., eosinophil ic cationic protein, and myeloperoxidases). Since 2006, as a result of the development of less invasive methods, there has been a large increase in the number of studies assessing ambient O 3 - associated changes in airway inflammation and oxidative stress, t he types of biological samples collected, and the types of indicators. Most of these recent studies have evaluated biomarkers of inflammation or oxidative stress in exhaled breath, nasal lavage fluid, or induced sputum (U.S. EPA, 2013, section 6.2.3.2). Th ese recent studies form a larger database to establish coherence with findings from controlled human exposure and animal studies that have measured the same or related biological markers. Additionally, results from these studies provide further biological plausibility for the associations observed between ambient O 3 concentrations and respiratory symptoms and asthma exacerbations

. A number of epidemiologic studies provide evidence that short

- term increases in ambient O 3 exposure increase pulmonary inflammation and oxidative stress in children, including those with asthma ( Sienra

- Monge et al., 2004 ; Barraza

- Villarreal et al., 2008 ; Romieu et al., 2008 ; Berhane et al., 2011 )

. Multiple studies examine d and found*** E.O. 12866 Review

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Page 75 of 647 increases in exhaled NO (eNO) 37 ( Berhane et al., 2011 ; Khatri et al., 2009 ; Barraza

Villarreal et al., 2008 ) . In some studies of subjects with asthma, increases in ambient O 3 concentration at the same lag were associated with both increases in pulmonary inflammation and respiratory symptoms ( Khatri et al., 2009 ; Barraza

- Villarreal et al.,
2008 ) . Although mor e limited in number, epidemiologic studies also found associations with cytokines such as IL

- 6 or IL

- 8 ( Barraza

- Villarreal et al., 2008 ; Sienra

- Monge et al.,
2004 ) , eosinophils ( Khatri et al., 2009 ) , antioxidants ( Sienra

- Monge et al., 2004 ) , and indicators of oxidative stress ( Romieu et al., 2008 ) (ISA, Section 6.2.3.2, U.S. EPA, 2013). Because associations with inflammation were attenuated with higher antioxidant intake the study by Sienra

- Monge et al. (2004 ) , this study provides additional evidence that inhaled O 3 is likely to be an important source of reactive oxygen species in airways and/or may inc rease pulmonary inflammation via oxidative stress

- mediated mechanisms among all age groups. L imitations in some recent studies have contributed to inconsistent results in adults (U.S. EPA, 2013, section 6.2.3.2). Exposure to ambient O 3 on multiple days ca n result in larger increases in pulmonary inflammation and oxidative stress, as discussed in section 6.2.3.2 of the ISA (U.S. EPA, 2013). In studies that examined multiple O 3 lags, multiday averages of
8

- hour maximum or 8

- hour average concentrations were a ssociated with larger increases in pulmonary inflammation and oxidative stress ( Berhane et al., 2011 ; Delfino et al.,
2010 ; Sienra

- Monge et al., 2004 ) , consistent with co ntrolled human exposure (U.S. EPA, 2013, section 6.2.3.1) and animal studies (U.S. EPA, 2013, section 6.2.3.3) reporting that

37 Exhaled NO has been shown to be a useful biomarker for airway inflammation in large population

- based studies ( Linn et al., 2009 ) (ISA, U.S. EPA, 2013, Section 7.2.4)

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Page 76 of 647 some markers of pulmonary inflammation remain elevated with O 3 exposures repeated over multiple days. Evidence from animal toxicol ogical studies also clearly indicates that
O 3 exposures result in damage and inflammation in the lung (ISA, Section 5.3, U.S. EPA, 2013). In the few studies that evaluated the potential for confounding, O 3 effect estimates were not confounded by temperatur e or humidity, and were robust to adjustment for
PM 2.5 or PM 10 ( Barraza

- Villarreal et al., 2008 ; Romieu et al., 2008 ; Sienra

- Monge et al.,
2004 )

. In conclusion, a relatively small number of controlled human exposure studies evaluating O 3 - induced airway inflammation have become available since the last review. For purposes of reviewing the current O 3 NAAQS, the most important of these recent studies reported a statistically signific ant increase in airway inflammation in healthy adults at moderate exertion following exposures to 60 ppb O 3 , the lowest concentration that has been evaluated for inflammation. In addition, a number of recent epidemiologic studies report O 3 - associated incre ases in markers of pulmonary inflammation, particularly in children. Thus, recent studies continue to support the evidence for airway inflammation and injury that was available in previous reviews, with new evidence for such effects following exposures to lower concentrations than had been evaluated previously. iii. Airway hyperresponsiveness Airway hyperresponsiveness (AHR) refers to a condition in which the conducting airways undergo enhanced bronchoconstriction in response to a variety of stimuli. Airwa y hyperresponsiveness is an important consequence of exposure to ambient O 3 because its presence reflects a change in airway smooth muscle reactivity, and indicates*** E.O. 12866 Review

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Page 77 of 647 that the airways are predisposed to narrowing upon inhalation of a variety of ambient stimu li including specific triggers (i.e., allergens) and nonspecific triggers (e.g., SO 2 , and cold air). People with asthma are generally more sensitive to bronchoconstricting agents than those without asthma, and the use of an airway challenge to inhaled bron choconstricting agents is a diagnostic test in asthma. Standards for airway responsiveness testing have been developed for the clinical laboratory ( ATS, 2000 ) , although variation in the methodology for administering the bronchoconstricting agent may affect the results ( Cockcroft et al., 2005 ) . There is a wide range of airway responsive ness in people without asthma, and responsiveness is influenced by a number of factors, including cigarette smoke, pollutant exposures, respiratory infections, occupational exposures, and respiratory irritants. Dietary antioxidants have been reported
to at tenuate O 3 - induced bronchial hyperresponsiveness in people with asthma ( Trenga et al., 2001 )

. Evidence for airway hyperresponsiveness following O 3 exposures is derived primarily from controlled human exposure and toxicological studies (U.S. EPA, 2013, section 6.2.2). Airway responsiveness is often quantified by measuring changes in pulmonary function following the inhalation of an aerosolized allerg en or a nonspecific bronchoconstricting agent (e.g., methacholine), or following exposure to a bronchoconstricting stimulus such as cold air. In the last review, controlled human exposure studies of mostly adults (≥ 18 years of age) had shown that exposure s to O 3 concentrations at or above 80 ppb increase airway responsiveness, as indicated by a reduction in the concentration of specific (e.g., ragweed) and non

- specific (e.g., methacholine) agents required to produce a given reduction in lung function (e.g. , as*** E.O. 12866 Review

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Page 78 of 647 measured by FEV 1 or specific airway resistance) (U.S. EPA, 2013, section 6.2.2.1). This
O 3 - induced AHR has been reported to be dose

- dependent (Horstman et al., 1990). Animal toxicology studies have reported O 3 - induced airway hyperresponsiveness in a

n umber of species, with some rat strains exhibiting hyperresponsiveness following 4

- hour exposures to O 3 concentrations as low as 50 ppb ( Depuydt et al., 1999 ) . Since the last review, there have been relatively few new controlled human exposure and animal toxicology studies of O 3 and airway hyperresponsiven ess, and no new studies have evaluated exposures to O 3 concentrations at or below 80 ppb (U.S. EPA, 2013, section 6.2.2.1)

. Airway hyperresponsiveness is linked with the accumulation and/or activation of eosinophils in the airways of asthmatics, which is followed by production of mucus and a late

- phase asthmatic response (75 FR 2970, January 19, 2010)

. In a study of 16 intermittent asthmatics, Hiltermann et al. (1999) found that there was a significant inverse correlation between the O 3 - induced change in the percentage of eosinophils in induced sputum and the concentration of methacholine causing a 20% decrease in FEV 1 . Hiltermann et al. (1999) concluded that the results point to the role of eosinophils in O 3 - induced airway hyperresponsiveness

. Increases i n O 3 - induced nonspecific airway responsiveness incidence and duration could have important clinical implications for children and adults with asthma, such as exacerbations of their disease

. Airway hyperresponsiveness after O 3 exposure appears to resolve more slowly than changes in FEV 1 or respiratory symptoms ( Folinsbee and Hazucha, 2000 ) . Studies suggest that O 3 - induced AHR usually resolves 18 to 24 hours after exposure, but may persist in some individuals for longer periods ( Folinsbee and Hazucha, 1989 )

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Page 79 of 647 Furthermore, in studies of repeated exposure to O 3 , changes in AHR tend to be somewhat less susceptible to attenuation with consecutive exposures than changes in FEV 1 ( Gong et al., 1997 ; Folinsbee et al., 1994 ; Kulle et al., 1982 ; Dimeo et al., 1981 ) (U.S. EPA, 2013, section 6.2.2)

. In animal studies a 3

- day continuous exposure resul ted in attenuation of
O 3 - induced airway hyperresponsiveness (Johnston et al., 2005) while repeated exposures for 2 hours per day over 10 days did not (Chhabra et al., 2010), suggesting that attenuation could be lost when repeated exposures are interspersed with periods of rest (U.S. EPA, 2013 , section 6.2.2.2). As mentioned above, in addition to human subjects a number of species, including nonhuman primates, dogs, cats, rabbits, and rodents, have been used to examine the effect of O 3 exposure on airway h yperresponsiveness (see Table 6

- 14, ( U.S. EPA, 1996 ) of the 1996 O 3 AQCD and Annex Table AX5

- 12 on page AX5

- 36 ( U.S. EPA, 2006a ) of the
2006 O 3 AQCD). A body of animal toxicology studies, including some recent studies conducted since the last review, provides support for the O 3 - induced AHR reported in humans (U.S. EPA, 2013, section 6.2.2.2). Although most of these studies evaluated O 3
concentrat ions above those typically found in ambient air in cities in the United States (i.e., most studies evaluated O 3 concentrations of 100 ppb or greater), one study reported that a very low exposure concentration (50 ppb for 4 hours) induced AHR in some rat
st rains ( Depuydt et al., 1999 ) . Additional recent rod ent studies reported O 3 - induced AHR following exposures to O 3 concentrations from 100 to 500 ppb (Johnston et al., 2005; Chhabra et al., 2010; Larsen et al., 2010)

. In characterizing the relevance of these exposure concentrations, the ISA noted that a stud y using radiolabeled O 3 suggests that even very high O 3 exposure concentrations in rodents could be equivalent to much lower*** E.O. 12866 Review

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Page 80 of 647 exposure concentrations in humans

. Specifically, a 2000 ppb (2 ppm) O 3 exposure concentration in resting rats was reported to be ro ughly equivalent to a 400 ppb exposure concentration in exercising humans (Hatch et al., 1994)

. Given this relationship, the ISA noted that animal data obtained in resting conditions could underestimate the risk of effects for humans (U.S. EPA, 2013, secti on 2.4, p. 2

- 14)

. The 2006 AQCD ( U.S. EPA, 2006a , p. 6

- 34) concluded that spirometric responses to O 3 are independent of inflammatory responses and markers of epithelial injury (Balmes et al., 1996; Blomberg et al., 1999; Torres et al., 1997). Significan t inflammatory responses to O 3 exposures that did not elicit significant spirometric responses have b een reported (Holz et al., 2005 ). A recent study (Que et al., 2011) indicates that airway hyper

- responsiveness also appears to be mediated by a differing
p hysiologic pathway. These results from controlled human exposure studies indicate that sub

- populations of healthy study subjects consistently experience larger than average lung function decrements, greater than average inflammatory responses and pulmonary injury as expressed by increased epithelial permeability, and greater than average airway responsiveness, and that these effects are mediated by apparently different physiologic pathways. Except for lung function decrments, we do not have concentraiton or exposure response informaiton about the other, potentially more sensitive, 38 clinical endpoints (i.e., inflammation, increased epithelial permeability, AHR) that would allow us to

38 CASAC noted that “...[W]hile measures of FEV1 a re quantitative and readily obtainable in humans, they are not the only measures

— and perhaps not the most sensitive measures

— of the adverse health effects induced by ozone exposure.” (Henderson, 2006 ).*** E.O. 12866 Review

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Page 81 of 647 quantitatively estimate the size of the population affetcted and the magnitu de of their
responses. In summary, a strong body of controlled human exposure and animal toxicological studies, most of which were available in the last review of the O 3 NAAQS, report O 3 - induced airway hyperresponsiveness after either acute or repeated exposures (U.S. EPA, 2013, section 6.2.2.2). People with asthma often exhibit increased airway responsiveness at baseline relative to healthy controls, and they can experience further increases in responsiveness following exposures to O 3 . Studies reporting increased airway responsiveness after O 3 exposure contribute to a plausible link between ambient
O 3 exposures and increased respiratory symptoms in asthmatics, and increased hospital admissions and emergency department visits for asthma (U.S. EPA, 2013, s ection 6.2.2.2). iv. Respiratory symptoms and medication use
R espiratory symptoms are associated with adverse outcomes such as limitations in activity , and are the primary reason for people with asthma to us e quick relief medication and seek medical care . S tudies evaluating the link between O 3 exposures and such symptoms allow a direct characterization of the clinical and public health significance of ambient O 3 exposure . Controlled human exposure and toxicological studies have described modes of action t hrough which short

- term O 3 exposure s may increase respiratory symptoms by demonstrating O 3 - induced airway hyperresponsiveness ( U.S. EPA, 2013 , section 6.2.2 ) and pulmonary inflammation (U.S. EPA, 2013 , section 6.2.3 ). The link between subjective respirat ory symptoms and O 3 exposures has been evaluated in both controlled human exposure and epidemiologic studies, and the link with*** E.O. 12866 Review

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Page 82 of 647 medication use has been evaluated in epidemiologic studies. In the last review, several controlled human exposure studies report ed respiratory symptoms following exposures to
O 3 concentrations at or above 80 ppb. In addition, one study reported such symptoms following exposures to 60 ppb O 3 , though the increase was not statistically different from filtered air controls. Epidemiolog ic studies reported associations between ambient O 3 and respiratory symptoms and medication use in a variety of locations and populations, including asthmatic children living in U.S. cities. In the current review, additional controlled human exposure studi es have evaluated respiratory symptoms following exposures to O 3 concentrations below 80 ppb and recent epidemiologic studies have evaluated associations with respiratory symptoms and medication use (U.S. EPA, 2013, sections 6.2.1, 6.2.4). In controlled human exposure studies available in the last review as well as newly available studies, s tatistically significant increases in respiratory symptoms have been consistently reported in healthy adult volunteers engaged in intermittent, moderate exertion following 6. 6 hour exposures to average O 3 concentrations at or above 72 ppb (Adams, 2003; Adams, 2006; Schelegle et al., 2009). Such symptoms have been reported to increase with increasing O 3 exposure concentrations, duration of exposure, and activity lev el ( McDonnell et al., 1999 )

. Results have been less consistent for lower exposure concentrations. A recent study by Schelegle et al. (2009) report ed a statistically significant increase in respiratory symptoms in healthy adults fo llo wing 6.6 hour exposures to an average O 3 concentration of 72 ppb , but not 60 ppb

. Kim et al. (2011) also did not find statistically significant increases in respiratory symptoms following exposures of healthy adults to 60 ppb O 3 .*** E.O. 12866 Review

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Page 83 of 647 Adams (2006) reported a n increase in respiratory symptoms in healthy adults during a 6.6 hour exposure protocol with an average O 3 exposure concentration of 60 ppb. This increase was significantly different from initial respiratory symptoms, but not from filtered air controls. T he findings for O 3 - induced respiratory symptoms in controlled human exposure studies , and the evidence integrated across disciplines describing underlying modes of action , provide biological plausibility for epidemiologic associations observed between shor t

- term increases in ambient O 3 concentration and increases in respiratory symptoms (U.S. EPA, 2013, section 6.2.4)

. In epidemiologic studies of respiratory symptom s, data typically are collected by having subjects (or their parents) record symptoms and medication use in a diary without direct supervision by study staff. Several limitations of symptom reports are well recognized , as described in the ISA (U.S. EPA, 2013 , section 6.2.4) . Nonetheless, symptom diaries remain a convenient tool to collect individual

- level data from a large number of subjects and allow modeling of associations between daily changes in O 3 concentration and daily changes in respiratory morbidity over multiple weeks or months. Importantly, many of the limitations in these studies are sources of random measurement error that can bias effect estimates to the null or increase the uncertainty around effect estimates (U.S. EPA, 2013, Section 6.2.4)

. B e cause respiratory symptoms are associated with limitations in activity and daily function and are the primary reason for using medication and seeking medical care, the evidence is directly coherent with the associations consistently observed between increa ses in ambient O 3 concentration and increases in asthma emergency department visits , discussed below (U.S. EPA, 2013, Section 6.2.4)

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Page 84 of 647 Most epidemiologic studies of O 3 and respiratory symptoms and medication use have been conducted in children and/or adul ts with asthma, with fewer studies, and less consistent results, in non

- asthmatic populations (U.S. EPA, 2013, section 6.2.4)

. The 2006 AQCD ( U.S. EPA, 2006a , U.S. EPA, 2013, section 6.2.4) concluded that the collective body of epidemiologic evidence indic ated that short

- term increases in ambient
O 3 concentrations are associated with increases in respiratory symptoms in children with asthma. A large body of s ingle

- city and single

- region studies of asthmatic children provide s consistent evi dence for associat ions between short

- term increases in ambient O 3 concentrations and increased respiratory symptoms and asthma medication use in children with asthma (U.S. EPA, 2013 , Figure 6

- 12 , Table 6

- 20 , p. 79 ). Methodological differences among studies make comparisons across recent multicity studies of respiratory symptoms difficult. Because of fewer person

- days of data ( Schildcrout et al., 2006 ) or examination of 19

- day averages of ambient O 3 concentrations ( O'Connor et al., 2008 ) , the ISA did not give greater weight to results from recent multicity studies than results from single

- city studies (U.S. EPA, 2013, section 6.2.4.5). While evidence from the few available U.S. multicity studies is less consistent ( O'Connor et al., 2008 ; Schildcrout et al., 2006 ; Mortimer et al., 2002 ) , the overall body of epidemiologic evidence with respect to the association betweeen exposure to O 3 and respiratory symptoms in asthmatic children remains compelling (U.S. EPA, 2013, section 6.2.4.1). Findings from a small body of studies indicate that O 3 is also associated with increased respiratory symptoms in adults with asthma ( Khatri et al., 2009 ; Feo Brito et al., 2007 ; Ross et al., 2002 ) (U.S. EPA, 2013 , section 6.2.4.2).*** E.O. 12866 Review

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Page 85 of 647 Available evidence indicates that O 3 - associated increases in respiratory symptoms are not confounded by temperature, pollen, or copollutants (primarily PM) ( U.S. EPA, 2013 , section 6.2.4.5; Table 6

- 25 ; Romieu et al., 1996; Romieu et al., 1997; Thurston et al., 1997; Gent et al., 2003). However, identifying the independent effects of O 3 in some studies was complicated due to the high correlations observed betwe en O 3 and PM or different lags and averaging times examined for copollutants. Nonetheless, the ISA noted that the robustness of associations in some studies of individuals with asthma, combined with findings from controlled human exposure studies for the d irect effects of O 3 exposure, provide substantial evidence supporting the independent effects of short

- term ambient O 3 exposure on respiratory symptoms (U.S. EPA, 2013, section 6.2.4.5). Epidemiologic studies of medication use have reported associations with
1

- hour maximum O 3 concentrations and with multiday average O 3 concentrations ( Romieu et al., 2006 ; Just et al., 2002 ) . Some studies reported O 3 associations for both respiratory sympt oms and asthma medication use ( Escamilla

- Nuñez et al., 2008 ; Romieu et al., 2006 ; Schildcrout et al., 2006 ; Jalaludin et al., 2004 ; Romieu et al., 1997 ; Thurston et al. , 1997 ) while others reported associations for either respiratory symptoms or medication use ( Romieu et al., 1996 ; Rabinovitch et al., 2004 ; Just et al., 2002 ; Ostro et al., 2001 )

. In summary, both controlled human exposure and epidemiologic studies have reported respiratory symptoms attributable to short

- term O 3 exposures. In the last review, the majority of the evidence from controlled human exposure studies in young, healthy

a dults was for symptoms following exposures to O 3 concentrations at or above 80 ppb. Although studies that have become available since the last review have not reported*** E.O. 12866 Review

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Page 86 of 647 increased respiratory symptoms in young, healthy adults following exposures with modera te exertion to 60 ppb, one recent study did report increased symptoms following exposure to 70 ppb O 3 . 39 As was concluded in the 2006 O 3 AQCD ( U.S. EPA, 2006a , 1996 ) , the collective body of epidemiologic evidence indicates that short

- term increases in ambient O 3 concentration are associated with increases in respiratory symptoms in children with asthma (U.S. EPA, 2013 , section 6.2.4). Recent studies of respiratory symptoms and medication use, primarily in asthmatic children, add to this evidence. In a smaller body of studies, increases in ambient O 3 concentration were associated with increases in respiratory symptoms in adults with asthma. v. Lung host defense The mammalian respiratory tract has a number of closely integrated defense mechanisms that, when functioning normally, provide protection from the potential health effects of exposures to a wide variety of inhaled particles and microbes. These defense mechanisms include mucociliary clearance, alveolobronchiolar transport mechanism, alveolar macrophage s , 40 and adaptive immunity 41 (U.S. EPA, 2013, section 6.2.5). The previous O 3 AQCD ( U.S. EPA, 2006a ) concluded that animal toxicological studies provided evidence that acute exposure to O 3 concentrations as low as 100 to 500 ppb can increase susceptibility to infectious diseases due to modulation of these lung host

39 As noted above, for the 70 ppb target exposure concentration , Schelegle et al. (2009) reported that the actual mean exposure concentration was 72 ppb. 40 Phagocytic white blood cells within the alveoli of the lungs that ingest inhaled particles. 41 The adaptive immune system , is also known as the acquir ed immune system . Acquired immunity creates immunological memory after an initial response to a specific pathogen, leading to an enhanced response to subsequent encounters with that same pathogen.*** E.O. 12866 Review

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Page 87 of 647 defenses. This conclusion was based , in large part , on animal studies of alveolar macrophage function and mucociliary clearance (U.S. EPA, 2013, section 6.2.5). Integrating animal study resul ts with human exposure evidence , the 2006 Criteria Document concluded that available evidence indicates that short

- term O 3 exposures have the potential to impair host defenses in humans, pri marily by interfering with alveolar macrophage function. Any impairment in alveolar macrophage function may lead to decreased clearance of microorganisms or nonviable particles. Compromised alveolar macrophage functions in asthmatics may increase their sus ceptibility to other O 3 effects, the effects of particles, and respiratory infections ( U.S. EPA, 2006a , p. 8

– 26). These conclusions were based largely on studies conducted in animals exposed for several hours up to several weeks to O 3 concentrations from 1 00 to 250 ppb ( Hurst et al., 1970 ; Driscoll et al., 1987 ; Cohen et al., 2002 ) . Consistent with the animal evidence, a controlled human exposure study available in the last review had reported decrements in t he ability of alveolar macrophages to phagocytize yeast following exposures of healthy volunteers to
O 3 concentrations of 80 and 100 ppb for 6.6

- hour during moderate exercise ( Devlin et al., 1991 )

. Alveolobronchiolar transport mechanisms refers to the transport of particles deposited in the deep lung (alveoli) which may be removed either up through the respiratory tract (bronchi) by alveolobronchiolar transport or through the lymphatic system. The pi votal mechanism of alveolobronchiolar transport involves the movement of alveolar macrophage s with ingested particles to the bottom of the conducting airways

. These airways are lined with ciliated epithelial cells and cells that produce mucous, which surro unds the macrophages. The ciliated epithelial cells move the mucous packets*** E.O. 12866 Review

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Page 88 of 647 up the resiratory tract, hence the term “mucociliary escalator.” Although some studies show reduced tracheobronchial clearance after O 3 exposure (U.S. EPA, 2013, section 6.2.5.1) , alveolar clearance of deposited material is accelerated, presumably due to macrophage influx, which in itself can be damaging. With r egard to adaptive immunity, a limited number of epidemiologic studies have examined associations between O 3 exposure and hospital admissions or ED visits for respiratory infection, pneumonia, or influenza. Results have been mixed, and in some cases conflic ting (U.S. EPA, 2013, Sections 6.2.7.2 and 6.2.7.3). With the exception of influenza, it is difficult to ascertain whether cases of respiratory infection or pneumonia are of viral or bacterial etiology. A recent study that examined the association between O 3 exposure and respiratory hospital admissions in response to an increase in influenza intensity did observe an increase in respiratory hospital admissions ( Wong et al., 2009 ) , but information from toxicological studies of O 3 and viral infections is ambiguous. In summary, relatively few studies conducted since the last review have evaluated the effects of O 3 exposures on lung host defense. When the available evidence is taken as a whole, the ISA concludes that acute O 3 exposures impair the host defense capability of animals, primarily by depressing alveolar macrophage function and perhaps also by decreasing mucociliary clearance of inhaled particles and microo rganisms. Coupled with limited evidence from controlled human exposure studies, this suggests that humans exposed to O 3 could be predisposed to bacterial infections in the lower respiratory tract (U.S. EPA , 2013, section 6.2.5.5)

. vi. Allergic and asthma

- related responses*** E.O. 12866 Review

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Page 89 of 647 Effects resulting from combined exposures to O 3 and allergens have been studied in a variety of animal species, gene rally as models of experimental asthma. P ulmonary function and AHR in animal models of asthma are discussed in detail in Section 6.2.1.3 and Section 6.2.2.2, respectively, in the ISA (U.S. EPA, 2013)

. Studies of allergic and asthma

- related responses are discussed in detail in sections 5.3.6 and 6.2.6 of the ISA (U.S. EPA, 2013). Evidence available in the last review indicates that O 3 exposure skews immune responses to ward an allergic phenotype and cou ld also make airborne allergens more allergenic

. In humans, allergic rhinoconjunctivitis symptoms are associated with increases in ambient O 3 concentrations ( Riediker et al., 2001 ) . Controlled human exposure studies have obs erved O 3 - induced changes indicating allergic skewing. Airway eosinophils, which are white blood cells that participate in allergic disease and inflammation, were observed to increase in volunteers with atopy 42 and mild asthma (Peden et al., 1997)

. In a more recent study, expression of IL

- 5, a cytokine involved in eosinophil recruitment and activation, was increased in subjects with atopy but not in healthy subjects (Hernandez et al., 2010). Epidemiologic studies describe associations between eosinophils in b oth short

- (U.S. EPA, 2013, Section 6.2.3.2) and long

- term (U.S. EPA, 2013, Section 7.2.5) O 3 exposure, as do chronic exposure studies in non

- human primates. Collectively, findings from these studies suggest that O 3 can induce or enhance certain components of allergic inflam mation in individuals with allergy or allergic asthma.

42 Atopy is a predisposition toward developing certain alle rgic hypersensitivity reactions. A person with atopy typically presents with one or more of the following: eczema (atopic dermatitis), allergic rhinitis (hay fever), allergic conjunctivitis, or allergic asthma.*** E.O. 12866 Review

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Page 90 of 647 Evidence available in the last review indicates that O 3 may also increase AHR to specific allergen triggers (75 FR 2970, January 19, 2010). Two studies (Jörres et al., 1996; Holz et al., 2002) observed increased airway responsiveness to O 3 exposure with bronchial allergen challenge in subjects with preexisting allergic airway disease

. Ozone

induced exacerbation of airway responsiveness persists longer and attenuates more slowly than O 3 - induced lung function decrements and respiratory symptom responses and can have important clinical implications for asthmatics

. Animal toxicology studies indicate that O 3 enhances inflammatory and allergic responses to allergen challenge in sensitized a nimals. In addition to exacerbating existing allergic responses, toxicology studies indicate that O 3 can also act as an adjuvant to produce sensitization in the respiratory tract. Along with its pro - allergic effects (inducing or enhancing certain component s of allergic inflam mation in individuals with allergy or allergic asthma ) , O 3 could also make airborne allergens more allergenic. W hen combined with NO 2 , O 3 has been shown to enhance nitration of common protein allergens, which may incr ease their allergen icity Franze et al. (2005 )

. vii. Hospital admissions and emergency department visits The 2006 O 3 AQCD evaluated numerous studies of respiratory

- related emergency department visits and hospital admissions. These were primarily time

- series studies conducted in the U.S., Canada, Europe, South America, Australia, and Asia. Based on such studies, the 200 6 O 3 AQCD concluded that “the overall evidence supports a causal relationship between acute ambient O 3 exposures and increased respiratory morbidity*** E.O. 12866 Review

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Page 91 of 647 resulting in increased ED visits and [hospital admissions] during the warm season 43 ” ( U.S. EPA, 2006a ) . This conclusion was “strongly supported by the human clinical, animal toxicologic[al], and epidemiologic evidence for [O 3 - induce d] lung function decrements, increased respiratory symptoms, airway inflammation, and airway hyperreactivity” ( U.S. EPA, 2006a )

. The results of recent studies largely support the conclusions of the 2006 O 3 AQCD (U.S. EPA, 2013, section 6.2.7). Since the completion of the 2006 O 3 AQCD, relatively fewer studies conducted in the U.S., Canada, and Europe have evaluated associations bet ween short

- term O 3 concentrations and respiratory hospital admissions and emergency department visits, with a growing number of studies conducted in Asia. This epidemiologic evidence is discussed in detail in the ISA (U.S. EPA, 2013, section 6.2.7).
In c onsidering this body of evidence, the ISA focused primarily on multicity studies because they examine associations with respiratory

- related hospital admissions and emergency department visits over large geographic areas using consistent statistical methodo logies (U.S. EPA, 2013, section 6.2.7.1). The ISA also focused on single

- city studies that encompassed a large number of daily hospital admissions or emergency department visits, included long study

- durations, were conducted in locations not represented by the larger studies, or examined population

- specific characteristics that
may impact the risk of O 3 - related health effects but were not evaluated in the larger

43 Epidemiologic associations for O 3 are more robust during the warm season than during cooler months (e.g., smaller measurement error, less potential confounding by copollutants). Rationale for focusing on warm season epidemiologic studies for O 3 can be found at 72 FR 37838

- 37840.*** E.O. 12866 Review

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Page 92 of 647 studies (U.S. EPA, 2013, section 6.2.7.1)

. When examining the association between short

- term O 3 exposure and respiratory health effects that require medical attention, the ISA distinguishes between hospital admissions and emergency department visits because it is likely that a small percentage of respiratory emergency department visits will be admitt ed to the hospital; therefore, respiratory emergency department visits may represent potentially less serious, but more common outcomes (U.S. EPA, 2013, section 6.2.7.1). Several recent multicity studies (e.g., Cakmak et al., 2006 ; Dales et al., 2006 ) and a multi

- continent study ( Ka tsouyanni et al., 2009 ) report associations between short

- term O 3 concentrations and increased respiratory

- related hospital admissions and emergency department visits. These multicity studies are supported by results from single

- city studies also report ing consistent positive associations using different exposure assignment approaches (i.e., average of multiple monitors, single monitor, population

weighted average) and averaging times (i.e., 1

- hour max and 8

- hour max) (U.S. EPA, 2013, sections 6.2.7.1 to 6.2.7.5). When examining cause

- specific respiratory outcomes,
recent studies report positive associations with hospital admissions and emergency department visits for asthma ( Strickland et al., 2010 ; Stieb et al., 2009 ) and COPD ( Stieb et al., 2009 ; Medina

- Ramon et al., 2006 ) , with more limited evidence for pneumonia ( Medina

- Ramon et al., 2006 ; Zanobetti and Schwartz, 2006 ) . In seasonal analyses (U.S. EPA, 2013, Figure 6

- 19, Table 6

- 28), stronger associations were reported in the warm season or summer months , when O 3 concentrations are higher, compared to the cold season, particularly for asthma ( Strickland et al., 2010 ; Ito et al., 2007 ) and COPD ( Medina

- Ramon et al., 2006 ) . The available evidence indicates that children are at*** E.O. 12866 Review

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Page 93 of 647 greatest risk for effects leading to O 3 - associated hospital admissions and emergency department visits ( Silverman and Ito, 2010 ; Mar and Koenig, 2009 ; Villeneuve et al.,
2007 )

. Although the collective evidence across studies indicates a mostly consistent positive association between O 3 exposure and respiratory

- related hospital admissions a nd ED visits, the magnitude of these associations may be underestimated due to behavioral modification in response to air quality forecasts (U.S. EPA, 2013, Section 4.6.6). Studies examining the potential confounding effects of copollutants have reported t hat O 3 effect estimates remained relatively robust upon the inclusion of PM and gaseous pollutants in
two

- pollutant models (U.S. 2013, Figure 6

- 20, Table 6

- 29). Additional studies that conducted copollutant analyses, but did not present quantitative result s, also support these conclusions ( Strickland et al., 2010 ; Tolbert et al., 2007 ; Medina

- Ramon et al., 2006 ) (U.S. 2013, section 6.2.7.5). In the last review, studies had not evaluated the concentration

- response relationship between short

- term O 3 exposure and respiratory

- related hospital admissions and emergency department visits. A preliminary examination of this relationship in studies that have become available since the last review found no evidence of a deviation from linearity when examining the asso ciation between short

- term O 3 exposure and asthma hospital admissions (U.S. EPA, 2013, page 6

- 157, and Silverman and Ito, 2010 )

. In addition, an examination of the concentration

- response relationship for O 3 exposure and pediatric asthma emergency department visits found no evidence of a threshold at O 3 concentrations as low as 30 ppb (for daily maximum 8

- hour concentrations) ( Strickland et al., 2010 ) . However, in both studies there is uncertainty in the shape of the*** E.O. 12866 Review

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Page 94 of 647 concentration

- response curve at the lower end of the distribution of O 3 concentrations due to the low density of data in this range (U.S. 2013, page 6

- 157). viii. Respiratory mortality The controlled human exposure, epidemiologic, and toxicological studies discussed in section 6.2 of the ISA (U.S. EPA, 1013, section 6.2) provide strong evidence for respiratory morbidity effects, including ED visits and hospital admissions, in response
to short

- term O 3 exposures. Moreover, evidence from experimental studies indicates multiple potential pathways of respiratory effects from short

- term O 3 exposures, which support the continuum of respiratory effects that could potentially result in respirator y related mortality in adults (U.S. EPA, 1013, section 6.2.8). The 2006 O 3 AQCD found inconsistent evidence for associations between short

- term O 3 concentrations and respiratory mortality ( U.S. EPA, 2006a ) . Although some studies reported a strong positive association between O 3 and respiratory mortality, additiona l studies reported small associations or no associations. New epidemiologic evidence for respiratory mortality is discussed in detail in section 6.2.8 of the ISA (U.S. EPA, 2013). The majority of recent multicity studies have reported positive associations between short

- term O 3 exposures and respiratory mortality, particularly during the summer months (U.S. EPA, 2013, Figure 6

- 36). Specifically, recent multicity studies from the U.S. ( Zanobetti and Schwartz, 2008b ) , Europ e ( Samoli et al., 2009 ) , Italy ( Stafoggia et al., 2010 ) , and Asia ( Wong et al.,
2010 ) , as well as a multi

- continent study ( Katsouyanni et al., 2009 ) , reported associations between short

- term O 3 concentrations and respiratory mortality (U.S. EPA, 2013, Figure
6

- 37, page 6

- 259). With respect to respiratory mortality, summer

- only analyses were*** E.O. 12866 Review

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Page 95 of 647 consistently positive and most were statistically significant. All

- year analyses had more mixed results, but most were positive

. Of the studies evaluated, only the studies by Katsouyanni et al. (2009 ) and by
St afoggia et al. (2010 ) analyzed the potential for copollutant confounding of the O 3 - respiratory mortality relationship. Based on the results of these analyses, the ISA concluded that O 3 respiratory mortality risk estimates appear to be moderately to subs tantially sensitive (e.g., increased or attenuated) to inclusion of PM 10 . However, in the APHENA study ( Katsouyanni et al., 2009 ) , the mostly every

- 6th

- day sampling schedule for PM 10 in the Canadian and U.S. datasets g reatly reduced their sample size and limits the interpretation of these results (U.S. EPA, 2013, section 6.2.8). In summary, recent epidemiologic studies support and reinforce the epidemiologic evidence for O 3 - associated respiratory hospital admissions an d emergency department visits from the last review. In addition, the evidence for associations with respiratory mortality has been strengthened considerably since the last review, with the addition of several large multicity studies. The biological plausib ility of the associations reported in these studies is supported by the experimental evidence for respiratory effects. b. Respiratory effects

– long

- term S ince the last review, the body of evidence indicating the occurrence of respiratory effects due to long

- term O 3 exposure has been considerably strengthened. This evidence is discussed in detail in the ISA (U.S. EPA, 2013, Chapter 7) and summarized below for new

- onset asthma and asthma prevalence, asthma hospital admissions, pulmonary structure and function, and respiratory mortality. i. New

- onset asthma and a sthma prevalence*** E.O. 12866 Review

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Page 96 of 647 Asthma is a heterogeneous disease with a high degree of temporal variability. The

on - set, progression, and symptoms can vary within an individual’s lifetime, and the course of asthma may vary markedly in young children, older children, a dolescents, and adults. In the previous review, longitudinal cohort studies that examined associations between long

- term O 3 exposures and the onset of asthma in adults and children indicated a direct effect of long

- term O 3 exposures on asthma risk in adult s (McDonnell et al., 1999 , 15

- year follow

- up ; Greer et al., 1993 , 10

- year follow

- up ) and effect modification by O 3 in children (McConnell et al., 2002). Since that review, new evidence has become available about the association between long

- term exposures to O 3 and new

- onset asthma that has increased our understanding of the gene

- environment interaction and the mechanisms and biological pathways most relevant to assessing O 3 - related effects. In children, the relationship between long

- term O 3 exposure and n ew - onset asthma has been extensively studied in the Children’s Health Study ( CHS ), a long

- term study that was initiated in the early 1990’s which has evaluated effects in several cohorts of children. The CHS was initially designed to examine whether long

- t erm exposure to ambient pollution was related to chronic respiratory outcomes in children in 12 communities in southern California. In th e CHS , new - onset asthma was classified as having no prior history of asthma at study entry with subsequent report of ph ysician

diagnosed asthma at follow

- up, with the date of onset assigned to be the midpoint of the interval between the interview date when asthma diagnosis was first reported and the previous interview date. The results of one study (McConnell et al., 2002) available in the previous review indicated that within high O 3 communities, asthma risk was 3.3 times*** E.O. 12866 Review

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Page 97 of 647 greater for children who played three or more outdoor sports as compared with children who played no sports. For this review, as discussed in section 7 .2.1.1 of the ISA (U.S. EPA 2013),

r ecent studies from the CHS provide evidence for gene

- environment interactions in effects on new

- onset asthma by indicating that the lower risks associated with specific genetic variants are found in children who live in lower O 3 communities. These studies indicate that the r isk for new

- onset asthma is related in part to genetic susceptibility, as well as behavioral factors and environmental exposure. The onset of a chronic disease, such as asthma, is partially the result of a sequence of biochemical reactions involving exposures to various environmental agents metabolized by enzymes related to a number of different genes. Oxidative stress has been p roposed to underlie the mechanistic hypotheses related to O 3 exposure . Gene tic variants may impact disease risk directly, or modify disease risk by affecting internal dose of pollutants and other environmental agents and/or their reaction products, or by altering cellular and molecular modes of action. Understanding the relation between genetic polymorphisms and environmental exposure can help identify high

- risk subgroups in the population and provide better insight into pathway mechanisms for these complex diseases.

The CHS analyses (Islam et al., 2008 ; Islam et al. 2009; Salam et al., 2009 ) have found that asthma risk is related to interactions between O 3 and variants in genes for enzymes such as heme

- oxygenase (HO

- 1), arginases (ARG1 and 2), and gluta thione S transferase P1 (GSTP1) . Biological plausibility for these findings i s provided by evidence that these enzymes have antioxidant and/or anti

- inflammatory

a ctivity and participate in well

- recognized modes of action in asthma pathogenesis. As O 3*** E.O. 12866 Review

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Page 98 of 647 is a source of oxidants in the airways, oxidative stress serves as the link among O 3 exposure, enzyme activity, and asthma. Further , several lines of evidence demonstrate that secondary oxidation products of O 3 initiate the key modes of action that mediate downstream health effects ( ISA, Section 5.3 , U.S. EPA, 2013 ). For example, HO

- 1

r esponds rapidly to oxidants, has anti

- inflammatory and anti oxidant effects, relaxes airway smooth muscle, and is induced in the airways during asthma. Cross

- sectional studies by Akinbami et al. (2010 ) and Hwang et al. (2005 ) provide further evidence relating O 3 exposures with asthma prevalence. Gene

- environment interactions are discussed in detail in Section 5.4.2.1 in the ISA ( U.S. EPA, 2013 )

. ii. Asthma hospital admissions In the 2006 AQCD, studies on O 3 - related hospital discharges and emergency department (ED) visits for asthma and respiratory disease mainly looked at short

- term ( daily ) metric s . T he short

- term O 3 studies presented in section 6.2.7.5 of the ISA (U.S.
EPA 2013 ) and discussed above in section 3.1.2.1 continue to indicate that there is evidence for increases in both hospital admissions and ED visits in children and adults related to all respiratory ou tcomes , including asthma , with stronger associations in the warm months. New studies , discussed in section 7.2.2 of the ISA (U.S. EPA, 2013) also evaluated long

- term O 3 exposure metrics, providing a new line of evidence that suggests a positive exposure

- re sponse relationship between the first hospital admission for asthma and long

- term O 3 exposure , although the ISA cautions in attributing the associations in that study to long

- term exposures since there is potential for short

- term exposures to contribute to the observed associations

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Page 99 of 647 Evidence associating long

- term O 3 exposure to first asthma hospital admission in

a positive concentration

- response relationship is provided in a retrospective cohort study (Lin et al., 2008b). This study investigated the associ ation between chronic exposure to
O 3 and childhood asthma admissions by following a birth cohort of more than 1.2 million babies born in New York State (1995

- 1999) to first asthma admission or until 31 December 2000. Three annual indicators (all 8

- h our max imum from 10:00 a.m. to 6:00 p.m.) were used to define chronic O 3 exposure: (1) mean concentration during the follow

up period (41.06 ppb); (2) mean concentration during the O 3 season (50.62 ppb); and (3) proportion of follow

- up days with O 3 le vels >70 ppb . The effects of co pollutants were controlled , and i nteraction terms were used to assess potential effect modifications. A positive association between chronic exposure to O 3 and childhood asthma hospital admissions was observed , indicating that children e xposed to high O 3 levels over time are more likely to develop asthma severe enough to be admitted to the hospital. The various factors were examined and differences were found for younger children (1

- 2 years), poor neighborhoods, Medicaid/self

- paid births, geographic region and others. As shown in the ISA, Figure 7

- 3 (U.S. EPA 2013, p. 7

- 16), positive concentration

- response relationships were observed

. Asthma admissions were significantly associated with increased O 3 levels for all chronic exposure indicators. In considering the relationship between long

- term pollutant exposures and chronic disease heath endpoints, where chronic pathologies are found with acute expression of chronic disease, Künzli (2012) hypothesiz es that if the associations of pollution with events are much larger in the long

- term studies, it provides some indirect evidence that air pollution increases the pool of subjects with chronic disease, and that more acute*** E.O. 12866 Review

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Page 100 of 647 events are to be expected to be se en for higher exposures

. The results of Lin et al (2008 a ) for first asthma hospital admission, presented in Figure 7

- 3 (U.S. EPA 2013, p. 7

- 16), show effects estimates that are larger than those reported in a study of childhood asthma hospital admission in New York state (Silverman and Ito, 2010), discussed in section 3.1.2.1 and 3.1.2.2 above. The ISA (U.S. EPA, 2013, p. 7

- 16) notes that this provides some support for the hypothesis that O 3 exposure may not only have triggered the events but also increased the pool of asthmatic children, but cautions in attributing the associations in Lin et al. (2008) study to long

- term exposures since there is potential for short

- term exposures to contribute to the observed associations

. iii. Pulmonary structure and func tion In the 2006 O 3 AQCD, few epidemiologic studies had investigated the effect of chronic O 3 exposure on pulmonary function. The definitive 8

- year follow

- up analysis of the first cohort of the CHS (U.S. EPA, 2013, section 7.2.3.1) provided little eviden ce that long

- term exposure to ambient O 3 was associated with significant deficits in the growth rate of lung function in children. The strongest evidence was for medium

- term effects of extended O 3 exposures over several summer months on lung function (FEV 1 ) in children, i.e., reduced lung function growth being associated with higher ambient O 3 levels. Short

term O 3 exposure studies presented in ISA (U.S. EPA , 2013, Section 6.2.1.2), and above in section 3.1.2.1, provide a cumulative body of epidemiologic ev idence that strongly supports associations between ambient O 3 exposure and decrements in lung function among children. A later CHS study (Islam et al., 2007) included in this review (U.S. EPA, 2013, section 7.2.3.1) also reported no substantial differences in the effect of O 3 on lung function. However, in a more recent CHS study, Breton et al. (2011) hypothesized*** E.O. 12866 Review

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Page 101 of 647 that genetic variation in genes on the glutathione metabolic pathway may influence the association between ambient air pollutant exposures and lun g function growth in children, and found that variation in the GSS locus was associated with differences in risk of children for lung function growth deficits associated ambient air pollutants, including
O 3 . A recent study (Rojas

- Martinez et al., 2007) of long

- term exposure to O 3, described in section 7.2.3.1 of the ISA (U.S. EPA, 2013, p. 7

- 19), observed a relationship with pulmonary function declines in school

- aged children where O 3 and other pollutant levels were higher (90 ppb at high end of the range) than those in the CHS. Two studies of adult cohorts provide mixed results where long

- term exposures were at the high end of the
range. Long

- term studies in animals allow for greater insight into the potential effects of prolonged exposure to O 3 that may not be easily measured in humans, such as structural changes in the respiratory tract

. Despite uncertainties, epidemiologic studies observing associations of O 3 exposure with functional changes in humans can attain biological plausibility in conjunction wi th long

- term toxicological studies, particularly O 3 - inhalation studies performed in non

- human primates whose respiratory systems most closely resembles that of the human. An important series of studies, discussed in section 7.2.3.2 of the ISA (U.S. EPA, 20 13), have used nonhuman primates to examine the effect of O 3 alone, or in combination with an inhaled allergen, house dust mite antigen (HDMA), on morphology and lung function. A nimals exhibit the hallmarks of allergic asthma defined for humans ( NHLBI, 2007 )

. These studies and others have demonstrated changes in pulmonary function and airway morphology in adult and infant nonhuman primates*** E.O. 12866 Review

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Page 102 of 647 repeatedly exposed to environmentally relevant concentrations of O 3 ( U.S. EPA, 2013 , section 7.2.3.2, 2013). The initial observations in adult nonhuman primates have been expanded in a series of experiments using infant rhesus monkeys repeatedly exposed to 0.5 ppm O 3 starting at 1 month of age ( Plopper et al., 2007 ; Schelegle et al. 2003 ) . The purpose of these studies was to determine if a cyclic regimen of O 3 inhalation would amplify the allergic responses and structural remodeling associated with allergic sensitization and inhalation in the infant rhesus monkey; they provide evidence of an O 3 - induced change in airway resistance and responsiveness provides biological plausibility of long

- term exposure, or repeated short

- term exposures, to O 3 contributing to the effects of asthma in children. In addition, significan t structural changes in the respiratory tract development, during which conducting airways increase in diameter and length, have been observed in infant rhesus monkeys after cyclic exposure to O 3 ( Fanucchi et al., 2006 ) . The se effects are noteworthy because of their potential contribution to airway obstruction and airway hyperresponsiveness which are central features of asthma. A number of studies in both

non - human primates and rodents demonstrate that O 3 exposure can increase collagen synthesis and deposition, including fibrotic

- like changes in the lung (ISA, section 7.2.3.2, U.S. EPA, 2013). Collectively, evidence from animal studies strongly suggests that chronic O 3 exposure is capable of damaging the distal airways and prox imal alveoli, resulting in lung tissue remodeling and leading to apparent irreversible changes. Potentially, persistent inflammation and interstitial remodeling play an important role in the progression and*** E.O. 12866 Review

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Page 103 of 647 development of chronic lung disease

. Further disc ussion of the modes of action that lead
to O 3 - induced morphological changes can be found in Section 5.3.7 of the ISA (U.S. EPA, 2013). Discussion of mechanisms involved in lifestage susceptibility and developmental effects can be found in Section 5.4.2.4 o f the ISA (U.S. EPA, 2013). The findings reported in chronic animal studies offer insight into potential biological mechanisms for the suggested association between seasonal O 3 exposure and reduced lung function development in children as observed in epide miologic studies (see Section 7.2.3.1). iv. Respiratory mortality A limited number of epidemiologic studies have assessed the relationship between long

- term exposure to O 3 and mortality in adults. The 2006 O 3 AQCD concluded that an insufficient amount of evidence existed “to suggest a causal relationship between chronic
O 3 exposure and increased risk for mortality in humans” ( U.S. EPA, 2006a ). Though total and cardio

- pulmonary mortality were considered in these studies, respiratory mortality was not speci fically considered. In the most recent follow

- up analysis of the ACS cohort (Jerrett et al., 2009), cardiopulmonary deaths were separately subdivided into respiratory and cardiovascular deaths, rather than combined as in the Pope et al. (2002) work. Incr eased O 3 exposure was associated with the risk of death from respiratory causes, and this effect was robust to the inclusion of PM 2.5 . The association between increased O 3 concentrations and increased risk of death from respiratory causes was insensitive t o the use of different models and to adjustment for several ecologic variables considered individually. The authors reported that when seasonal averages of 1

- hour daily maximum O 3*** E.O. 12866 Review

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Page 104 of 647 concentrations ranged from 33 to 104 ppb, there was no statistical deviation from a linear concentration

- response relationship between O 3 and respiratory mortality across 96 U.S. cities (U.S. EPA, 2013, section 7.7). However, the authors also reported “limited evidence” for an effect threshold at an O 3 concentration of 56 ppb (p=0 .06). Additionally, a recent multicity time series study (Zanobetti and Schwartz, 2011) , which followed (from 1985 to 2006) four cohorts of Medicare enrollees with chronic conditions that might predispose to O 3 - related effects, observed an association between long

- term (warm season) exposure to O 3 and elevated risk of mortality in the cohort that had previously experienced an emergency hospital admission due to COPD. A key limitation of this study i s the inability to control for PM 2.5 , because data were not available in these cities until 1999

. c. Cardiovascular effects
A relatively small number of studies have examined the potential effect of short

term O 3 exposure on the cardiovascular system. The 2006 O 3 AQCD ( U.S. EPA, 2006a , p.8

- 77) concluded that “O 3 directly and/or indirectly contributes to cardiovascular

- related morbidity” but added that the body of evidence was limited. This conclusion was based on a controlled human exposure study that in cluded hypertensive adult males; a few epidemiologic studies of physiologic effects, heart rate variability, arrhythmias, myocardial infar ctions, and hospital admissions; and toxicological studies of heart rate, heart rhythm, and blood pressure. More recently, the body of scientific ev idence available that has examined the effect of O 3 on the cardiovascular system has expanded. There is an emerging body of animal toxicological evidence demonstrating that short

- term exposure to O 3 can lead to*** E.O. 12866 Review

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Page 105 of 647 autonomic nervous system alterations (in hear t rate and/or heart rate variability) and suggesting that proinflammatory signals may mediate cardiovascular effects. Interactions of O 3 with respiratory tract components result in secondary oxidation product formation and subsequent production of inflamma tory mediators , which have the potential to penetrate the epithelial barrier and to initiate toxic effects systemically. In addition, animal toxicological studies of long

- term exposure to O 3 provide evidence of enhanced atherosclerosis and ischemia/reperfu sion ( I/R ) injury, corresponding with development of a systemic oxidative, proinflammatory environment. Recent experimental and epidemiologic studies have investigated O 3 - related cardiovascular events and are summarized in Section 6.3 of the ISA (U.S. EPA, 2013 , Section 6.3)

. Overall , the ISA summarized the evidence in this review as follows (U.S. EPA, 2013, p. 6

- 211). In conclusion, animal toxicological studies demonstrate O 3 - induced cardiovascular effects, and support the strong body of epidemiologic evidence indicating O 3 - induced cardiovascular mortality. Animal toxicological and controlled human exposure studies provide evidence for biologically plausible mech anisms underlying these O 3 - induced cardiovascular effects. However, a lack of coherence with epidemiologic studies of cardiovascular morbidity remains an important uncertainty. Controlled human exposure studies discussed in previous AQCDs have not demonstr ate d any consistent extrapulmonary effects. In this review, evidence from controlled human exposure studies suggests cardiovascular effects in response to short

term O 3 exposure (see ISA, U.S. EPA, 2013 , Section 6.3.1) and provides some coherence with evid ence from animal toxicology studies. Controlled human exposure studies also support the animal toxicological studies by demonstrating O 3 - induced effects on blood biomarkers of systemic inflammation and oxidative stress, as well as changes in biomarkers tha t can indicate the potential for increased clotting following O 3 exposures. Increases and decreases in high frequency HRV have been reported following relatively*** E.O. 12866 Review

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Page 106 of 647 low (120 ppb during rest) and high (300 ppb with exercise) O 3 exposures, respectively. These c hanges in cardiac function observed in animal and human studies provide preliminary evidence for O 3 - induced modulation of the autonomic nervous system through the activation of neural reflexes in the lung (see ISA,U.S. EPA 2013 , Section 5.3.2). Overall, t he ISA concludes that the available body of epidemiologic evidence examining the relationship between short

- term exposures to O 3 concentrations and cardiovascular morbidity is inconsistent (U.S. EPA, 2013 , Section 6.3.2.9). Across studies, different defini tions, ( i.e., ICD

- 9 diag n ostic codes ) were used for both all

- cause and cause

- specific cardiovascular morbidity (ISA, U.S. EPA, 2013 , see Tables 6

- 35 to 6

- 39), which may contribute to inconsistency in results. However, within diagnostic categories, no consi stent pattern of association was found with O 3 . Generally, the epidemiologic studies used nearest air monitors to assess O 3 concentrations, with a few exceptions that used modeling or personal exposure monitors. The inconsistencies in the associations obse rved between short

- term O 3 and cardiovascular disease ( CVD ) morbidities are unlikely to be explained by the different exposure assignment methods used (see Section 4.6, ISA, U.S. EPA 2013 ). The wide variety of biomarkers considered and the lack of consistency among definitions used for specific cardiovascular disease endpoints (e.g., arrhythmias, HRV) make comparisons across studies difficult

. Despite the inconsistent evidence for an association between O 3 concentration and CVD morbidity, mortality studies indicate a consistent positive association between short

- term O 3 exposure and cardiovascular mortality in multicity studies and in a multi

continent study. When examining mortality due to cardiovascular disease, epidemiologic*** E.O. 12866 Review

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Page 107 of 647 studies consistently observe positive associations with short

- term exposure to O 3 . Additionally, there is some evidence for an association between long

- term exposure to O 3 and mortality , although the association between long

- term ambient O 3 concentrations and cardiovascular mo rtality can be confounded by other pollutants as evident by a study of cardiovascular mortality that reported no association after adjustment for PM 2.5 concentrations

. The ISA (U.S. EPA 2013, section 6.3.4) states that taken together, the overall body of e vidence across the animal and human studies is sufficient to conclude that there is likely to be a causal re l ationship between relevant short

- term exposures to O 3 and cardiovascular system effects. d. Total Mortality The 2006 O 3 AQCD concluded that the o verall body of evidence was highly suggestive that short

- term exposure to O 3 directly or indirectly contributes to nonaccidental and cardiopulmonary

- related mortality in adults, but additional research was needed to more fully establish underlying mechanis ms by which such effects occur (U.S. EPA, 2013, p. 2

- 18)

. In building on the 2006 evidence, the ISA states the following (U.S. EPA, 2013, p. 6

- 261).
The evaluation of new multicity studies that examined the association between short

- term O 3 exposures and m ortality found evidence that supports the conclusions of the 2006 AQCD

. These new studies reported consistent positive associations between short

- term O 3 exposure and all

cause ( nonaccidental ) mortality, with associations persisting or increasing in magnitude during the warm season, and provide additional support for associations between O 3 exposure and cardiovas cular and respiratory mortality. The 2006 O 3 AQCD reviewed a large number of time

- series studies of associations between short

- term O 3 expos ures and total mortality including single

- and multicity studies, and meta

- analyses. In the large U.S. multicity studies that examined*** E.O. 12866 Review

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Page 108 of 647 all

- year data, effect estimates corresponding to single

- day lags ranged from a 0.5

- 1% increase in all

- cause (nonaccidenta l) total mortality per a 20 ppb (24

- hour), 30 ppb (8

- hour maximum), or 40 ppb (1

- hour maximum) increase in ambient O 3 (U.S. EPA, 2013, section 6.6.2). Available studies reported some evidence for heterogeneity in O 3 mortality risk estimates across cities a nd across studies. Studies that conducted seasonal analyses reported larger O 3 mortality risk estimates during the warm or summer season. Overall, the 2006 O 3 AQCD identified robust associations between various measures of daily ambient O 3 concentrations a nd all

- cause mortality, which could not be readily explained by confounding due to time, weather, or copollutants. With regard to cause

- specific mortality, consistent positive associations were reported between short

- term O 3 exposure and cardiovascular mor tality, with less consistent evidence for associations with respiratory mortality. The majority of the evidence for associations between O 3 and

cause - specific mortality were from single

- city studies, which had small daily mortality counts and subsequently limited statistical power to detect associations. The 2006 O 3 AQCD concluded that “the overall body of evidence is highly suggestive that O 3 directly or indirectly contributes to nonaccidental and cardiopulmonary

- related mortality” (U.S. EPA, 201 3 , section 6.6.1)

. Recent studies have strengthened the body of evidence that supports the association between short

- term O 3 concentrations and mortality in adults. This evidence includes a number of studies reporting associations with nonaccidental as well as caus e specific mortality. Multi

- continent and multicity studies have consistently reported positive and statistically significant associations between short

- term O 3 concentrations and all

- cause mortality, with evidence for larger mortality risk estimates durin g the warm*** E.O. 12866 Review

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Page 109 of 647 or summer months (U.S. EPA, 2013, Figure 6

- 27; Table 6

- 42). Similarly, evaluations of

cause - specific mortality have reported consistently positive associations with O 3 , particularly in analyses restricted to the warm season (U.S. EPA, 2013, Figu re 6

- 37; Table 6

- 53). 44 In assessing the evidence for O 3 - related mortality, the 2006 AQCD also noted that multiple uncertainties remained regarding the relationship between short

- term O 3 concentrations and mortality, including the exten t of residual con founding by

co pollutants; characterization of the factors that modify the O 3 - mortality association; the appropriate lag structure for identifying O 3 - mortality effects; and the shape of the
O 3 - mortality concentration

- response function and whether a threshol d exists

. Many of the studies, published since the last review, have attempted to address one or more of these uncertainties. The ISA (U.S. EPA, 2013; Section 6.6.2) discusses the extent to which recent studies have evaluated these uncertainties in the rel ationship between O 3 and mortality

. In particular, recent studies have evaluated different statistical approaches to examine the shape of the O 3 - mortality concentration

- response relationship and to evaluate whether a threshold exists for O 3 - related mortality. In an analysis of the NMMAPS data, Bell et al. (2006) evaluated the potential for a threshold in the O 3 - mortality relationship. The authors reported positive and statistically significant associations with mortality in a variety of restricted an alyses, including analyses restricted to days with 24

- hour area

- wide average O 3 concentrations below 60, 55, 50, 45, 40, 35, and 30 ppb. In these restricted analyses O 3 effect estimates were of similar

44 Respiratory morta lity is discussed in more detail above

.*** E.O. 12866 Review

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Page 110 of 647 magnitude, were statistically significant, and had sim ilar statistical precision. In analyses restricted to days with 24

- hour average O 3 concentrations below 25 ppb, the O 3 effect estimate was similar in magnitude to the effect estimates resulting from analyses with the higher cutoffs, but had somewhat lower statistical precision, with the estimate approaching statistical significance (i.e., based on observation of Figure 2 in Bell et al., 2006). In analyses restricted to days with lower 24

- hour average O 3 concentrations (i.e., below 20 and 15 ppb), effect est imates were similar in magnitude to analyses with higher cutoffs, but with notably less statistical precision, and were not statistically significant (i.e., confidence intervals included the null, indicating no O 3 - associated mortality , based on observation of Figure 2 in Bell et al., 2006). Ozone was no longer positively associated with mortality when the analysis was restricted to days with 24

- hour O 3 concentrations below 10 ppb

. Given the relatively small number of days included in these restricted analys es, especially for cut points of 20 ppb and below, 45 statistical uncertainty is increased

. Bell et al. (2006) also evaluated the shape of the concentration

- response relationship between O 3 and mortality. Although the results of this analysis suggested the lack of threshold in the O 3 - mortality relationship, the ISA noted that it is difficult to interpret such a curve because: (1) there is uncertainty around the shape of the concentration

- response curve at 24

- hour average O 3 concentrations generally below 20 ppb ; and (2) the concentration

- response curve does not take into consideration the

45 For example, Bell et al. (2006) reported that for analyses restricted to 24

- hour O 3 concentrations at or below 20 ppb, 73% of days were excluded on average across the 98 communities.*** E.O. 12866 Review

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Page 111 of 647 heterogeneity in O 3 - mortality risk estimates across cities (U.S. EPA, 2013, section 6.6.2.3)

. Several additional studies have used the NMMAPS dataset to evaluate the

concen tration

- response relationship between short

- term O 3 concentrations and mortality. For example, using the same data as Bell et al. ( 2006 ) , Smith et al. ( 2009 ) conducted a subset analysis, but instead of restricting the analysis to days with O 3 concentrations below a cutoff the authors only included days above a defined cutoff (cutoffs from 15 and 60 ppb)

. The results of this analysis were consistent with those reported by Bell et al. (2006)

. Specifically, the authors reported consistent positive associations for all cutoff concentrations up to concentrations where the total number of days available were so limited that the variability around the central estimate was increased (i.e., cutoff values at or above about 50 ppb) (U.S. EPA, 2013, section 6.6.2.3). In addition, using NMMAPS data for 1987

- 1994 for Chicago, Pittsburgh, and El Paso, Xia and Tong ( 2006 ) reported evidence for a threshold around a 24

- hour average O 3 concentration of 25 ppb, though the threshold values estimated in the analysis were sometimes in the range of where data density was low (U.S. EPA, 2013, section 6.6.2.3). Stylianou and Nicolich ( 2009 ) examined the existence of thresholds following an approach similar to Xia and T ong ( 2006 ) using data from NMMAPS for nine major U.S. cities (i.e., Baltimore, Chicago, Dallas/Fort Worth, Los Angeles, Miami, New York, Philadelphia, Pittsburgh, and Seattle) for the years 1987

- 2000. The authors reported that the estimated O 3 - mortality risks varied across the nine cities, with the models exhibiting apparent thresholds in the
10

- 45 ppb range for O 3 (24

- hour average). However, given the city

- to

- city variation in risk estimates, combining the city

- specific estimates into an overal l estimate complicate s*** E.O. 12866 Review

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Page 112 of 647 the interpretation of the results. Additional studies in Europe, Canada, and Asia did not report the existence of a threshold (Katsouyanni et al., 2009), with inconsistent and/or inconclusive results across cities, or a non

- linear re lationship in the O 3 - mortality concentration

- response curve (Wong et al., 2010)

. 3. Adversity of O 3 Effects In making judgments as to when various O 3 - related effects become regarded as adverse to the health of individuals, in previous NAAQS reviews EPA has relied upon the guidelines published by the American Thoracic Society (ATS) and the advice of CASAC. In 2000, the ATS published an official statement on “What Constitutes an Adverse Health Effect of Air Pollution?” (ATS, 2000), which updated and built upon its earlier guidance (ATS, 1985). The earlier guidance defined adverse respiratory health effects as “medically significant physiologic changes generally evidenced by one or more of the following: (1) interference with the normal activity of the affec ted person or persons, (2) episodic respiratory illness, (3) incapacitating illness, (4) permanent respiratory injury, and/or (5) progressive respiratory dysfunction” , while recognizing that perceptions of “medical significance” and “normal activity” may d iffer among physicians, lung physiologists and experimental subjects (ATS, 1985). The 2000 ATS guidance builds upon and expands the 1985 definition of adversity in several ways. T he guidance concludes that transient, reversible loss of lung function in combination with respiratory symptoms should be considered adverse

. There is also a more specific consideration of population risk (ATS, 2000). Exposure to air pollution that increases the risk of an adverse effect to the entire population is adverse, even though it may not increase the risk of any individual to an unacceptable level. For example, a population of*** E.O. 12866 Review

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Page 113 of 647 asthmatics could have a distribution of lung function such that no individual has a level associated with clinically important impairment. Exposur e to air pollution could shift the distribution to lower levels that still do not bring any individual to a level that is associated with clinically relevant effects. However, this would be considered to be adverse because individuals within the population would have diminished reserve function, and therefore would be at increased risk to further environmental insult (U.S. EPA, 2013, p. lxxi; and 75 FR at 35526/2, J une 22, 2010 )

. The ATS also concluded that elevations of biomarkers such as cell types, cyt okines and reactive oxygen species may signal risk for ongoing injury and more serious effects or may simply represent transient responses, illustrating the lack of clear boundaries that separate adverse from nonadverse events. More subtle health outcomes also may be connected mechanistically to health effects that are clearly adverse, so that small changes in physiological measures may not appear clearly adverse when considered alone, but may be part of a coherent and biologically plausible chain of relate d health outcomes that include responses that are clearly adverse, such as mortality (section 3.1.2.1, above)

. In this review, the new evidence provides further support for relationship s between O 3 exposure s and a spectrum of health effects, including ef fects that meet the ATS criteria for being adverse ( ATS , 1985 and 2000 ) . The ISA judgment that there is a causal relationship between short

- term O 3 exposure and a full range of respiratory effects, including respiratory morbidity (e.g., lung function decre ments, respiratory symptoms , inflammation , hospital admissions , and emergency department visits ) and mortality , provides support for concluding that short

- term O 3 exposure is associated with adverse*** E.O. 12866 Review

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Page 114 of 647 effects (U.S. EPA 2013 , section 2.5.2). Overall, includin g new evidence of cardiovascular system effects, the evidence supporting an association between short

- term O 3 exposures and total ( nonaccidental , cardiopulmonary) respiratory mortality is stronger in this review (U.S. EPA 2013 , section 2.5.2). And the judg ment of likely causal associations between long

- term measures of O 3 exposure and respiratory effects such as new

- onset asthma, prevalence of asthma, asthma symptoms and control, and asthma hospital a dmissions provides support for concludin g that long

- term O 3 exposure is associated with adverse effects ranging from episodic respiratory illness to permanent respiratory injury or progressive respiratory decline (U.S. EPA 2013 , section 7.2.8 ).
A pplication of the ATS guidelines to the least serious category of effects related to ambient O 3 exposures, which are also the most numerous and therefore are also potentially important from a public health perspective, involves judgments about which medical experts on CASAC pa nel s and public commenters have in the past expressed diverse views. To help frame such judgments, in past reviews EPA has defined gradations of individual functional responses (e.g., decrements in FEV 1 and airway responsiveness) and symptomatic responses (e.g., cough, chest pain, wheeze), together with judgments as to the potential impact on individuals experiencing varying degrees of severity of these responses

. These gradations were used in the 1997 O 3 NAAQS review and slightly revised in the 2008 review ( U.S. EPA, 1996, p. 59; 2007, p.3

- 72; 72 FR 37849, July 11, 2007). These gradations and impacts are summarized in Tables 3

- 2 and
3

- 3 in the 2007 O 3 Staff Paper ( U.S. EPA, 2007, pp.3

- 74 to 3

- 75). For active healthy people, including children, moderate lev els of functional responses (e.g., FEV 1 decrements of ≥ 10% but < 20%, lasting 4 to 24 hours) and/or*** E.O. 12866 Review

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Page 115 of 647 moderate symptomatic responses (e.g., frequent spontaneous cough, marked discomfort on exercise or deep breath, lasting 4 to 24 hours) would likely interfe re with normal activity for relatively few sensitive individuals ( U.S. EPA, 2007, p.3

- 72; 72 FR 37849, July 11, 2007) ; whereas large functional responses (e.g., FEV 1 decrements ≥ 20%, lasting longer than 24 hours) and/or severe symptomatic responses (e.g., persistent uncontrollable cough, severe discomfort on exercise or deep breath, lasting longer than 24 hours) would likely interfere with normal activities for many sensitive individuals ( U.S. EPA, 2007, p.3

- 72; 72 FR 37849, July 11, 2007) and therefore would be considered adverse under ATS guidelines

. For the purpose of estimating potentially adverse lung function decrements in active healthy people in the 2008 O 3 NAAQS review , the CASAC panel for that review indicated that a focus on the mid to upper en d of the range of moderate levels of functional responses is most appropriate (e.g., FEV 1 decrements ≥ 15% but < 20%) (Henderson, 2006; U.S. EPA, 2007, p. 3

- 76). In this review, CASAC concurred that the “[e]stimation of FEV 1 decrements of ≥15% is appropria te as a scientifically relevant surrogate for adverse health outcomes in active healthy adults ” (Frey, 2014c, p. 3). However, for children and adults with lung disease, even moderate functional (e.g., FEV 1 decrements ≥ 10% but < 20%, lasting up to 24 hours ) or symptomatic responses (e.g., frequent spontaneous cough, marked discomfort on exercise or with deep breath, wheeze accompanied by shortness of breath, lasting up to 24 hours) would likely interfere with normal activity for many individuals, and would likely result in additional and more frequent use of medication ( U.S. EPA, 2007, p.3

- 72; 72 FR 37849, July 11, 2007) . For people with lung disease, large functional responses (e.g.,
FEV 1 decrements ≥ 20%, lasting longer than 24 hours) and/or severe symptom atic*** E.O. 12866 Review

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Page 116 of 647 responses (e.g., persistent uncontrollable cough, severe discomfort on exercise or deep breath, persistent wheeze accompanied by shortness of breath, lasting longer than 24 hours) would likely interfere with normal activity for most individuals and wo uld increase the likelihood that these individuals would seek medical treatment ( U.S. EPA, 2007, p.3

- 72; 72 FR 37849, July 11, 2007). In the last O 3 NAAQS review , f or the purpose of estimating potentially adverse lung function decrements in people with lun g disease the CASAC panel indicated that a focus on the lower end of the range of moderate levels of functional responses is most appropriate (e.g., FEV 1 decrements
≥ 10%) (Henderson, 2006; U.S. EPA 2007 , p. 3

- 76). In addition, in the ir letter advising the Administrator on the reconsideration of the 2008 final decision, CASAC stated that “[a] 10% decrement in FEV1 can lead to respiratory symptoms, especially in individuals with pre

- existing pulmonary or cardiac disease. For example, people with chronic obstr uctive pulmonary disease have decreased ventilatory reserve (i.e., decreased baseline
FEV 1 ) such that a ≥10% decrement could lead to moderate to severe respiratory symptoms” (Samet, 2011) (section 3.1.2.1, above). In this review, CASAC concurred that “[a]n FEV1 decrement of ≥10% is a scientifically relevant surrogate for adverse health outcomes for people with asthma and lung disease” (Frey, 2014c, p. 3). In judging the extent to which these impacts represent effects that should be regarded as adverse to the health status of individuals, in previous NAAQS reviews EPA has also considered whether effects we re experienced repeatedly during the course of a year or only on a single occasion (U.S. EPA, 2007)

. Although some experts would judge single occurrences of moderate responses to be a nuisance, especially for healthy individuals, a more general consensus view of the adversity of such moderate responses*** E.O. 12866 Review

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Page 117 of 647 emerges as the frequency of occurrence increases. Thus it has been judged that repeated occurrences of mod erate responses, even in otherwise healthy individuals, may be considered to be adverse since they could well set the stage for more serious illness (61 FR 65723). The CASAC panel in the 1997 NAAQS review expressed a consensus view that these “criteria for the determination of an adverse physiological response were reasonable” (Wolff, 1995). In the review completed in 2008, estimates of repeated occurrences continued to be an important public health policy factor in judging the adversity of moderate lung fu nction decrements in healthy and asthmatic people (72 FR 37850, July 11, 2007)

. Evidence new to this review indicates that 6.6

- hour exposures to 60 ppb O 3 during moderate exertion can result in pulmonary inflammation in healthy adults. As discussed in se ction 3.1.2 above, the initiation of inflammation can be considered as evidence that injury has occurred. Inflammation induced by a single O 3 exposure can resolve entirely, but continued acute inflammation can evolve into a chronic inflammatory state (ISA, U.S. EPA, 2013, p. 6

- 76), which is clearly adverse. Responses measured in controlled human exposure studie s indicate that the range of effects elicited in humans exposed to ambient O 3 concentrations include: decreased inspiratory capacity; mild bronchoc onstriction; rapid, shallow breathing pattern during exercise; and symptoms of cough and pain on deep inspiration ( U.S. EPA, 2013 , section 6.2.1.1). Some young , healthy adults exposed to O 3 concentrations ≥ 60 ppb , while engaged in 6.6 hours of intermitten t moderate exertion, develop reversible, transient decrements in lung function, symptoms of breathing discomfort, and inflammation if minute ventilation or duration of exposure is increased sufficiently ( U.S. EPA, 2013 ,*** E.O. 12866 Review

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Page 118 of 647 section 6.2.1.1). Among healthy subjects there is considerable interindividual variability in the magnitude of the FEV 1 responses, but when data were combined across studies at 60 ppb (U.S. EPA , 2013 , pp. 6

- 17 to 6

- 18), 10% of healthy subjects had >10% FEV 1 decrements. Moreover, consiste nt with the findings of the ISA (U.S. EPA , 2013, section 6.2.1.1), CASAC concluded that “[a]sthmatic subjects appear to be at least as sensitive, if not more sensitive, than non

- asthmatic subjects in manifesting ozone

- induced pulmonary function decrements” (Frey, 2014c, p. 4). The combination of l ung function decrements and respiratory symptoms , which has been considered adverse in previous reviews, ha s been demonstrated in healthy adults following prolonged (6.6 hour) exposures , while at intermittent moder ate exertion, to 72 ppb

. For these types of effects, information from controlled human exposure studies , which provides an indication of the magnitude and thus adversity of effects at different O 3 concentrations, combined with estimates of occurrences in t he population from the HREA , provide information about their importance from a policy perspective.
4

. O zone - Related Impacts on Public Health Setting standards to provide appropriate public health protection requires consideration of the factors that put populations at greater risk from O 3 exposure. In order to estimate the potential for public health impacts, it is important to consider not only the adversity of the health effects, but also the populations at greater risk and potential behaviors that may reduce exposures. a. Identification of at

- risk populations and lifestages The currently available evidence expands the understanding of populations that were identified to be at greater risk of O 3 - related health effects at the time of the last review (i. e., people who are active outdoors, people with lung disease, children and older*** E.O. 12866 Review

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Page 119 of 647 adults and people with increased responsiveness to O 3 ) and supports the identification of additional factors that may lead to increased risk (U.S. EPA 2006, section 3.6.2; U.S

. EPA, 2013, chapter 8). P opulations and lifestages may be at greater risk for O 3 - related health effects due to factors that contribute to the ir susceptibility and/or vulnerability to
O 3 . The definitions of susceptibility and vulnerability have been found to vary across studies, but in most instances “susceptibility” refers to biological or intrinsic factors (e.g., lifestage, sex, preexisting disease/conditions) while “vulnerability” refe rs to non

biological or extrinsic factors (e.g., socioeconomic status [SES]) (U.S. EPA, 2013, p. 8

- 1; U.S. EPA, 2010c, 2009d)

. In some cases, the terms “at

- risk” and “sensitive” have been used to encompass these concepts more generally. In t he ISA and PA, “at

- risk” is the all

encompassing term used to define groups with specific factors that increase the ir risk of
O 3 - related health effects. There are multiple avenues by which groups may experience increased risk for
O 3 - induced health effects. A population or lifestage 46 may exhibit greater effects than other populations or lifestages exposed to the same concentration or dose, or they may be at greater risk due to increased exposure to an air pollutant (e.g., time spent outdoors). A group with i ntrinsically increased risk would have some factor(s) t hat increases risk through a biological mechanism and, i n general, would have a steeper concentration

- risk relationship, compared to those not in the group . F actors that are often considered intrinsic include pre - e xisting asthma, genetic background , and lifestage

. A group of people could also have extrinsically increased risk, which would be through an external,

46 Lifestages, which in this case includes childhood and older adulthood, are experienced by most people over the course of a lifetime, unlike other factors associated with at

- risk populations.*** E.O. 12866 Review

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Page 120 of 647 non - biological factor , such as socioeconomic status ( SES ) and diet. Some groups are at risk of i ncreased internal dose at a given exposure concentration, for example , because of breathing pattern s . This category would include p eople who work or exercise outdoors. Finally, there are those who might be placed at increased risk for experiencing greater
exposure s by being exposed to higher O 3 concentration s . This would include, for example, groups of people with greater exposure to ambient O 3 due to less availability or use of home air conditioners such that they are more likely to be in locations with open window s on high O 3 days

. Some groups may be at increased risk of O 3 - re lated health effect s through a combination of factors . For example, children tend to spend more time outdoors when O 3 levels are high, and at higher levels of activity than adults, which leads to increased exposure and dose , and they also have biological, or intrinsic, risk factors (e.g., their lungs are still developing) (U.S. EPA, 2013, Chapter 8 )

. An at

- risk population or lifestage is more likely to experience adverse health effects related to O 3 exposures and/or, develop more severe effects from exposure than the general population. i. People with Specific Genetic Variants
T here is ad equate evidence for populations with certain genotypes being more at

risk than others to the effects of O 3 exposure on health (U.S. EPA, 2013, section 8.1)

. Controlled human exposure and epidemiologic studies have reported evidence of O 3 - related increases in respiratory symptoms or decreases in lung function with variants including GSTM1, GSTP1, HMOX1, and NQO 1. NQO1 deficient mice were found to be resistant to O 3 - induced AHR and inflammation, providing biological plausibility for results of studies in humans. Additionally, studies of rodents have identified a number of other genes that may affect O 3 - related he alth outcomes, including genes related to innate*** E.O. 12866 Review

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Page 121 of 647 immune signaling and pro

- and anti

- inflammatory genes, which have not been investigated in human studies

. ii. People with Asthma Previous O 3 AQCDs identified individuals with asthma as a population at incr eased risk of O 3 - related health effects. Multiple new epidemiologic studies included in the ISA have evaluated the potential for increased risk of O 3 - related health effects in people with asthma, including: lung function; symptoms; medication use; airway
h yperresponsiveness (AHR); and airway inflammation (also measured as exhaled nitric oxide fraction, or FeNO) . A study of lifeguards in Texas reported decreased lung function with short

- term O 3 exposure among both indi viduals with and without asthma; however , the decrease was greater among those with asthma ( Thaller et al., 2008) . A Mexican study of children ages 6

- 14 detected an association between short

- term O 3 exposure and wheeze, cough, and bronchodilator use among asthmatics but not non

- asthmatics, although this may have been the result of a small non

- asthmatic population ( Escamilla

Nuñez et al., 2008) . A study of modification by AHR (a n obligate condition among asthmatics) report ed greater short

- term O 3 - associated decreases in lung function in elderly individuals with AHR, especially among those who were obese ( Alexeeff et al.,
2007 )

. With respect to airway inflammation, in one study, a positive association was reported for airway inflammation among asthmatic children following short

- term O 3 exposure, but the observed association was similar in magnitude to that of non

- asthmatics ( Barraza

- Villarreal et al., 2008 ) . Similarly, a nother study of children in California reported an association between O 3 concentration and FeNO that persisted both among childr en with and without asthma as well as those with and without respiratory allergy*** E.O. 12866 Review

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Page 1 22 of 647 ( Berhane et al., 2011 )

. Finally, Khatri et al. ( 2009 ) found no association between short

- term O 3 exposure and alt ered lung function for either asthmatic or non

- asthmatic adults, but did note a decrease in lung function among individuals with allergies

. New e vidence for difference in effects among asthmatics has been observed in studies that examined the association between O 3 exposure and altered lung function by asthma medication use. A study of children with asthma living in Detroit reported a greater association between short

- term O 3 and lung function for corticosteroid users compared with noncorticosteroid users ( Lewis et al., 2005 ) . Conversely, another study found decreased lung function among no ncorticosteroid users compared to users, although in this study, a large proportion of non

- users were considered to be persistent asthmatics ( Hernández

- Cadena et al., 2009 )

. Lung function was not related to short

- term O 3 exposure among corticosteroid users and non

- users in a study taking place during the winter months in Canada ( Liu et al., 2009 ) . Additionally, a study of airway inflammation reported a counterintuitive inver se association with O 3 of similar magnitude for all groups of corticosteroid users and non

- users ( Qian et al., 2009 )

. Controlled human exposure studies that have examined the effects of O 3 on adults with asthma and healthy controls are limited. Based on studies reviewed in the 1996 and
2006 O 3 AQCDs, subjects with asthma appeared to be more sensitive to acute effects of
O 3 in terms of FEV 1 and inf lammatory responses than healthy non

- asthmatic subjects. For instance, Horstman et al. ( 1995 ) observed that mild

- to

- moderate asthmatics, on average, experienced double the O 3 - induced FEV 1 decrement of healthy subjects (19% versus 10%, re spectively, p = 0.04)

. Moreover, a statistically significant positive correlation between FEV 1 responses to O 3 exposure and baseline lung function was*** E.O. 12866 Review

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Page 123 of 647 observed in individuals with asthma, i.e., responses increased with severity of disease. Minimal evidence exists suggesting that individuals with asthma have smaller O 3 - induced
FEV 1 decrements than healthy subjects (3% versus 8%, respectively) ( Mudway et al.,
2001 )

. However, the asthmatics in that study also tended to be older than the healthy subjects, which could partially explain their lesser response since FEV 1 responses to O 3 exposure diminish with age. Individua ls with asthma also had significantly more neutrophils in the BALF (18 hours postexposure) than similarly exposed healthy individuals ( Peden et al., 1997 ; Scannell et al., 1996 ; Basha et al., 1994 )

. Furthermore, a study examini ng the effects of O 3 on individuals with atopic asthma and healthy controls reported that greater numbers of neutrophils, higher levels of cytokines and hyaluronan, and greater expression of macrophage cell

- surface markers were observed in induced sputum o f atopic asthmatics compared with healthy controls ( Hernandez et al., 2010 )

. Differences in O 3 - induced epithelial cytokine expression were noted in bronchial biopsy samples from asthmatics and healthy controls ( Bosson et al., 2003 )

. Cell

- surface marker and cytokine expression results, and the presence of hyaluronan, are consistent with O 3 having greater effects on innate and adaptive immunity in these asthmatic individuals. In addition, studies have demons trated that O 3 exposure leads to increased bronchial reactivity to inhaled allergens in mild allergic asthmatics ( Kehrl et al., 1999 ; Jorres et al ., 1996 ) and to the influx of eosinophils in individuals with pre

- existing allergic disease ( Vagaggini et al., 2002 ; Peden et al., 1995 )

. Taken together, these results point to several mechanistic pathways which could account for the enhanced sensitivity to O 3 in subjects with asthma (see Section 5.4.2.2 in U.S. EPA, 2013 ).*** E.O. 12866 Review

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Page 124 of 647 Toxicological studies provide additional evidence of the biological basis for the greater effects of O 3 among those with asthma or AHR (U.S. EPA, 2013, section 8.2.2)

. In animal toxicological studies, an asthmatic phenotype is modeled by allergic sensitization of the respiratory tract. Many of the studies that provide evidence that O 3 exposure is an inducer of AHR and remodeling utilize these types of animal models. For example, a series of experiments in infant rhesus monkeys have shown these effects, but only in monkeys sensitized to house dust mite allergen. Similarly, adverse changes in pulmonary function were demonstrated in mice exposed to O 3 ; enhanced inflammatory
responses were in rats exposed to O 3 , but only in animals sensitized to allergen. In general, it is the combined effects of O 3 and allergic sensitization which result in measurable effects on pulmonary function. In a pulmonary fibrosis model, exposure O 3 for 5 days increased pulmonary inflammation and fibrosis, a long with the frequency of bronchopneumonia in rats. Thus, short

- term exposure to O 3 may enhance damage in a previously injured lung (U.S. EPA, 2013, section 8.2.2)

. In the 2006 O 3 AQCD, the potential for individuals with asthma to have greater risk of O 3 - related health effects was supported by a number of controlled human exposure studies, evidence from toxicological studies, and a limited number of epidemiologic studies. In section 8.2.2, the ISA reports that in the recent epidemiologic literature some, but not all, studies report greater risk of health effects among individuals with asthma. Studies examining effect measure modification of the relationship between short

- term O 3 exposure and altered lung function by corticosteroid use provided limited evi dence of O 3 - related health effects. However , recent studies of behavioral responses have found that studies do not take into account individual behavioral adaptations to*** E.O. 12866 Review

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Page 125 of 647 forecasted air pollution levels (such as avoidance and reduced time outdoors), which m ay underestimate the observed associations in studies that examined the effect of O 3 exposure on respiratory health ( Neidell and Kinney, 2010)

. This could explain some inconsistency observed among recent epidemiologic studies. The evidence from controlled human exposure studies provides support for increased detriments in FEV 1 and greater inflammatory responses to O 3 in individuals with asthma than in healthy individual s without a history of asthma. The collective evidence for increased risk of
O 3 - related health effects among individuals with asthma from controlled human exposure studies is supported by recent toxicological studies which provide biological plausibility
f or heightened risk of asthmatics to respiratory effects due to O 3 exposure. Overall, the ISA finds there is adequate evidence for asthmatics to be an at

- risk population

. iii. Children Children are considered to be at greater risk from O 3 exposure because their respiratory systems undergo lung growth until about 18

- 20 years of age and are therefore thought to be intrinsically more at risk for O 3 - induced damage ( U.S. EPA, 2006a ) . It is generally recognized that children spend more time outdoors than adults, and therefore would be expected to have higher exposure to O 3 than adults. Children aged 11 years and older and adults have higher absolute ventilation rates than younger children aged 1

- 11 years. However, younger children have higher ventilation rates relative to their lung volumes, which tends to increase dose n ormalized to lung surface area. In all ages,

e xercise intensity has a substantial effect on ventilation rate, high intensity activity result s in nearly double the ventilation rate for moderate activity. For more information on time*** E.O. 12866 Review

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Page 126 of 647 spent outdoors and venti lation rate differences by age group, see Section 4. 4.1 in the ISA (U.S. EPA, 2013)

. The 1996 O 3 AQCD reported clinical evidence that children, adolescents, and young adults (<18 years of age) appear, on average, to have nearly equivalent spirometric

re sponses to O 3 exposure, but have greater responses than middle

- aged and older adults ( U.S. EPA, 1996 ) . Symptomatic responses (e.g., cough, shortness of breath, pain on deep inspiration) to O 3 exposure, however, appear to increase with age until early adult hood and then gradually decrease with increasing age ( U.S. EPA, 1996 ) . Complete lung growth and development is not achieved u ntil 18

- 20 years of age in women and the early 20s for men; pulmonary function is at its maximum during this time as well.
Recent epidemiologic studies have examined different age groups and their risk to
O 3 - related respiratory hospital admissions and emergency department (ED) visits. Evidence for greater risk in children was reported in several studies. A study in Cyprus of short

- t erm O 3 concentrations and respiratory hospital admissions ( HA ) detected possible effect measure modification by age with a larger association among individuals < 15 years of age compared with those > 15 years of age ; the effect was apparent only with
a 2

- d ay lag (Middleton et al., 2008) . Similarly, a Canadian study of asthma

- ED visits reported the strongest O 3 - related associations among 5

- to 14

- year olds compared to the other age groups (ages examined 0

- 75+) ( Villeneuve et al. , 2007 ) . Greater O 3 - associated risk in asthma

- related ED visits were also reported among children (<15 years) as compared to adults (15 to 64 years) in a study from Finland ( Halonen et al., 2009 ) . A study of New York City hospital admissions demonstrated an increase in the association between O 3 exposure and asthma

- related hospital admissions for 6

- to 18

- year olds*** E.O. 12866 Review

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Page 127 of 647 compared to those < 6 years old and those > 18 years old ( Silverman an d Ito, 2010 )

. When examining long

- term O 3 exposure and asthma HA among children, associations were determined to be larger among children 1 to 2 years old compared to children 2 to 6 years old ( Lin et al., 2008 ) . A few studies reported positive associations among both children and adults and no modification of the effect by age

. The evidence reported in epidemiologic studies is supported by recent toxicologi cal studies which observed O 3 - induced health effects in immature animals. Early life exposures of multiple species of laboratory animals, including infant monkeys, resulted in changes in conducting airways at the cellular, functional, ultra

- structural, and morphological levels. The studies conducted on infant monkeys are most relevant for assessing effects in children. Carey et al. ( 2007 ) conduct ed a study of O 3 exposure in infant rhesus macaques, whose respiratory tract closely resemble that of humans. Monkeys were exposed either acutely o r in epi sodes designed to mimi c human exposure

. All monkeys acutely exposed to O 3 had moderate to marked nec rotizing rhinitis, with focal regions of epithelial exfoliation, numerous infiltrating neutrophils, and some eosinophils. The distribution, character, and severity of lesions in episodically exposed infant monkeys were similar to that of acutely exposed an imals. Neither exposure protocol for the infant monkeys produced mucous cell metaplasia proximal to the lesions, an adaptation observed in adult monkeys exposed in another study ( Harkema et al., 1987 )

. Functional and cellular changes in conducting airways were common manifestations of exposure to O 3 among both the adult and infant monkeys ( Plopper et al., 2007 )

. In addition, the lung growth of the distal conducting airways in the infant*** E.O. 12866 Review

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Page 128 of 647 monkeys was significantly stunted by O 3 and this aberrant development was persistent
6 months postexposure (Fanucchi et al., 2006)

. Age may also aff

ect the inflammatory response to O 3 exposure. Toxicological studies reported that the difference in effects among younger lifestage test animals may be due to age

- related changes in antioxidants levels and sensitivity to oxidative stress. Further discussio n of these studies may be found in section 8.3.1.1 of the ISA (U.S. EPA, 2013, p. 8

- 18)

. The previous and recent human clinical and toxicological studies reported evidence of increased risk from O 3 exposure for younger ages, which provides coherence and biological plausibility for the findings from epidemiologic studies. Although there was some inconsistency, generally, the epidemiologic studies reported positive associations among both children and adults or just among children. The interpretation of the se studies is limited by the lack of consistency in comparison age groups and outcomes examined. However, overall, the epidemiologic, controlled human exposure, and toxicological studies provide adequate evidence that children are potentially at increased risk of O 3 - related health effects. iv. Older adults The ISA notes that o lder adults are at greater risk of health effects associated with
O 3 exposure through a variety of intrinsic pathways (U.S. EPA, 2013, section 8.3.1.2) . In addition, older adults may differ in their exposure and internal dose. Older adults were outdoors for a slightly longer proportion of the day than adults aged 18

- 64 years. For more information on time spent outdoors by age group, see Section 4. 4 in the ISA (U.S. EPA, 2013) . The gra dual decline in physiological processes that occur s with aging may*** E.O. 12866 Review

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Page 129 of 647 lead to increased risk of O 3 - related health effects ( U.S. EPA, 2006a ) . Respiratory symptom responses to O 3 exposure appears to increase with age until early adulthood and then gradually decrease with increasing age ( U.S. EPA, 1996 ) ; lung function responses to
O 3 exposure also decline from early adulthood (U.S. EPA, 1996). The reductions of these responses with age may put older adults at increased risk for continued O 3 exposure. In addition, older adults, in general, have a higher prevalence of preexisting diseases compared to younger age groups and this may also lead to increased risk of O 3 - related health effe cts (U.S. EPA, 2013, section 8.3.1.2)

. With the number of older Americans increasing in upcoming years (estimated to increase from 12.4% of the U.S. population to 19.7% between 2000 to 2030, which is approximately 35 million and 71.5 million individuals, r espectively) this group represents a large population potentially at risk of
O 3 - related health effects ( SSDAN CensusScope, 2010a ; U.S. Census Bureau, 2010 )

. The majority of recent studies reported greater effects of short

- term O 3 exposure and mortality among older adults, which is consistent with the findings of the 2006 O 3 AQCD. A study (Medina

- Ramón and Schwartz, 2008) conducted in 48 cities across the U.S. reported lar ger effects among adults ≥65 years old compared to those < 65 years . F urther investigation of this study population revealed a trend of O 3 - related mortality risk that gets larger with increasing age starting at age 51 (Zanobetti and Schwartz, 2008)

. A nothe r study conducted in 7 urban centers in Chile reported similar results, with greater effects in adults ≥65 years old (Cakmak et al., 2007)

. More recently, a study conducted in the same area reported similar associations between O 3 exposure and mortality in adults aged < 64 years old and 65 to 74 years old, but the risk was increased among the older
age group (Cakmak et al., 2011)

. A study performed in China reported greater effects in*** E.O. 12866 Review

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Page 130 of 647 populations ≥45 years old (compared to 5 to 44 year olds), with statistically significant effects present only among those ≥65 years old (Kan et al., 2008)

. An Italian study reported higher risk of all

- cause mortality associated with increased O 3 concentrations among individuals ≥85 year old as compare d to those 35 to 84 years old (Stafoggia et al., 2010)

. The Air Pollution and Health: A European and North American Approach (APHENA) project examined the association between O 3 exposure and mortality for those <75 and ≥ 75 years of age. In Canada, the ass ociations for all

- cause and cardiovascular mortality were greater among those ≥75 years old. In the U.S., the association for all

- cause mortality was slightly greater for those <75 years of age compared to those ≥75 years old in summer

- only analyses. No co nsistent pattern was observed for CVD mortality. In Europe, slightly larger associations for all

- cause mortality were observed in those <75 years old in all

- year and summer

- only analyses. Larger associations were reported among those <75years for CVD morta lity in all

- year analyses, but the reverse was true for summer

- only analyses (Katsouyanni et al., 2009). With respect to epidemiologic studies of O 3 exposure and hospital admissions , a positive association was reported between short

- term O 3 exposure and respiratory hospital admissions for adults ≥65 years old but not for those adults aged 15 to 64 years (Halonen et al., 2009) . In the same study, no association was observed between O 3 concentration and respiratory mortality among those ≥65 years old or tho se 15 to 64 years old

. No modification by age (40 to 64 year olds versus >64 year olds) was observed in a study from Brazil examining O 3 levels and COPD ED visits. Although some outcomes reported mixed findings regarding an increase in risk for older adu lts, recent epidemiologic studies report consistent positive associations*** E.O. 12866 Review

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Page 131 of 647 between short

- term O 3 exposure and mortality in older adults. The evidence from mortality studies is consistent with the results reported in the 2006 O 3 AQCD and is supported by toxi cological studies providing biological plausibility for increased risk of effects in older adults. Also, older adults may be experiencing increased exposure compared to younger adults. Overall, the ISA (U.S. EPA 2013) concludes adequate evidence is availab le indicating that older adults are at increased risk of O 3 - related health effects

.

v. People with d iets l ower in v itamins C and E Diet was not examined as a factor potentially affecting risk in previous O 3 AQCDs, but recent studies have examined modifi cation of the association between O 3 and health effects by dietary factors. Because O 3 mediates some of its toxic effects through oxidative stress, the antioxidant status of an individual is an important factor that may contribute to increased risk of O 3 - r elated health effects. Supplementation with vitamins C and E has been investigated in a number of studies as a means of inhibiting
O 3 - mediated damage.
Two e pidemiologic studies have examined effect modification by diet and found evidence that certain dietary components are related to the effect O 3 has on respiratory
outcomes

. In one recent study the effects of fruit/vegetable intake and Mediterranean diet

were examined. Increases in these food patterns, which have been noted for their high vitamins C a nd E and omega

- 3 fatty acid content, were positively related to lung function in asthmatic children living in Mexico City , and modified by O 3 exposure (Romieu et al., 2009) . Another study examined supplementation of the diets of asthmatic children in Mexic o with vitamins C and E (Sienra

- Monge et al., 2004). Associations were detected*** E.O. 12866 Review

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Page 132 of 647 between short

- te rm O 3 exposure and nasal airway inflammation among children in the placebo group but not in those receiving the supplementation. The epidemiologic evidence is supported by controlled human exposure studies, discussed in section 8.4.1 of the ISA (U.S. EPA 2013), that have shown that the first line of defense against oxidative stress is antioxidants

- rich extracellular lining fluid (ELF) which scavenge free radicals and limit lipid peroxidation. Exposure to O 3 depletes antioxidant level s in nasal ELF probabl y due to scrubbing of O 3 ; however, the concentration and the activity of antioxidant enzymes either in ELF or plasma do not appear to be related to O 3 responsiveness . C ontrolled studies of dietary antioxidant supplementation have demonstrated some protective effects of α

- tocopherol (a form of vitamin E) and ascorbate (vitamin C) on spirometric measures of lung function after O 3 exposure but not on the intensity of sub jective symptoms and inflammatory response s. Dietary antioxidants have also afforded partial protection to asthmatics by attenuating postexposure bronchial hyperresponsivenes s . Toxicological studies discussed in section 8.4.1 of the ISA (U.S. EPA 2013) pro vide evidence of biological plausibility to the epidemiologic and controlled human exposure studies

. Overall, the ISA (U.S. EPA 2013) concludes adequate evidence is available indicating that individuals with diets lower in vitamins C and E are at risk fo r O 3 - related health effects. The evidence from epidemiologic studies is supported by controlled human exposure and toxicological studies. vi. Outdoor workers Studies included in the 2006 O 3 AQCD reported that individuals who participate in outdoor activities or work outside to be a population at increased risk based on*** E.O. 12866 Review

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Page 133 of 647 consistently reported associations between O 3 exposure and respiratory health outcomes in these groups ( U.S. EPA, 2006a b ) . Outdoor workers are exposed to ambient O 3 concentrations for a g reater period of time than individuals who spend their days indoors. As discussed in Section 4. 7 of the ISA (U

. S

. EPA, 201 3 ) outdoor workers sampled during the work shift had a higher ratio of personal exposure to fixed

- site monitor concentrations than hea lth clinic workers who spent most of their time indoors. Additionally, an increase in dose to the lower airways is possible during outdoor exercise due to both increases in the amount of air breathed (i.e., minute ventilation) and a shift from nasal to oro nasal breathing. The association between FEV 1 responses to O 3 exposure and minute ventilation is discussed more fully in Section 6.2.3.1 of the 2006 O 3 AQCD. Previous studies have shown that increased exposure to O 3 due to outdoor work leads to increased risk of O 3 - related health effects, specifically decrements in lung function ( U.S. EPA, 2006a b ). The strong evidence from the 2006 O 3 AQCD which demonstrated increased exposure, dose, and ultimately risk of O 3 - related health effects in this population supp orts the conclusion that there is adequate evidence to indicate that increased exposure to O 3 through outdoor work increases the risk of O 3 - related health effects. In some cases, it is difficult to determine a factor that results in increased risk of eff ects. For example, previous assessments have included controlled human exposure studies in which some healthy individuals demonstrate greater O 3 - related health effects compared to other h ealthy individuals. Interindividual variability has been observed for lung function decrements, symptomatic responses, pulmonary inflammation, AHR, and altered epithelial permeability in healthy adults exposed to O 3 and these results tend to be*** E.O. 12866 Review

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Page 134 of 647 reproducible within a given individual over a period of several months indicatin g differences in the intrinsic responsiveness . In many cases the reasons for the variability is not clear. This may be because one or some of the factors described above have not been evaluated in studies, or it may be that additional, unidentified factors influence individual responses to O 3 ( U.S. EPA, 2013, section 8.5 )

. As discussed in chapter 8 of the ISA, there is a lack of information regarding the extent to which some factors may increase risk from O 3 exposures. Due to this lack of information, the ISA concluded that for some factors, such as sex, SES, and obesity , there is only “suggestive” evidence of increased risk , or that for a number of factors the evidence i s inadequate to draw conclusions about potential increase in risk of effects.
Overa ll, the factors for which the ISA concludes there is adequate evidence of increased risk for experienc ing O 3 - related effects were related to asthma, lifestage (children and older adults), genetic variability, dietary factors, and working outdoors. b. Size of at

- risk populations
O ne consideration in the assessment of potential public health impacts is the size of various population groups for which there is adequate evidence of increased risk for health effects associated with O 3 - related air pollution expos ure (U.S. EPA 2014c, section 3.1.5.2). The factors for which the ISA judged the evidence to be “adequate” with respect
to contributing to increased risk of O 3 - related effects among various populations and lifestages included: asthma; childhood and older ad ulthood; diets lower in vitamins C and E; certain genetic variants and , working outdoors (U.S. EPA , 2013, section 8.5)

. No statistics are available to estimate the size of an at

- risk population based on nutritional status or genetic variability

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Page 135 of 647 With re gard to asthma, Table 3

- 7 in the PA (U.S. EPA, 2014c, section 3.1.5.2) summarizes information on the prevalence of current asthma by age in the U.S. adult population in 2010 (Schiller et al. 2012; children

- Bloom et al., 2011). Individuals with
current as thma constitute a fairly large proportion of the population, including more than 25 million people. Asthma prevalence tends to be higher in children than adults. Within the U.S., approximately 8.2 % of adults have reported currently having asthma (Schiller et al., 2012) and 9.5% of children have reported currently having asthma (Bloom et al., 2011)

. With regard to lifestages, b ased on U.S. census data from 2010 (Howden and Meyer, 2011) , about 74 million people, or 2 4 % of the U.S. population , are under 18 years of age and more than 40 million people, or about 13% of the U.S. population, are 65 years of age or older

. Hence, a large proportion of the U.S. population (i.e., more than a third) is included in age groups that are considered likely t o be at increased risk for health effects from ambient O 3 exposure. With regard to outdoor workers, in 2010 approximately 11.7% of the total number of people (143 million people) employed, or about 16.8 million people, worked outdoors one or more day per w eek (based on worker surveys). 47 Of these approximately 7.4% of the workforce, or about 7.8 million people, worked outdoors three or more days per week.

47 The O*NET program is the nation's primary source of occupatio nal information. Central to the project is the O*NET database, containing information on hundreds of standardized and occupation

- specific descriptors. The database, which is available to the public at no cost, is continually updated by surveying a broad ra nge of workers from each occupation. http://www.onetcenter.org/overview.html http://www.onetonline.org/find/descriptor/browse/Work_Context/4.C.2/*** E.O. 12866 Review

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Page 136 of 647 The health statistics data illustrate what is known as the “pyramid” of effects. At the top of the pyra mid, there are approximately 2.5 million deaths from all causes per year in the U.S. population, with about 250 thousand respiratory

- related deaths (CDC

WONDER, 2008)

. For respiratory health diseases, there are nearly 3.3 million hospital discharges per ye ar (HCUP, 2007), 8.7 million respiratory ED visits (HCUP, 2007) , 112 million ambulatory care visits (Woodwell and Cherry, 2004), and an estimated 700 million restricted activity days per year due to respiratory conditions (Adams et al., 1999). Combining sm all risk estimates with relatively large baseline levels of health outcomes can result in quite large public health impacts. Thus, even a small percentage reduction in O 3 health impacts on cardiopulmonary diseases would reflect a large number of avoided ca ses. c. Impacts of averting behavior The activity pattern of individuals is an important determinant of their exposure (ISA, U.S. EPA, 2013 , section 4.4.1)

. Variation in O 3 concentrations among various microenvironments means that the amount of time spen t in each location, as well as the level of activity, will influence an individual’s exposure to ambient O 3 . Activity patterns vary both among and within individuals, resulting in corresponding variations in exposure across a population and over time. Indi viduals can reduce their exposure to O 3 by altering their behaviors, such as by staying indoors, being active outdoors when air quality is better, and by reducing their activity levels or reducing the time being active outdoors on high

- O 3 days (U.S. EPA, 2 013, section 4.4.2)

. The widely reported Air Quality Index (AQI) conveys advice to the public, and particularly at

- risk populations, on reducing short

- or prolonged

- exposures on days when*** E.O. 12866 Review

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Page 137 of 647 ambient levels of common , criteria air pollutants (except lead), are elevated (www.airnow.gov)

. Information communicated by the AQI is based on the evidence and exposure/risk information assessed in the review of the NAAQS; it is updated and revised as necessary during the review of each standard. Proposed changes to th e AQI sub

- index for O 3 , based on evidence and exposure/risk information assessed in this review, are discussed in section III below. The AQI describes the potential for health effects from O 3 (and other individual pollutants) in six color

- coded categories of air

- quality, ranging from Good (green), Moderate (yellow), Unhealthy for Sensitive Groups (orange), Unhealthy (red), and Very Unhealthy (purple), and Hazardous (maroon). Levels in the unhealthy ranges (i.e., Unhealthy for Sensitive Groups and above) co me with recommendations about reducing exposure. Forecasted and actual AQI values for O 3 are reported to the public during the
O 3 season . The AQI advisories explicitly state that children, older adults, people with lung disease, and people who are active o utdoors, may be at greater risk from exposure to
O 3 . People are advised to reduce exposure depending on the predicted O 3 levels and the likelihood of risk. This advice includes being active outdoors when air quality is better, and reducing activity levels or reducing the time being active outdoors on high

- O 3 days. Staying indoors to reduce exposure is not recommended until air quality reaches the Very Unhealthy or Hazardous categories

. Evidence of individual averting behaviors in response to AQI advisories has been found in several studies, including activity pattern and epidemiologic studies, especially for the at

- risk populations, such as children, older adults, and people with asthma, who are targeted by the advisories. Such effects are less pronounced i n the general population,*** E.O. 12866 Review

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Page 138 of 647 possibly due to the opportunity cost of behavior modification. Epidemiologic evidence from a study (Neidell and Kinney, 2010) conducted in the 1990’s in Los Angeles, CA reports increased asthma hospital admissions among children a nd older adults when O 3 alert days (1

- hour max O 3 concentration >200 ppb) were excluded from the analysis of daily hospital admissions and O 3 concentrations (presumably thereby eliminating averting behavior based on high O 3 forecasts). The lower rate of ad missions observed when alert days were included in the analysis suggests that estimates of health effects based on concentration

- response functions that do not account for averting behavior may be underestimates (U.S. EPA, 2013, section 4.4.2)

. C

. Human Ex

posure and Health Risk Assessments To put judgments about health effects that are adverse for individuals into a broader public health context, the EPA has developed and applied models to estimate human exposures to O 3 and O 3 - associated health risks . Expos ure and risk estimates based on such models are presented and assessed in the HREA ( U.S. EPA, 2014a) . In reviewing the draft HREA, CASAC expressed the view that the document is “well

- written, founded based upon comprehensive analyses and adequate for its intended purpose” (Frey, 2014a, p. 1). Analyses in the HREA inform consideration of the O 3 exposures and health risks that co uld be allowed by the current standard and alternative standards , and consideration of the kind and degree of uncertainties inherent in estimates of O 3 exposures and health risks

. The following sections discuss the air quality adjustment approach used in the
HREA for exposure and health risk estimates (II.C.1) ; the approach taken to estimate*** E.O. 12866 Review

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Page 139 of 647 exposure s, key exposure results , and important uncertainties (II.C.2) ; and the approaches taken to estimate O 3 health risks, key risk results , and important uncertain ties (II.C.3).
1

. Air Quality Adjustment As discussed above ( section I. E ), O 3 is formed near the Earth’s surface due to chemical interactions involving solar radiation and precursor pollutants including VOCs,
NO X , CH 4 and CO

. T he response of O 3 to changes in precursor concentrations is nonlinear

. In particular, NO X causes both the formation and destruction of O 3 . The net impact of NO X emissions on O 3 concentrations depend s on the local quantities of NO X , VOC, and sunlight , which interact in a set of comple x chemical reactions

. In some areas, such as urban centers where NO X emissions typically are high, NO X leads to the net destruction of O 3 , decreasing O 3 concentrations in the immediate vicinity. This phenomenon is particularly pronounced under conditions that lead to low ambient O 3 concentrations (i.e. during cool, cloudy weather and at night when photochemical activity is limited or nonexistent)

. However, while NO X can initially destroy O 3 near e mission sources, these same NO X emissions eventually react to form O 3 downwind of those

sources . Photochemical m odel simulations suggest that reductions in NO X emissions will slightly increase O 3 concentrations near NO X sources on days with lower O 3

concen trations, while at the same time decreasing the highest O 3 concentrations in outlying areas. The atmospheric chemistry that influences ambient O 3 concentrations is discussed in more detail in the ISA (U.S. EPA, 2013, Chapter 3) and the PA (U.S. EPA, 2014c, Chapter 2). The HREA uses a photochemical model to estimate sensitivities of O 3 to c hanges
i n precursor emissions in order to estimate ambient O 3 concentrations that would just*** E.O. 12866 Review

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Page 140 of 647 meet the current and alternative standards (U.S. EPA, 2014 a , Chapter 4)

. 48 For the 15 urban study areas evaluated in the HREA, 49 this model

- based adjustment approach estimate s hourly O 3 concentrations at each monitor location when modeled U.S. anthropogenic precursor emissions (i.e., NO X , VOC) 50 a re reduced. T he HREA estimates air quality that just meet s the current and alternative standards for the 2006

- 2008 and
2008

- 2010 periods. 51 As discussed in Chapter 4 of the HREA (U.S. EPA, 2014a), this approach to adjusting air quality models the physical and chemical atmospheric proce sses that influence ambient O 3 concentrations. Compared to the quadratic rollback approach used in previous reviews, it provides more realistic estimates of the spatial and temporal responses of O 3 to reductions in precursor emissions. Because ambient NO X can contribute both to the formation and destruction of O 3 (U.S. EPA, 2014a, Chapter 4), the response of ambient O 3 concentrations to reductions in NO X emissions is more variable than indicated by the quadratic rollback approach. This improved approach to adjusting

48 The HREA uses the CMAQ photochemical model instrumented with the higher order direct decoupled method (HDDM) to estimate O 3 concentrations that would occur with the achievement of the current and alternative O 3 standards (U.S. EPA, 2014a, Chapter 4). 49 The urban study areas assessed are Atlanta, Baltimore, Boston, Chicago, Cleveland, Dallas, Denver , Detroit, Hou ston, Los Angeles, New York, Philadelphia, Sacramento, St. Louis, and Washington, DC. 50 Exposure and risk analyses for most urban study areas focus on reducing U.S. anthropogenic NO X emissions alone. The exceptions are Chicago and Denver. Exposure and ris k analyses for Chicago and Denver are based on reductions in emissions of both NO X and VOC (U.S. EPA, 2014a, section 4.3.3.1; Appendix 4D ). 51 These simulations are illustrative and do not reflect any consideration of specific control programs or strategies designed to achieve the reductions in emissions required to meet the specified standards. Further, these simulations do not represent predictions of when, whether, or how areas might meet the specified standards.*** E.O. 12866 Review

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Page 141 of 647 O 3 air quality is consistent with recommendations from the National Research Council of the National Academies (NRC, 2008). Consistent with the O 3 chemistry summarized above , in locations and time periods when NO X is predominantly contributing to O 3 formation (e.g., downwind of important NO X sources, where the highest O 3 concentrations often occur), model

- based adjustment to the current and alternative standards decreases estimated ambient O 3 concentrations compared to recent monitored concentrati ons (U.S. EPA, 2014 a , section 4.3.3.2). In contrast, in locations and time periods when NO X is predominantly contributing to O 3 titration (e.g., in urban centers with high concentrations of NO X emissions, where ambient O 3 concentrations are often suppressed and thus relatively low 52 ), model

- based adjustment increases ambient O 3 concentrations compared to recent monitored concentrations (U.S. EPA, 2014 a , section 4.3.3 .2)

. Within urban study areas , the overall impacts of mod el

- based air quality adjustment are to reduce the O 3 concentrations at the upper ends of ambient distributions and to increase the O 3 concentrations at the lower ends of those distributions (U.S. EPA,
2014 a , section 4.3.3.2, Figures 4

- 9 and 4

- 1 0 ). 53 Seasona l means of daily O 3 concentrations generally exhibit only modest changes upon model adjustment, reflecting the seasonal balance between daily decreases in relatively higher concentrations and increases in relatively lower concentrations (U.S. EPA, 2014 a , Figures 4

- 9 and 4

- 10 ).

52 Titration is also prominent du ring time periods when photochemistry is limited, and ambient O 3 concentrations are relatively low, such as at night and on cool, cloudy days (U.S. EPA, 2014a, Chapter 4). 53 It is important to note that sensitivity analyses in the HREA indicate that the i ncreases in low O 3 concentrations are smaller when NO X and VOC emissions are reduced than when only NO X emissions are reduced (U.S. EPA, 2014a, Appendix 4

- D , section 4.7 ).*** E.O. 12866 Review

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Page 142 of 647 The resulting compression in the seasonal distributions of ambient O 3 concentrations is evident in all of the urban study areas evaluated, though the degree of compression varies considerably across areas (U.S. EPA, 2014 a , Figures 4

- 9 and 4

- 10 ).
Th is compression in the distributions of ambient O 3 concentrations has important implications for exposure and risk estimates in urban study areas . Estimates influenced largely by the upper ends of the distribution of ambient concentrations ( i.e., exposures of concern and lung function risk estimates, as discussed in sections 3.2.2 and 3.2.3.1 of the PA ( U.S. EPA, 2014c ) ) decrease with adjustment of air quality to the current and alternative standards. In contrast, seasonal risk estimates infl uenced by the full distribution of ambient O 3 concentrations (i.e., epidemiology

- based risk estimates, as discussed in section 3.2.3.2 of the PA ) either decrease or increase in response to air quality adjustment, depending on the balance between the daily decreases in high O 3 concentrations and increases in low O 3 concentrations. 54
In their review of the second draft HREA, CASAC considered this issue , in particular noting that “reductions in nitrogen oxides emissions can lead to less scavenging of ozone and free radicals, resulting in locally higher levels of ozone” (Frey, 2014a, p. 10). CASAC recommended that “ the EPA should identify and discuss whether and to what extent healt h risks in the urban core may be affected by NO X reductions or other possible strategies ” and , in particular, concluded that it would “ be of interest to learn if there would be any children or outdoor workers in the more urban areas who would

54 In addition, because epidemiology

- based risk estimates use “area

- wide” average O 3 c oncentrations, calculated by averaging concentrations across multiple monitors in urban study areas (U.S. EPA, 2014c, section 3.2.3.2), risk estimates on a given day depend on the daily balance between increasing and decreasing O 3 concentrations at the ind ividual monitors that are averaged together to calculate the “area

- wide” concentration

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Page 143 of 647 experience si gnificantly higher exposures to ozone as a result of possible changes in the ozone NAAQS” (Frey, 2014a, p. 10)

. The exposure and risk implications of the spatial and temporal patterns of ambient O 3 following air quality adjustment in urban study areas

are discussed in the final HREA (U.S. EPA, 2014a, Chapter 9) and the final PA (U.S. EPA, 2014c, sections 3.2.2, 3.2.3), and are summarized below within the context of the
PA ’s consideration of exposure estimates (II. D.2.a) and risk estimates (II. D.2.b and
II.D .2.c ).
2

. Exposure Assessment This section discusses the HREA assessment of human exposures to O 3 . Section II.C.2.a provides an overview of the approach used in the HREA to assessing exposures and the approach in the PA to considering exposure estimates, and summarizes key results. Section II.C.2.b summarizes the important uncertainties in exposure estimates

. a. Overview and summary of key results The exposure assessment presented in the HREA (U.S. EPA, 2014 a, Chapter 5 ) provides estimates of the number a nd percent of people exposed to various concentrations of ambient O 3 , while at specified exertion levels

. The HREA estimates exposures in the 15 urban study areas for four study groups, all school

- age children (ages 5 to 18), asthmatic school

- age children, asthmatic adults (ages 19 to 95), and all older adults (ages 65 to 95), reflecting the strong evidence indicating that these populations are at increased risk for O 3 - attributable effects (U.S. EPA , 2013, Chapter 8)

. An important purpose of these exposure estimates is to provide perspective on the extent to which air quality adjusted to just meet the current O 3 NAAQS could be associated with exposures to O 3*** E.O. 12866 Review

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Page 144 of 647 concentrations reported to result in respiratory effects. 55 Estimates of such “exposures of concern” p rovide perspective on the potential public health impacts of O 3 - related effects , including effects that cannot currently be evaluated in a quantitative risk assessment

. 56 In the absence of large scale exposure studies that encompass the general population, as well as at

- risk populations, modeling is the preferred approach to estimating exposures to O 3 (U.S. EPA, 2014a, Chapter 5). The use of exposure modeling also facilitates the estimation of exposures resulting from ambient O 3 concentrations differing fro m those present during exposure studies. In the HREA, population exposures to ambient O 3 concentrations are estimated using the current ve rsion of the Air Pollutants Exposure (APEX) model. The APEX model simulates the movement of individuals through time a nd space and estimates their exposures to a given pollutant in indoor, outdoor, and in

- vehicle microenvironments ( U.S. EPA, 2014 a , section 5.1.3). APEX takes into account important factors that contribute to total human exposure to ambient
O 3 , including th e temporal and spatial distribution s of people and O 3 concentrations throughout an urban area, the variation of O 3 concentrations within various microenvironment s , and the effects of exertion on breathing rate in exposed individuals ( U.S. EPA, 2014 a , secti on 5.1.3 ). To the extent spatial and/or temporal patterns of

55 In addition, the range of modeled personal exposures to ambient O 3 provide an essential input to the portion of the health risk assessment based on exposure

- response functions (for lung function decrements) from controlled human exposure studies. The health risk assessment based on exposure

- response information is discus sed below (II.C.3). 56 In this review, the term “exposure of concern” is defined as a personal exposure , while at moderate or greater exertion , to 8

- hour average ambient O 3 concentrations at and above specific benchmarks. As discussed below, b enchmarks rep resent exposure concentrations at which O 3 - induced health effects are known to occur, or can reasonably be anticipated to occur, in some individuals.*** E.O. 12866 Review

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Page 145 of 647 ambient O 3 concentrations are altered upon model adjustment, as discussed above, exposure estimates reflect population exposures to those altered patterns. The HREA estimates 8

- hour exposures at or above benchmark concentrations of 60, 70, and 80 ppb for individuals engaged in moderate or greater exertion. Benchmarks reflect exposure concentrations at which O 3 - induced respiratory effects are known to occur in some healthy adults engaged in modera te, intermittent exertion, based on evidence from controlled human exposure studies (U.S. EPA, 2013, section 6.2; U.S. EPA, 2014c , section 3.1.2.1 ). The amount of weight to place on the estimates of exposures at or above specific benchmark concentrations d epends in part on the weight of the scientific evidence concerning health effects associated with O 3 exposures at those benchmark concentration s . It also depends on judgments about the importance, from a public health perspective, of the health effects that are known or can reasonably be inferred to occur as a result of exposures at benchmark concentrations ( U.S. EPA, 2014c , sections 3.1.3, 3.1.5 )

. As discussed in more detail above (II.B.2) , the health evidence that supports evaluating exposures of conc ern at or above benchmark concentrations of 60, 70, and 80 ppb comes from a large body of controlled human exposure studies reporting a variety of respiratory effects in healthy adults. The lowest O 3 exposure concentration for which controlled human exposu re studies have reported respiratory effects in healthy adults is 60 ppb, with more evidence supporting this benchmark concentration in the current review than in the last review. In healthy adults, exposures to 60 ppb O 3 have been reported to decrease lun g function and to increase airway inflammation. Exposures of healthy adults to 7 2 ppb O 3 have been reported to result in larger lung function*** E.O. 12866 Review

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Page 146 of 647 decrements, compared to 60 ppb, as well as in increased respiratory symptoms. 57 Exposures of healthy adults to 80 p pb O 3 have been reported to result in larger lung function decrements than following exposures to 60 or 7 2 ppb, increased airway inflammation, increased respiratory symptoms, increased airways responsiveness, and decreased lung host defense ( U.S. EPA, 2014 c , section 3.1.2.1 ). In commenting on the evidence for benchmark concentrations, CASAC stated the following (Frey, 2014c, p. 6): The 80 ppb

- 8hr benchmark level represents an exposure level for which there is substantial clinical evidence demonstrating a r ange of ozone

related effects including lung inflammation and airway responsiveness in healthy individuals. The 70 ppb

- 8hr benchmark level reflects the fact that in healthy subjects, decreases in lung function and respiratory symptoms occur at concentratio ns as low as 72 ppb and that these effects almost certainly occur in some people, including asthmatics and others with low lung function who are less tolerant of such effects, at levels of 70 ppb and below. The 60 ppb

- 8hr benchmark level represents the low est exposure level at which ozone

- related effects have been observed in clinical studies of healthy individuals. Based on its scientific judgment, the CASAC finds that the 60 ppb

- 8hr exposure benchmark is relevant for consideration with respect to adverse effects on asthmatics. In considering estimates of O 3 exposures of concern at or above be nchmarks of 60, 70, and 80 ppb , the PA focuses on modeled e xposures for school

- age children (ages 5

- 18) , including asthmatic school

- age children, which are key at

- risk populations identified in the ISA ( U.S. EPA, 2014c , section 3.1.5). The percentages of children estimated to experience exposures of concern a re considerably larger than the percentages estimated for adult populations (i.e., approximately 3

- fold larger across urban study areas ) (U.S. EPA, 2014a, section 5.3.2 and Figures 5

- 5 to 5

- 8 )

. T he larger exposure estimates for children are due primarily to the larger percentage of children

57 As noted above, for the 70 ppb exposure concentration Schelegle et al. (2009) reported that the actual 6.6

- hour mean exposure concentration was 72 ppb.*** E.O. 12866 Review

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Page 147 of 647 estimated to spend an extended period of time being physically active outdoors when O 3 concentrations are elevated (U.S. EPA, 2014 a , sections 5.3.2 and 5.4.1 ). Although exposure estimates differ between children and adults, the patterns of results across the urban study areas and years are simi lar among all of the populations evaluated (U.S. EPA, 2014a, Figures 5

- 5 to 5

- 8). Therefore, while the PA highlights estimates in children, including asthmatic school

- age children, it also notes that the patterns of exposures estimated for children represe nt the patterns estimated for adult asthmatics and older adults. Table 1 below summarizes key results from the exposure assessment. Table 1 presents estimates of the percentages and numbers of all school

- aged children estimated to experience exposures of concern when air quality was adjusted to just meet the current and alternative 8

- hour O 3 standards

. T he percentage of all school

- age children in the 15 urban study areas estimated to experience exposures of concern decline s when comparing just meeting the current standard to just meeting alternative 8

- hour O 3 standards. Substantial variability is evident across years and urban study areas , as indicated by the ranges of averaged estimates and estimates for worst

- case years and study areas . As discussed below , the inter individual variability in responsiveness following exposures of

concern means that only a subset of individuals who are exposed at and above a given benchmark concentration would actually be expected to experience respiratory effects.*** E.O. 12866 Review

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Page 148 of 647 Table 1. Summary of Estimated Exposures of Concern in All School
- age Children for the Current and Alternative O 3 Standards in Urban Study Areas Benchmark Concentration Standard

Level (ppb) Average %

Children Exposed 58 Average Number of

Children Exposed [Average Number of Asthmatic Children] 59 % Children

- Worst Year and Worst Area One or more exposures of concern per season ≥ 80 ppb 75 0

- 0.3 27,000 [3,000] 1.1

70 0

- 0.1 3,700 [300] 0.2 65 0 300 [0] 0 60 0 100 60 [0] 0 ≥ 70 ppb 75 0.6

- 3.3 362,000 [40,000] 8.1

70 0.1

- 1.2 94,000 [10,000] 3.2 65 0

- 0.2 14,000 [2,000] 0.5 60 0 1,400 [200] 0.1 ≥ 60 ppb 75 9.5

- 17 2,316,000 [246,000] 25.8

70 3.3

- 10.2 1,176,000 [126,000] 18.9 65 0

- 4.2 392,000 [42,000] 9.5 60 0

- 1.2 70,000 [8,000] 2.2 Two or more exposures of concern per season ≥ 80 ppb 75 0 600 [100] 0.1

70 0 0 [0] 0 65 0 0 [0] 0 60 0 0 [0] 0 ≥ 70 ppb 75 0.1

- 0.6 46,000 [5,000] 2.2

70 0

- 0.1 5,400 [600] 0.4 65 0 300 [100] 0 60 0 0 [0] 0 ≥ 60 ppb 75 3.1

- 7.6 865,000 [93,000] 14.4

70 0.5

- 3.5 320,000 [35,000] 9.2

58 Estimates for each urban case study area were averaged for the years evaluated in the HREA (2006 to 2010). Ranges reflect the ranges across urban study areas. Estimates smaller than 0. 05 % were rounded down ward to zero (from U.S. EPA, 2014a, Tables 5

- 11 and 5

- 12). 59 Numbers of children exposed in each urban case study area were averaged over the years 2006 to 2010. These averages were then summed across urban study areas

. Numbers are rounded to nearest thousand unless otherwise indicated. Estimates smaller than 50 were rounded downward to zero (from U.S. EPA, 2014a, Appendix 5F Table 5F

5). 60 As discussed in section 4.3.3 of the HREA, the model

- based air quality adjustmen t approach used to estimate risks associated with the current and alternative standards was unable to estimate the distribution of ambient O 3 concentrations in New York City upon just meeting an alternative standard with a level of 60 ppb. Therefore, for t he 60 ppb standard level the numbers of children and asthmatic children reflect all of the urban study areas except New York

.*** E.O. 12866 Review

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Page 149 of 647 65 0

- 0.8 67,000 [7,500] 2.8 60 0

- 0.2 5,100 [700] 0.3 b

. Key u ncertainties In considering exposure estimates within the context of the current and alternative
O 3 standards, t he PA also notes important unce rtainties in these estimates

. For example, d ue to variability in responsiveness, only a subset of individuals who experience exposures at or above a benchmark concentration can be expected to experience health effects. G iven the lack of sufficient exposure

- response information for most of the health effects that informed benchmark concentrations, estimates of the number of people likely to experience exposures at or above benchmark concentrations generally canno t be translated into quantitative estimates of the number of people likely to experience specific health effects. 61 The PA views health

- relevant exposures as a continuum with greater confidence and less uncertainty about the existence of adverse health effe cts at higher O 3 exposure concentrations , and less confidence and greater uncertainty as one considers lower exposure concentrations. This view draws from the overall body of available health evidence, which indicates that as exposure concentrations increa se , the incidence, magnitude, and severity of effects increases

. Though the PA indicates less confidence in the likelihood of adverse health effects as O 3 exposure concentrations decrease, it also notes that the controlled human exposure studies that prov ided the basis for health benchmark concentrations have not evaluated at

- risk populations. C ompared to the healthy individuals included in controlled human exposure studies, members of at

- risk populations (e.g., asthmatics, children) could

61 The exception to this is lung function decrements, as discussed below ( and in U.S. EPA, 2014c, section 3.2.3.1).*** E.O. 12866 Review

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Page 150 of 647 be more likely t o experience adverse effects, could experience larger and/or more serious effects , and/or could experience effects following exposures to lower O 3 concentrations.
I n considering estimated exposures of concern (U.S. EPA, 2014c, section 3.4), the PA notes th at concerns about the potential for adverse health effects, including effects in at

risk populations must be balanced against the increasing uncertainty regarding the likelihood of such effects following exposures to lower O 3 concentrations. Uncertainties associated with the APEX exposure modeling also have the potential to be important (U.S. EPA, 2014a, section 5.5.2, Table 5

- 6). For example, the HREA concludes that exposures of concern could be underestimated for some individuals who are frequently and r outinely active outdoors during the warm season ( U.S. EPA, 2014a, section 5.5.2). This could include outdoor workers and children who are frequently active outdoors. The HREA specifically notes that l ong - term diary profiles (i.e., monthly, annual) do not exist for such populations, limiting the extent to which APEX outputs reflect people who follow similar daily routines resulting in high
exposures, over extended periods of time. In order to evaluate the potential implications of this uncertainty for exposure estimates, the HREA reports the results of limited exposure model sensitivity analyses using subsets of activity diaries specifically selected to reflect groups spending a larger proportion of tim e being active outdoors during the O 3 season. When diaries were selected to mimic activity patterns performed by outdoor workers, the percent of modeled individuals estimated to experience exposures of concern were higher than the other adult populations e valuated. The percentages of outdoor workers estimated to experience exposures of concern were generally similar to the percentages estimated for children*** E.O. 12866 Review

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Page 151 of 647 (i.e., using the full database of diary profiles) in the worst

- case urban study area and year (i.e., urban study area and year with the largest percent of children estimated to experience exposures of concern) (U.S. EPA, 2014a, section 5.4.3.2, Figure 5

- 14). In addition, when diaries were restricted to children who did not report any time spent inside

a s chool or performing paid work (i.e., to mimic children spending large portions of their time outdoors during the summer), the number experiencing exposures of concern increased by approximately 30% (U.S. EPA, 2014a, section 5.4.3.1). Though these sensitivi ty analyses are limited to single urban study areas, and though there is uncertainty associated with diary selection approaches to mimic highly exposed populations, they suggest the possibility that some at

- risk groups could experience more frequent exposu res of concern than indicated by estimates made using the full database of activity diary profiles

. In further considering activity diaries, the HREA also notes that growing evidence indicates that people can change their behavior in re sponse to high O 3 c oncentrations , reducing the time spent being active outdoors (U.S. EPA, 2014 a , section 5.4.3 .3 ). Commonly termed “ averting behaviors, ” these altered activity patterns could reduce personal exposure concentrations. The refore, the HREA also performed limited sensitivity analyses to evaluate the potential implications of averting behavior for estimated exposures of concern. These analyses suggest that averting behavior could reduce the percentages of children estimated to experience exposures of concern at or above the 60 or 70 ppb benchmark concentrations by approximately 10 to 30%, with larger reductions possible for the 80 ppb benchmark (U.S. EPA, 2014 a , Figure 5

- 1 5 ). As discussed above for other sensitivity analyses, these analyses are limited to a single u rban*** E.O. 12866 Review

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Page 152 of 647 case study area and are subject to uncertainties associated with assumptions about the prevalence and duration of averting behaviors. However, the results suggest that exposures of concern could be overestimated, particularly in children (Neidell et a l., 2009; U.S. EPA, 2013, Figures 4

- 7 and 4

- 8), if the possibility for averting behavior is not incorporated into estimates

. 3

. Quantitative Health Risk Assessments
For some health endpoints, there is sufficient scientific evidence and information availab le to support the development of quantitative estimates of O 3 - related health risks. In the last review of the O 3 NAAQS, the quantitative health risk assessment estimated
O 3 - related lung function decrements, respiratory symptoms, respiratory

- related hospital admissions, and nonaccidental and cardiorespiratory

- related mortality (U.S. EPA, 2007)

. In those analyses, b oth controlled human exposure and epidemiologic studies were used for t he quantitative assessment of O 3 - related human health risks

. In the current review, for short

- term O 3 concentrations the HREA estimates lung function decrements; respiratory symptoms in asthmatics; hospital admissions and emergency department visits for r espiratory causes; and all

- cause mortality (U .S. EPA, 2014a). For long

- term O 3 concentrations, t he HREA estimates respiratory mortality (U.S. EPA, 2014a). 62 Estimates of O 3 - induced lung function decrements are based on exposure modeling, combined with expos ure - response relationships from controlled human exposure studies (U.S. EPA, 2014a, Chapter 6). Estimates of O 3 - associated respiratory symptoms; hospital admissions and emergency department visits; and mortality are based

62 Estimates o f O 3 - associated respiratory mortality are based on the study by Jerrett et al. (2009) . This study used seasonal averages of 1

- hour daily maximum O 3 concentrations to estimate long

- term concentrations.*** E.O. 12866 Review

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Page 153 of 647 on concentration

- response relation ships from epidemiologic studies (U.S. EPA, 2014a, Chapter 7). As with the exposure assessment discussed above, O 3 - associated health risks are estimated for recent air quality and for ambient concentrations adjusted to just meet the current and alternative O 3 standards, based on 2006

- 2010 air quality and adjusted precursor emissions. The following sections discuss the lung function risk assessment (II.C.3.a) and the epidemiology

- based morbidity and mortality risk assessment s (II.C.3.b) from the HREA , includ ing important sources of uncertainty in these estimates

. a. Lung function risk assessment Section II.C.3.a.i provides an overview of the approach used in the HREA to assessing lung function risks , an overview of the approach in the PA to considering lung function risk estimates, and a summary of key results . Section II.C.3.a.ii presents a
summary of key uncertainties in lung function risk estimates. i. Overview and summary of key results In the current review, the HREA estimates risks of lung function decrements in school

- aged children (ages 5 to 18), asthmatic school

- aged children, and the general adult population for the 15 urban study areas . The results presented in the HREA are based o n an updated dose

- threshold model that estimates FEV 1 responses for individuals following short

- term exposures to O 3 ( McDonnell et al., 201 2 ), reflecting methodological improvements since the last review (U.S. EPA, 2014 a , section 6.2.4). The impact of the dose threshold is that O 3 - induced FEV 1 decrements result primarily from exposures on*** E.O. 12866 Review

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Page 154 of 647 days with average ambient O 3 concentrations above about 40 ppb ( U.S. EPA, 2014a , section 6.3.1 , Figure 6

- 9 ). 63 The HREA estimates risks of moderate to large lung function decrements, defined
as FEV 1 decrements > 10%, 15%, or 20%. In evaluating these lung function risk estimates within the context of considering the current and alternative O 3 standard s , the PA focuses on the percent of children estimated to experience one or more and two or

more decrements > 10, 15, and 20%, noting that the percentage of asthmatic children estimated to experience such decrements is virtually indistinguishable from the percentage estimated for all children. 64 Compared to children, a small er per centage of adults were estimated to experience O 3 - induced FEV 1 decrements (U.S. EPA, 2014 a , section 6.3.1 , Table 6

- 4 ). As for exposures of concern (see above), the patterns of results

across urban study areas and over the years evaluated are similar in chi ldren and adults

. Therefore, while the PA highlights estimates in children, it notes that these results are also representative of the patterns estimated for adult populations

. Table 2 below summarizes key results from the lung function risk assessment. Table 2 presents estimates of the percentages of school

- aged children estimated to experience O 3 - induced FEV 1 decrements > 10, 15, or 20% when air quality was adjusted to just meet the c urrent and alternative 8

- hour O 3 standards. Table 2 also presents the

63 Analysis of this issue in the HREA is based on risk estimates in Los Angeles for 2006 unadjusted air quality. T he HREA shows that more than 90% of daily instances of FEV 1 decrements ≥ 10% occur when 8

- hr average ambient concentrations are above 40 ppb for this modeled scenario. The HREA notes that the distribution of responses will be different for different study areas, years, and air quality scenarios (U.S. EPA, 2014c, Chapter 6)

. 64 Though see below for discussion of uncertainty in lung function response s of children and asthmatics.*** E.O. 12866 Review

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Page 155 of 647 numbers of children, including children with asthma, estimated to experience such decrements. As shown in these tables, the percentage of school

- age children in the 15 urban study areas estimated to experience O 3 - induced FEV 1 decrements declines when comparing just meeting the current standard to just meeting alternative 8

- hour O 3 standards. Substantial variability is evident across years and urban study areas , as indicated by the ranges of averaged estimates and estimates for worst

- case years and locations.*** E.O. 12866 Review

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Page 156 of 647 Table 2 . Summary of Estimated O 3 - Induced Lung Function Decrements for the Current and Potential Alternative O 3 Standard s in Urban Case Study Areas Lung Function Decrement Alternative

Standard Level Average

% Children 65 Number of Children (5

to 18 years) [Number of Asthmatic Children] 66 % Children Worst Year and Area One or more decrements per season ≥ 10% 75 14

- 19 3,007,000 [312,000] 22

70 11

- 17 2,527,000 [261,000] 20 65 3

- 15 1,896,000 [191,000] 18 60 5

- 11 1,404,000 [139,000] 67 13 ≥ 15% 75 3

- 5 766,000 [80,000] 7

70 2

- 4 562,000 [58,000] 5 65 0

- 3 356,000 [36,000] 4 60 1

- 2 225,000 [22,000] 3 ≥ 20% 75 1

- 2 285,000 [30,000] 2.8

70 1

- 2 189,000 [20,000] 2.1 65 0

- 1 106,000 [11,000] 1.4 60 0

- 1 57,000 [6,000] 0.9 Two or more decrements per season ≥ 10% 75 7.5

- 12 1,730,000 [179,000] 14

70 5.5

- 11 1,414,000 [145,000] 13 65 1.3

- 8.8 1,023,000 [102,000] 11 60 2.1

- 6.4 741,000 [73,000] 7.3 ≥ 15% 75 1.7

- 2.9 391,000 [40,000] 3.8

70 0.9

- 2.4 276,000 [28,000] 3.1 65 0.1

- 1.8 168,000 [17,000] 2.3 60 0.2

- 1.0 101,000 [10,000] 1.4 ≥ 20% 75 0.5

- 1.1 128,000 [13,000] 1.5

70 0.3

- 0.8 81,000 [8,000] 1.1 65 0

- 0.5 43,000 [4,000] 0.8 60 0

- 0.2 21,000 [2,000] 0.4

65 Estimates in each urban case study area were averaged for the years evaluated in the HREA (2006 to 2010). Ranges reflect the ranges across urban study areas

. 66 Numbers of children estimated to experience decrements in each s tudy urban case study area were averaged over 2006 to 2010. These averages were then summed across urban study areas . Numbers are rounded to nearest thousand unless otherwise indicated. 67 As discussed in section 4.3.3 of the HREA, the model

- based air quali ty adjustment approach used to estimate risks associated with the current and alternative standards was unable to estimate the distribution of ambient O 3 concentrations in New York City upon just meeting an alternative standard with a level of 60 ppb. Ther efore, for the 60 ppb standard level the numbers of children and asthmatic children reflect all of the urban study areas except New York

.*** E.O. 12866 Review

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Page 157 of 647 ii. Key u ncertainties As for exposures of concern discussed above, the PA also considers important uncertainties in estimates of lung function risk. In addition to the uncertainties noted for exposure estimates, the HREA identifies several key uncertainties associated with estimates of O 3 - induced lung function decrements. An uncertainty with particular potential to impact consideration of risk estimates stems from the lack of exposure

response information in children. I n the near abs ence of controlled human exposure data for children , risk estimates are based on the assumption that children exhibit the same lung function response following O 3 exposures as healthy 18 year olds (i.e., the youngest age for which controlled human exposure data is available) (U.S. EPA, 2014a, section 6.5.3 ). This assumption i s justified in part by the findings of McDonnell et al. (1985), who reported that children 8

- 11 year old experienced FEV 1 responses similar to those observed in adults 18

- 35 years old. In addition, as discussed in the ISA (U.S. EPA, 2013, section 6.2.1), summer camp studies of school

- aged children reported O 3 - induced lung function decrements sim ilar in magnitude to those observed in controlled human exposure studies using adults

. In extending the risk model to children, the HREA fixes the age term in the model at its highest value, the value for age 18. This approach could result in either over

- or underestimates of O 3 - induced lung function decrements in children, depending on how children compare to the adults used in controlled human exposure studies (U.S. EPA, 2014a, section 6.5 .3 )

. A related source of uncertainty is that the risk assessment e stimates O 3 - induced decrements in asthmatics using the exposure

- response relationship developed from data collected from healthy individuals. Although the evidence has been mixed (U.S. EPA,*** E.O. 12866 Review

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Page 158 of 647 2013, section 6.2.1.1), several studies have reported larger O 3 - in duced lung function decrements in asthmatics than in non

- asthmatics (Kreit et al., 1989; Horstman et al., 1995; Jorres et al., 1996; Alexis et al., 2000). On this issue CASAC noted that “[a]sthmatic subjects appear to be at least as sensitive, if not more sensitive, than non

asthmatic subjects in manifesting ozone

- induced pulmonary function decrements” ( Frey, 2014c , p. 4). To the extent asthmatics experience larger O 3 - induced lung function decrements than the healthy adults used to develop exposure - response relationships, the HREA could underestimate the impacts of O 3 exposures on lung function in asthmatics, including asthmatic children. The HREA notes that the magnitude this uncertainty might have on risk estimates remains unknown at this time (U.S. EPA, 2 014a, section 6.5.4 ). b. Mortality and morbi dity risk assessment s As discussed above (II.B.2), epidemiologic studies provide evidence for the most serious O 3 - associated public health outcomes (e.g., mortality, hospital admissions, emergency department visits). Section II.C.3.b.i below provid es an overview of the approach used in the HREA to assessing mortality and morbidity risks based on information from epid emiologic studies , discusses the approach in the PA to considering epidemiology

- based risk estimates, and presents a summary of key results. Section II.C.3.b.ii summarizes key uncertainties in epidemiology

- base risk estimates. i. Overview and summary of k ey results Risk estimates based on epidemiologic studies can provide perspective on the most serious O 3 - associated public health outcomes (e.g., mortality, hospital admissions, emergency department visits) in populations that often include at

- risk groups. T he HREA*** E.O. 12866 Review

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Page 159 of 647 estimates O 3 - associated risks in 12 urban study areas 68 using concentration

- response relationships drawn from epidemiologic studies. These concentration

- response relationships are based on “area

- wide” average O 3 concentrations. 69 The HREA estimates risks for the years 2007 and 2009 in order to provide estimates of risk for a year with generally higher O 3 concentrations (2007) and a year with generally lower O 3 concentrations (2009) (U.S. EPA, 2014 a , section 7. 1.1 )

. As in the last review of the O 3 NAAQS (U.S. EPA, 2007, pp. 2

- 48 to 2

- 54) , the
PA recognize s that ambient O 3 concentrations, and therefore O 3 - associated health risks, result from precursor emissions from various types of sources. Based on the air quality modeling discussed in chapter 2 o f the PA ( U.S. EPA, 2014c ) , approximately 30 to 60% of average daytime O 3 during the warm season (i.e., daily maximum 8

- hour concentrations averaged from April to October) is attributable to precursor emissions from U.S. anthropogenic sources ( U.S. EPA, 20 14c , section 2.4.4). The remainder is attributable to precursor emissions from international anthropogen ic sources and natural

sources. Because the HREA characterizes health risks from all O 3 , regardless of source, risk estimates reflect emissions from U.S . anthropogenic, international anthropogenic, and natural sources.

68 The 12 urban areas evaluated are Atlanta, Baltimore, Boston, Cleveland, Denver, Detroit, Houston, Los Angeles, New York, Philadelphia, Sacramento, and St. Louis. 69 In the epidemiologic studies that provide the health basis for HREA risk assessments, conce ntration

- response relationships are based on daytime O 3 concentrations, averaged across multiple monitors within study areas. These daily averages are used as surrogates for the spatial and temporal patterns of exposures in study populations. Consistent wi th this approach, the HREA epidemiologic

- based risk estimates also utilize daytime O 3 concentrations, averaged across monitors, as surrogates for population exposures. In this notice, we refer to these averaged concentrations as “area

- wide” O 3 concentratio ns. Area

wide concentrations are discussed in more detail in section 3.1.4 of the PA (U.S. EPA, 2014c).*** E.O. 12866 Review

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Page 160 of 647 Compared to the weight given to HREA estimates of exposures of concern and lung function risks, and the weight given to the evidence (section 4.4.1), the PA places relatively less weight o n epidemiologic

- based risk estimates. In doing so, the PA notes that the overall conclusions from the HREA likewise reflect less confidence in estimates of epidemiologic

- based risks than in estimates of exposures and lung function risks. The determination to attach less weight to the epidemiologic

- based estimates reflects the uncertainties associated with mortality and morbidity risk estimates, including the heterogeneity in effect estimates between epidemiologic study areas, the potential for epidemiologic

- based exposure measurement error, and uncertainty in the interpretation of the shape of concentration

- response functions at lower O 3 concentrations (discussed below)

. The PA also notes the HREA conclusion that lower confidence should be placed in the resu lts of the assessment of respiratory mortality risks associated with long

- term O 3 exposures, primarily because that analysis is based on only one study (even though that study is well

- designed) and because of the uncertainty in that study about the existen ce and level of a potential threshold in the concentration

- response function (U.S. EPA, 2014a, section 9.6). In considering the epidemiology

- based risk estimates, the PA focuses on mortality risks associated with short

- term O 3 concentrations. In doing so, in addition to noting uncertainty in estimates of respiratory mortality associated with long

- term O 3 , the PA notes that the patterns of estimated respiratory morbidity risks across urban study areas , over years, and for different standards are similar to the patterns of total mortality risk. The PA considers estimates of total risk (i.e., based on the full distributions of ambient O 3 concentrations) and estimates of risk associated with O 3 concentrations in the*** E.O. 12866 Review

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Page 161 of 647 upper portions of ambient distributions. A focus on estimates of total risks would place greater weight on the possibility that concentration

- response relationships are linear over the entire distribution of ambient O 3 concentrations , and thus on the potential for morbidity and mortality to be aff ected by changes in relatively low O 3 concentrations . A focus on risks associated with O 3 concentrations in the upper po rtions of the ambient distribution would place greater weight on the uncertainty associated with the shapes of concentration

- response cu rves for O 3 concentrations in the lower portions of the distribution. Given that both types of risk estimates could reasonably inform a decision on standard level, depending on the weight placed on uncertainties in the occurrence and the estimation of O 3 - a ttributable effects at relatively low O 3 concentrations, the PA consider s both types of estimates. Key results for O 3 - associated mortality risk are summarized in Table 3 below. Table 3 presents estimates of the number of O 3 - a ssociated d eaths in urban study areas , for air quality adjusted to just meet the current and alternative standards.*** E.O. 12866 Review

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Page 162 of 647 Table 3 . Estimates of O 3 - Associated Deaths Attributable to the Full Distribution of 8
- Hour Area
- Wide O 3 Concentrations and to Concentrations at or above 20, 40, or 60 p pb O 3 (Deaths Summed Across Urban Case Study Areas) 70 Number of O 3 - Associated Deaths Summed Across Urban Case Study Areas Standard Level Total O 3 20+ ppb 40+ ppb 60+ ppb 2007 75 ppb 7,500 7, 500 5,4 00 500 70 ppb 7,200 7, 200 4, 900 240 65 ppb 6,5 00 6,5 00 2,8 00 90 60 ppb 71 6, 400 6, 400 2, 300 10 2009 75 ppb 7, 000 7,0 00 4,7 00 27 0 70 ppb 6,9 00 6, 900 4, 300 80 65 ppb 6,4 00 6,4 00 2, 600 40 60 ppb 6, 300 6, 300 2,100 10 i i

. Key Uncertainties
C ompared to estimates of O 3 exposures of concern and estimates of O 3 - induced lung function decrements (discussed above), the HREA conclusions reflect lower confidence in epidemiologic

- based risk estimates (U.S. EPA, 2014a, section 9.6 ) . In particular, the HREA highlights the heterogeneity in effect estimates between locati ons, the potential for exposure measurement errors, and uncertainty in the interpretation of the shape of concentration

- response functions at lower O 3 concentrations (U.S. EPA, 2014a,

70 Numbers of O 3 - associated deaths are rounded to the nearest hundred, unless otherwise indicated. 71 As discussed in section 4.3.3 of the HREA, the model

- based air quality adjustment approach used to estimate risks associated with the current and alternative standards was unable to estimate the distribution of ambient O 3 concentrations in New York City upon just meeting an alternative standard with a level of 60 ppb. Therefore, the total number of deaths indicated for the 60 ppb standard level reflect the 60 ppb estimates for all urban study areas except New York City. For New York City, the estimated number of O 3 - associated deaths for the 6 0 ppb stand ard level was assumed to be equal to the number for the 65 ppb level

.*** E.O. 12866 Review

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Page 163 of 647 section 9.6). The HREA also concludes that lower confidence should be pl aced in the results of the assessment of respiratory mortality risks associated with long

- term O 3 , primarily because that analysis is based on only one study , though that study is well

designed, and because of the uncertainty in that study about the existe nce and identification of a potential threshold in the concentration

- response function (U.S. EPA, 2014a, section 9.6). This section further discusses some of the key uncertainties in epidemiologic

- based risk estimates, as summarized in the PA ( U.S. EPA, 20 14c , section 3.2.3.2), with a focus on uncertainties that can have particularly important implications for the Administrator’s consideration of epide miology

- based risk estimates. The PA notes that reducing NO X emissions generally reduces O 3 - associated mortality and morbidity risk estimates in locations and time periods with relatively high ambient O 3 concentrations and increases risk estimates in locations and time periods with relatively low concentrations (II.C.1 , above ) . When evaluating uncertainties in epidemiologic risk estimates, it is important to consider (1) the extent to which the O 3 response to reductions in NO X emissions appropriately represent s the trends observed in ambient O 3 following actual reductions in NO X emissions; (2) the extent to which estimated changes in risks in urban study areas are representative of the changes that would be experienced broadly across the U.S. population; and (3) the extent to which the
O 3 response to reductions in precursor emissions could differ with emissio ns reduction strategies that are different from those used in H REA to generate risk estimates. To evaluate the first issue, the H REA conducted a national analysis evaluating trends in monitored ambient O 3 concentrations during a time period when the U.S. experienced large

- scale reductions in NO X emissions (i.e., 2001 to 2010). Analyses of*** E.O. 12866 Review

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Page 164 of 64 7 trends in monitored O 3 indicate that over such a time period, the upper end of the distribution of monitored O 3 concentrations (i.e., indicated by the 95 th percentile) generally decreased in urban and non

- urban locations across the U.S. (U.S. EPA, 2014 a , Figure 8

- 29). D uring this same time period , median O 3 concentrations decreased in suburban and rural locations , and in some urban locations. However , median concentrations i ncreased in some large urban centers (U.S. EPA, 2014 a , Figure 8

- 28). As discussed in the REA, and above (II.C.1), these increases in median concentrations likely reflect the increases in relatively low O 3 concentrations that can occur near important sources of NO X upon reductions in NO X emissions (U.S. EPA, 2014 a , section 8.2.3.1). These patterns of monitored O 3 during a period when the U.S. experienced large reductions in NO X emissions are qualitatively consistent with the modeled response s of
O 3 to reductions in NO X emissions. To evaluate the second issue, the HREA conducted national air quality modeling analyses. These analyses estimated the proportion of the U.S. population living in locations where seasonal averages of daily O 3 concentrations are estimated to decrease in response to reductions in NO X emissions, and the proportion living in locations where such seasonal averages are estimated to increase. Given the close relationship between changes in seasonal averages of daily O 3 concentrations and changes in seasonal mortality and morbidity risk estimates, this analysis informs consideration of the extent to which the risk results in urban study areas represent the U.S. population as a whole. This representativeness analysis indicates that the majority of the U

. S

. population lives in locations where reducing NO X emissions would be expected to result in decreases in warm season averages of daily maximum 8

- hour ambient O 3 concentrations. Because the*** E.O. 12866 Review

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Page 165 of 647 HREA urban study areas tend to underrepresent the populations living in such areas (e.g., suburban, smaller urban, and rural areas ) , risk estimates for the urban study areas are likely to understate the averag e reduction s in O 3 - associated mortality and morbidity risk s that would be experienced across the U.S. population as a whole upon reducing NO X emissions (U.S. EPA, 2014 a , section 8.2.3.2 ). To evaluate the third issue, the HREA assesse d the O 3 air quality r esponse to reducing both NO X and VOC emissions (i.e., in addition to assessing reductions in NO X emissions alone) for a subset of seven urban study areas . As discussed in the PA ( U.S. EPA, 2014c , section 3.2.1), in most of the urban study areas the inclusi on of VOC emissions reductions did not alter the NO X emissions reductions required to meet the current or alternative standards. 72 However, the addition of VOC reductions generally resulted in larger decreases in mid

- range O 3 concentrations (25 th to 75 th percentiles) (US EPA, 2014a, Appendix 4 D , section 4.7). 73 In addition, in all seven of the urban study

areas evaluated, the increases in low O 3 concentrations were smaller for the NO X /VOC scenarios than the NO X alone scenarios (US EPA, 2014a, Appendix 4 D , section 4.7). This was most apparent for Denver, Houston, Los Angeles, New York, and Philadelphia

. Given the impacts on total risk estimates of increases in low O 3 concentrations, these results suggest that in some locations optimized emissions reduction s trategies could

72 The exceptions are Chicago and Denver, for which the HREA risk estimates are based on reductions in both NO X and VOC (U.S. EPA, 2014a, section 4.3.3.1). Emissions of NO X and VOC were reduced by equal percentages, a scenario not likely to reflect the optimal combination for reducing risks. 73 This was the case for all of the urban study areas evaluated, with the exception of New York (U.S. EPA, 2014a, Appendix 4

- D , section 4.7 ).*** E.O. 12866 Review

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Page 166 of 647 result in larger reductions in O 3 - associated mortality and morbidity than indicated by HREA estimates.
S ection 7.4 of the HREA also highlights some additional uncertainties associated with epidemiologic

- based risk estimates ( U.S. EPA, 2014 a ). This section of the HREA identifies and discusses sources of uncertainty and p resents a qualitative evaluation of key parameters that can introduce uncertainty into risk estimates (U.S. EPA, 2014 a , Table
7

- 4) . For several of these parameters , the HREA also presents quantitative sensitivity analyses (U.S. EPA, 2014 a , sections 7.4.2 and 7.5.3). Of the uncertainties discussed in Chapter 7 of the HREA , those related to the application of concentration

- response functions from epidemiologic studies can have particularly important implications for consideration of epidemiology

- based risk estimates , as discussed below

. An important uncertainty is the shape of concentration

- response functions at low ambient O 3 concentrations (U.S. E PA, 2014 a , Table 7

- 4). 74 Consi stent with the ISA conclusion that there is no discernible population threshold in O 3 - associated health effects, the HREA estimates epidemiology

- based mortality and morbidity risks for entire distributions of ambient O 3 concentrations, based on the assumpt ion that concentration

response relationships remain linear over those distributions. In addition, in recognition of the ISA conclusion that certainty in the shape of O 3 concentration

- response functions decreases at low ambient concentrations, the HREA als o estimates total mortality associated with various ambient O 3 concentrations. The PA considers both types of r isk estimates, recognizing greater public health concern for adverse O 3 - attributable effects at

74 A related uncertainty is the existence, or not, of a threshold. The HREA addresses this issue for long

- term O 3 by evaluating risks in models that include potential thresholds (II.D.2.c).*** E.O. 12866 Review

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Page 167 of 647 higher ambient O 3 concentrations (which drive higher exposure concentrations, section
3.2.2 of the PA ( U.S. EPA, 2014c ) ), as compared to lower concentrations. A related uncertainty is that associated with the public health importance of the increases in relatively low O 3 concentrations following air quality adjustment. This uncertainty relates to the assumption that the concentration response function for O 3 is linear, such that that total risk estimates are equally influenced by decreasing high concentrations and increasi ng low concentrations, when the increases and decreases are of equal magnitude. Even on days with increases in relatively low area

- wide average concentrations, resulting in increases in estimated risks, some portions of the urban study

areas could experien ce decreases in high O 3 concentrations. To the extent adverse O 3 - attributable effects are more strongly supported for higher ambient concentrations (which are consistently reduced upon air quality adjustment) , t he impacts on risk estimates of increasing lo w O 3 concentrations reflect an important source of uncertainty. The HREA also notes important uncertainties associated with using a concentration

- response relationship developed for a particular population in a particular location to estimate health risks in different populations and locations (U.S. EPA, 2014 a , Table 7

- 4). As discussed above, concentration

- response relationships derived from epidemiologic studies reflect the spatial and temporal patterns of population exposures during the study. The HREA a pplies concentration

- response relationships from epidemiologic studies to adjusted air quality in study areas that are different from, and often larger in spatial extent than, the areas used to generate the relationships. This approach ensures the inclusio n of the actual nonattainment monitors that often determine the magnitude of emissions reductions for the air quality adjustments throughout the*** E.O. 12866 Review

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Page 168 of 647 urban study areas . This approach also allows the HREA to estimate patterns of health risks more broadly across a larger area, including a broader range of air quality concentrations and a larger population. The HREA notes that it is not possible to quantify the impacts of this uncertainty on risk estimates in most urban case study locations, though the HREA notes t hat mortality e ffect estimates for different portions of the New York City CBSA

- based assessment area vary by a factor of almost 1 0 (U.S. EPA, 2014 a , section 7.5.3). An additional, related uncertainty is that associated with applying concentration

respons e functions from epidemiologic studies to adjusted air quality. Concentration

response functions from the O 3 epidemiologic studies used in the HREA are based on associations between day to day variation in “area

- wide” O 3 concentrations (i.e., averaged across multiple monitors) and variation in health effects. Epidemiologic studies use these area

- wide O 3 concentrations, which reflect the particular spatial and temporal patterns of ambient O 3 present in study locations, as surrogates for the pattern of O 3 exposures experienced by study populations. To the extent adjusting O 3 concentrations to just meet the current standard results in important alterations in the spatial and/or temporal patterns of ambient O 3 , there is uncert ainty in the appropriateness of applying concentration

- response functions from epidemiologic studies (which necessarily reflect a different air quality distribution than the modelled distribution) to estimate health risks associated with adjusted O 3 air qu ality. In particular, this uncertainty could be important to the extent that (1) factors associated with space modify the effects of O 3 on health or (2) spatial mobility is a key driver of individual

- level exposures. Although the impact of this uncertainty on risk estimates cannot be quantified (U.S. EPA, 2014 a , Table 7

- 4), it*** E.O. 12866 Review

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Page 169 of 647 has the potential to become more important as model adjustment results in larger changes in spatial and temporal patterns of ambient O 3 concentrations across urban study areas

. The us e of a national concentration

- response function to estimate respiratory mortality associated with long

- term O 3 is a source of uncertainty. Risk estimates generated in sensitivity analyses using region

- specific effect estimates differ substantially from the core estimates based on a single national

- level effect estimate (U.S. EPA, 2014a; Table 7

- 14). Furthermore, the risk estimates generated using the regional effect estimates display considerable variability across urban study areas (U.S. EPA, 2014a; Table 7

- 14), reflecting the substantial variability in the underlying effect estimates (see Jerrett et al., 2009, Table 4). While the results of the HREA sensitivity analyses evaluating this uncertainty point to the potential for regional heterogeneity in the lo ng term risk estimates, the relatively large confidence intervals associated with regional effect estimates resulted in the HREA conclusion that staff does not have confidence in the regionally based risk estimates themselves. Finally, the HREA does not q uantify any reductions in risk that could be associate d with reductions in the ambient concentrations of pollutants other than O 3 , resulting from control of NO X . For example as discussed in chapter 2 of the PA ( U.S. EPA, 2014c ) , NO X emissions contribute to ambient NO 2 , and NO X and VOCs can contribute to secondary formation of PM 2.5 constituents, including ammonium sulfate (NH 4 SO 4 ), ammonium nitrate (NH 4 NO 3 ), and organic carbon (OC). Therefore, at some times and in some locations, con trol strategies that would reduce NO X emissions (i.e., t o meet an O 3 standard) could reduce ambient concentrations of NO 2 and PM 2.5 , resulting in health benefits beyond those directly associated with reducing ambient O 3 concentrations.*** E.O. 12866 Review

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Page 170 of 647 D

. Conclusions on t he Adequacy of the Current Primary Standard The initial issue to be addressed in the current review of the primary O 3 standard is whether, in view of the advances in scientific knowledge and additional information, the existing standard should be revised. In evaluating whether it is appropriate to retain or revise the current standard, the Administrator ’s considerations build upon those in the
2008 review, including consideration of the broader body of scientific evidence and exposure and health risk information now available , as summarized above (II.A to II.C)

. I n developing conclusions on the adequacy of the current primary O 3 standard , t he Administrator take s into account both evidence

- based and quantitative exposure

- and risk

- based considerations . Evidence

- based considerations include the assessment of evidence from controlled human exposure, animal toxicological, and epidemiologic studies for a variety of health endpoints. The Administrator focuses on health endpoints for which the evidence is st rong enough to support a "causal" or a “likely to be causal” relationship, based on the ISA's integrative synthesis of the entire body of evidence. The Administrator's c onside ration of quantitative exposure and risk information draws from the results of th e exposure and risk assessments presented in the HREA

. The Administrator's consideration of the evidence and exposure/risk information is informed by the considerations and conclusions presented in the PA (U.S. EPA, 2014c)

. T he purpose of the PA is to he lp "bridge the gap" between the scientific and technical information assessed in the ISA and HREA, and the policy decisions that are required of the Administrator (U.S. EPA, 2014c, Chapter 1)

. T he PA's evidence

- based and exposure

- /risk

- based considerations and conclusions are summarized below in sections II.D.1 to II.D. 3. CASAC advice to the Administrator and public commenter*** E.O. 12866 Review

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Page 171 of 647 views are summarized in section II.D.4. Section II.D.5 presents the Administrator’s proposed conclusions concerning the adequacy of the public health protection provided by the current standard , and her proposed decision to revise that standard

. 1

. Summary of Evidence

- Based Considerations in the PA In considering the available scientific evidence, t he PA evaluates the O 3 concentratio ns in health effects studies ( U.S. EPA, 2014c , section 3.1.4). Specifically, the
PA characterize s the extent to which effects have been reported for the O 3 exposure concentrations evaluated in controlled human exposure studies and over the distributions of ambient O 3 concentrations in locations where epidemiologic studies have been conducted. The se considerations, as they relate to the adequacy of the current standard, are presented in detail in section 3.1.4 of the PA (U.S. EPA, 2014c) and are summarized b riefly below for controlled human exposure and epidemiologic panel studies (II.D.1.a), epidemiologic studies of short

- term O 3 exposures (II.D.1.b), and epidemiologic studies of long

- term O 3 exposures (II.D.1.c). Section II.D.1.d summarizes the PA conclusio ns based on consideration of the scientific evidence. a. Concentrations in controlled human exposure and panel studies The evidence from controlled human exposure studies and panel studies is assessed in section 6.2 of the ISA (U.S. EPA, 2013) and is summarized in section 3.1.2 of the PA ( U.S. EPA, 2014c ). As discussed above (II.B), c ontrolled human exposure studies have generally been conducted with young, healthy adults, and have evaluated exposure durations less than 8 hours. P anel studies have eval uated a wider range of study*** E.O. 12866 Review

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Page 172 of 647 populations, including children, and have generally evaluated associations with O 3 concentrations averaged over several hours ( U.S. EPA, 2013 , section 6.2.1.2 ). 75
As summarized above (II.B) , a large number of controlled human exposure studies have reported lung function decrements, respiratory symptoms, airway inflammation, airway hyperresponsiveness, and/or impaired lung host defense in young, healthy adults engaged in moderate, intermittent exertion, following 6.6

- hour O 3 exp osures. These studies have consistently reported such effects following exposures to
O 3 concentrations of 80 ppb or greater. Available studies have also evaluated most of these effects (i.e., lung function decrements, respiratory symptoms, airway inflammat ion) following exposures to O 3 concentrations below 75 ppb

. Table 3

- 1 in the PA highlights the group mean results of individual controlled human exposure studies that have evaluated exposures of healthy adults to O 3 concentrations below 75 ppb ( U.S. EPA,
2 014c )

. The studies included in Table 3

- 1 of the PA indicate a combination of lung function decrements and respiratory symptoms following exposures to O 3 concentrations as low as 72 ppb, 76 and lung function decrements and airway inflammation following exposures to O 3 concentrations as low as 60 ppb. The PA also notes consistent results in some panel studies of O 3 - associated lung function decrements

. In particular , the PA notes that epidemiologic panel studies in children and adults indicate O 3 - associa ted lung function decrements when on

- site

75 The PA focuses on panel studies that used on

- site monito ring, and that are highlighted in the ISA for the extent to which monitored ambient O 3 concentrations reflect exposure concentrations in their study populations (U.S. EPA, 2013, section 6.2.1.2). 76 As noted above, for the 70 ppb exposure concentration Sche legle et al. (2009) reported that the actual 6.6

- hour mean exposure concentration was 72 ppb.*** E.O. 12866 Review

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Page 173 of 647 monitored concentrations were below 75 ppb, with the evidence becoming less consistent at lower O 3 concentrations (U.S. EPA, 2014c, section 3.1.4.1). Thus, controlled human exposure studies and panel studies have reported respiratory effects in adults and children following exposures to O 3 concentrations below 75 ppb. The PA notes that s uch impairments in respiratory function have the potential to be adverse, based on ATS guidelines for adversity and based on advic e from CASAC ( Frey, 2014c ) ( U.S. EPA, 2014c , section 3.1.3). In addition, the PA notes that if they become serious enough, these respiratory effects could lead to the types of clearly adverse effects commonly reported in O 3 epidemiologic studies (e.g., res piratory emergency department visits, hospital admissions). Therefore, the PA concludes that the respiratory effects experienced following exposures to O 3 co ncentrations lower than 75 ppb could be adverse in some individuals, particularly if experienced by members of at

risk populations (e.g., people with asthma , children). 77 b. Concentrations in epidemiologic studies

– short

- term The PA also considers distributions of ambient O 3 concentra tions in locations where epidemiologic studies have evaluated O 3 - associated hospital admissions,
emergency department visits, and/or mortality ( U.S. EPA, 2014c , section 3.1.4.2)

. When considering epidemiologic studies within the context of the current stan dard, the PA emphasize s those studies conducted in the U.S. and Canada. Such studies reflect air quality and exposure patterns that are likely more typical of the U.S. population than the

77 These effects were reported in healthy individuals. Consistent with past CASAC advice (Samet, 2011), it is a reasonable inference that the effects would be greater in magnitude and potential severity for at

- risk groups. See National Environmental Developm ent Ass’n Clean Air Project v. EPA, 686 F. 3d 803, 811 (D.C. Cir. (2012) (making this point).*** E.O. 12866 Review

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Page 174 of 647 air quality and exposure patterns reflected in studies conducted out side the U.S. and Canada ( U.S. EPA, 2014c , section 1.3.1.2)

. 78 The PA also emphasizes studies reporting associations with effects judged in the ISA to be robust to confounding by other factors, including co

- occurring air pollutants. In addition to these fac tors, the PA consider s the statistical precision of study results, the extent to which studies report associations in at

risk populations, and the extent to which the biological plausibility of associations at various ambient O 3 concentrations is supported by controlled human exposure and/or animal toxicological studies. T hese considerations help inform the range of ambient O 3 concentrations over which the evidence indicates the most confidence in O 3 - associated health effect s, and the range of concentration s over which confidence in such associations is appreciably lower. This section summarizes the PA conclusions regarding the extent to which health effect associations have been reported for ambient O 3 concentrations likely to have met the current O 3 standard. Section II.D.1.b.i summarizes PA analyses an d conclusions based on analyses evaluating the extent to which epidemiologic studies have reported health effect associations in locations that would likely have met the current O 3 standard

. Section II .D.1.b.ii summarizes PA conclusions based on analyses evaluating the O 3 air quality in locations where epidemiologic studies have characterized confidence intervals around cut point analyses or concentration

- response functions. Section II.D.1.b.iii summari zes the important uncertainties in these analyses. i. Associations in locations likely meeting current standard

78 Nonetheless, the PA recognizes the importance of all studies, including international studies, in the ISA’s assessment of the weight of the evidence that infor ms causality determinations.*** E.O. 12866 Review

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Page 175 of 647 The PA considers the extent to which U.S. and Canadian epidemiologic studies have reported associations with mortality or morbidity in locatio ns that would likely have met the current O 3 standard during the study period ( U.S. EPA, 2014c , section 3.14.2). Addressing this issue can provide important insights into the extent to which O 3 - health effect associations are present for distributions of ambient O 3 concentrations that would be allowed by the current standard. To the extent associations are reported in study areas that would have met the current standard, those associations indicate that the current standard could allo w the types of clearly adverse O 3 - associated effects reported in epidemiologic studies (e.g., mortality, hospital admissions, emergency department visits). 79 In considering these analyses, the PA also notes that the lack of such associations does not indica te that the current standard would prevent O 3 - associated health effects. Rather, the lack of health effect associations in locations meeting the current standard indicates increasing uncertainty in the extent to which O 3 - associated health effects would per sist upon reducing O 3 precursor emissions in order to meet the current standard. The PA identifies U.S. and Canadian studies of respiratory hospital admissions, respiratory emergency department visits, and mortality (total, respiratory, cardiovascular)
fr om the ISA (U.S. EPA, 2013, Tables 6

- 28, 6

- 42, and 6

- 53, and section 6.2.8; U.S. EPA, 2014c , Appendix 3D). Analysis of study area air quality indicates that the large majority of epidemiologic study areas evaluated would have violated the current standard during study periods ( U.S. EPA, 2014c , Appendix 3 D). However, the PA notes that a single

- city

79 See ATA III, 283 F.3d at 370 (EPA justified in revising NAAQS when health effect associations are observed in epidemiologic studies at levels allowed by the NAAQS).*** E.O. 12866 Review

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Page 176 of 647 study conducted in Seattle, a location that would have met the current standard over the entire study period , reported positive and statistically significant asso ciations with respiratory emergency department visits in children and adults (Mar and Koenig, 2009). The PA also notes four Canadian multicity studies that reported positive and statistically significant associations with respiratory morbidity or mortality , and for which the majority of study cities would have met the current standard over the entire study periods (Cakmak et al., 2006; Dales et al., 2006; Katsouyanni et al., 2009; Stieb et al., 2009). 80 The PA concludes that the single

- city study by Mar an d Koenig (2009) indicates the presence of associations with mortality and morbidity for an ambient distribution of
O 3 that would have met the current standard (U.S. EPA, 2014c, section 3.1.4.2). T he PA notes that interpretation of the air quality concentrations in the multicity study locations evaluated in this review is complicated by uncertainties in the extent to which multicity effect estimates can be attributed to ambient O 3 in the majority of locations, which would have met the current standa rd, versus O 3 in the smaller number of locations that would have violated the standard. While acknowledging this uncertainty in interpreting air quality in multicity studies, the PA notes that multicity effect estimates in the four studies cited above are largely influenced by locations meeting the current standard (i.e., given that most study areas would have met this standard). Therefore, the PA concludes that Canadian multicity studies, in addition to the single

- city study in Seattle, suggest confidence in the presence of associations with mortality and morbidity for ambient

80 In addition, a study by Vedal et al. (2003) was included i n the 2006 CD ( U.S. EPA, 2006a ). This study reported positive and statistically significant associations with mortality in Vancouver during a time period when the study area would have met the current standard (U.S. EPA, 2007). This study was not assessed in the ISA in the current review (U.S. EPA, 2013).*** E.O. 12866 Review

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Page 177 of 647 distributions of O 3 that would have met the current standard (U.S. EPA, 2014c, section 3.1.4.2). ii. Air quality associated with cut point analyses and c oncentration

- response function s The PA also considers the extent to which additional epidemiologic studies of mortality or morbidity, specifically those conducted in locations that would have violated the current standard, can inform consideration of adequacy of the current standard ( U.S. EPA, 2014c , section 3.1.4.2). In doing so, the PA notes that health effect associations reported in epidemiologic studies are influenced by the full distributions of ambient O 3 concentrations, including concentrations below the level of the current s tandard. The PA focuses on studies that have explicitly characterized O 3 health effect associations, including confidence in those associations, for various portions of distributions of ambient O 3 concentrations.
T he U.S. multicity study by Bell et al. (2006) reported health effect associations for air quality subsets restricted to ambient O 3 concentrations below one or more predetermined cut points . In these analyses, effect estimates were based only on the

s ubsets of days contributing to averaged O 3 concentrations below cut point s ranging from 5 to 60 ppb (see Figure 2 in Bell et al., 2006). 81 The PA notes that s uch “cut point” analyses can provide information on the magnitude and statistical precision of effect estimates for defined distributions of ambient concentrations, which may in some cases includ e distributions that would meet the current standard (U.S. EPA, 2014c, section 3.1.4.2)

. T he cut points below which confidence intervals become notably wider depend

81 In the published study, 2

- day rolling averages of 24

- hour average O 3 concentrations were calculated in each study location (based on averaging across monitors in study locations with multiple monitors).*** E.O. 12866 Review

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Page 178 of 647 in large part on data density and, th erefore, cut point analyses provide insight into the ambient concentrations below which the available air quality information becomes too sparse to support conclusions about the nature of concentration

- response relationships with a high degree of confidenc e (U.S. EPA, 2014c, section 3.1.4.2).
T he PA considers the extent to which the cut

- point analyses reported by Bell et al. (2006) indicate health effect associations for distributions of ambient O 3 concentrations that would likely have met the current sta ndard

. The PA particularly focuse s on t he lowest cut

- point for which the association between O 3 and mortality was reported to be statistically significant ( i.e., 30 ppb, based on visual inspection of Figure 2 in the published study). Based on the O 3 air quality concentrations that met the criteria for inclusion in the 30 ppb cut point analysis, 95% of study areas had 3

- year averages of annual 4 th highest daily maximum 8

- hour O 3 concentration at or below 75 ppb over the entire study period (U.S. EPA, 2014c, section 3.1.4.2, Table 3

- 6). Though there are important uncertainties in this analysis, as discussed below, the PA concludes that these results suggest that the large majority of air quality distributions that provided the basis for the positive and statistically significant association with mortality at the 30 ppb cut point would likely have met the current O 3 standard. The PA also analyzes air quality for studies that have reported confidence intervals around concentration

- response functions over distributions of ambient O 3 concentrations ( U.S. EPA, 2014c , section 3.1.4.2)

. Confidence intervals around concentration

- response functions can provide insights into the range of ambient concentrations over which the study indicates the most confidence in the reported health effect associations (i.e., where confidence intervals are narrowest), and into the range of*** E.O. 12866 Review

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Page 179 of 647 ambient concentrations below which the study indicates that uncertainty in the nature of such associations becomes notably greater (i.e., where confidence intervals become markedly wider). As with cut point analyses, t he concentrations below which confidence intervals become markedly wider are intrinsically related to data density, and do not

ne cessarily indicate the absence of an association. The PA focuses on two U.S. single

- city studies that have reported confidence intervals around concentration

- response functions ( Silverman and Ito, 2010 ; Strickland e t al., 2010)

. Based on the published analyses, the PA identifies the range s of ambient O 3

c oncentrations over which the se studies indicate the highest degree of confidence in the reported linear concentration

- response functions (U.S. EPA, 2014c, section 3.1.4.2) . F or the lower end s of the se ranges , air quality analyses in the PA indicate that o v er 99% of days had maximum 8

- hour O 3 concentrations (i.e., from highest monitors in study locations) at or below 75 ppb. For comparison, the annual 4 th highest daily maximum 8

- hour O 3 concentration generally corresponds to the 98 th or 99 th percentile of th e seasonal distribution, depending on the length of the O 3 season. The PA concludes that these analyses of air quality data from the study locations evaluated by Silverman and Ito (2010) and Strickland et al. (2010) indicate a relatively high degree of confidence in reported statistical associations with respiratory health
outcomes on days when vir tually all monitored 8

- hour O 3 concentrations were 75 ppb or below (U.S. EPA, 2014c, section 3.1.4.2) . Though these analyses do not identify true design values, the presence of O 3 - associated respiratory effects on such days provides insight into the types of health effects that could occur in locations with maximum ambient O 3 concentrations at or below the level of the current standard

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Page 180 of 647 iii. Important Uncertainties The PA also notes that there are important uncertainties associated with analyses of air q uality in locations of epidemiologic studies. For example , t he PA notes that while multicity studies generally have greater statistical power and geographic coverage than single

- city studies , there is often greater uncertainty in conclusions about the exte nt to which multicity effect estimates reflect associations with air quality meeting the current standard (U.S. EPA, 2014c, section 1.3.1.2.1). This is particularly the case for the multicity studies evaluated in this review with some study locations meeti ng the current standard and others violating that standard. Specifically f or the four Canadian multicity studies discussed above, t he PA notes that interp retation of air quality information is complicated by uncertainties in the extent to which multicity effect estimates can be attributed to ambient O 3 in the majority of locations, which would have met the current standard, versus O 3 in the smaller number of locations that would have violate d the standard. The PA also notes important uncer tainties in multicity studies that evaluate the potential for thresholds to exist, as was done in the study by Bell e t al. (2006). Specifically, the ISA highlights the regional heterogeneity in O 3 health e ffect associations as a factor that could obscure the presence of thresholds, should they exist, in multicity studies (U.S. EPA, 2013, sections 2.5.4.4 and 2.5.4.5). The ISA notes that community characteristics (e.g., activity patterns, housing type, age d istribution, prevalence of air conditioning) could be important contributors to reported regional heterogeneity (U.S. EPA, 2013, section 2.5.4.5). Given this heterogeneity, the ISA concludes that “a national or combined analysis may not be appropriate to i dentify whether a threshold exists in the*** E.O. 12866 Review

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Page 181 of 647 O 3 - mortality [concentration

- response] relationship” (U.S. EPA, 2013, p. 2

- 33). This represents an important source of uncertainty when characterizing confidence in reported concentration

- response relationships over distributions of ambient O 3 concentrations, based on multicity studies. The PA notes that t his uncertainty becomes increasingly important when interpreting concentration

- response relationships at lower ambient O 3 concentrations, particularly those concent rations corresponding to portions of distributions where data density decreases notably (U.S. EPA, 2014c, section 3.1.4.2)

. An other important uncertainty , related specifically to the PA analysis of cut points by Bell et al. (2006) , is that EPA staff was unable to obtain the air quality data used to generate the cut

- point analyses in the published study (U.S. EPA, 2014c, section 3.1.4.2)

. Therefore, the analyses in the PA identified 2

- day averages of 24

- hour O 3 concentrations in study locations using the a ir quality data available in AQS, combined with the published description of study area definitions. A n important uncertainty in this approach
i s the extent to which the PA appropriately recreate d the cut

- point analyses in the published study (U.S. EPA, 20 14c, section 3.1.4.2)

. An uncertainty that applies to epidemiologic studies in general is the extent to which reported health effects are caused by exposures to O 3 itself, as opposed to other factors such as co

- occurring pollutants or pollutant mixtures

. T he PA notes that this uncertainty becomes an increasingly important consideration as health effect associations are evaluated at lower ambient O 3 concentrations. In particular, there is increasing uncertainty as to whether the observed associations remain plausibly related to exposures to ambient O 3 , rather than to the broader mix of air pollutants present in the ambient air. In considering the pot ential importance of this uncertainty at the relatively low ambient*** E.O. 12866 Review

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Page 182 of 647 O 3 concentrations that are the focus of the PA analyses, the PA notes that Silverman and Ito (2010) and Strickland (2010) reported O 3 health effect associations in co

- pollutant models, 82 pr oviding support for associations with O 3 itself (U.S. EPA, 2014c, section 3.1.4.2). The PA also concludes that air quality analyses indicate c oherence with the results of experimental studies (i.e., in which the study design dictates that exposures to
O 3 i tself are res ponsible for reported effects) , and are consistent with the occurrence of
O 3 - attributable respiratory hospital admissions and emergency department visits, even when virtually all monitored concentrations were below the level of the current sta ndard (U.S. EPA, 2014c, section 3.1.4.2, Tables 3

- 4, 3

- 5)

.

c. Concentrations in e pidemi ologic s tudies

– long

- term The PA also considers the extent to which epidemiologic studies employing longer

- term ambient O 3 concentration metrics inform our understand ing of the air quality conditions associated with O 3 - attributable health effects, and specifically inform consideration of the extent to which such effects could occur under air quality conditions meeting the current standard ( U.S. EPA, 2014c , section 3.1. 4.3). Unlike for the studies of short

- term O 3 discussed above, the available U.S. and Canadian epidemiologic studies evaluating long

- term ambient O 3 concentration metric s have not been conducted in locations likely to have met the current 8

- hour O 3 standard during the study period , and have not reported concentration

- response functions that indicate confidence in health effect associations at O 3 concentrations meeting the current standard ( U.S. EPA, 2014c , section 3.1.4.3 )

. Therefore, although these studies contribute to understanding of health

82 In addition, Bell et al. (2006) reported that, based on a previous study (Bell et al., 2004), associations with mortality were robust to the inclusion of PM 10 in the model.*** E.O. 12866 Review

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Page 183 of 647 effects associated with long

- term or repeated exposures to ambient O 3 , consideration of study area air quality does not inform consideration of the extent to which those health effects may be occurring in loca tions that me e t the current standard. d. PA conclusions based on consideration of the evidence As discussed above (II.D.1.a to II.D.1.c), in considering the available scientific evidence as it relates to the degree of public health protection provided by the current primary O 3 standard, the PA evaluates the extent to which health effects have been reported for the O 3 exposure concentrations evaluated in controlled human exposure studies and over the distributions of ambient O 3 concentrations in locations where epidemiologic studies have been conducted. The PA concludes that (1) t he evidence from controlled human exposure studies provides strong support for the occurrence of adverse respiratory effects following exposures to O 3 concentrations below the leve l of the current standard and that (2) e pidemiologic studies provide support for the occurrence of adverse respiratory effects and mortality under air quality conditions that would likely meet the current standard. In further considering the public health protection provided by the current standard, the PA next considers the results of exposure and health risk
assessments. 2

. Summary of Exposure

- and Risk

- Based Considerations in the PA In order to further inform judgments about the potential public health implications of the current O 3 NAAQS, the PA considers the exposure and risk assessments presented in the HREA ( U.S. EPA, 2014c , section 3.2). Overviews of these exposure and risk assessments, including summaries of key results and uncertaint ies , are provided in section II.C ab ove. This section summarizes key observations from the PA related to the*** E.O. 12866 Review

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Page 184 of 647 adequacy of the current O 3 NAAQS, based on consideration of the HREA exposure assessment (II.D.2.a), lung function risk assessment (II.D.2.b), and mortality/morbidity risk assessments (II.D.2. c)

. a. Exposure assessment

– k ey observations As discussed above (II.C.2) , t he exposure assessment provides estimates of the number and percent of people who would experience exposures of concern at or above be nchmark concentrations of 60, 70, and 80 ppb. B enchmarks reflect exposure concentrations at which O 3 - induced respiratory effects are known to occur in some healthy adults engaged in moderate, intermittent exertion, based on evidence from controlled human e xposure studies ( U.S. EPA, 2014c , section 3.1.2.1; U.S. EPA, 2013, section 6.2).
T he PA focuses on exposure estimates in children. C ompared to re cent (i.e., unadjusted) air quality, the PA notes that adjusting air quality to just meet the current O 3 NAAQS consistently reduces the estimated occurrence of exposures of concern in children (U.S. EPA, 2014a , Appendix 5 F ). When averaged over the years evaluated in the HREA, reductions of up to about 70% were estimated . These reductions in estimated
exposur es of concern , relative to unadjusted air quality, reflect the consistent reductions in the highest ambient O 3 concentrations upon model adjustment to just meet the current standard ( U.S. EPA, 2014c , section 3.2.1; U.S. EPA, 2014 a , Chapter 4). Such reducti ons in estimated exposures of concern are evident throughout urban study areas , including in urban cores and in surrounding areas (U.S. EPA, 2014 a , Appendix 9A). Based o n Figures 3

- 7 to 3

- 10 in the PA ( U.S. EPA, 2014c ) , and the asso ciated details describe d in the HREA (U.S. EPA 2014a, Chapter 5), the PA further highlights*** E.O. 12866 Review

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Page 185 of 647 key observations with regard to exposures of concern in children that are estimated to be allowed by the current standard. These key observations are summarized below for exposures of con cern > 60, 70, and 80 ppb. For exposures of concern at or above 60 ppb, the PA highlights the following key observations: (1) On average over the years 2006 to 2010, the current standard is estimated to allow approximately 10 to 18% of children in urban stud y areas to experience one or

more exposure s of concern at or above 60 ppb. Summing across urban study

areas , these percentages correspond to almost 2.5 million children experiencing approximately 4 million exposures of concern at or above 60 ppb during a s ingle
O 3 season . Of these children, almost 250,000 are asthmatic s . (2) On average over the years 2006 to 2010, the current standard is estimated to allow approximately 3 to 8% of children in urban study areas to experience two or more exposures of concern to O 3 concentrations at or above 60 ppb. Summing across the urban study areas , these percentages correspond to almost 900,000 children (including almost 90,000 asthmatic children) estimated to experience at l east two O 3 exposure concentrations at or above 60 ppb during a single O 3 season. (3) In the worst

- case years (i.e., those with the largest exposure estimates ) , t he current standard is estimated to allow approximately 1 0 to 25% of children to experience

o ne o r more exposure s of concern at or above 60 ppb, and approximately 4 to 14% to experience two or more exposures of concern at or above 60 ppb. For exposures of concern at or above 70 ppb, the PA highlights the following key observations:*** E.O. 12866 Review

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Page 186 of 647 (1) On average over t he years 2006 to 2010, the current standard is estimated to allow up to approximately 3 % of children in urban study areas to experience o ne or

more exposure s of concern at or above 7 0 ppb. Summing across urban study

areas , almost 400,000 children (includin g almost 4 0,000 asthmatic children ) are estimated to experience O 3 exposure concentrations at or above 7 0 ppb during a single O 3 season. (2) On average over the years 2006 to 2010, the current standard is estimated to allow less than 1% of children in urban study areas to experience two or more exposures of concern to O 3 concentrations at or above 70 ppb. (3) In the worst

- case years , t he current standard is estimated to allow approximately 1
to 8 % of children to experience o ne or more exposure s of concern at or above 70 ppb, and up to approximately 2% to experience two or more exposures of

concern, at or above 7 0 ppb. For exposures of concern at or above 80 ppb , the PA highlights the observation that t he current standard is estimated to allow about 1% or fewer children in urban study areas to experience exposures of concern at or above 80 ppb, even in years with th e highest exposure estimates. b. L ung function risk assessment

– key o bservations As discussed above (II.C.3.a) , the HREA estimates risks of mo derate to large lung function decrements (i.e., FEV 1 decrements > 10%, 15%, or 20%) in school

- aged children (ages 5 to 18), asthmatic school

- aged children, and the general adult population for 15 urban study areas

. As for exposures of concern, the PA focus es on lung function risk estimates in children (including children with asthma).*** E.O. 12866 Review

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Page 187 of 647 Compared to risks associated with recent air quality, risk estimates for air quality just meeting the current standard are consistently smaller across urban study areas (U.S. EPA, 2014 a , Appendix 6 B ). When averaged over the years evaluated in the HREA, risk reductions of up to about 40 % were estimated compared to recent air quality. These reductions reflect the consistent decreases in relatively high ambient O 3 concentrations upon adjustment to just meet the current standard (U.S. EPA, 2014a, Chapter 4). Such reductions in estimated lung function risks are evident throughout urban study areas , including in urban cores and in surrounding areas (U.S. EPA, 2014, Ap pendix 9A). Based on Figures 3

- 11 to 3

- 14 in the PA ( U.S. EPA, 2014c ) , and the associated details described in the HREA (U.S. EPA 2014a, chapter 6), the PA highlights key observations with regard to lung function risks estimated in children for air quality adjusted to just meet the current standard. These key observations are presented below for
FEV 1 decrements > 10, 15, and 20%

. With regard to decrements > 10%, the PA highlights the following key observations: (1) On average over the years 2006 to 2010, the current standard is estimated to allow approximately 1 4 to 19 % of children in urban study areas to experience one or

more lung function decrements > 10% . Summing across urban study areas , this correspond s to approximately 3 million children experiencing 15 million O 3 - induced lung function decrements > 10% during a single O 3 season . Of these children, about 30 0,000 are asthmatic s . (2) On average over the years 2006 to 2010, the current standard is estimated to allow approximately 7 to 12% of children in urban study areas to experience two or*** E.O. 12866 Review

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Page 188 of 647 more O 3 - induced lung function decrements > 10%. Summing across the urban study areas , this corresponds to almost 2 million children (including almost 200,000 asthmatic children) estimated to experience two or more O 3 - induce d lung function decrements greater than 10% during a single O 3 season. (3) In the worst

- case years , the current standard is estimated to allow approximately
17 to 23 % of children in urban study areas to experience one or more lung function decrements > 10% , a nd approximately 10 to 14% to experience two or

more O 3 - induced lung function decrements > 10%

. With regard to decrements > 15%, the PA highlights the following key observations: (1) On average over the years 2006 to 2010, the current standard is estimated to allow approximately 3 to 5 % of children in urban study areas to experience one or more lung function decrements > 15% . Summing across urban study areas , this correspond s to approximately 800,000 children (including approximately 8 0,000 asthmatic childre n ) estimated to experience at least one O 3 - induced lung function decrement > 15% during a single O 3 season. (2) On average over the years 2006 to 2010, the current standard is estimated to allow approximately 2 to 3% of children in urban study areas to experience two or more
O 3 - induced lung function decrements > 15%. (3) In the worst

- case years, the current standard is estimated to allow approximately 4
to 6 % of children in urban study areas to experience one or more lung function decrements > 15% , and approximately 2 to 4% to experience two or more O 3 - induced lung function decrements > 15%

. With regard to decrements > 20%, the PA highlights the following key observations:*** E.O. 12866 Review

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Page 189 of 647 (1) On average over the years 2006 to 2010, the current standard is estimated to all ow approximately 1 to 2 % of children in urban study areas to experience one or more lung function decrements > 20% . Summing across urban study areas , this correspond s to approximately 300,000 children (including approximately 3 0,000 asthmatic children ) est imated to experience at least one O 3 - induced lung function decrement > 20% during a single O 3 season. (2) On average over the years 2006 to 2010, the current standard is estimated to allow less than 1% of children in urban study areas to experience two or more O 3 - induced lung function decrements > 20%. (3) In the worst

- case years , the current standard is estimated to allow approximately 2 to 3 % of children to experience one or more lung function decrements > 20% , and less than 2% to experience two or more O 3 - induced lung function decrements > 20%

. c. Mortality and morbidity risk assessment s

– key observations As discussed above (II.C.3.b), r isk estimates based on epidemiologic studies can provide perspective on the most serious O 3 - associated public health outcomes (e.g., mortality, hospital admissions, emergency department visits) in populations that often include at

- risk groups. T he HREA estimates such O 3 - associated risks in 12 urban study

areas 83 using concentration

- response relat ionships drawn from epidemiologic studies. These concentration

- response relationships are based on “area

- wide” average O 3

83 The 12 urban areas evaluated are Atlanta, Baltimore, Boston, Cleveland, Denver, Detroit, Houston, Los Angeles, New York, Philadelphia, Sacramento, and St. Louis. Morbidity endpoints were evaluated in subsets of these areas, based on availability of appropr iate studies (U.S. EPA, 2014a, Chapter 7).*** E.O. 12866 Review

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Page 190 of 647 concentrations. 84 The HREA estimates risks for the years 2007 and 2009 in order to provide estimates of risk for a year with generally higher O 3 concentrations (2007) and a year with generally lower O 3 concentrations (2009) (U.S. EPA, 2014a, section 7. 1.1 )

. In considering these estimates, the PA notes that HREA conclusions reflect somewhat lower confidence in epidemiologic

- based risk estimates than in estimates of O 3 exposures of concern and O 3 - induced lung function decrements (U.S. EPA, 2014a, section 9.6 ). In particular, the HREA highlights the unexplained heterogeneity in effect estimates between locations, the potential for exposur e measurement errors, and uncertainty in the interpretation of the shape of concentration

- response functions at lower
O 3 concentrations (U.S. EPA, 2014a, section 9.6). The HREA also concludes that lower confidence should be placed in the results of the ass essment of respiratory mortality risks associated with long

- term O 3 exposures, primarily because that analysis is based on only one study, though that study is well

- designed, and because of the uncertainty in that study about the existence and identificati on of a potential threshold in the concentration

response function (U.S. EPA, 2014a, section 9.6). These and other uncertainties are considered in the PA in reaching conclusions on the current and alternative standards (U.S. EPA, 2014c, sections 3.4, 4.6).

84 In the epidemiologic studies that provide the health basis for HREA risk assessments, concentration

- response relationships are based on daytime O 3 concentrations, averaged across multiple monitors within study areas. These daily averages are used as surrogates for the spatial and temporal patterns of exposures in study populations. Consistent with this approach, the HREA epidemiologic

- based risk estimates also utilize daytime O 3 concentrations, averaged across m onitors, as surrogates for population exposures. In this notice, these averaged concentrations are referred to as “area

- wide” O 3 concentrations. Area

- wide concentrations are discussed in more detail in section 3.1.4 of the PA (U.S. EPA, 2014c).*** E.O. 12866 Review

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Page 191 of 647 Key observations from the PA are summarized below for mortality and morbidity risks associated with air quality adjusted to simulate just meeting the current O 3 NAAQS

. These include key observations for estimates of total ( nonaccidental ) mortality associ ated with short

- term O 3 concentrations, respiratory morbidity associated with short

- term O 3 concentrations, and respiratory morta lity associated with long

- term O 3 concentrations ( U.S. EPA, 2014c , section 3.2.3.2). With regard to total mortality or morbidity associated with short

- term O 3 , the PA notes the following: (1) When air quality was adjusted to the current standard for the 2007 model year (the year with generally “higher” O 3 - associated risks), 10 of 12 urban study areas exhibited either decrea ses or virtually no change in estimates of the number of O 3 - associated deaths (U.S. EPA, 2014a, Appendix 7B). Increases were estimated in*** E.O. 12866 Review

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Page 192 of 647 two of the urban study areas (Houston, Los Angeles) 85 (U.S. EPA, 2014 a , Appendix 7B). 86 (2) In focusing on total risk, the c urrent standard is estimated to allow thousands of
O 3 - associated deaths per year in the urban study areas . In focusing on the risks associated with the upper portions of distributions of ambient concentrations (area

- wide concentrations > 40, 60 ppb), the c urrent standard is estimated to allow hundreds to thousands of O 3 - associated deaths per year in the urban study areas

. (3) The current standard is estimated to allow tens to thousands of O 3 - associated morbidity events per year (i.e., respiratory

- related hospi tal admissions, emergency department visits, and asthma exacerbations)

. With regard to r espiratory mortality associated with long

- term O 3 , the PA notes the following:

85 As discussed above (II.C.1), in locations and time periods when NO X is predominantly contributing to O 3 formation (e.g., downwind of important NO X sources, where the highest O 3 concentrations often occur), model

- based adjustment to the current and alterna tive standards decreases estimated ambient O 3 concentrations compared to recent monitored concentrations (U.S. EPA, 2014a, section 4.3.3.2). In contrast, in locations and time periods when NO X is predominantly contributing to O 3 titration (e.g., in urban c enters with high concentrations of NO X emissions, where ambient O 3 concentrations are often suppressed and thus relatively low), model

- based adjustment increases ambient O 3 concentrations compared to recent monitored concentrations (U.S. EPA, 2014a, sectio n 4.3.3.2). Changes in epidemiology

- based risk estimates depend on the balance between the daily decreases in high O 3 concentrations and increases in low O 3 concentrations following the model

- based air quality adjustment

. Commenting on this issue, CASAC no ted that “controls designed to reduce the peak levels of ozone (e.g., the 4 th highest annual MDA8) may not be effective at reducing lower levels of ozone on more typical days and may actually increase ozone levels on days where ozone concentrations are low” (Frey 2014a, p. 2). 86 For the 2009 adjusted year (i.e., the year with ge nerally lower O 3 concentrations), changes in risk were generally smaller than in 2007 (i.e., most changes about 2% or smaller). Increases were estimated for Houston, Los Angeles, and New York City.*** E.O. 12866 Review

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Page 193 of 647 (1) Based on a linear concentration

- response function, the current standard is estimated t o allow thousands of O 3 - associated respiratory deaths per year in the urban study areas

. (2) Based on threshold models, HREA sensitivity analyses indicate that the number of respiratory deaths associated with long

- term O 3 concentrations could potentially be considerably lower (i.e., by more than 75% if a threshold exists at 40 ppb, and by about 98% if a threshold exists at 56 ppb) ( U.S. EPA, 2014a, Figure 7

- 9 )

. 87
3 . CASAC Advice Following the 2008 decision to revise the primary O 3 standard by setting the level at 0.075 ppm (75 ppb), CASAC strongly questioned whether the standard met the requirements of the CAA . In September 2009, EPA announced its intention to reconsider the 2008 standards, issuing a notice of proposed ru lemaking in January 2010 (FR 75 2938). Soon after, EPA solicited CASAC review of that proposed rule and in January 2011 solicited additional a dvice. This proposal was based on the scientific and technical record from the 2008 rulemaking, including public c omments and CAS AC advice and recommendations. As further described above (I.C), in the fall of 2011 EPA did not

87 R isk estimates for respiratory mortality associated wit h long

- term O 3 exposures are based on the study by Jerrett et al. (2009) (U.S. EPA, 2014a, Chapter 7). As discussed above (II.B.2.b.iv) and in the PA (U.S. EPA, 2014c, section 3.1.4.3), Jerrett et al. (2009) reported that when seasonal averages of 1

- hour d aily maximum O 3 concentrations ranged from 33 to 104 ppb, there was no statistical deviation from a linear concentration

response relationship between O 3 and respiratory mortality across 96 U.S. cities (U.S. EPA, 2013, section 7.7). However, the authors re ported “limited evidence” for an effect threshold at an O 3 concentration of 56 ppb (p=0.06). In communications with EPA staff (Sasser, 2014), the study authors indicated that it is not clear whether a threshold model is a better predictor of respiratory mo rtality than the linear model, and that “considerable caution should be exercised in accepting any specific threshold.”*** E.O. 12866 Review

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Page 194 of 647 revise the standard as part of the reconsideration process but decided to defer decisions on revisions to the ozone standards to the next period ic review, which was already underway. Accordingly, in this section we describe CASAC’s advice related to the 2008 final decision and the subsequent reconsideration, as well as its advice on this current review of the O 3 NAAQS that was initiated in Septemb er 2008. In April 2008, the members of the CASAC Ozone Review Panel sent a letter to EPA stating “[I]n our most

- recent letters to you on this subject

— dated October 2006 and March 2007

— the CASAC unanimously recommended selection of an 8

- hour average
Ozone NAAQS within the range of 0.060 to 0.070 parts per million [60 to 70 ppb] for the primary (human health

- based) Ozone NAAQS” (Henderson, 2008). The letter cont inued: The CASAC now wishes to convey, by means of this letter, its additional, unsolicited advic e with regard to the primary and secondary Ozone NAAQS

. In doing so, the participating members of the CASAC Ozone Review Panel are unanimous in strongly urging you or your successor as EPA Administrator to ensure that these recommendations be considered du ring the next review cycle for the Ozone NAAQS that will begin next year ... numerous medical organizations and public health groups have also expressed their support of these CASAC recommendations’ ... [The CASAC did] not endorse the new primary ozone standar d as being sufficiently protective of public health

. The CASAC

— as the EPA ’s statutorily

- established science advisory committee for advising you on the national ambient air quality standards

— unanimously recommended decreasing the primary standard to within the range of 0.060

– 0.070 ppm [60 to 70 ppb]

. It is the Committee’s consensus scientific opinion that your decision to set the primary ozone standard above this range fails to satisfy the explicit stipulations of the Clean Air Act that you ensure an adequat e margin of safety for all individuals, including sensitive populations. In response to EPA’s solicitation of advice on the EPA ’s proposed rulemaking as part of the reconsideration, CASAC conveyed support (Samet, 2010). CASAC fully supports EPA’s proposed range of 0.060

– 0.070 parts per million (ppm) for the 8

- hour primary ozone standard. CASAC considers this range to be justified by the scientific evidence as presented in the Air Quality Criteria for Ozone and Related Photochemical Oxidants (March 2006) and Review of the National Ambient Air Quality Standards for*** E.O. 12866 Review

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Page 195 of 647 Ozone: Policy Assessment of Scientific and Technical Information, OAQPS Staff Paper (July 2007). As stated in our letters of October 24, 2006, March 26, 2007 and April 7, 2008 to former Administr ator Stephen L. Johnson, CASAC unanimously recommended selection of an 8

- hour average ozone NAAQS within the range proposed by EPA (0.060 to 0.070 ppm). In proposing this range, EPA has recognized the large body of data and risk analyses demonstrating that retention of the current standard would leave large numbers of individuals at risk for respiratory effects and/or other significant health impacts including asthma exacerbations, emergency room visits, hospital admissions and mortality. In response to EPA’s request for additional advice on the reconsideration in 2011, CASAC reaffirmed their conclusion that “the evidence from controlled human and epidemiologic al studies strongly supports the selection of a new primary ozone standard within the 60

– 70 ppb range for an 8

- hour averaging time” (Samet, 2011 , p ii ). As requested by EPA, CASAC’s advice and recommendations were based on the scientific and technical record from the 2008 rulemaking. In considering the record for the 2008 rulemaking, CASAC stated the following to summarize the basis for their conclusions (Samet, 2011, pp. ii to iii). (1) The evidence available on dose

- response for effects of ozone shows associations extending to levels within the range of concentrations currently experie nced in the United States. (2) There is scientific certainty that 6.6

- hour exposures with exercise of young, healthy, non

- smoking adult volunteers to concentrations ≥ 80 ppb cause clinically relevant decrements of lung function. (3) Some healthy individuals have b een shown to have clinically relevant responses, even at 60 ppb. (4) Since the majority of clinical studies involve young, healthy adult populations, less is known about health effects in such potentially*** E.O. 12866 Review

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Page 196 of 647 ozone sensitive populations as the elderly, children an d those with cardiopulmonary disease

. For these susceptible groups, decrements in lung function may be greater than in healthy volunteers and are likely to have a greater clinical significance. (5) Children and adults with asthma are at increased risk of acute exacerbations on or shortly after days when elevated ozone concentrations occur, even when exposures do not exceed the NAAQS concentration of 75 ppb. (6) Large segments of the population fall into what EPA terms a “sensitive population group,’’ i.e., those at increased risk because they are more intrinsically susceptible (children, the elderly, and individuals with chronic lung disease) and those who are more vulnerable due to increased exposure because they work outside or live in areas that are more polluted than the mean levels in their communities. With respect to evidence from epidemiologic studies, CASAC stated “while epidemiologic al studies are inherently more uncertain as exposures and risk estimates decrease (due to the greater potential for biases to dominate small effect estimates), specific evidence in the literature does not suggest that our confidence on the specific attribution of the estimated effects of ozone on health outcomes differs over the proposed range of 60

- 70 ppb ” (Samet, 2011, p.10). Following its review of the second draft PA in the current review, which considers an updated scientific and technical record since the 2008 rulemaking, CASAC concluded that “there is clear scientific support for the need to revise the*** E.O. 12866 Review

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Page 197 of 647 standard” ( Frey, 20 14c , p. ii). In particular, CASAC noted the following ( Frey, 2014c , p. 5): [T]he scientific evidence provides strong support for the occurrence of a range of adverse respiratory effects and mortality under air quality conditions that would meet the curren t standard. Therefore, CASAC unanimously recommends that the Administrator revise the current primary ozone standard to protect public health. In supporting these conclusions, CASAC judged that the strongest evidence comes from controlled human exposure studies of respiratory effects. The Committee specifically noted that “the combination of decrements in FEV 1 together with the statistically significant alterations in symptoms in human subjects exposed to 72 ppb ozone meets the American Thoracic Society’s
definition of an adverse health effect” ( Frey, 2014c , p . 5). CASAC further judged that “if subjects had been exposed to ozone using the 8

- hour averaging period used in the standard, adverse effects could have occurred at lower concentration ” and that “ the level at which adverse effects might be observed would likely be lower for more sensitive subgroups, such as those with asthma ” ( Frey, 2014c , p. 5). With regard to lung function risk estimates based on information from controlled human exposure studies, CASAC concluded that “estimation of FEV1 decrements of ≥15% is appropriate as a scientifically relevant surrogate for adverse health outcomes in active healthy adults, whereas an FEV1 decrement of ≥10% is a scientifically relevant surrogate for adverse hea lth outcomes for people with asthma and lung disease” ( Frey, 2014c , p. 3). The Committee further concluded that “[a]sthmatic subjects appear to be at least as sensitive, if not more sensitive, than non

- asthmatic subjects in manifesting O 3 - induced pulmonary*** E.O. 12866 Review

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Page 198 of 647 function decrements” ( Frey, 2014c , p. 4). In considering estimates of the occurrence of these decrements in urban study areas , CASAC specifically noted that the current standard is estimated to allow 11 to 22% of school age children to experience at least one day with an FEV 1 decrement > 10%. While CASAC judged that controlled human exposure studies of respiratory effects provide the strongest evidence supporting their conclusion on the current standard, the Committee judged that there is also “ sufficient scientific evidence based on epidemiologic studies for mortality and morbidity associated with
short

- term exposure to ozone at the level of the current standard” ( Frey, 2014c , p. 5). In support of the biological plausibility of the associations reported i n these epidemiologic studies, CASAC noted that “[r]ecent animal toxicological studies support identification of modes of action and, therefore, the biological plausibility associated with the epidemiologic al findings” ( Frey, 2014c , p. 5). Consistent with the advice of CASAC, several public commenters supported revising the primary O 3 standard to provide increased public health protection. In considering the available evidence as a basis for their views, these commenters generally noted that the health evidence is stronger in the current review than in past reviews , with new evidence for effects attributable to short

and long

- term exposures, and new evidence for effects at lower O 3 exposure concentrations

. O ther public commenters opposed considering re vised standards. These commenters discussed a variety of reasons for their views. A number of commenters expressed the view that EPA should not lower the level of the standard because a lower level would be closer to background O 3 concentrations.*** E.O. 12866 Review

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Page 199 of 647 In additi on, several commenters challenged the interpretation of the evidence presented in the ISA. With respect to the risk assessment, several commenters expressed the view that the EPA should only estimate risks above O 3 background concentrations, or above thres hold concentrations. Some commenters also expressed the view that, based on the mortality and morbidity risk estimates in the HREA, there is little to no difference between the risks estimated for the current
O 3 standard and the risks estimated for revised standards with lower levels. These commenters concluded that the HREA and PA have not shown that the public health improvements likely to be achieved by a revised O 3 standard would be greater than the improvements likely to be achieved by the current stan dard.
4. Policy Assessment Conclusions on the Current Standard As an initial matter, the PA concludes that reducing precursor emissions to achieve O 3 concentrations that meet the current standard will provide important improvements in public health protec tion. This initial conclusion is based on (1) the strong body of scientific evidence indicating a wide range of adverse health outcomes attributable to exposures to O 3 concentrations commonly found in the ambient air and (2) estimates indicating decreased occurrences of O 3 exposures of concern and decreased health risks upon meeting the current standard, compared to recent air quality. In particular, the PA concludes that s trong support for this initial conclusion is provided by controlled human exposure s tudies of respiratory effects, and by quantitative estimates of exposures of concern and lung function decrements based on information in these studies. Analyses in the HREA estimate that the percentages of children (i.e., all children and children with as thma) in urban study areas experiencing exposures of*** E.O. 12866 Review

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Page 200 of 647 concern, or experiencing abnormal and potentially adverse lung function decrements, are consistently lower for air quality that just meets the current O 3 standard than for recent air quality. The HREA estimates such reductions consistently across the urban study areas evaluated and throughout various portions of individual urban study areas , including in urban cores and the portions of urban study areas su rrounding urban cores. These reductions in exposures of concern and O 3 - induced lung function decrements reflect the consistent decreases in the highest O 3 concentrations following reductions in precursor emissions to meet the current standard. Thus, popula tions in both urban and non

- urban areas would be expected to experience important reductions in O 3 exposures and O 3 - induced lung function risks upon meeting the current standard. 88
The PA further concludes that s upport for this initial conclusion is also p rovided by estimates of O 3 - associated mortality and morbidity based on application of concentration

- response relationships from epidemiologic studies to air quality adjusted to just meet the current standard. These estimates, which are based on the assumpt ion that concentration

- response relationships are linear over entire distributions of ambient O 3 concentrations, are associated with uncertainties that complicate their interpretation ( II.C.3 ). However, risk estimates for effects associated with short

- and long

- term O 3 exposures, combined with the HREA’s national analysis of O 3 responsiveness to reductions in precursor emissions and the consistent reductions estimated for the highest ambient O 3 concentrations, suggest that O 3 - associated mortality and morbid ity would be

88 As discussed above (II.C.1), CASAC recommended that the EPA evaluate how health risks in urban centers, as well as outside urban cente rs, change upon reducing NO X emissions, given the varying impacts of NO X emissions reductions on ambient O 3 concentrations.*** E.O. 12866 Review

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Page 201 of 647 expected to decrease nationwide following reductions in precursor emissions to meet the
current O 3 standard.
R eductions in O 3 precursor emissions (i.e., NO X ) could also increase public health protection by reducing the ambient concentrations of pollutants other than O 3 . For example, in their advice on the second draft HREA CASAC acknowledged the potential for ambient NO 2 concentrations to be affected by changes in NO X emissions (Frey, 2014a, p. 10) . Consistent with this, the PA notes that NO X emissions contribute to ambient NO 2 , and NO X and VOCs can contribute to secondary formation of PM 2.5 constituents, including ammonium sulfate (NH 4 SO 4 ), ammonium nitrate (NH 4 NO 3 ), and organic carbon (OC). Therefore, at some times and in some locations, con trol strategies that would reduce NO X emissions (i.e., to meet an O 3 standard) could reduce ambient concentrations of NO 2 and PM 2.5 , resulting in health benefits beyond those directly associated with reducing ambient O 3 concentrations. After reaching the initial conclusion that meeting the current primary O 3 standard will provide important improvements in public health protection, and that it is not appropriate to consider a standard that is less protective than the current standard, the PA considers the a dequacy of the public health protection that is provided by the current standard

. In considering the available scientific evidence, exposure/risk information, advice from CASAC, and input from the public, the PA reaches the conclusion that the

a vailable ev idence and information clearly call into question the adequacy of public health protection p rovided by the current primary standard. In reaching this conclusion, the PA notes that evidence from controlled human exposure studies provides strong support for the occurrence of adverse respiratory effects following exposures to O 3*** E.O. 12866 Review

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Page 202 of 647 concentrations below the level of the current standard. Epidemiologic studies provide support for the occurrence of adverse respiratory effects and mortality under air quality conditio ns that would likely meet the current standard. In addition, based on the analyses in the HREA, the PA concludes that the exposures and risks projected to remain upon meeting the current standard are indicative of risks that can reasonably be judged to be important from a public health perspective. Thus, the PA concludes that the evidence and information provide strong support for giving consideration to revising the current primary standard in order to provide increased public health protection against an array of adverse health effects that range from decreased lung function and respiratory symptoms to more serious indicators of morbidity (e.g., including emergency department visits and hospital admissions), and mortality. In consideration of all of the ab ove, the PA draws the conclusion that it is appropriate for the Administrator to consider revision of the current primary O 3 standard to provide increase d public health protection

. 5 . Administrator’s Proposed Conclusions Concerning the Adequacy of the Current Standard This section discusses the Administrator’s proposed conclusions related to the adequacy of the public health protection provided by the current primary O 3 standard, resulting in her proposed decision to revise that standard. These proposed conclusions, and her proposed decision, are based on the Administrator’s consideration of the available scientific evidence, exposure/risk information, the comments and a dvice of CASAC, and public input received thus far, as summarized below. As an initial matter, the Administrator concludes that reducing precursor emissions to achieve O 3 concentrations that meet the current primary O 3 standard will*** E.O. 12866 Review

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Page 203 of 647 provide important impr ovements in public health protection, compared to recent air quality. In reaching this initial conclusion, she notes the discussion in section 3.4 of the PA (U.S. EPA, 2014c), summarized above (II.D.4). In particular, the Administrator notes that this init ial conclusion is supported by (1) the strong body of scientific evidence indicating a wide range of adverse health outcomes attributable to exposures to O 3 at concentrations commonly found in the ambient air lower than the level of current standard and (2 ) estimates indicating decreased occurrences of O 3 exposures of concern and decreased O 3 - associated health risks upon meeting the current standard, compared to recent air quality. Thus, she concludes that it would not be appropriate in this review to consi der a standard that is less protective than the current standard. 89 After reaching the initial conclusion that meeting the current primary O 3 standard will provide important improvements in public health protection, and that it is not appropriate to consid er a standard that is less protective than the current standard, the Administrator next considers the adequacy of the public health protection that is provided by the current standard . In doing so, the Administrator first notes that studies evaluated since the completion of the 2006 O 3 AQCD support and expand upon the strong body of evidence that, in the last review, indicated a causal relationship between short

- term O 3 exposures and respiratory health effects. This is the strongest causality finding possible under the ISA’s hierarchical system for classifying weight of evidence for causation. Together, experimental and epidemiologic studies support conclusions regarding a

89 W hile not analyzed quantitatively, consistent with CASAC advice (Frey, 2014a, p. 10), the Administrator notes that reductions in O 3 precursor emissions (e.g., NO X ; VOC) to achieve O 3 concentrations that meet the current standard could also increase public health protection by reducing the ambient concentrations of pollutants other than O 3 (i.e., PM 2.5 , NO 2 ).*** E.O. 12866 Review

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Page 204 of 647 continuum of O 3 respiratory effects ranging from small reversible changes in pul monary function, and pulmonary inflammation, to more serious effects that can result in respiratory

- related emergency department visits, hospital admissions, and premature mortality. Recent animal toxicolog y studies support descriptions of modes of action for the se respiratory effects and augment support for biological plausibility for the role of O 3 in reported effects

. With regard to mode of action, evidence indicates that antioxidant capacity may modify the risk of respiratory morbidity associated with O 3 exposure , and that the inherent capacity to quench (based on individual antioxidant capacity) can be overwhelmed, especially with exposure to elevated concentrations of O 3 . In addition, b ased on the consistency of findings across studies and evidence for the coherence of results from different scientific disciplines, strong evidence indicates that certain populations are at increased risk of experiencing O 3 - related effects , including the most severe effects. These include populations and lifestages identi fied in previous reviews (i.e., people with asthma, children, older adults , outdoor workers ) and populations identified since the last review (i.e., people with certain genotypes related to antioxidant and/or anti

- inflammatory status ; people with reduced i ntake of certain antioxidant nutrients , such as Vitamins C and E). The Administrator further notes that evidence for adverse respiratory health effects attributable to long

- term , or repeated short

- term, O 3 exposures is much stronger than in previous revie ws, and the ISA concludes that there is “likely to be” a causal relationship between such O 3 exposures and adverse respiratory health effects (the second strongest causality finding)

. Uncertainties related to the extrapolation of data generated by rodent t oxicology studies to the understanding of health effects in humans have been*** E.O. 12866 Review

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Page 205 of 647 reduced by studies in non

- human primates and by recent epidemiologic studies. The evidence available in this review includes new epidemiologic studies using a variety of designs and analysis methods , conducted by different research groups in different locations , evaluating the relationship s between long

- term O 3 exposures and measures of respiratory morbidity and mortality. New evid ence supports associations between long

term O 3 exposure s and the development of asthma in children, with several studies reporting interactions between genetic variants and such O 3 exposure s . S tudies also report associations between long

- term O 3 exposures and asthma prevalence, asthma severity and control, respirato ry symptoms among asthmatics, and respiratory mortality. In considering the O 3 exposure concentrations reported to elicit respiratory effects, the Administrator agrees with the conclusions of t he PA and with the advice of CASAC (Frey, 2014c) that controlled human exposure studies provide the most certain evidence indicating the occurrence of health effects in humans following exposures to specific O 3 concentrations. In particular, as discussed f urther in section II.E.4.d below, she notes that the effects reported in controlled human exposure studies are due solely to
O 3 exposures, and interpretation of study results is not complicated by the presence of co

occurring pollutants or pollutant mixtur es (as is the case in epidemiologic studies). Therefore, she places the most weight on information from these controlled human exposure studies. In considering the evidence from controlled human exposure studies, the Administrator first notes that these s tudies have reported a variety of respiratory effects in*** E.O. 12866 Review

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Page 206 of 647 healthy adults following exposures to O 3 concentrations of 60, 72, 90 or 80 ppb, and higher. The largest respiratory effects, and the broadest range of effects, have been studied and reported following exposures of healthy adults to 80 ppb O 3 or higher, with most exposure studies conducted at these higher concentrations. She further notes that recent evidence includes c ontrolled human exposure stud ies reporting the combination of lung function decrement s and respiratory symptoms in healthy adults engaged in intermittent, moderate exertion following 6.6 hour exposures to concentrations as low as
72 ppb , and lung function decrements and pulmonary inflammation following exposures to O 3 concentrations as low as 60 ppb

. As discussed below, c ompared to the evidence available in the last review, these studies have strengthened support for the occurrence of abnormal and adverse respiratory effects attributable to short

- term exposures to O 3

c oncentrations below the level of the current standard

. 91 T he Administrator concludes that such exposures to O 3 concentrations below the level of the current standard are potentially important from a public health perspective , given the following: (1) The combi nation of lung function decrements and respiratory symptoms reported to occur in healthy adults following exposures to 72 ppb O 3 or higher, while at moderate exer tion, meet ATS criteria for an adverse response. In specifically considering the 72 ppb exposu re concentration, CASAC noted that “the
combination of decrements in FEV 1 together with the statistically significant alterations in symptoms in human subjects exposed to 72 ppb ozone meets the

90 As noted above, for th e 70 ppb target exposure concentration , Schelegle et al. (2009) reported that the actual mean exposure concentration was 72 ppb. 91 Cf. Misisssippi . 744 F.3d 1350 (“Perhaps more studies like the Adams studies will yet reveal that the 0.060 ppm level produc es significant adverse decrements that simply cannot be attributed to normal variation in lung function.”).*** E.O. 12866 Review

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Page 207 of 647 American Thoracic Society’s definition of an adverse health ef fect” (Frey, 2014c, p. 5). (2) With regard to 60 ppb O 3 , CASAC agreed that “a level of 60 ppb corresponds to the lowest exposure concentration demonstrated to result in lung function decrements large enough to be judged an abnormal response by ATS and that

co uld be adverse in individuals with lung disease” (Frey, 2014c, p. 7). CASAC further noted that “a level of 60 ppb also corresponds to the lowest exposure concentration at which pulmonary inflammation has been reported” (Frey, 2014c, p. 7). (3) The controlled human exposure studies reporting these respiratory effects were conducted in healthy adults, while at

- risk groups (e.g., children, people with asthma) could experience larger and/or more serious effects. In their advice to the Administrator, CASAC concurre d with this reasoning (Frey, 2014c, p. 5). (4) These respiratory effects are coherent with the serious health outcomes that have been reported in epidemiologic studies evaluating exposure to O 3 (e.g., respiratory

- related hospital admissions, emergency departm ent visits, and mortality).
As noted above , t he Administrator’s proposed conclusions regarding the adequacy of the current primary O 3 standard place a large amount of weight on the results of controlled human exposure studies. In particular, given the com bination of lung function decrements and respiratory symptoms following 6.6 hour exposures to O 3 concentrations as low as 72 ppb, and given CASAC advice regarding effects at 72 ppb along with ATS adversity criteria, she concludes that there is strong evide nce in this review supporting the*** E.O. 12866 Review

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Page 208 of 647 occurrence of adverse respiratory effects following exposures to O 3 concentrations lower than the level of the current standard. As discussed b elow, t he Administrator further considers information from the broader body of controlled human exposure studies within the context of quantitative estimates of exposures of concern and O 3 - induced
FEV 1 decrements. In addition to controlled human exposure studies, the Administrator also considers what the available epidemiologic evid ence indicates with regard to the adequacy of the public health protection provided by the current primary O 3 standard. 92 She notes that recent epidemiologic studies provide support, beyond that available in the last review, for associations between short

- t erm O 3 exposures and a wide range of adverse respiratory outcomes (including respiratory

- related hospital admissions, emergency department visits, and mortality) and with total mortality. As sociations with morbidity and mortality are stronger during the wa rm or summer months , and remain robust after adjustment for copollutants. In considering information from epidemiologic studies within the context of her conclusions on the adequacy of the current standard, the Administrator considers the extent to which available studies support the occurrence of O 3 health effect associations with air quality likely to be allowed by the current standard. In doing so, she places the most weight on air quality analyses in locations of single

- city studies of short

- term O 3 , a s discussed in more detail in section II.E.4.d below. 93 In particular, she notes that a U.S.

92 As noted above, she places less weight on information from epidemiologic studies than on information from controlled human exposure studies. 93 As discussed in section II.E.4.d, t his judgment applies specifically to epidemiologic studies of short

- term O 3 concentrations where multicity effect estimates are presented,*** E.O. 12866 Review

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Page 209 of 647 single

- city study reported associations with respiratory emergency department visits in children and adults in a location that would likely have met the current O 3 standard over the entire study period (Mar and Koenig, 2009). In addition, even in some single

- city study locations where the current standard was likely not met (i.e., Silverman and Ito, 2010; Strickland et al., 2010), the Administrator notes PA analyses indicating that reported concentration

- response functions and available air quality data support the occurrence of O 3 - health effect associations on subsets of days with ambient O 3 concentrations below the level of the current standard (II.D.1). Compared to single

- city studies, the Administrator notes additional uncertainty in interpreting the relationships between air quality in individual study cities and health effects based on multicity analyses (discussed further in sections II.D.1 and II.E.4.d). While such uncertainties limit the extent to which the Administrator bases her conclusions on air quality in locations of multicity epidemiologic studies, she does note that O 3 associations with respiratory morbidity or mortality have been reported in several mu lticity studies when the majority of study locations (though not all study locations) would likely have met the current O 3 standard. When taken together, the Administrator reaches the conclusion that single

- city epidemiologic studies and associated air qua lity information support the occurrence of

based on combining the effect estimates from multiple individual cities , and where individual city effect estimates are not presented (as is the case for key multicity studies analyzed in the PA). Because these reported multicity effect estimates do not allow health effect associations to be disaggregated by individual city, it is not possible to assign the health effect association to the air quality in any one study location, or to the air quality in a subset of locations. In contrast, for epidemiologic studies of long

- term concentrations, where multicity effect estimates a re based on comparisons across cities, different judgments have been made with regard to the utility of multicity studies ( see, e.g. 78 FR 3086 at 3103/2) (January 15, 2013) (and see discussion below of study by Jerrett et al., (2009)).*** E.O. 12866 Review

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Page 210 of 647 O 3 - associated hospital admissions and emergency department visits for ambient O 3 concentrations likely to have met the current standard , and that air quality analyses in locations of multicity studies provide some support for this conclusion for a broader range of effects (i.e., including mortality)

. Beyond her consideration of the scientific evidence, the Administrator also considers the results of the HREA exposure and risk analyses in reaching initi al conclusions regarding the adequacy of the current primary O 3 standard. In doing so, as noted above, she focuses primarily on exposure and risk estimates based on information from controlled human exposure studies (i.e., exposures of concern and O 3 - induc ed lung function decrements). She places relatively less weight on epidemiologic

- based risk estimates, noting that the overall conclusions from the HREA likewise reflect less confidence in estimates of epidemiologic

- based risks than in estimates of exposur es and lung function risks (U.S. EPA, 2014, section 9.6). Consistent with the conclusions in the PA, her determination to attach less weight to the epidemiologic

- based risk estimates reflects her consideration of key uncertainties, including the heterogene ity in effect estimates between locations, the potential for exposure measurement errors, and uncertainty in the interpretation of the shape of concentration

- response functions for O 3 concentrations in the lower portions of ambient distributions (U.S. EPA, 2014, section 9.6) (II.D.2). In particular, she concludes that lower confidence should be placed in the results of the assessment of respiratory mortality risks associated with long

- term O 3 exposures, primarily because that analysis is based on only one s tudy (even though that study is well

- designed) and because of the uncertainty in that study about the existence*** E.O. 12866 Review

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Page 211 of 647 and level of a potential threshold in the concentration

- response function (U.S. EPA, 2014a, section 9.6) (II.D.2). 94 With regard to estimates of exposures of concern, the Administrator considers the extent to which the current standard provides protection against exposures to O 3 concentrations at or above 60, 70, and 80 ppb , noting CASAC advice that 60 ppb “is an appropriate exposure of concern fo r asthmatic children” (Frey, 2014c, p. 8). She further notes that while single exposures of concern could be adverse for some people, particularly for the higher benchmark concentrations (70, 80 ppb) where there is stronger evidence for the occurrence of a dverse effects (discussed further in II.E.4.d, below), she becomes increasingly concerned about the potential for adverse responses as the frequency of occurrences increases. 95 In particular, she notes that r epeated occurrences of the types of effects shown to occur following exposures of concern can have potential ly adverse outcomes . For example, repeated occurrences of airway inflammation could potentially result in the induction of a chronic inflammatory state ; alter ed pulmonary structure and function, le ading to diseases such as asthma; alter ed lung host defense

res ponse to inhaled microorganisms; and alter ed lung response to other agents such as allergens or toxins (U.S. EPA, 2013, Section 6.2.3). Thus, the Administrator notes that the types of lung inju ry shown to occur following exposures to O 3 concentrations from 60 to 80 ppb, particularly if experienced repeatedly, provide a mode of action by which O 3

94 CASAC also called into question the extent to which it is appropriate to place confidence in risk estimates for respiratory mortality (Frey, 2014a, p. 11). 95 Not all people who experience an exposure of concern will experience an adverse effect (even members of at

- risk po pulation s ). For most of the endpoints evaluated in controlled human exposure studies (with the exception of O 3 - induced FEV 1 decrements, as discussed below) , the number of those experiencing exposures of concern who will experience adverse effects cannot be reliably quantified.*** E.O. 12866 Review

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Page 212 of 647 may cause other more serious effects (e.g., asthma exacerbations). Therefore, the Administrator places the most weight on estimates of two or more exposures of concern (i.e., as a surrogate for the occurrence of repeated exposures), though she also considers estimates of one or more , particularly for the 70 and 80 ppb benchmarks

. Consistent with CAS AC advice (Frey, 2014c), the Administrator focuses on children in these analyses of O 3 exposures, noting that estimates for all children and asthmatic children are virtually indistinguishable (in terms of the percent estimated to experience exposures of co ncern). Though she focuses on children, she also recognizes that exposures to O 3 concentrations at or above 60 or 70 ppb could be of concern for adults. As discussed in the HREA and PA, the patterns of exposure estimates over years and across urban study a reas are similar in adults with asthma, older adults, all children, and children with asthma, though smaller percentages of adult populations are estimated to experience exposures of concern than children and children with asthma. Thus, the Administrator r ecognizes that the exposure patterns for children across years and urban study areas are indicative of exposure patterns in a broader group of at

- risk populations that also includes asthmatic adults and older adults. As illustrated in Table 1 (above), the Administrator notes that if the 15 urban study areas evaluated in the HREA were to just meet the current O 3 standard, fewer than 1% of children in those areas would be estimated to experience two or more exposures of concern at or above 70 ppb, though app roximately 3 to 8% of children, including approximately 3 to 8% of asthmatic children, would be estimated to experience two or*** E.O. 12866 Review

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Page 213 of 647 more exposures of concern to O 3 concentrations at or above 60 ppb 96 (based on estimates averaged over the years of analysis). To p rovide some perspective on these percentages, the Administrator notes that they correspond to almost 900,000 children in urban study areas, including about 90,000 asthmatic children , estimated to experience two or more exposures of concern at or above 60 p pb . Nationally, if the current standard were to be just met the number of children experiencing such exposures would be larger. In the
worst

- case year and location (i.e., year and location with the largest exposure estimates), the Administrator notes that over 2% of children are estimated to experience two or more exposures of concern at or above 70 ppb and over 14% are estimated to experience two or more exposures of concern at or above 60 ppb. Although, as discussed above and in section II.E.4.d, the Adm inistrator is less concerned about single occurrences of exposures of concern, she notes that even single occurrences can cause adverse effects in some people, particularly for the 70 and 80 ppb benchmarks. Therefore, she also considers estimates of one or more exposures of concern. As illustrated in Table 1 (above), if the 15 urban study areas evaluated in the HREA were to just meet the current O 3 standard, fewer than 1% of children in those areas would be estimated to experience one or more exposures of c oncern at or above 80 ppb (based on estimates averaged over the years of analysis). However, approximately 1 to 3% of children, including 1 to 3% of asthmatic children, would be estimated to experience one or more exposures of concern to O 3 concentrations at or above 70 ppb and approximately 10 to 17% would be estimated to experience one or more exposures of

96 Almost no children in those areas would be estimated to experience two or more exposures of co ncern at or above 80 ppb.*** E.O. 12866 Review

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Page 214 of 647 concern to O 3 concentrations at or above 60 ppb. In the worst

- case year and location, the Administrator notes that over 1% of children are estimated to experience one or more exposures of concern at or above 80 ppb, over 8% are estimated to experience one or more exposures of concern at or above 70 ppb, and about 26% are estimated to experience one or more exposures of concern at or above 60 ppb. In add ition to estimated exposures of concern, the Administrator also considers HREA estimates of the occurrence of O 3 - induced lung function decrements. In doing so, she particularly notes CASAC advice that “ estimation of FEV 1 decrements of ≥ 15% is appropriate as a scientifically relevant surrogate for adverse health outcomes in active healthy adults, whereas an FEV 1 decrement of ≥ 10% is a scientifically relevant surrogate for adverse health outcomes for people with asthma and lung disease ” (Frey, 2014c, p. 3)

. The Administrator notes that while single occurrences of O 3 - induced lung function decrements could be adverse for some people, as discussed above (II.B.3), a more general consensus view of the potential adversity of such decrements emerges as the frequency of

occurrence s increases . Therefore, the Administrator focuses primarily on the estimates of
two or more O 3 - induced lung function decrements. When averaged over the years evaluated in the HREA, the Administrator notes that the current standard is estimated to allow about 1 to 3% of children in the 15 urban study areas (corresponding to almost 400,000 children) to experience two or more O 3 - induced lung function decrements > 15%, and to allow about 8 to 12% of children*** E.O. 12866 Review

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Page 215 of 647 (corresponding to about 180,00 0 asthmatic children 97 ) to experience two or more O 3 - induced lung function decrements > 10%. Nationally, larger numbers of children would be expected to experience such O 3 - induced decrements if the current standard were to be just met. The current standard is also estimated to allow about 3 to 5% of children in the urban study areas to experience one or more decrements > 15% and about 14 to 19% of children to experience one or more decrements > 10%. In the worst

- case year and location, the current standard i s estimated to allow 4% of children in the urban study areas to experience two or more decrements > 15% (and 7% to experience one or more such decrements) and 14% of children to experience two or more decrements > 10% (and 22% to experience one or more suc h decrements). In further considering the HREA results, the Administrator considers the epidemiology

- based risk estimates. As discussed above, compared to the weight given to HREA estimates of exposures of concern and lung function risks, she places relat ively less weight on epidemiology

- based risk estimates. In giving some consideration to these risk estimates, the Administrator notes estimates of total risk s (i.e., based on the full distributions of ambient O 3 concentrations) and risk s associated with O 3 concentrations in the upper portions of ambient distributions. The Administrator notes that estimates of total risks are based on the assumption that concentration

- response relationships remain linear over the entire distributions of ambient O 3 concentrat ions. With regard to total risks, she notes that the HREA estimates thousands of O 3 - associated hospital admissions,

97 As noted above, CASAC concluded that “an FEV1 decrement of ≥10% is a scientifically relevant surrogate for a dverse health outcomes for people with asthma and lung disease” (Frey, 2014c, p. 3) and that such decrements “could be adverse for people with lung disease” (Frey, 2014c, p. 7).*** E.O. 12866 Review

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Page 216 of 647 emergency department visits, and deaths per year for air quality conditions associated with just meeting the current standard in the 12 urba n study areas (II.C.3)

. However, the Administrator also notes the increasing uncertainty associated with the shapes of concentration

- response curves for O 3 concentrations in the lower portions of ambient distributions. She particularly notes that there is less certainty in the shape of concentration

- response functions for area

- wide O 3 concentrations at the lower ends of warm season distributions (i.e., below about 20 to 40 ppb depending on the O 3 metric, health endpoint, and study population) (U.S. EPA, 2013, section 2.5.4.4) . The Administrator further notes the evidence from controlled human exposure studies, which provide the strongest support for O 3 - induced effects following exposures to O 3

con centrations corresponding to the upper portions of typical ambient distributions (i.e., 60 ppb and above). Therefore, the Administrator judges it appropriate to focus on risks associated with O 3 concentrations in the upper po rtions of ambient distributions

. Even when considering only area - wide O 3 concentrations from the upper portions of seasonal distributions, the Administrator notes that the current standard is estimated to allow hundreds to thousands of O 3 - associated deaths per year in urban study areas (II.C.3)

. A lthough the Administrator note s the HREA conclusions indicating somewhat less confidence in estimates of O 3 - associated mortality and morbidity risks , compared to estimates of exposures of concern and risk of lung function decrements , she conclu de s that the general magnitude of mortality and morbidity risk estimates suggests the potential for a substantial number of O 3 - associated deaths and adverse resp iratory events to occur nationally, even when the current standard is met. She especially notes that t his*** E.O. 12866 Review

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Page 217 of 647 is the case based on the risks associated with the upper ends of distributions of ambient
O 3 concentrations, where she has the greatest confidence in O 3 - attributable effects

. In addition to the evidence and exposure/risk information discussed above, the Administrator also takes note of the CASAC advice in the current review and in the 2010 proposed reconsideration of the 2008 decision establishing the current standard. As discussed in more detail above, the current CASAC “unanimously recommends that the Administrator revise the current primary ozone standard to protect public health” (Frey, 2014, p. 6). Consistent with this advice from the current CASAC, in commenting on the proposed reconsideration, the prior CASAC O 3 Panel also recommended rev ision of the current standard to one with a lower level. This earlier recommendation was based entirely on the evidence and information in the record for the 2008 standard decision, which, as discussed above, has been substantially strengthened in the curr ent review (Samet, 2011; Samet, 2012). In consideration of all of the above, the Administrator proposes that the current primary O 3 standard is not adequate to protect public health, and that it should be revised to provide increased public health protect ion. This proposed decision is based on the Administrator’s initial conclusions that the available evidence and exposure and risk information clearly call into question the adequacy of public health protection provided by the current primary standard and, therefore, that the current standard is not requisite to protect public health with an adequate margin of safety . With regard to the evidence she specifically notes that (1) controlled human exposure studies provide strong support for the occurrence of adv erse respiratory effects following exposures to O 3 concentrations below the level of the current standard (i.e., as low as 72 ppb) , and that (2) single

- city*** E.O. 12866 Review

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Page 218 of 647 epidemiologic studies provide support for the occurrence of adverse respiratory effects under air q uality conditions that would likely meet the current standard , with multicity studies providing some support for this conclusion for a broader range of effects (i.e., including mortality) . Courts have repeatedly held that this type of evidence justifies an Administrator’s conclusion that it is “appropriate” (within the meaning of section 109 (d)(1) of the Act) to revise a primary NAAQS to provide further protection of public health. 98 In addition, based on the analyses in the HREA, the Administrator conclude s that the exposures and risks projected to remain upon meeting the current standard can reasonably be judged to be important from a public health perspective. Thus, she reaches the proposed conclusion that the evidence and information, together with CASAC advice based on their consideration of that evidence and information, provide strong support for revising the current primary standard in order to increase public health protection against an array of adverse effects that range from decreased lung functio n and respiratory symptoms to more serious indicators of morbidity (e.g ., including emergency department visits and hospi tal admissions), and mortality. The Administrator solicits comment on her proposed decision to revise the current primary O 3 NAAQS, including on her considerations and proposed conclusions based on the scientific evidence, exposure/risk information, and CASAC advice. In doing so, she recognizes that some have expressed alternative approaches to viewing th e evidence and informat ion, including alternative approaches to viewing , evaluating, and weighing important uncertainties. In some cases, these alternative approaches have le d some public

98 See e.g. State of Mississippi , 744 F. 3d at 13435; American Farm Bureau , 559 F. 3d at 525

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Page 219 of 647 commenters to recommend retaining the current standard

. Given these alternative views , in a ddition to proposing to revise the current primary O 3 standard, the Administrator also solicits comment on the option of retaining that standard

. E. Conclusions on the Elements of the Primary Standard Having reached the proposed conclusion that the currently available scientific evidence and exposure/risk information call into question the adequacy of the current O 3 standard, the Administrator next considers the range of alternative standards supported by that evidence and information. Consistent wit h her consideration of the adequacy of th e current standard, the Administrator's proposed conclusions on alternative standards are informed by the available scientific evidence assessed in the ISA, exposure/risk information presented and assessed in the HR EA, the evidence

- based and exposure

- /risk

based considerations and conclusions in the PA, CASAC advice, and input from members of the public. The sections below discuss the evidence and exposure/risk information, CASAC advice and public input, and the Admi nistrator's proposed conclusions , for the major elements of the NAAQS: indicator (II.E.1), averaging time (II.E.2), form (II.E.3), and level (II.E.4). 1. Indicator In the last review, EPA focused on O 3 as the most appropriate indicator for a standard mea nt to provide protection against ambient photochemical oxidants. In this review, while the complex atmospheric chemistry in which O 3 plays a key role has been highlighted, no alternatives to O 3 have been advanced as being a more appropriate indicator for a mbient photochemical oxidants. More specifically, the ISA noted that O 3 is the only photochemical oxidant (other than NO 2 ) that is routinely monitored and for*** E.O. 12866 Review

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Page 220 of 647 which a comprehensive database exists (ISA section 3.6). Data for other photochemical oxidants (e .g., PAN, H 2 O 2 , etc.) typically have been obtained only as part of special field studies. Consequently, no data on nationwide patterns of occurrence are available for these other oxidants; nor are extensive data available on the relationships of
concentrat ions and patterns of these oxidants to those of O 3 (ISA section 3.6). In its review of the second draft PA, CASAC stated “The indicator of ozone is appropriate based on its causal or likely causal associations with multiple adverse health outcomes and its representation of a class of pollutants known as photochemical oxidants” ( Frey, 2014c , p. ii). In addition, the PA notes that meeting an O 3 standard can be expected to provide some degree of protection against potential health effects that may be independently associated with other photochemical oxidants, even though such effects are not discernible from currently available studies indexed by O 3 alone ( U.S. EPA, 2014c , section 4.1). That is, since the precursor emissions that lead to the formation of O 3 generally also lead to the formation of other photochemical oxidants, measures leading to reductions in population exposures to O 3 can general ly be expected to lead to reductions in population exposures to other photochemical oxidants. In considering this information , and CASAC’s advice, the Administrator reaches the proposed conclusion that O 3 remains the most appropriate indicator for a standa rd meant to provide protection against photochemical oxidants. 99

99 The D.C. Circuit upheld the use of O 3 as the indicator for photochemical oxidants based on these same considerations. American Petroleum Inst. v. Costle , 665 F. 2d 1176, 1186 (D.C. Cir. 1981).*** E.O. 12866 Review

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Page 221 of 647 2. Averaging Time The EPA established t he current 8

- hour averaging time 100 for the primary O 3 NAAQS in 1997 (62 FR 38856). The decision on averaging time in that review was based on numerous co ntrolled human exposure and epidemiologic studies reporting associations between 6 to 8 hour O 3 concentrations and adverse respiratory effects ( 62 FR 38861 ) . It was also noted that a standard with a max 8

- hour averaging time is likely to provide substantia l protection against respiratory effects associated with 1

- hour peak O 3 concentrations. Similar conclusions were reached in the last O 3 NAAQS review and thus, the 8

- hour averaging time was retained in 2008.
In reaching a proposed conclusion on averaging time in the current review, the Administrator considers the extent to which the available evidence continue s to support the appropriateness of a standard with an 8

- hour averaging time . Specifically, the Administrator considers the extent to which the available information indicates that a standard with the current 8

- hour averaging time provides appropriate protection against short

- and long

- term O 3 exposures.

a. Short

- term As an initial consideration with respect to the most appropriate averaging time for the O 3 NAAQS, the Administrator notes that the strongest evidence for O 3 - associated health effects is for respiratory effects following short

- term exposures. More specifically, the Administrator notes the ISA conclu sion that the evidence is “suff icient to infer a

caus al relationship ” between short

- term O 3 exposures and respiratory effects. The ISA also judges that for short

- term O 3 exposures , the evidence indicate s “likely to be causal”

100 This 8

- hour averaging time reflects dail y max 8

- hour average O 3 concentrations.*** E.O. 12866 Review

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Page 222 of 647 relationships with both cardiovascular effects and mortality ( U.S. EPA, 2013, section 2.5.2) . Therefore, as in past reviews, the strength of the available scientific evidence provides strong support for a standard that protects the public health against short

- term exposures to O 3 . In first considering the level of support available for specific short

- term averaging times, the Administrator note s the evidence available from controlled h uman exposure studies. As discussed in more detail in chapter 3 of th e PA, substantial health effects evidence from controlled human exposure studies demonstrates that a wide range of respiratory effects (e.g., pulmonary function decrements, increases in respiratory symptoms, lung inflammation, lung permeability, decreased l ung host defense, and airway hyperresponsiveness) occur in healthy adults following 6.6 hour exposures to O 3 (U.S. EPA 2013, section 6.2.1.1). Compared to studies evaluating shorter exposure durations (e.g., 1

- hour), studies evaluating 6.6 hour exposures i n healthy adults have reported respiratory effects at lower O 3 exposure concentrations and at more moderate levels of exertion. The Administrator a lso note s the strength of evidence from epidemiologic studies that have evaluated a wide variety of populat ions (e.g., including at

- risk lifestages and populations, such as children and people with asthma, respectively). A number of different averaging times are used in O 3 epidemiologic studies, with the most common being the max 1

- hour concentration within a 2 4

- hour period (1

- hour max), the max 8

- hour average concentration within a 24

- hour period (8

- hr max), and the 24

- hour average. These studies are summarized above and assessed in detail in chapter 6 of the ISA (U.S. EPA, 2013). Limited evidence from time

- ser ies and panel epidemiologic studies*** E.O. 12866 Review

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Page 223 of 647 comparing risk estimates across averaging times does not indicate that one exposure metric is more consistently or strongly associated with respiratory health effects or mortality, though the ISA notes some evidence for “smaller O 3 risk estimates when using
a 24

- hour average exposure metric” (U.S. EPA 2013, section 2.5.4.2; p. 2

- 31). For single

and multi

- day average O 3 concentrations, lung function decrements were associated with
1

- hour max, 8

- hour max, and 24

- hour avera ge ambient O 3 concentrations, with no strong difference in the consistency or magnitude of association among the averaging times (U.S. EPA 2013, p. 6

- 71). Similarly, in studies of short

- term exposure to O 3 and mortality, Smith et al. (2009) and Darrow et a l. (2011) have reported high correlations between risk estimates calculated using 24

- hour average, 8

- hour max, and 1

- hour max averaging times (U.S. EPA 2013, p. 6

- 253). Thus, the Administrator notes that the epidemiologic evidence alone does not provide a strong basis for distinguishing between the appropriateness of 1

- hour, 8

- hour, and 24

- hour averaging times. Considering the health information discussed above, the Administrator concludes that an 8

- hour averaging time remains appropriate for addressing h ealth effects associated with short

- term exposures to ambient O 3 . An 8

- hour averaging time is similar to the exposure periods evaluated in controlled human exposure studies, including recent studies that provide evidence for respiratory effects following e xposures to O 3 concentrations below the level of the current standard. In addition, epidemiologic studies provide evidence for health effect associations with 8

- hour O 3 concentrations, as well as with 1

- hour and 24

- hour concentrations. As in previous revie ws, the Administrator notes that a standard with an 8

- hour averaging time (combined with an appropriate standard form and level) would also be expected to provide substantial protection against health*** E.O. 12866 Review

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Page 224 of 647 effects attributable to 1

- hour and 24

- hour exposures (e .g., 62 FR 38861, July 18, 1997). This conclusion is consistent with the advice received from CASAC that “ the current 8

- hour averaging time is justified by the combined evidence from epidemiologic and clinical studies ” ( Frey, 2014c , p. 6 ). b. Long

- term The ISA concludes that the evidence for long

- term O 3 exposures indicates that there is “likely to be a causal relationship” with respiratory effects (US EPA, 2013, chapter 7). Thus, in this review the Administrator also consider s the extent to which

curren tly available evidence and exposure/risk information suggests that a standard with
an 8

- hour averaging time can provide protection against respiratory effects associated with longer term exposures to ambient O 3 . In considering this issue in the last revi ew of the O 3 NAAQS, the Staff Paper noted that “b ecause long

- term air quality patterns would be improved in areas coming into attainment with an 8

- hr standard, the potential risk of health effects associated with long

- term exposures would be reduced in an y area meeting an 8

- hr standard” (U

. S

. EPA, 2007 , p. 6

- 57) . In the current review, the PA further evaluate s this issue, with a focus on the long

- term O 3 metrics reported to be associated with mortality or morbidity in recent epidemiologic studies. As discus sed in section 3.1.3 of the PA ( U.S. EPA, 2014c , section 4.2) , much of the recent evidence for such associations is based on studies that defined long

- term O 3 in terms of seasonal averages of daily maximum 1

- hour or 8

- hour

c oncentrations

. As an initial consideration, the Administrator notes the risk results from the HREA for respiratory mortality associated with long

- term O 3 concentrations. These*** E.O. 12866 Review

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Page 225 of 647 HREA analyses indicate that as air quality is adjusted to just meet the current 8

- hour standard , most urban study areas are estimated to experience reduction s in respiratory mortality associated with long

- term O 3 concentrations based on the seasonal averages of
1

- hour daily max imum O 3 concentrations evaluated in the study by Jerrett et al. (2009) ( U .S. EPA, 2014 a , chapter 7 ). 101 A s air quality is adjusted to meet low er alternative standard levels, for standards based on 3

- year averages of the annual fourth

- highest daily

max imum 8

- hour O 3 concentrations, respiratory mortality risk s are estimated to be

r educed further in urban study areas . This analysis indicates that an O 3 standard with an
8

- hour averaging time, when coupled with an appropriate form and level, can reduce respiratory mortality reported to be associate d with long

- term O 3 concentrations. In further considering the study by Jerrett et al. (2009), the Administrator notes the PA comparison of long

- term O 3 concentrations following model adjustment in urban study areas (i.e., adjusted to meet the current and alternative 8

- hour standards) to the concentrations present in study cities that provided the basis for the positive and statistically significant association with respiratory mortality . As indicated in Table 4

- 3 of the PA ( U.S. EPA, 2014c , section 4.2) , this compari son suggests that a standard with an
8

- hour averaging time can decrease seasonal averages of 1

- hour daily max imum O 3 concentrations , and can maintain those O 3 concentrations below the seasonal average concentration where the study indicates the most confid ence in the reported concentration

- response relationship with respiratory mortality ( U.S. EPA, 2014c , sections 4.2 and 4.4.1).

101 Though the Administrator also notes important uncertainties associated with these risk estimates, as discussed above (II.C.3.b)

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Page 226 of 647 The Administrator also notes that the HREA conducted analyses evaluating the impacts of reducing regional NO X emissions on the seasonal averages of daily maximum
8

- hour O 3 concentrations. Seasonal averages of 8

- hour daily max O 3 concentrations reflect long

- term metrics that have been reported to be associated with respiratory morbidity effects in several recent O 3 epidemiologic st udies (e.g., Islam et al., 2008; Lin et al., 2008; Salam et al., 2009). The HREA analyses indicate that the large majority of the U

. S

. population lives in locations where reducing NO X emissions would be expected to result in decreases in seasonal averages of daily max 8

- hour ambient O 3 concentrations (U.S. EPA, 2014 a , chapter 8). Thus, consistent with the respiratory mortality risk estimates noted above, this analysis suggests that reductions in O 3 precursor emissions in order to meet a standard with an 8

- hour averaging time would also be expected to reduce the long

- term O 3 concentrations that have been reported in recent epidemiologic studies to be associated with respiratory morbidity. c. Adminis trator’s proposed conclusion on averaging time Taken together, the Administrator notes that the analyses summarized above indicate that a standard with an 8

- hour averaging time, coupled with the current 4 th high form and an appropriate level , would be exp ected to provide appropriate protection against the short

- and long

- term O 3 concentrations that have been reported to be associated with respiratory morbidity and mortality. The CASAC agreed with this conclusion, stating that “[t]he current 8

- hour averagin g time is justified by the combined evidence from epidemiologic and clinical studies” and that “[t]he 8

- hour averaging window also provides protection against the adverse impacts of long

- term ozone exposures, which were found to be “likely causal” for resp iratory effects and premature*** E.O. 12866 Review

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Page 227 of 647 mortality” ( Frey, 2014c , p. 6). Therefore, considering the available evidence and exposure risk information, and CASAC’s advice, the Administrator proposes to retain the
current 8

- hour averaging time, and not to set an additio nal standard with a different averaging time.
3. Form The “form” of a standard defines the air quality statistic that is to be compared to the level of the standard in determi ning whether an area attains that standard. The fo remost consideration in selec ting a form is the adequacy of the public health protection provided by the combination of the form and the other elements of the standard. In this review , the Administrator considers the extent to which the available evidence and/or information continue t o support the appropriateness of a standard with the current form , defined by the 3

- year average of annual 4 th

- highest 8

- hour daily max imum O 3 concentrations

. The EPA established the current form of the primary O 3 NAAQS in 1997 (62 FR 38856). Prior to that time, the standard had a “1

- expected

- exceedance” form. 102 An advantage of the current concentration

- based form recognized in the 1997 review is that such a form better reflects the continuum of health effects assoc iated with increasing ambient O 3 concentrations. Unlike an expected exceedance form, a concentration

- based form giv es proportionally more weight to years when 8

- hour O 3 concentrations are well above the level of the standard than years when 8

- hour O 3 conce ntrations are just above the level of the standard. It was judged appropriate to give more weight to higher O 3

102 For a standard with a 1

- expected

- exceedance form to be met at an air quality monitoring site, the fourth

- highest air quality value in 3 years, given adjustments for missing data, must be less than or equal to the level of the standard.*** E.O. 12866 Review

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Page 228 of 647 concentrations, given that available health evidence indicated a continuum of effects associated with exposures to varying concentrations of O 3 , and given that the extent to which public health is affected by exposure to ambient O 3 is related to the actual magnitude of the O 3 concentration, not just whether the concentration is above a specified level. During the 1997 review, EPA considered a range of alternative “concentration

based” forms, including the second

- , third

- , fourth

- and f ifth

- highest daily max 8

- hour concentrations in an O 3 season. The fourth

- highest daily max was selected, recognizing that a less restrictive form (e.g., fifth hig hest) would allow a larger percentage of sites to experience O 3 peaks above the level of the standard, and would allow more days on which the level of the standard may be exceeded when the site attains the standard (62 FR 38856). Consideration was also giv en to setting a standard with a form that would provide a margin of safety against possible but uncertain chronic effects, and would provide greater stability to ongoing control programs. 103 A more restrictive form was not selected, recognizing that the diff erences in the degree of protection afforded by the alternatives were not well enough understood to use any such differences as a basis for choosing the most restrictive forms (62 FR 38856). In the 2008 review, EPA additionally considered the potential v alue of a percentile

- based form. In doing so, EPA recognized that such a statistic is useful for comparing datasets of varying length because it samples approximately the same place in the distribution of air quality values, whether the dataset is several months or several

103 See American Trucking Assn’s v. EPA, 283 F. 3d 355, 374

- 75 (D.C. Cir. 2002) (less stable imple mentation programs may be less effective, and therefore EPA can consider programmatic stability in determining the form of a NAAQS).*** E.O. 12866 Review

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Page 229 of 647 years long. However, EPA concluded that a percentile

- based statistic would not be effective in ensuring the same degree of public health protection across the country. Specifically, a percentile

- based form would allow more days with highe r air quality values in locations with longer O 3 seasons relative to places with shorter O 3 seasons. Thus, in the 2008 review EPA concluded that a form based on the nth

- highest max imum
O 3 concentration would more effectively ensure that people who live in areas with different length O 3 seasons receive the same degree of public health protection. Based on analyses of forms specified in terms of an nth

- highest concentration (n ranged from 3 to 5), advice from CASAC, and public comment, 104 the Administrator

co ncluded that a 4th

- highest daily max imum should be retained (73 FR 16465). In reaching this decision, t he Administrator recognized that “there is not a clear health

based threshold for selecting a particular nth

- highest daily maximum form of the standard” and that “the adequacy of the public health protection provided by the combination of the level and form is a foremost consideration” (73 FR 16475). Based on this, the Administrator judged that the existing form (4th

- highest daily maximum 8

- hour
average co ncentration) should be retained, recognizing the increase in public health protection provided by combining this form with a lower standard level (i.e., 75 ppb).

104 In the 2008 review, one group of commenters expressed the view that the standard was not adequate and supported a more hea lth

- protective form (e.g., a second

- or third

- highest daily max form). Another group of commenters expressed the view that the standard was adequate and did not provide any views on alternative forms that would be appropriate should the Administrator consi der revisions to the standard. The Administrator considered the protection afforded by the combination of level and form in revising the standard in 2008 to 75 ppb, as a 3

- year average of the annual fourth

- highest daily max 8

- hour concentrations (73 FR 164 75).*** E.O. 12866 Review

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Page 230 of 647 The Administrator also recognized that it is important to have a form that provides stabilit y with regard to implementation of the standard. In the case of O 3 , for example, he noted the importance of a form insulated from the impacts of the meteorological events that are conducive to O 3 formation. Such events could have the effect of reducing pub lic health protection, to the extent they result in frequent shifts in and out of attainment due to meteorological conditions. The Administrator noted that such frequent shifting could disrupt an area’s ongoing implementation plans and associated control p rograms (73 FR 16474). In his final decision, the Administrator judged that a “4 th high form provides a stable target for implementing programs to improve air quality” (73 FR 16475). In the current review, the Administrator consider s the extent to which newly available information provides support for the current form. In so doing, she takes note of the conclusions of prior reviews summarized above. She recognize s the value of an nth

high statistic over that of an expected exceedance or percentile

- based form in the case of the O 3 standard, for the reasons summarized above. The Administrator additionally take s note of the importance of stability in implementation to achieving the level of protection specified by the NAAQS . Specifically, she note s that to the extent areas engaged in implementing the O 3 NAAQS frequently shift from meeting the standard to violating the standard, it is possible that ongoing implementation plans and associated control
programs could be disrupted, thereby re du cing public health protection

. In light of this, wh ile giving foremost consideration to the adequacy of public health protection provided by the combination of all elements of the standard, including the form, the Administrator considers particularly fin dings from prior reviews with regard*** E.O. 12866 Review

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Page 231 of 647 to the use of the nth

- high metric. As noted above, the 4 th

- highest daily max imum was selected in recognition of the public health protection provided by this form, when coupled with an appropriate averaging time and lev el, and recognizing that such a form can provide stabilit y for implementation programs. The Administrator concludes that t he currently available evid ence and information do not call into question these conclusions from previous reviews. In reaching this co nclusion, the Administrator notes that CASAC concurred that the O 3 standard should be based on the fourth highest, daily maximum 8

- hour average value (averaged over three years), stating that this form “ provides health protection while allowing for atypical meteorological conditions that can lead to abnormally high ambient ozone concentrations which, in turn, provides programmatic stability ” ( Frey, 2014c , p. 6 ). Thus a standard with the current 4 th high form, coup led with a level lower than 75 ppb as discussed below, would be expected to increase public health protection relative to the current standard while continuing to provide stability for implementation programs. Therefore, the Administrator proposes to retai n the current 4 th

- highest daily max imum form for an O 3 standard with an 8

- hour averaging time and a revised level, as discussed below. 4. Level The Administrator next considers the extent to whic h alternative levels below 75 ppb could provide greater pro tection than the current primary standard against short

- and long

- term exposures to O 3 in ambient air , for a standard based on the 3

- year average of the annual 4 th highest daily maximum 8

- hour O 3 concentration . In doing so, she particularly notes the evid ence - based and exposure - /risk

- based considerations in the PA, which take into account the experimental and epidemiologic evidence as assessed in the*** E.O. 12866 Review

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Page 232 of 647 ISA; quantitative estimates of O 3 exposure s and health risks in at

- risk populations provided by the HREA; uncertainties and limitations associated with this evidence and information; CASAC advice ; and public input ( U.S. EPA, 2014c , sections 4.4 and 4.5)

. Section II.E.4.a below summarize s the PA’s approach to considering the scientific evidence and the exposure /risk information related to level of the primary standard

. Section II.E.4.b summarizes CASAC advice on the level of the primary standard , and public input received thus far. Section II.E.4.c presents the PA’s conclusions on alternative primary O 3 standard levels. Section II.E.4.d presents the Administrator’s proposed conclusions on primary O 3 standard levels

. a. PA approach to considering the evidence and information related to alternative levels of the primary standard The PA's approach to reaching conc lusions on alternative standard levels focuses on the evidence from controlled human exposure and epidemiologic studies, as assessed in the ISA (U.S. EPA, 2013), and the exposure and health risk analyses presented in the HREA (U.S. EPA, 2014a). This approa ch is discussed in detail in Chapter s 1 and 4 of the PA (U.S. EPA, 2014c, section s 1.3 , 4.6 ), and is summarized below. As an initial matter, the PA notes that controlled human exposure studies provide the most certain evidence indicating the occurrence of health effects in humans following exposures to specific O 3 concentrations. Consistent with this , CASAC concluded that “the scientific evidence supporting the finding that the current standard is inadequate to protect public health is strongest based on the controlled human exposure studies of respiratory effects” (Frey, 2014, p. 5). As discussed above and in section 3.1.2.1 of the PA (U.S. EPA, 2014c), controlled human exposure studies have reported a variety of*** E.O. 12866 Review

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Page 233 of 647 respiratory effects in healthy adults fol lowing exposures to O 3 concentrations of 60, 72, 105 or 80 ppb, and higher. Given the evidence for respiratory effects from controlled human exposure studies, the PA considers the extent to which standards with revised levels would be estimated to protect a t

- risk populations against exposures of concern to O 3 concentrations at or above the health benchmark concentrations of 60, 70, and 80 ppb (i.e., based on HREA estimates of one or more and two or more exposures of concern). In doing so, the PA notes that, d ue t o individual variability in responsiveness, only a subset of people who experience exposures at or above the three benchmark concentration s can be expected to experience associated health effects , and that available data are not sufficient to quantify that subset of people for most of the endpoints that have been evaluated in controlled human exposure studies (i.e., with the exception of FEV 1 decrements)

. The PA views the health effects evidence as a continuum with greater confidence and less uncertain ty about the occurrence of adverse health effects at higher O 3 exposure concentrations , and less confidence and greater uncertainty as one considers lower exposure concentrations (U.S. EPA, 2014c, section 3.2.2 , p. 3

- 101 ). While there is greater uncertai nty regarding the occurrence of adverse health effects at lower concentrations, the PA also notes that the controlled human exposure studies that provided the basis for benchmark concentrations have not evaluated responses in populations at the greatest ri sk from exposures to O 3 (e.g., children, people with asthma). Compared to the healthy people included in most controlled human

105 As noted above, for the 70 ppb exposure concentration Schelegle et al. (2009) reported that the actual 6.6

- hour mean exposure concentration was 72 ppb.*** E.O. 12866 Review

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Page 234 of 647 exposure studies, members of at

- risk populations and lifestages are at greater risk of experiencing adverse effects. Thus, the ef fects reported in healthy adults at each of the benchmark concentrations may underestimate effects in these at

- risk groups. I n considering the health evidence within the context of drawing conclusions on alternative standard levels , the PA balance s concerns about the potential for adverse health effects, especially in at

- risk populations, with the increasing uncertainty regarding the likelihood of such effects following exposures to lower O 3 concentrations. With respect to the lung function decrem ents that have been evaluated in controlled human exposure studies, the PA consider s the extent to which standards with revised levels would be estimated to protect healthy and at

- risk populations against O 3 - induced lung function decrements large enough to be adverse in some people (based on quantitative risk estimates in the HREA)

. As discussed in section 3.1.3 of the PA (U.S. EPA, 2014c) and section II.B.3 above , although some experts would judge single

occurrences of moderate responses to be a nuisance, especially for healthy individuals, a more general consensus view of the adversity of moderate lung function decrements emerges as the frequency of occurrence increases. Repeated occurrences of moderate responses, even in otherwise healthy individuals, may be considered to be adverse, since they could well set the stage for more serious illness (61 FR 65723). In reaching conclusions on alternative standard levels, the PA consider s the extent to which standards with revised levels would be estimated to prote ct healthy and at

- risk populations against one or more, and two or more, moderate (i.e., FEV 1 decrements ≥ 10% and ≥ 15%) and large (i.e., FEV 1 decrements ≥ 20%) lung function decrements

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Page 235 of 647 In evaluating the epidemiologic evidence within the context of dra wing conclusions on alternative standard levels , the PA consider s the extent to which available studies have reported associations with emergency department visits, hospital admissions, and/or mortality in locations that would likely have met alternative s tandards with levels below 75 ppb. In evaluating the epidemiologic evidence in this way, the PA considers both multicity and single

- city studies, recognizing the strengths and limitations of each. In particular , while single

- city studies are more limited t han multicity studies in terms of statistical power and geographic coverage, conclusions linking air quality in a specific area with health effect associations in that same area can be made with greater certainty for single

- city studies (i.e., compared to multicity studies reporting only multicity effect estimates). The PA also considers the epidemiologic evidence within the context of epidemiology

- based risk estimates

. Compared to the weight given to HREA estimates of exposures of concern and lung functi on risks (sections 4.4.2.1 and 4.4.2.2, above), and the weight given to the evidence (section 4.4.1), the PA places relatively less weight on epidemiologic

- based risk estimates. In doing so, the PA notes that the overall conclusions from the HREA likewise reflect less confidence in estimates of epidemiologic

- based risks than in estimates of exposures and lung function risks. The determination to attach less weight to the epidemiologic

- based estimates reflects the uncertainties associated with mortality and morbidity risk estimates, including the heterogeneity in effect estimates between locations, the potential for exposure measurement errors, and uncertainty in the interpretation of the shape of concentration

- response functions at lower O 3 concentrations (U.S. EPA, 2014a, section 9.6). The HREA also concludes that lower confidence should*** E.O. 12866 Review

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Page 236 of 647 be placed in the results of the assessment of respiratory mortality risks associated with long

- term O 3 exposures, primarily because that analysis is based on only one study (even though that study is well

- designed) and because of the uncertainty in that study about the existence and level of a potential threshold in the concentration

- response function (U.S. EPA, 2014a, section 9.6). In considering the epid emiology

- based risk estimates, the PA focuses on the extent to which potential alternative O 3 standards with levels below 75 ppb are estimated to reduce the risk of O 3 - associated mortality. 106 As discussed for the current standard (II.D.2.c), the PA consider s estimates of total risk (i.e., based on the full distributions of ambient O 3 concentrations) and estimates of risk associated with O 3 concentrations in the upper portions of ambient distributions. b. CASAC Advice The PA recognizes that decisions regardi ng the weight to place on various types of evidence, exposure/risk information, and associated uncertainties reflect public health policy judgments that are ultimately left to the Administrator. To help inform those judgments with regard to the range of al ternative primary O 3 standard levels appropriate for consideration, CASAC has provided advice to the Administrator based on their reviews of draft versions of the O 3 ISA, HREA, and PA. This section summarizes the advice provided by CASAC regarding alternat ive standard levels, as well as the views expressed at the CASAC meetings by public commenters. This section includes CASAC advice from the reconsideration of the 2008 final decision on the level of the standard, as

106 Differences in estimated respiratory morbidity risks between alternative standard levels are similar to the differences estimated for total mortality associated with short

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Page 237 of 647 well as CASAC advice received during the current review as it pertains to alternative standards. Consistent with its advice in 2008, CASAC reiterated during the reconsideration its support for an 8

- hour primary O 3 standard with a level ranging from 60 to 70 ppb, combined with the current indica tor, averaging time, and form. Specifically, in response to EPA’s solicitation of CASAC advice during the reconsideration, the CASAC letter (Samet 2010) to the Administrator stated: CASAC fully supports EPA’s proposed range of 0.060

– 0.070 parts per million (ppm) for the 8

- hour primary ozone standard. CASAC considers this range to be justified by the scientific evidence as presented in the Air Quality Criteria for Ozone and Related Photochemical Oxidants (March 2006) and Review of the National Ambient Air Quality Standards for Ozone: Policy Assessment of Scientific and Technical Information, OAQPS Staff Paper (July 2007). Similarly, in response to EPA’s request for additional advice on the reconsideration in 2011, CASAC reaffirmed its conclusion that “ the evidence from controlled human and epidemiologic studies strongly supports the selection of a new primary ozone standard within the 60

– 70 ppb range for an 8

- hour averaging time” (Samet, 2011). CASAC further concluded that this range “ would provide li ttle margin of safety at its upper end” (Samet, 2011, p. 2).
In the current review of the Second Draft PA , CASAC concurred with staff’s conclusions that it is appropriate to consider retaining the current indicator (O 3 ), averaging time (8

- hour average) an d form (three

- year average of the 4th highest maximum daily 8

- hour average

. With regard to level, CASAC stated the following (Frey,
2014 c , p. ii to iii ): The CASAC further concludes that there is adequate scientific evidence to recommend a range of levels for a revised primary ozone standard from 70 ppb to 60 ppb. The CASAC reached this conclusion based on the scientific*** E.O. 12866 Review

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Page 238 of 647 evidence from clinical studies, epidemiologic studies, and animal toxicology studies, as summarized in the Integrated Science Assessment (ISA), the findings from the exposure and risk assessments as summarized in the HREA, and the interpretation of the implications of these sources of information as given in the Second Draft PA. The CASAC acknowledges that the choice of a level within the r ange recommended based on scientific evidence [i.e., 70 to 60 ppb] is a policy judgment under the statutory mandate of the Clean Air Act. The CASAC advises that, based on the scientific evidence, a level of 70 ppb provides little margin of safety for the p rotection of public health, particularly for sensitive subpopulations. Thus, our policy advice is to set the level of the standard lower than 70 ppb within a range down to 60 ppb, taking into account your judgment regarding the desired margin of safety to protect public health, and taking into account that lower levels will provide incrementally greater margins of safety. The public commenters who expressed the view that the current primary O 3 standard is not adequate (II.D.4) also submitted comments that supported revising the level of the primary O 3 standard . Several of these commenters expressed the view that the level should be revised to the lower end of the range of 70 to 60 ppb , or in some cases to a level below 60 ppb

. These commenters often placed a large amount of emphasis on evidence from controlled human exposure studies for respiratory effects following exposures to 60 ppb O 3 . In addition, as discussed above (II.D.4), some p ublic c ommenters expressed the view that revision of the current stand ard is not necessary . Consistent with their view that it would not be appropriate to revise t he current standard, these commenters did not provide any provisional views on alternative levels below 75 ppb that would be appropriate for consideration.

c . PA conclusions on alternative O 3 standard levels*** E.O. 12866 Review

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Page 239 of 647 Using the approach discussed above to consider the scientific evidence and exposure/risk information, CASAC advice, and public comments, the PA reaches the conclusion that it is appropriate for the Administrat or to consider alternative primary O 3 standard levels from 70 to 60 ppb. The basis for this conclusion is discussed in detail in sections 4.4.1 and 4.4.2 of the PA (U.S. EPA, 2014c), and is summarized below. With regard to controlled human exposure studi es , the PA considers the lowest O 3 exposure concentrations at which various effects have been evaluated and statistically significant effects reported. The PA also consider s the potential for reported effects to be adverse, including in at

- risk populations and lifestages

. As discussed in section 3.1.2.1 of the PA (U.S. EPA, 2014c), controlled human exposure studies provide evidence of respiratory symptoms combined wit h lung function decrements (an adverse response based on ATS criteria) in healthy adults fo llowing 6.6 hour exposures to O 3 concentrations as low as 72 ppb , and evidence of potentially adverse lung function decrements and airway inflammation following 6.6 hour exposures to O 3 concentrations as low as 60 ppb. A lthough some studies show that respi ratory symptoms also develop during exposures to 60 ppb O 3 , the increase in symptoms has not been reported to reach statistical significance by the end of the 6.6 hour exposure period (Adams 2006; Schelegle et al. 2009). Thus, while significant increases in respiratory symptoms combined with lung function decrements have not been reported following exposures to 60 ppb O 3 , this combination of effects is likely to occur to some degree in healthy adults*** E.O. 12866 Review

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Page 240 of 647 with 6.6

- hour exposures to c oncentrations below 7 2 ppb, and also are more likely to

occur with longer (i.e., 8

- hour ) exposures. 107 With regard to the lowest exposure concentration shown to cause respiratory effects (i.e., 60 ppb), 108 the PA notes that m ost controlled human exposure stu dies have not evaluated O 3 c oncentrations below 60 ppb. Therefore, 60 ppb does not necessarily reflect an exposure concentration below which effects such as lung function decrements and airway inflammation no longer occur. This is particularly the case giv en that controlled human exposure studies w ere conducted in healthy adults, while people with asthma, including asthmatic children, are likely to be more sensitive to O 3 - induced respiratory effects. In support of this, some epidemiologic panel studies, whi ch can include members of at

- risk groups such as children and outdoor workers, have found respiratory effects at ambient concentrations lower than 60 ppb (U.S. EPA, 2014c, section 3.1.2.1). With regard to other O 3 - induced effects, the PA note s that airwa y hyperresponsiveness and impaired lung host defense capabilities have been reported in healthy adults engaged in moderate exertion following exposures to O 3 concentrations as low as 80 ppb, the lowest concentration evaluated for these effects. As discusse d in

107 In addition, CASAC observed that, “adverse health effects in young healthy adults occur with exposures to 72 ppb of ozone for 6.6 hours” and that “[i] t is the judgment of CASAC that if subjects had been exposed to ozone using the 8

- hour averaging period used in the standard, adverse effects could have occurred at [a] lower concentration. Further, in our judgment, the level at which adverse effects might be observed would likely be lower for more sensitive subgroups, such as those with asthma” (Frey, 2014, p. 5). 108 As discussed above (II.B.2), p rolonged exposure to 40 ppb O 3 has been shown to result in a small decrease in group mean FEV 1 that is not statistically different from responses following exposure to filtered air (Adams, 2002; Adams, 2006)

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Page 241 of 647 section 3.1.2.1 of the PA (U.S. EPA, 2014c) , these physiological effects have been linked to aggravation of asthma and increased susceptibility to respiratory infection, potentially leading to increased medication use, increased school and work absenc es, increased visits to doctors’ offices and emergency departments, and increased hospital admissions. These are all indicators of adverse O 3 - related morbidity effects, which are consistent with, and provide plausibility for, the adverse morbidity effects and mortality effects observed in epidemiolog ic studies. Based on consideration of the above evidence, the PA conclude s that available controlled human exposure studies support a level no higher than 70 ppb as the upper end of the range for consideration in the current review

. In reaching this conclusion, the PA
note s that 70 ppb is just below the O 3 exposure concentration reported to result in lung function decrements and respiratory symptoms in healthy adults (i.e., 72 ppb), a combination of effects tha t meet ATS criteria for an adverse response. In addition, while 70 ppb is well below the 80 ppb exposure concentration shown to cause potentially adverse respiratory effects such as airway hyperresponsiveness and impaired host

defense capabilities, these e ffects have not been evaluated at exposure concentrations below 80 ppb and there is no reason to believe that 80 ppb represents a threshold for such effects. The PA further conclude s t hat the evidence from controlled human exposure studies 109 supports considering alternative O 3 standard levels at least as low as 60 ppb. Potentially adverse lung function decrements and pulmonary inflammation have been

109 As discussed in sections 3.1.2.1 and 4.4.1 of the PA (U.S. EPA, 2014c) , panel studies also provide supporting evidence for these conclusions.*** E.O. 12866 Review

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Page 242 of 647 demonstrated to oc cur in healthy adults at 60 ppb . Thus, 60 ppb is a short

- term exposure

conce ntration that may be reasonably concluded to elicit adverse effects in at

- risk groups. Pulmonary inflammation, particularly if experienced repeatedly, provides a mechanism by which O 3 may cause other more serious respiratory morbidity effects (e.g., asthma exacerbations) and possibly extrapulmonary effects. As discussed in section 3.1.2.1 of the PA (U.S. EPA, 2014c) , the physiological effects reported in controlled human exposure studies down to 60 ppb O 3 have been linked to aggravation of asthma and increa sed susceptibility to respiratory infection, potentially leading to increased medication use, increased school and work absences, increased visits to doctors’ offices and emergency departments, and increased hospital admissions. The PA further note s that the range of alternative levels from 70 to 60 ppb is supported by evidence from epidemiologic studies and by exposure and risk estimates from the HREA. This evidence and exposure/risk information indicate that a level from anywhere in the range of 70 to 6 0 ppb would be expected to result in important public health improvements over the current standard. In particular, compared to the current standard a revised standard with a level from 70 to 60 ppb would be expected to ( 1 ) more effectively maintain short

- and long

- term O 3 concentrations below those present in the epidemiologic studies that reported significant O 3 health effect associations in locations likely to have met the current standard ; (2) reduce the occurrence of exposures of concern
to O 3 concentr ations that result in respiratory effects in healthy adults ( at or above 60 , 70, and 80 ppb); (3) reduce the occurrence of moderate

- to

- large O 3 - induced lung function decrements ; and ( 4 ) reduce the risk of O 3 - ass ociated mortality and morbidity, p articularl y*** E.O. 12866 Review

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Page 243 of 647 the risk associated with the upper portions of the distributions of ambient O 3 concentrations. In reaching a conclusion on whether it is appropriate to consider alternative standard levels below 60 ppb, the PA note s the following: (1) While controlled human exposure studies provide evidence for O 3 - induced respiratory effects following exposures to O 3 concentrations as low as 60 ppb, they do not provide evidence for adverse effects following exposures to lower concentrations. On this issue, CASAC concurr ed that 60 ppb O 3 is an appropriate and justifiable scientifically based lower bound for a revised primary standard, based upon findings of “adverse effects, including clinically significant lung function decrements and airway inflammation, after exposures to 60 ppb ozone in healthy adults with moderate exertion (Adams 2006; Schelegle et al., 2009; Brown et al. 2008; Kim et al., 2011), with limited evidence of adverse effects below 60 ppb” (Frey, 2014, p. 7). (2) Based on the HREA results, meeting an O 3 standa rd with a level of 60 ppb would be expected to almost eliminate exposures of concern to O 3 concentrations at or above 60 ppb. To the extent lower exposure concentrations may result in adverse health effects in some people, a standard level of 60 ppb would be expected to also reduce exposures to O 3 concentrations below 60 ppb. (3) U.S. and Canadian epidemiologic studies have not reported O 3 health effect associations based primarily on study locations likely to have met a standard with a level of 60 ppb.*** E.O. 12866 Review

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Page 244 of 647 (4) In al l of the urban study areas evaluated, a standard with a level of 60 ppb would be expected to maintain long

- term O 3 concentrations below those where a key study indicates the most confidence in a linear concentration

- response relationship with respiratory m ortality. Beyond the above considerations, the PA also note s the HREA estimates indicating that meeting an O 3 standard with a level of 60 ppb would result in important reductions in the risk of O 3 - induced lung function decrements and O 3 - associated mortal ity and morbidity. Although some risk is estimated to remain based on these metrics, even with a level of 60 ppb, the PA concludes that there is decreasing confidence in further public health improvements with levels below 60 ppb . The PA reaches this concl usion because, as noted above, at a level of 60 ppb virtually no one in the population would be expected to experience exposures of concern a t or above 60 ppb, and because epidemiologic studies have not reported O 3 health effect associations based primaril y on study locations likely to have met a standard with a level of 60 ppb. Given all of the above considerations the PA concludes that, compared to standards with levels from 70 to 60 ppb, the extent to which standards with levels below 60 ppb could result in further public health improvements becomes notably less certain. Therefore, the PA conclude s that it is not appropriate in this review to consider standard levels below 60 ppb. The range of levels from 70 to 60 ppb corresponds to the range of levels recommended for consideration by CASAC, based on the available evidence and information (Frey, 2014). While CASAC further offered what it characterized as “policy advice” to set the level below 70 ppb, based on margin of safety considerations, the Committe e acknowledged that “the choice of a level within the range recommended*** E.O. 12866 Review

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Page 245 of 647 based on scientific evidence [i.e., 70 to 60 ppb] is a policy judgment under the statutory mandate of the Clean Air Act” (Frey, 2014). Therefore, the PA conclusions on the appropriate range for alternative primary O 3 standard levels are consistent with CASAC conclusions that the scientific evidence and exposure/risk information supports consideration of levels from 70 to 60 ppb, and that the ultimate iden tification of a standard that protects public health with an adequate margin of safety will reflect policy judgments that are explicitly reserved for the Administrator (section 1.2.1). The following sections summarize the specific scientific evidence and exposure/risk information as they relate to revised O 3 standards with levels from the upper (70 ppb) (II.E.4.b.i), middle (65 ppb) (II.E.4.b.ii), and lower (60 ppb) (II.E.4.b.iii) portions of the range of 70 to 60 ppb. Key exposure/risk information consid ered in the PA is summarize d in Tables 4 and 5 , below (from U.S. EPA, 2014c, Tables 4

- 4 and 4

- 5)

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Page 246 of 647 Table 4 . Summary of Estimated Exposures of Concern for Potential Alternative O 3 Standard Levels of 70, 65, and 60 ppb in Urban Case Study Areas 110

Benchmark Level Alternative

Standard Level (ppb) Average

% Children Exposed 111 Number of

Children (5 to 18 years) [ Number of Asthmatic C hildren] 112 Average %

Reduction from Current Standard 113 % Children

-

Worst Year and Worst Area One or more exposures of concern per season ≥ 70 ppb 70 0.1

- 1.2 94,000 [10,000] 73 3.2

65 0

- 0.2 14,000 [2,000] 95 0.5 60 0 114 1,400 [200] 115 100 0.1
≥ 60 ppb 70 3.3

- 10.2 1,176,000 [126,000] 46 18.9 65 0

- 4.2 392,000 [42,000] 80 9.5 60 0

- 1.2 70,000 [8,000] 96 2.2 Two or more exposures of concern per season ≥ 70 ppb 70 0

- 0.1 5,400 [600] 95 0.4

65 0 300 [100] 100 0 60 0 0 [0] 100 0 ≥ 60 ppb 70 0.5

- 3.5 320,000 [35,000] 61 9.2

65 0

- 0.8 67,000 [7,500] 92 2.8 60 0

- 0.2 5,100 [700] 100 0.3

110 All alternative standard level s evaluated in the HREA were effective at limiting exposures of concern at or above 80 ppb (U.S. EPA, 2014c, Figures 4

- 1 to 4

- 4 )

. Therefore, Table 4 focuses on exposures of concern at or above the 70 and 60 ppb benchmark concentra tions. 111 Estimates for each urban case study area were averaged for the years evaluated in the HREA (2006 to 2010). Ranges reflect the ranges across urban study areas

. 112 Numbers of children exposed in each urban case study area were averaged over the years 2006 to 2010. These averages were then summed across urban study areas

. Numbers are rounded to nearest thousand unless otherwise indicated. 113 Percent reductions in eac h urban study area were calculated and averaged across areas. 114 Estimates smaller than 0. 05 % were rounded to zero. 115 As discussed in section 4.3.3 of the HREA (U.S. EPA, 2014a) , the model

- based air quality adjustment approach used to estimate risks associ ated with the current and alternative standards was unable to estimate the distribution of ambient O 3 concentrations in New York City upon just meeting an alternative standard with a level of 60 ppb. Therefore, for the 60 ppb standard level the numbers of children and asthmatic children reflect all of the urban study areas except New York.*** E.O. 12866 Review

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Page 247 of 647 Table 5 . Summary of Estimated Lung Function Decrements for Potential Alternative O 3 Standard Levels of 70, 65, and 60 ppb in Urban Case Study Areas Lung Function Decrement Alternative

Standard Level Average %

Children 116 Number of Children (5

to 18 years) [ Number of Asthmatic C hildren] 117 Average % Reduction from Current Standard % Children

Worst Year and Area One or more decrements per season ≥ 10% 70 11

- 17 2,527,000 [261,000] 15 20

65 3

- 15 1,896,000 [191,000] 31 18 60 5

- 11 1,404,000 [139,000] 118 45 13 ≥ 15% 70 2

- 4 562,000 [58,000] 26 5

65 0

- 3 356,000 [36,000] 50 4 60 1

- 2 225,000 [22,000] 67 3 ≥ 20% 70 1

- 2 189,000 [20,000] 32 2.1

65 0

- 1 106,000 [11,000] 59 1.4 60 0

- 1 57,000 [6,000] 77 0.7

Two or more decrements per season ≥ 10% 70 5.5

- 11 1,414,000 [145,000] 17 13

65 1.3

- 8.8 1,023,000 [102,000] 37 11 60 2.1

- 6.4 741,000 [73,000] 51 7.3 ≥ 15% 70 0.9

- 2.4 276,000 [28,000] 29 3.1

65 0.1

- 1.8 168,000 [17,000] 54 2.3 60 0.2

- 1.0 101,000 [10,000] 71 1.4 ≥ 20% 70 0.3

- 0.8 81,000 [8,000] 34 1.1

65 0

- 0.5 43,000 [4,000] 66 0.8 60 0

- 0.2 21,000 [2,000] 83 0.4

116 Estimates in each urban case study area were averaged for the years evaluated in the HREA (2006 to 2010). Ranges reflect the ranges across urban study areas

. 117 Number s of children estimated to experience decrements in each study urban case study area were averaged over 2006 to 2010. These averages were then summed across urban study areas . Numbers are rounded to nearest thousand unless otherwise indicated. 118 As discuss ed in section 4.3.3 of the HREA (U.S. EPA, 2014a) , the model

- based air quality adjustment approach used to estimate risks associated with the current and alternative standards was unable to estimate the distribution of ambient O 3 concentrations in New York City upon just meeting an alternative standard with a level of 60 ppb. Therefore, for the 60 ppb standard level the numbers of children and asthmatic children reflect all of the urban study areas except New York.*** E.O. 12866 Review

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Page 248 of 647 i. O 3 standard level of 70 ppb As noted above, a level of 70 ppb is below the lowest O 3 exposure concentration that has been reported to elicit a range of respiratory effects that includes airway hyperresponsiveness and decreased lung host defense, in addition to lung function decrements, airway inflammation, and respiratory symptoms (i.e., 80 ppb). A level of 70 ppb is also below the lowest exposure concentration at which the combined occurrence of respiratory symptoms and lung function decrements have been reported (i.e., 72 ppb), a combination judged adverse by the ATS (section 3.1.3). A l evel of 70 ppb is above the lowest exposure concentration demonstrated to result in lung function decrements large enough to be judged an abnormal response by ATS and above the lowest exposure concentration demonstrated to result in pulmonary inflammation (i.e., 60 ppb). Compared to the current standard, the HREA estimates that a revised O 3 standard with a level of 70 ppb would reduce exposures of concern to O 3 concentrations of 60, 70, and 80 ppb in urban study areas , with such a standard level estimated to be most effective at limiting exposures at or above the higher health benchmark concentrations and at limiting multiple occurrences of such exposures. On average over the years 2006 to 201 0, for a standard with a level of 70 ppb , up to about 1% of children (i.e., ages 5 to 18) are estimated to experience e xposures of concern at or above 70 ppb (73% reduction, compared to current standard), and far less than 1% are estimated to experience two or more such exposures (95% reduction, compared to current standard). In the worst

- case location and year (i.e., location and year with the largest exposure estimate), about 3% of children are estimated to experience one or more exposures of concern at or above 70 ppb, and less than 1% are estimated to experience two or more. Far less than 1% of*** E.O. 12866 Review

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Page 249 of 647 children are estimated to experience exposures of concern at or above the 80 ppb benchmark concentration, even i n the worst

- case year (Table 4, above ). 119 As noted above, CASAC advised EPA that 60 ppb is an appropriate exp osure of

concern with respect to adverse effects on people with asthma, including children (Frey, 2014, p. 6, 8)

. For a n O 3 standard with a level of 70 ppb , a bout 3 to 10% of children , including asthmatic children, are estimated to experience one or more e xposure s of concern at or above 60 ppb in a single O 3 season. Compared to the current standard, this reflects about a 46% reduction, on average across the urban study areas

. A bout 1% to 4% of children are estimated to experience two or more exposure s of co ncern at or above 60 ppb (approximately 60% reduction, compared to current standard). I n the worst

- case location and year, for a standard set at 70 ppb, about 1 9% of children are estimated to experience one or more exposures of concern at or above 60 ppb, and 9 % are estimated to experience two or more such exposures (Table 4, above)

. Compared to the current standard, the HREA estimates that a revised O 3 standard with a level of 70 ppb would also reduce O 3 - induced lung function decrements in children. A level of 70 ppb is estimated to be most effective at limiting the occurrences of moderate and large lung function decrements (i.e., FEV 1 decrements ≥ 15% and ≥ 20% , respectively ) , and at limiting multiple oc currences of O 3 - induced decrements

. On average over the years 2006 to 2010, for a standard with a level of 70 ppb , about 2 to 4% of children in the urban study areas are estimated to experience one or more moderate O 3 -

119 As noted above, due to interindividual variability, children (or adults) exposed at these levels will not necessarily experience health effects; the information available for some health effects is not sufficient to quantify the numbers of children in the urban study areas who might experience these effects.*** E.O. 12866 Review

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Page 2 50 of 647 induced lung function decrements (i.e. , FEV 1 decrement ≥ 15% ), which would be of concern for healthy people , and about 1 to 2.5% of children are estimated to experience two or more such decrements (approximately 30% reduction, compared to the current standard) . In the worst

- case location and year , up to 5 % of children are estimated to experience one or more O 3 - induced lung function decrements ≥ 15%, and up to 3 % are estimated to experience two or more such decrements. For a standard set at 70 ppb , about 2% or fewer chi ldren are estimated to experience large O 3 - induced lung function decrements (i.e., FEV 1 decrement ≥ 20% ), and about 1% or fewer children are estimated to experience two or more such decrements , even in the worst

- case years and locations (Table 5 , above )

. On average over the years 2006 to 2010, for an O 3 standard set at 70 ppb , a bout
11 to 1 7% of children in the urban study areas are estimated to experience one or more moderate O 3 - induced lung function decrements (i.e., FEV 1 decrement ≥ 10% ), which could be adverse for people with lung disease. This reflects an average reduction of about 15 %, compared to the current standard. A bout 6 to 11% of children are estimated to experience two or more such decrements (17% reduction, compared to current standard).
In the worst

- case location and year , for a standard set at 70 ppb , a bout 20 % of children in the urban study areas are estimated to experience one or more O 3 - induced lung function decrements ≥ 10%, and 1 3 % are estimated to experience two or more such decremen ts (Table 5 , above ). Compared to the current standard, a revised standard with a level of 70 ppb would also more effectively maintain short

- term ambient O 3 concentrations below those present in the epidemiologic studies that reported significant O 3 healt h effect associations in*** E.O. 12866 Review

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Page 251 of 647 locations likely to have met the current standard. In particular, the single

- city study by Mar and Koenig (2009) reported positive and statistically significant associations with respiratory emergency department visits in children and adults in a location that likely would have met the current O 3 standard over the entire study period but violated a revised

s tandard with a level of 70 ppb or below. None of the single

- city studies evaluated in section 4.4.1 of the PA (U.S. EPA, 2014c) provide evidence for O 3 health effect associations in locations meeting a standard with a level of 70 ppb or below. While this analysis does not provide information on the extent to which the reported O 3 - associated emergency dep artment visits would persist upon meeting an O 3 standard with a level of 70 ppb, or on the extent to which standard levels below 70 ppb could further reduce the incidence of such emergency department visits, 120 it suggests that a revised O 3 standard with a l evel at or below 70 ppb would require reductions in the ambient O 3 concentrations that provided the basis for the health effect associations reported by Mar and Koenig. As discussed above, compared to single

- city studies, there is greater uncertainty
in linking air quality concentrations from individual study cities to multicity effect estimates . With regard to the multicity studies in this review , the PA note s that Dales et al. (2006) reported significant associations with respiratory hospital admissions based on air quality in 11 Canadian cities, most of which would likely have met the current standard over the entire study period but violated a revised standard with a level of 70 ppb or below over at least part of th at period (Table 4

- 1). This analysis suggests that

120 Put another way, one cannot infer from this analysis the extent to which effects would occur at O 3 concentrations b elow those observed in the study.*** E.O. 12866 Review

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Page 252 of 647 while the current standard would allow the ambient O 3 concentrations in most of the study locations that provided the basis for the association with hospital admissions, a revised O 3 standard with a level at or below 70 ppb would require redu ctions in those ambient O 3 concentrations. As with the study by Mar and Koenig, this analysis does not provide information on the extent to which the reported O 3 - associated hospital admissions would persist upon meeting an O 3 standard with a level of 70 pp b, or on the extent to which standard levels below 70 ppb could further reduce the incidence of such hospital admissions. 121 With regard to long

- term O 3 concentrations, the PA evaluates the long

- term O 3 metrics reported to be associated with mortality or morbidity in recent epidemiologic studies (e.g., seasonal averages of 1

- hour or 8

- hour daily max concentrations) . Compared to the current standard, a revised standard with a level of 70 ppb would be expe cted to reduce the risk of respiratory mortality associated with long

- term O 3 concentrations, based on information from the study by Jerrett et al. (2009), though the PA notes the HREA conclusion, discussed above, that lower confidence should be placed in respiratory mortality risk estimates based on this study (U.S. EPA, 2014a, section 9.6). In addition, a standard with a level of 70 ppb would be expected to more effectively maintain long

- term O 3 concentrations below those where the study by Jerrett et al. (2009) indicates the most confidence in the reported association with respiratory mortality. 122

121 In addition, for the other multicity studies identified in Table 4

- 1 (Cakmak et al., 2006; Stieb et al., 2009; Katsouyanni et al., 2009), and for the study by Bell et al. (2006) (for the 30 ppb cut point) (Table 4

- 2), the majority of study locations would likely have met a standard with a level of 70 ppb. 122 As discussed in section 3.1.4.3 of the PA (U.S. EPA, 2014c) , the study by Jerrett et al. (2009) suggests notably decreased confidence in the reported linear concentration

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Page 253 of 647 Specifically, air quality analyses indicate this to be the case in 9 out of the 12 urban study

areas for a level of 70 ppb, compared to 6 out of 12 areas for the current standard. Finally, a revised standard with a level of 70 ppb would be expected to reduce long

- term O 3 concentrations based on the types of metrics that have been reported in recent epidemiologic studies to be associated with respiratory morbidity (i.e., seasonal averages of daily maximum 8

- hour concentrations). In further considering the potential implications of epidemiology studies for alternative standard levels, the PA note s estimates of total mortality associated with short

- term O 3 concentra tions. 123 As discussed above, the PA consider s estimates of total risk (i.e., based on the full distributions of ambient O 3 concentrations) and estimates of risk associated with O 3 concentrations in the upper portions of ambient distributions. With regard to total risk the PA notes that, when summed across urban study areas , a standard with a level of 70 ppb is estimated to reduce the number of deaths associated with short

- term O 3 concentrations by about 4% (2007) and 2% (2009), compared to the current standa rd. 124 Based on a national modeling analysis, the majority of the U.S.

r esponse function for long

- term O 3 concentrations in the first quartile (i.e ., at or below about 53 ppb), given the widening in confidence intervals for lower concentrations; the fact that most study cities contributing to the linear function had O 3 concentrations in the highest three quartiles, accounting for approximately 72% of the respiratory deaths in the cohort (based on Table 2 in the published study); and the limited evidence presented in the published study for a threshold at or near 56 ppb. 123 As discussed above, compared to the weight given to the evidence and to HREA es timates of exposures of concern and lung function risks, we place relatively less weight on epidemiologic

- based risk estimates. 124 A standard with a level of 70 ppb is also estimated to reduce respiratory mortality associated with long

- term O 3 concentrations in urban study areas . However, given uncertainties associated with these risk estimates, as discussed above, we give them limited weight.*** E.O. 12866 Review

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Page 254 of 647 population would be expected to experience reductions in such risks upon reducing precursor emissions. Compared to the total risk estimates noted above, an O 3 standard with a level of
70 ppb is estimated to be more effective at reducing the number of deaths associated with short

- term O 3 concentrations at the upper ends of ambient distributions. Specifically, for

area - wide O 3 concentrations at or above 40 ppb , a standard with a level of 70 ppb is estimated to reduce the number of deaths associated with short

- term O 3 concentrations by about 10% compared to the current standard. In addition, for area - wide concentrations at or above 6 0 ppb , a standard with a level of 70 ppb is estimated to r educe O 3 - associated deaths by about 50% to 70% (Figure 4

- 13). The PA noted that in providing the advice that 70 ppb is an appropriate upper bound for consideration, CASAC advised that a level of 70 ppb would provide little margin of safety for protection of public health, particularly for sensitive subpopulations (Frey, 2014, p. 8). In particular, CASAC stated that: At 70 ppb, there is substantial scientific certainty of a variety of adverse effects, including decrease in lung function, increase in respi ratory symptoms, and increase in airway inflammation. Although a level of 70 ppb is more protective of public health than the current standard, it may not meet the statutory requirement to protect public health with an adequate margin of safety (Frey, 2014 , p.8). However, the c ommittee also acknowledged that “the choice of a level within the range recommended based on scientific evidence [i.e., 70 to 60 ppb] is a policy judgment under the statutory mandate of the Clean Air Act” (Frey, 2014). In summary, c ompared to the current standard, the PA concludes that a revised O 3 standard with a level of 70 ppb would be expected to (1) reduce the occurrence of exposures of concern to O 3 concentrations that result in respiratory effects in healthy*** E.O. 12866 Review

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Page 255 of 647 adults ( at or above 60 and 70 ppb) by about 45 to 95%, almost eliminating the occurrence of multiple exposures at or above 70 ppb; (2) reduce the occurrence of moderate

- to

- large O 3 - induced lung function decrements ( FEV 1 decrements > 10, 15, 20%) by about 15 to 35 %, most effectively limiting the occurrence of multiple decrements and decrements > 15, 20%; (3) more effectively maintain short

- and long

term O 3 concentrations below those present in the epidemiologic studies that reported significant O 3 health effect as sociations in locations likely to have met the current standard ; 125 and ( 4 ) reduce the risk of O 3 - associated mortality and morbidity, particularly the risk associated with the upper portions of the distributions of ambient O 3 concentrations. ii. O 3 standard level of 65 ppb The PA also considers a standard with a level of 65 ppb. A level of 65 ppb is well below 80 ppb, an O 3 exposure concentration that has been reported to elicit a range of respiratory effects that includes airway hyperresponsiveness and dec reased lung host defense, in addition to lung function decrements, airway inflammation, and respiratory symptoms. A standard level of 65 ppb is also below the lowest exposure concentration at which the combined occurrence of respiratory symptoms and lung f unction decrements has been reported (i.e., 72 ppb), a combination judged adverse by the ATS (section 3.1.3). A level of 65 ppb is above the lowest exposure concentration demonstrated to result in lung function decrements large enough to be judged an abnor mal response by ATS, where statistically significant changes in group mean responses would be judged to

125 E pidemiologic studies also provide some evidence for O 3 health effect associations in locations lik ely to have met a standard with a level of 70 ppb, as discussed below for lower standard levels.*** E.O. 12866 Review

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Page 256 of 647 be adverse by ATS, and which the CASAC has indic a ted could be adverse in people with lung disease (i.e., 60 ppb). A level of 65 ppb is also above the lo west exposure concentration at which pulmonary inflammation has been reported in healthy adults (i.e., 60 ppb). Compared to the current standard and a revised standard with a level of 70 ppb, the HREA estimates that a standard with a level of 65 ppb woul d reduce exposures of concern to the range of O 3 benchmark concentrations analyzed (i.e., 60, 70, and 80 ppb). The HREA estimates that meeting a standard with a level of 65 ppb would eliminate exposures of concern at or above 80 ppb in the urban study areas . Such a standard is estimated to allow far less than 1% of children in the urban study areas to experience one or more exposures of concern at or above the 70 ppb benchmark level, even in the worst

case years and locations, and is estimated to elimin ate the occurrence of two or more exposures at or above 70 ppb ( Table 4, above ). In addition, for a standard with a level of 65 ppb , b etween 0 and about 4 % of children (including asthmatic children) in urban study areas are estimated to experience

e xposu res of concern at or above 6 0 ppb , which CASAC has indicated is an appropriate exposure of concern for people with asthma, including children. This reflects an 80% reduction (on average across areas), relative to the current standard. L ess than 1 % of child ren are estimated to experience two or more e xposures of concern at or above 6 0 ppb (> 90% reduction, compared to current standard). In the worst

- case location and year, about 10% of children are estimated to experience one or more exposures of concern at or above 60 ppb, with about 3% estimated to experience two or more such exposures ( Table 4, above ).*** E.O. 12866 Review

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Page 257 of 647 Compared to the current standard and a revised standard with a level of 70 ppb, the HREA estimates that a standard with a level of 65 ppb would also further reduce the occurrence of O 3 - induced lung function decrements. For a level of 65 ppb, about 4% of children , or less, are estimated to experience moderate O 3 - induced FEV 1 decrements ≥ 15% (50% reduction, compared to current standard), even considering the worst

- case location and year. A bout 2% of children , or less, are estimated to experience two or more such decrements. Only about 1% of children , or less, are estimated to experience large
O 3 - induced lung function decrements (i.e., FEV 1 decrement ≥ 20% ) , even in the worst

case year and location

. In addition , for a standard with a level of 65 ppb , a bout 3 to 15% of children are estimated to experience one or more moderate O 3 - induced lung f unction decrements (i.e.,
FEV 1 decrement ≥ 10% ), which CASAC has indicated could be adverse for people with lung disease. This reflects an average reduction of about 30 %, relative to the current standard. A bout 1 to 9% of children in the urban study areas are estimated to experience
two or more such decrements (37% reduction, compared to current standard). In the
worst

- case location and year , for a standard set at 65 ppb , u p to about 18 % of these children are estimated to experience one or more moderate O 3 - induced lung function decrements ≥ 10%, and up to 11 % are estimated to experience two or more such decrements

. With regard to O 3 epidemiologic studies , the PA notes that, compared to a standard with a level of 70 ppb, a revised standard with a level of 65 ppb would more effectively maintain short

- term O 3 concentrations below those present in the epidemiologic studies that reported significant O 3 health effect associations in locations*** E.O. 12866 Review

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Page 258 of 647 likely to have met the current standard. In particular, Katsouyanni et al. (2009) reported statistically significant associations with mortality based on air quality in 12 Canadian cities, most of which would likely have met a standard with a level of 70 ppb over the entire study period but violated a revised standard with a level of 65 ppb or below over at least part of th at period (Table 4

- 1). This analysis suggests that while the current standard or a standard with a level of 70 ppb would allow the ambient O 3 concentrations in most of the study locations that provided the basis for the association with mortality in this study, a revised O 3 standard with a level at or below 65 ppb would require reductions in those ambient O 3 concentrations. As discussed above for a level of 70 ppb, this analysis does not provide information on the extent to which O 3 - associated mortality would persist upon meeting an O 3 standard with a level of 65 ppb, or on the extent to which standard levels below 65 ppb could further reduce the incidence of this mortality. 126 With regard to long

- term O 3 concentrations, as for 70 ppb (above) the PA evaluates the long

- term O 3 metrics reported to be associated with mortality or morbidity in recent epidemiologic studies (e.g., seasonal averages of 1

- hour or 8

- hour daily max concentrations) . Compared to the c urrent standard or a revised O 3 standard with a level of 70 ppb, a revised standard with a level of 65 ppb would be expected to further reduce the risk of respiratory mortality associated with long

- term O 3 concentrations, based on information from the stud y by Jerrett et al. (2009). 127 In addition, a standard with a level

126 For the other multicity studies identified in Table 4

- 1 (Cakmak et al., 2006; Stieb et al., 2009; Katsouyanni et al., 2009 (for hospital admissions)), and f or the study by Bell et al. (2006) (for the 30 ppb cut point) (Table 4

- 2), the majority of study locations would have met a standard with a level of 65 ppb. 127 Though as discussed above, the PA notes the lower confidence we place in these risk results (U.S . EPA, 2014a, section 9.6).*** E.O. 12866 Review

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Page 259 of 647 of 65 ppb would be expected to more effectively maintain long

- term O 3 concentrations below those where the study by Jerrett et al. (2009) indicates the most confidence in the reported associ ation with respiratory mortality. Specifically, air quality analyses indicate this to be the case in 10 out of the 12 urban study areas for a level of 65 ppb, compared to 6 out of 12 areas for the current standard and 9 out of 12 for a standard with a leve l of 70 ppb (Table 4

- 3). Finally, a revised standard with a level of 65 ppb would be expected to further reduce long

- term O 3 concentrations based on the types of metrics that have been reported in recent epidemiologic studies to be associated with respirat ory morbidity (i.e., seasonal averages of daily maximum 8

- hour concentrations). In further considering the potential implications of epidemiology studies for alternative standard levels, the PA notes estimates of total mortality associated with short

- ter m O 3 . 128 As discussed above, the PA considers estimates of total risk (i.e., based on the full distributions of ambient O 3 concentrations) and estimates of risk associated with O 3 concentrations in the upper portions of ambient distributions. With regard to total risk the PA notes that, when summed across urban study areas , a standard with a level of 65 ppb is estimated to reduce the number of deaths associated with short

- term O 3 exposures by about 13% (2007) and 9% (2009), compared to the current standard. 129 For

area - wide concentrations at or above 40 ppb , a standard level of 65 ppb is estimated to reduce O 3 - associated deaths by almost 50% compared to the current standard, when

128 As discussed above, compared to the weight given to the evidence and to HREA estimates of exposures of concern and lung function risks, the PA places relatively less weight on epidemiologic

- based risk estimates. 129 A standard with a level of 65 ppb is also estimated to reduce respiratory mortality associated with long

- term O 3 concentrations in urban study areas . However, given uncertainties associated with these risk estimates, as discussed above, we give them limited weight.*** E.O. 12866 Review

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Page 260 of 647 summed across urban study areas . For area - wide concentrations at or above 6 0 ppb , a standard level of 65 ppb is estimated to reduce O 3 - associated deaths by more than 80% (Figure 4

- 13). In summarizing CASAC’s advice regarding a standard with a level of 65, the PA noted CASAC’s conclusion that an alternative standard with a level of 65 p pb would further reduce , though not eliminate, the frequency of lung function decrements > 15% and w ould lead to lower frequency of short

- term premature mortality (i.e., compared to a standard with a level of 70 ppb) (Frey, 2014, p. 8). In summary, comp ared to a standard with a level of 70 ppb, the PA concludes that a revised standard with a level of 65 ppb would be expected to further reduce O 3 exposures and health risks. In particular, a standard with a level of 65 ppb is estimated to (1) reduce the oc currence of exposures of concern by about 80 to 100% , compared to the current standard , decreasing exposures at or above 60 ppb and almost eliminating exposures at or above 70 and 80 ppb; (2) reduce the occurrence of FEV 1 decrements > 10, 15, and 20% by ab out 30 to 65%, c ompared to the current standard ; (3) more effectively maintain short

- and long

- term O 3 concentrations below those present in the epidemiologic studies that reported significant O 3 health effect associations in locations likely to have met the current standard ; 130 and (4) further reduce the risk of O 3 - asso ciated mortality and morbidity , particularly the risk associated with the upper portion of the distribution of ambient O 3 concentra tions. iii. O 3 standard level of 60 ppb

130 Though epidemiologic studies also provide evidence for O 3 health effect associations in locations likely to have met a standard with a level of 65 ppb, as discussed below for a level of 60 ppb.*** E.O. 12866 Review

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Page 261 of 647 The PA also c onsider s a standard with a level of 60 ppb. A level of 60 ppb is well below the O 3 exposure concentration that has been reported to elicit a wide range of potentially adverse respiratory effects in hea lthy adults (i.e., 80 ppb). A level of 60 ppb is also below the lowest concentration where the combined occurrence of respiratory symptoms and lung function decrements was observed, a combination judged adverse by the ATS (i.e., 72 ppb, discussed in sectio n 3.1.3). A level of 60 ppb corresponds to the lowest exposure concentration demonstrated to result in lung function decrements that are large enough to be judged an abnormal response by ATS, that meet ATS criteria for adversity based on a downward shift i n the distribution of FEV1, and that the CASAC indicated could be adverse in people with lung disease. A level of 60 ppb also corresponds to the lowest exposure concentration at which pulmonary inflammation has been reported in a single c ontrolled human ex posure study

. Based on the HREA analyses of O 3 exposures of concern, a standard with a level of 60 ppb is estimated to eliminate exposures of concern at or above the 70 and 80 ppb benchmark concentrations and t o be more effective than the higher standard levels at limiting expos ures of concern at or above 60 ppb

. On average over the years 2006 to 2010, for a standard with a level of 60 ppb , between 0 and about 1 % of children , including asthmatic children, in urban study areas are estimated to experience e xposures of concern at or above 6 0 ppb , which CASAC indicated is an appropriate exposure of concern for asthmatic children. This reflects a 96% reduction (on average across areas), compared to the current standard. V irtually no children are estimated to ex perience two

or more e xposures of concern at or above 6 0 ppb . In the worst

- case location and year, about 2% of children are estimated to experience exposures of concern at or above 60*** E.O. 12866 Review

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Page 262 of 647 ppb, with far less than 1% estimated to experience two or more such expo sures ( Table 4, above ). Based on the HREA analyses of O 3 - induced lung function decrements, a standard with a level of 60 ppb would be expected to be more effective than a level of 65 or 70 ppb at limiting the occurrence of O 3 - induced lung function decrem ents. For a standard with a level of 60 ppb , about 2% of children , or less, in the urban study areas are estimated to experience one or more moderate O 3 - induced FEV 1 decrements ≥ 15% (almost 70% reduction, compared to current standard), and about 1% or les s are estimated to experience two or more such decrements (3% in the location and year with the largest estimates)

. A bout 1% of children, or less, are estimated to experience large
O 3 - induced lung function decrements (i.e., FEV 1 decrement ≥ 20% ) , even in the worst

case locations and year (Table 5 , above )

. In addition , for a standard with a level of 60 ppb , a bout 5 to 11% of children in the urban study areas are estimated to experience one or more moderate O 3 - induced lung function decrements tha t CASAC indicated could be adverse for people with lung disease (i.e., FEV 1 decrements ≥ 10% ). This reflects an average reduction of about 45 %, compared to the current standard. A bout 2 to 6% of children in these areas are estimated to experience two or mo re such decrements (51% reduction, compared to current standard). In the worst

- case location and year, for a standard set at 60 ppb , up to about
13 % of children are estimated to experience one or more moderate O 3 - induced FEV 1 decrements ≥ 10%, and 7 % are estimated to experience two or more such decrements (Table 5 , above ).*** E.O. 12866 Review

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Page 263 of 647 With regard to O 3 epidemiologic studies the PA notes that, compared to a standard with a level of 65 or 70 ppb, a revised standard with a level of 60 ppb would more effectively mai ntain short

- term O 3 concentrations below those present in the epidemiologic studies that reported significant O 3 health effect associations in locations likely to have met the current standard. Specifically, in all of the U.S. and Canadian epidemiologic st udies evaluated, the majority of study cities had ambient O 3 concentrations that would likely have violated a standard with a level of 60 ppb. Thus, none of the U.S. and Canadian epidemiologic studies analyzed provide evidence for O 3 health effect associat ions when the majority of study locations would likely have met a standard with a level of 60 ppb (Tables 4

- 1 and 4

- 2). As discussed above, while this analysis does not provide information on the extent to which the O 3 - associated morbidity or mortality wou ld persist upon meeting an O 3 standard with a level of 60 ppb, it suggests that a revised O 3 standard with a level of 60 ppb would require reductions in the ambient
O 3 concentrations that provided the basis for those health effect associations. With regard to long

- term O 3 concentrations, compared to the current standard or a revised O 3 standard with a level of 65 or 70 ppb, a revised standard with a level of 60 ppb would be expected to further reduce the risk of respiratory mortality associated with l ong term O 3 concentrations, based on information from the study by Jerrett et al. (2009). 131 In addition, a standard with a level of 60 ppb would be expected to more effectively maintain long

- term O 3 concentrations below those where the study by Jerrett et a l. (2009) indicates the most confidence in the reported association with respiratory mortality.

131 Though as discussed above, the PA notes the lower confidence we place in these risk results (U.S. EPA, 2014a, section 9.6).*** E.O. 12866 Review

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Page 264 of 647 Specifically, air quality analyses indicate this to be the case in all of the urban study areas evaluated at a level of 60 ppb, compared to 6 out of 12 areas fo r the current standard, 9 out of 12 for a standard with a level of 70 ppb, and 10 out of 12 for a standard with a level of 65 ppb (Table 4

- 3). Finally, a revised standard with a level of 60 ppb would be expected to further reduce long

- term O 3 concentration s based on the types of metrics that have been reported in recent epidemiologic studies to be associated with respiratory morbidity (i.e., seasonal averages of daily maximum 8

- hour concentrations). In further considering the potential implications of epi demiology studies for alternative standard levels, the PA notes estimates of total mortality associated with short

- term O 3 concentrations. 132 As discussed above, the PA consider s estimates of total risk (i.e., based on the full distributions of ambient O 3 co ncentrations) and estimates of risk associated with O 3 concentrations in the upper portions of ambient distributions. With regard to total risk the PA notes that, when summed across urban study areas , a standard with a level of 60 ppb is estimated to reduc e the number of deaths associated with short

- term O 3 exposures by about 15% (2007) and 11% (2009), compared to the current standard (Figure 4

- 13). 133 For area - wide concentrations at or above 40 ppb , a standard with a level set at 60 ppb is estimated to reduc e O 3 - associated deaths by almost 60% compared to the current standard. For area - wide concentrations at or above 6 0 ppb ,

132 As discussed above, compared to the weight given to the evidence and to HREA estimates of exposures of concern and lung function risks, we place relatively less weight on epidemiologic

- based risk estimates. 133 A standard with a level of 60 ppb is also estimated to reduce respiratory mortality associated with long

- term O 3 concentrations in urban study areas . However, given uncertaint ies associated with these risk estimates, as discussed above, we give them limited weight.*** E.O. 12866 Review

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Page 265 of 647 a standard level of 60 ppb is estimated to reduce O 3 - associated deaths by over 95%

c ompared to the current standard

. In summarizing CASAC’s advice, the PA notes CASAC’s statement that, relative to the current standard, or alternative O 3 standards with levels of 65 or 70 ppb: The frequency of lung function decrements and premature mortality from short

- term exposure to ozone decreases ev en further when the alternative standard is lowered to 60 ppb (Frey, 2014, p.8). CASAC also concluded that “the recommended lower bound of 60 ppb would certainly offer more public health protection than levels of 70 ppb or 65 ppb and would provide an adeq uate margin of safety” (Frey, 2014, p. ii). In summary, compared to a standard with a level of 65 or 70 ppb, the PA concludes that a revised standard with a level of 60 ppb would be expected to further reduce O 3 exposures and health risks. In particular , a standard with a level of 60 ppb is estimated to (1) reduce the occu rrence of exposures of concern by about 95 to 100%, compared to the current standard, almost eliminating exposures at or above 60 ppb; (2) reduce the occurrence of FEV 1 decrements > 10, 15, and 20% by about 45 to 85% , compared to the current standard; (3) more effectively maintain short

- and long

- term O 3 concentrations below those present in the epidemiologic studies that reported significant
O 3 health effect associations in locations likely to have met the current standard ; 134 and (4) further reduce the risk of O 3 - asso ciated mortality and morbidity , particularly the risk associated with the upper portion of the distribution of ambient O 3 concentra tions

. d. Administrator’s proposed conclusions on level

134 As discussed above, these studies do not provide information on the extent to which O 3 health effect associations would persist following reductions in ambient O 3 concentrations in order to meet a standard with a level of 60 ppb.*** E.O. 12866 Review

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Page 266 of 647 This section discusses the Administrator’s proposed conclusions on the level of the primary O 3 standard. In conjunction with her proposed decisions to retain the current indicator, averaging time, a nd form (II.E.1 to II.E.3, above), the Administrator proposes to revise the level of the primary O 3 s tandard to within the range of 65 to 70 ppb. In doing so, she is mindful that the selection of a primary O 3 standard that is requisite to protect public he alth with an adequate margin of safety requires judgment s based on an interpretation of the scientific evidence and exposure/risk information that neither
overstate s nor understate s the strength s and limitations of that evidence and information, nor the ap propriate inferences to be drawn therefrom

. The rationale supporting the Administrator's proposed conclusions on alternative standard levels is discussed below. The Administrator’s proposed conclusions on alternative standard levels build upon her proposed conclusion that the overall body of scientific evidence and exposure/risk information call into question the adequacy of public health protection af forded by the current primary O 3 standard , particularly for at

- risk populations and lifestages (II. D.5). These proposed conclusions are based on consideration of the scientific evidence assessed in the ISA (U.S. EPA, 2013); t he results of the exposure and risk assessments in the HREA (U.S. EPA, 2014a); the evidence

- based and exposure

- /risk

based conside rations and conclusions in the PA (U.S. EPA, 2014c); CASAC advice and recommendations, as reflected in CASAC’s letters to the Administrator and in public discussions of drafts of the ISA, HREA, and PA ; and public input received during the development of th ese documents

. In reaching proposed conclusions on alternative levels for the primary O 3 standard, the Administrator considers the extent to which various alternatives would be*** E.O. 12866 Review

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Page 267 of 647 expected to protect the public, including at

- risk populations, against the wid e range of adverse health effects that have been linked with short

- or long

- term O 3 exposures. At

risk populations include people with asthma; children and older adults ; people who are activ e outdoors, including outdoor workers ; people with certain genetic variants; and people with reduced intake of certain nutrients. As was the case for her consideration of the adequacy of the current primary O 3 standard (II.D.5) , the Administrator places the greatest weight on the results of controlled human exposure stu dies and on exposure and risk analyses based on information from these studies. In doing so, she notes that controlled human exposure studies provide the most certain evidence indicating the occurrence of health effects in humans following exposures to spe cific O 3 concentrations. The effects reported in these studies are due solely to O 3 exposures, and interpretation of study results is not complicated by the presence of co

- occurring pollutants or pollutant mixtures (as is the case in epidemiologic studies) . She further notes the CASAC judgment that “the scientific evidence supporting the finding that the current standard is inadequate to protect public health is strongest based on the controlled human exposure studies of respirat ory effects” (Frey, 2014, p. 5). Consistent with this emphasis, the HREA conclusions reflect relatively greater confidence in the results of the exposure and risk analyses based on information from controlled human exposure studies (i.e., exposures of concern and risk of lung functio n decrements) than the results of epidemiology

- based risk analyses, given the greater uncertainties in the epidemiology

- based risk estimates (U.S. EPA, 2014a, section 9.6). For all of these reasons, the Administrator has the most confidence in using the*** E.O. 12866 Review

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Page 268 of 647 in formation from controlled human exposure studies to reach proposed conclusions on alternative standard levels. In considering the evidence from controlled human exposure studies, the Administrator first notes that these studies have reported a variety of respiratory effects in healthy adults following exposures to O 3 concentrations of 60, 135 72, 136 or 80 ppb, and higher. The largest respiratory effects, and the broadest range of effects, have been studied and reported following exposures of healthy adults to 80 ppb O 3 or higher, with most exposure studies conducted at these higher concentrations. Ex posures of healthy adults to O 3 concentrations of 80 ppb or higher have been reported to decrease lung function, increase airway inflammation, increase respiratory symptoms, result in airway hyperresponsiveness, and decrease lung host defenses (II.B.2).
M ost of these effects have also been shown in healthy adults following exposures
to O 3 concentrations lower than 80 ppb, with generally smaller effects following exposures to lower concentrations. In particular, the Administrator notes that O 3 exposure

conc entrations as low as 72 ppb have been shown to both decrease lung function and increase respiratory symptoms (Schelegle et al., 2009), a combination that meets the ATS criteria for an adverse response. In considering effects at 72 ppb, CASAC likewise noted that “ the combination of decrements in FEV 1 together with the statistically significant alterations in symptoms in human subjects exposed to 72 ppb ozone meets the American

135 As discussed above (II.B.2), exposures to 60 ppb O 3 have been evaluated in studies by Adams ( 2002 , 2006), Schelegle et al., 2009, and Kim et al. ( 2011 ). In the study by Schelegle, f

or the 60 ppb target exposure concentration , study authors reported that the actual mean exposure concentration was 63 ppb. 136 As noted above, for the 70 ppb target exposure concentration , Schelegle et al. (2009) reported that the actual mean exposure concent ration was 72 ppb.*** E.O. 12866 Review

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Page 269 of 647 Thoracic Society’s definition of an adverse health effect” (Frey, 2014c, p. 5). Wi th regard to lower exposure concentrations, although the combination of statistically significant increases in respiratory symptoms and lung function decrements ha s not been reported, 137
the Administrator notes that e xposures to 60 ppb O 3 have been shown to decrease lung function in several studies and, in one study (Kim et al., 2011), to increase airway inflammation (II.B.2)

. Based on this evidence, the Administrator reaches the initial conclusion that the results of controlled human exposure studies strong ly support setting the level of a revised O 3 standard no higher than 70 ppb. In reaching this initial conclusion, the Administrator places a large amount of weight on the importance of setting the level of the standard well below 80 ppb, the O 3 exposure concentration shown in healthy adults to result in the broadest range of respiratory effects, and below 72 ppb, the lowest O 3 exposure concentration shown in healthy adults to result in the adverse combination of respiratory symptoms and lung fun ction decrements. In further considering the potential public health implications of a standard with a level of 70 ppb, the Administrator also considers the extent to which such a standard would be expected to limit population exposures to the broader ran ge of O 3 concentrations reported in controlled human exposure studie s to cause respiratory effects. Given the range of effects reported following exposures to 80 ppb O 3 , and the evidence

137 More specifically, the Administrator notes that respiratory symptoms have been evaluated following 6.6

- hour exposures to average O 3 concentrations of 60 ppb (Adams, 2006; Kim et al., 2011) and 63 ppb (Schelegle et al., 2009 ). None of t hese studies reported a statistically significant increase in respiratory symptoms, compared to filtered air controls, though Adams (2006) report ed a significant i ncrease in symptoms , compared to initial symptoms.*** E.O. 12866 Review

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Page 270 of 647 for the adverse combination of lung function decrements and respirato ry symptoms in healthy adults following exposures as low as 72 ppb, the Administrator concludes that there is strong evidence in this review supporting the occurrence of adverse respiratory effects for exposures to O 3 con centrations at or above 72 ppb.
T h e Administrator has decreasing confidence that adverse effects will occur following exposures to O 3 concentrations below 72 ppb. In particular, compared to O 3 exposure concentrations at or above 72 ppb, she has less confidence that adverse effects will occ ur following exposures to O 3 concentrations as low as 60 ppb. In reaching this conclusion, she notes that , as discussed above, statistically significant increases in respiratory symptoms, combined with lung function decrements, have not been reported follo wing exposures to 60 or 63 ppb O 3 , though several studies have evaluated the potential for such effects. Although she has decreasing confidence in the occurrence of adverse effects following exposures to O 3 concentrations below 72 ppb, the Administrator n ote s the CASAC judgment that the adverse combination of lung function decrements and respiratory symptoms “almost certainly occur in some people ” following exposures to lower concentrations (Frey, 2014c, p. 6) . In particular, when commenting on the extent to which the study by Schelegle et al. (2009) suggests the potential for adverse effects following O 3 exposures below 72 ppb, CASAC judged that: [I] f subjects had been exposed to ozone using the 8

- hour averaging period used in the standard [i.e., Rather than the 6.6 hour exposures evaluated in the study] , adverse effects could have occurred at lower concentration. Further, in our judgment, the level at which adverse effects might be observed would likely be lower for more sensitive subgroup s, such as those with asthma [i.e., compared to the healthy adults evaluated in the study] (Frey, 2014c, p. 5).*** E.O. 12866 Review

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Page 271 of 647 Though CASAC did not provide advice as to how far below 72 ppb adverse effects would likely occur , the Administrator agrees that such effects co uld occur following exposures at least somewhat below 72 ppb

. Based on the evidence and CASAC advice noted above, when considering the extent to which a standard with a level of 70 ppb would be expected to limit population exposures to the broader range o f O 3 concentrations shown to cause respiratory effects, the Administrator considers the extent to which such a standard would be expected to limit the occurrence of O 3 exposures of concern at or ab ove 60, 70, and 80 ppb

. 138 In doing so, she notes that an O 3 standard established at a particular level can provide protection against a range of exposure concentrations, including concentrations below the standard level. This is because the degree of protection provided by any NAAQS is due to the combination of all of the elements of the standard (i.e., indicator, averaging time, form, level). In the case of the 4 th maximum form of the O 3 NAAQS, which the Administrator is proposing to retain in the current review (II.E.3), the large majority of days in areas that me et the standard will have 8

- hour O 3 concentrations below the level of the standard. In considering exposures of concern at or above 60, 70, and 80 ppb, the Administrator judges that the evidence supporting the occurrence of adverse respiratory

138 As for her consideration of the current standard (II.D.5), the Ad ministrator focuses on estimated exposures of concern in children , including asthmatic children , noting the HREA analyses indicating that exposures of concern occur in a larger percentage of children than adults (given that a larger percentage of children are estimated to spend an extended period of time being physically active outdoors when O 3 concentrations are elevated) (II.C.2). To the extent alternative standards provide an appropriate degree of protection for children, sh e judges that those standards will also protect adult populations (including at

- risk adult populations).*** E.O. 12866 Review

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Page 272 of 647 effects is s trongest for exposures at or above the 70 and 80 ppb benchmarks. While the Administrator has less confidence that adverse effects will occur following exposures to
O 3 concentrations as low as 60 ppb, she notes the possibility for adverse effects following such exposures given that (1) CASAC has indicated the moderate lung function decrements (i.e., FEV 1 decrements ≥ 10%) that occur in some healthy adults following exposures to 60 ppb O 3 , which are large enough to be judged an abnormal response by ATS, could be adverse to people with lung disease (II.B.3), and that (2) airway inflammation has been reported following exposures as low as 60 ppb O 3 . She also takes note of CASAC advice that t he occurrence of exposures of concern at or above 60 ppb is an appropriate consideration for people (including children) with asthma (Frey, 2014c, p. 6).
D ue to interindividual variability in responsiveness , the Administrator further notes that not every occurrence of an exposure of concern will result in an adverse effect. 139 R epeated occurrences of some of the effects demonstrated following exposures of concern could increase the likelihood of adversity. For example, as discussed in the ISA (U.S. EPA, 201 3, Section 6.2.3), repeated occurrences of airway inflammation could lead to the induction of a chronic inflammatory state ; alter ed pulmonary structure and function, leading to diseases such as asthma; alter ed lung host defense response to inhaled microorg anisms, particularly in potentially at

- risk populations such as the very young and old ; and alter ed lung response to other agents such as allergens or toxins . The

139 F or most of the effects demonstrated in controlled human exposure studies (e.g., airway inflammation, airway hyperresponsiveness, decreased lung host defense , respiratory symptoms ) the available data are not sufficient to quantify the number of people who would experience adverse effects due to O 3 exposures.*** E.O. 12866 Review

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Page 273 of 647 Administrator notes that the types of lung injury that can occur following exposures of

conce rn, particularly if experienced repeatedly, provide a plausible mode of action by which O 3 may cause other more serious effects. Therefore, the Administrator is most concerned about protecting at

- risk populations against repeated occurrences of exposures

o f concern. Based on the above considerations, the Administrator focuses on the extent to which a revised standard would be expected to protect populations from experiencing two
or more O 3 exposures of concern (i.e., as a surrogate for repeated exposures). While she emphasizes the importance of limiting two or more exposures and reducing their occurrence, compared to the current standard, s he balances this emphasis by noting that (1 ) not all exposures of concern will result in adverse effects; (2) she has l ess confidence in the occurrence of adverse effects at the 60 ppb benchmark than at the 70 or 80 ppb benchmarks; and (3) the NAAQS are not meant to be zero

- risk standards

. 140 Therefore, in using estimates of exposures of concern to inform her decisions on al ternative standard levels, the Administrator judges that it would not be appropriate to set a standard intended to eliminate all exposures of concern for all benchmarks , particularly the 60 ppb benchmark. Her consideration of specific estimates of exposures of concern is discussed below. As illustrated in Table 1 (above), the Administrator notes that, in urban study areas, a revised standard with a level of 70 ppb would be expected to eliminate the

occurre nce of two or more exposures of concern to O 3 concentrations at and above 80 ppb and to virtually eliminate the occurrence of two or more exposures of concern to O 3

140 State of Mississippi , 744 F. 3d at 1343.*** E.O. 12866 Review

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Page 274 of 647 con centrations at and above 70 ppb, even in the worst

- case urban study area and year . For
t he 70 ppb benchmark, this reflects about a 95% reduction in the occurrence of two or more exposures of concern, compared to the current standard (Table 4). Though the Administrator acknowledges greater uncertainty with regard to the occurrence of adverse effects following exposures of concern at or above 60 ppb, she notes that a revised standard with a level of 70 ppb would also be expected to protect the large majority of children in urban study areas (i.e., about 96% to more than 99% of children in indiv idual urban study areas) from experiencing two or more exposures of concern at or above 60 ppb. Compared to the current standard, this represents a reduction of more than 60% in the occurrence of two or more exposures of concern (Tables 1 and 4). Based on the above information, the Administrator concludes that a revised O 3 standard with a level of 70 ppb would be expected to virtually eliminate the occurrence of
two or more O 3 exposures of concern for the 70 and 80 ppb benchmarks, and to substantially redu ce the occurrence of two or more O 3 exposures of concern for the 60 ppb benchmark, compared to the current standard. Although the Administrator is less concerned about single occur rences of exposures of concern , she acknowledges that even single exposures to O 3 concentrations at or above benchmark concentrations (particularly for the 70 and 80 ppb benchmarks) could potentially result in adverse effects. To the extent this may be the case, the Administrator notes that a standard with a level of 70 ppb would also be expected to (1) virtually eliminate all occurrences of exposures of concern at or above 80 ppb, even in the worst

- case year and location and (2) achieve important reductions, compared to the*** E.O. 12866 Review

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Page 275 of 647 current standard, in the occurrence of one or more expos ures of concern at or above 70 and 60 ppb (i.e., about a 70% reduction for the 70 ppb benchmark and almost a 50% reduction for the 60 ppb benchmark) (Tables 1 and 4). In further evaluating the potential public health impacts of a standard with a level of 70 ppb, the Administrator also considers the HREA estimates of O 3 - induced lung function decrements . To inform her consideration of these decrements , the Administrator takes note of CASAC advice that “estimation of FEV 1 decrements o f > 15% is appropriate as a scientifically relevant surrogate for adverse health outcomes in active healthy adults, whereas an FEV 1 decrement of > 10% is a scientifically relevant surrogate for adverse health outcomes for people with asthma and lu ng disease” (Frey, 2014, p. 3).
Co nsistent with this advice, she considers estimates of the occurrence of O 3 - induced
FEV 1 decrements > 10 and 15% as surrogates for the occurren ce of adverse health
outcomes. While these surrogates provide perspective on the potential for the occurrence of adverse respiratory effects following O 3 exposures, the Administrator agrees with the conclusion in past reviews that a more general consensus view of the adversity of moderate responses emerges as the frequency of occurrence increases (61 FR 65722

- 3) (Dec , 13, 1996). Specifically, she concludes that not every estimated occurrence of an
O 3 - induced FEV 1 decrement will be adverse and that repeated occurrences of moderate responses, even in otherwise healthy individuals, may be considered to be adverse since
t hey could set the stage for more serious illness. Therefore, the Administrator becomes increasingly concerned about the potential for adversity as the fre quency of occurrences*** E.O. 12866 Review

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Page 276 of 647 increases and, a s a result, s he focuses primarily on estimates of two or more O 3 - induced
FEV 1 decrements (i.e., as a surrogate for repeated exposures)

. Given the above considerations, the Administrator does not believe it would be appropriate to set a standard that is intended to eliminate all O 3 - induced FEV 1 decrements. She notes th at this is consistent with CASAC advice, which did not include a recommendation to set the standard level low enough to eliminate all O 3 - induced FEV 1 decrements > 10 or 15% (Frey, 2014c). Rather, the Administrator considers the extent to which a standard w ith a level of 70 ppb would be expected to protect the population from experiencing O 3 - induced FEV 1 decrements > 10 and 15%, including the extent to which such a standard would be expected to achieve reductions in the occurrence of O 3 - induced
FEV 1 decrements, relative to the current standard. 141
T he Administrator notes that a revised O 3 standard with a level of 70 ppb is estimated to protect about 98 to 99% of children in urban study areas from experiencing
two or more O 3 - induced FEV 1 decrements > 1 5%, and about 89 to 94% from experiencing two or more decrements > 10%. 142 Compared to the current standard, these estimates represent decreases in the occurrence of two or more O 3 - induced decrements of

141 The Administrator additionally notes that, unlike exposures of concern, the variability in lung function risk estimates across urban study areas is often greater than the differences in risk estimates between various standard levels (Table 2, above). Given this, and the resulting considerable overlap bet ween the ranges of lung function risk estimates for different standard levels, while the Administrator has confidence in the lung function risk estimates themselves, she views them as providing a more limited basis than exposures of concern for distinguish ing between the degree of public health protection provided by alternative standard levels. 142 I n the worst

- case year and location, a standard with a level of 70 ppb is estimated to protect about 97% of children in urban study areas from experiencing two or more O 3 - induced FEV 1 decrements > 15%, and about 87% from experiencing two or more decrements > 10%.*** E.O. 12866 Review

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Page 277 of 647 about 29 and 17%, respectively (Tables 2 and 5). Althou gh the Administrator is less concerned about the public health implications of single O 3 - induced lung function decrements, she also gives some consideration to estimates of one or more O 3 - induced
FEV 1 decrements. In particular, she notes that a revised sta ndard with a level of 70 ppb is estimated to reduce the occurrence of one or more O 3 - induced decrements, compared to the current standard, by about 26% (for decrements > 15%) and 15% (for decrements > 10%) (Tables 2 and 5). Given all of the above informat ion, the Administrator concludes that a revised standard with a level of 70 ppb would be expected to provide substantial protection against O 3 exposures of concern (for benchmark concentrations of 60, 70, 80 ppb) and
O 3 - induced lung function decrements, an d would be expected to result in important reductions in the occurrence of such exposures and decrements, compared to the current standard. This is particularly the case for estimates of two or more occurrences of exposures of concern and lung function dec rements. In next considering the additional protection that would be expected from standard levels below 70 ppb, the Administrator evaluates the extent to which a standard with a level of 65 ppb would be expected to further limit O 3 exposures of concern and
O 3 - induced lung function decrements. In addition to eliminating almost all exposures of concern to O 3 concentrations at or above 80 and 70 ppb, even in the worst

- case years and locations, the Administrator notes that a revised st andard with a level of 65 ppb would be expected to protect more than 99% of children in urban study areas (and 100% of children in some urban study areas) from experiencing two or more exposures of concern at or above 60 ppb.*** E.O. 12866 Review

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Page 278 of 647 Compared to the current standa rd, this represents about a 95% reduction in the occurrence of two or more exposures of concern for the 60 ppb benchmark (Tables 1 and 4). In addition, the Administrator notes that a revised standard with a level of 65 ppb is estimated to reduce the occurr ence of one or more exposures of concern for the 60 ppb benchmark by about 80%, compared to the current standard (Tables 1 and 4). With regard to O 3 - induced lung function decrements, the Administrator notes that
an O 3 standard with a level of 65 ppb is es timated to protect about 98% to more than 99% of children from experiencing two or more O 3 - induced FEV 1 decrements > 15%, even considering the worst

- case year and location, and about 91 to 99% from experiencing two or more decrements > 10% (89% in worst

- ca se year and location). These estimates reflects reductions, compared to the current standard, of about 54 and 37%, respectively. A revised standard with a level of 65 ppb is also estimated to reduce the occurrence of one or more lung function decrements > 15 and 10%, compared to the current standard, by about 50 and 31%, respectively. Taken together, the Administrator concludes that the evidence from controlled human exposure studies, and the information from quantitative analyses that draw upon these stud ies (i.e., exposures of concern, O 3 - induced FEV 1 decrements), provide strong support for standard levels from 65 to 70 ppb. In particular, she bases this conclusion on the fact that such standard levels would be well below the O 3 exposure concentration sho wn to result in the widest range of respiratory effects (i.e., 80 ppb), and below the lowest O 3 exposure concentration shown to result in the adverse combination of lung function decrements and respiratory symptoms (i.e., 72 ppb) . A standard with a level
f rom 65 to 70 ppb would also be expected to result in important reductions, compared to*** E.O. 12866 Review

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Page 279 of 647 the current standard, in the occurrence of O 3 exposures of concern for all of the benchmarks evaluated (i.e., 60, 70, and 80 ppb) and in the risk of O 3 - induced lung func tion decrements > 10 and 15%. In further considering the evidence and exposure/risk information, the Administrator considers the extent to which the epidemiologic evidence, and the quantitative risk estimates based on information from epidemiologic studie s, also provide support for standard levels from 65 to 70 ppb. In doing so, as in her consideration of the adequacy of the current O 3 standard, the Administrator focuses on epidemiologic studies of respiratory

- related hospital admissions, emergency d epartm ent visits, and mortality

. These considerations are discussed below.
T he Administrator first considers the extent to which available epidemiologic studies have reported associations between short

- term O 3 concentrations and emergency department visits, hospital admissions, and/or mortality in locations that would likely have met alternative standards w ith levels from 65 to 70 ppb (U.S. EPA, 2014c, section 4.4.1). In evaluating the epidemiologic evidence in this way, the Administrator places the most weight on single

- city studies of short

- term O 3 concentrations, recognizing that there were no multicity studies for which air quality data indicated that all cities included in the analyses would likely have met alternative standard levels. In particular, she notes that while single

- city studies are more limited than multicity studies in terms of statistical power and geographic coverage, conclusions linking air quality in a given city with health effect associat ions in that same city can be made with greater certainty for single

city studies of short

- term O 3 , compared to health effect associations aggregated across multiple cities in multicity studies. In particular, the Administrator notes considerable*** E.O. 12866 Review

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Page 280 of 647 uncertain ty in linking multicity effect estimates (aggregated across multiple cities) for short

- term O 3 with the air quality for subsets of study locations (rather than all locations) likely to have met an alternative standard. 143 Given the above, the Administrator notes analyses in the PA (U.S. EPA, 2014c, section 4.4.1) indicating that a revised standard with a level of 65 or 70 ppb would be expected to maintain short

- term ambient O 3 concentrations below those present in the locations of all of the single

- city stud ies analyzed. As discussed in the PA (U.S. EPA, 2014c, section 4.4.1), this includes several single

- city studies conduc ted in locations that would have violated the current standard, and the single

- city study by Mar and Koenig (2009) that reported positive and statistically significant associations with respiratory emergency department visits with children and adults in a location that likely would have met the current standard over the entire study period but that would likely not have met a revised standa rd with a level of 70 ppb or below. Thus, the Administrator notes that, while the current standard would allow the ambient O 3 concentrations that provided the basis for the health effect associations reported by Mar and Koenig, a revised O 3 standard

143 In recognizing that multicity studies are often emphasized over single

- city studies for purposes of making weight of evidence judgments (U.S. EPA, 20 13), the Administrator’s judgment in this case applies specifically to interpreting air quality analyses for epidemiologic studies of short

- term O 3 concentrations where multicity effect estimates are aggregated across cities, and where individual city effe ct estimates are not presented (as is the case for the key O 3 studies analyzed in the PA, with the exception of the study by Stieb et al. (2009) where none of the city

- specific effect estimates for asthma emergency department visits were statistically sign ificant). Because reported multicity effect estimates do not allow health effect associations to be disaggregated by individual city, it is not possible to assign the multicity health effect association to the air quality in any one study location, or to t he air quality in a particular subset of locations. In contrast, for epidemiologic studies of long

- term concentrations, where multicity effect estimates are based on comparisons across cities, different judgments have been made with regard to the utility of multicity studies (see, e.g. 78 FR 3086 at 3103/2) (January 15, 2013) (and see discussion below of study by Jerrett et al., 2009).*** E.O. 12866 Review

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Page 281 of 647 with a level at or below 70 ppb would require reductions in those ambient O 3 concentrations. While the Administrator acknowledges uncertainty in the extent to which the reported O 3 - associated emergency department visits could be further reduced by standard level s below 65 or 70 ppb, she concludes that this analysis indicates that a revised standard with a level at least as low as 70 ppb would result in improvements in public health, beyond the protection provided by the current standard, in the locations of the s ingle

- city epidemiologic studies that reported significant health effect associations. As discussed above, the Administrator notes the greater uncertainty in interpreting air quality in locations of multicity epidemiologic studies of short

- term O 3 for the purpose of evaluating alternative standard levels (II.D.1 and U.S. EPA, 2014c, section 4.4.1). Therefore, she places less weight on these studies than on the single

- city studies noted above. Despite this uncertainty, she notes that PA analyses s ug gest that standard levels of 65 or 70 ppb would more effectively maintain short

- term ambient O 3 concentrations below those present in several of the epidemiologic studies that reported significant O 3 health effect associations with morbidity or mortality i n locations likely to have met the current standard. For example, she notes that Dales et al. (2006) reported significant associations with respiratory hospital admissions based on air quality in 11 Canadian cities, most of which would likely have met the current standard over the entire study period (i.e., seven cities) but would have violated a standard with a level of 70 ppb or below over at least part of th at period ( U.S. EPA, 2014c, Table 4

- 1). She further notes that Katsouyanni et al. (2009) reported statistically significant associations with mortality based on air quality in 12 Canadian cities, most of which would likely have met the current standard (i.e., eight study cities) and a standard with a level of 70 ppb (i.e., seven*** E.O. 12866 Review

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Page 282 of 647 study cities) over the entire study period , but would have violated a standard with a level of 65 ppb over at least part of th at period ( U.S. EPA, 2014c, Table 4

- 1). While most of the other multicity epidemiologic studies evaluated also suggest that a level from 65 to 70 ppb wou ld result in public health improvements, compared to the current standard, the Administrator acknowledges that several multicity epidemiologic studies reported O 3 health effect associations when the majority of study cities would likely have met standards with levels from 65 to 70 ppb. However, given the important uncertainties in interpreting the air quality in these multicity studies, the Administrator places limited weight on them overall, relative to the single

- city studies noted above (and relative to the information based on controlled human exposure studies). With regard to long

- term O 3 concentrations, the Adminis trator considers the long

term O 3 metrics reported to be associated with mortality or morbidity in recent epidemiologic studies (e.g., seas onal averages of 1

- hour or 8

- hour daily max concentrations) . Compared to the current standard, she notes that analyses in the PA (U.S. EPA, 2014c, section 4.4.1) suggest a re vised standard with a level of 65 or 70 ppb would more effectively maintain long

- t erm O 3 concentrations below those where the multicity study by Jerrett et al. (2009) indicates the most confidence in the reported association with respiratory mortality (II.B.2, II.D.1). Based on additional information from the study by Jerrett (2009), th e Administrator also notes HREA analyses indicating that a revised standard with a level of 65 or 70 ppb would be expected to reduce the risk of respiratory mortality associated with long

- term O 3 concentrations (though she also notes important uncertainties with these risk estimates, as described below). Finally, she notes analyses in the HREA suggesting that a rev ised standard with a level of 65 or 70*** E.O. 12866 Review

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Page 283 of 647 ppb would be expected to reduce long

- term O 3 concentrations, defined in terms of O 3 metrics similar to the long

- term metrics that have been reported in recent epidemiologic studies to be associated with respiratory morbidity (i.e., seasonal averages of daily maximum 8

- hour concentrations). Given the above evidence and information, the Administrator concludes that a revised 8

- hour standard with a level from 70 to 65 ppb could increase public health protection, compared to the current standard, against effects associated with long

- term O 3 exposures. In further evaluating information from epidemiologic studies, the Administrator also considers the HREA’s epidemiology

- based risk estimates of morbidity and mortality associated with short

- term O 3 (U.S. EPA, 2014a). Compared to the weight given to the eviden ce from controlled human exposure studies, and to HREA estimates of exposures of concern and lung function risks, she places relatively less weight on epidemiology

based risk estimates. In doing so, she notes that the overall conclusions from the HREA like wise reflect relatively less confidence in estimates of epidemiology

- based risks than in estimates of exposures of concern and lung function risks. As discussed above (II.C.3.b), this is based on the greater uncertainties associated with mortality and morb idity risk estimates, including the heterogeneity in effect estimates between locations, the potential for exposure measurement errors, and uncertainty in the interpretation of the shape of concentration

- response functions at lower O 3 concentrations. The A dministrator further notes the HREA conclusion that lower confidence should be placed in the results of the assessment of respiratory mortality risks associated with long

- term O 3 exposures, primarily because that analysis is based on only one study (even t hough that study is well

- designed) and because of the uncertainty in that*** E.O. 12866 Review

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Page 284 of 647 study regarding the existence and identification of a potential threshold in the concentration

- response function (U.S. EPA, 2014a, section 9.6). In considering epidemiology

- based ri sk estimates, the Administrator focuses on the extent to which potential alternative O 3 standards are estimated to reduce the risk of mortality associated with short

- term exposures to O 3 , noting the similar patterns of risk

across urban study areas and air quality scenarios for respiratory morbidity endpoints (II.C.3) . Given the uncertainties in epidemiology

- based risk estimates , the Administrator focuses on the general magnitudes of risk changes es timated for standard levels of 65 and
70 ppb , compared to t he current standard, rather than placing a large amount of weight on the absolute estimates of O 3 - associated deaths. In doing so, she notes the CASAC conclusion that “[a]lthough the estimates for short

- term exposure impacts are subject to uncertainty, the data supports a conclusion that there are meaningful reductions in mean premature mortality associated with ozone levels lower than the current standard” (Frey, 2014a, p. 10). She further notes that, as discussed above (II.C.3.b), the HREA risk estimates f

or urban study areas are likely to understate the average reductions in O 3 - associated mortality and morbidity risks that would be experienced across the U.S. population as a whole upon meeting standards with lower levels. The Administrator’s primary focus is on risks associated with O 3 concentrations in the upper portions of ambient distributions, given the greater uncertainty associated with the shapes of concentration

- response curves for O 3 concentrations in the lower portions of ambient distributions. 144 The Administrator further notes that experimental

144 The ISA conclu des that there is less certainty in the shape of concentration

- response functions for area

- wide O 3 concen trations at the lower ends of warm season distributions (i.e., below about 20 to 40 ppb) (U.S. EPA, 2013, section 2.5.4.4)

.*** E.O. 12866 Review

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Page 285 of 647 studies provide the strongest evidence for O 3 - induced effects following exposures to O 3 concentrations corresponding to the upper portions of typical ambient distributions. In particular, as discussed abov e, she notes controlled human exposure studies showing respiratory effects following exposures to O 3 c oncentrations at or above 60 ppb (II.B)

. In considering risks associated with O 3 concentrations in the upper portions of ambient distributions, the Admin istrator focuses on area

- wide O 3 concentrations at or above 40 ppb and 60 ppb. For area - wide O 3 concentrations at or above 40 ppb , the Administrator notes that re vised standards with levels of 65 or 70 ppb are estimated to reduce the number of deaths assoc iated with short

- term O 3 concentrations by about 10% and almost 50%, respectively, compared to the current standard. In addition, for area wide concentrations at or above 6 0 ppb , revised standards are estimated to reduce O 3 - associated deaths by about 50% t o 70% for a standard level of 70 ppb, and by more than 80% for a standard level of 65 ppb. 145 Risk reductions are smaller when total risks are considered (II.C.3.b). Given all of the above evidence, exposure/risk information, and advice from CASAC, the Adm inistrator propose s to revise the level of the current primary O 3 standard to within the range of 65 to 70 ppb. She concludes that a standard with a level from within this range could reasonably be judged to be requisite to protect public health with an ad equate margin of safety, based on her consideration of the evidence and information discussed above. In reaching this conclusion, the Administrator notes that the determination of what constitutes an adequate margin of safety is expressly left to the

145 Though only a relatively small number of days in urban study areas had area

- wide O 3 concentrations at or above 60 ppb.*** E.O. 12866 Review

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Page 286 of 647 EPA Administrator. She further notes that in evaluating how particular standards address the requirement to provide an adequate margin of safety, the Administrator must consider such factors as the nature and severity of the health effects, the size of sen sitive population(s) at risk, and the kind and degree of the uncertainties that must be addressed

. Consistent with past practice and long

- standing judicial precedent, she takes the need for an adequate margin of safety into account as an integral part of h er decision

- making on the appropriate level, averaging time, form, and indicator of the standard. 146 The Administrator notes that the NAAQS are not designed to be zero

- risk or background standards, and that the sizeable risk reductions that are estimated in the HREA to be associated with standard levels of 65 or 70 ppb represent substantial improvements in public health for important segments of the population, including at

- risk groups such as children and people with asthma. W hile the rationale supporting a decision to set a specific level within the range of 65 to 70 ppb would discuss the full body of evidence and information, the Administrator notes that certain aspects of this evidence and information could be particularly important in distinguishing betw een the
approp riateness of a level closer to 65 ppb versus a level closer to 70 ppb. 147 For example , a level at or near 65 ppb could be judged requisite to protect public health with an adequate margin of safety to the extent the Administrator places greate r weight on the importance of: (1) setting the level of the standard well below the lowest

146 See, e.g. NRDC v. EPA , 902 F. 2d 962, 973

- 74 (D.C. Cir. 1990). 147 Although this discussion refers to suppo rting rationale for a level of 65 ppb or 70 ppb, the Administrator is proposing the entire range between 65 and 70 ppb. The Administrator notes that a l though neither the PA nor CASAC reached conclusions or provided advice on a standard set at a specific level between 65 ppb and 70 ppb, there is nothing in either the evidence, exposure/risk information, or CASAC advice that would preclude such a standard level.*** E.O. 12866 Review

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Page 287 of 647 O 3 exposure concentration shown to result in the adverse combination of respiratory symptoms and lung function decrements, particularly given that 8

- hour exposures c ould result in effects at lower concentrations than indicated in 6.6 controlled human exposure studies and that members of at risk populations could experience more serious effects than the healthy subjects evaluated in these studies ; (2) eliminating almos t all exposures of concern (even single exposures) at or above 70 and 80 ppb, even in worst

- case years and locations; (3) almost eliminating the occurrence of two or more exposures of concern at or above 60 ppb; (4) achieving additional reductions in O 3 - in duced FEV 1 decrements, beyond those achieved with a level of 70 ppb ( 5 ) maintaining ambient concentration s below those in locations of si ngle

- city studies and more effectively doing so for multicity studies (i.e., more effectively than 70 ppb); and ( 6 ) ac hieving substantial reductions, compared to a standard with a level of 70 ppb, in mortality associated with the upper portion of the distribution of ambient O 3 concentrations, despite uncertainties in risk estimates. In contrast, a level at or near 70 ppb could be judged requisite to protect public health with an adequate margin of safety to the extent the Administrator places a greater amount of weight (i.e., greater than for 65 ppb) on the importance of: (1) setting the level of the standard just below t he lowest O 3 exposure concentration shown to result in the adverse combination of respiratory symptoms and lung function decrements (i.e., 72 ppb), given increasing uncertainty in the extent to which adverse effects occur following lower exposure concentra tions; (2) almost eliminating the occurrence of two or more exposures of c oncern at or above 70 and 80 ppb , even in the worst

- case year and location ; (3) substantially reducing , but not eliminating, the occurrence of two or more exposures*** E.O. 12866 Review

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Page 288 of 647 of concern at or above 60 ppb , noting conclusions regarding increasing uncertainty in adverse effects for the 60 ppb benchmark ; ( 4 ) reducing , but not eliminating, the occurrence of one or more exposures of concern , noting that not all exposures of concern result in adverse effects; ( 5 ) maintaining ambient O 3 concentrations below those in locations of single

- city epidemiologic studies, and uncertainties in analyses of air quality in multicity study locations; and ( 6 ) recognizing uncertainties in epidemiology

- based risk estim ates. In considering CASAC advice on the range of standard levels, the Administrator first notes CASAC’s conclusion that there is adequate scientific evidence to consider a range of levels for a primary standard that includes an upper end at 70 ppb. For t he reasons discussed above, she agrees with this advice. She also notes CASAC’s conclusion that a standard at a level of 70 ppb “may not meet the statutory requirement to protect public health with an adequate margin of safety” (Frey, 2014c, p. 8). While s he
agrees with CASAC that it is appropriate to consider levels below 70 ppb, as reflected in her range of proposed levels from 65 to 70 ppb , for the reasons discussed above she concludes that a standard level as high as 70 ppb could reasonably be judged to be requisite to protect public health with an adequate margin of safety. The Administrator has also considered the appropriateness of standard levels below 65 ppb. In doing so, she notes the conclusions of the PA and the advice of CASAC that it would be appropriate for her to consider standard levels as low as 60 ppb. In particular, she notes that a decision to set the primary O 3 standard level at 60 ppb would place a large amount of weight on the potential public health importance of virtually eliminating even single occurrences of exposures of concern at and above 60 ppb; on the*** E.O. 12866 Review

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Page 289 of 647 potential public health importance of providing su bstantially greater protection (i.e., than that provided by a level of 65 ppb) against the occurrence of moderate to large O 3 - induced lung function decrements; on analyses of ambient O 3 concentrations in locations of multicity epidemiologic studies, despit e uncertainties in linking multicity effect estimates for short

- term O 3 with air quality in individual study cities; and on epidemiology

- based risk estimates, despite the important uncertainties in those estimates

. As discussed more fully above, given the uncertainties associated with such estimates, analyses, and assumptions, the Administrator does not agree that it is appropriate to place significant weight on these factors. C ompared to O 3 standard levels from 65 to 70 ppb, the Administrator concludes tha t the extent to which standard levels below 65 ppb could result in further public health improvements becomes notably less certain. Therefore, she concludes that it is not appropriate to propose standard levels below 65 ppb

. 148
T he Administrator acknowledge s that her proposed range of 65 to 70 ppb does not include the lower portion of the range supported by CASAC. In reaching the conclusion that this is appropriate, she focuses on CASAC’s rationale for levels as low as 60 ppb. In particular, she notes the fo llowing CASAC advice: The CASAC concurs that 60 ppb is an appropriate and justifiable scientifically based lower bound for a revised primary standard. This is based upon findings of adverse effects, including clinically significant lung function decrements and airway inflammati on, after exposures to 60 ppb ozone in healthy adults with moderate exertion (Adams 2006; Schelegle et al., 2009; Brown et al. 2008; Kim et al., 2011), with limited evidence of adverse effects below 60 ppb.

148 Al though, as discussed below, she solicits comment on standard levels as low as 60 ppb.*** E.O. 12866 Review

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Page 290 of 647 In considering this advice, the Administrator notes that CASAC focused on the importance of limiting exposures to O 3 concentrations as low as 60 ppb. As discussed above, the Administrator agrees with this advice. In particular, she notes that standard s within the proposed range of 65 to 70 ppb would b e expected to substantially limit the occurrence of exposures of concern to O 3 concentrations at or above 60 ppb, particularly the occurrence of two or more exposures. When she further considers that not all exposures of concern lead to adverse effects, an d that the NAAQS are not meant to be

zero - risk or background standards, the Administrator judges that alternative standard levels below 65 ppb are not needed to further reduce such exposures. Therefore, her initial conclusion is that standard levels below 65 ppb would be more than requisite to protect public health with an adequate margin of safety. In reaching this initial conclusion, the Administrator acknowledges that alternative approaches to viewing the available scientific evidence and exposure/risk information, and to viewing the uncertainties inherent in that evidence and information, could lead one to reach a different conclusion. In particular, as noted above, she recognizes that levels as low as 60 ppb could potentially be supported, to the exten t substantial weight is placed on the public health importance of estimates of one or more occurrences of exposures of concern at or above 60 ppb and O 3 - induced lung function decrements > 10%; analyses of ambient O 3 concentrations in locations of multicity epidemiologic studies; and epidemiology

- based estimates of total risk. This approach would also place a large amount of weight on the possibility that at

- risk groups would experience effects at lower levels than the benchmarks derived from clinical studie s conducted using healthy adult subjects. Such an approach to viewing the evidence and*** E.O. 12866 Review

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Page 291 of 647 exposure/risk information would place very little weight on the uncertainties in these estimates and analyses. In some cases, elements of this approach have been support ed by
p ublic commenters , leading some commenters to recommend setting the level of the primary O 3 standard at least as low as 60 ppb

. In recognition of such an alternative approach to viewing the evidence and information, in addition to proposing to set th e level of the O 3 standard from 65 to 70 ppb, the Administrator solicits comment on alternative standard levels below 65 ppb, and as low as 60 ppb. In doing so, the Administrator reiterates that t he CAA does not require the establishment of a primary NAAQS at a zero

- risk level or at background concentration levels, but rather at a level that reduces risk sufficiently so as to protect public health with an adequate margin of safety (I.A).
F

. Proposed Decision on the Primary Standard For the reasons discussed above, and taking into account information and assessments presented in the 20 13 ISA, 2014 HREA and integration of this information and assessments into staff conclusions in the 2014 PA, the advice and recommendations of CASAC, and public comment s received during the development of these documents , the Administrator proposes to retain the current indicator, averaging time and form of the primary O 3 standard, and to set a new level for the 8

- hour primary O 3 standard

. Specifically, the Administrator proposes to set the level of the 8

- hour primary O 3 standard to within a range of 65 to 70 ppb. The proposed 8

- hour primary standard would be met at an ambient air monitoring site when the 3

- year average of the annual fo u rth

highest daily maximum 8

- hour av erage O 3 concentration is less than or equal to the level of the revised standard that is promulgated. Thus, the Administrator proposes to set a*** E.O. 12866 Review

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Page 292 of 64 7 standard with a level within this range. For the reasons discussed above, the Administrator also solicits comme nt on setting the level of the primary O 3 standard below 65 ppb, and as low as 60 ppb.
III. Communication of Public Health Information Information on the public health implications of ambient concentrations of criteria pollutants is currently made availabl e primarily through EPA's Air Quality Index (AQI)
program . The current Air Quality Index has been in use since its inception in 1999 (64 FR 42530). It provides accurate, timely, and easily understandable information about daily levels of pollution ( 40 CFR 58.50 ). The AQI establishes a nationally uniform system of indexing pollution concentrations for O 3 , carbon monoxide, nitrogen dioxide, particulate matter and sulfur dioxide. The AQI converts pollutant concentrations in a community's air to a number on a s cale from 0 to 500. Reported AQI values enable the public to know whether air pollution concentrations in a particular location are characterized as good (0

- 50), moderate (51

- 100), unhealthy for sensitive groups (101

- 150), unhealthy (151

- 200), very unhealthy (201

- 300), or hazardous (300

- 500). The AQI index value of 100 typically corresponds to the level of the short

- term NAAQS for each pollutant. For the current O 3 NAAQS, an 8

- hour average concentration of 75 ppb corresponds to an AQI value of 1 00. An AQI value greater than 100 means that a pollutant is in one of the unhealthy categories (i.e., unhealthy for sensitive groups, unhealthy, very unhealthy, or hazardous) on a given day; an AQI value at or below 100 means that a pollutant concentration is in one of the satisfactory categories (i.e., moderate or good). Decisions about the pollutant concentrations at which to set the various AQI*** E.O. 12866 Review

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Page 293 of 647 breakpoints, that delineate the various AQI categories, draw directly from the underlying health information th at supports the NAAQS review. The Agency recognizes the importance of revising the AQI in a timely manner to be consistent with any revisions to the NAAQS. Therefore EPA is proposing conforming changes to the AQI, in connection with the Agency's proposed d ecision on revisions to the O 3 NAAQS if revisions to the primary standard are promulgated. These conforming changes would include setting the 100 level of the AQI at the same level as the revised primary O 3 NAAQS and also making adjustments based on health information from this NAAQS review to AQI breakpoints at the lower end of each range (i.e., AQI values of 50, 150, 200 and 300). The EPA does not propose to change the level at the top of the index (i.e., AQI value of 500) that typically is set equal to the Significant Harm Level (40 CFR 51.16), which would apply to state contingency plans. The EPA is proposing to revise the AQI for O 3 by setting an AQI value of 100 equal to the level of the revised O 3 standard. The EPA is also proposing to revise the following breakpoints: an AQI value of 50 to 50 ppb; an AQI value of 150 to 85 ppb; an AQI value of 200 to 105 ppb, and an AQI value of 300 to 200 ppb. All these levels are averaged over 8 hours. The EP A is proposing to set an AQI value of 50, the breakpoint between the good and moderate categories , at 50 ppb. This level is well below the lowest concentration (i.e., 60 ppb) that has been shown in controlled human exposure studies of healthy adults to cau se moderate lung function decrements (i.e., FEV 1 decrements ≥ 10%, which could be adverse to people with lung disease) and airway inflammation in some people. The EPA is proposing to set an AQI value of 150, the breakpoint between the unhealthy for sensiti ve groups and unhealthy categories, at 85 ppb. At this level,*** E.O. 12866 Review

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Page 294 of 647 controlled human exposure studies of healthy adults indicate that up to 25% of exposed people are likely to have moderate lung function decrements (i.e., 25% have FEV 1 decrements ≥ 10%; 12% have FEV 1 decrements ≥ 15%) and up to 7% are likely to have large lung function decrements (i.e., FEV 1 decrements ≥ 20%) (McDonnell et al., 2012; Figure 7). Large lung function decrements would likely interfere with normal activity for most individuals and wou ld increase the likelihood that these individuals would seek medical treatment ( U.S. EPA, 2007, p.3

- 72; 72 FR 37849, July 11, 2007). The EPA is proposing to set an AQI value of 200, the breakpoint between the unhealthy and very unhealthy categories, at 105 ppb. At this level, controlled human exposure studies of healthy adults indicate that up to 38% of exposed people are likely to have moderate lung function decrements (i.e., 38% have FEV 1 decrements ≥ 10%; 22% have FEV 1 decrements ≥ 15%) and up to 13% are likely to have large lung function decrements (i.e.,
FEV 1 decrements ≥ 20%). The EPA is proposing to set an AQI value of 300, the breakpoint between the very unhealthy and hazardous categories, at 200 ppb. At this level, controlled human exposure studies of healthy adults indicate that up to 25% of exposed people are likely to have large lung function decrements (i.e., FEV 1 decrements ≥ 20%), which would interfere with daily activities for most healthy people and likely cause many of them to seek medical a ttention

. Effects would likely be greater in people with asthma. Table 6. Proposed AQI Breakpoints AQI Category Index Values Existing Breakpoints (ppb, 8

- hour average) Proposed Breakpoints

(ppb, 8

- hour average)
Good 0

- 50 0

- 59 0

- 50 Moderate 51

- 100 60

- 75 51

- (65 to 70) Unhealthy for Sensitive Groups 101

- 150 76

- 95 (66 to 71)

- 85*** E.O. 12866 Review

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Page 295 of 647 Unhealthy 151

- 200 96

- 115 86

- 105 Very Unhealthy 201

- 300 116

- 374 106

- 200 Hazardous 301

- 400 375

- 201

-

401

- 500 In selecting breakpoints to propose, an additional consideration was for each category to span at least a 15 ppb range to allow for more accurate forecasting

. EPA believes that the proposed breakpoints reflect a n appropriate balance between reflecting the health evidence that is the basis for the proposed primary O 3 standard and providing category ranges that are large enough to be forecasted accurately, so that the new AQI for
O 3 can be implemented more easily in the public forum for which the AQI ultimately exists. With respect to r eporting requirements (40 CFR Part 58, §58.50), EPA proposes
to revise 40 CFR Part 58, §58.50 (c) to require the AQI reporting requirements to be based on the latest available census figures, rather than the most recent decennial U.S.

census . This change i s consistent with our current practice of using the latest population figures to make monitoring requirements more responsive to changes in population. IV. Rationale for Proposed Decision on the Secondary Standard This section presents the rationale for th e Administrator’s proposed decision s regarding the need to revise the current secondary O 3 NAAQS and the appropriate revisions to the standard, including her proposed decisions that the current secondary standard is not requisite to protect public welfare and should be revised to provide additional public welfare protection. The Administrator proposes to conclude that ambient O 3 concentrations in terms of a W126 index value, averaged across three consecutive years, within the range from 13 ppm

- hrs to 17 pp m - hrs would provide the requisite protection against known or anticipated adverse effects to the public welfare. To*** E.O. 12866 Review

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Page 296 of 647 achieve that level of air quality, the Administrator proposes to revise the level of the current secondary standard within the range propose d for the primary standard of 0.065 to 0.070 ppm

. As discussed more fully below, this proposal is based on a thorough review, in the ISA, of the latest scientific information on O 3 - induced environmental effects. This proposed decision also takes into acc ount: (1) staff assessments in the PA of the most policy

- relevant information in the ISA and WREA analyses of air quality, exposure, and ecological risks and associated ecosystem services; ( 2 ) CASAC advice and recommendations ; and , ( 3 ) public comments rece ived during the development of these documents, either in connection with CASAC meetings or separately. This proposed decision draws on the ISA’s integrative synthesis of the entire body of evidence, published through July 2011, on environmental effects associated with the presence of O 3 and related photochemical oxidants in the ambient air. As summarized in section IV.B below , this body of evidence addresses the range of environmental responses associated with exposure to ambient levels of O 3 ( U.S. EPA, 2013, ISA chapters 9

- 10), and includes more than four hundred new studies that build on the extensive evidence base from the last review. This rationale also draws upon the results of quantitative exposure and risk assessments, summarized in section IV.C b elow

. Section IV.D presents the Administrator’s proposed decisions on the adequacy of the current secondary standard (section IV.D.3) drawing on both evidence

- based and exposure/risk

- based considerations in the PA (section IV.D.1) and advice from CASAC (se ction IV.D.2). Proposed conclusions on alternative standards are summarized in section IV.E.*** E.O. 12866 Review

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Page 297 of 647 A. Approach In evaluating whether it is appropriate to retain or revise the current secondary O 3 standard, the Administrator adopts an approach in this review th at builds upon the general approach used in the 2008 review 149 and reflects the broader body of scientific evidence now available, updated exposure/risk information, advances in O 3 air quality modeling, and air monitoring information. This review of the stan dard also considers the July 2013 remand of the secondary standard by the U.S. Court of Appeals for the D.C. Circuit, such that the proposed decision described herein incorporates the EPA’s response to this
remand. The Administrator’s decisions in the 200 8 review were based on an integration of information on welfare effects associated with exposure to O 3 , judgments on the adversity and public welfare significance of key effects, and judgments as to wh at standard would be requisite to protect public welfar e. These considerations were informed by air quality and related analyses, quantitative exposure and risk assessments, and qualitative assessment of impacts that could not be quantified. As a result of the 2008 review, the Administrator concluded the then

- current secondary standard did not provide the requisite public welfare protection and it was revised. The current secondary standard is 75 pp b based on the annual fourth

- highest daily maximum 8

- h ou r average concentration, averaged over three consecutive y ears , which is identical to the current primary standard . In 2008, the Administrator considered the then

- available monitoring data with regard to relationships between the revised primary standard and degree of

149 T he 2008 revision of the O 3 secondary standard, the proposed reconsideration of the 2008 decision, and the 2013 court decision on the 2008 revision of the secondary standard are summarized in section I.C above

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Page 298 of 647 protection of public welfare from cumulative seasonal O 3 exposures, expressed in terms of the W126 exposure index (described in section IV.B.1 below) , and decided to revise the secondary standard to be equal to the revised primary standard (73 FR 16499

- 16500 , March 27, 2008 ). In remanding the 2008 decision on the secondary standard back to the
EPA (described in section I.C above) , the U.S. Court of Appeals for the D.C. Circuit determined that EPA did not specify what level of air quality was requisite to protect public welfare from adverse public we lfare effects or explain why any such level would be requisite. Mississippi , 744 F.3d at 272

- 73. In addition to reviewing the most recent scientific information as required by the CAA, this rulemaking responds to the remand and fully explains the Administ rator’s proposed conclusions as to the level of air quality requisite to protect public welfare from known or anticipated effects. Our general approach in considering the scientific information available in this review involves consideration of the integra tive synthesis of the entire body of available scientific evidence in the ISA (U.S. EPA, 2013), including information on biologically relevant exposure indices , exposure/risk and air quality modeling analyses presented in the WREA (U.S. EPA, 2014 b ) , staff analyses in the PA; advice and recommendations from CASAC (Frey, 2014 b , c) , and public comments. We note that in drawing conclusions on the secondary standard, the final decision to retain or revise the standard is a public welfare policy judgment to be ma de by the Administrator. The Administrator’s final decision will draw upon the available scientific evidence for
O 3 - attributable welfare effects and on analyses of exposures and public welfare risks based on impacts to vegetation, ecosystems and their ass ociated services, as well as judgments about the appropriate weight to place on the range of uncertainties inherent in*** E.O. 12866 Review

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Page 299 of 647 the evidence and analyses

. Such judgments in the context of this review include: the weight to place on the evidence of specific vegetati on - related effects estimated to result across a range of cumulative seasonal concentration

- weighted O 3 exposures; the weight to give associated uncertainties, including those related to the variability in occurrence of such effects in areas of the U.S. , es pecially areas of particular public welfare significance ; and , judgments on the extent to which such effects in such areas may be considered adverse to public welfare.
As provided in the CAA, section 109(b)(2), the secondary standard is to “specify a level of air quality the attainment and maintenance of which in the judgment of the Administrator

... is requisite to protect the public welfare from any known or anticipated adverse eff

ects associated with the presence of such air pollutant in the ambient air.”
E ffects on welfare 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 ” (CAA section 302(h)). As recognized in the last review, t he secondary standard is not meant to protect against all known or anticipated O 3 - related effects, but rather those that are judged to be adverse to the public welfare (73 FR 1649 6, March 27, 2008 ). Thus, th e level of protection from known or anticipated adverse effects to public welfare that is requisite for the secondary standard is a public welfare policy judgment to be made by the Administrator. In the current review, the Administrator’s judgment is informed by c onclusions drawn with regard to adversity of effects to public welfare in decisions on secondary O 3 standards in past reviews.*** E.O. 12866 Review

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Page 300 of 647 In the 2008 decision, the Administrator concluded that the degree to which O 3 effects on vegetation should be considered to be adverse depends on the intended use of the vegetation and the significance of the vegetation to the public w elfare, and applied this concept beyond the species level to the ecosystem level (73 FR 16496 , March 27,
2008 ). In so doing, the Administrator took note of “a number of actions taken by Congress to establish public lands that are set aside for spe cific uses that are intended to provide benefits to the public welfare, including lands that are to be protected so as to conserve the scenic value and the natural vegetation and wildlife within such areas, and to leave them unimpaired for the enjoyment of future generations” (73 FR 16496, March 27, 2008). The notice for the 2008 decision further noted that [s]uch public lands that are protected areas of national interest include national parks and forests, wildlife refuges, and wilderness areas” (73 FR 164 96, March 27, 2008). 150 , 151 The Administrator additionally recognized that “States, Tribes and public interest groups also set aside areas that are intended to provide similar benefits to the public welfare, for residents on State and Tribal lands, as well as for visitors to those areas” ( 73 FR 16496, March 27, 2008 ).

150 For example, the National Park Service Organic Act of 1916 established the National Park Service (NPS) and, in describing the role of the NPS with regard to “Federal areas known as national parks, m onuments, and reservations”, stated that the “fundamental purpose” for these Federal areas “is to conserve the scenery and the natural and historic objects and the wild life therein and to provide for the enjoyment of the same in such manner and by such me ans as will leave them unimpaired for the enjoyment of future generations .” 16 U.S.C. § 1. 151 As a second example, the Wilderness Act of 1964 defines designated “wilderness areas” in part as areas “protected and managed so as to preserve [their] natural con ditions” and requires that these areas “shall be administered for the use and enjoyment of the American people in such manner as will leave them unimpaired for future use and enjoyment as wilderness, and so as to provide for the protection of these areas, [and] the preservation of their wilderness character ...” 16 U.S.C. § 1131 (a).*** E.O. 12866 Review

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Page 301 of 647 The Administrator took note of the “ clear public interest in and value of maintaining these areas in a condition that does not impair their intended use and the fact that many of these lands contain O 3 - sensitive species ” (73 FR 16496, March 27, 2008). Similarly , in judgments of adversity to public welfare in the 2010 proposed reconsideration, the Administrator proposed to place the highest priority and signif icance on vegetation and ecosystem effects to sensitive species that are known to or are likely to occur in federally protected areas such as national parks and other Class I areas, 152 or on lands set aside by states, tribes and public interest groups to pro vide similar benefits to the public welfare (75 FR 3023

- 24 , January 19, 2010 ). In the current review, our c onsideration of the scientific evidence for effects on vegetation is based fundamentally on using information from controlled chamber studies, free air methodologies, and field

- based observational, survey and gradient studies. Such evidence, discussed below, informs consideration of welfare endpoints and at

- risk species and ecosystems on which to focus the current review, and consideration of the ambi ent O 3 conditions under which various welfare effec ts are known or anticipated to occur. As in past reviews, we recognize that the available evidence has not provided identification of a thres hold in exposure or ambient O 3 concentrations below which it can be concluded with confidence that O 3 - attributable effects on vegetation do not occur , when considering the broad range of O 3 - sensitive plant species growing within the U.S and the array of

152 As defined by section 162 of the CAA, Class I areas include all international parks, national wilderness areas which exceed 5,000 acres in size, national memorial parks which exceed 5,000 acres in size, and national parks which exceed six thousand acres in size, provided the park or wilderness area was in existence on August 7, 1977, as well as other areas designated as Class I consistent with that section of the Act. The curr ent Class I areas are specified at 40 CFR part 81.*** E.O. 12866 Review

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Page 302 of 647 effects. This is due in part to the fact that research shows that there is variability in sensitivity between and within species and that numerous factors, i.e., chemical, physical, biological, and genetic, can influence the direction and magnitude of the studied effect (U.S. EPA, 2013, section 9.4.8). In the absence of evidence for a discernible threshold, the general approach to considering the available O 3 welfare effects evidence involves characterizing the confidence in conclusions regarding O 3 - attributable vegetation effects over the ranges of cumulative seasonal O 3 exposure values evaluated in chamber studies and in field studies in areas where O 3 - sensitive vegetation are known to occur, as well as characterizing the extent to whic h these effects can be considered adverse at the plant level and beyond

. With this app roach, we consider the evidence for O 3 affecting other ecosystem components (such as soils, water, and wildlife) and their associated goods and services, through its effects on vegetation , as well as the associated uncertainties

. O ur general approach furt her recognizes the complexity of judgments to be made regarding the identification of particular vegetation effects as welfare effects and regarding the point that known or anticipated vegetation

- related effects become adverse to the public welfare. For ex ample, in addition to the magnitude of the ambient concentrations, the species present , their sensitivity to O 3 , and their public welfare importance are also essential considerations in drawing conclusions regarding the significance of public welfare impact. Taking this into account, we recognize the existence of a continuum from relatively higher ambient O 3 concentrations and conditions, in areas with sensitive species and public welfare significance, for which there might be general agreement that ef fects on public welfare are likely to occur,*** E.O. 12866 Review

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Page 303 of 647 through lower concentrations at which the degree to which public welfare might be expected to be affected becomes increasingly uncertain.
T he evidence base for this review, summarized in section IV.B below, inc ludes quantitative information across a broad array of vegetation effects (e.g., growth impairment during seedling, sapling and mature tree growth stages, visible foliar injury, and yield loss in annual crops) and across a diverse set of exposure m ethods f rom laboratory and field studies. While considering the full breadth of information available, we place greater weight on U.S. studies due to the often species

- , site

- , and climate

specific nature of O 3 - related vegetation responses , and particularly emphas ize those studies that include O 3 exposures that fall within the range of those likely to occur in the ambient air. We additionally recognize differences across different study types in what information they provide. For example, because conditions can be controlled in laboratory studies, responses in such studies may be less variable and smaller differences may be easier to detect. However, the control conditions may limit the range of responses or incompletely reflect pollutant bioavailability, so they ma y not reflect responses that would occur in the natural environment. Alternatively, field data can provide important information for assessments of multiple stressors or where site

- specific factors significantly influence exposure. They are also often usef ul for analyses of larger geographic scales and higher levels of biological organization. However, because most field study conditions cannot be controlled, variability is expected to be higher and differences harder to detect. The presence of confounding factors can also make it difficult to attribute observed effects to specific stressors.*** E.O. 12866 Review

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Page 304 of 647 In developing quantitative exposure and risk assessments for this review, summarized in section IV.C below, we have place d greatest emphasis on studies that have evalu ated plant response over multiple exposure levels and developed exposure

response (E

- R) relationships that allow the estimation of plant responses over the range of O 3 exposures pertinent to judgments on the current and potential alternative standards.
In considering the information from these assessments, we f ocus particularly on the quantitative risks related to three types of O 3 effects on vegetation and associated ecosystem services: visible foliar injury, biomass loss in trees , and crop yield loss. The se risks were assessed in a range of analyses primarily involving national

- scale air quality scenarios developed using model adjustments and interpolation methods. We consider particularly the national scale assessments for these scenarios, while recognizi ng the uncertainties with regard to the conditions they represent. With regard to the appropriate characterization of exposure s associated with ambient O 3 concentrations, as in the 2008 and 1997 reviews, we continue to recognize the relevance of cumulative , seasonal, concentration

- weighted exposures for assessing vegetation effects. More specifically, in the 2008 review, the EPA concluded and the CASAC agreed that the W126 cumulative exposure metric was the most appropriate to use to evaluate both the adequacy of the current secondary standard and the appropriateness of any potential revisions. As discussed in section IV.B.1 below , the information available in this review continues to support the use of such a metric and it is used in considering potent ial public welfare impacts in the sections below. B. Welfare Effects Information 1. Nature of Effects and Biologically Relevant Exposure Metric*** E.O. 12866 Review

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Page 305 of 647 This section describes the nature of O 3 - induced welfare effects, including the nature of the exposures that dri ve the biological and ecological responses (U.S. EPA, 2013, chapter 9). Ozone’s phytotoxic effects were first identified on grape leaves in a study published in 1958 (Richards et al., 1958). In the almost fifty years that have followed, extensive research has been conducted both in and outside of the U.S. to examine the impacts of O 3 on plants and their associated ecosystems, since “of the phytotoxic compounds commonly found in the ambient air, O 3 is the most prevalent, impairing crop production and injurin g native vegetation and ecosystems more than any other air pollutant” (U.S. EPA, 1989, 1996 a ). As was established in prior reviews, O 3 can interfere with carbon gain (photosynthesis) and allocation of carbon within the plant. As a result of decreased carbo hydrate availability, fewer carbohydrates are available for plant growth, reproduction, and/or yield. For seed

- bearing plants, these reproductive effects will culminate in reduced seed production or yield (U.S. EPA, 1996a, pp. 5

- 28 and 5

- 29)

. Recent studi es, assessed in the ISA, together with this longstanding and well

- established literature on O 3 - related vegetation effects, further contribute to the coherence and consistency of the vegetation effects evidence. As described in the ISA, a variety of factors in natural environments can either mitigate or exacerbate predicted O 3 - plant interactions and are recognized sources of uncertainty and variability. These include: 1) multiple genetically influenced determinants of O 3 sensitivity; 2) changing sensitivity to O 3 across vegetative growth stages; 3) co

- occurring stressors and/or modifying environmental factors (U.S. EPA, 2013, section 9.4.8).*** E.O. 12866 Review

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Page 306 of 647 Among the studies of vegetation effects, the ISA recognizes controlled chamber studies as the best method for isolatin g or characterizing the role of O 3 in inducing the observed plant effects, and in assessing plant response to O 3 at the finer scales (U.S. EPA, 2013, sections 9.2 and 9.3). Recent controlled studies have focused on a variety of plant responses to O 3 includ ing the underlying mechanisms governing such responses. These mechanisms includ e : 1) reduced carbon dioxide uptake due to stomatal closure (U.S. EPA, 2 013, section 9.3.2.1); 2) the upregulation of genes associated with plant defense, signaling, hormone syn thesis and secondary metabolism (U.S. EPA, 2 013, section 9.3.3.2); 3) the down regulation of genes related to photosynthesis and general metabolism (U.S. EPA, 2 013, section 9.3.3.2); 4) the loss of carbon assimilation capacity due to declines in the quanti ty and activity of key proteins and enzymes (U.S. EPA, 2013, section 9.3.5.1); and 5) the negative impacts on the efficiency of the photosynthetic light reactions (U.S. EPA, 2013, section 9.3.5.1). As described in the ISA, these new studies “have increased knowledge of the molecular, biochemical and cellular mechanisms occurring in plants in response to O 3 ”, adding “to the understanding of the basic biology of how plants are affected by oxidative stress...” (U.S. EPA, 2013, p. 9

- 11). The ISA further conclude s that controlled studies “have clearly shown that exposure to O 3 is causally linked to visible foliar injury, decreased photosynthesis, changes in reproduction, and decreased growth” in many species of vegetation (U.S. EPA, 2 013, p.
1

- 15). Such effects at the plant scale can also be linked to an array of effects at larger spatial scales. For example, recent field studies at larger spatial scales, together with previously available evidence, support the controlled exposure study results and indicate*** E.O. 12866 Review

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Page 307 of 647 that “a mbient O 3 exposures can affect ecosystem productivity, crop yield, water cycling, and ecosystem community composition” (U.S. EPA, 2013, p. 1

- 15; Chapter 9, section 9.4). The current body of O 3 welfare effects evidence confirms th e conclusions reached in the last review on the nature of O 3 - induced welfare effects and is sum marized in the ISA as follows (U.S. EPA, 2013, p. 1

- 8)

. The welfare effects of O 3 can be observed across spatial scales, starting at the subcellular and cellular level, then the whole plant and finally, ecosystem

- level processes. Ozone effects at small spatial scales, such as the leaf of an individual plant, can result in effects along a continuum of larger spatial scales. These effects include altered rates of le af gas exchange, growth, and reproduction at the individual plant level, and can result in broad changes in ecosystems, such as productivity, carbon storage, water cycling, nutrient cycling, and community composition. Based on its assessment of this extens ive body of science, the ISA determine s that, with respect to vegetation and ecosystems, a causal relationship exists between exposure to O 3 in ambient air and visible foliar injury effects on vegetation, reduced vegetation growth, reduced productivity in terrestrial ecosystems, reduced yield and quality of agricultural crops and alteration of below

- ground biogeochemical cycles 153 (U.S. EPA, 2013, Table 1

- 2). In consideration of the evidence of O 3 exposure and alterations in stomatal performance, “which may a ffect plant and stand transpiration and therefore possibly affecting hydrological cycling,” the ISA concludes that “[a]lthough the direction of the response differed among studies ,” the evidence is sufficient to conclude a likely causal relationship betwee n O 3 exposure and the altera tion of ecosystem water cycling (U.S. EPA, 2013, section 2.6.3). The ISA also concludes that the evidence is

153 Based on studies focused on O 3 - associated alterations in quality and quantity of carbon input to soil, microbial communi t y composition, and carbon and nutrient cycling, the ISA concludes that t he evidenc e is sufficient “ to infer that there is a causal relationship between O 3 exposure and the alteration of below

- ground biogeochemical cycles” (U.S. EPA, 2013, pp. 2

- 41 to 2

- 42).*** E.O. 12866 Review

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Page 308 of 647 sufficient to conclude a likely causal relationship between O 3 exposure and the alteration of community composition of some terrestrial ecosystems (U.S. EPA, 2013, section 2.6.5). Related to the effects on vegetation growth, productivity and, to some extent, below

- ground biogeochemical cycles, the ISA additionally determine s that a likely causal relationship exists betwee n exposures to O 3 in ambient air and reduced carbon sequestration (also termed carbon storage) 154 in terrestrial ecosystems (U.S. EPA, 2013, p. 1

- 10 and section 2.6.2). Modeling studies available in this review consistently found negative impacts of O 3 on c arbon sequestration, although the severity of impact was influenced by “multiple interactions of biological and environmental factors” (U.S. EPA, 2013, p. 2

- 39). The ISA notes that “[t]he suppression of ecosystem [carbon] sinks results in more [carbon di oxide] accumulation in the atmosphere” and that a recent study has suggested that “the indirect radiative forcing caused by O 3 exposure through lowering the ecosystem [carbon] sink could have an even greater impact on global warming than the direct radiative forcing of O 3 ” (U.S. EPA, 2013, p. 2

- 39). With regard to direct radiative forcing, however, the ISA makes a stronger causal ity conclusion that the evidence supports a causal relationship between changes in tropospheric O 3 concentrations and radiative forcing 155 (U.S. EPA, 2013, section 2.7.1). There are, however, “large uncertainties in the magnitude of the radiative forcing est imate attributed to tropospheric

154 The terms sequestration and storage are used somewhat interchangeably in the ISA and other documents in this review. 155 Radiative forcing by a greenhouse gas or aerosol is a metric used to quantify the change in balance between radiation coming into and going out of the atmosphere caused by the presence of that substance. For exam ple, a reduction in outgoing infrared radiation has been associated with O 3 by satellite data (U.S. EPA, 2013, p. 2

- 47).*** E.O. 12866 Review

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Page 309 of 647 O 3 , making the impact of tropospheric O 3 on climate more uncertain than the effect of the longer

- lived greenhouse gases ” (U.S. EPA, 2013, p. 2

- 47)

. In this regard, the ISA observes that “ radiative forcing does not take into account the climate feedbacks that could amplify or dampen the actual surface temperature response ,” that “[q] uantifying the change in surface temperature requires a complex climate simulation in which all important feedbacks and interactions are accounte d for ” and that “[t] he modeled surface temperature response to a given radiative forcing is highly uncertain and can vary greatly among models and from region to region within the same model ” (U.S. EPA, 2013, p. 2

- 47)

. Even with these uncertainties, the IS A notes that “ global climate models indicate that tropospheric O 3 has contributed to observed changes in global mean and regional surface temperatures ” and as a r esult of such evidence presented in climate modeling studies, concludes that there is likely t o be a causal relationship between changes in tropospheric
O 3 concentrations and effects on climate (U.S. EPA, 2013, p. 2

- 47). The ISA additionally notes, however, that “[i]mportant uncertainties remain regarding the effect of tropospheric O 3 on future cli mate change” (U.S. EPA, 2013, p. 10

- 31). Given the strong evidence base, and findings of causal or likely causal relationships with O 3 in ambient air, including the quantitative assessments of relationships between O 3 exposure and occurrence and magnitude of effects, we give a primary focus to three main areas of effects

. The three main areas, for which the evidence is summarized in more detail below, are : 1) impacts on tree growth, productivity and carbon storage (section IV.B.1.b) ; 2) crop yield loss (section IV.B.1.c) ; and 3) visible foliar injury (section IV.B.1.a)

. Consideration of these three areas includes, as*** E.O. 12866 Review

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Page 310 of 647 appropriate, consideration of evidence of associated effects at larger scales, including ecosystems, and on associated ecosystem services

. With regard to biologically based indices of exposure pertinent to O 3 effects on vegetation, the ISA states the following (U.S. EPA, 2013, p. 2

- 44)

. The main conclusions from the 1996 and 2006 O 3 AQCDs [Air Quality Criteria Documents] regarding indices b ased on ambient exposure remain valid. These key conclusions can be restated as follows: ozone effects in plants are cumulative; higher O 3 concentrations appear to be more important than lower concentrations in eliciting a response; plant sensitivity to O 3 varies with time of day and plant development stage; [and] quantifying exposure with indices that cumulate hourly O 3 concentrations and preferentially weight the higher concentrations improves the explanatory power of exposure/response models for growth a nd yield, over using indices based on mean and peak exposure values. The long

- standing body of available evidence upon which these conclusions are based provides a wealth of information on aspects of O 3 exposure that are important in influencing plant res ponse. Specifically, a variety of “factors with known or suspected bearing on the exposure

- response relationship, including concentration, time of day, respite time, frequency of peak occurrence, plant phenology, predisposition, etc.,” have
been identified (U.S. EPA, 2013, section 9.5.2). In addition, the importance of the duration of the exposure and the relatively greater importance of higher concentrations over lower concentrations in determining plant response to O 3 have been consistently well documente d (U.S. EPA, 2013, section 9.5.3). Much of this evidence was assessed in the 1996 Criteria Document (CD) (U.S. EPA, 1996 a ), while more recent work substantiating this evidence is assessed in the subsequent 2006 CD and 2013 ISA. Understanding of the biol ogical basis for plant response to O 3 exposure led to the development of a large number of “mathematical approaches for summarizing ambient air quality information in biologically meaningful forms for O 3 vegetation effects*** E.O. 12866 Review

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Page 311 of 647 assessment purposes” (U.S. EPA, 2 013, section 9.5.3), including those that cumulate exposures over some specified period while weighting higher concentrations more than lower (U.S. EPA, 2013, section 9.5.2) . As with any summary statistic, these exposure indices retain information on some, but not all, characteristics of the original observations. The 1996 CD contained an extensive review of the published literature on different types of exposure

- response metrics, including comparisons between metrics, from which the 1996 Staff Paper built its assessment of forms appropriate to consider in the context of the secondary NAAQS review. The result of these assessments was a decision by the EPA to focus on cumulative, concentration

- weighted indices, which were recognized as the most appropriate bi ologically based metrics to consider in this context, with attention given primarily to two cumulative, concentration

- weighted index forms: SUM06 and W126. 156 In both the 1997 and 2008 reviews, the EPA concluded that the risk to vegetation comes primarily from cumulative exposures to O 3 over a season or seasons 157 and focused on metrics intended to characterize such exposures: SUM06 (61 FR 65716 , December 13, 1996 ) and W126 (72 FR 37818 , July 11, 2007 ) in the 1997 and 2008 reviews, respectively. Although in b oth reviews the policy decision was made to set the

156 The SUM06 index is a threshold

- based approach described as the sum of all hourly O 3 concentrations greater or equal to 0.06 ppm obser ved during a specified daily and seasonal time window (U.S. EPA, 2013, section 9.5.2). The W126 index is a non

threshold approach described as the sigmoidally weighted sum of all hourly O 3 concentrations observed during a specified daily and seasonal time window, where each hourly O 3 concentration is given a weight that increases from zero to one with increasing concentration (U.S. EPA, 2013, section 9.5.2). 157 In describing the form as “seasonal”, the EPA is referring generally to the growing season of O 3 - sensitive vegetation, not to the seasons of the year (i.e., spring, summer, fall, winter).*** E.O. 12866 Review

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Page 312 of 647 secondary standard to be identical to a revised primary standard (with an 8

- hour averaging time), the Administrator, in both cases, also concluded, consistent with CASAC advice, that a cumulative, seasona l index was the most biologically relevant way to relate exposure to plant growth response (62 FR 38856 , July 18, 1997; 73 FR 16436 , March 27, 2008; 75 FR 2938 , January 19, 2010 ). T his approach for characterizing O 3 exposure concentrations that are biologi cal ly relevant with regard to potential vegetation effects received strong support from CASAC in the last review and again in this review, including strong support for use of such a metric as the form for the secondary standard (Henderson, 2006, 2008; Same t, 2010; Frey, 2014 c ). An alternative to using ambient exposure durations and concentrations to predict plant response has been developed in recent years, primarily in Europe, i.e., flux models. While “some researchers have claimed that using flux models can be used {sic} to better predict vegetation responses to O 3 than exposure

- based approaches” because flux models estimate the ambient O 3 concentration that actually enters the leaf (i.e., flux or deposition) (U.S. EPA, 2013, p. 9

- 114) , it is important to note that “[f]lux calculations are data intensive and must be carefully implemented” (U.S. EPA, 2013, p. 9

- 114). Further, the ISA state s , “[t]his uptake

- based approach to quantify the vegetation impact of O 3 requires inclusion of those factors that contro l the diurnal and seasonal O 3 flux to vegetation (e.g., climate patterns, species and/or vegetation

- type factors and site

- specific factors)” (U.S. EPA, 2013, p. 9

- 114). In addition to these data requirements, e ach species has different amounts of internal detoxification potential that may protect species to differing degrees. The lack of detailed species

- and site

- specific data required for flux modeling in the U.S. and the lack of understanding of detoxification processes have*** E.O. 12866 Review

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Page 313 of 647 continued to make this techni que less viable for use in vulnerability and risk assessments at the national scale in the U.S. (U.S. EPA, 2013, section 9.5.4). Therefore, consistent with the ISA conclusions regarding the appropriateness of considering cumulative exposure indices that pr eferentially weight higher concentrations over lower for predicting O 3 effects of concern based on the long

- established conclusions and long

- standing supporting evidence described above, and in light of continued CASAC support, we continue to focus on cumu lative concentration

- weighted indices as the most biologically relevant metrics for consideration of O 3 exposures eliciting vegetation

- related effects. Such a metric has an “explanatory power” that is improved “over using indices based on mean and peak exposure values” (U.S. EPA, 2013, section 2.6.6.1, p. 2

- 44). In this review as in the last review, we use the W126 cumulative, seasonal metric (U .S. EPA, 2013, sections 2.6.6.1 and 9.5.2) for consideration of the effects evidence and in the exposure and risk analyses in the WREA.
T he subsections below summarize key aspects of the welfare effects information for O 3 - elicited visible foliar injury (s ection IV.B.1.a), effects on forest tree growth, productivity and carbon storage (section IV.B.1.b) and reductions in crop yie ld (section IV.B.1.c), as well as associated effects. a. Visible Foliar Injury Visible foliar injury resulting from exposure to O 3 has been well characterized and documented over several decades of research on many tree, shrub, herbaceous, and crop species (U.S. EPA, 2013 , p. 1

- 10; U.S. EPA, 2006 a , 1996 a , 1984, 1978). Additionally, O 3 - induced visible foliar injury symptoms on certai n plant species, such as black cherry, yellow

- poplar and common milkweed, are considered diagnostic of*** E.O. 12866 Review

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Page 314 of 647 exposure to O 3 based on the consistent association established with experimental evidence (U.S. EPA, 2013, p. 1

- 10). The significance of O 3 injury at the leaf and whole plant levels depends on an array of factors, and therefore, it is difficult to quantitatively relate visible foliar injury symptoms to vegetation effects such as individual tree growth, or effects at population or ecosystem levels (U.S. EPA , 2013, p. 9

- 39). The ISA notes that visible foliar injury “is not always a reliable indicator of other negative effects on vegetation” (U.S. EPA, 2013, p. 9

- 39). Factors th at influence the significance to the leaf and whole plant include the amount of tot al leaf area affected, age of plant, size, developmental stage , and degree of functional redundancy among the existing leaf area (U.S. EPA, section 9.4.2). Visible foliar injury by itself is an indication of phytotoxicity due to O 3 exposure, which occurs o nly when sensitive plants are exposed to elevated O 3 concentrations in a predisposing environment, a major aspect of which is the lack of drought conditions during the year such injury is assessed (U.S. EPA, 2013, section 9.4.2). Recent research continu es to build and substantiate the previous conclusions and findings drawn from several decades of research on many tree, shrub, herbaceous, and crop species (U.S. EPA, 2013, 2006, 1996, 1984, 1978) that O 3 - induced visible foliar injury symptoms are well cha racterized and considered diagnostic on certain bioindicator plant species. Diagnostic usage for these plants has been verified experimentally in
exposure - response studies, using exposure methodologies such as continuous stirred tank reactors (CSTRs), open

- top chambers (OTCs), and free

- air fumigation (FACE). Although there remains a lack of robust exposure

- response functions that would allow prediction of visible foliar injury severity and incidence under varying air quality and environmental*** E.O. 12866 Review

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Page 315 of 647 conditions, “ e xperimental evidence has clearly established a consistent association of the presence of visible foliar injury symptoms with O 3 exposure, with greater exposure often resulting in greater and more prevalent injury ” (U.S. EPA, 2013, section 9.4.2, p. 9

- 41). The research newly available in this review includes: 1) controlled exposure studies conducted to test and verify the O 3 sensitivity and response of potential new bioindicator plant species; 2) multi

- year field surveys in several National Wildlife Refuges (NWR) documenting the presence of foliar injury in valued areas; and 3) ongoing data collection and assessment by the U.S. Forest Service’s Forest Health Monitoring Forest Inventory and Analysis ( USFS FHM/FIA ) program, including multi

- year trend analysis ( U.S. EPA,
2 013, section 9.4.2). These recent studies, in combination with the entire body of available evidence, thus form the basis for the ISA determinations of a causal relationship between ambient O 3 exposure and the occurrence of O 3 - induced visible fo liar injury on sensitive vegetation across the U.S. (U.S. EPA, 2 013, p. 9

- 42). Recently available evidence confirms the evidence available in previous reviews that visible foliar injury can occur when sensitive plants are exposed to elevated O 3
concentrat ions in a predisposing environment (i.e., adequate soil moisture) (U.S. EPA, 2013, section 9.4.2). Recent evidence also continues to support previous findings that indicate d the occurrence of visible foliar injury at cumulative ambient O 3 exposures previou sly examined

. With regard to evidence from controlled exposure studies, a recent study , using continuously stirred tank reactor (CSTR) chambers , evaluated the occurrence of O 3 characteristic visible foliar injury symptoms on 28 species of plants that were suspected of being O 3 sensitive and most of which grow naturally throughout the northeast and*** E.O. 12866 Review

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Page 316 of 647 midwest U

. S

. , including in national parks and wilderness areas (U.S. EPA, 2013, section 9.4.2.1 ; Kline et al., 2008). Across the 28 tested species, t he study reported O 3 - induced responses in 12, 20, 28 and 28 species at the 30, 60, 90 and 120 ppb exposure concentrations , 158 respectively ; the plants were exposed for 7 hours per each weekday over 21 to 29 summer days (Kline et al., 2008). A string of recently published multi

- year field studies provide a compl e mentary line of field

- based evidence by documenting the incidence of visible foliar injury symptoms on a variety of O 3 - sensitive species over multiple years and across a range of cumulative, seaso nal exposure values in several eastern and midwestern NWRs (U.S. EPA, 2 013, section 9.4.2.1; Davis and Orendovici, 2006; Davis, 2007a, b; Davis, 2009). Some of these studies also included information regarding soil moisture stress using the Palmer Drought Severity Index (PDSI). While environmental conditions and species varied across the four NWRs, visible foliar injury was documented to a varying degree at each site. By far the most extensive field

- based dataset of visible foliar injury incidence is that obtained by the USFS FHM/FIA biomonitoring network program. A trend analysis of data from the sites located in the Northeast and North Central U.S. for the 16 year period from 1994 through 2009 (Smith, 2012) describes evidence of visible foliar injury

occu rrence in the field as well as some insight into the influence of changes in air quality

158 Two of the target exposure levels, 30 and 60 ppb, fall below the level of the current standard (75 ppb) , although the exposures were average concentrations for 7

- hour exposures across durations shorter than a month. Because the form of the current standard targets peak concentrations in a season, an area that just meets the current standard can be expected to have mean concentrations well below that level due to v ariability in ambient O 3 concentrations

.*** E.O. 12866 Review

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Page 317 of 647 and soil moisture on visible foliar injury and the difficulty inherent in predicting foliar injury response under different air quality/soil moisture scenarios (Smith, 2012; U.S. EPA, 2 013, section 9.2.4.1). Study results showed that incidence and severity of foliar injury were dependent on local site conditions for soil moisture availability and O 3 exposure . Overall, there was a declining trend in the incidence of visi ble foliar injury as peak O 3 concentrations declined , although the study additionally indicated that moderate
O 3 exposures continued to cause visible foliar injury at sites throughout the region (U.S. EPA, 2013, p. 9

- 40) . In a similar assessment of the USF S FHM/FIA data in the West, six years (2000 to 2005) of biomonitoring data , during a period where a large proportion of California sites did not meet the current standard, indicated O 3 - related visible foliar injury in 25

- 37% of biosites in California (Camp bell et al., 2007; U.S. EPA, 2 013, section 9.4.2.1). 159 These recent studies provide additional evidence of O 3 - induced visible foliar injury in many areas across the U.S. and augment the EPA’s understanding of O 3 - related visible foliar injury and of factors , such as soil moisture, that influence associations between O 3 exposures or concentrations and visible foliar injury. b. Effects on Forest Tree Growth, Productivity and Carbon Storage Ozone has been shown to affect a number of important U.S. tree species with respect to growth, productivity, and carbon storage. Ambient O 3 concentrations have long been known to cause decreases in photosynthetic rates and plant growth. As discussed in the ISA, research published since the 2006 AQCD substantiates prior concl usions regarding O 3 - related effects on forest tree growth, productivity and carbon storage. The ISA states, “previous O 3 AQCDs concluded that there is strong evidence that exposure to

159 S ee: http://www.epa.gov/airtrends/values.html.*** E.O. 12866 Review

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Page 318 of 647 O 3 decreases photosynthesis and growth in numerous plant species” and that “[s]tudies published since the 2008 review support those conclusions” (U.S. EPA, 2013, p. 9

- 42). The available studies come from a variety of different study types that cover an array of different species, effects endpoints, levels of biological organization and exposure methods and durations. The O 3 - induced effects at the plant scale may translate to the ecosystem scale, with changes in productivity and carbon storage. As stated in th e ISA, “[s] tudies conducted during the past four decades have demonstrated unequivocally that
O 3 alters biomass allocation and plant reproduction ” (U.S. EPA, 2013, p. 1

- 10). The previously available strong evidence for trees includes robust E

- R functions for seedling relative biomass loss (RBL) 160 in 11 species developed under the National Health and Environmental Effects Research Laboratory

- Western Ecology Division program. This series of experiments used open

- top

- chambers (OTC) to study seedling growth res ponse for a single growing season under a variety of O 3 exposures (ranging from near background to well above current ambient concentrations) and growing conditions (U.S. EPA, 2 013, section 9.6. 2; Lee and Hogsett, 1996). T he evidence from these studies sho ws that there is a wide range in sensitivity across the studied species in the seedling growth stage over the course of a single growing season, with some species being extremely sensitive and others being very insensitive over the range of cumulative
O 3 e xposures studied (U.S. EPA, 2014c, Figure 5

- 1). At the other end of the organizational spectrum, field

- based studies of species growing in natural stands have compared observed plant response across a number of different sites and/or years when

160 These functions for RBL estimate reduction in a year’s growth as a percentage of that expected in the absence of O 3 (U.S. EPA, 2013, section 9.6.2; U.S. EPA, 2014b , section 6.2).*** E.O. 12866 Review

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Page 319 of 647 exposed to varying ambient O 3 exposure conditions only. For example, a study conducted in forest stands in the southern Appalachian Mountains during a period when O 3 concentrations exceeded the current standard found that the cumulative effects of O 3 decreased seasonal stem growth (measured as a change in circumference) by 30

- 50 percent for most of the examined tree species (i.e., tulip poplar, black cherry, red maple, sugar maple) in a high O 3 year in comparison to a low O 3 year ( U.S. EPA, 2013, section 9.4.3.1 ; McLaughlin et al., 2007a). The study also reported that high ambient O 3 concentrations can increase whole

- tree water use and in turn reduce late

- season streamflow (McLaughlin et al., 2007b; U.S. EPA, 2013, p. 9

- 43). The magnitude of O 3 impact on ecosys tem productivity and on forest composition
can vary among plant communities based on several factors including: the type of stand or community in which the sensitive species occurs (e.g., single species versus mixed canopy), the role or position of the sp ecies in the stand (e.g., dominant, sub

- dominant, canopy, understory), the sensitivity of co

- occurring species and environmental factors (e.g., drought and other factors). For example, O 3 has been found to ha ve little impact on white fir, but to greatly re duce growth of ponderosa pine in southern California , and

cause decreased net primary production of most forest types in the Mid

- Atlantic region, although only small impacts on spruce

- fir forest ( U.S. EPA, 2013, section 9.4.3.4). As noted above, long

- standing evidence has demonstrated that O 3 alters biomass allocation and plant reproduction (U.S. EPA, 2013, section 9.4.3) . S everal studies published since the 2006 O 3 AQCD further demonstrate that O 3 can alter reproductive
processes, such as timing of flowering and number of flowers, fruits and seeds, in herbaceous and woody plant species (U.S. EPA, section 9.4.3.3). Further, l imited*** E.O. 12866 Review

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Page 320 of 647 evidence in previous reviews reported that vegetation effects from a single yea r of exposure to elevat ed O 3 could be observed in the following year. For example, growth affected by a reduction in carbohydrate storage in one year may result in the limitation of growth in the following year

. S uch “carry

- over” effects have been documented in the growth of som e tree seedlings and in roots (U.S. EPA, 2013, section 9.4.8; Andersen, et al., 1997). In the current review, additional field

- based evidence expands the EPA’s understanding of the consequences of single and multi

- year O 3 exposures in subsequent years. A n umber of studies were conducted at a planted forest at the Aspen Free

- Air Carbon Dioxide Enrichment (FACE) site in Wisconsin. These studies, which occurred in a field setting ( more similar to natural forest stands than OTC studies ) , observed tree growth re sponses when grown in single or two species stands within 30

- m diameter rings and exposed over a period of ten years to existing ambient conditions and elevated O 3 concentrations . Some studies indicate the potential for carry

- over effects , such as those sh owing that the effects of O 3 on birch seeds (reduced weight, germination, and starch levels) could lead to a negative impact on species regeneration in subsequent years, and that the effect of reduced aspen bud size might have been related to the observed delay in spring leaf development. These effects suggest that elevated O 3 exposures have the potential to alter carbon metabolism of overwintering buds, which may have subsequent effects in the following year (Darbah, et al., 2008, 2007; Riikonen et al., 20 08; U.S. EPA, 2013, section 9.4.3). Other studies found that, in addition to affecting tree heights, diameters, and main stem volumes in the aspen community, elevated O 3 over a 7

- year study period was reported to increase the rate of conversion from a mixe d aspen

- birch community to a community dominated by the more tolerant birch, leading the authors to*** E.O. 12866 Review

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Page 321 of 647 conclude that elevated O 3 may alter intra

- and inter

- species competition within a forest stand (U.S. EPA, 2013, section 9.4.3 ; Kubiske et al., 2006; Kubiske et al., 2007). These studies confirm earlier FACE results of aspen growth reductions from a 6

- 7 year
exposure to elevated O 3 and of cumulative biomass impacts associated with changes in annual production in studied tree communities ( U.S. EPA, 2013, sectio n 9.4.3; King et al., 2005). In addition to individual studies, recent meta

- analyses have quantitatively analyzed the effect of O 3 on trees across large numbers of studies. In particular, a recent
meta

- analysis of 55 peer reviewed studies from the past 40 years indicates a negative relationship between O 3 concentrations in the northern hemisphere during that period and stomatal conductance and photosynthesis, which decrease s growth (U.S. EPA, 2013, section 9.4.3 .1; Wittig et al., 2007 )

. In this analysis, y ounger trees (less than 4 years) were affected less by O 3 than older trees (U.S. EPA, 2013, section 9.4.3.1; Wittig, et al., 2007). A second meta

- analysis that quantitatively compiled 263 peer - reviewed studies

“ demonstrates the coherence of O 3 effects across numerous studies and species that used a variety of experimental techniques, and these results support the conclusion of the previous AQCD that exposure to O 3 decreases plant growth ” (U.S. EPA, 2013, p. 9

- 4 3)

. Other meta

- analyses have examined the effect of O 3 exposure on root growth and generally found that O 3 exposure reduced carbon allocated to roots (U.S. EPA, 2013, pp.
9

- 45 to 9

- 46 ). As noted above, robust E

- R functions have been developed for 11 tree species (black cherry, Douglas fir, loblolly pine, ponderosa pine, quaking aspen, red alder, red maple, sugar maple, tulip poplar, Virginia pine, white pine) from the extensive evidence*** E.O. 12866 Review

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Page 322 of 647 base of O 3 –

induced growth effects that was also available and relied upon in the previous review. While the species for which robust E

- R functions have been developed represent only a small fraction (0.8 percent) of the total number of native tree species in the contiguous U.S. (1,497), this small subset includes eastern an d western species, deciduous and coniferous species, and species that grow in a variety of ecosystems and represent a range of tolerance to O 3 (U.S. EPA, 2 013, section 9.6.2; U.S. EPA, 2014b, section 6.2, Figure 6

- 2, Table 6

- 1). Each of these species were studied in OTCs, with most species studied multiple times under a wide range of exposure and/or growing conditions, with separate E

- R functions developed for each combination of species , exposure condition and growing condition scenario. These species

- spec ific composite E

R functions have been successfully used to predict the biomass loss response from tree seedling species over a range of cumulative exposure conditions (U.S. EPA, 2013, section 9.6.2)

. The 11 robust composite E

- R functions available in the last review , as well

as the E

- R for eastern cottonwood (derived from a field study in which O 3 and climate conditions were not controlled) , are described in the ISA and graphed in the WREA to illustrate the predicted responses of these species over a wide range of cumulative exposures (U.S. EPA, 2014b, section 6.2, Table 6

- 1 and Figure 6

- 2 ; U.S. EPA, 2 013, section 9.6.2)

. For some of these species , the E

- R function is based on a single study (e.g., red maple), while for other species there were as many as 1 1 studies available (ponderosa pine). In total, the E

- R functions developed for these 12 species (the 11 with robust composite E

- R functions plus eastern cottonwood) reflect 52 tree seedling studies

. A stochastic analysis in WREA, summarized in section IV. C below, indicates the potential for within species variability to contribute appreciably to estimates for each*** E.O. 12866 Review

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Page 323 of 647 species. Consideration of biomass loss estimates in the PA and in discussions below, however, is based on conventional method and focuses on est imates for the 11 species for which the robust datasets from OTC experiments are available, in consideration of CASAC advice. 161 c. Crop Yield Loss The “ detrimental effect of O 3 on crop production has been recognized since the 1960s ” (U.S. EPA, 2 013, p. 1

- 10, section 9.4.4). The newly available scientific information has added more support for prior conclusions regarding O 3 crop yield loss. On the whole, this evidence supports previous conclusions that exposure to O 3 decreases growth and yield of crops. The ISA describes average yield loss reported across a number of meta

- analy ses that have been published recently for soybean , wheat, rice, semi

- natural vegetation, potato, bean and barley (U.S. EPA, 2 013, section 9.4.4.1). Further, several new exposure stu dies continue to show decreasing yield and biomass in a variety of crops with increased O 3 exposure (U.S. EPA, 2 013, section 9.4.4.1, Table 9

- 17). Studies ha ve

“ linked increasing O 3 concentration to decreased photosynthetic rates and accelerated aging in leaves, which are related to yield ” and described effects of O 3 on crop quality, such as nutritive quality of grasses, macro

- and micronutrient concentrations in fruits and vegetable crops and cotton fiber quality ( U.S. EPA, p. 1

- 10, s ection 9.4.4). The fi ndings of the newly available studies d o not change the basic understanding of O 3 - related crop

161 The CASAC cautioned EPA against placing too much emphasis on the eastern cottonwood data, stating that while the cottonwood data are important results, they are not as strong as those from other experiments that developed E

- R functions b ased on controlled O 3 exposure in OTCs ; they are from a single gradient study that did not control for O 3 and climatic conditions and that show s extreme sensitivity to O 3 compared to other studies (Frey, 2014c, p. 10).*** E.O. 12866 Review

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Page 324 of 647 yield loss since the last review and little additional information is available in this review on factors that influence associations between O 3 levels and crop yield loss (U.S. EPA,
2 013, section 9.4.4.). The new evidence has strengthened support for previously established E

- R functions for 10 crops (barley, field corn, cotton, kidney bean, lettuce, peanut, potato, grain sorghum, soybean and winter wheat), reduc ing two important areas of uncertainty, especially for soybean. The established E

- R functions were developed from OTC

- type experiments (U.S. EPA, 2013, section 9.6.3; U.S. EPA, 2014b, section 6.2; U.S. EPA, 2014c, Figure 5

- 4)

. In this review, the ISA inclu ded an analysis comparing OTC data from NCLAN with field

- based data for soybean from SoyFACE (U.S. EPA, 2013, section 9.6.3.2). 162 Yield loss in soybean from O 3 exposure at the SoyFACE field experiment was reliably predicted by soybean E

- R functions develope d in NCLAN . This finding indicates that the average response of soybean yield to O 3 exposure has not changed in current cultivars (U.S. EPA, 2013, Section 9.6) , demonstrating a robustness of the E

- R functions developed in NCLAN to predict relative yield l oss from O 3 exposure and supporting the use of these functions . A second area of uncertainty that was reduced is that regarding the application of the NCLAN E

- R functions, developed in the 1980s, to more recent cultivars currently growing in the field. R ecent studies , especially those focused on soybean, provide little evidence that crops are becoming more tolerant of O 3

162 The NCLAN program, which was under taken in the early to mid

- 1980s, assessed multiple U.S. crops, locations, and O 3 exposure levels, using consistent methods, to provide the largest, most uniform database on the effects of O 3 on agricultural crop yields (U.S. EPA 1996; U.S. EPA, 2006; U.S. EPA, 2013, sections 9.2, 9.4, and 9.6, Frey, 2014c, p. 9). The SoyFACE experiment was a chamberless field

- based exposure study in Illinois that was conducted from 2001

– 2009 (U.S. EPA, 2013, section 9.2.4).*** E.O. 12866 Review

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Page 325 of 647 (U.S. EPA, 2006a; U.S. EPA, 2 013). A meta

- analysis of 53 studies found consistent deleterious effects of O 3 exposures on soybean from st udies published between 1973 and
2001 ( Morgan et al. , 2003). Further, Betzelberger et al. (2010) utilized the SoyFACE facility to compare the impact of elevated O 3 concentrations across 10 soybean cultivars to investigate intraspecific variability of the O 3 response , finding that t he E

- R functions derived for these 10 current cultivars were similar to the response functions derived from the NCLAN studies conducted in the 1980s (Heagle, 1989). Thus, the evidence available in the current review has reduced un certainties in two areas with regard to the use of E

- R functions for soybean crop yield loss

. During past O 3 NAAQS reviews, there were very few studies that estimated O 3 impacts on crop yields at large geographical scales (i.e., regional, national or globa l). Recent modeling studies of the historical impact of O 3 concentrations found that increased O 3 generally reduced crop yield, but the impacts varied across regions and crop species (U.S. EPA, 2013, Section 9.4.4.1). The largest O 3 - induced crop yield loss es were estimated to occur in high

- production areas exposed to elevated O 3 concentrations, such as the Midwest and the Mississippi Valley regions of the U.S. Among crop species, the estimated yield loss for wheat and soybean were higher than rice and maize (i.e., field corn) . Additionally, satellite and ground

- based O 3 measurements have assessed yield loss caused by O 3 over the continuous area of Illinois, Iowa, and Wisconsin and found reduced soybean yield, which correlates well with the previous results f rom FACE

- and
OTC

- type experiments (U.S. EPA, 2 013, section 9.4.4.1). Thus, the recent scientific literature in the ISA support s the conclusions of the 1996 and 2006 CDs that O 3 concentrations in ambient air can reduce the yield of major*** E.O. 12866 Review

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Page 326 of 647 commodity crops in the U.S. and focuses on use of crop E

- R functions based on OTC experiments to characteriz e the quantitative relationship between ambient O 3 concentrations and yield loss (U.S. EPA, 2 013, section 9.4.4)

. In the PA, as summarized in sections IV.D and IV.E below, relative yield loss (RYL) is estimated for 10 different crops using the individual E

- R functions described in the WREA 163 (U.S. EPA, 2014b, section 6.2; U.S. EPA, 2014c, section 6.3). 2. Potential Im

pacts on Public Welfare The magnitude of a public welfare impact or the degree to which it may be considered adverse is dependent upon the nature and severity of the specific welfare or ecological effect, the use or service (and value) of the affected ecos ystem and the relevance and significance of that use 164 to the public welfare. In the preamble of the 2012 final notice of rulemaking on the secondary standards for oxides of nitrogen and sulfur (NOx/SOx) , the EPA stated that “[a]n evaluation of adversity to the public welfare might consider the likelihood, type, magnitude, and spatial scale of the effect, as well as the potential for recovery and any uncertainties relating to these conditions” (77 FR
20232 , April 3, 2012 ). The EPA additionally stated that “[ c]onceptually, changes in

163 These functions for RYL estimate reduction in a year’s growth as a percentage of that expected in the absence of O 3 (U.S. EPA, 2013, section 9.6.2; U.S. EPA, 2014b, section 6.2). 164 Ecosystem services have been defined as “the benefits that people obtain from ecosystems” (U.S. EPA, 2013, Preamble, p. 1xxii; UNEP, 2003) and thus are an aspect of the use of a type of vegetation or ecosystem

. Similarly, a definition used for the purposes of EPA benefits assessment s states that ecological goods and services are the ‘‘outputs of ecological functions or p rocesses that directly or indirectly contribute to social welfare or have the potential to do so in the future” and that “[s]ome outputs may be bought and sold, but most are not marketed’’ (U.S. EPA, 2006b).*** E.O. 12866 Review

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Page 327 of 647 ecosystem services may be used to aid in characterizing a known or anticipated adverse effect to public welfare” (77 FR 20232 , April 3, 2012 )

. 165 Potential public welfare impacts associated with ecosystems and associated services have a range of dimensions, including spatial, temporal, and social, and these likely will vary depending on the type of effect being characterized. For example, ecosystems can cover a range of spatial scales, and the services they provide can accrue local ly or be distributed more broadly, such as when crops are sold and eaten locally and/or also sold in regional, national and world markets. Accordingly, impacts can be localized or more widely distributed. Further, ecosystem services can be realized over a range of temporal scales from immediate up to long er term. The size of the societal unit receiving benefits from ecosystem services can also vary dramatically. For example, a national park can provide direct recreational services to the thousands of visito rs that come each year, but also provide an indirect value to the millions who may not visit but receive satisfaction from knowing it exists and is preserved for the future (U.S. EPA, 2014b, chapter 5, section 5.5.1). As recognized in the last review, ju dgments regarding adverse effects to the public welfare depend on the intended use for and significance of the affected vegetation, ecological receptors, ecosystems and resources to the public welfare (73 FR 16496 ,

165 Ecosystem services analyses were one of the to ols used in that review to inform the decisions made with regard to adequacy and as such, were used in conjunction with other considerations in the discussion of adversity to public welfare (77 FR 20241).*** E.O. 12866 Review

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Page 328 of 647 March 27, 2008 ). 166 For example, a number o f different types of locations provide services of special significance to the public welfare. As emphasized in previous O 3 NAAQS decisions, and summarized in section IV.A above, Class I areas and other parks have been afforded special federal protection t o preserve services that provide for the enjoyment of these resources for current and future generations . Surveys have indicated that Americans rank as very important the existence of the resource, the option or availability of the resource and the ability to bequest or pass on to future generations ( USDA, 2010)

. These and other services provided by Class I areas and other areas that have been afforded special protection can flow in part or entirely from the vegetation that grows there. Aesthetic value and outdoor recreation depend on the perceived scenic beauty of the environment. Many outdoor recreation activities directly depend on the scenic value of the area, in particular scenic viewing, wildlife

- watching, hiking, and camping (U.S. EPA, 2014b, chapters 5 and 7). Further, analyses have reported that the American public values

– in monetary as well as nonmonetary ways

– the protection of forests from air pollution damage. In fact , s tudies that have assessed willingness

- to

- pay for spruc e - fir forest protection in the southeastern U.S. from air pollution and insect damage have found that values held by the survey respondents for the more abstract services (existence, option and bequest) were greater than those for recreation or other servi ces (U.S. EPA, 2014b, Table 5

- 6; Haefele et al., 1991 ; Holmes and Kramer, 1995).

166 As noted in section IV.A above, i n judgments rega rding public welfare significance in the last review, emphasis was placed on vegetation and ecosystem effects to sensitive species that are known to or are likely to occur in federally protected areas such as national parks and other Class I areas, or on l ands set aside by states, tribes and public interest groups to provide similar benefits to the public welfare (73 FR 16496, March 27, 2008; 75 FR 3023

- 24, January 19, 2010).*** E.O. 12866 Review

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Page 329 of 647 There are several potential public welfare impacts related to the three main categories of O 3 effects on vegetation (i.e., effects on tree growth , productivity and carbon stor age; crop yield loss; and , visible foliar injury , as described in section IV.B.1 above) and their associated ecosystem services. At the same time, these three categories of effects differ with regard to aspects important to judging their public welfare sig nificance. Judgments regarding crop yield loss, for example, depend on considerations related to the heavy management of agriculture in the U.S., while judgments regarding the other categories of effects generally relate to considerations regarding foreste d areas. For example, while both tree growth

- related effects and visible foliar injury have the potential to be significant to the public welfare through impacts in Class I and other protected areas, they differ in how they might be significant and with r egard to the clarity of the data which describes the relationship between the effect and the services potentially affected. With regard to effects on tree growth, reduced growth is associated with e ffects on an array of ecosystem services including reduce d productivity , altered forest and forest community (plant, insect and microbe) composition, reduced carbon storage and altered water cycling (U.S. EPA, 2013, Figure 9

- 1, sections 9.4.1.1 and 9.4.1.2; U.S. EPA, 2014b, section 6.1). For example, forest or f orest community composition can be affected through O 3 effects on growth and reproductive success of sensitive species in the community, with the extent of compositional changes dependent on factors such as competitive interactions (U.S. EPA, 2013, section s 9.4.3 and 9.4.3.1). D epending on the type and location of the affected ecosystem, services benefitting the public in other ways can be affected as well

. For example, other services valued by people that can be affected*** E.O. 12866 Review

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Page 330 of 647 by reduced tree growth, productivit y and carbon storage include aesthetic value, food, fiber, timber, other forest products, habitat, recreational opportunities, climate and water regulation, erosion control, air pollution removal, hydrologic and fire regime stabilization ( U.S. EPA 2013, se ctions 9.4.1.1 and 9.4.1.2; U.S. EPA, 2014b, section 6.1, Figure 6

- 1, section 6.4, Table 6

- 13). Further, impacts on some of these services (e.g., forest or forest community composition) may be considered of greater public welfare when occurring in Class I or other protected areas. Consideration of the magnitude of tree seedling growth effects that might cause or contribute to adverse effects for trees, forests, forested ecosystems or the public welfare is complicated by limitations in the available informa tion. For example, the evidence on tree seedling growth effects, deriving from the E

- R functions for 11 species, provides no clear threshold or breakpoint in the response to O 3 exposure. Additionally, there are no established relationships between magnitud e of tree seedling growth reduction and forest ecosystem impacts and, as noted in section IV.B.1.b above, other factors can influence the degree to which O 3 - induced growth effects in a sensitive species affect forest and forest community composition and other ecosystem service flows from forested ecosystems . These include: 1) the type of stand or community in which the sensitive species is found (i.e., single species versus mixed canopy); 2) the role or position the species has in the stand (i.e., dominan t, sub

- dominant, canopy, understory); 3) the O 3 sensitivity of the other co

- occurring species (O 3 sensitive or tolerant); and 4) environmental factors , such as soil moisture and others

. The lack of such established relationships complicates judgments as to the extent to which different amounts of tree*** E.O. 12866 Review

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Page 331 of 647 seedling growth would be significant to the public welfare and thus an important consideration in the level of protection for the secondary standard. During the 1997 review of the secondary standard, views re lated to this issue were provided by a 1996 workshop of 16 then

- leading scientists in the context of discussing their views for a secondary O 3 standard (Heck and Cowling, 1997). In their consideration of tree growth effects as an indicator for forest ecosy stems and crop yield reduction as an indicator of agricultural systems, the workshop participants identified annual percentages, of RBL for forest tree seedlings and RYL for agricultural crops, considered important to their judgments on the standard. With regard to forest ecosystems and seedling growth effects as an indicator, the participants selected a range of 1

- 2% RBL per year “to avoid cumulative effects of yearly reductions of 2% .” With regard to crops, they indicated an interest in protecting agains t crop yield reductions of 5% RYL yet noted uncertainties surrounding such a percentage which led them to identifying 10% RYL for the crop yield endpoint (Heck and Cowling, 1997). The workshop report provides no explicit rationale for the percentages ident ified (2% RBL and 5% or 10% RYL); nor does it describe their connection to ecosystem impacts of a specific magnitude or type and judgments on significance of the effects for public welfare, e.g., taking into consideration the intended use and significance of the affected vegetation ( Heck and Cowling , 1997) . Thus, in both the 1997 and 2008 reviews, EPA’s consideration of tree growth effects and effects on crop yield, in recognizing the complexity of assessing the adversity of those effects in the broader con text of public welfare, extended beyond the consideration of various benchmark responses for the studied species. With regard to crops, EPA additionally*** E.O. 12866 Review

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Page 332 of 647 recognized the heavy management of agricultural systems which poses an additional complication. While, as noted above, public welfare benefits of forested lands can be particular to the type of area in which the forest occurs, some of the potential public welfare benefits associated with forest ecosystems are not location dependent. A potentially extremely valuable ecosystem service provided by forested lands and for which the ISA concludes a likely causal relationship with O 3 in ambient air is c arbon storage , a regulating service that is “of paramount importance for human society” (U.S. EPA, 2013,
section 2 .6.2.1 and p. 9

- 37 ) . T h e service of carbon storage is potentially important to the public welfare no matter in what location the sensitive trees are growing, or what their intended current or future use. In other words, the benefit exists as long as the tr ee is growing, regardless of what additional functions and services it provides.
An other example of locations potentially vulnerable to O 3 - related impacts but not necessarily identified for such protection might be forested lands, both public and private, where trees are grown for timber production, particularly where they are dominated by a single timber species stand that is sensitive to O 3 , such as p onderosa pine. Further, forests in urbanized areas provide a number of services that are important to the public in those areas, including air pollution removal, cooling of the heat island effect, and beautification ( U.S. EPA, 2014b, section 6.6.2 and Appendix 6D; Akbari, 2002). 167 The presence of O 3 - sensitive trees in such areas may place them at risk from elevated O 3 exposures, contributing to potential impacts on important services provided by urban forests (U.S. EPA, 2014b, sections 6.6.2 and 6.7). There are many other tree species, such as species

167 For example, see http://www.fs.fed.us/research/urban/environmental

- justice.php

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Page 333 of 647 used in the USFS biomonitoring network, and various ornam ental and agricultural species (i.e., Christmas trees, fruit and nut trees) that provide ecosystem services that may be judged important to the public welfare but whose vulnerability to impacts from O 3 on tree growth, productivity and carbon storage has no t been quantitatively characterized (U.S. EPA, 2014b, Chapter 6; Abt Associates, 1995). As noted above, in addition to tree growth

- related effects, O 3 - induced visible foliar injury also has the potential to be significant to the public welfare through impa cts in Class I and other similarly protected areas. Visible foliar injury is a visible bioindicator of O 3 exposure in species sensitive to this effect, with the injury affecting the physical appearance of the plant. Accordingly v isible foliar injury survey s are used by federal land
managers as tools in assessing potential air quality impacts in Class I areas. These surveys may focus on plant species that have been identified as potentially sensitive air quality related values ( AQRVs ) due to their sensitivit y to O 3 - induced foliar injury (USFS, NPS, FWS, 2010). An AQRV is defined by the National Park Services as a “resource, as identified by the FLM for one or more Federal areas that may be adversely affected by a change in air quality” and the resource “may i nclude visibility or a specific scenic, cultural, physical, biological, ecological, or recreational resource identified by the FLM for a particular area” ( USFS, NPS, USFWS, 2010). 168 No criteria have been established,

168 The identification, monitoring and assessment of AQRVs with regard to an adverse effect is an a pproach used for assessing the potential for air pollution impacts from pending permit actions in Class I areas ( USFS, NPS, USFWS, 2010). An adverse impact is recognized by the National Park Service as one that results in diminishment of the Class I areas’s national significance or the impairment of the ecosystem structure or funct i o ning, as well as impairment of the quality of the visitor experience ( USFS, NPS, USFWS, 2010). Federal land managers (FLMs) make such adverse impact determinations on a case

- by

- case basis, using technical and other information which they provide for consideration by permitting authorities.*** E.O. 12866 Review

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Page 334 of 647 however, regarding a level or prevalence of visible foliar injury considered to be adverse to the affected vegetation, and, a s noted in section IV.B.1.a above, there is not a clear relationship between visible foliar injury and other effects, such as reduced growth and productivity. Thus, key co nsiderations with regard to public welfare significance of this endpoint have related to qualitative consideration of the plant’s aesthetic value in protected forested areas. Depending on the extent and severity, O 3 - induced visible foliar injury might be e xpect e d to have the potential to impact the public welfare in scenic and/or recreational areas during the growing season, particularly in areas with special protection, such as Class I areas

. The ecosystem services most likely to be affected by O 3 - induced visible foliar injury (some of which are also recognized above for tree growth

- related effects) are cultural services, including aesthetic value and outdoor recreation. In addition, several tribes have indicated that many of the species identified as O 3 - sensitive (including bioindicator species) are culturally significant (U.S. EPA, 2014c, Table 5

- 1). The geographic extent of protected areas that may be vulnerable to such public welfare effects of O 3 is potentially appreciable. Sixty six species th at occur on NPS and U

. S

. Fish and Wildlife Service lands 169 have been identified as sensitive to O 3 - induced visible foliar injury and some also have particular cultural importance to some tribes (U.S. EPA, 2014c, Table 5

- 1 and Appendix 5

- A; U.S. EPA, 2014b, section 6.4.2). N ot all species are equally sensitive to O 3 , however, and quantitative relationships between O 3 exposure and other important effects , such as seedling growth reduction, are only available for a subset of the 66, as described in section IV.B .1. above. A diverse array of ecosystem services

169 See http://www2.nature.nps.gov/air/Pubs/pdf/flag/NPSozonesensppFLAG06.pdf*** E.O. 12866 Review

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Page 335 of 647 has been identified for these twelve species (U.S. EPA, 2014c, Table 5

- 1). Two of the species in this group that are relative ly more sensitive with regard to effects on growth are the p onderosa p ine and q uaking a spen (U.S. EPA, 2014b, section 6.2), the ranges for which overlap with many lands that are protected or preserved for enjoyment of current and future generations (consistent with the discussion above on Class I and other protected areas) , including such lands located in the west and southwest regions of the U.S. where ambient O 3 concentrations and associated cumulative seasonal exposures can be highest (U.S. EPA, 2014c, Appendix 2B). 170 With regard to agriculture

- related effects such as crop yield lo ss, EPA has recognized other complexities, stating that the degree to which O 3 impacts on vegetation that could occur in areas and on species that are already heavily managed to obtain a particular output (such as commodity crops or commercial timber produ ction) would impair the intended use at a level that might be judged adverse to the public welfare has been less clear ( 73 FR 16497, March 27, 2008; 75 FR 3024 ; January 19, 2010 ). We note that while having sufficient crop yields is of high public welfare v alue, important commodity crops are typically heavily managed to produce optimum yields. In light of all of the inputs that go into achieving these yields, such as fertilizer, herbicides, pesticides, and irrigation, it is difficult to determine at what poi nt O 3 - induced yield loss creates an adverse impact for the producer in the way of requiring increased inputs in order to maintain the desired yields. Moreover, based on the economic theory of supply and demand, increases in crop yields would be expected to result in lower prices for affected

170 Basal area for resident species in national forests and parks are available in fi les accessible at: http://www.fs.fed.us/foresthealth/technology/nidrm2012.shtml*** E.O. 12866 Review

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Page 336 of 647 crops and their associated goods, which would primarily benefit consumers. Given these competing impacts on producers and consumers, it is unclear how to consider these effects in terms of potential adversity to the pub lic welfare (U.S. EPA, 2014c, sections 5.3.2 and 5.7). When agricultural impacts or vegetation effects in other areas are contrasted with the emphasis on forest ecosystem effects in Class I and similarly protected areas, it can be seen that the Administrator has in past reviews judg ed the significance to the public welfare of O 3 - induced effects on sensitive vegetation growing within the U.S. to differ depending on the nature of the effect, the intended use of the sensitive plants or ecosystem s, and the types of environments in which the sensitive vegetation and ecosystems are located, with greater significance ascribed to areas identified for specific uses and benefits to the public welfare , such as Class I areas, than to areas for which such uses have not been established. In summary , several considerations are recognized as important to judgments on the public welfare significance of the array of effects of different O 3 exposure conditions on vegetation. While t here are complexities associate d with the consideration of the magnitude of key vegetation effects that might be concluded to be adverse to ecosystem s and associated services, there are numerous locations where
O 3 - sensitive tree species are present that may be vulnerable to impacts from O 3 on tree growth, productivity and carbon storage and their associated ecosystems and services. It is not possible to generalize across all studied species regarding which cumulative exposures are of greatest concern, however, as this can vary by situati on due to differences in exposed species sensitivity, the importance of the observed or predicted
O 3 - induced effect, the role that the species plays in the ecosystem, the intended use of the*** E.O. 12866 Review

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Page 337 of 647 affected species and its associated ecosystem and services, the p resence of other co

occurring predisposing or mitigating factors, and associated uncertainties and limitations. These factors contribute to the complexity of the Administrator’s judgments regarding the adversity of known and anticipated effects to the publ ic welfare. C. Exposure and Risk Assessment Information The WREA characterized ambient O 3 exposure and its relationship to tree biomass loss, crop yield loss, and visible foliar injury and the associated ecosystem services 171 in national

- scale and case study analyses. The WREA also qualitatively assessed impacts to some ecosystem services, including impacts on the hydrologic cycle, pollination regulation, and fire regulation; commercial non

- timber forest products and insect da mage; and aesthetic and non

- use values. I n the quantitative analyses , the WREA characterized effects associated with exposures to O 3 in ambient air using the W126 metric. The following sections summarize the analyses and adjustment approach used to develop the O 3 concentrations used as inputs to the vegetation risk analyses for tree biomass and crop yield loss , and the analyses, including key results and uncertainties, for tree seedling growth, productivity, carbon storage and associated ecosystem services (section IV.C.2); crop yield loss (section IV.C.3); and visible foliar injury (section IV.C.4). 1. Air Quality Analyses

171 In its review of drafts of the WREA and PA, the CASAC conveyed support for analyses and considerations of ecosystem services that may be affected by O 3 exposures (Frey, 2014b , 2014c).*** E.O. 12866 Review

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Page 338 of 647 The WREA evaluate d O 3 exposure and risks for several air quality scenarios: recent conditions (2006 to 2008) , 172 just meeting the current secondary standard, and just meeting alternative W126 index values of 15 ppm

- hrs, 11 ppm

- hrs, and 7 ppm

- hrs , using
3

- year averages (USEPA, 2014b, chapter 4)

. For each of these scenarios, three

- year average W126 index values were estimated at each 12 km by 12 km grid cell in a national

- scale spatial surface. Additionally, some analyses were based on single

- year surfaces. 173 The method for creating the five scenarios generally involved two steps ( summarized in Table 5

- 4 of the PA ) . The first is derivation of t he average W126 index value (across the three years) at each monitor location. This value is based on unadjusted
O 3 concentrations from monitoring data for recent conditions and adjusted concentrations for the four other scenarios. Concentrations were adju sted based on model predicted relationships between O 3 and U.S.

- wide emissions reductions in oxides of nitrogen (NOx) . The adjusted air quality do es not represent an optimized control scenario that just meets the current standard (or target W126 index values for other scenarios), but rather characterize s one potential distribution of air quality across a region when all monitor locations meet the standard (U.S. EPA, 2 014b, section 4.3.4.2 ). The development of adjusted concentrations was done for each of nine regions independently (see U.S. EPA, 2014b, section 4.3.4.1). In the second step, national

- scale spatial surfaces (W126 index

172 Certain visible foliar injury analyses assessed recent conditions from 2006 to 2010 on an annual basis. 173 An analysis using data from USFS FHM/FIA O 3 biomonitoring sampling sites ( “biosites” ) and a screening

- level assessment in 214 national par ks were done using national

- scale spatial surface s of unadjusted O 3 concentrations (in terms of the W126 index) created for each year from 2006 through 2010 using the VNA interpolation technique (U.S. EPA, 2014b, section 4.3.2, Appendix 4A).*** E.O. 12866 Review

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Page 339 of 647 values for each 12 km x 12 km grid ce ll used ini the air quality model ) were created using the monitor

- location values and the Voronoi Neighbor Averaging (VNA) spatial interpolation technique (details on the VNA technique are presented in U.S. EPA, 2014b, Appendix 4A).
In the dataset used to create the recent conditions scenario , the 3

- year average W126 index values at the monitor locations (before application of the VNA technique) ranged from below 5 ppm

- hrs to 48.6 ppm

- hrs (U.S. EPA, 2014b, Figure 4

- 4 and Table
4

- 3). In the nine modeling re gions, the maximum 3

- year average W126 index values at monitor locations ranged from 48.6 ppm

- hrs in the W est region down to 6.6 ppm

- hrs in the N orthwest region. 174 After adjust ment of the monitor location concentrations to just meet the current standard in each region (using relationships described above) , the region

- specific maximum three

- year average W126 values range d from 18.9 ppm

- hrs in the W est region to 2.6 ppm

- hrs in the N ortheast region (U.S. EPA, 2014b, Table 4

- 3). With the next step, creation of t he national surface of air quality values at grid cell centroids, the highest values were reduced, such that all t he three

- year average W126 index values were below 15 ppm

- hrs across the national surface with the exception of a very small area of the S outh west region (near Phoenix) where average W126 index values w ere just above 15 ppm

- hrs. Thus, it can be seen that application of the VNA interpolation method to estimate W126 index values at the centroid of every 12 x 12 km 2 grid cell rather than only at ea ch monitor location results in a lowering of the highest values.

174 The regions referenced here and also with regard to monitoring data analyses described in section IV.D.4 below are NOAA climate regions, as shown in Figure 2B

- 1 of the PA.*** E.O. 12866 Review

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Page 340 of 647 Because the W126 estimates generated for the different air quality scenarios assessed are inputs to the vegetation risk analyses for tree biomass and crop yield loss, and also used in the fol iar injury analyses, any uncertainties in the air quality analyses are propagated into the those analyses (U.S. EPA, 2014b, section 8.5). The WREA identified sources of uncertainty for the W126 estimates for each air quality scenario and qualitatively char acterized the magnitude of uncertainty and potential for directional bias ( U.S. EPA, 2014b, T able 4

- 5). As discussed in Chapter 4 and 8 of the WREA, an important large uncertainty in the analyses is the assumed response of the W126 concentrations to emissi ons reductions needed to meet the existing standard (U.S. EPA, 2014b, section 8.5.1). Any approach to characterizing O 3 air quality over broad geographic areas based on concentrations at monitor locations will convey inherent uncertainty. The model

- based a djustments are based on U.S.

- wide emissions reductions in NOx and characterize only one potential distribution of air quality across a region when all monitor locations meet the standard (U.S. EPA, 2014b, section 4.3.4.2). 175 Additionally, the surface is created from the three

- year average at the monitor locations, rather than creating a surface for each year and then averaging across years at each grid

175 The WREA analyses used U.S.

- wide NOx emissions reductions to simulate air quality that indepen dently in each region would just meet the existing standard and the three W126 scenarios

. The NOx emissions reductions were determined such that the highest monitor within each region would just meet the target level. In this way, the adjustment results in broad regional reductions in O 3 and includes reductions in O 3 at some monitors that were already meeting or below the target level. Thus, the adjustments performed to develop a scenario meeting a target level at the highest monitor in each region did resu lt in substantial reduction below the target level in some areas of the region. This result at the monitors already well below the target indicates an uncertainty with regard to air quality expected from specific control strategies that might be implemented to meet a particular target level

.*** E.O. 12866 Review

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Page 341 of 647 cell; the potential impact of this on the resultant estimates is considere d in the WREA (U.S. EPA, 2014b, Appendix 4A). An additional uncertainty related to the W126 index value estimates for each air quality scenario comes from the creation of a national W126 surface using the VNA technique to interpolate recent air quality me asurements of O 3 . In general, spatial interpolation techniques perform better in areas where the O 3 monitoring network is denser. Therefore, the W126 index values estimated in the rural areas in the West, Northwest, Southwest, and West North Central with f ew or no monitors ( U.S. EPA, 2014b, Figure 2

- 1) are more uncertain than those estimated for areas with dense r monitoring. Further, this interpolation method generally under

- predicts higher 12

- h ou r W126 exposures. Due to the important influence of higher ex posures in determining risks to plants, the potential for the VNA interpolation approach to underpredict higher W126 exposures could result in an underestimation of risks to vegetation in some areas. Underestimation of the highest W126 index values for the current standard scenario is an additional impact of the interpolation method that is important to consider.
2

. Tree Seedling Growth, P roductivity, Carbon S torage and Associated Ecosystem Services For the WREA assessments related to tree growth, product ivity, carbon storage and associated ecosystem services, the sections below provide an overview of the analyses along with the key results (section IV.C.2.a) and summarize the key uncertainties (section IV.C.2.b).

a. Overview and Summary of Key Results*** E.O. 12866 Review

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Page 342 of 647 The assessments to estimate the exposures and risks for tree seedling growth, productivity, and carbon storage reflect a range of spatial scales ranging from the county scale up to the national park, urban area, and national scales. For the air quality scenar ios described above, the WREA applied the species

- specific E

- R functions to develop estimates of O 3 - associated RBL , productivity, carbon storage and associated ecosystem services (U.S. EPA, 2014b, Chapter 6). Some analyses also apply the median across
spec ies E

- R function s . The WREA examined multiple approaches for characterizing the median tree response to O 3 exposure based on the 11 robust E

- R functions for tree seedlings from the OTC research and the E

- R function for eastern cottonwood (U.S. EPA, 2014b, section 6.2.1.2 and Figure 6

- 5). For some species, only one study was available (e.g., red maple), and for other species there were as many as 11 studies available (e.g., ponderosa pine). To illustrate the effect of within

- species variability associated w ith the E

- R data available on estimates for a median response across the 12 species, the WREA performed a stochastic sampling analysis involving multiple iterations of random selection of E

- R functions from the studies available for each of the 12 species. This analysis produced median values at each cumulative exposure level that were higher than medians derived by two conventional, deterministic methods (U.S. EPA, 2014 b , section 6.2.1.2 and Figure
6

- 5)

. 176 For example , the median seasonal W126 index value for which a two percent biomass loss is estimated in seedlings for the studied species ranges from approximately
7 ppm - hrs using the conventional methods up to 14 ppm

- hrs when derived by the

176 These methods were calculating a median using the composite functions and calculating a median using all tree seedling studies available.*** E.O. 12866 Review

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Page 343 of 647 stochastic method

. Althoug h the stochastic method provides some illustration of the effect of within

– species variability, we focus on the conventional approach that gives equal weight to each studied species , calculating the median response based on the composite E

- R functions , con sistent with CASAC advice (Frey, 2014b) The WREA estimates indicate substantial heterogeneity in plant responses to O 3 , both within species, between species, and across regions of the U.S. The O 3 - sensitive tree species are different in the eastern and wes tern U.S. and the eastern U.S. has far more such species. Ozone exposure and risk is somewhat easier to assess in the eastern U.S. because of the availability of more data and the greater number of species to analyze. In addition, there are more O 3 monitor s in the eastern U.S. but fewer national parks (U.S. EPA, 2014b, chapter 8). In consideration of CASAC advice, the WREA derived RBL and weighted RBL (wRBL) estimates separately with and without the eastern cottonwood. The results summarized here are for t he analyses that exclude cottonwood. 177 The WREA reported RBL estimates relative to a benchmark of 2% RBL for tree seedling s, as well as relative to other percent RBL values. The 2% RBL benchmark was considered based on CASAC advice that stated that “ focus o n a 2% loss level for trees

... is appropriate. ” (Frey, 2014b, p. 6 ). The main WREA analyses for effects related to tree growth, productivity and carbon storage are summarized below, with the key findings for each. Relative biomass loss nationally was estima ted for each of the 12 studied species

177 The C ASAC advised that the eastern cottonwood response data “receiv e too much emphasis” in a draft version of the PA, explaining that these “results are from a gradient study that did not control for ozone and climatic conditions and show extreme sensitivity to ozone compared to other studies” and that “[a] lthough they ar e important results, they are not as strong as those from other experiments that developed E

- R functions based on controlled ozone exposure” (Frey, 2014b, p. 10).*** E.O. 12866 Review

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Page 344 of 647 from the composite E

- R functions for each species described above and information on the distribution of those species across the U.S. (U.S. EPA, 2014b, section 6.2.1.3 and Appendix 6A). As one example of a tree speci es near the median of the studied species, relative biomass loss estimates (reduced growth) for ponderosa pine in the current standard air quality scenario are below two percent for most areas where this species is found but estimates of RBL for this speci es in some areas of the southwest fall above two percent biomass loss (U.S. EPA, 2014b, Figure 6

- 8). Maximum estimates of RBL for all areas where ponderosa pine is found decrease to just over three percent and just over two percent for the 15 and 7 ppm

- hrs scenarios, respectively (U.S. EPA, 2014b, Table 6

- 6). To provide an indication of ecosystem

- level impacts, weighted estimates of RBL (wRBL) were also developed for each grid cell nationwide. This is estimated from the species

- specific E

- R functions and a weighting approach based on information on prevalence of the studied species across the U.S. (i.e., the proportion of the total basal area modeled by USFS across all species for which data were available). An overall wRBL value for each grid cell is genera ted by summing the wRBL values for each studied tree species found within that grid cell. The wRBL is intended to be an indication of the potential magnitude of the ecological effect that could occur in some ecosystems. In general, the higher the wRBL is i n a given ecosystem, the larger the potential ecological effect. (U.S. EPA, 2014b, section 6.8, Table 6

- 25). For the national

- scale analysis, the WREA presents the percent of total basal area with wRBL greater than 2%. The estimates for the weighted biomas s loss analysis reflecting the 11 tree species with robust E

- R functions are as follows (U.S. EPA, 2014b, Table 6

- 25):*** E.O. 12866 Review

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Page 345 of 647  For the current standard scenario, the percent of total basal area that exceeds a two percent wRBL is 0.2 percent.

 For the W126 scenario s of 15, 11 and 7 ppm

- hrs, t he percent of total basal area that exceeds a two percent wRBL is 0.2 percent, 0.1 percent, and less than 0.1 percent respectively (U.S. EPA, 2014b, Table 6

- 25). In the wRBL analysis for Class I areas, the number of Class I are as with wRBL greater than 2% is estimated for the grid cells located in the 145 of the 156 Class I areas for which data were available (U.S.EPA, 2014b, Table 6

- 26).

 For the current standard scenario , t wo of the 145 assessed Class I areas have weighted RBL values above two percent (U.S. EPA, 2014b, Table 6

- 26).

 For the W126 scenarios of 15, 11 and 7 ppm

- hrs, t he re are two, two and one Class
I area with w RBL above two percent , respectively

. In the count y analysis, the WREA estimated the n umber of U.S. counties in which any of the studied tree species is estimated to experience more than two percent RBL, the number of species affected, and the number of counties for which the median of the species

- specifi c functions exceeds two percent RBL. In addition to the estimates based on all 12 studied species and also the 11 species with the exclusion of eastern cottonwood (in response to CASAC advice) , a dditional estimates were developed without black cherry to sh ow contribution of that sensitive species to the multi

- species estimates (U.S. EPA, 2014b, Table 6

- 7).

 In the current standard scenarios, 66% of the 3,109 assessed counties are estimated to have at least one of the 11 species (excluding cottonwood) with an RBL greater than two percent, with three counties having three species exceeding*** E.O. 12866 Review

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Page 346 of 647 two percent. The median RBL (across the species present) is above two percent in 239 counties. T he maximum number of species in any one county with an RBL greater than two percent is three (excluding cottonwood). (U.S. EPA, 2014b, Table 6

- 7).

 For the 15, 11 and 7 ppm

- hrs scenarios, the proportion of 3,109 countie s with one or more species with an RBL above two percent decreases to 61 percent, 59 percent, and 58 percent, respectively. For the 7 ppm

- hrs scenario, the median RBL is above two percent in six percent of the counties (U.S. EPA, 2014b, Table
6

- 7).

 The cou nty RBL estimates are appreciably influenced by black cherry, a very sensitive species that is widespread in the Eastern U.S. For 1,805 of the 1,929 counties estimated to have at least one species with an RBL greater than two percent when air quality is me eting the current standard , only black cherry exceeds this level of RBL. If black cherry is excluded, the median RBL for the 10 remaining species decreases . For the median RBL values, 203 of the 239 counties estimated to have a median RBL above two percent when air quality is meeting the current standard are because of the presence of black cherry (U.S. EPA, 2014b, Table 6

- 7). Additionally, the WREA estimated r elative yield loss in timber production and associated changes in consumer and producer/farmer ec onomic surplus using E

- R functions for tree seedlings to calculate relative yield loss (equivalent to relative biomass loss) across full tree lifespans and through modeling of the resulting market

- based welfare effects. Becaus e the forestry and agriculture sectors are related and trade

- offs*** E.O. 12866 Review

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Page 347 of 647 occur between the sectors, the WREA calculated the resulting market

- based welfare effects of O 3 exposure in the forestry and agriculture sectors on consumer and producer surplus. 178 Because demand for most forestry and agricultural commodities is not highly responsive to changes in price, producer surplus (i.e., producer gains) often declines

. T hese declines can be more than offset by changes in consumer surplus gains from lower prices , but, in some cases, lower prices r educe producer gains more than can be offset by consumer surplus (U.S. EPA, 2014b, Appendix 6B, Table and B

- 9)

.

 In the current standard scenario, e stimates of the relative yield loss for timber production are below one percent other than in the Southwest, Southeast, Central, and South regions (U.S. EPA, 2014b, section 6.3, Table 6

- 9) (see U.S. EPA, 2014b, Table 6

- 8 for clarification on region names). The highest yield loss occurs in upland hardwood forests in the South Central and Southeast regions at over three percent per year and in Corn Belt hardwoods at just over two percent loss
per year (U.S. EPA, 2014b, section 6.3, Table 6

- 9).

 For the 15 and 11 ppm

- hrs scenarios, r elative yield loss estimate s for timber production are above one percent in parts of the Southeast, Central, and South regions and above two percent in parts of the Southeast and Central U.S.

 For the 7 ppm

- hrs scenario , relative yield loss estimates for timber production are above one percent in the Southeast and South regions (U.S. EPA, 2 014b, section

178 The WREA used the Forest and Agricultural Sector Optimization Model with Greenhouse Gases (FASOMGHG). FASOMGHG is a national

- scale model that provides a complete representation of the impacts of meeting alternative standards on the U.S. forest and agricul tural sectors. FASOMGHG simulates the allocation of land over time to competing activities in both the forest and agricultural sectors. FASOMGHG results include multi

- period, multi

- commodity results over 60 to 100 years in 5

- year time intervals when runnin g the combined forest

- agriculture version of the model.*** E.O. 12866 Review

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Page 348 of 647 6.3, Table 6

- 9). The WREA also estimated impacts on tree growth and two ecosystem services provided by urban trees: removal of air pollutants and carbon storage. The estimates of the tons of carbon monoxide, nitrogen dioxide, ozone and sulf ur dioxide removed are for a 25

- year period in five urban case study areas: Baltimore, Syracuse, the Chicago region, Atlanta, and the urban areas of Tennes see (U.S. EPA, 2014b, section 6.7). 179

 Estimates for all five urban case study areas indicate increase d pollutant removal of O 3 , nitrogen dioxide, carbon monoxide, and sulfur dioxide in the current standard scenario (U.S. EPA, 2014b, sections 6.7). The results for the 15 ppm

- hrs scenario were very similar to those for meeting the current standard. For the 11 and 7 ppm

- hrs scenarios, all five case study areas indicate smaller additional increases in air pollutant removal beyond moving from current conditions to the current standard (U.S. EPA, 2014b, sections 6.7).

The WREA estimated carbon storage related to O 3 - induced biomass loss in forests and agricultural crops nationally and also in forests in five urban areas using the FASOMGHG and i

- Tree models noted above (U.S. EPA, 2014b, section 6.6). Ozone effects on tree growth affects the climate regulation service provided by ecosystems by reducing carbon sequestration and storage (U.S. EPA, 2013, section 9.4.3.4; U.S. EPA, 2014b, chapter 6, section 6.6). Because O 3 exposure affects photosynthesis and CO 2 uptake by trees, forests sequester less carbon and th us more carbon stays in the atmosphere. In the model used to calculate national

- level impacts to forests and

179 The WREA used the i

- Tree model for the urban case studies. i

- Tree is a peer

- reviewed suite of software tools provided by USFS.*** E.O. 12866 Review

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Page 349 of 647 agriculture from O 3 - related biomass loss, carbon sequestration reflects carbon in standing (live and dead) trees, forest soils, the forest understo ry vegetation, forest floor including litter and large woody debris, and wood products both in use and in landfills (U.S. EPA, 2014b, chapter 6, Appendix 6B, section 2.7.1).

 Over 30 years for the national

- scale analysis , carbon storage in the forestry sect or estimated for the current standard scenario is just over 89 ,000 million metric tons of CO 2 equivalents (MMtCO 2 e) ; this is 11,840 more MMtCO 2 e storage associated with the reduced O3

- related growth impact from meeting the current standard as compared with recent conditions

. 180 The estimates of carbon storage in the agricultural sector are much smaller (i.e., 8,469 MMtCO 2 e for the current standard scenario which is 606 MMtCO 2 e more than the recent conditions scenario) (U.S. EPA, 2014b, section 6.6.1 and Appen dix 6B). The forestry sector carbon storage estimated for each of the three W126 scenarios is just slightly greater than that estimated for the current standard. As a percentage of the current standard estimate, the three scenario estimates are less than 0.1% (13 MMtCO 2 e ), just under 1% (593 MMtCO 2 e ) and under 2% (1,600 MMtCO 2 e ) f or the 15, 11 and 7 ppm

- hrs scenarios, respectively (U.S. EPA, 2014b, Table s 6

- 1 9 and B

- 10 ).

 Estimates of the effects of avoided O 3 - related biomass loss on carbon sequestration in forests in the five urban area case studies indicate the potential for an increase in carbon sequestration of somewhat more than one MMtCO 2 e for

180 One MMtCO 2 e is equivalent to 208,000 passenger vehicles or the elect ricity to run 138,000 homes for 1 year as calculated by the EPA Greenhouse Gas Equivalencies Calculator (updated September 2013 and available at http://www.epa.gov/cleanenergy/energy

- resources/calculator.html).*** E.O. 12866 Review

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Page 350 of 647 the current standard scenario compared to the recent condition s estimate (U.S. EPA, 2014b, section 6.6.2 and Appendix 6D). The additional increases in O 3 - related carbon sequestration estimated across the five case studies for the three W126 scenarios are relatively small (U.S. EPA, 2014b, section 6.6.2 and Appendix 6 D).
Although not discussed in detail here, the WREA also describes qualitative assessments for some ecosystem services that may be affected by O 3 effects on tree growth and productivity , such as commercial non

- timber forest products and recreation (U.S. EP A, 2014b, section 6.4), aesthetic and non

- use values (U.S. EPA, 2014b, section 6.4), increased susceptibility to insect attack and fire damage (U.S. EPA, 2014b, sections 5.3 and 5.4, respectively). Other ecological effects that are causally or likely causa lly associated with O 3 exposure , such as effects on terrestrial productivity, the water cycle, the biogeochemical cycle, and community composition (U.S. EPA, 2 013, Table 9

- 19) , were not quantitatively addressed in the WREA due to a lack of sufficient quant itative information. b. Key Uncertainties The WREA identified several key limitations and uncertainties in the biomass loss assessments for trees, which may have a large impact on both overall confidence and confidence in individual analyses. Key uncertai nties that affect the assessment of impacts on ecosystem services at the national and case

- study scales, as well as across species, U.S. geographic regions and future years , include those associated with the interpolated and adjusted O 3 concentrations used to estimate W126 exposures in the air quality scenarios, the available seedling E

- R functions, combining effects across sensitive*** E.O. 12866 Review

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Page 351 of 647 species, the effects of compounding over time, and modeling impacts of biomass loss on timber harvesting and urban air pollut ant removal. With regard to the robust seedling E

- R functions, the WREA provided some characterization of the variability of individual study results and the impact of that on estimates of W126 index values that might elicit different percentages of biomas s loss in tree seedlings (U.S. EPA, 2014b, section 6.2.1.2). Even though the evidence shows that there are additional species affected by O 3 - related biomass loss, the WREA only has E

- R functions available to quantify this loss for 12 tree species. This lim ited information only allows a partial characterization of the O 3 - related biomass loss impacts in trees associated with recent O 3 index values and with just meeting the existing and potential alternative secondary standards. In addition, there are uncertainties inherent in these E

- R functions, including the extrapolation of relative biomass loss rates from tree seedlings to adult tr ees and information regarding within

- species variability. The overall confidence in the E

- R function varies by species based on the number of studies available for that species. Some species have low within

- species variability (e.g., many agricultural crop s) and high seedling/adult comparability (e.g., aspen), while other species do not (e.g., black cherry). The uncertainties in the E

- R functions for biomass loss and in the air quality analyses are propagated into the analysis of the impact of biomass loss on ecosystem services, including provisioning and regulating services (U.S. EPA, 2014b, Table 6

- 27). The WREA characterizes the direction of potential influence of E

- R function uncertainty as unknown, yet its magnitude as high, concluding that further stud ies are needed to determine how accurately the assessed species reflect the larger suite of O 3 - sensitive tree species in the U.S. (U.S. EPA, 2014b, Table 6

- 27).*** E.O. 12866 Review

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Page 352 of 647 Another uncertainty associated with interpretation of the WREA biomass loss

related estimates c oncerns the potential for underestimation of compounding of growth effects across multiple years of varying concentrations. Though tree biomass loss impacts were estimated using air quality scenarios of 3

- year average W126 index values, the WREA also condu cted an analysis to compare the impact of using a variable compounding rate based on yearly variations in W126 exposures to that of using a W126 index value averaged across three years. The WREA compared the compounded values for an example species occurri ng in the eastern U.S. and another example species occurring in the western U.S . In both examples, one species (tulip polar and ponderosa pine , respectively ) and one climate region where that species occurred (Southeast and Southwest regions , respectively ) were chosen and air quality values associated with just meeting the existing standard of 75 ppb were used. Within each region, the WREA analysis used both the W126 index value at each monitor in the region for each year and the three

- year average W126 ind ex value using the method described in Chapter 4 of the
WREA . The results show that the use of the three

- year average W126 index value may underestimate RBL values slightly (U.S. EPA, 2014b, section 6.2.1.4 and Figure 6

- 14). In both regions, the three

- year average W126 index value is sometimes above and sometimes below the individual year W126 index value. The WREA recognize s uncertainty regarding the extent to which the subset of studied tree species encompass the O 3 sensitive species in the U.S. and the extent to which it represents U.S. vegetation as a whole (U.S. EPA, pp. 9

- 123 to 9

- 125; U.S. EAP, 2014b, Table 6

- 27). There are also uncertainties associated with estimating the national scale ecosystem

- level impacts using wRBL. For example the wRBL esti mates are likely*** E.O. 12866 Review

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Page 353 of 647 biased low as there may be other unstudied O 3 - sensitive tree species in some areas that are also being affected at those levels , although this analysis does not take into account the effects of competition, which could further affect fore st biomass loss. Uncertainties are recognized i n the national

- scale analyses of timber production, agricultural harvesting, and carbon sequestration, for which the WREA used the FASOMGHG model . These uncertainties include those associated with the functio ns for carbon sequestration, the assumptions made regarding proxy species where there are insufficient data , and the non - W126 E

- R functions for three crops. The FASOMGHG model does not include agriculture and forestry on public lands, changes in exports du e to O 3 into international trade projections, or forest adaptation. Despite the inherent limitations and uncertainties, the WREA concludes that the FASOMGHG model reflects reasonable and appropriate assumptions for a national

- scale assessment of changes in the agricultural and forestry sectors due to changes in vegetation biomass associated with O 3 exposure (U.S. EPA, 2014b, sections 6.3, 6.5, 6.6, and 8.5.2 , and Table 6

- 27 ). In the case study analyses of five urban areas, the WREA used the i

- Tree model,

w hich includes an urban tree inventory for each area and species

- specific pollution removal and carbon sequestration functions. However, i

- Tree does not account for the potential additional VOC emissions from tree growth, which could contribute to O 3 format ion. Uncertainties are also recognized with regard to the base inventory of city trees, the functions used for air pollutant removal and for carbon storage (U.S. EPA, 2014b, sections 6.6.2 and 6.7, and Table 6

- 27). Despite the inherent limitations and

unce rtainties, the WREA concludes that the i

- Tree model reflects reasonable and appropriate assumptions for a case study assessment of pollution removal and carbon*** E.O. 12866 Review

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Page 354 of 647 sequestration for changes in biomass associated with O 3 exposure (U.S. EPA, 2014b, sections 6.6. 2, 6.7, and 8.5.2).
3

. Crop Yield Section IV.C.3.a below provides an overview of the assessments performed in the
WREA to estimate the exposures and risks for crop yield, as well as the key results. Section IV.C.3.b summarizes the key uncertainties.

a. Overview and Summary of Key Results The WREA conducted two analyses to estimate O 3 impacts related to crop yield, including annual yield losses estimated for 10 commodity crops grown in the U.S. with
E

- R functions and how these losses affect producer and consumer economic surpluses (U.S. EPA, 2014b, sections 6.2, 6.5). Summary estimates for crop yield loss related effects in the WREA are presented relative to a 5% yield loss benchmark based on consideration of CASAC ’s recommendation to consider a benchmark of 5% for median crop yield loss and to consider 5% yield loss for individual crop species. In addition, other benchmarks levels are considered in the WREA (e.g. 10% and 20%). The WREA derived estimates of crop RYL estimates nationally and in a county

sp ecific analysis. Crop

- specific estimates of O 3 - related RYL nationally were derived for each of the air quality scenarios from the 10 E

- R functions for crops described above combined with information regarding crop distribution (U.S. EPA, 2014b, section 6. 5). The WREA also reported crop RYL results at the county

- level , as well as the number of
crop - producing counties with greater than five percent RYL (U.S. EPA, 2014b, section 6.5.1, Appendix 6B).

 The largest reduction in O 3 - induced crop yield loss and yield changes occurs*** E.O. 12866 Review

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Page 355 of 647 when moving from the recent conditions scenario to the current standard scenario (U.S. EPA, 2014b, section 6.5). Among the major commercial crops, winter wheat and soybeans are more sensitive to ambient O 3 l evels than other crops.

 In the current standard scenario, n o counties have RYL estimates at or above 5% (U.S. EPA, 2014b, section 6.5). 181
The WREA also estimated O 3 - related crop impacts on producer and consumer surplus. 182 These are nati onal

- scale estimates of the effects of yield loss on agricultural harvesting, which supply provisioning services of food and fiber for each of the air quality scenarios. Overall effect on agricultural yields and producer and consumer surplus depends on (1) the ability of producers/farmers to substitute other crops that are less O 3 sensitive, and (2) the responsiveness, or elasticity, of demand and supply (U.S. EPA, 2014b, section 6.5).

 Estimates of consumer surplus, or consumer gains, were generally higher in the current standard scenario in the agricultural sector because higher productivity under lower O 3 concentrations increased total yields and reduced market prices (U.S. EPA, 2014b, Table s 6

- 17 and 6

- 18). Combined gains in producer and

181 In the air quality scenario for the current standard, a monitor that already met the current standard but was located within the same region as another monitor that was above the current standard would have had its concentration adjusted downward. This is due to the fact that concentrations were ad justed independently for each region , applying reductions to all monitors within the region, such that all monitors located within a region meet the standard (U.S. EPA, 2014b, section 4.3.4.2). 182 Welfare economics focuses on the optimal allocation of reso urces and goods and how those allocations affect total social welfare. Total welfare is also referred to as economic surplus, which is the overall benefit a society, composed of consumers and producers, receives when a good or service is bought or sold, g iven a quantity provided and a market price. Economic surplus is divided into two parts: consumer and producer surplus (U.S. EPA, 2014, p. ES

- 6)

.*** E.O. 12866 Review

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Page 356 of 647 consumer surplus for forestry and agriculture were essentially unchanged for the 15 ppm

- hrs scenario, but annualized gains increased by $21 million beyond the current standard scenario for the 11 ppm

- hrs scenario and $231 million for the 7
ppm - hrs scenario. In some cases, lower prices reduce producer gains more than can be offset by higher yields (U.S. EPA, 2014b, Table 6

- 18).

 Because demand for most agricultural commodities is not highly responsive to changes in price, producer surplus or producer gains often declined. For agricultural welfare, annualized combined consumer and producer surplus gains were estimated to be $2.6 trillion in 2010 for the current standard scenario (U.S. EPA, 2014b, Table 6

- 1 7 ). b. Key Uncertainties The WREA discusses multiple areas of uncertaint y associated with the crop yield loss estimates, including those associated with the model

- based adjustment methodology as well as those associated with the projection of yield loss using the FASOMGHG model at the estimated O 3 concentrations (U.S. EPA, 201 4b, Table 6

- 27, section 8.5). Because the W126 estimates generated in the air quality analyses are inputs to the vegetation risk analyses for crop yield loss, any uncertainties in the air quality analyses are propagated into the those analyses (U.S. EPA, 2 014b, Table 6

- 27, section 8.5). Therefore, the air quality scenarios in the crop yield analyses have the same uncertainties and limitations as in the biomass loss analyses (summarized above), including those associated with the model

- based adjustment metho dology (U.S. EPA, 2014b, section 8.5).
4

. Visible Foliar Injury*** E.O. 12866 Review

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Page 357 of 647 Section IV.C.4.a below provides an overview of the assessment in the WREA of
O 3 - related visible foliar injury and associated ecosystem services impacts , as well as the key results. Section IV .C.4.b summarizes the key uncertainties.

a. Overview and Summary of Key Results The WREA presents a number of analyses of O 3 - related visible foliar injury and associated ecosystem services impacts (U.S. EPA, 2014b, Chapter 7). An initial analysis using USFS FHM/FIA biosite data included the development of benchmark criteria reflecting different prevalences of visible foliar inj ury at different W126 exposures and soil moisture conditions. These criteria were then used in a screening

- level characterization of the potential risk of foliar injury incidence in 214 national parks and a case study assessment of three national parks, wh ich also provides limited characterization of the associated ecosystem services. In the biosite data analysis, the WREA used the biomonitoring site data from the USFS FHM/FIA Network (USFS, 2011), 183 associated soil moisture data during the sample years, an d national surfaces of ambient air O 3 concentrations based on spatial interpolation of monitoring data from 2006 to 2010 to calculate the proportion of biosites with any visible foliar injury. The proportion of biosites metric is derived by first ordering the data (across biosites and sample years) by W126 index value estimated for that biosite and year. Then for each W126 index value, the proportion of biosites is calculated with any foliar injury for all observations at or below that W126 index value. (U. S. EPA, 2014b, section 7.2). This analysis indicates that the proportion of biosites

183 Data were not available for several western states (Montana, Idaho, Wyoming, Nevada, Utah, Colorado, Arizo na, New Mexico, Oklahoma, and portions of Texas).*** E.O. 12866 Review

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Page 358 of 647 showing the presence of any foliar injury increases rapidly from zero to about 20 percent at relatively low W126 index values

. Specifically: (1) the proportion of biosites exhibiting foliar injury rises rapidly at increasing W126 index values below approximately 10 ppm

- hrs (W126 < 10.46 ppm

- hrs), and (2) there is relatively little change in the proportions above W126 index values of approximately 10 ppm

- hrs (W126 >10.46 ppm

- hrs). The data for biosites during normal moisture years are very similar to the dataset as a whole, with an overall proportion of close to 18 percent for presence of any foliar injury. Among the biosites with a relatively wet season, the proportion of bio sites showing injury is much higher and the relationship with annual W126 index value is much steeper. Much lower proportions of biosites show injury with relatively dry

seasons (U.S. EPA, 2014b, section 7.2.3, Figures 7

- 10), consistent with the ISA findin g that many studies have shown that dry periods tend to decrease the incidence and severity of O 3 - induced visible foliar injury (U.S. EPA, 2013, section 9.4.2) . While these analyses indicate the potential for foliar injury to occur under conditions that me et the current standard, the extent of foliar injury that might be expected under such conditions is unclear from these analyses. The national

- scale screening

- level assessment in 214 parks employed benchmark*** E.O. 12866 Review

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Page 359 of 647 criteria developed from the above analysis. 184 , 185 F or example, annual O 3 concentrations corresponding to a W126 index value of 10.46 ppm

- hrs represents the O 3 exposure concentration where the slope of exposure

- response relationship changes for FHM biosites , with the percentage of biosites showing injury re maining relatively constant for higher W126 index values . The WREA refers to this as the “base scenario” benchmark. The W126 benchmarks across this and the other four scenarios range from 3.05 ppm

- hrs ( foliar injury observed at five percent of biosites, no rmal moisture) up to 24.61 ppm

- hrs ( foliar injury observed at 10 percent of biosites, dry). For the scenario of 10 percent biosites with injury, W126 index values were approximately 4, 6, and 25 ppm

- hrs for wet, normal and dry years, respectively. The nati onal

- scale screening

- level assessment applied these benchmarks to 42 parks with O 3 monitors and a total of 214 parks with O 3 exposure estimated from the interpolated national O 3 surfaces for individual years from 2006 to 2010 (U.S. EPA, 2014b, Appendix 7A and section 7.3).

 Based on NPS lists, 95 percent of the 214 parks in th is screening

- level assessment contain at least one vegetation species sensitive to O 3 - induced foliar injury (NPS,

184 The parks assessed in the WREA include lands managed by the NPS in the continental U.S., which includes National Parks, Monuments, Seashores, Scenic Rivers, Historic Parks, Battlefields, Reservations, Rec reation Areas, Memorials, Parkways, Military Parks, Preserves, and Scenic Trails. 185 This analysis considered the approach in Kohut (2007), which assessed the risk of O3

- induced visible foliar injury on O3 bioindicators (i.e., O3

- sensitive vegetation) in 24 4 parks managed by the NPS. Consistent with advice from CASAC (Frey and Samet, 2012a), however, the WREA modified the approach used by Kohut (2007) to apply the W126 metric alone. The WREA applied different foliar injury benchmarks in this assessment after further investigation into the benchmarks applied in Kohut (2007), which were derived from biomass loss rather than visible foliar injury. Kohut cited a threshold of 5.9 ppm

- hrs for highly sensitive species from Lefohn (1997), which was based on the lowes t W126 estimate corresponding to a 10 percent growth loss for black cherry. For soil moisture, Kohut (2007) qualitatively assessed whether there appeared to be an inverse relationship between soil moisture and high O3 exposure.*** E.O. 12866 Review

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Page 360 of 647 2003, 2006).

 In the current standard scenario, n one of the 214 parks had O 3 concentrations estimated to exceed the annual benchmark of a W126 index value above 10.46
ppm - hrs (U.S. EPA, 2014b, section 7.3. 3.3 ). The case study analys e s focused on Great Smoky Mountains National Park (GRSM ), Rocky Mountain National Park (ROMO), and Sequoia and Kings Canyon National Parks (SEKI). Information on visitation patterns, recreational activities and visitor expenditures was considered. For example, visitor spending in 2011 exceeded $800 million, $170 million and $97 million dollars in G RSM, ROMO and SEKI, respectively. In each park, the percent cover of species sensitive to foliar injury was estimated and the overlap between recreation areas within the park and elevated W126 concentrations was described. (U.S. EPA, 2014b, section 7.4).

 I n the current standard scenario, the three

- year average W126 index values were at or below 7 ppm

- hrs in all areas of two of the three parks (GRSM and SEKI). Three

- year average W126 index values were below 7 ppm

- hrs in a little more than half of the area of the third park (ROMO) and between 7 and 11 ppm

- hrs in the remainder of the park (U.S. EPA, 2014b, section 7.4).

 For the 15, 11 and 7 ppm

- hrs scenarios , all areas of the three specific national parks evaluated ( GRSM, SEKI, and ROM O) had three

- year average W126 index value s at or below 7 ppm

- hrs , well below the 10.46 ppm

- hrs benchmark. However, the extent of foliar injury that might be expected under these scenarios is unclear from these analyses.*** E.O. 12866 Review

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Page 361 of 647 Although not discussed in detail here, the WREA also describe s qualitative assessments for some of the ecosystem services most likely to be affected by O 3 - induced foliar injury such as cultural services, including aesthetic value and outdoor recreation. Aesthetic value and outdoor recreation depend on the perceived scenic beauty of the environment. Many outdoor recreation activities directly depend on the scenic value of the area, in particular scenic viewing, wildlife

- watching, hiking, and camping. These activities and services are of significant importance to publi c welfare as they are enjoyed by millions of Americans every year and generate millions of dollars in economic value (U.S. EPA, 2014b, Chapters 5 and 7). Although data are not available to explicitly quantify O 3 effects on ecosystem services, the WREA incl udes several qualitative analyses. b. Key Uncertainties Uncertainties associated with these analyses are discussed in the WREA, sections 7.5 and 8.5.3, and in WREA Table 7

- 24 , and also summarized in the PA (e.g., U.S. EPA, 2014c, section 6.3) . As discussed in the WREA (section 8.5.3), evaluating soil moisture is more subjective than evaluating O 3 exposure because of its high spatial and temporal variability within the O 3 season, and there is considerable subjectivity in the categorization of relative drough t. The WREA generally concludes that the spatial and temporal resolution for the soil moisture data is likely to underestimate the potential for foliar injury to occur in some areas. In addition, there is lack of a clear threshold for drought below which v isible foliar injury would not occur. In general, low soil moisture reduces the potential for foliar injury, but injury could still occur, and the degree of drought necessary to reduce potential injury is not clear. Studies in the ISA provide*** E.O. 12866 Review

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Page 362 of 647 additional in formation regarding the role of soil moisture in influencing visible foliar injury response, (U.S. EPA, 2 013, section 9.4.2). These studies confirm that adequate soil moisture creates an environment conducive to greater visible foliar injury in the presenc e of O 3 than drier conditions. As stated in the ISA, “[a] major modifying factor for O 3 - induced visible foliar injury is the amount of soil moisture available to a plant during the year that the visible foliar injury is being assessed ... because lack of soi l moisture generally decreases stomatal conductance of plants and, therefore, limits the amount of
O 3 entering the leaf that can cause injury” (U.S. EPA, 2013, p. 9

- 39). As a result, “many studies have shown that dry periods in local areas tend to decrease the incidence and severity of O 3 - induced visible foliar injury; therefore, the incidence of visible foliar injury is not always higher in years and areas with higher O 3 , especially with co

occurring drought (Smith, 2012; Smith et al., 2003)” (U.S. EPA, 20 13, p. 9

- 39). This “...partial ‘protection’ against the effects of O 3 afforded by drought has been observed in field experiments (Low et al., 2006) and modeled in computer simulations (Broadmeadow and Jackson, 2000)” (U.S. EPA, 2013, p. 9

- 87). In considering the extent of any protective role of drought conditions, however, the ISA also notes that other studies have shown that “drought may exacerbate the effects of O 3 on plants (Pollastrini et al., 2010; Grulke et al., 2003)” and that “[t]here is also some evi dence that O 3 can predispose plants to drought stress (Maier

- Maercker, 1998)”. Accordingly, the ISA concludes that “the nature of the response is largely species

- specific and will depend to some extent upon the sequence in which the stressors oc cur” (U.S. EPA, 2013, p. 9

- 87). Due to the absence of biosite injury data in the Southwest region and limited biosite data in the West and West North Central regions, the W126 benchmarks for foliar*** E.O. 12866 Review

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Page 363 of 647 injury that the WREA developed and applied in the national park scree ning assessment may not be applicable to these regions. The WREA applied the benchmarks from the national

- scale analysis to a screening

- level assessment of 214 national parks and case studies of three national parks. Therefore, uncertainties in the foliar injury benchmarks are propagated into the se analyses

. Other uncertainties associated with these analyses include uncertainty associated with our understanding of the number and sensitivity of O 3 sensitive species, uncertainties associated with spatial ass ignment of foliar injury biosite data to 12 km x 12 km grid cells, and uncertainties associated with O 3 exposure data of vegetation and recreational areas within parks (U.S. EPA, 2014b, Table 7

- 22). There are also important uncertainties in the estimated O 3 concentrations for the different air quality scenarios evaluated (U.S. EPA, 2014b, section 8.5), as discussed earlier in this section. These uncertainties only apply to the national park case studies because these are the only foliar injury analyses that rely on the air quality scenarios, but any uncertainties in the air quality analyses are propagated into those analyses. The WREA identifies additional uncertainties that are associated with the national park case studies. Specifically, there is uncertain ty inherent in survey estimates of participation rates, visitor spending/economic impacts, and willingness

- to

- pay. These surveys potentially double

- count impacts based on the allocation of expenditures across activities but also potentially exclude other a ctivities with economic value. In general, the national level surveys apply standard approaches, which minimize potential bias. Other sources of uncertainty are associated with the mapping, including park boundaries, vegetation species cover, and park amen ities, such as scenic overlooks and trails. In general, the*** E.O. 12866 Review

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Page 364 of 647 WREA concludes that there is high confidence in the park mapping (U.S. EPA, 2014b, Table 7

- 24). D. Conclusions on Adequacy of the Current Secondary Standard The initial issue to be addressed in the current review of the secondary O 3 standard is whether, in view of the currently available scientific evidence, exposure and risk information and air quality analyses, discussed in the PA, the existing standard should be revised. In drawing conclusions on adequacy of the current O 3 secondary standard, the Administrator has taken into account both evidence

- based and quantitative
exposure - and risk

- based considerations, and advice from CASAC. Evidence

- based considerations draw upon the EPA’s assessment an d integrated synthesis of the scientific evidence from experimental and field studies evaluating welfare effect s related to O 3 exposure, with a focus on policy

- relevant considerations, as discussed in the PA. Air quality analyses inform these consideration s with regard to cumulative, seasonal exposures occurring in areas of the U.S. that meet the current standard. Exposure

- and risk

- based considerations draw upon EPA assessments of risk of key welfare effects, including O 3 effects on forest growth, producti v ity , carbon storage, crop yield and visible foliar injury, expected to occur in model

- based scenarios for the current standard, with appropriate consideration of associated uncertainties. The following sections describe consideration of the evidence and t he exposure/risk information in the PA and advice received from CASAC, as well as the comments received from various parties, and the Administrator’s proposed conclusions regarding the adequacy of the current secondary standard. 1. Evidence and Exposure/Ri sk

- Based Considerations in the Policy Assessment*** E.O. 12866 Review

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Page 365 of 647 Staff assessments in the PA focus on the policy

- relevant aspects of the assessment and integrative synthesis of the currently available welfare effects evidence in the ISA, analyses of air quality relationships with exposure metrics of interest, the exposure and risk assessments in the WREA , comments and advice of CASAC and public comment on drafts of the PA, ISA and WREA. T he PA describes evidence

- and exposure/risk

- based considerations and present s staff conclusions for the Administrator to consider in reaching her proposed decision on the current standard. The focus of the initial PA conclusions is consideration of the question: Does the currently available scientific evidence and exposure/risk i nformation, as reflected in the ISA and WREA, support or call into question the adequacy and/or appropriateness of the protection afforded by the current secondary O 3 standard? The PA’s general approach to informing judgments by the Administrator recognize s that the available welfare effects evidence demonstrates a range of O 3 sensitivity across studied plant species and documents an array of O 3 - induced effects that extend from lower to higher levels of biological organization. These effects range from thos e affecting cell processes and individual plant leaves to effects on the physiology of whole plants, as well as the range from species effects and effects on plant communities to effects on related ecosystem processes and services. Given this evidence, the PA notes that it is not possible to generalize across all studied species regarding which cumulative exposures are of greatest concern, as this can vary by situation due to differences in exposed species sensitivity, the importance of the observed or pred icted O 3 - induced effect, the role that the species plays in the ecosystem, the intended use of the affected species and its associated ecosystem and services, the presence of other co

- occurring*** E.O. 12866 Review

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Page 366 of 647 predisposing or mitigating factors, and associated uncertainti es and limitations. Therefore, in developing conclusions in the PA, staff takes note of the complexity of judgments to be made by the Administrator regarding the adversity of known and anticipated effects to the public welfare and are mindful that the Adm inistrator’s ultimate judgments on the secondary standard will most appropriately reflect an interpretation of the available scientific evidence and exposure/risk information that neither overstates nor understates the strengths and limitations of that evi dence and information (U.S. EPA, 2014c, section 5.7). In considering the estimates of exposures and risks for air quality scenarios assessed in the WREA, the PA: 1) evaluates the weight of the scientific evidence concerning vegetation effects associated with those O 3 exposures; 2) considers the importance, from a public welfare perspective, of the O 3 - induced effects on sensitive vegetation and associated ecosystem services that are known or anticipated to occur as a result of exposures in the assessed air quality scenarios; and, 3) recognizes that predictions of effects associated with any given O 3 exposure may be mitigated or exacerbated by actual conditions in the environment (i.e., co

- occurring modifying environmental and genetic factors). When consider ing WREA analyses that involve discrete exposure levels or varying levels of severity of effects, the PA’s approach recognizes that the available welfare effects evidence demonstrates a wide range in O 3 sensitivities across studied plant species. The PA ad ditionally considers the uncertainties associated with this information. As an initial matter, the PA recognizes that the CAA does not require that a secondary standard be protective of all effects associated with a pollutant in the ambient*** E.O. 12866 Review

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Page 367 of 647 air, but rather those considered adverse to the public welfare (as described in section IV.B.2 above). In considering the extent to which it may be appropriate to consider particular welfare effects adverse, the PA applies a paradigm used in past reviews. As discussed in section IV.B.2 above, this paradigm recognizes that the significance to the public welfare of O 3 - induced effects on sensitive vegetation growing within the U.S. can vary depending on the nature of the effect, the intended use of the sensitive plants or

ec osystems, and the types of environments in which the sensitive vegetation and ecosystems are located. Accordingly, any given O 3 - related effect on vegetation and ecosystems (e.g., biomass loss, crop yield loss, visible foliar injury) may be judged to have a different degree of impact on the public welfare depending, for example, on whether that effect occurs in a Class I area, a city park, or commercial cropland. In the last review, the Administrator took note of actions taken by Congress to establish public lands that are set aside for specific uses that are intended to provide benefits to the public welfare, including lands that are to be protected so as to conserve the scenic value and the natural vegetation and wildlife within such areas for the enjoyment of future generations (73 FR 16497, March 27, 2008) . Such public lands that are protected areas of national interest include national parks and forests, wildlife refuges, and wilderness areas (73 FR 16497, March 27, 2008). The PA notes that effects occurr ing in such areas would likely have the highest potential for being classified as adverse to the public welfare, given the expectation of preserving these areas to ensure their intended use is met (U.S. EPA, 2014c, section 5.1). In considering uses of vege tation and forested lands, the paradigm also includes consideration of impacts to ecosystem goods and services. In summary, the paradigm considered in the PA, consistent with the discussion in section IV.B.2 above,*** E.O. 12866 Review

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Page 368 of 647 integrates the concepts of: 1) variabilit y in public welfare significance given intended use and value of the affected entity, such as individual species; 2) relevance of associated ecosystem services to public welfare; and 3) variability in spatial, temporal, and social distribution of ecosystem services associated with known and anticipated welfare effects. Further, the PA recognizes that there is no bright

- line rule delineating the set of conditions or scales at which known or anticipated effects become adverse to public welfare. With respect to the scientific evidence, the PA takes note of the longstanding evidence base that demonstrates O 3 - induced effects that occur across a range of biological and ecological scales of organization, as described in the ISA and summarized in section IV.B.1 ab ove (U.S. EPA, 2013, p. 1

- 8). Many of the recent studies evaluated in this review have focused on and further increased our understanding of the molecular, biochemical and physiological mechanisms that explain how plants are affected by O 3 in the absence o f other stressors (U.S. EPA, 2013, section 9.3). These recent studies, in combination with the extensive and long

- standing evidence, have further strengthened the coherence and consistency of the entire body of research since the last review. Consistent w ith conclusions in the 2006 CD, the ISA determined that a causal relationship exists between O 3 exposure and visible foliar injury on sensitive vegetation, reduced plant growth, reduced productivity in terrestrial ecosystems, reduced yield and quality of a gricultural crops and alteration of below

- ground biogeochemical cycles (U.S. EPA, 2013, Table 1

- 2 and section 2.6). The relationship between O 3 exposures and reduced carbon sequestration in terrestrial ecosystems, alteration of terrestrial ecosystem*** E.O. 12866 Review

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Page 369 of 647 water cycling and alteration of terrestrial community composition was concluded to be likely causal (U.S. EPA, 2013, Table 1

- 2). The PA recognizes that consistent with conclusions drawn in the last review, the currently available evidence base also strongly s upports that effects on vegetation are attributable to cumulative seasonal O 3 exposures. Moreover, on the basis of the entire body of evidence in this regard, the ISA concludes that “quantifying exposure with indices that cumulate hourly O 3 concentrations and preferentially weight the higher concentrations improves the explanatory power of exposure/response models for growth and yield, over using indices based on mean and peak exposure values” (U.S. EPA, 2013, p. 2

- 44). Accordingly, as in other recent revie ws, the evidence continues to provide a strong basis for concluding that it is appropriate to judge impacts of O 3 on vegetation, related effects and services, and the level of public welfare protection achieved, using a cumulative, seasonal exposure metric , such as the W126

- based metric. In this review, as in the last review, the CASAC concurs with this conclusion (Frey, 2014c, p. iii). Thus, based on the consistent and well

- established evidence described above, the PA concludes that the most appropriate an d biologically relevant way to relate O 3 exposure to plant growth, and to determine what would be adequate protection for public welfare effects attributable to the presence of O 3 in the ambient air is to characterize exposures in terms of a cumulative sea sonal form, and in particular the W126 metric. In considering the current standard with regard to protection from the array of O 3 - related effects recognized in this review, the PA first considers effects related to forest tree growth, productivity and carbon storage, effects for which the ISA concludes the evidence supports a causal or likely causal relationship with exposures to O 3 in ambient*** E.O. 12866 Review

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Page 370 of 647 air (U.S. EPA, 2014c, sections 5.2 and 5.7). In so doing, the PA notes that while changes in biomass affect ind ividual tree species, the overall effect on forest ecosystem productivity depends on the composition of forest stands and the relative sensitivity of trees within those stands. In considering the evidence for these effects and the extent to which they migh t be expected to occur under conditions that meet the current secondary standard, the PA focused particularly on RBL estimates for the 11 species for which robust E

- R functions have been developed. The PA recognized that recent studies, such as multiple

- ye ar exposures of aspen and birch, have provided additional evidence on tree biomass or growth effects associated with multiple year exposures in the field, including the potential for cumulative and carry

- over effects. For example, findings from these studi es indicate that effects of O 3 on birch seeds (reduced weight, germination, and starch levels) could lead to a negative impact on species regeneration in subsequent years and may have the potential to alter carbon metabolism of overwintering buds, potentia lly affecting growth in the following year. Other studies have reported that multiple

- year exposures reduced tree size parameters in an aspen community, and increased the rate of conversion from a mixed aspen

- birch community to a community dominated by the more tolerant birch, such that elevated O 3 may alter intra

- and inter

- species competition within a forest stand (U.S. EPA, 2013, section 9.4.3; U.S. EPA, 2014c, section 5.2). In giving particular attention to tree seedling biomass loss estimates, the PA n otes that CASAC “concurs that biomass loss in trees is a relevant surrogate for damage to tree growth that affects ecosystem services such as habitat provision for wildlife, carbon storage, provision of food and fiber, and pollution removal” (Frey, 2014c, p. 10).*** E.O. 12866 Review

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Page 371 of 647 In evaluating the current evidence and exposure/risk information associated with tree growth, productivity and carbon storage, with regard to the adequacy of public welfare protection afforded by the current standard, the PA consider s the eviden ce of vegetation and welfare impacts in areas of the U.S. likely to have met the current standard. With regard to O 3 effects on tree growth, productivity and carbon storage and associated ecosystems and services, the PA focuses on relative biomass loss est imates based on the OTC

- based E

- R functions, noting that analyses newly performed in this review have reduced the uncertainty associated with using OTC E

- R functions to predict tree growth effects in the field (U.S. EPA, 2014c, section 5.2.1; U.S. EPA, 201 3, section 9.6.3.2). In focusing on RBL estimates, the PA recognized that comparison to an array of benchmarks would be informative to considerations of significance to public welfare. Included in this array were RBL values of 2% and 6% given emphasis by CASAC (Frey, 2014c). In considering the RBL estimates for different O 3 conditions associated with the current standard, the PA focused first on the median of the species

- specific (composite)
E

- R functions. In so doing, the PA takes note of CASAC’s comment s that a 6% median RBL is “unacceptably high”, and that the 2% median RBL is an important benchmark to*** E.O. 12866 Review

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Page 372 of 647 consider (Frey, 2014c). 186 Based on the summary of RBL estimates in the PA, the PA notes that the median species RBL estimate is at or below 2% for W126 ex posure index values less than or equal to 7 ppm

- hrs (U. S. EPA, 2014c, Table 6

- 1 and Appendix 5C). The median species RBL is at or above 6% for W126 index values of 19 ppm

- hrs and higher. In recognition of the significance of welfare effects in Class I areas, the PA gives appreciable weight to consideration of the occurrence of O 3 concentrations associated with the potential fo r RBL estimates above benchmarks of interest in Class I areas that meet the current standard. Based on air quality data for the period from 1998 to 2012, the PA focused consideration on 22 Class I areas , in which during one or more three

- year periods the a ir quality met the current standard and the 3

- year average W126 index value was at or above 15 ppm

- hrs ( see Table 7 below, drawn from U.S. EPA, 2014c, Table 5

- 2). Across these 22 Class I areas , the highest single

- year W126 index values for these three

- year periods ranged from 17.4 to 29.0 ppm

- hrs. In 2 0 of the areas, distributed across eight states (AZ, CA, CO, KY, NM, SD, UT, WY) and four regions ( W est, S outhwest,
W est N orth C entral and C entral), this range was 19.1 to 29.0 ppm

- hrs, exposure values for which the corresponding median species RBL estimates equal or exceed 6%, which

186 The CASAC provided several comments related to 2% RBL for tree seedlings both with regard to its use in summarizing WREA results and with regard to consideration of the potential significance of vegetation effects, as summarized in sections IV.D.2 and IV. E. 3 . In identifying 2% as an important benchmark, CASAC referenced the 1996 workshop sponsored by the Southern Oxidant s Study g roup at which, as noted in section IV.B.2 above, participants identified annual percentages of tree seedling growth reduction and crop yield loss they considered important to their judgments on a secondary standard . T he workshop report provides no explicit rationale for the percentages identified or specification with regard to number or proportion of species for which such percenta ges should be met (Heck and Cowling, 1997).*** E.O. 12866 Review

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Page 373 of 647 CASAC has termed “unacceptably high”. R ecogniz ing that in any given year, other environmental factors can influ ence the extent to which O 3 may have the impact predicted by the E

- R functions, the PA looked beyond single year occurrences of such magnitudes of W126 index values. For example, focusing on the highest three

- year periods that include these highest annual values for 21 areas, the PA notes that in 10 areas (across five states in the W est and S outhwest regions), the three

- year average W126 values ( for the highest three

- year period that includes these annual values) are at or above 19 ppm - hrs , ranging up to 22

. 5 ppm - hrs ( for which the median species RBL estimate is above 7%). This indicates that the W126 value above 19 ppm

- hrs is not simply a single year in a period of lower years, but that in these cases there were sustained higher values that contributed to a 3

- year W126 also above 19 ppm

- hrs. In terms of the highest three

year values observed (regardless of single

- year values), the PA additionally notes that the highest three

- year average W126 index value (during periods meeting the current standard) was at o r above 19 (ranging up to 22.5 ppm

- hrs) in 1 1 areas, distributed among five states in the W est and S outhwest regions (U.S. EPA, 2014c, Table 5

- 2 , Appendix 5B).*** E.O. 12866 Review

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Page 374 of 647 Table 7 . O 3 Concentrations in Class I Areas During Period From 1998 to 2012 that Met the Curre nt Standard and Where Three
- year Average W126 Index Value was at or Above 15 ppm
- hrs

Class I Area State / County Design Value (ppb)* 3
- y ea r Average W126

(ppm
- hrs)* (# ≥ 19 ppm - hrs , range) Annual W126 (ppm
- hrs)* (# ≥ 19 ppm - hrs , range) Number of 3
- year Periods Bandelier Wilderness Area QA, DF, PP NM / Sandoval 70

- 74 15.8

- 20.8 (2, 20.0

- 20.8) 12.1

- 25.3 (4, 19.2

- 25.3) 8 Bridger Wilderness Area QA, DF WY / Sublette 69

- 72 15.1

- 17.4 9.9

- 19.2 (1, 19.2) 5 Canyonlands National Park QA, DF, PP, UT / San Juan 69

- 73 15.0

- 20.5 (2, 19.8

- 20.5) 9.9

- 24.8 (5, 19.3

- 24.8) 9 Carlsbad Caverns National Park PP NM / Eddy 69 15.0

- 15.3 8.6

- 26.7 (1, 26.7) 3 Chiricahua National Monument DF, PP AZ / Cochise 69

- 73 15.7

- 18.0 13.2

- 21.6 (2, 19.3

- 21.6) 7 Grand Canyon National Park QA, DF, PP AZ / Coconino 68

- 74 15. 3

- 22.2 (7, 19.2

- 22. 2 ) 11.3

- 26.7 (7, 19.8

- 26.7) 12 John Muir Wilderness Area QA, DF, PP CA / Inyo 71

- 72 16.5

- 18.6 10.1

- 25.8 (2, 23.9

- 25.8) 3 Lassen Volcanic National Park DF, PP CA / Shasta 75 15.3 13.6

- 18.7 1 Mammoth Cave National Park BC, C, LP, RM, SM , VP, YP KY / Edmonson 74 15.9 12.5

- 22.5 (1, 22.5) 1 Mesa Verde National Park DF CO / Montezuma 67

- 73 15. 5

- 21.0 (2, 19.0

- 21.0) 10.7

- 23.6 (4, 19.7

- 23.6) 10 Mokelumne Wilderness Area DF, PP CA / Amador 74 17.6 14.8

- 22.6 (1, 22.6) 1 Petrified Forest National Park AZ / Navajo 70 15.7 12.9

- 19.2 (1, 19.2) 1 Pinnacles National Monument CA / San Benito 74 15.1 13.1

- 17.4 1 Rocky Mountain National Park QA, DF, PP CO / Boulder 73

- 75 15.1

- 19.3 (1, 19.3) 9.5

- 25.1 (5, 20.7

- 25.1) 6 CO / Larimer 74 15.0

- 18.3 8 .1

- 25.8 (3, 19.1

- 25.8) 3 Saguaro National Park DF, PP AZ / Pima 69

- 74 15.4

- 18.9 11.0

- 23.1 (3, 20.0

- 23.1) 6 Sierra Ancha Wilderness Area DF, PP AZ / Gila 72

- 75 17.9

- 22.4 (3, 20.2

- 22.4) 14.8

- 27.5 (4, 20.3

- 27.5) 4 Superstition Wilderness Area PP AZ / Maricopa 75 22.4 (1, 22.4) 14.5

- 28.6 (2, 27.4

- 28.6) 1 AZ / Pinal 73

- 75 18.7

- 22.5 (2, 20. 8

- 22.5) 14.8

- 29.0 (3, 22.6

- 29.0) 3 Weminuche Wilderness Area QA, DF, PP CO / La Plata 70

- 74 15.0

- 19.1 (1, 19.1) 10.9

- 21.0 (2, 20.8

- 21.0) 5 West Elk Wilderness Area QA, DF CO / Gunnison 68

- 73 15.6

- 20.1 (1, 20.1) 12.9

- 23.9 (3, 21.1

- 23.9) 8 Wind Cave National Park QA, PP SD / Custer 70 15.4 12.2

- 20.6 (1, 20.6) 1 Yosemite National Park QA, DF, PP CA / Tuolumne 73

- 74 20.7

- 20.8 (2, 20.7

- 20.8) 19.7

- 22.1 (4, 19.7

- 22.1) 2 Zion National Park QA, DF, PP UT / Washington 70

- 73 17.8

- 21.1 (2, 20.3

- 21.1) 14.9

- 24.2 (5, 19.3

- 24.2) 4*** E.O. 12866 Review

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Page 375 of 647 *Based on data from http://www.epa.gov/ttn/airs/airsaqs/detaildata/downloadaqsdata.htm

. W126 values are truncated after first decimal place. Superscript letters refer to species present for which E

- R functions have been developed. QA=Quaking Aspen, BC=Black Cherry, C=Cottonwood, DF=Douglas Fir, LP=Loblolly Pine, PP=Ponderosa Pine, RM=Red Maple, SM=Sugar Maple, VP=Virginia Pine, YP=Yellow (Tulip) Poplar. Sources include USDA

- NRCS (2014, http://plants.usda.gov ), USDA

- FS (2014 , http://www.fs.fed.us/foresthealth/technology/nidrm2012.shtml ) UM

- CFCWI (2014, http://www.wilderness.net/printFactSheet.cfm?WID=583 ) and Phillips and Comus (2000).*** E.O. 12866 Review

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Page 376 of 647 In considering the data analysis for 2 2 Class I areas described above, the PA additionally consider s the species

- specific RBL estimates for quaking aspen and ponderosa pine, two tree species that are found in many of these 22 area s and have a sensitivity to O 3 exposure that places them near the middle of the group for which E

- R functions have been establ ished (U.S. EPA, 2014c, sections 5.2 and 5.7). In the Class I areas where ponderosa pine is present, the highest single year W12 6 index values ranged from 18.7 to 29.0 ppm

- hrs and the highest 3

- year average W126 values in which these single year values we re represented ranged from 15 to 22.5 ppm

- hrs, with these three

year values above 19 ppm

- hrs in eight areas across five states . The p onderosa p ine RBL estimates for 29 and 22.5 ppm

- hrs are approximately 12% and 9%, respectively (U.S. EPA, 2014c, Appendix 5 C). In Class I areas where quaking aspen is present, the highest single year W12 6 i ndex values ranged from 19.2 to 26.7 ppm

- hrs and the highest 3

- year average W126 values in which these single year values we re represented ranged from 15.0 to 22.2 ppm

- hrs, with these three

- year values above 19 ppm

- hrs in eight areas across five states. The quaking aspen RBL estimates for 26.7 and 22.2 ppm

- hrs are approximately 16% and 13%, respectively (U.S. EPA, 2014c, Appendix 5C). The PA describes the above observations, particularly in light of advice from CASAC, summarized in section IV.D.2 below, as evidence of the occurrence in Class I areas during periods where the current standard is met of cumulative seasonal O 3 exposures of a magnitude for which the tree growth im pacts indicated by the estimated median species RBL might reasonably be concluded to be important to public welfare (U.S. EPA, 2014c, sections 5.2.1 and 5.7)

.*** E.O. 12866 Review

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Page 377 of 647 In considering the WREA analyses of effects on tree growth and associated ecosystem services in the air quality scenario for the current standard, the PA first takes note of the potential for the interpolation method used in creating the national surface of
O 3 concentrations for the air quality scenarios to underestimate the higher W126 values such that W126

- based exposures would be expected to be somewhat higher than those included in each scenario (U.S. EPA, 2014b, pp. 5

- 31 to 5

- 32). While recognizing this, the PA considers results of the WREA analyses for the current standard scenario and the
11 s pecies of trees, for which robust E

- R functions are available. These results indicate that O 3 can impact growth of these species across the U.S

. , as well as an array of associated ecosystem services provided by forests , including timber production, carbon storage and air pollution removal (U.S. EPA, 2014b, sections 6.2

- 6.8; U.S. EPA, 2014c, section 5.2). With regard to WREA analyses of ecosystem services, the PA notes that the national

- scale analysis of O 3 impacts on carbon storage indicates appreciably mo re storage in the air quality scenario for the current standard (approximately 11,000
MMtCO 2 e, over 30 years) compared to the scenario for recent, higher O 3 conditions (U.S. EPA, 2014b, Appendix 6B, Table B

- 10). The PA additionally considers the WREA estim ates of tree growth and ecosystem services provided by urban trees over a 25

- year period for five urban areas based on case

- study scale analyses that quantified the effects of biomass loss on carbon storage and pollution removal (U.S. EPA, 2014b, sections 6.6.2 and 6.7; U.S. EPA, 2014c, sections 5.2 and 5.7). The urban areas included in this analysis represent diverse geography in the Northeast, Southeast, and Central regions, although they do not include an urban area in the western U.S. Estimates of the e ffects of*** E.O. 12866 Review

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Page 3 78 of 647 O 3 - related biomass loss on carbon sequestration indicate the potential for an increase of somewhat more than a MMtCO 2 e for the current standard scenario as compared to the recent conditions scenario (U.S. EPA, 2014b, section 6.6.2 and Appendix 6D ; U.S. EPA, 2014c, sections 5.2 and 5.7). The PA also notes the WREA estimates of increased pollution removal in the current standard scenario as compared to the scenario for recent conditions (U.S. EPA, 2014b, section 6.6.2; U.S. EPA, 2014c, section 5.2.2 ). In considering the significance of these WREA analyses of risks for the associated ecosystem services for timber production, air pollution removal, and carbon sequestration, the PA takes note of the large uncertainties associated with these analyses (se e U.S. EPA, 2014b, Table 6

- 27), and the potential for these findings to underestimate the response at the national scale. While noting the potential usefulness of considering predicted and anticipated impacts to these services in assessing the extent to wh ich the current information supports or calls into question the adequacy of the protection afforded by the current standard, the PA also notes that staff places limited weight on the absolute magnitude of the risk results for these ecosystem service endpoi nts due to the identification of significant associated uncertainties (U.S. EPA, 2014c, sections 5.2 and 5.7). In reaching conclusions regarding support for the adequacy of the current secondary standard provided by the currently available information on O 3 - induced effects on trees and associated services, the PA takes note of: 1) the robust evidence supporting the causal relationship between cumulative O 3 exposures and effects on tree growth and productivity, and information from model simulations supporting the determination of a likely causal relationships for carbon storage in terrestrial ecosystems (U.S. EPA, 2013,*** E.O. 12866 Review

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Page 379 of 647 sections 2.6.2.1 and 9.4.3); 2) the t ree seedling E

- R functions evidence, which has been strengthened and demonstrates variability in sensitivity to O 3 across species; 3) estimates of median species RBL at or above 6% associated with W126

- based exposure levels in several areas when O 3 concent rations were at or below the current standard; 4) growth effects estimates associated with exposure concentrations in several Class I areas based
on O 3 concentrations from 1998

- 2012 that were at or below the current standard; 5) evidence that impacts from single year exposures can carry over to the subsequent year and/or cumulate over multiple years with repeated annual exposures; 6) evidence from recent mechanistic studies and field based studies that support earlier findings from OTC studies; and 7) WREA analyses indicating that O 3 - induced biomass loss can impact ecosystem services provided by forests, including timber production, carbon storage, and air pollution removal, even when air quality is adjusted to just meet the current standard. Given the abov e, and noting CASAC views (described in section IV.D.2 below), the PA concludes that the current evidence and exposure/risk information call into question the adequacy of public welfare protection afforded by the current standard from the known and anticip ated adverse effects associated with O 3 - induced impacts on tree growth, productivity and carbon storage, including the associated ecosystem services assessed in this review. Therefore, the PA concludes that it is appropriate to consider revision of the

sec ondary standard to provide increased protection. With respect to crops, the PA takes note of the extensive and long

- standing evidence on the detrimental effect of O 3 on crop production, which continues to be confirmed by newly available evidence (U.S. EPA , 2013, section 9.4.4; U.S. EPA, 2014c, sections 5.3 and 5.7). The PA additionally notes that recent studies have highlighted the*** E.O. 12866 Review

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Page 380 of 647 effects of O 3 on crop quality, such as through decreases in the nutritive quality of grasses, and in the macro

- and micro

- nutr ient concentrations in fruits and vegetable crops (U.S. EPA, 2013, section 9.4.4; U.S. EPA, 2014c, section 5.3). Further, the PA notes that there has been little published evidence that crops are becoming more tolerant of O 3 , taking note particularly of th e ISA analyses of data from cultivars used in NCLAN studies, and yield data for modern cultivars from SoyFACE which confirm that the average response of soybean yield to O 3 exposure has not changed in current cultivars (U.S. EPA, 2006a; U.S. EPA, 2013, sec tion 9.6.3; U.S. EPA, 2014c, section 5.3). The PA further takes note of a recent analysis of satellite and ground

- based O 3 measurements to assess yield loss associated with ambient O 3 concentrations during the 2002 through 2006 growing seasons over the co ntinuous tri

- state area of Illinois, Iowa, and Wisconsin. This analysis found that O 3 concentrations contributed to reduced soybean yield, which correlates well with the previous results from FACE

- and OTC

- type experiments (U.S. EPA, 2013, section 9.4.4.1) . In consideration of the currently available evidence for O 3 effects on crops, the PA concludes that the recently available evidence, as assessed in the ISA, continues to support the conclusions of the 1996 and 2006 CDs that ambient O 3 concentrations can reduce the yield of major commodity crops in the U.S, and that the currently available evidence continues to support the use of the E

- R functions developed for 10 crops from OTC experiment data. Further, the PA recognizes that important uncertainties have been reduced regarding the exposure

- response functions for crop yield loss, especially for soybean, the second

- most planted field crop in the U.S., 187 with the

187 See http://www.ers.usda.gov/topics/crops/soybeans

- oil

- crops/background.aspx.*** E.O. 12866 Review

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Page 381 of 647 ISA generally reporting consistent results across exposure techniques and across crop varieties (U .S. EPA, 2013, section 9.6.3.2). With regard to consideration of the quantitative impacts of O 3 on crop yield, the PA considers RYL estimates for O 3 conditions associated with the current standard. As in the case of the PA considerations of RBL estimate s for tree seedlings, the PA recognized CASAC comments, which described greater than 5% RYL for the median crop species as “unacceptably high” and 5% RYL for the median crop species as adverse, while noting the opportunities to alter management of annual c rops (Frey, 2014c, pp. iii and 14). T he PA notes that staff analyses of recent monitoring data (2009

- 2011) indicate that O 3 concentrations in multiple agricultural areas in the U.S. that meet the current standard correspond to W126 index levels above 12 p pm - hrs, a value for which soybean
RYL estimates are greater than 5%. In particular, the PA notes that while the design values for two counties in the Midwest met the current standard in 2009

- 2011, both had a maximum annual W126 of 19 ppm

- hrs (in 2011) for which the soybean annual RYL estimate, based on the E

- R function, is 9%. 188 In considering the evidence and exposure/risk

- based information for effects on crops, the PA notes the CASAC comments regarding the use of crop yields as a surrogate for consideratio n of public welfare impacts, in which it noted that “[c]rops provide food and fiber services to humans” and that “[e]valuation of market

- based welfare effects of

188 The monitoring data reflect observations in locations that meet the current standard. The WREA analysis that assessed crop yield loss used a model

- developed air quality scenario to reflect air quality associated with the current standard (as described in section IV.C.1 above). In so doing, adjustments are made to create air quality that meets the standard and when the highest monito r in an area is adjusted downward to meet the standard, concentrations at nearby monitors that already meet the standard are also reduced.*** E.O. 12866 Review

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Page 382 of 647 O 3 exposure in forestry and agricultural sectors is an appropriate approach to take into

accou nt damage that is adverse to public welfare” (Frey, 2014c, p. 10; U .S. EPA, 2014c, section 5.7). The PA additionally notes, however, as recognized in section IV.B.2 above that the determination of the point at which O 3 - induced crop yield loss becomes adve rse to the public welfare is still unclear, given that crops are heavily managed with additional inputs that have their own associated markets and that benefits can be unevenly distributed between producers and consumers. The PA further notes that to the e xtent protection is provided by the current standard with regard to impacts on trees, protection may also be provided for commodity crops (U.S. EPA, 2014c, sections 5.3 and 5.7). In reaching conclusions regarding support provided for the adequacy of the current secondary standard by the currently available information on O 3 - related crop effects, the PA notes: (1) the clear and robust evidence supporting the causal relationship between cumulative O 3 exposures and effects on crop yields and quality (U.S. EP A, 2013, section 9.4.4); (2) the evidence supporting E

- R functions for 10 crops, which has been strengthened in this review and which demonstrates variability in sensitivity to O 3 across species; (3) evidence from recent mechanistic studies and field based studies supporting earlier findings from OTC studies; (4) evidence that crops, and in particular soybean, have not become more toler ant of O 3 (U.S. EPA, 2013, section 9.6.3, 9.4.4.1); and, ( 5) WREA analysis results indicating that O 3 - induced crop yield loss can impact producer and consumer surpluses and the interaction between agriculture and timber production. With regard to visible foliar injury, the PA recognizes the long

- standing evidence that has established that O 3 causes diagn ostic visible injury symptoms on studied*** E.O. 12866 Review

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Page 383 of 647 bioindicator species and that soil moisture is a major confounding effect that can decrease the incidence and severity of visible foliar injury under dry conditions and vice versa (U.S. EPA, 2014c, sections 5.4 and 5.7). As at the time of the last review, the most extensive dataset regarding visible foliar injury incidence across the U.S. is that collected by the U.S. Forest Service (USFS) Forest Health Monitoring/Forest Inventory and Analysis (FHM/FIA) Program , whic h has documented incidence of visible foliar injury in both the eastern and western U.S . Evidence available in the current review includes studies using controlled exposures as well as multi

- year field surveys. In addition to supporting prior conclusions, the newly available studies also address some uncertainties identified in the last review, such as the influence of soil moisture on visible injury development (U.S. EPA, 2013, section 9.4.2). As stated in the ISA, “many studies have shown that dry period s in local areas tend to decrease the incidence and severity of O 3 - induced visible foliar injury; therefore, the incidence of visible foliar injury is not always higher in years and areas with higher O 3 , especially with co

- occurring drought” (U.S. EPA, 201 3, p. 9

- 39). The ISA additionally concludes, however, that “the nature of the response is largely species

- specific and will depend to some extent upon the sequence in which the stressors occur” (U.S. EPA, 2013, p. 9

- 87). As recognized in the PA, this area of uncertainty complicates characterization of the potential for visible foliar injury and its severity or extent of occurrence for any given air quality conditions and thus complicates identification of air quality conditions that might be expected to pro vide a specific level of protection from this effect (U.S. EPA, 2014c, sections 5.4 and 5.7). Information available in this review indicates the occurrence of visible foliar injury in some Class I areas during times when O 3 concentrations met or would be*** E.O. 12866 Review

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Page 384 of 647 expected to meet the current standard (U.S. EPA, 2014c, sections 5.4.1 and 5.7). In noting this occurrence in Class I areas, the PA notes it has particular public welfare significance in light of direction from Congress that these areas merit a high level of protection (U.S. EPA, 2014c, sections 5.1, 5.4.1 and 5.7). T he PA also notes that visible foliar injury surveys are used by the federal land managers to assess potential O 3 impacts in Class I areas (USFS, NPS, FWS, 2010). Given this focus on visible f oliar injury, the PA concludes that such O 3 - induced impacts have the potential to impact the public welfare in scenic and/or recreational areas on an annual basis. Visible foliar injury is associated with important cultural and recreational ecosystem servi ces to the public, such as scenic viewing, wildlife

- watching, hiking, and camping, that are of significance to the public welfare and enjoyed by millions of Americans every year, generating millions of dollars in economic value (U.S. EPA, 2 014b, section 7. 1). In addition, several tribes have indicated that many of the O 3 - sensitive species (including bioindicator species) are culturally significant (U.S. EPA, 2014c, Table 5

- 1). With respect to agricultural species, such visible effects of O 3 exposure can aff ect the market value of certain crops and ornamentals for which leaves are the product, such as spinach (U.S. EPA, 20 06b , p . AX

- 9

- 189 )

. The PA additionally notes CASAC comments that “visible foliar injury can impact public welfare by damaging or impairing the intended use or service of a resource”, including through “visible damage to ornamental or leafy crops that affects their economic value, yield, or usability; visible damage to plants with special cultural significance; and visible damage to species o ccurring in natural settings valued for scenic beauty or recreational appeal” (Frey, 2014c, p. 10).*** E.O. 12866 Review

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Page 385 of 647 With regard to the exposure and risk

- based information, the PA takes note of the WREA analyses of the nationwide dataset (2006

- 2010) for USFS/FHM biosites, including the observation that the proportion of biosites with injury varies with soil moisture conditions and O 3 W126 index values (U.S. EPA, 2014b, Chapter 7, Figure 7

- 10; U.S. EPA, 2014c, section 5.4.2). These analyses indicate that the proportion of bi osites showing visible foliar injury incidence increases steeply with W126 index values up to approximately 10 ppm

- hrs, with little difference in incidence across higher W126 index levels. The screening

- level assessment of national parks indicated that ris k of visible foliar injury is likely to be lower in most national parks after simulating just meeting the current standard , although visible foliar injury would likely continue to occur at lower O 3 exposures, including some sensitive species growing in National Parks and other Class I areas that may provide important cultural ecosystem services to the public. The PA also notes the WREA recognition that many of the outdoor recreational activities which directly depend on the scenic value of the area are o f significant importance to public welfare as they are enjoyed by millions of Americans every year and generate millions of dollars in economic value (U.S. EPA, 2014b, Chapter 5, Chapter 7). In reaching conclusions regarding support for the adequacy of th e current secondary standard provided by the currently available information on O 3 - induced visible foliar injury, the PA took note of: (1) the evidence for many species of native plants, including trees, that have been observed to have visible foliar injur y symptoms in both OTC and field settings, some of which have also been identified as bioindicators of O 3 exposure by the USFS; (2) the finding that visible foliar injury incidence can occur at very low cumulative exposures, but due to confounding by soil moisture and other*** E.O. 12866 Review

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Page 386 of 647 factors, it is difficult to predictively relate a given O 3 exposure to plant response; (3) information indicating the occurrence of visible foliar injury in some Class I areas under air quality conditions expected to meet the current sta ndard; and, (4) WREA analyses, based on USFS biosite data, indicating a relationship of the proportion of biosites showing visible foliar injury incidence with W126 index values below approximately 10
ppm - hrs (U.S. EPA, 2014c, section 5.7). The PA additi onally recognizes a lack of guidance for federal land managers regarding what spatial scale or degree of severity of visible foliar injury is considered sufficient to trigger protective action for O 3 sensitive AQRVs. Further, there does not appear to be an y consensus in the literature in this regard, and CASAC, while identifying benchmarks to consider for percent biomass loss and yield loss for tree seedlings and commodity crops, respectively, did not provide a similar recommendation for this endpoint. Like wise, as in previous reviews, the ISA notes the difficulty in relating visible foliar injury symptoms to other vegetation effects such as individual plant growth, stand growth, or ecosystem characteristics (U.S. EPA, 2013, section 9.4.2, p. 9

- 39) and furth er notes that the full body of evidence indicates that there is wide variability in this endpoint, such that although evidence shows visible foliar injury can occur under very low cumulative O 3 concentrations, “...the degree and extent of visible foliar inju ry development varies from year to year and site to site..., even among co

- members of a population exposed to similar O 3 levels, due to the influence of co

- occurring environmental and genetic factors” (U.S. EPA, 2013, section 9.4.2, p. 9

- 38). Given the abo ve, and taking note of CASAC views, the PA recognizes visible foliar injury as an important O 3 effect which, depending on severity and spatial extent,*** E.O. 12866 Review

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Page 387 of 647 may reasonably be concluded to be of public welfare significance, especially when occurring in nationally protected areas. While noting the uncertainties associated with describing the potential for visible foliar injury and its severity or extent of occurrence for any given air quality conditions, the PA notes the occurrence of O 3 - induced visible foliar inju ry in areas, including federally protected Class I areas that meet the current standard, and suggests it may be appropriate to consider revising the standard to achieve greater protection, while recognizing that the degree to which O 3 - induced visible folia r injury would be judged important and potentially adverse to public welfare is uncertain (U.S. EPA, 2014c, section 5.7). With regard to other welfare effects, for which the ISA determined a causal or likely causal relationships with O 3 in ambient air, su ch as alteration of ecosystem water cycling and changes in climate, the PA concludes there are limitations in the available information which affect our ability to consider potential impacts of air quality conditions associated with the current standard.
I n reaching conclusions on options for the Administrator’s consideration, the PA indicates that the final decision to retain or revise the current secondary O 3 standard is a public welfare policy judgment to be made by the Administrator, based on her judgme nt as to what level of air quality would be requisite (i.e., neither more nor less stringent than necessary) to protect the public welfare from any known or anticipated adverse effects. This final decision will draw upon the available scientific evidence f or O 3 - attributable welfare effects and on quantitative analyses of vegetation and ecosystem exposures and associated risks to vegetation, ecosystems and their associated services, and judgments about the appropriate weight to place on the range of uncertai nties inherent in the*** E.O. 12866 Review

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Page 388 of 647 evidence and analyses. In making this decision, the Administrator will need to weigh the importance of these effects and their associated ecosystem services in the overall context of public welfare protection. Based on the considerations described in the PA and summarized here, the PA concludes that the currently available evidence and exposure/risk information call into question the adequacy of the public welfare protection provided by the current standard and provides support for considering potential alternative standards to achieve increased public welfare protection, especially for sensitive vegetation and ecosystems in federally protected Class I and similar ly protected areas. In this conclusion, staff give s particular weight to the evidence indicating the occurrence in Class I areas that meet the current standard of cumulative seasonal O 3 exposures associated with estimates of tree growt h impacts of a magnitude that may reasonably be considered important to public welfare. 2. CASAC Advice Beyond the evidence

- and exposure/risk

- based considerations in the PA discussed above, EPA’s consideration of the adequacy of the current secondary standard also takes into account the advice and recommendations of CASAC

. In its advice offered in the current review, based on the updated scientific and technical record since the 2008 rulemaking, the CASAC stated that they “support the conclusion in the Second Draft PA that the current secondary standard is not adequate to protect against current and anticipated welfare effects of ozone on vegetation” (Frey, 2014c, p. iii) and that the PA “ clearly demonstrat es that ozone

- induced injury may occur in areas that meet the current standard” (Frey, 2014c, p. 12). The Panel further stated “[w]e support EPA’s continued emphasis on Class I and other protected areas” (Frey,*** E.O. 12866 Review

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Page 389 of 647 2014c, p. 9). Additionally, the CASAC indicat ed support for the concept of ecosystem services “as part of the scope of characterizing damage that is adverse to public welfare” and “concurs that trees are important from a public welfare perspective because they provide valued services to humans, inclu ding aesthetic value, food, fiber, timber, other forest products, habitat, recreational opportunities, climate regulation, erosion control, air pollution removal, and hydrologic and fire regime stabilizatio n” (Frey, 2014c, p. 9). Similar to comments from C ASAC in the last review, including comments on the proposed reconsideration, t he current CASAC also endorsed the PA discussions and conclusions on biologically relevant exposure metrics and the focus on the W126 index accumulated over a 12

- hour period (8am

– 8pm) over the three

- month summation period of a year resulting in the maximum value (Frey, 2014c, p. iii)

. In addition, CASAC stated that “relative biomass loss for tree species, crop yield loss, and visible foliar injury are appropriate surrogates for a wide range of damage that is adverse to public welfare” (Frey, 2014c, p. 10). With respect to relative biomass loss for tree species, CASAC states that it is appropriate to “include levels that aim for not greater than 2% RBL for the median tree species ” and that a media n tree species RBL of 6% is “unacceptably high." With respect to crop yield loss, CASAC points to a benchmark of 5%, stating that a crop RYL for median species over 5% is “unacceptably high ” (Frey, 2014c, p. 13). 3. Administrator’s Propos ed Conclusions on Adequacy of the Current Standard In considering the adequacy of the current secondary O 3 standard, the Administrator has considered the assessment of the current evidence in the ISA , findings of the WREA, including associated limitations and uncertainties, considerations and staff*** E.O. 12866 Review

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Page 390 of 647 conclusions and associated rationales presented in the PA, views expressed by CASAC, and public comments. In taking into account the information discussed above with regard to the nature of O 3 - related effects o n vegetation , the Administrator has taken particular note of: the PA analysis of the magnitude of tree seedling growth effects (biomass loss) estimated for different cumulative, seasonal, concentration

- weighted exposures in terms of the W126 metric; the m onitoring analysis in the PA of W126 exposures occurring in locations where the current standard is met, including those locations in C lass I areas, and associated estimates of tree seedling growth effects; the analyses in the W REA illustrating the geograp hic distribution of tree species for which E

R functions are available and relative differences estimated for O 3 - related growth impacts across areas of the U.S. for the air quality scenarios , taking into account the identified potential for the WREA’s scen ario for the current standard to underestimate the highest
W126

- based O 3 values that would be expected to occur. As an initial matter, the Administrator recognizes the appropriateness and usefulness of the W126 metric, as described in sections IV.B.1 and IV.D.1 above, in evaluating O 3 exposures of potential concern for vegetation effects. In so doing, the Administrator additionally notes support conveyed by CASAC for such a use for this metric. With regard to considering the adequacy of public welfare protection provided by the current secondary standard, the Administrator focuses first on welfare effects related to reduced native plant growth and productivity in terrestrial ecosystems, taking no te of the ISA conclusion of a causal relationship between O 3 in the ambient air and these effects. In considering the assessment of the information available in this review with*** E.O. 12866 Review

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Page 391 of 647 regard to O 3 effects on vegetation growth and productivity, the Administrator takes note of the evidence from OTC studies of the effects of O 3 exposure on tree seedling growth that support robust E

- R functions for 11 tree seedling species, and the characterization of growth effects across these species for different cumulative seaso nal concentration

weighted exposures using the W126 metric. Reductions in growth of sensitive species, as recognized in section IV.B above, have the potential to result in effects on ecosystem productivity, as well as, on forest and forest community compos ition. The Administrator takes particular note of the evidence, described in section IV.D.1 above, of the occurrence in Class I areas during periods where the current standard is met of cumulative seasonal O 3 exposures for which median species RBL estimate s are of a magnitude that CASAC has termed “unacceptably high .” In so doing, the Administrator also takes note of a number of actions taken by Congress to establish public lands that are set aside for specific uses intended to provide benefits to the publi c welfare, including lands that are to be protected so as to conserve the scenic value and the natural vegetation and wildlife within such areas for the enjoyment of future generations. Such public lands that are protected areas of national interest inclu de national parks and forests, wildlife refuges, and wilderness areas (many of which have been designated Class I areas). 189
W hile recognizing the variability in the various environmental factors that can influence the occurrence and severity of the effect of ambient O 3 concentrations on vegetation in different locations, the Administrator concludes that the information referenced above including the currently available, extensive evidence base and also

189 As noted in section IV.A above, Congress has established areas such as national parks and wilderness areas with spe cific purposes including the preservation of the areas for future generations, and has identified many of those areas as Class I areas

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Page 392 of 647 factors affecting the significance of impacts to publi c welfare, as well as WREA estimates regarding the potential for occurrence of impacts important to public welfare, provides an appropriate b asis to inform a conclusion as to whether the current standards provide adequate protection against O 3 - related vege tation effects on public welfare

. With regard to the results of the monitoring analysis, the Administrator takes note of the PA conclusions that the impacts on tree growth ( and the potential for associated ecosystem effects ) estimated for W126 values found to occur in Class I areas when meeting the current standard are reasonably concluded to be important from a public welfare standpoint in terms of both the magnitude of the vegetation effects and the significance to public welfare of such effects in such a reas, calling into question the adequacy of the current secondary standard. The Administrator also recognizes t he causal relationship s between O 3 in the ambient air and visible foliar injury, reduced yield and quality of agricultural crops and alteration of below

- ground biogeochemical cycles associated with effects on growth and productivity. As to visible foliar injury, the Administrator takes note of the complexities and limitations in the evidence base regarding characterizing air quality conditions wi th respect to the magnitude and extent of risk for visible foliar injury. She additionally recognizes the challenges of associated judgments with regard to adversity of such effects to public welfare. In taking note of the conclusions with regard to crop s, s he recognizes the complexity of considering adverse O 3 impacts to public welfare due to the heavy management common for achieving optimum yields and market factors that influence associated services and additionally takes note of the PA conclusions tha t placing*** E.O. 12866 Review

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Page 393 of 647 emphasis on the protection afforded to trees inherently also recognizes a level of protection afforded for crops

. Based on her consideration of the conclusions in the PA , and with particular weight given to PA findings pertaining to tree growth

- r elated effects, as well as with consideration of CASAC’s conclusion that the current standard is not adequate, the Administrator pro poses to conclude that the current standard is not requisite to protect public welfare from known or anticipated effects and that revision is needed to provide increased public welfare protection, especially for sensitive vegetation and ecosystems in federally protected Class I areas and in other areas providing similar public welfare benefits. T he Administrator further conclud e s that the scientific evidence and quantitative analyses on tree growth

- related effects provide strong support for consideration of alternative standards that would provide increased public welfare protection beyond that afforded by the current O 3 seconda ry standard. She further notes that a revised standard would provide increased protection for other growth

- related effects, including for carbon storage and for areas for which it is more difficult to determine public welfare significance, as recognized in section IV.B.2 above, as well other welfare effects of O 3 , including visible foliar injury and crop yield loss.
In giving particular focus to growth

- related effects on public welfare, the Administrator additionally recognizes that there are alternative a pproaches to viewing the evidence and information, including alternative approaches to viewing, evaluating, and weighing important uncertainties. In some cases, these alternative approaches have been expressed by public commenters, leading some public comm enters to recommend retaining the current standard. Given these alternative views, in addition to proposing to*** E.O. 12866 Review

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Page 394 of 647 revise the current secondary standard, the Administrator also solicits comment on the option of retaining the standard without revision

. E. Consi deration of Alternative Secondary Standards Given her proposed conclusion that the current secondary standard is inadequate, the Administrator has then considered what revisions to the standard may be appropriate, focusing on revisions to the key standard elements of indicator, form, averaging time, and level. On the basis of the strength and coherence of the vegetation effects evidence indicating a cumulative, seasonal, concentration

- weighted metric as the most appropriate approach for judging potential im pacts of and protection from O 3 in ambient air, the Administrator judges that it is appropriate to consider revisions to the secondary standard that reflect this understanding and to use such a metric in identifying an appropriate level of protection and c onsidering the protection afforded by potential alternative standards. The Administrator also judges that the current averaging time and form may also provide protection to vegetation when set at an appropriate level. Therefore, the Administrator considere d whether revision to the level of the current secondary standard might provide sufficient protection to also achieve the level of air quality that is determined requisite to protect the public welfare. The sections below address the indicator for the sec ondary standard (section IV.E.1), consideration of a cumulative, seasonal exposure

- based standard in the PA (section IV.E.2), CASAC advice and public input (section IV.E.3), analyses of air quality in the PA and subsequent to the PA (section IV.E.4) and th e Administrator’s proposed conclusions regarding an alternative secondary standard (section IV.E.5) 1. Indicator*** E.O. 12866 Review

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Page 395 of 647 In the last review of the air quality for O 3 and other photochemical oxidants and of the O 3 standard, as in other prior reviews, the EPA focus ed on a standard for O 3 as the most appropriate surrogate for ambient photochemical oxidants. Ozone is a long

established surrogate for ambient photochemical oxidants, among which it is by far the most widely studied with regard to effects on welfare and specifically on vegetati on. The information available in this review adds to the understanding of the atmospheric chemistry for photochemical oxidants an d O 3 in particular (as described in the ISA, sections 3.2 and 3.6, and summarized in section 2.2 in the PA ). The 1996 Staff Pap er noted that the database on vegetation effects is generally considered to raise concern at levels found in the ambient air for O 3 and, therefore, control of ambient O 3 levels has previously been concluded to provide the best means of controlling other ph otochemical oxidants of potential welfare concern (U.S. EPA, 1996b, p. 277). In the current review, while the complex atmospheric chemistry in which O 3 plays a key role has been highlighted, no alternatives to O 3 have been advanced as being a more appropri ate surrogate for ambient photochemical oxidants. Ozone continues to be the only photochemical oxidant ( other than nitrogen dioxide ) that is routinely monitored and for which a comprehensive database exists (U.S. EPA, 2013, section 3.6). Thus, the Adminis trator concludes that ozone is the appropriate indicator and proposes to continue to use O 3 as indicator for a secondary standard that is intended to address effects associated with exposure to O 3 , alone and in combination with related photochemical oxidan ts. In so doing, the Administrator recognizes that measures leading to reductions in ecosystem exposures to O 3 will also reduce exposures to other photochemical oxidants.*** E.O. 12866 Review

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Page 396 of 647 2. Consideration of a Cumulative, Seasonal Exposu re - based Standard in the Policy
Asse ssment
I n recognition of the extensive evidence supporting a cumulative, seasonal exposure index as a biologically relevant metric for assessing potential for O 3 effects on vegetation , discussed in sections IV.B.1 above, as well as advice from CASAC in the current and last O 3 NAAQS reviews, summarized in sections IV.D.3 above and IV.E.3 below, the PA focused its consideration of alternative standards on a revised secondary standard based on a cumulative, seasonal, concentration

- weighted form. The PA conside r ed the currently available information that has been critically analyzed and characterized in the ISA, the risk and exposure information presented in the WREA, and CASAC advice and public comment w ith regard to support for consideration of options for alt ernative standards that might be expected to provide increased protection from ambient O 3 exposures over the current standard. a. Form and Averaging Time In considering potential forms for a revised secondary standard, the PA considers the characterization of the evidence in the ISA, summarized in section IV.B.1 above, including the ISA conclusion that exposure indices that cumulate and differentially weight the higher hourly average concentrations over a season and also include the mid

level values , such as the W126 index, offer the most scientifically defensible approach for characterizing vegetation response to ambient O 3 and comparing study findings, as well as for defining indices for vegetation protection (U.S. EPA, 2013, section 2.6.6.1). The PA additionally considers CASAC advice in the current review, as well as that from the last review, all of which provided support for such a form. Thus, in considering*** E.O. 12866 Review

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Page 397 of 647 alternative forms of a revised standard , the PA conclude s that it is reasonable and appropriate to consider a cumulative, concentration

- weighted form to provide protection against cumulative, seasonal exposures to O 3 that are known or anticipated to harm sensitive vegetation or ecosystems. The PA recognizes that s uch a metric is specifically designed to focus on the kind of O 3 exposures that have been shown to cause harm to vegetation and states that it would have a distinct advantage over the form of the current standard in characterizing air quality conditions p otentially of concern for vegetation and in more directly demonstrating that the des ired degree of protection against those conditions was being achieved (U.S. EPA, 2014c, sections 6.2 and 6.6). With regard to the appropriate index for a cumulative seaso nal form, the PA considers the evidence and background for a number of different cumulative concentration weighted indices that have been developed and evaluated in the scientific literature and in past NAAQS reviews in terms of their ability to predict ve getation response and their usefulness in the NAAQS context (U.S. EPA, 2006, pp. 9

- 11 to 9

- 15 and pp. AX9

- 159 to AX9

- 187; U.S. EPA, 2007, pp. 7

- 15 to 7

- 16 ). While these various forms have different strengths and limitations, the PA notes the ISA conclusio n that the W126 index , described in section IV.B.1 above, has some important advantages over other non

- sigmoidally weighted cumulative indices , including its lack of a cut

- off in its weighting scheme which allows fo r cumulation of lower O 3 concentrations ( U.S. EPA, 2013, section 9.5; U.S. EPA, 2014c, sections 6.2 and 6.6). Additionally, the W126 metric adds increasing weight to hourly concentrations from about 40 ppb to about 100 ppb, which is an important feature because “as hourly concentrations become h igher, they become increasingly likely to overwhelm plant defenses and are known to be more*** E.O. 12866 Review

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Page 398 of 647 detrimental to vegetation” (U.S. EPA, 2013, p. 9

- 104). The PA additionally take s note of CASAC advice in the current and last review that concurred with a focus on the W126 form (Frey, 2014c, p. iii ; Henderson, 2006; Samet, 2010). Based on the considerations summarized here, the PA conclude s that the W126 index is the most appropriate cumulative seasonal form to consider in the context of the secondary O 3 NAAQS revie w. The PA next considers the exposure periods

– diurnal and seasonal

– over which the W126 index would be summed in any given year. T he currently available information continues to provide support for a definition of the diurnal period of interest as the 12

- hour period from 8:00 am to 8:00 pm , which EPA identified in past reviews as appropriately capturing the diurnal window with most relevance to the photosynthetic process (U.S. EPA, 2013, section 9.5.3 ; 72 FR 37900 , July 11, 2007 ) . The CASAC has
genera lly supported th is 12

- hour daylight period as well (Frey, 2014c ; Henderson, 2006, 2007). Based on these considerations, the PA conclude s that the 12

- hour daylight window (8:00 am to 8:00 pm) represents the portion of the diurnal exposure period that is

mo st relevant to predicting or inducing plant effects related to photosynthesis and growth and thus is an appropriate diurnal period to use in conjunction with a W126 cumulative metric (U.S. EPA, 2014c, sections 6.2 and 6.6) . With regard to a seasonal period of interest, the current evidence base continues to provide support for a seasonal period with a minimum duration of three months, as described more fully in the ISA and considered in the PA (U.S. EPA, 2013, section 9.5.3; U.S. EPA, 2014c, sections 6.2 an d 6.6). The CASAC has also indicated support for such a th ree month period (Frey, 2014c ; Samet, 2010; Henderson , 2006). The PA thus concludes that it is appropriate to identify the*** E.O. 12866 Review

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Page 399 of 647 seasonal W126 index value as that derived from the consecutive 3

- month peri od within the O 3 season with the highest W126 index value. The PA a dditionally consider s the period of time over which a cumulative seasonal W126

- based standard should be evaluated , considering the support for both a single year form and a form averaged over three years ( U.S. EPA, 2014c , pp. 6

- 29 through 6

- 33 ). T he PA consider s the evidence of effects associated with single year and multiple year exposures as well as their potential public welfare significance. The PA also consider s comments from CASAC, including their comment in the current review that “[t]he CASAC does not recommend the use of a three

- year averaging period” and that they “favor a single

- year period for determining the highest three

- month summation which will provide more protection for annual crops and for the anticipated cumulative effects on perennial species” (Frey, 2014c, p. iii). The PA considered O 3 - induced effects that can occur with a single year’s exposure, including visible foliar injury, growth reduction in annual and perenn ial species and yield loss in annual crops (U.S. EPA, 2014c, section 6.3). While recognizing that there are a number of O 3 - induced effects that have the potential for public welfare significance within the annual timeframe , the PA also notes the uncertaint ies associated with these effects that complicate consideration of the level of appropriate protection on an annual basis for such effects in ord er to protect the public welfare from known or anticipated adverse effects , and thus recognizes the possibility that a multiple

- year form could be considered to provide a more consistent target level of protection for certain effects (U.S. EPA, 2014c, pp. 6

- 29 to 6

- 31). With regard to visible foliar injury, the ISA notes that “the degree and extent of visible folia r injury development varies from year to*** E.O. 12866 Review

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Page 400 of 647 year and site to site ... even among co

- members of a population exposed to similar O 3 levels, due to the influence of co

- occurring environmental and genetic factors” (U.S. EPA, 2013, p. 9

- 38; U.S. EPA, 2014c, p. 6

- 30) . Additionally, the PA takes note of the difficulty and complexity shown by the WREA analyses with regard to identifying W126 index values that would provide consistent protection on an annual basis given likely fluctuations in annual O 3 and soil moisture conditions (U.S. EPA, 2014c, p. 6

- 30). The PA additionally notes evidence of some O 3 effects on perennial species that may result from a single season’s elevated O 3 exposures, such as reduced bud size or starch content, which may have the potential for som e “carry over” of effects on plant growth or reproduction in the subsequent season. Another effect where such potential for “carry over” has been noted with elevated O 3 exposure is reduction in below

- ground carbohydrate reserves which can impair growth in subsequent seasons ( U.S. EPA, 2014c, pp. 6

- 30 to 6

- 31; U.S. EPA, 2013, pp. 9

- 43 to 9

- 44 and p. 9

- 86). The PA notes that the occurrence of such annual effects of elevated O 3 exposures over multiple years may contribute to a potential to be compounded, incre asing the potential for effects at larger scales (e.g., population, ecosystem). In the PA, staff notes that multiple consecutive years of critical O 3 exposures might be expected to result in larger impacts on forested areas than intermittent occurrences of such exposures due to the potential for compounding or
carry - over effects on tree growth (U.S. EPA, 2014c, pp. 6

- 29 to 6

- 31). In light of the above summarized considerations for potential compounding of
carry - over effects, the PA conclude s that the publi c welfare significance of the effects that can occur as a result of three

- year O 3 exposures are potentially greater than those associated with a single year of such exposure. Thus, to the extent that the focus for*** E.O. 12866 Review

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Page 401 of 647 public welfare protection to be afforded b y the secondary O 3 standard is on long

- term effects that occur in sensitive tree species in natural forested ecosystems, including federally protected areas such as Class I areas or on lands set aside by States, Tribes and public interest groups to provide similar benefits to the public welfare, the PA concludes that a standard with a form that evaluates the cumulative seasonal index across multiple years might be considered to provide a more appropriate match to the nature of O 3 - related effects on vegetati on upon which the secondary O 3 standard is focused. In considering such forms, the PA focuses on one that ave rages the W126 index values across three years (U.S. EPA, 2014c, section 6.2). With regard to single

- year and three

- year forms, the PA considers a WREA analysis that examined the extent to which cumulative RBL across a three

- year period might be underestimated when each year’s RBL is derived from the three

- year average W126 index value versus each single

- year W126 index value for each of three years (in which no other influence on plant growth is presumed to change). This analysis indicates that use of th e 3

- year average may lead to an underestimation , although of relatively small magnitude (U.S. EPA, 2014b, section 6.2.1.4). The PA notes that this limited analysis does not account for moisture levels and other environmental factors that could affect plant growth and that vary from year to year. W hen considering an appropriate level for a form that averages W126 index values across three years, the P A also recognizes the importance of considering the extent to which the cumulative effect of diff erent average W126 exposures across the three

- year period would be judged adverse (U.S. EPA, 2014c, p. 6

- 31).*** E.O. 12866 Review

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Page 402 of 647 Although single

- year W126 index values were not s eparately analyzed in th e PA analysis of recent monitor ing data, the data indicate appreciable variation in cumulative, seasonal O 3 concentrations among monitor locations meeting different levels of a standard of the current form (U.S. EPA 2014c, section 6 .Appendix 2B)

. Therefore, a standard with an annual form would have the cumulative seasonal index values be at or lower than the level of the standard in all years and, noting the inter

- annual observed variability in seasonal W126 index values, could be app reciably below the standard level in some years. For a standard with a form that averages the cumulative seasonal index values across three consecutive years, the annual seasonal index value could be above the level in some years, but would have to be belo w it in others within the same 3

- year period, thus restricting the air quality for a given area to have no more than two years out of three with a W126 index value above the standard level, and depending on magnitude of each year’s index, potentially havin g no more than one. In its consideration of one year as compared to three year forms, the PA also considers implications with regard to stability of air quality programs that implement the NAAQS (U.S. EPA, 2014c, pp. 6

- 31 to 6

- 32). The PA notes that a sta ndard based on a single year W126 index would be expected to have a less stability relative to a standard based on a form that averages seasonal indices across three consecutive years, given the potential for large year

- to

- year variability in annual W126 i ndex values in areas across the country. Thus, a three

- year evaluation period can contribute to greater public welfare protection by limiting year

- to

- year disruptions in ongoing control programs that would occur if an area was frequently shifting in and ou t of attainment due to extreme year

- to

year variations in meteorological conditions. This greater stability in air quality*** E.O. 12866 Review

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Page 403 of 647 management programs would thus facilitate achievement of the protection intended by a standard. Such considerations of stability ofte n receive particular weight in NAAQS reviews, such as those resulting in selection of the form for the current O 3 primary and secondary standards (62 FR 38856, July 18, 1997), as well as the primary standards for nitrogen dioxide ( 75 FR 6474 , February 9, 2 010) and sulfur dioxide ( 75 FR 35520 , June 22, 2010). See also ATA III , 283 F. 3d at 374

- 75 (recognizing programmatic stability as a legitimate consideration in the NAAQS standard

- setting process). Thus, to the extent that emphasis continues to be placed o n protecting against effects associated with multi

- year exposures and maintaining more year

- to

- year stability of public welfare protection, the PA conclude s that it is appropriate to consider a secondary standard form that is an average of the seasonal W12 6 index values across three consecutive years. The PA conclude s that such a form might be appropriate for a standard intended to achieve the desired level of protection from longer

- term effects, including those associated with potential compounding , and th at such a form might be concluded to contribute to greater stability in air quality management programs, and thus, greater effectiveness in achieving the desired level of publ ic welfare protection, than that might result from a single year form (U.S. EPA, 2014c, section 6.6). The PA additionally recognized that to the extent the Administrator finds it useful to consider the public welfare protection that might be afforded by a revised primary standard, this is appropriately judged by evaluating the impact of attainment of such a revised primary standard on O 3 exposures in terms of the cumulative seasonal W126

- based exposure index. b. Level*** E.O. 12866 Review

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Page 404 of 647 In considering an appropriate range of levels to consider for a W126

- based standard, the PA notes that , due to the var iability in the importance of the associated ecosystem services provided by different species at different exposures and in different locations, as well as differences in associated uncertainties and limitations, both the species present and their public w elfare significance , in addition to the magnitude of the ambient concentrations, are essential considerations in drawing conclusions regarding the significance or magnitude of public welfare impact. Therefore, in development of the PA conclusions, staff to ok note of the complexity of judgments to be made by the Administrator regarding the adversity of known and anticipated effects to the public welfare and recognized that the Administrator’s ultimate judgments on the secondary standard will most appropriate ly reflect an interpretation of the available scientific evidence and exposure/risk information that neither overstates nor understates the strengths and limitations of that evidence and information. As described in section IV.D.1 above, the PA employed a paradigm, which has evolved over the course of the O 3 and other secondary NAAQS reviews , t o assist in putting the available science and exposure/risk information into the public welfare
context (U.S. EPA, 2014c, section 5.1). This paradigm recognizes that the significance to the public welfare of O 3 - induced effects on sensitive vegetation growing within the U.S. can vary depending on the nature of the effect, the intended use of the sensitive plants or ecosystems, and the types of environments in which the sensitive vegetation and ecosystems are located. Accordingly, any given O 3 - related effect on vegetation and ecosystems (e.g., biomass loss, crop yield loss, visible foliar injury) may be judged to have a different degree of impact on or significance to th e public welfare depending, for*** E.O. 12866 Review

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Page 405 of 647 example, on whether that effect occurs in a Class I area, a city park, or commercial cropland. This approach also includes consideration of impacts to ecosystem goods and services , which are an important category of public w elfare effects with an obvious relationship to consideration of intended use (73 FR 16492 , March 27, 2008 ). In considering potential levels for an alternative standard based on the W126 metric, the PA focus ed primarily on impacts on tree growth , crop yiel d loss , and visible foliar injury , as well as impacts on the associated ecosystem services, while taking note of the uncertainties and limitations associated with several key aspects of this information. In addition to uncertainties related to the WREA air quality scenarios and assessments summarized in section IV.C above, the PA also recognized uncertainties associated with the evidence underlying the tree seedling and crop E

- R functions (U.S. EPA, 2014c, section 6.3). These include u ncertainties regarding intra

- species variability due to the different numbers of studies that exist for different species so that the weight of evidence is not the same for each species. Those species with more than one study show variability in response and E

- R functions. The potential variability in less well

- studied species is, however, unknown (U.S. EPA, 2013, pp. 9

- 123 to 9

- 125; U.S. EPA, 2014b, section 6.2.1.2, and Table 6

- 27). The PA also recognizes uncertainty regarding the extent to which tree seedling E

- R functions can be used to represent mature trees since seedling sensitivity has been shown in some cases to not reflect mature tree O 3 sensitivity in the same species and uncertainty in the relationship of O 3 effects on tree seedlings (e.g., relative biomass loss) in one or a few growing seasons to effects that might be expected to accrue over the life of the trees extending into adulthood (U.S. EPA, 2013, section 9.6*** E.O. 12866 Review

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Page 406 of 647 and pp. 9

- 52 to 9

- 53; U.S. EPA, 2014b, sec tions 6.2.1.1, 6.2.1.4 and Tables 6

- 5 and 6

- 27). With respect to tree growth, the PA gave primary consideration to relative biomass loss estimates derived from the E

- R functions, described in section IV.B.1.b above and in the PA , while also considering W REA risk/exposure estimates related to this effect (U.S. EPA, 2014c, section 6.4). The PA takes note of the different index value estimates presented in Table 6

- 1 of PA (Table 8 below) with regard to the number of

s tudied species below different response b enchmarks, as well as with reg ard to the median response. The PA additionally considers the WREA estimates regarding: (1) percent of assessed geographic area exceeding 2% weighted relative biomass (U.S. EPA, 2014c, Table 6

- 2); (2) number of assessed Class I areas with tree seedling weighted relative biomass loss estimates below 2% (U.S. EPA, 2014c, Table 6

- 3); and (3) the percent median biomass loss across counties for different air quality scenarios (U.S. EPA, 2014c, Table 5

- 5). The PA further notes other WREA estimates for effects on ecosystem services related to public welfare, such as carbon sequestration and air pollutant removal. With respect to crop yield loss, the PA notes the summary of RYL estimates for individual crop species and for the median ac ross species (Table 8 ), and the WREA risk/exposure estimates (U.S. EP A , 2014 b , Section 6.3). The PA also notes information available on visible foliar damage to species occurring in areas preserved for their natural character , such as federal Class I areas , and the analyses in the WREA evaluating biosite data and several benchmarks of injury (U.S. EPA, 2014b, section 5.4.2 )

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Page 407 of 647 Table 8. Tree Seedling Biomass Loss and Crop Yield Loss Estimated for O 3 Exposure over a Season
W126 value for exposure period Tree seedling RBL A Crop RYL C

Median Value Individual Species Median Value Individual Species 21 ppm - hrs Median species w.

6.8 % loss B < 2% loss: 3/11 species

< 5% loss : 5/11 species < 10% loss : 7/11 species < 15% loss : 10/11 species >40% loss: 1/11 species Median species w. 7.7 % loss D < 5% loss: 4/10 species

>5,<10% loss : 3/10 species >10,<20% loss : 3/10 species

19 ppm - hrs Median species w.

6.0 % loss B < 2% loss: 3/11 species

<5% loss : 5/11 species < 10% loss : 7/11 species < 15% loss : 10/11 species >30% loss: 1/11 species Median species w. 6.4 % loss D < 5% loss: 5/10 s pecies

>5, <10% loss : 3/10 species >10,<20% loss : 2/10 species

17 ppm - hrs Median species w.

5.3 % loss B < 2% loss: 5/11 species

<5% loss: 5/11 species < 10% loss: 9/11 species < 15% loss: 10/11 species >30% loss: 1/11 species Median species w. 5.1 % loss D < 5% loss: 5/10 species

>5, <10% loss : 3/10 species >10,<20% loss : 2/10 species

15 ppm - hrs Median species w.

4.5 % loss B < 2% loss: 5/11 species

< 5% loss: 6/11 species < 10% loss: 10/11 species >30% loss: 1/11 species Median species w. < 5% loss D < 5% loss: 6/10 species

>5, <10% loss : 4/10 species

13 ppm - hrs Median species w.

3.8 % loss B < 2% loss: 5/11 species

<5% loss: 7/11 species <10% loss: 10/11 species >20% loss: 1/11 species Median species w. < 5% loss D < 5% loss: 6 /10 species

>5, <10% loss : 4/10 species

11 ppm - hrs Median species w.

3.1 % loss B < 2% loss: 5/11 species

< 5% loss: 8/11 species < 10% loss: 10/11 species >20% loss: 1/11 species Median species w. < 5% loss D < 5% loss: 9/10 species

>5, <10% loss : 1/10 species

9 ppm - hrs Median species w.

2.4% loss B < 2% loss: 5/11 species

< 5% loss: 10/11 species >20% loss: 1/11 species Median species w. < 5% loss D < 5% loss: all species

7 ppm - hrs Median species w.

< 2% loss B < 2% loss: 7/11 species

< 5% loss: 10/11 species >15% loss: 1/11 species Median species w. < 5% loss D < 5% loss: all species

A Estimates are based on the 11 E

- R functions for tree seedlings described in WREA, Appendix 6F and discussed in the PA, section 5.2.1, with the exclusion of cottonwood in consideration of CASAC comments on differences of that study from the other controlled E

- R studies (Frey, 2014b, 2014c)

. B This is the median of the composite E

- R functions for 11 tree species from the WREA, Appendix 6F (discussed in the PA, section 5.2.1). C Estimates here are based on the 10 E

- R functions for crops (from the PA, Appendix 6F and section 5.3.1). D This median value is the median of the composi te E

- R functions for 10 crops from WREA, Appendix 6F (als o discussed in the PA, section 5.3.1).*** E.O. 12866 Review

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Page 408 of 647 Given the wide variation in sensitivity of studied tree species to O 3 - induced relative biomass loss , the PA focused consideration on both median species valu es and individual species responses and RBL estimates for a given range of W126 index values

. In this consideration, the PA took note of CASAC’s advice regarding RBL levels, specifically their emphasis on a benchmark of median relative tree biomass loss a t or below 2% and their view that a 6% median relative biomass loss is “unacceptably high

. ” The median tree species RBL estimate is at or below 2% only at the lowest W126 level assessed, 7 ppm

- hrs. A t incrementally higher W126 index level s , the median RBL is also incrementally higher , so that at W126 index values of 9, 11, 13, 15, 17 and 19 ppm - hrs , the median RBL increases to 2.4%, 3.1%, 3.8%, 4.5%, 5.3% and 6.0%, respectively. Thus , the median species biomass loss is below 6%, the level characterized by the CASAC as unacceptably high, across the W126 range of 7 to 17 ppm

- hrs, for which it varies from approximately 2% to approximately 5%. Given this finding, the PA discussion of a range of levels appropriate to consider focuses on this range. In focusing on this range , the PA considers the full array of CASAC advice with regard to interpretation of the evidence and exposure/risk information on vegetation

- related effects of O 3 , as well as the role of the Administrator’s judgments in identifying the level of air*** E.O. 12866 Review

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Page 409 of 647 quality that is requisite to protect public welfare from adverse effects, as noted in section IV.A above. 190
The PA recognizes that public welfare judgments may reasonably be informed by a range of biomass loss benchmarks , in contexts of considering both median RBL estimates and RBL estimates for individual species

. Accordingly, in considering individual tree species estimates, the PA notes the value of additionally characterizing the RBL estimates in comparison to higher loss levels such as 10% or 15 %.
For every W126 value over the full range from 7 to 17 ppm

- hrs, the RBLs for each of 5 species is less than 2% (Table 8), which is the lower benchmark that CASAC identified for tree species

. Accordingly, the PA focused attention on the remaining 6 studi ed species (i.e., eastern white pine, aspen, tulip poplar, ponderosa pine, red alder, and black cherry) to evaluate the protection against tree seedling biomass loss at different W126 levels within the range from 17 to 7 ppm

- hrs

. At a W126 index value of 1 7 ppm

hrs, one of these species (red alder) has a RBL estimate below 6% , while at the W126 index value of 7 ppm

- hrs, five species have RBLs below 6% (eastern white pine, aspen, tulip poplar, ponderosa pine, red alder). Taken together with the more tolerant species, the proportion of the studied tree species with RBLs below 6% are 6 of 11, 7 of 11, 8 of 11, and 10 of 11 at W126 index values of 17, 15, 13, and 11 ppm

- hrs, respectively.

190 In the context of the O 3 standard, such judgments include: the weight to give the evidence of specific vegetation

- rela ted effects estimated to result across a range of cumulative seasonal concentration

- weighted O 3 exposures; the weight to give associated uncertainties, including those related to the variability in occurrence of such effects in specific areas of U.S. , such as those of particular public welfare significance ; and , judgments on the extent to which such effects in such areas may be considered adverse to public welfare.*** E.O. 12866 Review

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Page 410 of 647 With regard to other , higher, RBL benchmark levels and estimates for all 11 species, the PA notes that 9 of 11 studied tree species have a predicted RBL below 10% at the W126 level of 17 ppm

- hrs, while 10 of 11 species have a predicted RBL below 10% for W126 levels of 15 to 7 ppm

- hrs. In addition, 10 of 11 studied tree species have a predicted RBL below 15% for W126 levels of 17 to 7 ppm

- hrs. The PA notes that the RBL estimates for black cherry, the most sensitive of the 11 species, remain above 15% for W126 index values across the range from 17 to 7 ppm

- hrs , making unclear the extent to which black cherry estimates might inform consideration of different W126 exposures within this range (U.S EPA, 2014c, section 6.6 and Table 6

- 1; U.S. EPA, 2014b, section 6.2 and Appendix 6A). While recognizing the limitations and uncertainties associated with the WREA air quality scenarios with regard to their representation of conditions just meeting different
3

- year average W126 index values (as summarized in section IV.C.1 above), including the potential underestimation of the highest O 3 conc entrations, the PA additionally considers several WREA RBL analyses (U.S. EPA, 2014c, section 6.3). In t he WREA characteriz ation of the number of counties where the median RBLs were greater than 2% , 7 % of the counties have median RBLs g reater than 2% in t he 15 and 11 ppm

- hrs W126 scenario s, as compared to 8% for the current standard (U.S. EPA, 2014c, Table 5

- 5; U.S. EPA, 2014b, Table 6

- 7). The percentage is 6 % inthe 7 ppm

- hrs W126 scenario . Of the
221 counties ( 7 % of counties) estimated to have a median RB L above 2% for the 15
ppm - hrs scenario , 203 of those counties have a RBL greater than 2% because of the presence of black cherry. (U.S. EPA, 2014c, section 6.3).*** E.O. 12866 Review

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Page 411 of 647 In considering the potential magnitude of the ecosystem impact of O 3 - related biomass effects on tree growth , the PA additionally focused on the WREA estimates of weighted RBL for the W126 air quality scenarios (U.S. EPA, 2014 b , section 6.8). For the current standard and the three W126 scenarios, the percent of total assessed ar ea having weighted R BL greater than 2% was 0.2%, 0.2%, 0.1% and <0.1%, respectively (U.S. EPA, 2014c, Table 6

- 2; U.S. EPA 2014b, Table 6

- 25). In giving particular attention to estimates for Class I areas , the PA notes that f or all four scenarios , the WREA estimates indicate w eighted RBL greater than 2% in one or two of the 145 assessed nationally protected Class I areas (U.S. EPA, 2014c, sections 6.3 and 6.6)

. In considering potential impacts on ecosystem services related to reductions in O 3 effects on tree growth, the PA particularly recognize s that impacts on climate regulation can reasonably be concluded to be potentially significant from a public welfare perspective . In additionally recognizing that carbon sequestration has been identifi ed as a potentially important tool for managing anthropogenic impacts on climate , the PA considers the WREA estimates of potential increases in forestry carbon storage for ambient O 3 reductions in the th ree W126 air quality scenarios (U.S. EPA, 2014c, sect ion s 6.3 and 6.6; U.S. EPA, 2014b, section 6.6.1). The WREA estimates additional forestry carbon storage potential of 13, 593 and 1,600 MMtCO 2 e (over 30 years) for the W 126 scenarios of 15, 11 and 7 ppm

- hrs, respectively, as compared to the current standar d (U.S. EPA, 2014b , Table 6

- 18). Compared to the absolute estimate for the current standard scenario (approximately 89,000 MMtCO 2 e , over 30 years), hese amounts represent additional storage of less than 0.1 %, just under 1% and under 2% f or the 15, 11*** E.O. 12866 Review

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Page 412 of 647 and 7 ppm

- hrs scenarios, respectively (U.S. EPA, 2014b, section 6.6.1 and Appendix 6B). The PA additionally consider s the WREA estimates for five urban areas of ho w reduced growth of O 3 - sensitive trees in urban forests may affect air pollutant removal (U.S. E PA, 2014b, sections 6.6.2 and 6.7 and Appendix 6D). As with the national estimates, e stimates for all five case study areas indicate generally small differences between the current standard and the three W126 scenarios (U.S. EPA, 2014c, Table 6

- 5)

. The PA additionally notes significant uncertainties and limitations associated with
WRE A estimates related to carbon sequestration and air pollution removal ( U.S. EPA, 2014b, Table 6

- 27; U.S. EPA, 2014c, sections 6.3 and 6.6 ) , some of which are summariz ed in section IV.C.2.b above. The PA recognizes that , as with consideration of other pertinent evidence and exposure/risk information, the Administrator’s consideration of WREA estimates for these ecosystem services will involve judgments regarding the
app ropriate weight to place on such uncertainties as well as the potential impacts to the public welfare of the estimates

. The PA additionally considers the biomass effects of O 3 on crops estimated for different W126 index values across the range identified above. For this consideration, the PA focuses on the 10 crops for which robust E

- R functions have been established, as described in section IV.B.1 above: barley, lettuce, field corn, grain sorghum, peanut, winter wheat, field cotton, soybean, potato and ki dney bean (U.S. EPA, 2013; U.S. EPA, 2014b, section 6.5 and Figure 6

- 3 ). In evaluatin g this information, the PA t akes note of CASAC’s comment regarding significance of 5% for median crop relative yield loss (RYL). The PA finds that the median crop RYL is a t or below 5% for all W126 index*** E.O. 12866 Review

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Page 413 of 647 values from 7 to 17 ppm

- hrs and observes that this finding makes it unclear to what extent this information informs consideration of levels within this range. The RBL estimates for half of the ten individual species are bel ow 5% RYL at 17 ppm

- hrs

. The number of the ten individual crops with RYL below 5% is six for W126 values of 15 and 13 ppm

- hrs, nine for a W126 value of 11 ppm

- hrs and ten for W126 levels of 9 and 7
ppm - hrs. Recognizing that different crops are likely to have different values or importance to public welfare, the PA also considers the RYL estimates across the W126 range for individual species . For example, less than 5% yield loss was estimated for soybeans at W126 index value s at and below 12 ppm

- hrs , while five crops are more O 3 tolerant . The RYL estimates for four of the five (barley, lettuce, field corn, and grain sorghum) are below 1% for all W126 values across the range from 7 to 17 ppm

- hrs , and the RYL estimates for the fifth, peanut, are below 4% RYL across th is range. The RYL estimates for the other four studied crops are below 5% for W126 index values at or below 15 ppm

hrs ( winter wheat ) , 13 ppm

- hrs ( cotton ) , 9 ppm

- hrs ( kidney bean ) and 7 ppm

- hrs ( potato )

. In considering these RYL estimates, the PA recognizes that they do not reflect the influence of the heavy management of agricultural crops that is common in the U.S. and so cannot be easily interpreted with regard to potential public welfare significance

. In light of the median RYL estimates of approximately 5% or lower for W126 index values at and below 17 ppm

- hrs, the PA gives less emphasis to consideration of crop RYL, while noting that this information indicates that a secondary standard revised to provide additional protection for vegetation with attention to tree growth, would be expected to*** E.O. 12866 Review

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Page 414 of 647 also provide additional protection to crops over that provided by the current standard (U.S. EPA, 2014c, section 6.6)

. The PA also considers the evidence and exposure/risk information with regard to visible foliar injury and the extent to which that might inform consideration of potential alternative secondary standards appropriate for the Administrator to consider. Specif ically, the PA notes the findings of the WREA analyses of the nationwide USFS/FHM biosite dataset (2006

- 2010) that while soil moisture conditions influence the proportion of biosites with O 3 - related visible foliar injury, as described in section
IV.B.1.a a bove, the proportion of such sites increases appreciably with increasing W126 index values up to approximately 10 ppm

- hrs, while relatively little or no change in incidence of injury is seen with O 3 exposures at higher W126 index values (U.S. EPA 2014 b , Ch apter 7, Figure 7

- 10). The PA additionally notes that v isible foliar injury has been identified by the federal land managers as a diagnostic tool for informing conclusions regarding potential O 3 impacts on potentially s ensitive AQRVs (USFS, NPS, FWS, 2010) , which the PA conclude s indicate s that such O 3 - induced impacts might be considered to have the potential to impact the public welfare in scenic and/or recreational areas during years they occur. The PA was unable, however, to identify any guidance for f ederal land managers regarding at what spatial scale or what degree of severity visible foliar injury might be sufficient to trigger protective action based on this potential impact on AQRV s . The PA states that there does not appear to be consensus in the literature regarding severity of visible foliar injury and risks to plant functions or services, additionally noting that CASAC, while identifying percent biomass loss and yield loss benchmarks for tree*** E.O. 12866 Review

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Page 415 of 647 seedlings and commodity crops, respectively, did not provide any benchmark or criteria for consideration of O 3 impacts related to this endpoint. Further , as in previous reviews, the ISA concludes visible foliar injury is not always a reliable indicator of other negative effects on vegetation, making it diff icult to relat e visible foliar injury symptoms to other vegetation effects such as individual plant growth, stand growth, or ecosystem characteristics (U.S. EPA, 2013, section 9.4.2, p. 9

- 39) . Additionally, although evidence shows visible foliar injury can occur under very low cumulative O 3 exposures , “...the degree and extent of visible foliar injury development varies from year to year and site to site..., even among co

- members of a population exposed to similar O 3 levels, due to the influence of co

- occurring environmental and genetic factors” (U.S. EPA 2013, section 9.4.2, p. 9

- 38). Thus, while the PA recognize s visible foliar injury as an important O 3 effect which, depending on severity and spatial extent may reas onably be concluded to be of public welfare significance, most particularly in nationally protected areas such as Class I areas, it additionally recognizes the appreciable variability in this endpoint , which poses challenges to giving it primary emphasis i n identifying potential alternative standard levels. On the basis of all the considerations described above, including the evidence and exposure/risk analyses, and advice from CASAC, the PA conclude s that a range of W126 index values appropriate for the Administrator to consider in identifying a secondary standard that might be expected to provide the requisite protection to the public welfare from any known or anticipated adverse effects, extends from 7 to 17 ppm

- hrs. The PA
note s , however, the role of j udgments by the Administrator in such decisions , as recognized above. In selecting th is range, the PA primarily consider s the evidence

- and*** E.O. 12866 Review

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Page 416 of 647 exposure/risk

- based information for cumulative seasonal O 3 exposures represented by W126 index values (including tho se represented by the WREA average W126 scenarios) associated with biomass loss in studied tree species, both in and outside areas that have been afforded special protections. The PA recognizes that tree biomass loss can be an indicator of more significant ecosystem

- wide effects which might reasonably be concluded to be significant to public welfare. For example, when biomass loss occurs over multiple years at a sufficient magnitude, it is linked to some level of effects on an array of ecosystem

- level proce sses, such as nutrient and water cycles, changes in above and below ground communities, carbon storage and air pollution removal, that benefit the public welfare (U.S. EPA, 2014 c , Figure 5

- 1). In focusing on tree biomass effects, the PA gave emphasis to CA SAC’s judgment that a 6% median RBL is unacceptably high, and that the 2% median RBL is an important benchmark to consider . The PA notes that for the lower W126 value of 7 ppm

- hrs that the median tree species biomass loss is at or below 2% and that for the upper value of 17 ppm

- hrs that the median tree biomass loss is below 6%

. 191 In considering the stability and potential for associated greater public welfare protection offered by a three

- year form, as well as based on the recognition that in any given year in the environment, other environmental factors can influence the extent to which O 3 may have the impact predicted by the E

- R functions on which much of the range discussion above focuses, the PA gave careful consideration to the support for

191 We note that a W126 index value of 19 ppm

- hrs is estimated to result in a median RBL value of 6%, as shown in Table 2 above.*** E.O. 12866 Review

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Page 417 of 647 consideration of potential alternative W126 based standards with levels in the range identified above (17 ppm

- hrs to 7 ppm

- hrs) with a three

- year average form. Thus, the PA concludes that in staff’s view, the evidence

- and exposure/risk

based information relevant to tr ee biomass loss and the associated ecosystem services important to the public welfare support consideration of a W126

- based secondary standard with index values within the range of 7 to 17 ppm

- hrs , and a form averaged over three years

. In reaching this con clusion , the PA gave particular consideration to the importance of considering the lasting or carry

- over effects that can derive from single year exposures of perennial plants, recognizing the importance of considering the available evidence and exposure/r isk based information related to such effects, as well as associated uncertainties. The PA additionally recognize d that there is limited information to discern differences in the level of protection afforded for cumulative growth

- related effects by potenti al alternative W126

- based standards of a single year form as compared
to a three

- year average form. Lastly, the PA recognizes the role of policy judgments required of the Administrator with regard to the public welfare significance of identified effects, t he appropriate weight to assign the range of uncertainties inherent in the evidence and analyses , and, ultimately, in identifying the requisite protection for the secondary O 3 standard. Examples of areas where the Administrator’s judgments would be expecte d include those stemming from consideration of the effects associated with longer

- term conditions and the role that year

- to

- year exposure variability may play in associated public welfare impacts , as well as the objectives for consideration of tree species biomass loss estimates in relationship to identified benchmarks (e.g. 2% or greater).*** E.O. 12866 Review

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Page 418 of 647 The PA also concludes that, to the extent the Administrator finds it useful to consider the public welfare protection that might be afforded by a revised primary stand ard, this is appropriately judged through the use of a cumulative seasonal W126

- based exposure metric , a metric considered appropriate for evaluating impacts on vegetation . For example, comparison of the air quality conditions (expressed in terms of
W126 e xposures) expected to result from a revised primary standard to the W126

- based
exposures concluded to provide requisite public welfare protection would thus inform a judgment of whether a secondary standard set identical to a revised primary standard woul d be expected to achieve the appropriate level of air quality

. The PA notes that s uch a comparison would be in terms of a metric considered appropriate for evaluating impacts on vegetation which inform conclusions on public welfare impacts. The PA further conclude s that the drawing of conclusions with regard to the public welfare protection afforded by such a standard should entail consideration of the air quality conditions likely to be achieved in terms of the cumulative seasonal W126

- based metric describ ed above. Accordingly, the PA describes several analyses of air quality data that might inform such consideration (U.S. EPA, 2014c, section 6.4), and notes the importance of taking into account associated uncertainties, including those associated with the limited monitor coverage in many rural areas, such as those in the W est and S outhwest regions and at high elevation sites. Additional such analyses, based on more recent O 3 monitoring data, have been developed since the completion of the PA. All of these analyses are summarized in section IV.E.4 below. In reaching conclusions on appropriate policy options for a revised secondary standard the Administrator has considered the findings of these ana lyses, as described in section IV.E.5 below.*** E.O. 12866 Review

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Page 419 of 647 3 . CASAC Advice Beyond the evidence

- and exposure /risk

- based considerations in the PA discussed above, EPA’s consideration of a revised secondary standard also takes into account the advice and recommendations of CASAC . The EPA also considered public comments received to date, some of which urge d the consideration of a secondary standard with a cumulative seasonal form using the W126 metric and a level within the range of 7 to 15
ppm - hrs or in the low end of thi s range, 192 while others have urged retaining the existing form and averaging time due to their view of a lack of new information to support a distinct secondary standard

. In advice offered on a revised secondary standard in the current review , similar to

a dvice in the last review, including advice offered on the 2010 proposed reconsideration, the CASAC recommended “ retaining the current indicator (ozone) but establishing a revised form of the secondary standard to be the biologically relevant W126 index

acc umulated over a 12

- hour period (8 a. m.

– 8 p.m.) over the 3

- month summation period of a single year resulting in the maximum value of W126” (Frey, 2014c, p. iii). With regard to the level, the CASAC recommended that “ that the level associated with this fo rm be within the range of 7 ppm

- hrs to 15 ppm

- hrs to protect against current and anticipated welfare effects of ozone ” and that “ CASAC does not support a level higher than 15 ppm

- hrs ” (Frey, 2014c, p. iii)

. The CASAC additionally stated that “[i]n reaching its scientific judgment regarding the indicator, form, summation time, and range of levels for a revised secondary standard, the CASAC has focused on the scientific evidence for

192 Public comment received thus far in this review are in the docket EPA

– HQ

– OAR

2008

- 0699, accessible at www.regulations.gov.*** E.O. 12866 Review

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Page 420 of 64 7 the identification of the kind and extent of adverse effects on public welfar e , ” while also acknowledging “ that the choice of a level within the range recommended based on scientific evidence is a policy judgment under the statutory mandate of the Clean Air
Act ” ( Frey, 2014c , p. iii). In providing advice on a range for the second ary standard, the CASAC noted a W126 index value for which the median tree species RBL estimate was 6 percent , and the median crop species RBL estimate w as over 5 percent, stating that “[t] hese levels are unacceptably high” ( Frey, 2014c , p. iii)

. 193 In addition, regarding consideration of relative biomass loss benchmarks for tree seedlings, the CASAC state d that “[a] 2% biomass loss is an appropriate scientifically based value to consider as a benchmark of adverse impact for long

- lived perennial spec ies such as trees, because effects are cumulative over multiple years” (Frey, 2014c, p. 14). In so stating, the CASAC referenced findings for biomass loss in aspen exposed to elevated O 3 over seven years, citing Wittig et al., 2009. 194 The CASAC additionally pointed to the report of the 1996 workshop sponsored by the Southern Oxidants Study group (Heck and Cowling, 1997, noted in section IV.B.2 above) which described a general consideration of 1

- 2% per year growth reduction in making judgments the group ident ified as appropriate for the endpoint of growth effects

193 The CASAC made this comment while focusing on Table 6

- 1 in the second draft PA and the entry fo r 17 ppm

- hrs. That table was revised for inclusion in the final PA in consideration of CASAC comments on the E

- R function for eastern cottonwood, such that the RBL estimates for 17 ppm

- hrs in the final table (see Table 2 above) are below the values CASAC viewed as “unacceptably high”. 194 The way in which the statement pointing to the aspen seven

- year biomass loss value from Wittig et al (2009) relates to CASAC’s view with regard to 2%, however, is unclear as the original source for this finding (cited in Wi ttig et al., 2009) indicates yearly relative biomass loss values during this seven year exposure that are each well above 2%, and, in fact, are all above 20% (King, et al., 2005).*** E.O. 12866 Review

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Page 421 of 647 in trees, without providing an explicit rationale for the identified percentages (Frey, 2014c, p. 14). The CASAC also commented that “it is appropriate to identify a range of levels of alternative W12 6

- based standards that includes levels that aim for not greater than 2% RBL for the median tree species” (Frey, 2014c, p. 14). The CASAC noted that the “ level of 7 ppm

- hrs is the only level analyzed for which the relative biomass loss for the median tree s pecies is less than or equal to 2 percent ” indicating that 7 ppm was appropriate lower bound for the recommended range (Frey, 2014c, p. 14). With regard to consideration of effects on crops, the CASAC, as noted above, described median species RYL over 5% y ield loss as “unacceptably high.” The CASAC
further noted that “[c]rop loss appears to be less sensitive than these other indicators, largely because of the CASAC judgment that a 5% yield loss represents an adverse impact, and in part due to more opportuni ties to alter management of annual crops” ( Frey, 2014c , p. 14). The CASAC acknowledge d that “ the choice of a level within the range recommended based on scientific evidence is a policy judgment under the statutory mandate of the Clean Air Act ”, while furth er providing its own policy recommendation s , including the following (Frey, 2014c, p. iii). [T]he CASAC advises that a level of 15 ppm

- hrs for the highest 3

- month sum in a single year is requisite to protect crop yield loss, but that lower levels provide a dditional protection against crop yield loss. Furthermore, there are specific economically significant crops, such as soybeans, that may not be protected at 15 ppm

- hrs but would be protected at lower levels. A level below 10 ppm

- hrs is required to reduce f oliar injury. A level of 7 ppm

- hrs is protective of relative biomass loss for trees and offers additional protection against crop yield loss and foliar injury. Therefore, 7 ppm

- hrs is protective of ecosystem services. Thus, lower levels within the recommen ded range offer a greater degree of protection of more endpoints than do higher levels within the range.*** E.O. 12866 Review

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Page 422 of 647 Additionally, in regard to consideration of form, the CASAC note d that “[i]f, as a policy matter, the Administrator prefers to base the secondary stan dard on a three

- year averaging period for the purpose of program stability, then the level of the standard should be revised downward such that the level for the highest three

- month summation in any given year of the three

- year period would not exceed the scientifically recommended range of 7 ppm

- hrs to 15 ppm

- hrs ” (Frey, 2014c, pp. iii and iv). In related manner, the CASAC noted that a three

- year average W126 level of 13 ppm

- hrs may be appropriate depending on consideration of year

- to

- year variability and such policy considerations (Frey, 2014c, p. iv). Lastly, in comments recognizing uncertainties associated with the evidence and exposure and risk analyses, the CASAC stated that “ there is sufficient scientific evidence, and sufficient confidence in the av ailable research results, to support the advice we have given above for this review cycle of the primary and secondary standards” ( Frey, 2014c , p. iv).
4 . Air Quality Analyses As described in section II.D. above, the PA conclude s with regard to the prima ry standard that it is appropriate for the Administrator to consider revis ion of the level to within t he range of 60 to 70 ppb. In consideration of this conclusion for the primary standard , although the PA also concludes it is appropriate to consider a rev ised secondary standard with a cumulative, seasonal , concentration

- weighted form, the PA recognized that, it may be practical to consider the extent to which a revised secondary standard in the form of the primary standard might be expected to also reduce and provide protection from cumulative seasonal exposures of concern , noting that, f or example, if a clear and*** E.O. 12866 Review

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Page 423 of 647 robust relationship was found to exist between 8

- hour daily peak O 3 concentrations and cumulative, seasonal exposures, the averaging time and for m of the current standard might be concluded to have the potential to be effective as a surrogate (U.S. EPA, 2014c, section 6.4)

. Therefore, the PA evaluated w hat the available information indicated with regard to control of cumulative O 3 exposures that m ight be afforded by alternative secondary stand ards with the averaging time and form of the current standard (a 3

- year average of 4th highest 8

- hour average concentrations) . The available information a ddressing this point includes a “focus study” in the IS A, and several air quality analyses described in the PA, chapters 2, 5 and 6 and Appendix 2b. 195 Additionally, a similar air quality analysis performed with more recent monitoring data is now available and is also described here.
T he focus study described in the ISA examined the diel variability in O 3 concentrations in six rural areas between 2007 and 2009 (U.S. EPA, 2013, pp. 3

- 131 to 3

- 133). The ISA reported that “[t]here was considerable variability in the diel patterns observed in the six rural focus area s” with the three mountainous eastern sites exhibiting a “generally flat profile with little hourly variability in the median concentration and the upper percentiles , ” while the three western rural areas demonstrated a “clear diel pattern to the hourly O 3 data with a peak in concentration in the afternoon similar to those seen in the urban areas , ” which was especially obvious at the San Bernardino National Forest site, 90 km east of Los Angeles at an elevation of 1,384 meters (U.S. EPA, 2013, p. 3

- 132). Thu s, while the western sites that are influenced by upwind urban plumes may have

195 This information and analyses were included in the second draft PA (U.S. E PA, 2014d), reviewed by CASAC in early 2014, and drafts of the ISA, reviewed by CASAC earlier in the review.*** E.O. 12866 Review

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Page 424 of 647 increased cumulative seasonal values coincident with increased daily 8

- hour peak O 3 concentrations, this analysis indicates that, in sites without such an urban influence (the

e astern sites in this analysis), such a relationship does not occur (U.S. EPA, 2013, section 3.6.3.2). Thus, the lack of such a relationship indicates that in some locations, O 3 air quality patterns can lead to elevated cumulative, seasonal O 3 exposures wit hout the occurrence of elevated daily maximum 8

- hour average O 3 concentrations (U.S. EPA, 2013, section 3.6.3.2). Further, staff notes that the prevalence and geographic extent of such locations is unclear, since as in the last review, there continue to be relatively fewer monitors in the w est ern U.S. , including in high elevation remote sites. In considering the findings of this analysis, the PA additionally recognized, however, that the cumulative seasonal values for the eastern rural sites, where cumulati ve seasonal O 3 concentrations appear to be relatively less related to daily maximum 8

- hour concentrations, are lower in general than those of the western, urban

- influenced sites. In addition to the focus study described in the ISA (U.S. EPA, 2013, section 3.6.3.2), the PA consider s additional analyses of air quality monitoring data. For example, Chapter 2 of the PA characterized recent monitoring data o f O 3 air quality in rural areas. While approximately 80 percent of the O 3 monitoring network is urban focused, about 120 rural monitors are divided among CASTNET, NCore, and portable O 3 monitors (POMs) sites ( U.S. EPA, 2014c, Chapter 2, pp. 2

- 2 to 2

- 3, Figure 2.1). Specifically, as stated in C hapter 2 of the PA, “[a]lthough rural monitoring sites tend to
b e less directly affected by anthropogenic pollution sources than urban sites, rural sites can be affected by transport of O 3 or O 3 precursors from upwind urban areas and by local anthropogenic sources such as motor vehicles, power generation, biomass combu stion, or*** E.O. 12866 Review

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Page 425 of 647 oil and gas operations” (U.S. EPA, 2013, section 3.6.2.2). In addition, O 3 tends to persist longer in rural than in urban areas due to lower rates of chemical scavenging in non

urban environments. At higher elevations, increased O 3 concentrations can also result from stratospheric intrusions (U.S. EPA, 2013, sections 3.4, 3.6.2.2). As a result, O 3 concentrations measured in some rural sites can be higher than those measured in nearby urban areas (U.S. EPA, 2013, section 3.6.2.2) and the ISA conclu des that “cumulative exposures for humans and vegetation in rural areas can be substantial, and often higher than cumulative exposures in urban areas” (U.S. EPA, 2013, p. 3

- 120). These known differences between urban and rural sites suggest that there is t he potential for an inconsistent relationship between 8

- hour daily peak O 3 concentrations and cumulative, seasonal exposures in those areas. However, the PA also notes that reductions in NOx emissions that occur in urban areas to attain primary standards w ould also have the effect of reducing downwind, rural concentrations over the season (U.S. EPA, 2014c, section 6.4). In addition, as was done in both the 1997 and 2008 reviews, the PA analyzed relationships between O 3 levels in terms of the current averag ing time and form and a W126 cumulative form, based on recent air quality data. One analysis in the PA describes the W126 index values and current standard design values at each monitor for two periods: 2001

- 2003 and 2009

- 2011 (e.g., U.S. EPA, 2014c, Appen dix 2B, Figures 2B

- 2 and 2B

- 3). This shows that between the two periods, during which broad scale O 3 precursor emission reductions occurred, O 3 concentrations in terms of both metrics were reduced. There is a fairly strong, positive degree of correlation b etween the two metrics*** E.O. 12866 Review

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Page 426 of 647 ( U.S. EPA, 2014c, Appendix 2B). 196 Focusing only on the latter dataset (2009

- 2011), it can be seen that at monitors just meeting the current standard (3

- year average fourth

highest daily maximum 8

- hour average concentration equal to 0.075 ppm), W126 index values (in this case 3

- year averages) varied from less than 3 ppm

- hrs to approximately 20
ppm - hrs ( U.S. EPA, 2014c, Appendix 2B, Figure 2B

- 3b). At sites with a 3

- year average fourth

- highest daily maximum 8

- hour average concentration at or below a potential alternative primary standard level of 70 ppb, 3

- year W126 index values were above 17
ppm - hrs at no monitors, above 15 ppm

- hrs at one monitor, and above 13 ppm

- hrs at 8 monitors in the West and Southwest NOAA climate regions

. At site s with a 3

- year average fourth

- highest daily maximum 8

- hour average concentration at or below a potential alternative primary standard level of 65 ppb, 3

- year W126 index values were above 1 1 ppm - hrs at no monitors, above 9 ppm - hrs at three monitors, and ab ove 7 ppm

hrs at 9 monitors (distributed across five regions) . The majority of these nine monit oring sites are located in the West and S outhwest regions and include the states of Arizona, California, Colorado, Nevada, New Mexico, and Utah. At sites with a 3

- year average fourth

- highest daily maximum 8

- hour average concentration at or below a potential alternative primary standard level of 60 ppb, 3

- year W126 index values were at or below 7 ppm

- hrs at all monitors (U.S. EPA, 2014c, Figure 2B

- 3b).
An other anal ysis in Chapter 2 of the PA presents the data for sets of rec ent 3

- year periods back to 2006

- 2008 and indicates that among the counties with O 3 concentrations that met the current standard, the number of counties with 3

- year W126 index values

196 Appendix 2B in the PA additionally observes that the program implemented for reducing precursor emissions, especially NOx, appears to have been an effective strategy for lowering both design values and W126 index values.*** E.O. 12866 Review

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Page 427 of 647 above 15 ppm

- hrs ranges from fewer than 10 to 24 ( U.S. EPA, 2014c, Appendix 2B, Figure 2B

- 9). In general during this longer period, W126 index values above 15 ppm

- hrs and meeting the current standard were predominantly in Southwest region. As the first analysis in Appe ndix 2B of the PA (for the 2001

- 2003 and 2009

- 2011 perio ds) indicates, monitors in the west and s outhwest tend to have higher W126 index values relative to their design values than do monitors in other regions. This pattern is noteworthy because the southw est region has a less dense monitoring network than regions in the eastern U.S. (see U.S. EPA, 2014c, Figure 2

- 1), so that the extent to which this pattern occurs throughout these regions is uncertain.
An additional air quality analysis was performed for this review that is documented in a technical memorandum (Wells, 2014). This analysis examines the

r elationships between O 3 levels in terms of the primary standard design value and a 3

- year average, W126

- based metric. The first part of the analyses focus o n the air quality values for the most recent 3

- year period, 2011

- 2013. Based on this information, it can be seen that at monitors just meeting the current standard (3

- year average fourth

- highest daily maximum 8

- hour average concentration equal to 0.075 ppm ), W126 index values (in this case 3

- year averages) varied from less than 3 ppm

- hrs to up to 23 ppm

- hrs (Figure 5a ). At sites with a 3

- year average fourth

- highest daily maximum 8

- hour average concentration at or below a level of 70 ppb (566 monitors distri buted across all regions of the U.S.) , 3

- year W126 index values were above 17 ppm

- hrs at no monitors, above 15
ppm - hrs at 4 monitor s , and above 1 3 ppm - hrs at 16 monitors (1% of the monitors in full dataset and less than 3% in this group)

. These 16 monitors are located in the S outhwest (15 monitors) and West North Central NOAA climate regions and include the states of*** E.O. 12866 Review

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Page 428 of 647 Arizona, Colorado, New Mexico, Utah and Wyoming. A t sites with a 3

- year average fourth

- highest daily maximum 8

- hour average concentration at or below a level of 65 ppb (220 monitors distributed across all regions of the U.S. 197 ) , 3

- year W126 index values were above 1 1 ppm - hrs at no monitors, above 7 ppm

- hrs at 15 monitors. The se 15 monitoring sites are predominantly located in th e West North Central and Southwest regions

. At all sites with a 3

- year average fourth

- highest daily maximum 8

- hour average concentration at or below a level of 60 ppb, 3

- year W126 index values were at or below 7
ppm - hrs (Wells, 2014, Figure 5b)

. Further an alysis in the technical memorandum focused on a comparison of monitors with a 3

- year average fourth

- highest daily maximum 8

- hour average concentration at or below a level of 70 ppb and a 3

- year W126 index values above 13
ppm - hrs for sets of 3

- year periods between 2001

- 2003 and 2011

- 2013 (Wells, 2014 , Figure 8). This analysis found that the number of sites meeting 70 ppb while exceeding 13 ppm

- hrs has remained relatively constant over the past decade, with these sites consistently being limited to a small nu mber in the west and southwest. In addition, the number of sites meeting both 70 ppb and 13 ppm

- hrs has increased over time, while the number of sites exceeding both 70 ppb and 13 ppm

- hrs has decreased by a similar
amount. The second part of the analysis i n the technical memorandum focused on trends in the r elationships between O 3 levels in terms of the primary standard design value and a 3

- year average W126 metric, starting with the 2001

- 2003 period and ending with the 2011

-

197 This memo utilizes the same regi onal specifications as are used in the PA and WREA (e.g., U.S. EPA, 2014c, Appendix 2B, Figure 2B

- 1).*** E.O. 12866 Review

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Page 429 of 647 2013 period. Based on analysis o f 729 monitors, trends in both the primary standard design value and the 3

- year average, W126 metric showed decreasing values between
2001

- 2003 and 2011

- 2013. In addition, the amount of year

- to

- year variability in the two metrics tended to decrease over ti me with decreasing O 3 concentrations, especially for the W126 metric. Most sites in the e astern U.S. and California saw large, widespread decreases in both the primary standard design value and the 3

- year average W126 metrics over the past decade as a resu lt of regional NOx control p rograms. In the inter

- mountain

w est, where control programs have been more localized, the decreases observed in the primary standard design value and 3

- year average W126 metrics were typically much smaller in magnitude, with a s mall numbe r of sites showing significant increases

. As part of this analysis, regional comparisons were included on the relative changes in the r elationships between O 3 levels in terms of the primary standard design value and a 3

- year average W126 metrics between the periods of 2001

- 2003 and 2011

- 2013. Figure 12 in the technical memorandum shows that a positive, linear relationship persists within each region between the changes in primary standard design value and 3

- year average W126 metrics . Nationally, the 3

- year average W126 metric decreased by approximately 0.7 ppm

- hrs per unit ppb decrease in the primary standard design value metric. In addition, the southwest and we st regions, which have the greatest potential for sites to measure elevated cumulative, seasonal O 3 exposures without the occurrence of elevated daily maximum 8

- hour average O 3 concentrations , exhibited the greatest response in W126 value change per unit c hange in primary design value ( Wells, 2014 , Table 6).*** E.O. 12866 Review

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Page 430 of 647 The technical memorandum concludes that the primary standard design value and
a 3

- year average W126 metric are highly correlated, as are the relative changes in these two metrics over the past decade. I n this way, the technical memorandum concludes that that future control programs designed to help meet a revised primary O 3 standard based on the 3

- year average of the 4 th highest daily maximum 8

- hour concentration are expected to also result in decreases in the values of a 3

- year average W126 metric. The above information suggests that depending on the level for a standard of the current averaging time and form, the current form and averaging time of the secondary standard can be expected to achieve control of cumulative seasonal O 3 exposures , providing air quality that may meet specific three

- year average W126 index values . As discussed above, w e recognize limitations in the dataset and associated analyses, including those related to monitor coverage , which may contribute uncertainties to conclusions related to the relationships described. With respect to monitor coverage, the
current O 3 monitoring network is urban focused, with fewer monitors in some parts of the country, particular rural areas of th e s outhwestern and w estern U.S. Because of this, there are potential uncertainties in the extent to which the monitoring information discussed above represents air quality patterns and relationships that would occur in areas without monitors

. There is some information suggesting that there is a potential for inconsistencies in the relationship between W126 measures of seasonal O 3 concentrations and the fourth highest peak O 3 concentration s assessed by the current standard averaging time and form , but the available data suggest that air quality in areas meeting a primary standard in the range of 65 to 70 ppb would also meet a three

- year W126 index value falling in the range of 13 to 17 ppm - hrs, and that to the extent areas need to take action to*** E.O. 12866 Review

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Page 431 of 647 attain a st andard in the range of 65 to 70 ppb, those actions would also improve air quality as measured by the W126 metric. 198 To the extent to which the monitoring data can be expected to describe future relationships in air quality, we acknowledge potential uncertai nties in specifying future air quality but note that these uncertainties are limited by the fact that the data analysis includes over a decade of O 3 measurements, with similar patterns and trends observed in air quality over this period of time. 5. Adminis trator’s Proposed Conclusions In considering what revisions to the secondary standard are appropriate, the Administrator has drawn on the ISA conclusions regarding the weight of the evidence for a range of welfare effects associated with O 3 in ambient ai r, and associated areas of uncertainty; quantitative risk and exposure analyses in the WREA for different adjusted air quality scenarios and associated limitations and uncertainties; staff evaluations of the evidence, exposure/risk information and air qual ity information in the PA; additional air quality analyses of relationships between air quality metrics based on form and averaging time of the current standards and a cumulative seasonal exposure index; and CASAC advice; and, public comments received thus far in the review. As described in section IV.E.1 above, the Administrator concludes it is appropriate to continue to use O 3 as the indicator for a secondary standard intended to

198 EPA notes that areas can be expected to have air quality at least as good as that specified by the primary standard, so to the extent there are inconsis tencies between fourth highest peak concentrations and W126 values such that some areas meeting a standard of 0.065 to 0.070 ppm might be well below the range of 13 to17 ppm

- hours, those inconsistencies are less relevant to consideration of the appropriate form and level for the secondary standard.*** E.O. 12866 Review

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Page 432 of 647 address adverse effects to public welfare associated with exposure to O 3 al one and in combination with related photochemical oxidants. In this review, no alternatives to O 3 have been advanced as being a more appropriate surrogate for ambient photochemical oxidants. Thus, as is the case for the primary standard (discussed above i n section II.E.1), the Administrator proposes to continue to use O 3 as the indicator for a standard that is intended to address effects associated with exposure to O 3 alone and in combination with related photochemical oxidants. In so doing, the Administra tor recognizes that measures leading to reductions in ecosystem exposures to O 3 would also be expected to reduce exposures to other photochemical oxidants. The Administrator has next considered the array of information with regard to identifying policy opt ions for a revised secondary standard for O 3 that in her judgment would provide appropriate protection for public welfare effects associated with O 3 in ambient air. This information includes ISA conclusions, WREA analysis findings, staff considerations and conclusions in the PA and CASAC advice, as well as the Administrator’s conclusions in the last review, with regard to a biologically relevant exposure metric for O 3 vegetation

- related effects. The information also includes PA conclusions and CASAC advice with regard to key aspects of the definition of such a metric, as summarized in section IV.E.2 and IV.E.3 above. Additionally, the Administrator has considered findings of staff evaluations in the PA with regard to potential impacts on vegetation and fores ted ecosystems associated with a range of values for such a metric and identified uncertainties and limitations of such information, as summarized in section IV.E.2 above. Additionally important to her deliberations here are findings of air quality analyse s of relationships between the W126

- based exposure metric*** E.O. 12866 Review

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Page 433 of 647 and levels of a standard of the same form and averaging time as the current standards, as described in section IV.E.4 above. Based on consideration of this array of information, as described below, the Administrator has drawn conclusions with regard to policy options for a revised secondary standard. In drawing conclusions on such options, she recognizes that the Act does not require that NAAQS be set at zero

- risk or background levels, but rather at levels that reduce risk sufficiently to protect public welfare from adverse effects. As an initial matter, the Administrator recognizes the longstanding evidence, described in the ISA, of O 3 effects on vegetation and associated terrestrial ecosystems.
Fu rther, in reaching a proposed conclusion on the appropriate form and averaging time for a revised secondary standard that would provide increased protection against vegetation

- related effects on public welfare, the Administrator takes note of the conclusio ns drawn in the ISA, the PA and by CASAC in this review that the scientific evidence continues to demonstrate the cumulative nature of O 3 - induced plant effects and the need to give greater weight to higher concentrations, as summarized in sections IV.B.1, IV.D.1, IV.D.2, IV.E.2.a and IV.E.3 above. Based on these considerations, the Administrator concurs with the CASAC that a cumulative, seasonal, concentration

weighted exposure

- based form and averaging time provides the most direct link between
O 3 in ambien t air and O 3 - related effects on vegetation. The Administrator further concludes that in judging the extent of public welfare protection that might be afforded by a revised standard, it is appropriate to use a cumulative , seasonal concentration

weighted met ric

. In identifying a cumulative, seasonal, concentration

- weighted metric for use in judging public welfare protection, the Administrator gives weight to the PA conclu sions*** E.O. 12866 Review

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Page 434 of 647 regarding consider ation of a revised secondary standard in terms of the cumulative, seasonal, concentration

- weighted form, the W126 index . As described in section IV.B.1 above, the ISA has recognized the strengths of the W126 index in its weighting of potential damaging O 3 concentrations that contribute to the advantages it offers over

o ther weighted cumulative indices. The Administrator notes the PA conclusions regarding the W126 metric, specifically use of the three consecutive month period within the O 3 season with the maximum index value as the seasonal period over which to cumulate h ourly O 3 exposures and the cumulation of daily exposures for the 12

- hour period from 8:00 am to 8:00 pm. The Administrator additionally takes note of CASAC support for consideration of the W126 index defined in this way and concludes it is appropriate to u se the cumulative seasonal W126

- based metric derived in this way. In further considering the PA conclusions regarding a revised secondary standard in terms of the W126 index , the Administrator takes note of considerations in the PA of a three

- year or sin gle

- year evaluation period. Such considerations include the variability in ambient air O 3 concentrations from year to year, as well as variability and uncertainties related to environmental factors that influence the occurrence and magnitude of O 3 - related effects. The Administrator additionally notes the PA observation of greater significance for effects associated with multiple

- year exposures. Based on these and related considerations described in the PA (and summarized in section IV.E.2 above), the Admini strator, in identifying a metric for use in judging public welfare protection afforded, agrees with the PA conclusion that it is appropriate to consider a form that averages W126 index values across three consecutive years , and to do so in conjunction with identification of levels for such a form that might be judged to provide the*** E.O. 12866 Review

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Page 435 of 647 appropriate degree of public welfare protection from O 3 effects across multiple years. In so doing, the Administrator takes note of the ISA conclusions regarding the role of environmental factors in variability associated with effects of ambient air O 3 and the
year - to

- year variability commonly observed in such environmental factors. Further , the Administrator also recognizes uncertainties associated with determining the degree of vegetation impacts for annual effects that would be adverse to public welfare. Even in the case of annual crops, the assessment of public welfare significance is un clear for the reasons discussed below related to agricultural practices. The considerations identified here lead the Administrator to conclude it is appropriate to use an index averaged across three years. In reaching this conclusion regarding a three

- year average metric, the Administrator has considered CASAC comments that it favors a W126

- based secondary standard with a single year form and that its recommended range of levels relates to such a form. The Administrator concurs with CASAC that it is importa nt to consider impacts associated with a single year that may be of a magnitude concluded to represent an adverse effect on public welfare. The Administrator further concludes that such an occurrence can be addressed through use of a three

- year average met ric, chosen with consideration of the relevant factors. As noted above, the Administrator gives consideration to the variabilities, as well as the uncertainties, associated with single year and multiple year impacts. Based on all of these considerations, t he Administrator recognizes greater confidence in judgments based on a three

- year average metric. Thus, based on all of the above, the Administrator proposes, for purposes of judging the extent of public welfare protection that might be afforded by a revis ed*** E.O. 12866 Review

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Page 436 of 647 standard and whether it meets the appropriate level of protection, to use the average W126 index value across three years, with each year’s value identified as that for the
three

- month period yielding the highest seasonal value and with daily O 3 exposur es within a three

- month period cumulated for the 12

- hour period from 8:00 am to 8:00 pm. In reaching a conclusion on the appropriate range of W126 index values that describe the O 3 conditions expected to provide the requisite protection of public welfare, the Administrator has given careful consideration to the following: (1) the nature and degree of effects of O 3 to the public welfare, including what constitutes an adverse effect; (2) the strengths and limitations of the evidence that is available regard ing known or anticipated adverse effects from cumulative, seasonal exposures, and its usefulness in informing selection of a proposed range; and (3) CASAC’s views regarding a range of W126 levels appropriate to consider, as well as on the strength of the e vidence and its adequacy to inform a range of levels. In this consideration, the Administrator recognizes that the choice of a range of W126 index values (and the form of the W126 index) that might be expected to provide protection of the public welfare fr om any known or anticipated adverse effects requires judgments about the interpretation of the evidence and other information, such as the quantitative analyses of air quality monitoring, exposure and risk, that neither overstates nor understates the stren gths and limitations of the evidence and information nor the appropriate inferences to be drawn as to risks to public welfare. The CAA does not require that a secondary standard be protective of all effects associated with a pollutant in the ambient air bu t rather those considered adverse to the public welfare (as described in section IV.B.2 above). The Administrator additionally recognizes that there is not a bright line clearly directing the choice of a*** E.O. 12866 Review

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Page 437 of 647 range of W126 index values and that the choice of wh at is appropriate is a public welfare policy judgment entrusted to the Administrator. In determining the range of three

- year average W126 index values that might be expected to provide the appropriate level of public welfare protection, the Administrator first considers the nature and degree of effects of O 3 on the public welfare. The Administrator recognizes that the significance to the public welfare of O 3 - induced effects on sensitive vegetation growing within the U.S. can vary, depending on the nature o f the effect, the intended use of the sensitive plants or ecosystems, and the types of environments in which the sensitive vegetation and ecosystems are located. Any given
O 3 - related effect on vegetation and ecosystems (e.g., biomass loss, visible foliar i njury), therefore, may be judged to have a different degree of impact on the public depending, for example, on whether that effect occurs in a Class I area, or a residential or commercial setting. The Administrator notes that such a distinction is supporte d by CASAC advice in this review. In her judgment, like those of the Administrator in the last review, it is appropriate that this variation in the significance of O 3 - related vegetation effects should be taken into consideration in making judgments with re gard to the level of ambient O 3 concentrations that is requisite to protect the public welfare from any known or anticipated adverse effects. As a result, the Administrator concludes that of those known and anticipated O 3 - related vegetation and ecosystem e ffects identified and discussed in this notice, particular significance should be ascribed to those that occur on sensitive species that are known to or are likely to occur in federally protected areas such*** E.O. 12866 Review

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Page 438 of 647 as Class I areas 199 or on lands set aside by States , Tribes and public interest groups to provide similar benefits to the public welfare, for residents on those lands, as well as visitors to those areas. Likewise, the Administrator also notes that the same known or anticipated O 3 - induced effects occurring in other areas may call for less protection. For example, the maintenance of adequate agricultural crop yields is extremely important to the public welfare and is currently achieved through the application of intensive management practices. With respect t o commercial production of commodities, the Administrator notes that judgments about the extent to which O 3 - related effects on commercially managed vegetation are adverse from a public welfare perspective are particularly difficult to reach, given that the extensive management of such vegetation (which, as CASAC noted, may reduce yield variability) may also to some degree mitigate potential
O 3 - related effects. The management practices used on these lands are highly variable and are designed to achieve optim al yields, taking into consideration various environmental conditions. In addition, changes in yield of commercial crops and timber may affect producers and consumers differently, further complicating the question of assessing overall public welfare impact s. Thus, the Administrator concludes that agricultural crops do not have same need for additional protection from the NAAQS as forested ecosystems and, while research on agricultural crop species remains useful in illuminating

199 For example, the Wilderness Act of 1964 defines designated ‘‘wilderness areas’’ in part as areas “protected and managed so as to preserve [their] natural conditions” and requires that these areas ‘‘shall be administered for the use and enjoyment of the American people in such manner as will leave them unimpaired for future use and enjoyment as wilderness, and so as to provide for the protection of these areas [and] the preservation of their wilderness charact er . ’’ 16 U.S.C. §1131(a ).*** E.O. 12866 Review

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Page 439 of 647 mechanisms of action and phys iological processes, information from this sector on O 3 - induced effects is considered less useful in informing judgments on what level(s) would be sufficient but not more than necessary to protect the public welfare. The CASAC identified a crop RYL benchm ark of 5% for the median species and indicated they found higher percentages unacceptably high. Although the Administrator has not drawn a conclusion with regard to this specific benchmark, the Administrator finds the public welfare impacts associated with crop yield loss to be less significant , for the reasons discussed above, and thus is not focusing on crop yield loss in selecting a revised standard. She notes, however, the PA finding that median species crop RYL estimates for W126 index values in the PA identified range (17 to 7 ppm

- hrs) fall below the 5% benchmark emphasized by CASAC for this endpoint. The Administrator a lso notes that a standard revised to increase protection for forested ecosystems would also be expected to provide some increased prot ection for agricultural crops. The Administrator also recognizes that O 3 - related effects on sensitive vegetation can occur in other areas that have not been afforded special Federal protections, ranging from effects on vegetation growing in managed city parks and residential or commercial settings, such as ornamentals used in urban/suburban landscaping or vegetation grown in land use categories that are heavily managed for commercial production of commodities such as timber. For vegetation used for residential or commercial ornamental purposes, the Administrator believes that t here is not adequate information at this time to establish a secondary standard based specifically on impairment of these categories of vegetation, but notes that a secondary standard revised to provide protection for sensitive natural*** E.O. 12866 Review

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Page 440 of 647 vegetation and ecosy stems would likely also provide some degree of protection for such vegetation. Based on the above, the Administrator finds that the type of information most useful in informing the selection of an appropriate range of protective levels is appropriately foc used on information regarding exposures and responses of sensitive trees and other native species known or anticipated to occur in protected areas such as Class I areas or on lands set aside by States, Tribes and public interest groups to provide similar b enefits to the public welfare, for residents on those lands, as well as visitors to those areas. With regard to the available evidence, the Administrator finds the coherence and strength of the weight of evidence from the large body of available literatur e compelling. This evidence addresses a broad array of O 3 - induced effects on a variety of tree species across a range of growth stages (i.e., seedlings, saplings and mature trees) using diverse field

- based (e.g., free air, gradient and ambient) and OTC exp osure methods. The Administrator gives particular attention to the effects related to native tree growth and productivity, recognizing their relationship to a range of ecosystem services, including forest and forest community composition. With regard to selection of the values for use with the W126 index for the purpose of identifying a range of O 3 conditions expected to provide the appropriate level of protection from vegetation effects of particular concern, the Administrator, as an initial matter, take s note of the PA conclusion that, with regard to a target level of protection for a revised standard, it is appropriate to give consideration to a range of levels from 17
ppm - hrs to 7 ppm - hrs, expressed in terms of the W126 index averaged across three*** E.O. 12866 Review

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Page 441 of 647 cons ecutive years

. As summarized in section IV.E.2.b above, this PA conclusion draws heavily on considerations related to estimates of tree seedling growth impacts (in terms of relative biomass loss) associated with a range of W126

- based index values developed from the robust E

- R functions for 11 tree species. This conclusion also gives weight to CASAC comments as to an unacceptably high magnitude of relative biomass loss (6%) for the median species and a magnitude of median relative biomass loss on which to fo cus considerations (2%). The Administrator takes particular note of the CASAC view of a median species RBL of 6% as unacceptably high. In considering the basis for the range of W126 index levels identified by the PA, for which 17 ppm

- hrs is the upper end, the Administrator considers the CASAC advice, including their view that a 6% median tree seedling species RBL is unacceptably high, their consideration of Table 6

- 1 in the second draft PA which indicated such a RBL estimate for a W126 index value of 17 ppm

- hrs, and their consequent lack of support for levels higher than 15 ppm

- hrs (Frey, 2014c, p. iii; U.S. EPA 2014d, Table 6

- 1). Revisions to this table in the final PA, made in consideration of CASAC comments on the study supporting the E

- R function for ea stern cottonwood have resulted in changes to the median species RBL estimates such that the median is below 6% for a W126 index value of 17 ppm

- hrs (U.S. EPA, 2014c, Table 6

- 1), and thus, not of a magnitude that CASAC described as unacceptably high. In fac t, the median species RBL estimate for a W126 index value of 17 ppm

- hrs in this table in the final PA (5.3%) is nearly identical to the median species estimate for 15 ppm

- hrs (the value corresponding to the upper end of the CASAC

- identified range) in the s econd draft PA (5.2%) (U.S. EPA, 2014c, Table 6

- 1; U.S. EPA, 2014d, Table 6

- 1).*** E.O. 12866 Review

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Page 442 of 647 The Administrator additionally takes note of the PA observations that the number and proportion of individual species with RBL estimates at or below 2%, a benchmark given empha sis by CASAC, do not vary across W126 index values from 17 ppm

- hrs down to 9 ppm

- hrs (as seen in Table 8 above), providing little distinction with regard to the significance of growth impacts for exposures across this large portion of the PA range. The Adm inistrator also notes the CASAC recommendation regarding a lowering of the level with consideration of a three

- year average index; however, the Administrator’s judgments on a three

- year average index, as described above, focus on confidence in conclusions that might be drawn with regard to single as compared to multiple year impacts. For example, the Administrator, while recognizing the strength of the evidence with regard to quantitative characterization of O 3 effects on growth of tree seedlings and crops, in addition to noting the additional difficulties for assessing welfare impacts of crops, takes note of the uncertainty associated with drawing conclusions with regard to the extent to which small percent reductions in annual growth contribute to adverse effects on public welfare and the role of annual variability in environmental factors that affect plant responses to O 3 . Moreover, as explained above, the Administrator concludes that concerns related to the possibility of a singly unusually damaging year can be addressed through use of a three

- year average metric, chosen with consideration of the relevant factors. Accordingly, she judges it appropriate to include 17 ppm

- hrs, without adjustment, in the range of three

- year average W126 index values appropria te to consider in determining what secondary standard will provide air quality associated with the appropriate level of public welfare protection. She thus judges it appropriate to focus on a range for three

- year average W126 levels with 17 ppm

- hrs at the upper end. In so doing,*** E.O. 12866 Review

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Page 443 of 647 she additionally notes CASAC’s recognition that the choice of levels is a public policy judgment by the Administrator. In turning to consideration of the low end for the W126 index range, the Administrator considers the full range of W126 levels identified in the PA with regard to the evidence and exposure/risk

- based information, and associated uncertainties, identified in the PA, as well as CASAC advice. The Administrator notes the CASAC policy view regarding protection provided f or trees and associated ecosystem services from a W126 index value of 7 ppm

- hrs, which is based on the W126 index value for which the median species estimate falls below 2% RBL. The Administrator recognizes, however, as noted above, the greater uncertainty associated with the extent to which estimates of benefits in terms of ecosystem services and reduced effects on vegetation at lower O 3 exposures might be judged significant to the public welfare. The Administrator additionally notes the results of EPA’s quantitative exposure and risk assessments for the air quality scenarios for W126 levels at and below 11 ppm

hrs, including the relatively small additional benefits and increased uncertainty with the ecosystem services estimates in these lower W126 scenari os. With regard to the PA evaluation of RBL estimates, the Administrator, while noting the PA observations of similarity in the number of species with less than 2% RBL across the W126 range from 17 to 9 ppm

- hrs, as stated above, additionally notes PA obser vations of a similar number of studied species with RBL estimates below 5% for W126 index values of 13 and 11
ppm - hrs. Thus, to the extent that weight is given to the importance of 5% RBL for individual species, both W126 index values are observed to provi de RBL estimates below this benchmark.*** E.O. 12866 Review

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Page 444 of 647 With regard to considerations of O 3 effects beyond biomass loss in tree seedlings, the Administrator takes note of the lack of new quantitative E

- R relationships for larger trees growing in the field that would help inform consideration of a standard level within the lower part of PA range. Thus, the Administrator recognizes that important uncertainties remain in interpreting the quantitative O 3 - related growth effects for tree seedlings assessed in OTC studies for the purpose of characterizing long

- term growth effects, and other more subtle but important effects on sensitive tree species, natural forests, and forested ecosystems in the broader context of protection of public welfare. Additionally, while the Administrat or notes that there is evidence that O 3 - related visible foliar injury can occur at such lower levels (below a W126 index value of 13 ppm

- hrs), she recognizes, as summarized in sections IV.C.3.c and IV.D.1 above, the significant challenges in jud ging the ex tent to which such effects should be considered adverse to public welfare, in light of the variability and the lack of clear quantitative relationship with other effects on vegetation, as well as the lack of established criteria or objectives that might i nform consideration of potential public welfare impacts related to this vegetation effect. Thus, in the Administrator’s judgment, focus on a 3

- year average W126 index value below 13 ppm

- hrs would not give sufficient attention to the important uncertaintie s and limitations inherent in the currently available scientific evidence and in the quantitative assessments conducted for the current review. Taking into account the uncertainties that remain in interpreting the evidence, the Administrator observes that the likelihood of obtaining benefits to public welfare decreases with a standard set below a level of 13 ppm

- hrs, while the likelihood of requiring reductions in ambient*** E.O. 12866 Review

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Page 445 of 647 concentrations that go beyond those that are needed to reduce adverse impacts to publ ic welfare increases. Based on the above considerations and based on the entire body of evidence and information currently available, the Administrator identifies the range of three

- year average W126 index values extending from 13 to 17 ppm

- hrs as appropri ate to consider in identifying the ambient O 3 concentrations that would provide the appropriate level of public welfare protection. In so doing, the Administrator notes CASAC recognition that a three

- year average W126 level of 13 ppm

- hrs may be appropriate depending on consideration of year

- to

- year variability and policy considerations. Thus, based on the discussion above, and with consideration of CASAC advice on these issues, the Administrator proposes that ambient O 3 concentrations resulting in cumulativ e seasonal
O 3 exposures of a level within the range from 13 ppm

- hrs to 17 ppm

- hrs, in terms of a W126 index averaged across three consecutive years, would provide the requisite protection against known or anticipated adverse effects to the public welfare. The EPA solicits comments on levels within this range. The Administrator next turns to consideration of policy options for a revised secondary standard that would provide this level of protection. The Administrator takes note of staff conclusions that i t is appropriate to consider a revised secondary standard in terms of the cumulative, seasonal, concentration

- weighted form, the W126 index. Further, she gives extensive consideration to CASAC advice to set such a secondary standard. Such a standard, as m entioned above, would be directly linked to O 3 exposures to which vegetation are most responsive and thus might be expected to provide some confidence that such exposures of concern would be controlled.*** E.O. 12866 Review

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Page 446 of 647 In considering different policy options for a revised secondary standard, the Administrator finds it useful to consider what can be concluded from the available information with regard to relationships between air quality characterized in terms of the current form and averaging time and also in terms of the W126 metric. She has considered particularly what such analyses and relationships indicate with regard to the extent to which W126

- based O 3 concentrations may be controlled by a revised secondary standard set identical to a revised primary standard (in the range identified in section II.F above). In so doing, she considers the air quality analyses in the PA and also the analyses of more recent air quality data summarized in the EPA technical memo (described in section IV.E.4 above), focusing particularly o n analyses examining the W126

- based O 3 exposure achieved in locations found to meet potential alternative standards within the range of primary standards proposed in section II.F above. Findings from these analyses of recent O 3 measurements and trends in the relationship between the primary standard and the W126 metrics were substantially similar for the various time periods examined over the past decade. There is some information suggesting that there is a potential for inconsistencies in the relationship between W126 measures of seasonal O 3 concentrations and the fourth highest peak O 3 concentration s assessed by the current standard averaging time and form , but the available data suggest that air quality in areas meeting a primary stand ard in the range of 65 to 70 ppb would also meet a three

- year W126 index value falling in the range of 13 to 17 ppm

- hrs, and that to the extent areas need to take action to attain a standard in the range of 0.0 65 to 0.0 70 pp m , those actions would also impr ove air quality as measured by the W126 metric. The Administrator also recognizes that the relatively lesser density of*** E.O. 12866 Review

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Page 447 of 647 monitors in rural areas, including in areas of the west and southwest regions currently meeting the current standard where O 3 W126 index values are generally higher, makes uncertain the degree to which a revised level for the current standard would provide the appropriate degree of protection for vegetation

- related effects on public welfare in these areas. The Administrator takes note of t he PA finding, referenced in section IV.D.3 above, that reductions in NOx emissions that occur in urban areas to attain primary standards would also have the effect of reducing downwind, rural concentrations over the season. Thus, while the potential for u nderprotection may exist, depending on the specific levels chosen, the extent of such areas and of such a risk is not clear. Based on the most recent period of monitoring data, the Administrator notes that in all areas in which the O 3 concentrations would have met a primary standard with a revised level of 70 ppb (which includes over 500 monitors distributed across all regions of U.S), the three

- year average W126 index values are at or below 17 ppm

- hrs. In the same areas, only 16 monitors (or less than 3 % of all monitors in this group, all but one of which is located in the southwest region ) had three

- year average W126 index value s above 13 ppm

- hrs. She further notes that in all areas in which the O 3 concentrations would have met a primary standard with a r evised level of 65 ppb (which includes 220 monitors distributed across all regions of U.S), the three

- year average W126 index values are at or below 13 ppm

- hrs. In considering these findings regarding cumulative seasonal O 3 exposures in areas that would have met a primary standard with a revised level within the proposed range, the Administrator also takes note of the high correlation observed between the design value for the current secondary (and primary) standard and valu es for the three

- year*** E.O. 12866 Review

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Page 448 of 647 average, W126 metric, as well as the high correlation in the relative changes in these two metrics based on air quality analyses of O 3 measurements from over the past decade. This finding supports a conclusion that the air quality ana lyses indicate that future control programs designed to reduce O 3 concentrations to help meet a revised primary O 3 standard that retains the current form and averaging time (3

- year average of the 4th highest daily maximum 8

- hour concentration) would also b e expected to result in reductions in three

- year average, W126 index values. Further, she notes the conclusion from the air quality analysis that the southwest and west regions, which have the greatest potential for sites to measure elevated cumulative, se asonal O 3 exposures without the occurrence of elevated daily maximum 8

- hour average O 3 concentrations, exhibited the greatest response in W126 index value change per unit change in primary design value. While recognizing the limitations of such analyses i n projections of future air quality patterns, the Administrator also notes that the time period over which the analyses focused involved emissions control programs to achieve O 3 reductions such that their findings would be expected to be informative of fur ther similar control activities, such as those to meet a revised standard with a lower level, in the future. Based on the findings from these analyses, the Administrator finds it appropriate to consider the policy option of revising the secondary standar d level to within a range identical to the proposed range for the primary standard. In such consideration, the Administrator first notes her proposed conclusion that the requisite protection from known or anticipated adverse effects to public welfare may b e achieved by cumulative, seasonal, concentration

- weighted O 3 concentrations characterized in terms of a W126 index value that falls within the range from 13 to 17 ppm

- hrs. Her final decision on the*** E.O. 12866 Review

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Page 449 of 647 W126 index value in this range that affords the requisit e protection will be based on a series of judgments, as described above. Given the focus on tree seedling growth effects in identifying this range, such judgments will include the weight to give the evidence of specific vegetation

- related effects estimated to result from W126 index values within this range, including the objectives for consideration of tree species biomass loss estimates in relationship to identified benchmarks (e.g., median species RBL of 2% and greater), the weight to give associated unce rtainties, including those related to the variability in occurrence of such effects in forested areas, the associated ecosystem services including those of particular public welfare significance, and judgments on the extent to which such effects in foreste d areas may be considered adverse to public welfare. This final decision will also take into account judgments with regard to the weight to give the evidence and quantitative analyses, and associated uncertainties , related to other effects of O 3 (summarized in section s IV.C , IV.D.1 and IV.E.2 above) , particularly including those for which the ISA conclude s causal or likely causal relationships with O 3 exposures. As noted above, a standard that provides the appropriate level of protection for grow th effects would also be expected to provide additional protection for other effects including visible foliar injury, crops and carbon storage. The Administrator notes that based on the above analyses, the proposed range of levels for a revised primary sta ndard provide air quality, in terms of three

- year average W126 index values, of a range at or below the range which the Administrator has identified for consideration with regard to the requisite public welfare protection. Thus, depending on final judgment s on revisions to the primary standard and the requisite protection for the secondary standard, a revised secondary standard identical to the*** E.O. 12866 Review

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Page 450 of 647 revised primary standard may provide sufficient protection for public welfare. Therefore, the Administrator propos es to retain the current averaging time and form of the secondary standard and revise the level to within the range proposed for the primary standard. In reaching such a conclusion, the Administrator recognizes that such a strengthening of the secondary st andard would be expected to provide significant additional protection for public welfare, including effects related to vegetation and associated ecosystem services (and others discussed above), over that afforded by the current secondary standard. Thus, based on her consideration of the full range of information as described above, the Administrator judges that ambient O 3 concentrations in terms of a three

- year average W126 index value within the range extending from 13 ppm

- hrs to 17 ppm

- hrs would provide requisite public welfare protection. She further judges that it would be appropriate to achieve that level of air quality by retaining the existing averaging time and form, and revising the level to within the range proposed for the primary standard. In

r ecognition of CASAC’s recommendation and the PA conclusion with regard to a distinct secondary standard, the Administrator additionally solicits comment on the policy option of revising the form and averaging time for the secondary standard to a W126 index value, averaged across three years, with each year’s value identified as that for the three

month period yielding the highest seasonal value and with daily O 3 exposures within a three

- month period cumulated for the 12

- hour period from 8:00 am to 8:00 pm, and a level within the range from 13 ppm

- hrs to 17 ppm

- hrs. F. Proposed Decision on the Secondary Standard*** E.O. 12866 Review

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Page 451 of 647 The Administrator proposes to revise the level of the current secondary standard within the range proposed for the primary standard of 0.065 to 0.0 70 ppm

. The EPA solicits comments on this proposed revision of the secondary standard. Further, the EPA solicits comments on the proposed conclusion that air quality in terms of a W126 index value, averaged across three consecutive years, within the range of 1 3 ppm - hrs to 17
ppm - hrs would provide requisite protection against known or anticipated adverse effects to the public welfare. Additionally, the EPA solicits comments on alternative values for a three

- year average W126 index for such a purpose within the range extending below 13
ppm - hrs down to 7 ppm

- hrs. The EPA also solicits comments on the alternative approach of revising the secondary standard to a cumulative, seasonal, concentration

- weighted form, the W126 index based on the three consecutive month period within the O 3 season with the maximum index value, with daily exposures cumulated for the 12

- hour period from
8:00am to 8 :00pm and with a form that averages seasonal W126 values across three consecutive years and a level within the range of 13 to 17 ppm

- hrs. The EPA additionally solicits comments on such a distinct secondary standard with a level within the range extending b elow 13 ppm

- hrs down to 7 ppm

- hrs. Further, the EPA solicits comments on retaining the current secondary standard, without revision. V. Appendix U: Interpretation of the Primary and Secondary NAAQS for O 3 A. Background The EPA is proposing to create Ap pendix U to 40 CFR p art 50 to reflect the proposed revisions to the primary and secondary national ambient air quality standards (NAAQS) for ozone ( O 3 ) discussed in previous sections of this preamble. The proposed*** E.O. 12866 Review

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Page 452 of 647 Appendix U explains the computations neces sary for determining when the proposed primary and secondary O 3 NAAQS are met at an ambient air quality monitoring site, similar to Appendix P to 40 CFR part 50 which deals with revisions to the O 3 NAAQS promulgated in 2008. Specifically, the proposed Appe ndix U addresses data selection requirements (s ection V.B), data reporting and data handling requirements (s ection V.C), and data completeness requirements. The EPA is proposing to maintain the data completeness requirements from the previous O 3 NAAQS. Giv en that the EPA is soliciting public comment on a distinct secondary standard based on the W126 metric, section V.D contains a discussion o f additional data handling requirements that would be adopted in Appendix U in the event that the Administrator decid es to set a distinct secondary standard based on public comments received. The proposed Appendix U also provide s specific requirements for the handling of data affected by exceptional events in accordance with 40 CFR 50.14. Section V.E of this preamble add resses deadlines related to the flagging and submission of demonstrations for exceptional event data for the proposed O 3 NAAQS.
B. Data Selection Requirements The EPA is proposing to clarify which data are to be used in comparisons with the NAAQS. First, the EPA proposes to maintain the existing regulatory requirements that only O 3 data collected by a federal reference method spe cified in Appendix D to 40 CFR
p art 50, or an equivalent method designated in accordance with 40 CFR p art 53, and meeting all ap plicable monitoring requirements listed in 40 CFR p art 58, are eligible for comparison to the proposed O 3 NAAQS

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Page 453 of 647 Second, the EPA is proposing in Appendix U that O 3 design values are to be calculated on a site

- level basis. Past practice has been to calcula te a design value for each individual O 3 monitor. However, t his practice could be viewed as inconsistent with the stated purpose of the previous ozone data handling appendix, which is to determine

“ whether the national 8

- hour primary and secondary ambient air quality standards for ozone (O 3 ) specified in §50.15 are met at an ambient O 3 air quality monitoring site

. ” (40 CFR part 50, appendix P, section 1 (emphasis added).) Given the level of consistency in the measurement data obtained across the various fed eral reference and equivalent O 3 monitoring instruments currently in operation 200 , the EPA believes that it would be appropriate to combine data across O 3 monitors operating at the same site. Therefore, the EPA is proposing an analytic approach for combining data collected from multiple O 3 monitors at a site in order to obtain a single set of hourly O 3 concentration data for each site. The proposed approach allows the monitoring agencies to designate one monitor as the “primary monitor” for each site. In the absence of a primary monitor designation, the primary monitor would default to the monitor with the most complete hourly dataset in each year. Once a primary monitor has been determined for the site, missing hourly O 3
concentrat ions for the primary monitor would be substituted from any other monitors at the site. In the event of three or more monitors operating at the same site, missing hourly
O 3 concentrat ions for the primary monitor would be substituted with hourly values averaged across the other monitor s. The EPA notes that at the time of this proposal, there

200 See Final Integrated Science Assessment for Ozone and Related Photochemical Oxidants (EPA 600/R

- 10/076F, Feb. 2013), section 3.5.2.1*** E.O. 12866 Review

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Page 454 of 647 were approximately 20 sites operating two monitors simultaneously, and no O 3 sites operating three or more monitors simultaneously. This proposed approach for combining data across monitors at a site is consistent with the existing approach described in Appendix N to Part 50 for the PM 2.5 NAAQS. The EPA invites public comment on t he scientific validity of combining data across O 3 monitors, and the merits of the proposed approach for combining data across multiple O 3 monitors at a site. Third, the EPA proposes to maintain t he existing practice of combining data from nearby monitorin g sites in order to determine a valid design value, known as a “site combination”. Site combinations typically involve situations where sites have been replaced or relocated a short distance away , and the monitoring agency wishes to combine the data from t he two sites in order to maintain a continuous data record . The EPA regional offices have approved over 100 site combinations for O 3 since the promulgation of the 1997 O 3 NAAQS revisions

. The EPA has maintained records of approved site combinations, but th ese records are not easily accessible by the public

. The EPA proposes to replace the current procedure for approving O 3 site combinations with a more formal procedure in Appendix U , which would require s tates to submit site combination requests to the appr opriate Regional Administrator. Site combinations may be approved by the Regional Administrator, after he or she has determined that the measured air quality concentrations do not differ substantially between the two sites. In order to make this determinat ion, the Regional Administrator may request a dditional information from the s tates, including detailed information on the locations and distance between the two sites, levels of ambient concentrations measured at the two sites, and local emissions or meteo rology data.*** E.O. 12866 Review

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Page 455 of 647 In order to improve transparency, the EPA will make records of all approved site combinations available in their Air Quality System (AQS) database , and will update design value calculations in AQS so that approved site combinations are impleme nted

. The EPA invites public comment on the merits of the proposed process for approving site combinations in order to obtain valid design values for the O 3 NAAQS. C. Data Reporting and Data Handling Requirements The EPA is proposing to maintain the requirement that hourly O 3 concentration data be reported in parts per million (ppm) to three decimal places. Any decimal digits reported beyond three decimal digits will be truncated, consistent with past practice (40 CFR part 50, appendix P, section 2.1) and the typical measurement uncertainty associated with most O 3 monitoring instruments. The proposed Appendix U clarifies that hourly O 3 concentrations are to be reported in Local Standard Time (LST), consistent with how the values are currently stored in AQS. The EPA is proposing to maintain the existing procedures for calculating moving
8

- hour averages from the hourly O 3 data (40 CFR part 50, appendix P, section 2.1) , with one minor exception. In instances where fewer than six hourly O 3 concentrations a re available during an 8

- hour period (i. e. less than 75% completeness), the EPA is pro posing to substitute zero (i.e. 0.000 ppm) instead of one half of the O 3 monitoring instrument’s minimum detectable limit (MDL) for the missing concentration values to de termine if the resulting 8

- hour average is greater than the level of the NAAQS. The purpose of this “data substitution test” is to identify any 8

- hour periods that do not meet the requirements for a valid 8

- hour average, but have reported concentrations th at are so high that the NAAQS is exceeded even when substituting low values for the missing concentrations.*** E.O. 12866 Review

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Page 456 of 647 The EPA believes that a constant substitution value of zero is preferable to 1/2 MDL, which may vary across O 3 monitoring instruments. The MDL value for most O 3 monitoring instruments is 0.005 ppm, and the 1/2 MDL value is 0.002 ppm (with truncation); thus in practice the difference is slight. The EPA notes that a value of zero micrograms per cubic meter (ug/m 3 ) is used in data substitution tests for 24

- hour average
PM 2.5 concentrations, as specified in Appendix N to 40 CFR p art 50. The EPA invites public comment on the merits of using zero instead of 1/2 MDL for the 8

- hour average data substitution test. The EPA is proposing new procedures for determi ning daily maximum 8

- hour average O 3 concentrations. Past practice allows for daily maximum 8

- hour average O 3 concentrations from two consecutive days to have some hours in common (40 CFR part 40, appendix P, section 2.1) . One implication of this is that a n O 3 site may be counted as having exceeded the NAAQS on two distinct days based on two 8

- hour periods having up to seven hours in common. Theoretically, this could result in an annual fourth

- highest value greater than the NAAQS based on high overnight O 3 concentrations occurring only twice during the year. The EPA performed an analysis based on ambient O 3 concentration data from 2006 to 2011 [ insert reference to docketed memo, once it is available ] , which showed that at least one instance of overlapping daily maximum 8

- hour averages occurred at 97% of O 3 sites during that time period. Overlapping daily maximum 8

- hour averages were infrequent at most sites, but in some cases these values occurred quite regularly (up to 60 times per year). Overlapping daily maximum 8

- hour averages contributed to additional exceedances of the proposed O 3 NAAQS at 9% of sites for a level of 0.070 ppm, and at*** E.O. 12866 Review

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Page 457 of 647 14% of sites for a level of 0.065 ppm. In addition, 15% of sites had overlapping daily maximum 8

- hour averages which contributed to a higher annual 4 th highest daily maximum value in one or more years, resulting in higher design values at 2 to 3% of sites for a given 3

- year period. Finally, the analysis showed that O 3 sites located in non

- urban areas affected by long

- ran ge transport, especially those sites at higher elevations, were most likely to have additional exceedances of the proposed O 3 NAAQS due to the occurrence of overlapping daily maximum 8

- hour averages. Based on this analysis, the EPA initially concludes that overlapping daily maximum 8

- hour averages are more likely to contribute to additional exceedances of the
O 3 NAAQS as the level of the standard is lowered . T herefore, the EPA is proposing a new procedure for determining daily maximum 8

- hour average O 3 conc entrations for the proposed NAAQS that is based on 17 consecutive 8

- hour periods in each day, beginning with the 8

- hour period from 7:00 AM to 3:00 PM, and ending with the 8

- hour period from 11:00 PM to 7:00 AM. Given that 8

- hour averages are stored in the beginning hour of each period, this corresponds to the 8

- hour averages from 7:00 AM to 11:00 PM. The rationale for the proposed approach is twofold. First, it avoids any possibility of “double counting” exceedances of the NAAQS based on 8

- hour periods wit h one or more hours in common, while continuing to make use of all of the hourly concentration data, and keeping the calculations simple and straightforward. Second, it is more consistent with the physical processes involved in the formation and transport of ground

level ozone. Specifically, the chemical reactions involved in the formation of new ground

- level ozone require sunlight. Therefore, it is appropriate to begin the “ozone day” at sunrise, which for simplicity is assumed to be 7:00 AM LST. Similarly , any daily*** E.O. 12866 Review

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Page 458 of 647 maximum 8

- hour averages occurring after sunset are assumed to be caused by transport of ozone molecules which originated before sunset . Therefore, it is appropriate to end the “ozone day” with the 8

- hour period beginning at 11:00 PM and ending at 7:00 AM. In order to accommodate the above proposed approach to the hours considered in an “ozone day”, the EPA is also proposing to modify the requirement for determining whether a daily maximum 8

- hour average O 3 concentration is valid for assessing

co mpliance with the NAAQS (40 CFR part 50, appendix P, section 2.1)

. The proposed Appendix U requires valid 8

- hour averages for 13 of the 17 8

- hour periods in a day in order to determine a valid daily maximum value. The requirement of 13 valid 8

- hour
average s was chosen because 13/17 is the smallest ratio greater than 75%, which is consistent with the long standing requirement of 75% data completeness for daily and annual NAAQS

- related statistics. In addition, the EPA is proposing to maintain the existing pro vision allowing daily maximum 8

- hour averages greater than the level of the NAAQS to be considered valid (40 CFR part 50, appendix P, section 2.1)

. The EPA invites public comment on the merits of the proposed procedure for determining daily maximum 8

- hour average O 3 concentrations, and the merits of the proposed daily validity criteria. Finally, the EPA has included additional language in the proposed Appendix U codifying existing data handling procedures for the previous O 3 NAAQS. First, the proposed Appen dix U maintains the provision that hourly O 3 concentrations approved under 40 CFR 50.14 as having been affected by exceptional events are to be counted as missing or unavailable when calculating 8

- hour averages, and that these concentrations are to be incl uded when determining whether the daily validity criteria have been met for*** E.O. 12866 Review

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Page 459 of 647 a given day. Effectively, this means that it is possible for an 8

- hour period affected by exceptional events to lack sufficient data to determine an 8

- hour average, yet the 8

- hour period may still be counted toward meeting the daily validity criteria. Second, the proposed Appendix U maintains the existing practice of including monitored days outside of the O 3 monitoring season when determining the annual fourth

- highest daily maximum value. Finally, the proposed Appendix U maintains the existing practice of using only daily maximum 8

- hour average values for days where the daily validity criteria have been met when determining the annual fourth

- highest daily maximum value.
D. Considera tions for the Possibility of a Distinct Secondary Standard Given that the EPA is soliciting public comment on setting a distinct secondary
O 3 NAAQS based on the W126 index, the EPA is including a discussion on the data handling requirements for a distinct secondary standard. In the event that the Administrator decides to set a distinct secondary O 3 standard based on the W126 index, the EPA will adopt data handling requirements for the secondary standard similar to those proposed during the reconsideration o f the 2008 O 3 NAAQS in 2010 (see 75 FR 30 49

- 3052). Two changes would need to be made to the data handling provisions for the secondary standard proposed in 2010 in order to provide consistency with what the EPA is proposing for the primary standard in Appendix U. First, the secondary standard design value (i.e. the 3

- year average of the annual W126 index) would be truncated after the decimal point, instead of being rounded to the ne arest whole number. Second, paragraph 4(c)(ii) would be modified to read:*** E.O. 12866 Review

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Page 460 of 647 “If one or more months during the ozone monitoring seasons of three consecutive years has less than 75% data completeness, the three years shall nevertheless be used in the computati on of a valid design value for the site, if, after adjusting the monthly W126 index values for the months with less than 75% data completeness by a factor of 4/3, the resulting design value is greater than the level of the standard.”
E

. Exceptional Event s Information Submission Schedule
States 201 are responsible for identifying air quality data that they believe warrant special consideration, including data affected by exceptional events. States identify such data by flagging (making a notation in a designate d field in the electronic data record) specific values in the Air Quality System (AQS) database. States flag the data and submit supporting documentation showing that the data have been affected by exceptional events if they wish the EPA to consider exclud ing the data in regulatory decisions, including determining whether or not an area is attaining the proposed new O 3 NAAQS , if a different standard is finalized

. All states and areas of Indian country that include areas that could exceed or contribute to an exceedance of any revised O 3 NAAQS in a nearby area and could therefore be designated as nonattainment for the proposed O 3 NAAQS have the potential to be affected by this rulemaking. Therefore, this action applies to all states; to local air quality agencies to which a state has delegated relevant responsibilities for air quality management including air quality monitoring and data analysis; and to tribal air quality agencies , where appropriate.

201 R eferences to “state” are meant to include state, local and tribal agencies responsible for preparing and submitting exceptional event documentation as identified in the Exceptional Events Rule.*** E.O. 12866 Review

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Page 461 of 647 The “Treatment of Data Influenced by Exceptional Events ; Final Rule” (72 FR 13560, March 22, 2007), known as the Exceptional Events Rule and codified at 40 CFR 50.1, 50.14 and 51.930 , contains generic deadlines for a state to submit to the EPA specified information about exceptional events and associated air p ollutant concentration data. Under this generic flagging schedule in 40 CFR 50.14(c)(2)( iii ) , a state must initially notify the EPA that data have been affected by an event by July 1 of the calendar year following the year in which the event occurred. This is done by flagging the data in AQS and providing an initial event description. According to the generic demonstration schedule in 40 CFR 50.14(c)( 3 )( i ) , t he state must also, after notice and opportunity for public comment, submit a demonstration to justi fy any claim within 3 years after the quarter in which the data were collected. This section of the regulation also states that if the EPA must make a regulatory decision based on the data , the state must submit all information to the EPA no later than 1 y ear before the decision is to be made. These generic deadlines in the Exceptional Events Rule apply to data influencing redesignation efforts or other regulatory decisions made by the EPA after the EPA promulgates initial area designations for a new or rev ised NAAQS

. However, these same generic deadlines in the Exceptional Events Rule may not work well with the timing of the initial area designation process and schedule under a new or re vised NAAQS. Until the EPA promulgates the level and form of the NAAQS, a state does not know whether the criteria for excluding data (which are tied to the level and form of the NAAQS) were met for a given event. In some cases, the generic deadlines, especially the deadlines for flagging some relevant data, may have already passed by the time the EPA promulgates the new or revised NAAQS. This scheduling constraint could result in the EPA ’s being*** E.O. 12866 Review

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Page 462 of 647 unable to consider whether an exceptional event has affected the data relied on for initial area designations and further result in an area being designated nonattainment based on data that might have been excluded as having been influenced by an exceptional event if the EPA had been able to consider it during the designation process. For this reason, the EPA has historically undertake n rulemaking as part of the NAAQS promulgation process to adjust the generic deadlines in sections 50.14(c)(2)( iii) and 50.14(c)( 3 )( i ) of the Exceptional Events Rule to accommodate the initial area designation process and schedule under a new or re vised NAAQS. The Exceptional Events Rule at section 50.14(c)(2)(vi) indicates “when EPA sets a NAAQS for a new pollutant or revises the NAAQS for an existing pollutant, it may revise or set a new schedule for flagging exceptional event data, providing initial da ta descriptions and providing detailed data documentation in AQS for the initial designations of areas for those NAAQS.” As indicated in this proposal, the EPA intends to issue its final action promulgating a revised O 3 NAAQS or determining that it is not necessary to do so in October 2015. The CAA provides requirements regarding the schedule for initial area designations. Section 107(d)(1) of the C AA states that, “By such date as the Administrator may reasonably require, but not later than 1 year after pr omulgation of a new or revised national ambient air quality standard for any pollutant under section 109, the Governor of each state shall

... submit to the Administrator a list of all areas (or portions thereof) in the S tate , designating ” those areas as no nattainment, attainment, or*** E.O. 12866 Review

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Page 463 of 647 unclassifiable. 202 N o later than 120 days prior to promulgating designations, the EPA is

r equired to notify states of any intended modifications to their designation recommendations as the EPA may deem necessary

. Section 107(d)(1) (B)(i) further provides, “Upon promulgation or revision of a NAAQS, the Administrator shall promulgate the designations of all areas (or portions thereof)

... as expeditiously as practicable, but in no case later than 2 years from the date of promulgation

. S uch period may be extended for up to one year in the event the Administrator has insufficient information to promulgate the designations .” As described in more detail in section VII.C of this proposal, the EPA inten ds to complete designations for any revis ed O 3 NAAQS promulgated in 2015 following the standard 2

- year process. The EPA is required by
Court Order to take final action for this O 3 NAAQS review no later than October 1, 2015. The EPA does not intend to establish a date earlier than the 1 year submi ssion period provided in CAA section 107(d)(4) of the CAA ; thus, state Governors (and tribes, if they choose) would be required to submit their initial designation recommendations for any revised NAAQS no later than 1 year after promulgation ( i.e., by October 1, 2016 , if the EPA promulgates a revised NAAQS on October 1, 2015 )

. State Governors (and tribes, if they choose) would likely use air quality data from the years 201 3 to 201 5 as the basis for their recommendations

. The EPA would notify states and tribes of intended modifications to their recommendations no later than June 2017 and the EPA would promulgate i nitial designations for any revised NAAQS in October 2017. We anticipate that the EPA’s
notification of intended modifications and the final designations would be based on air

202 While the CAA says “designating” with respect to the Governor’s letter, in the full context of the CAA section it is clear that the Governor actually m akes a recommendation.*** E.O. 12866 Review

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Page 464 of 647 quality data from the years 201 4 to 201 6, because air quality data from 2016 is required to be certified by the state no later than May 1, 2017, and thus would be available for consideration for purposes of initial area designations by October 2017

. As indicated above, and as explained in additional detail in section VII.C of this preamble, section 107(d)(1)(B) of the CAA allows the Administrator to extend the designations schedule for up to 1 year in the event the Admini strator has insufficient information to promulgate the designations for a newly promulgated NAAQS. If EPA were to determine that it is necessary to extend the schedule for designating areas for a revised O 3 NAAQS promulgated in October 2015 from 2017 to 20 18, then it is possible that air quality data from 2017 could be considered for designations. This could raise concerns about whether influences from exceptional events in 2017 could be investigated and submitted by the state and reviewed by the EPA in suf ficient time for consideration during the designation process. For purposes of designations, where the EPA considers the most recent air quality monitoring data in a relatively quick timeframe, the EPA is proposing revisions to the flagging and data submi ssion schedule in 40 CFR 50.14 applicable to the area designations process

. Th e proposed exceptional events schedul e is based on following a standard 2 year process . However, because the CAA also provides for a 3 year process in the event the Administrator has insufficient information to promulgate the designations for a newly promulgated NAAQS within 2 years and provides for the promulgation of designations as “expeditiously as practicable,” which could include accelerat ing the designations schedule ahead of the 2 year schedule , the proposed exceptional event schedule also includes provisions for both an accelerated designations process and a 3*** E.O. 12866 Review

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Page 465 of 647 year process. If EPA were to pursue a designations schedule other than a 2 or 3 y ear process, the EPA would notify the State Governors of th e intended date for final designations through notification letters, guidance and/or Federal Register notices. These proposed revised exceptional event scheduling provisions would, if promulgate d, apply to submission of information supporting claimed exceptional events affecting pollutant data for initial area designations under any new or revised NAAQS, including any revised O 3 NAAQS promulgated in October 2015. The general data flagging deadlin es in the Exceptional Events Rule at 40 CFR 50.14(c)(2)(iii) and the general schedule for submission of demonstrations at 40 CFR 50.14(c)(3)(i) would continue to apply to regulatory decisions other than those related to the initial area designations proces s under a new or revised NAAQS. The EPA believes these proposed revisions to the exceptional events scheduling provisions will provide adequate time for states to review the impact of exceptional events on any revised standards, to notify the EPA by flaggi ng the relevant data and providing an initial description in AQS, and to submit documentation to support claims for exceptional events. Therefore, using the authority provided in CAA section 319(b)(2), the EPA proposes to modify the schedule for data flag ging and submission of demonstrations for exceptional events data considered for initial area designations as presented in Table 9

. The EPA is also providing Table 10 to illustrate how the proposed schedule might apply to the designations process for any revised O 3 NAAQS promulgated in October 2015 or to designations processes for future new or revised NAAQS. The EPA invites comment on these proposed changes, shown in Table 9 , to the exceptional event data flagging and*** E.O. 12866 Review

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Page 466 of 647 documentation submission deadlines for future new or revised NAAQS, including any revised O 3 NAAQS promulgated in 2015.
Table 9 . Pr oposed Schedule for Exceptional Event Flagging and Documentation Submiss ion for Data to be Used in Initial Area Designations Exceptional Event / Regulatory

Action Exceptional Event Deadline Schedule d

Exceptional event data flagging and initial description deadline for data years 1, 2 and 3 a If state and tribal initial designation recommendations for the new/revised NAAQS are due August through January, then the flagging and initial description deadline will be the July 1 prior to the recommendation deadline. If state and tribal recommendation s for the new/revised NAAQS are due February through July, then the flagging and initial description deadline will be the January 1 prior to the recommendation deadline. Exceptional event demonstration submittal deadline for data years 1, 2 and 3 a No later than the date that state and tribal recommendations are due to EPA

Exceptional event data flagging, initial description, and exceptional event demonstration submittal deadline for data year 4 b and potential data year 5 c By the last day of the month that is 1 year and 7 months after promulgation of a new or revised NAAQS, unless either option a or b applies. a. If the EPA follows a 3 year designation schedule, the deadline is 2 years and 7 months after promulgation of a new or revised NAAQS. b. I f the EPA notifies the state/tribe via Federal Register notice, letter or guidance that it intends to complete the initial area designations process according to a schedule other than a 2 year or 3 year timeline, the deadline is 5 months prior to the date of final designations decisions

. a Where data years 1, 2, and 3 are those years expected to be considered in state and tribal recommendations b Where data year 4 is the additional year of data that the EPA may consider when it makes final area designations for the new/revised NAAQS under the standard designations schedule.

c Where data year 5 is the additional year of data that the EPA may consid er when it makes final area designations for the new/revised NAAQS under an extended designations schedule.*** E.O. 12866 Review

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Page 467 of 647 d The date by which air agencies must certify their ambient air quality monitoring data in AQS is annually on May 1 of the year following the year o f data collection. EPA cannot require air agencies to certify data prior to this date. In some cases, however, air agencies may choose to certify a prior year's data in advance of May 1 of the following year, particularly if EPA has indicated its intent to promulgate final designations in the months of May, June, July or August. Exceptional event flagging, initial description, and demonstration deadlines for “early certified” data will follow the deadlines for “year 4” and “year 5” data.*** E.O. 12866 Review

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Page 468 of 647 Table 10 . Examples by Month of How the Proposed Revised Schedule for Exceptional Event Flagging and Documentation Submission for Data to be Used in Initial Area Designations Would Apply Month of NAAQS Promulgation, State and Tribal Recommendation, and Final Designations Exceptional Event / Regulatory Action Exceptional Event Deadline Schedule c Oct Nov Dec Jan Feb Mar Apr May d Jun d Jul d Aug d Sep Oct Oct 2015 Nov

2015 Dec

2015 Jan

2016 Feb

2016 Mar

2016 Apr

2016 May

2016 Jun

2016 Jul

2016 Aug

2016 Sep

2016 Oct

2016

Exceptional event data flagging and initial description deadline for data years 1, 2, and 3 a If state and tribal recommendations for

the new/revised NAAQS are due August through January, then the flagging and initial description deadline will be the July 1 prior to the recommendation deadline. If state and tribal recommendations for the new/revised NAAQS are due Feb through July, then the flagging and initial description deadline will be the January 1 prior to the recommendation deadline. July 1, 2016 (data years 2013, 2014, 2015) July 1,

2016 (data years 2013, 2014, 2015) July 1,

2016 (data years 2013, 2014, 2015) July 1,

2016 (data years 2013, 2014, 2015) Jan 1,

2017 (data years 2013, 2014, 2015) Jan 1,

2017 (data years 2013, 2014, 2015) Jan 1,

2017 (data years 2013, 2014, 2015) Jan 1,

2017 (data years 2013, 2014, 2015) Jan 1,

2017 (data years 2014, 2015, 2016) Jan 1,

2017 (data years 2014, 2015, 2016) July 1,

2017 (data years 2014, 2015, 2016) July 1,

2017 (data years 2014, 2015, 2016) Ju ly 1,

2017 (data years 2014, 2015, 2016)
Exceptional event demonstration submittal deadline for data years 1, 2, and 3 a No later than the date that state and

tribal recommendations are due to EPA by Oct 2016 (data years 2013, 2014, 2015) by No v

2016 (data years 2013, 2014, 2015) by Dec

2016 (data years 2013, 2014, 2015) by Jan

2017 (data years 2013, 2014, 2015) by Feb

2017 (data years 2013, 2014, 2015) by Mar

2017 (data years 2013, 2014, 2015) by Apr

2017 (data years 2013, 2014, 2015) by May

2 017 (data years 2013, 2014, 2015) by June

2017 (data years 2014, 2015, 2016) by July

2017 (data years 2014, 2015, 2016) by Aug

2017 (data years 2014, 2015, 2016) by Sep

2017 (data years 2014, 2015, 2016) by Oct

2017 (data years 2014, 2015, 2016) AQS Q&A and data certification Annually on May 1 of the year

following the year of data collection May 1 May 1 May 1 May 1 May 1 May 1 May 1 May 1 May 1 May 1 May 1 May 1 May 1

Exceptional event data flagging, initial description, an d exceptional event demonstration submittal deadline for data year 4 b and potential data year 5 c By the last day of the month that is 1

year and 7 months after promulgation of a new or revised NAAQS, unless either option a or b applies. a. If the EPA follows a 3 year designation schedule, the deadline is 2 years and 7 months after promulgation of a new or revised NAAQS. b. If the EPA notifies the state/tribe via Federal Register notice, letter or guidance that it intends to complete the initial area desi gnations process according to a schedule other than a 2 year or 3 year timeline, the deadline is 5 months prior to the date of final designations decisions. by May 31, 2017 (data year 2016) by June

30, 2017 (data year 2016) by July

31, 2017 (data year 201 6) by Aug

31, 2017 (data year 2016 and potentia lly 2017) by Sep

30, 2017 (data year 2016 and potentia lly 2017) by Oct

31, 2017 (data year 2016 and potentia lly 2017) by Nov

30, 2017 (data year 2016 and potentia lly 2017) by Dec

31, 2017 (data year 2016 and p otentia lly 2017) by Jan

31, 2018 (data year 2017) by Feb

28/29, 2018 (data year 2017) by Mar

31, 2018 (data year 2017) by Apr

30, 2018 (data year 2017) by May

31, 2018 (data year 2017) State & Tribal Recommendations to EPA Oct 2016 Nov

2016 Dec

2016 Jan

2017 Feb

2017 Mar

2017 Apr

2017 May

2017 June

2017 July

2017 Aug

2017 Sep

2017 Oct

2017*** E.O. 12866 Review

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Page 469 of 647 EPA notifies States/Tribes of intended modifications to recommendations (RAs send 120
- day letters) June 2017 July

2017 Aug

2017 Sep

2017 Oct

2017 Nov

2017 Dec

2017 Jan

2018 Feb

2018 Mar

2018 Apr

2018 May

2018 June

2018 Administrator Promulgates Final Designations Oct 2017 Nov

2017 Dec

2017 Jan

2018 Feb

2018 Mar

2018 Apr

2018 May

2018 June

2018 July

2018 Aug

2018 Sep

2018 Oct

2018

a - Where data years 1, 2, and 3 are those years expected to be considered in state and tribal recommendations b

- Where data year 4 is the additional year of data that the EPA may consider when it makes final area designations for the new/ revised NAAQS.

c - W here data year 5 is the additional year of data that the EPA may consider when it makes final area designations for the new/revised NAAQS unde r an extended designations schedule. d

- The date by which air agencies must certify their ambient air quality monitoring data in A QS is annually on May 1 of the year following the year of data collection. EPA cannot require air agencies to certify data prior to this date. In some cases, however, air agencies may choose to certify a prior year's data in advance of May 1 o f the followi ng year, particularly if EPA has indicated its intent to promulgate final designations in the months of May, June, July or August. Exceptional event flagging, initial description, and demonstration d eadlines for "early certified" data will follow the deadl ines for "year 4" and “year 5” data

.

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Page 470 of 647 Additionally, in conjunction with proposing exceptional event schedules related to implementing any revised O 3 standards, the EPA is also proposing to remove obsolete regulatory language F This section presents the rationale for the Administrator’s proposed decision s regarding the need to revise the current secondary O 3 NAAQS This section presents the rationale for the Administrator’s proposed decision s regarding the need to revise the current secondary O 3 NAAQS with exceptional event schedules for historical standards. The EPA expects to propose additional revisions to the Excepti onal Events Rule in a future notice and comment rulemaking effort and will solicit public comment on other, non

- schedule related, aspects of the E xceptional Events Rule at that time.
VI. Ambient Monitoring Related to Proposed O zone Standards A. Background EPA is proposing to: revise the state

- by

- state O 3 monitoring seasons; revise the PAMS monitoring requirements; revise the Federal Reference Method (FRM) for measuring O 3 ; and revise the Federal Equivalent Method (FEM) testing requirements. EPA is also prop osing to make additional minor changes to the FEM testing requirements for NO 2 and particulate matter in part 53 as discussed below

. EPA is proposing to extend the length of the required O 3 monitoring season in some
states to be appropriate for the O 3 NAAQ S revision finalized in 2008, as well as a final revised
O 3 standard, if a revision is finalized in 2015

. EPA is proposing to make changes to the PAMS monitoring requirements in 40 CFR part 58, Appendix D section 5. Section VI.C of this preamble provides background on the current PAMS monitoring requirements, recent efforts to re

- evaluate the current PAMS requirements, and a summary of the proposed PAMS requirement revisions.*** E.O. 12866 Review

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Page 471 of 647 EPA is proposing to revise the FRM to establish a new, additional technique for

m easuring O 3 in the ambient air. This new technique is based on Nitric Oxide

chemiluminescence (NO

- CL) methodology. Because of the similarity of this new chemiluminescence technique to the existing ethylene

- chemiluminescence (ET

- CL) methodology, EPA propose s that it be incorporated into the existing O 3 FRM, using the same calibration procedure. Appendix D of 40 CFR part 50 would be revised to include both the original ET

- CL as well as the new NO

- CL methodology. A minor change is proposed to the existing O 3 FRM calibration procedure, which would be applicable to both of the chemiluminescence FRM methodologies. The proposed change in section 4.5.2.3 of the calibration procedure in appendix D provides for more flexibility in the range of the linearity
test.
T he only substantial changes proposed to the requirements of 40 CFR part 53 are in Tables B

- 1 and B

- 3 of s ubpart B. Table B

- 1 has b een updated in recent years with regard to FRM and FEM methods for SO 2 (74 F R 64877; December 8, 2009) and CO (76 FR 54294;
Au gust 31, 2011) to be more consistent with current analyzer performance capabilities. Similar changes to Table B

- 1 are proposed here for methods for O 3 . M odest changes to Table B

- 3 would add new interferent test concentrations specifically for NO

- CL analyze rs, adding a test for NO 2 . Also , the table would clarify that the existing test concentrations apply to ethylene

chemiluminescence O 3 analyzers. In addition, EPA is making minor additional changes to part 53 including: conforming changes to the FEM testing requirements in Table B

- 1 and Figure B

- 5 for NO 2 ; extending the period of time for the Administrator to take action on a request for modification of a FRM or*** E.O. 12866 Review

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Page 472 of 647 FEM from 30 days to 90 days; and removing an obsolete provision for manufacturers to submit Produ ct Manufacturing Checklists for certain PM monitors. B. Revisions to the Length of the Required Ozone Monitoring Seasons Unlike the ambient monitoring requirements for other criteria pollutants that mandate
year - round monitoring, O 3 monitoring is currently only required during the seasons of the year that are conducive to O 3 formation. These seasons vary in length from place to place as the conditions that determine the likely O 3 formation (i.e., seasonally

- dependent factors such as ambient temperature, str ength of solar insolation, and length of day) differ by location. 203 In some locations, conditions conducive to O 3 formation are limited to a few summer months of the
year. For example, in states with colder climates such as Montana and South Dakota, the

cur rently required O 3 monitoring season is 4 months long . However, in other states with warmer climates such as California, Nevada, and Arizona, the currently required O 3 monitoring season for most sites continues all 12 months of the year. 204
Based on the O 3 NAAQS revision that was finalized in 2008 as well as the proposed NAAQS revisions discussed elsewhere in this rulemaking, l engthening of the O 3 monitoring

season s may be appropriate . A mbient O 3 concentrations could approach or exceed the level of the 2008 NAAQS as well as the proposed NAAQS more frequently and during more months of the year

. As noted later in this section, a related issue is the status of any currently effective Regional Administrator

- granted waiver approvals to O 3 monitoring seasons, and the impact of the proposed changes to monitoring season requirements on such waiver approvals. For the

203 See 40 CFR part 58 Appendix D, section 2.5, Table D

- 3 for a table of required O 3 seasons. 204 Certain states, such as California and Arizona, have approved shorter seasons for a subset of O3 sites, based on Regional Administrator review and approval (see 40 CFR part 58, Appendix D, section 4.1(i) for the waiver authority).*** E.O. 12866 Review

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Page 473 of 647 reasons explained below, EPA is proposing to revoke any existing waivers

. As appropriate, areas could seek new waivers so that monitoring agencies and th e EPA can evaluate the length of monitoring seasons in consideration of the 2008 NAAQS and the final 2015 O 3 standard, if it is revised. EPA has done an analysis to address the issue of whether extensions of currently required monitoring seasons are approp riate in light of the proposed NAAQS. 205 In the analysis, we determined the number of days where one or more monitors had a daily maximum 8

- hour O 3 average equal to or above 0.060 ppm in the months outside the currently

- required state O 3 monitoring season us ing data from monitors that collected O 3 data year

- round in 2010

- 201 3

. 206 Although we refer to these days as “exceedance days” in the analysis, this threshold is actually a conservative benchmark that is at a level below those proposed for the revised NAAQS. We find that this level, taking into consideration reasonable uncertainty, serves as an appropriate indicator of ambient conditions that may be conducive to the formation of O 3 concentrations that approach or exceed the 8

- hour average range of 0.065 to 0.070 ppm

. 207 Proposals for revising each state’s required monitoring season are based on observed exceedance days equal to or above the 0.060 ppm level in and surrounding the state. EPA considered a number of factors including out of season exceedance days either before or after the current O 3 monitoring season, the pattern of exceedance days in the out of season months, and regional consistency. We note that year

- to

-

205 Memo to docket to be prepared regarding documentation of O 3 Monitoring Season Analysis for the Proposed Rule

. 206 Approximately 800 O 3 monitors are currently ope rated year

- round, representing greater than 50 percent of the total O 3 monitoring network of about 1500 monitors . They include monitors that are mandated to operate year

- round due t o the required O 3 season and other monitors that are voluntarily operated year

- round by states and other organizations including EPA

- operated monitors at Clean Air Status and Trends Network ( CASTNET ) sites. 207 A n 8

- hour concentration of 0.060 ppm also corresponds to the thr eshold defining the current AQI breakpoint between the Good and Moderate indicator level ( 40 CFR part 58, appendix G ).*** E.O. 12866 Review

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Page 474 of 647 year variability occurs in seasonal O 3 patterns based on highly variable and unpredictable meteorological conditions which can support the formation of early or late season elevated O 3 concentrations in some years and not others. Given the impracticality of forecasting such variations in seasonal weather patterns, the EPA believes it is importan t that O 3 monitors operate during all periods when there is a reasonable possibility of ambient levels approaching the level of the proposed NAAQS. EPA reviewed the year

- round , O 3 data for 2010 through 2013 . A year

- round monitor was identified as “ year - rou nd ” if it had at least 20 daily observations in all 12 months, for at least 1 year of the 4 year period. During the 2010

- 2013 data period, all states operated a portion of their monitoring network outside of their required O 3 monitoring season and reported the data to the EPA Air Quality System (AQS). EPA’s analysis found the frequency of observed exceedance days of maximum 8

- hour average O 3 readings of at least 0.060 ppm to be quite high in several states across the country in months outside of the current ly required monitoring season. A total of 4 2 states experienced at least 1 exceedance day outside of the current O 3 season; 2 1 states had exceedance days only before the required monitoring season; 4 states had exceedance days only after the required monit oring season ; and 17 states had exceedance days both before and after the required monitoring season. In some cases, the frequency of exceedance days before the current
O 3 season was high, with 4 states experiencing between 31 and 122 out

- of

- season exceeda nce days from 2010 to 201 3 at monitors operating year

- round. 208
B asing O 3 monitoring season requirements on the goal of ensuring monitoring when ambient O 3 levels approach or exceed the level of the proposed NAAQS supports established

208 Colorado, South Dakota, Utah, and Wyoming.*** E.O. 12866 Review

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Page 475 of 647 monitoring network objectives described in Appendix D of part 58, including the requirement to provide air pollution data to the general public in a timely manner 209 and to support comparisons of an area's air pollution levels against the NAAQS. EPA believes that these exceeda nce s of 8

- hour O 3 levels greater than or equal to a threshold level that approaches the level of the proposed NAAQS i n months outside the currently required O 3 monitoring season support the proposed lengthening of the O 3 m onitoring season requirements for certain states.
T he operation of O 3 monitors during periods of time when ambient levels approach or exceed the level of the proposed NAAQS ensures that persons unusually sensitive to O 3 are alerted t o potential levels of health concern allowing them to tak e precautionary measures. The majority of O 3 monitors in the U.S. report to AIRNOW, 210 as well as to state

- operated websites and auto mated phone reporting systems. These programs support many objectives including real

time air quality reporting to the public , O 3 forecasting programs, and the verification of real

- time air quality forecast models. The specific proposed changes to the required state O 3 monitoring seasons are detailed in the proposed changes to Table D

- 3 of 40 CFR part 58 Appendix D (O 3 Monitorin g Season by
S tate). Although 4 2 states had at least one exceedance day outside the current monitoring season, changes are proposed for only 3 3 of those states. These proposed changes would entail a n incre ase of 1 month for 24 states (Connecticut, Delaware, District of Columbia, Idaho, Illinois, Indiana, Iowa, Kansas, Maryland, Massachusetts, Minnesota, Missouri, Nebraska, New Hampshire, New Jersey, New York, North Carolina, Ohio, Pennsylvania, Rhode Island, South Carolina, Northern Texas, Virginia, and West Virginia) , an increase of 1.5 months for

209 Public reporting requirements are detailed in 40 CFR part 58 Appendix G, Uniform Air Qual ity Index (AQI) and Daily Reporting. 210 See http://airnow.gov/*** E.O. 12866 Review

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Page 476 of 647 Wisconsin , an increase of 2 months for 3 states (Michigan, Montana, and North Dakota) , an increase of 4 months for Florida and South Dakota , an increase of 5 months for Colorado, and an increase of 7 months for Utah. For Wyoming, we are proposing to add 3 months at the beginning of the season and remove 1 month at the end of the season, resulting in a net increase of 2 months. O 3 season requirements are currently split by Air Quality Control Region (AQCR) in Loui siana and Texas. Included in the state

- by

- state accounting is the proposal to lengthen the required season in the no rthern part of Texas (AQCR 022, 210, 211, 212, 215, 217, and 218) by 1 month. S outhern Texas O 3 monitors would remain on a year

- round schedu le. In some states with limited available data and few exceedance days outside the current season, proposed changes were made by considering regional consistency and using supporting information from the surrounding states; these changes were all minor, in volving the proposed addition of 1 month to the current required season in Iowa, Missouri, Rhode Island, and West Virginia. EPA solicits comment on the proposed changes to the required O 3 monitoring seasons. We note that EPA Regional Administrators have p reviously approved certain deviations from the required O 3 monitoring seasons through rulemakings

. 211 The current ambient monitoring rule, in paragraph 4.1(i) of 40 CFR part 58 Appendix D (71 FR 61319 ; October 17, 2006 ) , allows EPA Regional Administrators to approve changes to the O 3 monitoring season without rulemaking. EPA is retaining the rule language allowing such deviations from the required O 3 monitoring seasons in the proposed revision to p aragraph 4.1( i ) of 40 CFR part 58, Appendix D. The proposed ch anges to O 3 monitoring season requirements, if finalized, will revoke previous Regional Administrator

- granted waiver approvals. Post

- final rule requests submitted along with relevant supporting information by states for monitoring season waivers from the r evised

211 64 FR 3028, 67 FR 57332, 69 FR 52836*** E.O. 12866 Review

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Page 477 of 647 requirements will be reviewed by Regional Administrators using, at a minimum, occurrences of the moderate Air Quality Index (AQI) level , the frequency of out

- of

- season O 3 NAAQS exceedances , and regional consistency. Any deviations based on the Regional Administrator’s waiver of requirements must be described in the state’s annual monitoring network plan and updated in the AQS. Current regulations permit O 3 monitors located at NCore multi

- pollutant stations to be
count ed toward meeting minimum network monitoring requirements. The NCore network requirements were promulgated in the October 17, 2006 (71 FR 61318) revisions to ambient monitoring regulations in order to build a long

- term, nationwide network that supports mul tiple objectives including air quality trends analyses, model evaluation, ecosystem studies, and assessment of transport between urban and rural areas. In the 2006 rulemaking, EPA did not propose a different O 3 monitoring season for NCore stations.
NCore stations are required to operate a full suite of gaseous and particulate matter monitors as well as basic meteorology to support the objectives. Given the potential value of NCore data to support year

- round scientific studies, EPA believes that it is appro priate to require
O 3 monitors at NCore stations to be o perated on a year

- round basis. Accordingly, EPA proposes that the required monitoring season for NCore stations be January through December regardless of the length of the required O 3 monitoring season for the remainder of the SLAMS (State and Local Air Monitoring Stations) monitors within a state. Considering the timing of this proposal and the final rule making (court ordered deadline of October 1, 2015) and associated burden on state/local monitoring agencies, we propose that implementation of the revised O 3 seasons become effective at SLAMS (including NCore sites) on January 1, 2017 . EPA is proposing to add paragraph 58.13 (g) of 40 CFR part 58 to require*** E.O. 12866 Review

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Page 478 of 647 that monitors operating under the requirements of section 4.1 of 40 CFR part 58, Appendix D operate on the applicable required O 3 monitoring seasons effective January 1, 2017 as listed in Table D

- 3 of appendix D to this part. We solicit comment on whether the revised s easons could be implemented beginning January 1, 2016 for all monitors or for a subset of monitors, such as those currently operating year round or on a schedule that corresponds to the proposed ozone season. If we determine, based on any such comments tha t implementation could occur earlier in such cases, we could proceed to final action requiring earlier implementation. C. Revisions to the Photochemical Assessment Monitoring Stations (PAMS) Network Design Section 182 (c)(1) of the CAA required the EPA t o promulgate rules for enhanced monitoring of O 3 , NO x , and volatile organic compounds (VOC) for nonattainment areas classified as serious (or above) to obtain more comprehensive and representative data on O 3 air pollution. In addition, Section 185 B of the CAA required EPA to work with the National Academy of Sciences (NAS) to conduct a study on the role of O 3 precursors in tropospheric O 3 formation and control. In 1992, the NAS issued the report entitled “Rethinking the Ozone Problem in Urban and Re gional Air Pollution” (National Academy of Sciences, 1992). In response to the CAA requirements and the reco mmendations of the NAS report, o n February 12, 1993 (58 FR 8452), the EPA revised the ambient air quality surveillance regulations to require Photo chemical Assessment Monitoring Stations (PAMS) in each O 3 nonattainment area classified as serious, severe, or extreme (“PAMS areas ”). 212 As noted in EPA’s Technical Assistance Document (TAD) for Sampling and Analysis of Ozone

212 Additional information on the O 3 designation process can be obtained at EPA’s O 3 designations webpage at http://www.epa.gov/groundlevelozone/designations /*** E.O. 12866 Review

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Page 479 of 647 Precursors , 213 the current objec tives of the PAMS program are to: 1) pr ovide a speciated ambient air database which is both representative and useful in evaluating control strategies and understanding the mechanisms of pollutant transport by ascertaining ambient profiles and distinguishi ng among various individual volatile organic compounds ( VOC s); 2) p rovide local, current meteorological and ambient data to serve as initial and boundary condition information for photochemical grid models ; 3) provide a representative, speciated ambient ai r database which is characteristic of source emission impacts to be used in analyzing emissions inventory issues and corrobor ating progress toward attainment; 4) provide ambient data measurements which would allow later preparation of unadjusted and a djust ed pollutant trends reports; 5) provide additional measurements of selected criteria pollutants for attainment/nonattainment decisions and to construct NAAQS maintenance plans ; and 6) provide additional measurements of selected criteria and non

- criteria po llutants to be used for evaluating population exposure to air toxics as well as criteria pollutants

. The original PAMS requirements called for two to five PAMS sites per PAMS area depending on the PAMS area’s population. Four types of PAMS sites were iden tified including upwind (Type 1), maximum precursor emission rate (Type 2), maximum O 3 (Type 3), and extreme downwind (Type 4) sites. Each PAMS site was required to measure O 3 , nitrogen oxide (NO), nitrogen dioxide (NO 2 ), speciated VOCs, selected carbonyl compounds, and sele cted meteorological parameters. In addition, upper air meteorological monitoring was required at one site in each PAMS area.

213 Technical Assistance Document (TAD) for Sampling and Analysis of Ozone Precursors, USEPA, 1998*** E.O. 12866 Review

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Page 480 of 647 In the 2006 monitoring rule ( 71 FR 61236 ), the EPA revised the PAMS requirements to only require two PAMS sites per PAMS area

. 214 The intent of the revision was to “allow PAMS monitoring to be more customized to local data needs rather than meeting so many specific requirements common to all subject O 3 nonattainment areas; the PAMS changes would also give

s tates the f

lexibility to reduce the overall size of their PAMS programs

— within limits

— and to use the associated resources for other types of monito ring they consider more useful.” In addition to reducing the number of required sites per PAMS area, the 2006 revisions also limited the requirement for carbonyl measurements (specifically formaldehyde, acetaldehyde, and acetone) to areas classified as serious or above for the 8

- hour O 3 standard. This change was made in recognition of carbonyl sampling issues which were bel ieved to cause significant uncertainty in the measured concentrations. Twenty

- two areas were classified as serious or above O 3 non - attainment at the time the PAMS requirements were promulgated in 1993. On July 18, 1997 (62 FR 38856), the EPA revised the av eraging time of the O 3 NAAQS from a 1

- hour averaging period to an 8

- hour averaging period. On June 15, 200 5 (70 FR 44470), the EPA revoked the 1

- hour standard in most areas of the country, however, PAMS requirements were identified as requirements that had to be retained in the anti

- backsliding provisions 215 included in that action. Therefore, PAMS requirements continue to be applicable to areas that were classified as serious or above non

attainment for the 1

- hour O 3 as of June 15, 2004. Currently, 25 areas are subject to the PAMS requirements with a total of 75 sites. As will be discussed in detail later, the current PAMS sites

214 A Type 2 site and either a Type 1 or a Type 3 site are currently required. 215 Refer to 40 CFR part 51.905*** E.O. 12866 Review

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Page 481 of 647 are concentrated in the North East and California with relatively limited coverage in the rest of the country. 216 As discussed above, t he first PAMS sites began operation in 1994, and have been in operation for over 20 years. Many changes have occurred during those times that have changed the O 3 problem in the U

. S

. as well as our understanding of it. The O 3 standard has been revised multiple times since the PAMS program was first implemented. On July 18, 1997, the EPA revised the O 3 NAAQS to a level of 0.08 parts per million (ppm), with a form based on the 3

- year average of the annual fourth

- highest daily maximum 8

- hour average O 3 con centration. On March 28, 2008, the EPA revised the O 3 standard to a level of 0.075 ppm, with a form based on the 3

- year average of the annual fourth

- highest daily maximum 8

- hour average O 3 concentration (73 FR 16436). These changes in the level and form of the O 3 NAAQS, along with notable decreases in O 3 levels in most parts of the U

. S

. , ha ve changed the landscape of the O 3 problem in the U.S

. At the time of the first round of designations for the 8

- hour standard (June 15, 2005), only 5 areas were classifie d as serious or above for the 8

- hour standard as compared to 2 2 areas that were classified as serious or above for the 1

- hour standard. 217 While the number of serious and above areas decreased, the number of non

- attainment areas remained nearly the same. In addition to the change in the landscape of O 3 non - attainment issues, much of the equipment used at PAMS sites is old and in need of replacement. New technologies have been developed since the inception of the PAMS program th at should be considered for use in the network. For these

216 Figure 1, Cavender 2014, “Network Design Conside rations for the PAMS Network”, to be added to the docket. 217 PAMS requirements continue to apply to all areas classified as serious or above as of June 15, 2005 due to anti

- backsliding provisions of 40 CFR 51.905.*** E.O. 12866 Review

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Page 482 of 647 reasons, the EPA determined that it would be appropriate to re

- evaluate the PAMS program and associated requirements in light of current O 3 issues.
In 201 1 , the EPA initiated an effort to re

- evaluate the PAMS requirements in light of changes in the needs of PAMS data users and the improvements in monitoring technology. The
EPA consulted with the Clean Air Science Advisory Committee (CASAC), Air Monitoring and Methods Subcommittee (AMMS) to seek advice on potential revisions to the technical and regulatory aspects of the PAMS program; including changes to required measurements and associated network design requirements. The EPA also requested advice on appropriate technology, sampling frequency, a nd overall program objectives in the context of the most recently revised O 3 NAAQS and changes to atmospheric chemistry that have occurred over the past 10

- 15 years in the significantly impacted areas. The CASAC AMMS met on May 16 and May 17, 2011, and pro vided a report with their advice on the PAMS program on September 28,
2011. 218 In addition, the EPA met multiple times with the N ational Association of Clean Air Agencies (NA CAA ) Monitoring Steering Committee (MSC) to seek advice on the PAMS program. The MSC includes monitoring experts from various State and local agencies actively engaged in ambient air monitoring and many members of the MSC have direct experience with running PAMS sites. Specific advice obtained from the CASAC AMMS and the MSC that was

cons idered in making the proposed changes to the PAMS requirements is discussed in the appropriate sections below. Based on the findings of the PAMS evaluation and the consultations with the CASAC AMMS and NACAA MSC, the EPA is proposing to revise several asp ects of the PAMS

218 CASAC Review of EPA’s Photochemical Assessment Monitoring Stations (PAMS) Network Re

- engineering Project; to be added to the Docket.*** E.O. 12866 Review

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Page 483 of 647 monitoring requirements including c hanges in 1) network design, 2) VOC sampling, 3) c arbonyl sampling, 4) n itrogen oxides sampling, and 5) u pper air meteorology measurements

. The following paragraphs describe the changes being proposed inc luding the rationale for the proposed changes. Timing and other implementation issues associated with these proposed changes are discussed at the end of this section. Network Design . As discussed above, the current PAMS network design calls for two sites (a Type 2, and a Type 1 or Type 3) per PAMS area. In their report, the CASAC AMMS
f ound “ that the existing uniform national network design model for PAMS is outdated and too resource intensive, ” and recommend ed “that greater flexibility for network design and implementation of the PAM S program be transferred to state and local monitoring agencies to allow monitoring, research and data analysis to be better tailored to the specific needs of each O 3 problem area. ” While stating that the current PAMS objective s were appropriate, the AMMS report also stated that “ objectives may need to be revised to include both a national and regional focus because national objectives may be different from regional objectives. ” The NACAA MSC also advised the EPA that the existi ng PAMS requirements were too prescriptive and may hinder state efforts to collect other types of data that were more useful in understanding their local O 3 problems. The EPA agrees with CASAC that the PAMS objectives include both local and national object ives, and believes that the current PAMS network design is no longer suited for meeting either sets of objectives. As part of the PAMS evaluation, it was determined that at the national level the primary use of the PAMS data has been to evaluate photochemi cal model performance. Due to the locations of the current PAMS areas and the current network design, existing PAMS sites are clustered along the n orth e ast and w est coasts leading to significant redundancy in these*** E.O. 12866 Review

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Page 484 of 647 areas and very limited coverage th r oughout the remainder of the count r y. 219 The resulting uneven spatial coverage greatly limits the value of the PAMS data for evaluation of model performance. CASAC noted the spatial coverage issue and advised that EPA should consider requiring PAMS

measureme nts in areas in addition to “ areas classified as serious and above for the O 3 NAAQS to improve spatial coverage. ” The EPA also agrees with CASAC and the NACAA that the PAMS requirements should be revised to provide monitoring agencies greater flexibility i n meeting local objectives. The EPA is proposing changes to the network design requirements that we believe will better serve both national and local objectives. The EPA is proposing a two part network design. The first part of the design includes a netwo rk of fixed sites (“required PAMS sites”) intended to support O 3 model development and the tracking of trends of important O 3 precursor concentrations. The second part of the network design includes monitoring agency directed “Enhanced Monitoring Plans” w hich allow monitoring agencies the needed flexibility to implement additional monitoring capabilities to suit the needs of their area. To implement the fixed site portion of the network design, the EPA is proposing to require PAMS measurements at any exis ting NCore site in an O 3 non - attainment area (either based on the 2008 O 3 NAAQS or the 2015 O 3 NAAQS) in lieu of the current PAMS network design requirements. 220 The NCore network is a multi

- pollutant monitoring network consisting of 80 sites (63 urban, 17 r ural) and is intended to support multiple air quality objectives

219 Figure 1, Cavender 2014, “Network Design Considerations for the PAMS Network”, to be added to the docket. 220 Although enh anced monitoring for ozone, oxides of nitrogen, and VOCs is specifically required for areas classified at least serious for the ozone NAAQS by section 182(c)(1) of the CAA, EPA has concluded that requiring enhanced monitoring for all ozone nonattainment ar eas is appropriate for the purposes of monitoring ambient air quality and better understanding ozone pollution.*** E.O. 12866 Review

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Page 485 of 647 including the development and model evaluation of photochemical models (including both PM 2.5 and O 3 models), and the tracking of regional precursor trends. NCore sites are sited in typical

ne ighborhood scale locations which are more suitable than source impacted locations for evaluation of grid models typical of current photochemical models and tracking of trends in pre

cursor concentrations. The EPA believes NCore sites are well suited for O 3 model development and evaluation. The proposal to require PAMS measurements at existing NCore sites in O 3 non attainment areas would replace the existing PAMS network design. 221 This change would keep roughly the same number of required PAMS sites while im proving spatial coverage

. 222 Based on the range of the O 3 NAAQS being proposed today and current O 3 design value estimates (based
on 2011

- 2013 air quality data), the number of required sites is estimated to be between 48 and 65 , which compares to 50 c urrentl y required sites, and 75 currently operating sites. Potential redundancy in the existing network would be reduced while important network coverage in the south east and mid

- west would be added. The improved spatial coverage will also improve EPA’s ability to track trends in precursor concentrations regionally. The EPA notes that in limited situations, an O 3 non - attainment area may not have an NCore site and in those cases, the area would only be subject to the requirement for a n Enhanced Monitoring Plan as discussed in more detail below . The EPA believes that the network coverage provided by existing NCore sites in O 3

non - attainment areas would be adequate for the national PAMS objectives discuss ed above, and

221 While the EPA is proposing to replace the multi

- site design, monitoring agencies would be encouraged to identify the type of PAMS site the NCo re site represents. In most cases, NCore sites would likely be classified as either a Type 2 or Type 3 site. In limited situations rural NCore sites might be subject to these proposed requirements, in which case, these sites would likely be either Type 1 o r Type 4 sites. 222 Figure 2, Cavender 2014, “Network Design Considerations for the PAMS Network” , to be added to the docket.*** E.O. 12866 Review

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Page 486 of 647 that requiring PAM S sites , in addition to Enhanced Monitoring Plans, in those O 3 non - attainment areas without NCore sites would not substantially improve the network coverage. In addition to the reduction in the number of required sites, the EPA notes that the proposed network design change would provide significant cost efficiencies. By adding PAMS measurements to existing NCore sites, the PAMS network would be taking advantage of existing infrastructure and measurements currently being coll ected at NCore sites. NCore sites already have the larger, climate

- controlled shelters that are necessary to operate the automated gas chromatographs (“auto

- GCs”) used to collect speciated VOCs. In addition, existing NCore sites currently collect data on m any of the required PAMS measurements including O 3 , carbon monoxide (CO), total reactive nitrogen (NO y ), and meteorological measurements including wind speed and direction, temperature, and relative humidity

. While the EPA believes these proposed changes will result in cost savings on an overall network basis, individual monitoring agencies may see either an increase or a decrease in burden as a result of these proposed changes. Many monitoring agencies in O 3 non - attainment areas who are not currently affe cted by the existing PAMS requirements would be required to add PAMS measurements to their existing NCore sites, while several monitoring agencies with existing PAMS sites would not be required to continue PAMS monitoring if these proposed requirements

are promulgated. 223 As discussed later in this preamble, the EPA is proposing a staggered compliance schedule for the proposed PAMS requirements in recognition of the need for capital investment and staff training at these sites.

223 Monitoring agencies would be able to seek approval to shut down non

- required PAMS sites at their discretion pursuant to the requi rements detailed in 40 CFR part 58.14 for O 3 and NO x monitors.*** E.O. 12866 Review

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Page 487 of 647 The EPA recognizes that in lim ited situations existing NCore sites may not be the most appropriate locations for making PAMS measurements. For example, an existing PAMS site in
an O 3 non - attainment area may be sited at a different location than the existing NCore site. In this case, it may be appropriate to continue monitoring at the existing PAMS site to support ongoing research and to maintain trends information. To account for these situations, the EPA is also proposing to provide the EPA Regional Administrator the authority to appro ve an alternative location for a required PAMS sites where appropriate

. The EPA seeks comment on the proposed addition of PAMS measurements at NCore sites in O 3 non - attainment areas, and the removal of current multi

- site PAMS network design requirements. The second part of the proposed PAMS network design includes monitoring agency directed enhanced O 3 monitoring activities intended to provide data needed to understand an area’s specific O 3 issues

. To implement this part of the PAMS network design , the EPA is proposing to add a requirement for states with O 3 non - attainment areas to develop a “ Enhanced Monitoring Plan .” These Enhanced Monitoring Plans, which are to be submitted as part of their required Annual Monitoring Network Plan, would be reviewed and approved by the EPA Regional Administrator as part of the annual plan review process

. The purpose of the Enhanced Monitoring Plan is to improve monitoring for ambient concentrations of O 3 , NO x /NO y , VOC, and meteorology. Types of acti vities that might be included in the state directed Enhanced Monitoring Plan include (but are not limited to) additional PAMS sites (e.g., upwind or downwind sites), additional O 3 and NO x monitoring, ozonesondes or other aloft measurements, rural measureme nts, mobile PAMS sites, additional meteorological measurements, and episodic or intensive studies. The intent of this part is to allow monitoring agencies flexibility in determining and collecting the data they need to understand their O 3 problems , consist ent with*** E.O. 12866 Review

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Page 488 of 647 the advice obtained from the CASAC AMMS and the NACAA MSC . The savings from a smaller less costly fixed network of required PAMS sites would be available for re

- investment in the development and implementation of the proposed Enhanced Monitoring P lans

. Speciated VOC Measurements

. Measurement of speciated VOCs important to O 3 formation is a key aspect of the PAMS program. Currently, the existing PAMS requirements allow for a number of options in measuring speciated VOCs at PAMS sites which include 1)
h ourly measurements using an auto

- GC, 2) e ight 3

- hour samples daily using canisters, or 3) o ne morning and one afternoon sample with a 3

- hour or less averaging time daily using canisters plus continuous Total Non

- methane Hydrocarbon (TNMHC) measurements

. The EPA believes that the options provided for VOC measurement limit the comparative value of the data being collected, and is proposing to instead require all required PAMS sites to measure and report hourly speciated VOCs using an auto GC

. More complet e and consistent speciated VOC data nationally would better help meet certain objectives of the PAMS program described above (e.g., a speciated ambient air database useful in evaluating control strategies, analyzing emissions inventory issues, corroboratin g progress toward attainment, and evaluating population exposure to air toxics). Furthermore, as noted by the CASAC AMMS, h ourly VOC data are “ particularly useful in evaluating air quality models and performing diagnostic emission attribution studies. These data can be provided on a near real

- time basis and presented along with other precursor species (e.g., oxides of nitrogen and carbon monoxide) collected over similar averaging times. ” L onger time

- averaged data are of significantly lower value for mod el*** E.O. 12866 Review

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Page 489 of 647 evaluation. 224 In addition, creating consistent monitoring requirements across the network will provide better data for analyzing regional trends and spatial patterns. At the time the original PAMS requirements were promulgated, the canister options were included because the EPA recognized that the technologies necessary to measure hourly average speciated VOCs concentrations were relatively new and may not have been suitable for broad network use. At that time, gas chromatographs designed for laboratory use were equipped with
auto

- samplers designed to “trap” the VOC compounds from a gas sample, and then “purge” the compounds onto the GC column. The EPA did not believe that auto

- GCs were universally appropriate due to the technical skill and effort necessa ry at that time to properly operate an auto

GC. While the basic principles of auto

- GC technology have not changed, the hardware and software of modern auto

- GCs are greatly improved over that available at the time of the original PAMS requirements. Based o n advice from the CASAC AMMS, the EPA has initiated an evaluation of current auto

- GCs potentially suitable for use in the PAMS network. Based on the preliminary results, the EPA believes that typical NCore site operators, with appropriate training, will ha ve the skill necessary to operate a modern auto

- GC successfully

. Considering the advances in auto

- GC technology, the added value obtained from hourly data , and the proposed move of PAMS measurements to NCore sites in O 3 non - attainment areas, the EPA is pro posing to require hourly speciated VOC sampling at all PAMS sites. The EPA notes that this proposed requirement would effectively prevent the use of canisters to collect speciated VOCs at the

224 Data of longer than a one hour average are often not used in model evaluations due to the complexity of trying to accommodate non

- hourly averaged data.*** E.O. 12866 Review

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Page 490 of 647 required PAMS sites. However, canister sampling may continue to be an appropriate method for collecting speciated VOCs at other locations as part of the proposed Enhanced Monitoring Plans. While the EPA believes that the proposed transition to hourly speciated VOC sampling is the appropriate strategy to take advantage of improved technology and to broaden the utility of collected data, we are also mindful of the additional rigidity that the proposed mandatory use of
auto

- GCs may have for monitoring agencies, especially those that have experience with and have establish ed effective and reliable canister sampling programs. Therefore, the EPA is requesting comment on the proposed requirement for hourly VOC sampling as well as the range of alternatives that might be appropriate in lieu of a strict requirement. Such alterna tives could range from a more formal process where monitoring agencies could request a Regional Administrator granted waiver from the hourly VOC requirements through the Annual Monitoring Network Plan process to collect canister

- based speciated VOC data, t o a more flexible set of alternatives where canister sampling could be retained based on each monitoring agency’s evaluation of programmatic needs as well as their own logistical and technical capabilities. Carbonyl Sampling

. Carbonyls include a number of compounds important to O 3 formation that cannot currently be measured using the auto

- GCs or canisters used at PAMS sites to measure speciated VOCs. 225 The current method for measuring carbonyls in the PAMS program is Compendium Method TO

- 11A

. 226 In this method , carbonyl compounds are adsorbed

225 Carbonyls compounds including formaldehyde and acetaldehyde are difficult to analyze by GC with Flame Ionization Detectors (FID). Both of these compounds in their free state, do not respond well to FID detectors. GC analysis is difficult due to the chemic al composition of these compounds, increased polarity and their inherently low boiling points. 226 “ Determination of Formaldehyde in Ambient Air Using Adsorbent Cartridge Followed by High Performance Liquid Chromatography (HPLC) ” (EPA 1996), to be added to t he docket

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Page 491 of 647 and converted into stable hydrazones using dinitrophenylhydrazine (DNPH) cartridges. These cartridges are then analyzed for the individual carbonyl compounds using liquid chromatography (LC) techniques. Three carbonyls are currently required to be measured in the PAMS program

- formaldehyde, acetaldehyde, and acetone.
In 2006 , the EPA revised the PAMS requirements such that carbonyl sampling was only required in areas classified as serious or above non

- attainment for O 3 und er the 8

- hour O 3 standard which effectively reduced the applicability of carbonyl sampling to a few areas in California. This change was made in recognition that there were a number of issues with Method
TO

- 11A that raised concerns with the uncertainty in the carbonyl data being collected. These issues include interferences (humidity and O 3 ) and breakthrough (i.e., overloading of the DNPH cartridge) at high concentrations. While solutions for these issues have been investigated , these improvements have not been incorporated into Method TO

- 11A. A recent evaluation of the importance of VOCs and carbonyls to O 3 formation determined that carbonyls, especially formaldehyde, are very important to O 3 formation

. 227 CASAC AMMS also noted the importance of carbonyls stating that “ There are many compelling scientific reasons to measure carbonyls. They are a very important part of O 3 chemistry almost everywhere .” Due to the importance of carbonyls to understanding O 3 ch emistry, the EPA believes the need for carbonyl data outweighs the concerns over the uncertainty in the data. Therefore , the EPA is proposing to require all required PAMS sites to measure the carbonyls formaldehyde, acetaldehyde, and acetone. In addition, EPA is investigating alternatives to further reduce uncertainties in carbonyl data as described below.

227 Cavender, 2013 “Revisions to the Photochemical Assessment Monitoring Stations Compound Target List”, to be added to the docket.*** E.O. 12866 Review

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Page 492 of 647 To improve the carbonyl data that would be collected at required PAMS sites (and National Air Toxics Trends Station, or NATTS sites which are currently m easuring carbonyls), the EPA has undertaken an effort to improve carbonyl sampling and analysis methods to reduce the uncertainty in carbonyl data. This effort will lead to improvements to the current Method TO

11A by incorporating solutions to sampling an d analysis issues that have been identified since Method TO

- 11A was finalized in 1996, such as the inclusion of an O 3 scrubber in the sampling system to reduce the interference from oxidants such as O 3 . Also as part of this effort, the EPA is investigating alternative cartridge materials that have been identified in the literature as a replacement for DNPH that may have better collection efficiency with fewer interferences. Nitrogen Oxides Sampling

. It is well known that n itr ic o xide (NO) and n itrogen diox ide (NO 2 ) play important roles in O 3 formation. 228 Under the current network design, Type 2 PAMS sites are required to measure nitrogen oxides (NO x , which by definition is the sum of NO and
NO 2 ), and Types 1, 3, and 4 sites are required to measure total reac tive nitrogen (NO y ) which by definition includes NO, NO 2 , and other oxidized nitrogen compounds (NO z ). NCore sites are also currently required to measure NO y but are not required to measure NO 2 . In conventional NO x analyzers, NO 2 is determined as the difference between the measured NO and NO x concentrations. However, due to the non

- selective reduction of oxidized nitrogen compounds by the molybedenum converter used in conventional NO x monitors, the
NO 2 measurement made by conventi onal NO x monitors can be biased high due to the varying

228 See ISA section 3.2.2.*** E.O. 12866 Review

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Page 493 of 647 presence of NO z compounds that may be reported as NO 2 . 229 The unknown bias from the NO z compounds is undesir able when attempting to understand O 3 chemistry. Improvements in reactive nitrogen measurement s have been made since the original PAMS requirements were promulgated that allow for improved NO 2 measurements. Selective photolytic converters have been developed that are not significantly biased by NO z compounds

. 230 Monitors using photolytic converters a re commercially available and have been approved as FEMs for the measurement of NO 2 . In addition, methods that directly read NO 2 have been developed that allow for very accurate readings of NO 2 without some of the issues inherent to the “difference method” used in converter based NO x analyzers. However, these direct reading NO 2 analyzers generally do not provide a n NO estimate, and would need to be paired with a converter

- based NO x monitor or NO y monitor in order to also measure NO. As discussed above, the EPA is propo sing to change the PAMS network design such that PAMS measurements would be required at existing NCore sites in O 3 non - attainment areas. NCore sites currently are required to measure NO and NO y . NCore sites are not curr ently required to measure NO 2 . Due to the importance of accurate NO 2 data to the understanding of O 3 formation, the EPA is proposing to require NO 2 measurements at required PAMS sites. Since existing NCore sites currently measure NO y , either a direct readi ng NO 2 analyzer or a photolytic

converter NO x analyzer sh ould be used to meet the proposed requirement. The EPA believes

229 Nitrogen compounds that would likely be reported (along with NO 2 ) as NO 2 with a conventi onal NOx monitor include peroxyacetyl nitrate (PAN), peroxypropionyl nitrate (PPN), peroxymethacryloyl nitrate (MPAN), and nitric acid (HNO 3 ), and as well as other nitrogen compounds not listed here. 230 Ryerson, et al, 2000 “An Efficient Photolysis System for Fast

- Response NO 2 Measurements, Journal of Geophysical Research, Volume 105, Issue D21.*** E.O. 12866 Review

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Page 494 of 647 c onventional NO x analyzers would not be appropriate for making PAMS measurements due to the uncertainty caused by interferences caused by NO z compounds. Meteorology Measurements

. The current PAMS requirements require m onitoring agencies to collect surface meteorology at all required PAMS sites. As noted in EPA’s TAD 231 for the PAMS program, the PAMS requirements do not provide specific surf ace meteorological parameters to be monitored. As part of the implementation efforts for the original PAMS program, a list of r ecommend ed parameters was developed and incorporated into the TAD which include s wind direction, wind speed, temperature, humidit y, atmospheric pressure, precipitation, solar radiation, and ultraviolet (UV) radiation. Currently , NCore sites are required to measure the above parameters with the exceptions of atmospheric pressure, precipitation, solar radiation, and UV radiation. In r ecognition of the importance of these ad ditional measurements for O 3 the EPA is proposing to specify that required PAMS sites are required to collect wind direction, wind speed, temperature, humidity, atmospheric pressure, precipitation, solar radiation, and UV radiation

. This proposed revision will provide clarity and consistency to the collection of surface meteorological parameters important to the understanding of O 3 formation. If PAMS measurements are moved to NCore sites in O 3 non - attainment areas, a s is being proposed, the net impact of this proposed revision to the surface meteorological requirements for PAMS sites is to add the requirement for the monitoring of atmospheric pressure, precipitation, solar radiation, and UV radiation at affected NCore sites. The existing PAMS requirements also require the collection of upper air meteorological measurements at one site in each PAMS area. The term upper air meteorological is not well

231 Technical Assistance Document (TAD) for Sampling and Analysis of Ozone Precursors, USEPA, 1998*** E.O. 12866 Review

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Page 495 of 647 defined in the existing PAMS requirements

. As part of the implementati on efforts for the original PAMS program mixing height was added to the PAMS TAD as a recommended meteorological parameter to be monitored.
M ost monitoring agencies installed radar profile r s to me e t the requirement to collect upper air meteorology

. Radar profile r s provide data on wind and speed at multiple heights in the atmosphere. Radio acoustic sounding system ( RASS ) profilers are often included with radar profilers to obtain atmospheric temperature at multiple heights in the atmosphere and to estimate mixing height. The EPA recognizes that the upper air data on wind speed and wind direction from radar profilers can be very useful in O 3 modeling. However, many of the current PAMS radar profilers are old and in need of replacement or expensive maintenance

. In addition, the cost to install and operate radar profilers at all NCore sites would be prohibitive. Therefore , the EPA is not proposing to add upper air wind speed and direction as required meteorological parameters to be monitored at required PAMS sit es. Where monitoring agenc ies find the radar profiler data valuable, continued operation of existing radar profilers or the installation of new radar profilers would be appropriate to consider as part of the state’s Enhanced Monitoring Plan

. As discussed a bove, mixing height is one upper air meteorological measurement that has historically been measured at PAMS sites. A number of methods can be used to measure mixing height i n addition to radar profiler technology discussed above. Recent developments in cei lometer technology allow for the measurement of mixing height by changes in particulate concentrations at the top of the bound a ry layer. 232 Ceilometers provide the potential for continuous mixing height data at a fraction of the cost of radar profilers. Due to the importance

232 Eresmaa, N, et al, (2006), “Mixing Height Determination by Ceilom eter”, Atmospheric Chemistry and Physics, 6. 1485

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Page 496 of 647 of mixing height measurements for O 3 modeling, the EPA is proposing to add the requirement for monitoring agencies to measure mixing height at required PAMS sites

. The EPA is aware of a large network of ceilometers operated by the Nat ional Oceanic and Atmospheric Administration ( NOAA ) as part of the Automated Surface Observing System (ASOS). The EPA has been in discussions with NOAA regarding the potential for these systems to provide the needed mixing height data, however, the ASOS ce ilometers are not currently equipped to provide mixing height data. Nonetheless, the EPA will continue to work with NOAA to determine if the ASOS ceilometers can be upgraded to meet the need for mixing height data, and is including proposed regulatory lang uage that will allow states a waiver to use nearby mixing height data from ASOS or other sources to meet the requirement to collect mixing height data at required PAMS sites.
PAMS Season

. Currently, PAMS measurements are required to be taken during the

mon ths of June, July, and August. This three month period is referred to as the “PAMS Season”. As part of the PAMS re

- evaluation, the EPA considered changes to the PAMS season. The three month PAMS season was originally selected to represent the most active p eriod for O 3 formation . However, the EPA notes that in many areas the highest O 3 concentrations are observed outside of the PAMS season. 233 As an example, the highest O 3 concentrations in the mountain

- west often occur during the winter months. Data collected during the current PAMS season would have limited value in understanding winter O 3 episodes. The CASAC AMMS noted in their report to the EPA that “it would be desirable to extend the PAMS monitoring season beyond the current June, July, August sampling p eriod.”

233 The current O 3 monitoring season by state in 40 CFR part 58, appendix D, requires monitoring seasons from 4 to 12 months. As noted in section VI.B. of this rulemaking, the EPA proposes to lengthen t he seasons further for 33 states.*** E.O. 12866 Review

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Page 497 of 647 But that “the monitoring season should not be mandated and rigid; it should be flexible and adopted and coordinated on a regional airshed basis (i.e., within the same O 3 region).” The EPA agrees with CASAC on the need for flexibility in determining when PAMS measurements should be taken to meet local monitoring needs but also agrees with CASAC that the flexibility “should not conflict with national goals for the PAMS program.” A significant benefit of the standard PAMS season is that it ensures data availability from all PAMS sites for national

- or regional

- scale modeling efforts. While EPA agrees with the potential benefit of extending the availability of PAMS measurements outside of the current season, we also considered the burden of requiring

mon itoring agencies to operate additional PAMS measurements (e.g., hourly speciated VOC) for periods that in some cases, might be much longer than the current 3

- month season, for example, if the PAMS season was extended to match each state’s required O 3 monit oring season. Being mindful of the potential burden associated with a lengthening of the PAMS season as well as the potential benefits of the additional data, the EPA is proposing to maintain the current 3

- month PAMS monitoring season for required PAMS sit es rather than extending the PAMS season to other periods where elevated O 3 may be expected. The EPA believes that the 3

- month PAMS season will provide a consistent data set of O 3 and O 3 precursor measurements for addressing the national PAMS objectives. M onitoring agencies are encouraged to consider collecting PAMS measurements in additional periods beyond the required PAMS season as part of the proposed Enhanced Monitoring Plan . The monitoring agencies should consider factors such as the periods of expect ed O 3 exceedances and regional consistency when determining potential expansion of the specific monitoring periods beyond the required PAMS season.*** E.O. 12866 Review

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Page 498 of 647 Timing and Other Implementation Issues . The EPA recognizes that the proposed changes to the PAMS requirement will require resources and a reasonable implementation schedule if they are promulgated. The proposed network design changes would require monitoring agencies to start collection of PAMS measurements at many NCore sites that are not currently collecting
P AMS measurements. These affected monitoring agencies would need to make capital investments (primarily for the installation of auto

- GCs, NO 2 monitors, and ceilometers). Monitoring agencies will also need time to develop the expertise, by training existing staff or otherwise, to successfully collect PAMS measurements. The EPA believes that the current national funding level of the PAMS program is sufficient to support these proposed changes, especially in light of the staggered compliance schedule described below. The current grant guidance includes the maintenance of a PAMS capital equipment reserve that could be used to assist monitoring agencies with the purchase of needed equipment. We also recognize that the proposed revisions would result in a potential shifting of PAMS resources, and we would work with the regional offices, affected states, and monitoring organizations such as the NACAA and the Association of Air Pollution Control Agencies (AAPCA) to facilitate any shifts in funding during the implement ation phase of the program. For these reasons, the EPA is proposing a staggered compliance schedule for the proposed changes to the PAMS requirements (including both the monitoring at required PAMS sites and the Enhanced Monitoring Plans). For areas curren tly designated as non

- attainment for
O 3 based on the 2008 NAAQS, the EPA is proposing to require monitoring agencies to incorporate the proposed PAMS requirements into their next annual monitoring network plan following promulgation of these proposed chang es (July 1, 2016 based on current schedules) and to comply with these proposed PAMS requirements by the following PAMS season (June 1,*** E.O. 12866 Review

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Page 499 of 647 2017 based on current schedules). For new areas designated as O 3 non - attainment based on the initial round of designations following the promulgation of a revised O 3 standard, the EPA is proposing to require monitoring agencies to incorporate the proposed PAMS requirements into their next annual monitoring network plan following designations (due July 1, 2018 based on current schedules) and to comply with new PAMS requirements by the following PAMS season (June 1, 201 9 based on current schedules). Finally, the EPA is proposing that areas designated as
O 3 non - attainment following the initial round of designations be allowed 2 years after designation to comply with the proposed PAMS requirements. The EPA believes that the proposed compliance schedule will allow monitoring agencies adequate time to implement the proposed PA MS requirements. The EPA solicits comments on whether the proposed implementation schedule is practicable, or whether additional time would be warranted for installation of new PAMS sites, the development of Enhanced Monitoring Plans, or other specific new PAMS requirements

. D. Revision of the Federal Reference Method (FRM) for Ozone To be used in a determination of compliance with the O 3 NAAQS, O 3 monitoring data must be obtained using either a Federal Reference Method (FRM) or a Federal Equivalent Metho d (FEM), as defined in 40 CFR parts 50 and 53. Nearly all the monitoring methods for O 3 currently used by state and local monitoring agencies are FEM continuous analyzers utilizing a measurement principle based on quantitative measurement of the absorption of UV light by O 3 . This type of O 3 analyzer was introduced into the monitoring networks in the 1980s and has since become the most predominant type of method used because of its all

- optoelectronic design and ease of installation and use. The existing O 3 F RM utilizes a measurement principle based on quantitative measurement of the chemiluminescence from the reaction of O 3 with ethylene.*** E.O. 12866 Review

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Page 500 of 647 Ozone analyzers based on this FRM principle are no longer used for routine O 3 field monitoring and no longer commercially available. The current list of all approved FRMs and FEMs capable of providing ambient O 3 data for use in NAAQS attainment decisions may be found on the EPA’s website and in the docket for this action. 234 The EPA proposes to revise the FRM to establish a new technique for measuring O 3 in the ambient air. This new technique would be a new type of analyzer based on Nitric Oxide

chemiluminescence (NO

- CL) methodology. Because of the similarity of this new chemiluminescence technique to the existing ethylene

- chemi luminescence (ET

- CL) methodology, EPA proposes that it be incorporated into the existing O 3 FRM, using the same calibration procedure. Appendix D of 40 CFR part 50 would be revised to include both the original ET

- CL as well as the new NO

- CL methodology. A minor change is proposed to the existing O 3 FRM calibration procedure, which would be applicable to both chemiluminescence FRM methodologies. The proposed change in section 4.5.2.3 of the calibration procedure in part 50 provides for more flexibility in th e range of the linearity test. FRMs, as set forth in several appendices to 40 CFR part 50, serve two primary purposes. The first is to provide a specified, definitive methodology for routinely measuring concentrations of various ambient air pollutants for comparison to the NAAQS in part 50, for quality assurance assessment of monitoring data, and for other air monitoring objectives. The second is to provide a standard of comparison for determining equivalence to the specified reference method of alternativ e and perhaps more practical pollutant measurement methods (equivalent methods, or FEMs) that can be used in lieu of the FRM for routine monitoring.

234 List of Designated Reference and Equivalent Methods; US EPA, Office of Research and Development; National Exposure Research Laboratory; http://www.epa.gov/ttn/amtic/files/ambient/criteria/reference

- equivalent

- methods

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Page 501 of 647 Some of the FRMs contained in appendices to part 50 (such as the original SO 2 FRM and the lead FRM) are man ual methods that are completely specified in a step

- by

- step manner. Others (such as the O 3 FRM) are in the form of a measurement principle along with an associated calibration procedure that must be implemented in a commercially

- produced FRM analyzer model . Such FRM

- type analyzers must be tested and shown to meet explicit performance and other qualification requirements that are set forth in 40 CFR part 53 (Ambient Air Monitoring Reference and Equivalent Methods) . Each analyzer model is then considered to b e an FRM only upon specific designation as an FRM by EPA under the provisions of 53.2 (General requirements for a reference method determination). As pollutant measurement technology advances and changes, the reference methods in part 50 are assessed by t he EPA to determine if improved or more suitable measurement technology is available to better meet current FRM needs as well as potential future FRM requirements. New technology can either be presented to the EPA for evaluation by an FEM applicant under 5 3.16 (Supersession of reference methods), or (as in this case) the EPA can originate the process as provided in 53.7 (Testing of methods at the initiative of the Administrator). The current FRM for measuring O 3 in the ambient air was promulgated on April 30, 1971 (36 FR 8186), in conjunction with the EPA’s establishment (originally as 42 CFR part 410) of the first national ambient air quality standards for six criteria pollutants (including O 3 ), as now set forth in 40 CFR part 50. On February 8, 1979 (44 FR 8224), the original O 3 FRM calibration procedure was changed from a wet

- chemical standard to a UV photometric calibration procedure. Minor updates to technical references were made on July 18, 1997 (62 FR 38895). This FRM is specified as a measurement p rinciple and calibration procedure in Appendix D of*** E.O. 12866 Review

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Page 502 of 647 part 50. The measurement principle of the FRM is based on the quantitative measurement of chemiluminescent light intensity emitted by the chemical reaction of O 3 in an air sample with ethylene gas mixed i n a measurement cell. This ET

- CL measurement is calibrated by the specified calibration procedure, which is based on photometric assay of O 3 calibration concentrations in a dynamic flowing system, using measurement of the absorption of UV light by the O 3 c alibration concentrations at a nominal wavelength of 254 nm. At the time of the FRM’s original promulgation, analyzers based on the ET

- CL FRM were widely used for field monitoring of O 3 . Laboratory testing prior to, during, and following analyzer developme nt indicated that interferences to which the method was susceptible were few and relatively minor in magnitude. Further, subsequent field experience with the FRM analyzers showed them to be stable, accurate, and reliable. Operation of these FRM analyzers r equires a supply of ethylene gas, provided by an attendant high

- pressure compressed gas cylinder. Installation of this high

- pressure cylinder of flammable and potentially explosive gas proved problematic at many field

- monitoring sites due to fire codes or other safety restrictions. Further, the ethylene gas cylinder required periodic replacement

– a considerable cost and operational inconvenience. Following the development of FEM O 3 analyzers based on UV absorption, use of these newer UV FEM analyzers event ually supplanted the ET

- CL FRM analyzers because the UV analyzers required no gas supply or other reagents and were much easier to install and operate. Currently, nearly all compliance monitoring in the U.S. is carried out with UV absorption type FEM analy zers . 235 This transition from ET

- CL FRM analyzers to UV absorption analyzers in U.S. (as well as world

- wide) monitoring networks has become so extensive that analyzer manufacturers no longer manufacture the ET

- CL FRM analyzers. The last new O 3 FRM analyzer w as designated by EPA in 1979. As a result, no FRM O 3 analyzers are commercially available to serve as reference standards for testing and designation of new O 3 FEM analyzers, for O 3 compliance monitoring, and for quality assurance of field monitors. FRM un its manufactured years ago are becoming increasingly difficult to maintain in operational condition due to aging of

235 Draft

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Page 503 of 647 components and lack of replacement parts (several of the original FRM analyzer manufacturers no longer exist). Until the last few years, rel atively few measurement techniques have been successfully implemented in a continuous ambient O 3 analyzer model that has achieved designation by EPA as either an FRM or FEM. 236 These include the ET

- CL technique, the UV absorption technique and differential o ptical absorption spectroscopy (DOAS, an open

- path method represented by two FEM instrument models from different manufacturers). A relatively new technology is nitric oxide (NO)

- O 3 chemiluminescence, which is represented by two FEM instrument models from a single manufacturer. An even newer technology is a “scrubberless” UV absorption technique that is represented by a single analyzer model for which FEM designation was recently achieved. As noted above, the ET

- CL technique is technically advantageous as a n FRM, but its ethylene supply requirement and the lack of commercially available analyzers severely limit its ability to fulfill the needs for an O 3 FRM. Differential optical absorption spectroscopy (DOAS) analyzers are not suitable for some FRM purposes because of their open

- path nature. Commercial availability of conventional UV

- absorption O 3 analyzers is excellent, and their widespread use makes the measurement technique desirable for consideration as an FRM. However, the technique is susceptible to potential measurement interference from mercury, some volatile aromatic hydrocarbons, water, a nd other compounds that sometimes occur in ambient air. 237 These interferences are substantially reduced by the use of scrubbers (as discussed below) in UV FEM analyzers, such that the technique can be used extensively for compliance

236 List of Designated Reference and Equivalent Methods; US EPA, Office of Research and Development; National Exposure Research Laboratory; http://www.epa.gov/ttn/amtic/files/ambient/criteria/reference

- equivalent

- methods

- list.pdf

. 237 Spicer et al., (2010). A re

- examination of ambient air ozone monitor interferences. J. Air and Waste Management Association, 60: 1353

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Page 504 of 647 monitoring. Although the interferences are substantially reduced by the use of scrubbers, the potential for interferences prevents the technique from consideration as an FRM. It is important to make a distinction between use of the UV

- absorption measurement technique for assay of O 3 concentrations, as described in the FRM calibration procedure of part 50, Appendix D, and use of the UV absorption technique for measurement of O 3 in ambient air. For assay of calibration concentrations, the technique is used in a system with clean, ze ro air ( air that must be free of contaminants which would cause a detectable response from the O 3 analyzer) such that potential ambient

- air

- borne interferences are not an issue. Under these clean

- air conditions, the UV assay technique is very accurate and highly reproducible

– so much so that the National Institute of Standards and Technology (NIST) utilizes it for its O 3 Standard Reference Photometer. In contrast, use of the UV

- absorption technique to measure O 3 in ambient air is much more difficult becaus e of the need to deal with UV

- absorbing (and hence potential interfering) species present in ambient air. Ambient UV O 3 monitors typically suppress interferences by using an “O 3 scrubber” that attempts to remove O 3 from ambient air without removing potenti ally interfering species, to create a zero

- O 3 reference air that still contains any potentially interfering species. In a differential measurement process that compares the UV absorption measurement of O 3 in the ambient air sample with that in this zero

- O 3 reference air, the net effect of interferences is minimized by “cancellation.” FEM analyzers using such O 3 scrubbers are able to meet the FEM interference test requirements of 40 CFR part 53 and provide adequate
O 3 monitoring data at most typical O 3 mon itoring sites. On October 7, 2011, EPA designated two NO

- CL O 3 analyzers as FEMs (76 FR 62402). These analyzers use a variation of the current FRM measurement principle, based on*** E.O. 12866 Review

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Page 505 of 647 measurement of the chemiluminescence produced by the chemical reaction of O 3 with NO rather than with ethylene. As explained below, EPA believes that this variation has performance suitable for an O 3 FRM and offers a substantial implementation advantage over the existing
FRM. The NO

- CL measurement technique for O 3 is quite similar to the existing ET

- CL FRM technique, in that both are based on the measurement of the intensity of the chemiluminescence resulting from a chemical reaction of a reactant with the O 3 in the ambient air sample. The principle difference is t hat the reactant is NO rather than ethylene. As a potential variation of the FRM measurement principle, the measurement would be calibrated with the same calibration procedure specified in the FRM. The performance of NO

- CL analyzers has been shown to be ve ry similar to the performance of ET

- CL FRM analyzers

– providing stable, accurate, highly reproducible measurements of ambient O 3 with minimal potential interferences. 238 As with ET

- CL , some minor interference from variable humidity in ambient air can be min imized with a sample air dryer. The analyzers require a supply of NO gas, typically from a high

- pressure compressed gas cylinder. However, unlike ethylene, NO is neither flammable nor explosive, so use of the method in field applications is eased considera bly relative to use of ET

- CL analyzers. NO gas is toxic, but it is possible to use a cylinder of much less toxic, non

- combustible nitrous oxide (N 2 O) gas with a photolytic N 2 O

- to

- NO converter to supply NO gas for the instrument as needed. There will be no requirement for states to switch to NO

- CL analyzers; therefore, UV

- absorption FEM

238 U.S.EPA, “P erformance of the Proposed New Federal Reference Method for Measuring Ozone Concentrations in Ambient Air. ” Report Number EPA #######; prepared by Office of Research and Development, National Exposure Research Laboratory, U.S. Environmental Protection Agen cy, Research Triangle Park, NC (2014)*** E.O. 12866 Review

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Page 5 06 of 647 analyzers can still be used for routine O 3 monitoring. As noted previously, EPA has designated
two NO

- CL FEM analyzers (from the same manufacturer), both of which would quali fy for re

designation as FRMs if the NO

- CL technique is finalized as an FRM. NO

- CL analyzers would then be available for those applications where an FRM analyzer is needed. Because of the similarity of the NO

- CL technique to the existing ET

- CL technique, EPA is proposing to amend the ET

- CL FRM by adding the NO

- CL technique as a variation to the existing FRM measurement principle specified in Appendix D of Part 50. The specified calibration procedure would be applicable to both FRM ET

- CL and NO

- CL measureme nt techniques. Since the existing ET

- CL FRM measurement principle remains a technically adequate FRM, and the proposed new NO

- CL FRM is technically adequate, it is prudent to retain the existing FRM measurement principle. The designation of all currently d esignated O 3 FEMs is based on comparison to the ET

- CL FRM, so retention of the ET

- CL FRM allows those FEM designations to be retained. Adding the proposed NO

- CL measurement technique to the current O 3 FRM would allow at least two commercially available FR M analyzer models (currently FEMs) to be re

- designated as FRMs to fulfill FRM analyzer needs. Some older FRM analyzers based on the existing ET

- CL measurement principle may still be in operable condition, and there is no technical reason to cancel their de signation by withdrawing the original ET

- CL FRM technique. Additionally, retaining the existing ET

- CL FRM technique allows for the possibility of an instrument manufacturer offering an ET

- CL FRM analyzer in the future. The second of the newly introduced O 3 measurement techniques is known as the “scrubberless” UV absorption (UV

- SL) technique. It utilizes the UV

- absorption measurement technique that is widely used in O 3 monitoring networks. The new UV

- SL technique specifies*** E.O. 12866 Review

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Page 507 of 647 removal of O 3 from the sample air f or the zero reference by a gas

- phase reaction with NO rather than via a conventional chemical scrubber. The NO reacts with the O 3 much faster than with other potential interfering compounds and is very effective at removing the O 3 without affecting other c ompounds that may be present in the ambient air sample. The differential UV measurement can effectively eliminate interferences to an insignificant level. Other potential interference arising from changes in water vapor concentration can be minimized with a sample air dryer. The UV

- SL technique appears to have characteristics that are advantageous for meeting the requirements of a new O 3 FRM. Analyzers implementing this technique require a supply of NO (such as a high

- pressure gas cylinder). As noted previo usly in connection with the NO

- CL technique, NO is neither flammable nor explosive, so use of the method in field applications is eased considerably relative to use of ET

- CL analyzers. Use of N 2 O gas, also supplied in compressed gas cylinders but less toxi c than NO, is also possible with a photolytic N 2 O to NO converter. One commercially available UV

- SL analyzer was approved as an FEM on June 18, 2014 (79 FR 34734). The performance of the analyzer, as reported by the manufacturer 239 and some initial field and laboratory studies performed by the EPA 240 , suggests that the analyzer may meet existing, as well as the proposed, requirements for an O 3 FRM

. The CASAC AMMS provided a peer review of the proposed FRM and changes to the part 53 requirements on April 3, 201 4. The CASAC AMMS recommended that the EPA consider the UV

- SL as a FRM. The EPA is independently conducting further laboratory and field tests of

239 2B FEM test data via http://www.twobtech.com/model_211.htm 240 U.S.EPA, “Performance of the Proposed New Federal Reference Method for Measuring Ozone Concentrations in Ambient Air .” Report Number EPA #######; prepared by Office of Research and Development, National Exposure Research Laboratory, U.S. Environmental Protection Agency, Research Triangle Park, NC (2014)*** E.O. 12866 Review

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Page 508 of 647 the UV

- SL analyzer to verify its performance. Although this new UV

- SL methodology shows substantial promise fo r future consideration as a new O 3 FRM, there is currently insufficient documented test and performance information available on the method to propose it as a new FRM at this time. The EPA is continuing to study the method and assess its potential suitabil ity
as a new O 3 FRM, and the EPA solicits comment on its potential and suitability as an FRM. EPA is not proposing to supersede (replace) the existing O 3 FRM measurement principle under the provisions of 40 CFR 53.16. Rather, for the reasons in the preamb le and having conducted the necessary tests, EPA is proposing, consistent with 40 CFR 53.7 , to revise the existing O 3 FRM to widen the scope of its ET

- CL measurement principle to include the NO

- CL measurement technique as well. Following promulgation of the proposed revised O 3 FRM measurement principle, any new candidate O 3 FRM analyzers would be required to use either the ET

- CL or NO

- CL measurement principle, and would also be subject to the O 3 FRM performance requirements proposed in 40 CFR part 53. The FRM calibration procedure specified in Appendix D would apply to both O 3 FRM measurement techniques. A substantial number of laboratory tests have confirmed the excellent performance of the
NO

- CL analyzers as well as very close agreement with both ET

- CL a nd UV analyzers in collocated field tests. Therefore, the EPA believes the proposed FRM measurement principle that incorporates the NO

- CL methodology is the best approach to improve the availability of FRM analyzers for O 3 . No other currently known approac h or alternative methodology appears to be more appropriate for a new FRM. Adding the NO

- CL technology to the existing O 3 FRM is also endorsed by the EPA’s CASAC AMMS. EPA solicits comment on the proposal to retain the*** E.O. 12866 Review

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Page 509 of 647 existing O 3 FRM measurement principle and amend it to include the NO

- CL variation as well. Comments are also solicited on the nature and adequacy of the proposed revised FRM. The generic description of the FRM measurement principle for the existing ET

- CL FRM in Appendix D would be amended to include the NO

- CL variation (see the proposed rule text for Appendix D). As noted previously, the new NO

- CL technique would also use the same calibration procedure in Appendix D and would be similarly coupled with the explicit O 3 FRM analyzer performance r equirements specified in subpart B of 40 CFR part 53. In addition to the incorporation of the NO

- CL methodology, numerous minor clarifications, wording changes, additional details, and a more refined numbering system are being proposed for Appendix D.
Acco rdingly, the entire Appendix D is proposed to be revised as identified in the proposed regulatory text. Because the new NO

- CL technique is proposed to be added to the existing FRM measurement principle, while the existing ET

- CL FRM principle would be retai ned and remain in effect, all existing designated FEM analyzer models will continue their designated status. Thus, this action would cause no negative consequences on monitoring agencies, and no disruption of, or required change to, their O 3 monitoring pro grams. Comparative testing has been carried out at several field monitoring sites under a variety of ambient conditions, and the results confirm that the proposed new NO

- CL FRM measurement technique provides ambient O 3 measurements that compare and correla te excellently with measurements using the existing ET

CL measurement principle, with no significant bias, offset, or discrepancy. 241

241 U.S.EPA, “Performance of the Proposed New Federal Reference Method for Measuring Ozone Concentrations in Ambient Air.” Report Number EPA #######; prepared by Office of Research and Development, National Exposure Research Laboratory, U.S. Environmental Pro tection Agency, Research Triangle Park, NC (2014)*** E.O. 12866 Review

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Page 510 of 647 E. Revisions to the Procedures for Testing Performance Characteristics and Determining Comparability Between Candidate Meth ods and Reference Methods The only substantial changes proposed to the requirements of Part 53 are in Tables B

- 1 and B

- 3 of Subpart B. Table B

- 1 has been updated in recent years with regard to FRM and FEM methods for SO 2 (74 FR 64877) and CO (76 FR 54294)

. Similar update changes to Table B

- 1 are proposed here for O 3 . M odest changes proposed for Table B

- 3 would add new interferent test concentrations specifically for NO

- CL analyzers, adding a test for NO 2 . T he table would also clarify that the existing test concentrations apply to ET

- CL O 3 analyzers. Figure B

- 5 is revised to correct a minor inconsistency in the “Calculation s ” column for the two “ Precision ” rows to change “% URL” to “ % Standard Deviation. ” Several changes to the performance requirements given in Table B

- 1 are proposed for O 3 . The performance requirements for “standard range” instruments would be updated to be more consistent with current O 3 analyzer performance capabilities. The noise requir ement limit would be reduced from 0.005 to 0.001 ppm for O 3 analyzers, the lower detectable limit would be reduced from 0.010 to 0.003 ppm, and the maximum interference equivalent limits would be reduced from 0.02 to 0.005 ppm for each potential interferin g agent (interferent). T he performance limit requirement for the total of all interferents is proposed to be withdrawn for O 3 methods. This withdrawal is appropriate because O 3 analyzer test performance, as reported in recent FEM applications, has shown th at the limits established for individual interferents are sufficiently effective to define adequate analyzer performance, and the separate limit for the total of all interferences is unnecessary . Maximum zero drift for O 3 analyzers would be reduced from 0 .02 to 0.004 ppm. The existing limit for span drift at 20 per cent of the upper range limit (URL) is proposed to be withdrawn. Analyzer performance test results have clearly shown that the existing 80% URL*** E.O. 12866 Review

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Page 511 of 647 limits are fully adequate and better specify span drift performance and that the 20% URL span drift limits are ineffective and unnecessary. The span drift limit applicable to O 3 analyzers is proposed to be reduced from ±5.0% to ±3.0%. Lag time limits would be reduced from 20 to 2 minutes, and rise and fal l time limits would be similarly reduced from 15 to 2 minutes. For precision, EPA proposes to change the form of the precision limit specifications (at both 20% and 80% of URL) for O 3 analyzers from ppm to percent (of the URL). This change would make the l imits responsive to higher and lower measurement ranges, as appropriate, and is consistent with the same change previously made in the corresponding precision requirements for SO 2 and CO analyzers. Both limits would be set at 2 percent for O 3 analyzers, wh ich is equivalent to, and therefore effectively unchanged, from the existing limits of 0.01 ppm (for a URL of 0.5 ppm). Although the changes to Part 53 proposed here are generally restricted to methods for O 3 , this change in form for the precision limits i s proposed to be extended to methods for NO 2 , as well, to simplify Table B

- 1 and make it consistent for all pollutants covered by the Table. The precision limits that would be applicable to methods for NO 2 are proposed to be changed to 4% and 6% of the URL (for 20% and 80% of the URL, respectively). These values are exactly equivalent to the existing limits of 0.020 ppm and 0.030 ppm, respectively, for the specified URL of 0.5 ppm. Therefore, these precision limits for NO 2 remain effectively unchanged, but specified as a percent rather than an absolute concentration. A new footnote is proposed for Table B

- 1 to clarify that these revised precision limits are given as “standard deviation expressed as percent of the URL.” Therefore, Figure B

- 5 will be revised t o correct a minor inconsistency in the “Calculation” column for the two “Precision” rows to change the “% URL” to “% Standard Deviation”.*** E.O. 12866 Review

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Page 512 of 647 The EPA has reviewed the documented performance of currently designated FRM and FEM methods for O 3 (that are still in commercial production or in service in monitoring networks) and has verified that all would meet the proposed new performance requirements for
O 3 methods

. 242 Therefore, adoption of the proposed new performance requirements in Table B

- 1 would not require the withdrawal or cancelation of the FRM or FEM designation of any such O 3 analyzers. Finally, to meet a need for analyzers with more sensitive measurement ranges for monitoring in relatively clean areas, new, “lower range” performance limit requirements are proposed for O 3 analyzers. These lower range limits are set forth in a new “lower range” column
in Table B

- 1 and would be optional. But where a lower measurement range is included in the FRM or FEM designation, these proposed new requirements would provide more stringent performance for analyzers commensurate with greater accuracy for low

- level measurements in lower

- level concentration ranges. The EPA believes that these proposed changes in the performance requirements of Tables
B

- 1 and B

- 3 are appropriate, based on analyzer performance data available from analyzer manuals and recent FRM and FEM applications. The EPA solicits comment as to whether t he proposed changes are reasonable, appropriate, benefi cial , and achievable without undue burden

. EPA is propos ing minor change s to the general provisions in subpart A of Part 53 to ease the administrative burden associated with processing and reviewing modification requests to existing FRMs and FEMs. This change in 53.14(c) will extend the length of time for the
A dministrator to take action on a request for modification of a reference or equivalent method

242 Draft

- Modern O3 Instrument Deployment and Performance Data.xlsx, (2013) to be placed in the docket.*** E.O. 12866 Review

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Page 513 of 647 from 30 days to 90 days. Section 53.14(c) would read: "Within 90 calendar days after receiving a report under paragraph (a) of this section, the Administrator wil l take one or more of the following actions:" EPA is also propos ing to remove the obsolete provision that manufacture r s who offered PM 2.5 or PM 10

- 2.5 samplers or analyzers for sale as part of a FRM or FEM may continue to do so only so long as updates of th e Product Manufacturing Checklist are submitted annually. This change is accomplished through the removal of section ( i ) from 53.9 and Figure
E

- 2 from subpart E of part 53

. VII. Implementation of Proposed O 3 Standards The proposed revisions to the primary and secondary O 3 NAAQS discussed in sections II.E and IV.G, if finalized, would trigger a process under which states 243 make recommendations to the Administrator regarding area designations, and the EPA promulgates the final area designations. States would also be required to review, modify, and supplement their existing state implementation plans (SIPs). The proposed O 3 NAAQS revisions would also affect the transportation conformity and general conformity processes. The revised O 3 NAAQS and the subsequent designations process could affect which preconstruction permitting requirements apply to O 3 in some areas and the nature of those requirements in others

. The EPA has regulations in place addressing the requirements for state implementation plans and sever al provisions in these existing rules cover O 3 . 40 CFR Part 51. States likewise have provisions in their SIPs to address air quality for O 3 and to implement the existing O 3 NAAQS. The EPA has also provided general guidance on the development of state imple mentation plans for all pollutants and administration of construction permitting programs,

243 This and all subsequent references to “state” are meant to include state, local, and tribal agencies responsible for the implementation of an O 3 control program.*** E.O. 12866 Review

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Page 514 of 647 as well as specific guidance on implementing the O 3 NAAQS in some contexts under the Clean Air Act and EPA regulations. When the EPA proposes to revise a NAAQS for a particular criteria pollutant, it considers the extent to which existing EPA regulations and guidance are sufficient to implement the standard and whether any revisions or updates to those regulation and guidance would be helpful or appropriate in facili tating the implementation of the revised standard by states. The
C A A does not require that the EPA promulgate new implementing regulations every time that a NAAQS is revised. Likewise, the CA A does not require the issuance of additional implementing regula tions or guidance by the EPA before a revised NAAQS becomes effective. Existing EPA regulations may be sufficient in many cases to enable the EPA and the states to begin the process of implementing a revised NAAQS. However, where the nature of revisions to a NAAQS indicate that additional EPA regulations or guidance (or revisions to existing regulations or guidance) may be helpful to implement unique aspects of the revised standard, the EPA endeavors to provide those regulations and guidance in a timely way to facilitate preparation of state implementation plans. It is important to note, however, that the existing EPA regulations in 40 CFR Part 51 applicable to SIPs generally and to particular pollutants continue to apply even without such updates. According ly, the discussion below provides the EPA’s current thoughts about the extent to which revisions to existing regulations and additional guidance might be helpful or appropriate to aid in the implementation of a revised O 3 NAAQS, should one be finalized thr ough this rulemaking. This section also provides background information for understanding the possible implications of the proposed NAAQS changes in some areas , and describes the EPA’s plans for providing revised rules or additional guidance on some subje cts in a timely manner to assist*** E.O. 12866 Review

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Page 515 of 647 states with their implementation efforts under the requirements of the CAA . This section also describes existing EPA interpretations of CAA requirements and other EPA guidance relevant to implementation of revised O 3 NAAQS. Relevant CAA provisions that provide potential flexibility with regard to meeting implementation timelines are also discussed. This section also contains a discussion of how existing requirements to reduce the impact
on O 3 concentrations from the stationary source construction in permit programs under the CAA may be affected by the proposed revisions of the O 3 NAAQS. These are the Prevention of Significant Deterioration (PSD) and Nonattainment New Source Review (NNSR) programs. To facilitate th e timely implementation of the PSD requirements, the EPA proposes as part of this rulemaking to add a grandfathering provision to its regulations that would apply to certain PSD permit applications that are pending on the effective date of the revised O 3 N AAQS. If the proposed NAAQS revisions are finalized, this grandfathering provision could be finalized at the same time as the revised NAAQS (see section VII. D ). The EPA intends to propose additional regulations and issue additional guidance, as
necessary, related to the implementation requirements for any revised O 3 NAAQS resulting from this proposal. The EPA intends to take these actions on a schedule that provides timely assistance to air agencies. Accordingly, in this section, the EPA solicits comment o n several issues that the Agency anticipates address ing in future guidance or regulatory actions to assist with implementation of the revised O 3 NAAQS . Because these issues are not relevant to the establishment of the NAAQS, and the CAA does not require th at the EPA provide implementation rules or guidance for each revised NAAQS, the EPA does not expect to respond, nor is the Agency required to respond, to these comments in the final action on this proposal.*** E.O. 12866 Review

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Page 516 of 647 However the EPA expects these comments will be he lpful as future guidance and regulations are developed. A. NAAQS Implementation 1. Background As directed by the Clean Air Act, reducing pollution to meet national air quality standards always has been a shared task, one involving the federal government, states, tribes and local air quality management agencies. The EPA develops regulations and strategies to reduce pollution on a broad scale, while states and tribes are responsible for implementation planning and any additional emission reduction measures necessary to bring areas into attainment. The Agency supports implementation planning with technical resources and guidance, while states and local agencies use their knowledge of local needs and opportunities in designing emission reduction strategies tha t will work best for their industries and communities. This partnership has proved effective since the EPA first issued O 3 standards more than three decades ago. For example, 101 areas were designated as nonattainment for the 1

- hour O 3 standards issued in 1979. As of the end of 2013, air quality in 98 of those areas meets the 1

- hour standards. The EPA strengthened the O 3 standards in 1997, shifting to an 8

- hour standard to improve public health protection, particularly for children, the elderly, and other sensitive individuals, against effects such as reduced lung function and respiratory symptoms, hospital and emergency room visits for asthma, and possible irreversible damage to the lungs. The 1997 standards drew significant public attention when they were proposed, with numerous parties voicing concerns about states’ ability to comply. However, after close collaboration between the EPA states, tribes and local governments to reduce O 3 - forming pollutants, significant progress has been made. Air quality in 9 0% of the original 113 areas designated as nonattainment for the*** E.O. 12866 Review

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Page 517 of 647 1997 O 3 NAAQS now meets the 1997 standards. The EPA designated 46 areas as nonattainment for the 2008 O 3 NAAQS in 2012. We expect these areas to make similar progress in achieving clean air. The majority of man

- made NO X and VOC emissions that contribute to O 3 formation in the United States come from the following sectors: on

- road and nonroad mobile sources, industrial processes (including solvents), consumer and commercial products, and the e lectric power industry. In 2011, the most recent year for which the National Emissions Inventory (NEI) is available, onroad and nonroad mobile sources accounted for about 60 % of annual NO X emissions; and the electric power industry accounted for about near ly 15% . With respect to VOC, industrial processes (including solvents) accounted for about 57 % of manmade VOC emissions; and mobile sources accounted for about 39 % . Emissions from natural sources, such as trees, also comprise around 70 % of total VOC emissi ons nationally, with a higher proportion during the O 3 season and in areas with more vegetative cover. See section VII.F for more detail on background O 3 . Since 2000, the EPA has issued numerous emissions and fuels standards for on

- road and nonroad mobile sources, as well as emissions standards for many types of stationary sources. Benefits from new engine standards increase each year as older, more

- polluting vehicles and engines are replaced with newer, cleaner models. Benefits from fuel programs generall y begin as soon as a new fuel is available. The ongoing emission reductions from federal programs such as these will provide for substantial emissions reductions well into the future, and will complement state and local efforts to attain any revised O 3 NAA QS. Over the past fifteen years, the EPA has established new emissions standards under title II of the CAA, 42 U.S.C. 7521

– 7574 , for numerous classes of automobile, truck, bus,*** E.O. 12866 Review

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Page 518 of 647 motorcycle, earth mover, aircraft, and locomotive engines, and for the fuels u sed to power these engines. The EPA also established new standards for the smaller engines used in small watercraft, and lawn and garden equipment. In March 2008, the EPA promulgated new standards for locomotive and for marine diesel engines and in April 2 010 the EPA promulgated new standards for Category 3 (C3) engines installed on U.S. ocean

- going vessels and to marine diesel fuels produced and distributed in the United States. In September 2011, the EPA and the National Highway Transportation Safety Admi nistration established greenhouse gas and fuel efficiency standards for new 2014

– 2018 model year medium and heavy

- duty engines and vehicles. In addition to improving fuel efficiency and reducing greenhouse gas emissions this rule reduces emissions of NO X from the subject vehicles. In March 2014, the EPA promulgated Tier 3 standards for tailpipe and evaporative emissions from passenger cars, light

- duty trucks, medium

- duty passenger vehicles, and some heavy

- duty vehicles. The associated gasoline sulfur
stan dard will enable more stringent vehicle emissions standards and will make existing emissions control systems more effective. Compared to current standards, the VOC and NO X tailpipe standards for light

- duty vehicles represent approximately an 80% reduction from today’s fleet average, and the heavy

- duty tailpipe standards represent about a 60% reduction in VOC and
NO X . The emission reductions from all of these mobile source programs are significant and will continue to be realized throughout the implementati on period for any revised O 3 NAAQS. T he EPA projects that between 2011 and 2025, onroad and nonroad mobile NO X will decline by more than 60 % and onroad and nonroad mobile VOC will decline by more than 50 %

. 244

244 [Placeholder for RIA citation ] “Regulatory Impact Analysis for the Proposed Revisions to the National Ambient Air Quality Standards for Ozone,” (December 2014) at http://www.epa.gov/ttnecas1/r ia.html

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Page 519 of 647 The reduction of VOC emissions from industrial p rocesses has been achieved either directly or indirectly through implementation of control technology standards, including maximum achievable control technology (MACT), reasonably available control technology (RACT), and best available control technology ( BACT) standards; or is anticipated due to proposed or upcoming proposals based on generally available control technology or best available controls under provisions related to consumer and commercial products. These standards have resulted in VOC emission reductions of almost a million tons per year accumulated starting in 1997 from a variety of sources including combustion sources, coating categories, and chemical manufacturing. The EPA also finalized emission standards and fuel requirements for new statio nary engines. In the area of consumer and commercial products, the EPA finalized new national VOC emission standards for aerosol coatings in 2008 and will review and revise, as necessary, existing rules for household and institutional consumer products,

ar chitectural and industrial maintenance coatings, and automobile refinish coatings. Additionally, in O 3 nonattainment areas, we anticipate reductions of an additional 10,000 tons per year as states adopt rules implementing control techniques recommendations issued in 2008 for 4 additional categories of consumer and commercial products, such as surface coatings and adhesives used in industrial manufacturing operations. These emission reductions primarily result from solvent controls and typically occur where and when the solvent is used, such as during manufacturing
processes. As noted above, the power industry is responsible for a nearly 15 % of NO X emissions

across the United States. Power industry emission sources include large electric generating units (E GU) and some large industrial boilers and turbines. The EPA’s Clean Air Interstate Rule (CAIR), issued on March 10, 2005, was designed to permanently reduce power industry*** E.O. 12866 Review

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Page 520 of 647 emissions of NO X in the eastern United States. The first phase of the cap was to beg in in 2009, and a lower second phase cap was to begin in 2015. The EPA had projected that by 2015, the CAIR and other programs would reduce NO X emissions during the O 3 season by about 50 % and annual NO X emissions by about 60 % from 2003 levels in the Easter n U.S. However, on July 11, 2008 and December 23, 2008, the U.S. Court of Appeals for the D.C. Circuit (D.C. Circuit) issued decisions on petitions for review of the CAIR. In its July 11 opinion, the court found CAIR unlawful and decided to vacate CAIR and its associated Federal implementation plans (FIPs) in their entirety. State of North Carolina v. EPA, 531 F. 3d 896

. On December 23, 2008, however, the court granted EPA’s petition for rehearing to the extent that it remanded without vacatur for EPA to co nduct further proceedings consistent with the Court’s prior opinion. Under this decision, CAIR will remain in place only until replaced by EPA with a rule that is consistent with the Court’s July 11 opinion. The EPA issued the final Cross State Air Pollu tion Rule (CSAPR) on July 6, 2011, to replace CAIR. CSAPR requires states to significantly improve air quality by reducing power plant emissions that contribute to O 3 and/or fine particle pollution in other states. CSAPR requires a total of 28 states to reduce annual SO 2 emissions, annual NO X emissions and/or O 3 season NO X emissions to assist downwind states in attaining the 1997 O 3 and fine particle and
2006 PM 2.5 NAAQS. On December 30, 2011, the D.C. Circuit issued an order staying CSAPR and ordering the EPA to continue implementing CAIR. Subsequently, on August 21, 2012, the D.C. Circuit issued an opinion vacating CSAPR. EME Homer City Generation LP v. EPA, 696 F. 3d 7

. In its decision the Court again instructed the EPA to continue administering CAIR. The United States and other parties appealed the D.C. Circuit decision to the U.S. Supreme Court and on April 29, 201 4 , the U.S. Sup reme Court issued an opinion reversing the judgment of the D.C.*** E.O. 12866 Review

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Page 521 of 647 Circuit , upholding EPA’s interpretation of the CAA “good neighbor” provision (CAA section 110 (a)(2)(d)(ii)), and remanding the case back to the D.C. Circuit for further proceedings consistent with the Supreme Court opinion. EME Homer City Generation LP v. EPA , 134 S. Ct. 1584. On June 26, 2014, the U.S. Government filed a motion with the D.C. Circuit to lift the stay of the CSAPR. While the Court considers the motion, CAIR remains in place and no immediate action from states or affected sources is expected. The EPA proposed the Clean Power Plan for existing power plants on June 2, 2014 (79 FR 34830; June 18, 20 14). In this action the EPA proposed state

- specific rate

- based goals for carbon dioxide emissions from the power sector, as well as guidelines for states to follow in developing plans to achieve the state

- specific goals. This rule, as proposed, would conti nue progress already underway to reduce carbon dioxide emissions from existing fossil fuel

- fired power plants in the United States. Actions taken to comply with the proposed guidelines would reduce emissions of CO 2 and other air pollutants, including SO 2 , NOx and directly emitted
PM 2.5 , from the electric power industry. The EPA estimates that the Clean Power Plan, as proposed, would reduce precursors for both ozone and particulate matter leading to decreases in the concentrations of those pollutants of appr oximately 25% in 2030. It should also be noted , in general, that new electric generating units (EGUs) are subject
to NO X limits under New Source Performance Standards (NSPS) under CAA section 111, as well as either PSD or NNSR requirements. The EPA’s regu lations for commercial, industrial and solid waste incinerators set standards for NO X and several air toxics for all commercial incinerators, as required under Section 129 of the Act. Air toxics rules for industrial boilers will yield co

- benefit NO X reduct ions as a result of tune

- ups and energy efficiency measures, especially from boilers that burn coal. And several new source performance standards and air*** E.O. 12866 Review

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Page 522 of 647 toxics standards are expected to make further cuts to NO X and VOC emissions from new and existing sour ces of pollution. These include upcoming review and revisions for gas turbines and municipal waste combustors, along with proposed requirements for the petroleum refining industry. The new source performance standards and air toxics standards that have rec ently taken effect for stationary engines w ill also make cuts to NO X and VOC emissions. The EPA also anticipates reductions in O 3 precursors to result from implementation of the Mercury and Air Toxics Standard rule, as well as from measures to address Regi onal Haze best available retrofit technology (BART) determinations. While the EPA uses its regulatory opportunities to reduce NO X and VOCs, the Agency also is pursuing non

- regulatory efforts as we strive toward cleaner air. Energy Star, a joint program of the EPA and the U.S. Department of Energy, protects the environment and saves money through energy efficient products and practices. Improving energy efficiency in homes, buildings and industry helps reduce all emissions from the power sector

– including NO X – while reducing compliance costs for electricity providers. As part of its new Advance Program, the EPA is working collaboratively with state, local, and tribal governments that want to take steps to reduce air pollution in O 3 and particulate matter a ttainment areas. Although these areas are not currently subject to nonattainment planning requirements, Advance Program participants are interested in undertaking their own planning efforts with the goal of keeping their air healthy and creating an improve d buffer against future air quality violations. Participating areas are implementing a mix of voluntary and mandatory measures relating to mobile, area, and point sources as well as energy efficiency measures, and they are also pursuing education and

aware ness programs to improve their communities’ understanding of air quality issues.*** E.O. 12866 Review

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Page 523 of 647 The EPA recognizes that a number of areas of the country have been working to reduce
O 3 precursors for many years and now may need to turn to newer, more innovative approach es for reducing emissions as they develop their implementation plans. These approaches, such as smart growth policies and renewable energy portfolios, hold great promise for improved air quality and health, and the EPA is working with air quality agencies and stakeholders to identify ways to include these types of programs in implementation plans. For example, the EPA developed a roadmap for giving SIP credit to energy efficiency/renewable energy projects. 245 Recognition of innovative programs will allow states and tribes to pursue effective strategies that address some of the more challenging issues affecting air quality, such as land use planning, ever increasing motor vehicle use, and planning for long

- term energy needs. With respect to agricultural sources, the U.S. Department of Agriculture (USDA) has approved conservation systems and activities that reduce agricultural emissions of NO X and VOC. The EPA recognizes that USDA has been working with the agric ultural community to develop site

- specific conservation systems and activities to control emissions of O 3 precursors. The EPA will continue to work with USDA on these activities with efforts to identify and/or improve the control efficiencies, prioritize t he adoption of these conservation systems and activities, and ensure that appropriate criteria are used for identifying the most effective application of conservation systems and activities. The EPA will work together with USDA and with states to identify appropriate measures to meet the primary and secondary standards, including site

- specific conservation systems and activities. Based on prior experience identifying conservation measures and practices to meet the

245 “The Roadmap for Incorporating Energy Efficiency/Renewable Energy Policies and Programs into State and Tribal Implementation Plans,” (July 2012) at http://epa.gov/airquality/eere/

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Page 524 of 647 PM NAAQS requirements, the EPA will use a similar process to identify measures that could meet the O 3 requirements. The EPA anticipates that certain USDA approved conservation systems and activities that reduce agricultural emissions of NO X and VOC may be able to satisfy the requirements for appli cable sources to implement reasonably available control measures for purposes of attaining the primary and secondary O 3 NAAQS. The Agency also is active in work to reduce the international transport of O 3 and other pollutants that can contribute to “backg round” O 3 levels in the U.S. Under the Convention on Long

- Range Transboundary Air Pollution (LRTAP) of the United Nations Economic Commission for Europe, the United States has been a party to the Protocol to Abate Acidification, Eutrophication, and Ground

- level Ozone (known as the Gothenburg Protocol) since 2005. The U.S. is also active in the LRTAP Task Force for Hemispheric Transport of Air Pollution, which in 2010 produced a comprehensive assessment of the intercontinental transport of air pollution (inc luding O 3 ) in the northern hemisphere. The United States has worked bilaterally with Canada under the US

- Canada Air Quality Agreement to adopt an Ozone Annex to address transboundary O 3 impacts. The EPA also continues to work with rapidly growing countrie s such as China on air quality management activities and the development of analytical tools to help these countries address significant air quality problems, including the emissions of O 3 - forming pollutants. This work includes supporting China’s efforts t o rapidly deploy power plant pollution controls that can achieve NO X reductions of at least 80 to 90 %

. We know that developing the implementation plans that outline the steps a nonattainment area will take to meet an air quality standard requires a significant amount of work on the part of state, tribal or local air agencies. The EPA routinely looks for way s to reduce this workload,*** E.O. 12866 Review

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Page 525 of 647 including assisting with air quality modeling by providing inputs such as emissions, meteorological and boundary conditions; and sharing national

- scale model results that states can leverage in their development of their attainme nt demonstrations. At the same time, we work with air agencies to provide implementation flexibility to the extent allowed by law. 2. Timing of Rules and Guidance In public comment periods associated with several recent rulemakings, the EPA received

comm ents from a variety of states and organizations asking for rules and guidance associated with a revised NAAQS to be issued in a timely manner. Although issuance of such rules and guidance is not a part of the NAAQS review process, National Ass’n of Manufac turers v
. EPA , 750 F. 3d 921, 926

- 27 (D.C. Cir. 2014), t oward that end the EPA intends to produce appropriate revisions to necessary implementation rules and provided additional guidance in time frames that would be more useful to states when developing th eir implementation plans than has been the case with some previous rules and guidance

. Certain requirements under the PSD preconstruction permit review program apply immediately to a revised NAAQS upon the effective date of that NAAQS, unless the EPA has established a grandfathering provision through rulemaking . To ensure a smooth transition to a revised O 3 NAAQS, the EPA is proposing a grandfathering provision similar to the one finalized in the 2012 PM 2.5 NAAQS Rule. See section VII. D of this proposal for more details on the PSD
program. Promulgation of the NAAQS starts a clock for the EPA to designate areas as either attainment or nonattainment. State recommendations for area designations are due to the EPA within 12 months of promul gation of the NAAQS. In an effort to allow states to make more informed recommendations, the EPA intends to issue guidance concerning the designations*** E.O. 12866 Review

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Page 526 of 647 process within 4 months of promulgation of the NAAQS, or approximately 8 months before state recommendati ons are due. The EPA has issued designation guidance for several NAAQS in recent years. While generally the EPA considers information related to the same factors in making designation decisions, the guidance is tailored to the particular NAAQS. The EPA
ant icipates that the guidance for a revised NAAQS resulting from this proposal would be similar to the designation guidance for the 2008 O 3 NAAQS

. The EPA generally completes area designations 2 years after promulgation of a NAAQS. See section VII. C for addit ional details on designations. Clean Air Act section 110 requires state implementation plans (SIPs) to be submitted within 3 years of promulgation of a revised NAAQS. These SIPs are referred to as “infrastructure SIPs.” The EPA issued general guidance on submitting infrastructure SIPs on September 13, 2013. 246 It should be noted that this guidance did not address certain state planning and emissions control requirements related to interstate pollution transport. Should this guidance need to be modified for t his prospective O 3 NAAQS, the EPA intends to issue that updated guidance no later than one year after promulgation of a revised O 3 NAAQS. See section VII.B.3 for additional information on infrastructure SIPs. The EPA intends to propose any appropriate ru les for assisting with implementing any revised O 3 NAAQS resulting from this proposal within 1 year after a revised NAAQS is established. The rules that EPA is considering , as with implementation of previous NAAQS, would address nonattainment area classifi cation methodologies, SIP due dates, attainment dates, and required implementation programs such as NNSR and conformity. At that same time the

246 See memorandum from Stephen D. Page to Regional Air Directors , “Guidance on Infrastructure State Implementation Plan (SIP) Elements under Clean Air Act Sections 110(a)(1) and 110(a)(2)” September 13, 2013.*** E.O. 12866 Review

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Page 527 of 647 EPA intends to address any modifications needed as a result of this revised NAAQS to guidance pertaining to devel oping nonattainment area emissions inventories and attainment demonstrations, and demonstrating conformity. The EPA anticipates finalizing these items by the time areas are designated nonattainment. Finalizing rules and guidance by this time would provide air agencies with the information to develop any CAA

- required SIPs associated with nonattainment designations. In an area designated as nonattainment, new major sources and major modifications at existing sources are required to comply with NNSR requiremen ts including the application of “lowest achievable emission rate” (LAER) and emissions offsets at ratios prescribed by the CAA. See section VII.B.4 for additional information on nonattainment
SIPs. 3. Section 110 State Implementation Plans The CAA section 110 specifies the general requirements for SIPs. Within 3 years after the promulgation of revised NAAQS (or such shorter period as the Administrator may prescribe 247 ) each state must adopt and submit ‘‘infrastructure’’ SIPs to the EPA to address the requirements of section 110(a)(1) and (2), as applicable. These ‘‘infrastructure SIPs’’ establish the basic state programs to implement, maintain, and enforce revised NAAQ S and provide assurances of state resources and authorities. States are to develop and maintain an air quality management infrastructure that includes enforceable emission limitations, a permitting program, an ambient monitoring program, an enforcement pro gram, air quality modeling capabilities, and adequate personnel, resources, and legal authority. Section 110(b) of the CAA provides that the EPA may extend the deadline for the ‘‘infrastructure’’ SIP submission for a revised secondary

247 While the CAA allows the EPA to set a shorter time for submission of these SIPs, the EPA does not currently intend to do so.*** E.O. 12866 Review

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Page 528 of 647 standard by up to 18 months beyond the initial 3 years. If both the primary NAAQS and a distinct secondary NAAQS are finalized, the EPA currently believes it would be more efficient for states and the EPA if each affected state submits a single section 110 infrastructure SIP t hat addresses both standards at the same time (i.e., within 3 years of promulgation of the O 3 NAAQS), because the EPA does not at present discern any need for there to be any significant substantive difference in the infrastructure SIPs for the two standar ds. However, the EPA also recognizes that states may prefer the flexibility to submit the secondary NAAQS infrastructure SIP at a later date. The EPA solicits comment on these infrastructure SIP submittal timing considerations, and specifically on challeng es that would justify needing 18 additional months to complete the submission of an infrastructure SIP for the secondary standard

. It is the responsibility of each state to review its air quality management program’s infrastructure SIP provisions in ligh t of each revised NAAQS. Most states have revised and updated their infrastructure SIPs in recent years to address requirements associated with recently revised NAAQS. It may be the case that for a number of infrastructure elements, the state may believe i t has adequate state regulations already adopted and approved into the SIP to address a particular requirement with respect to the revised O 3 NAAQS. For such portions of the state’s infrastructure SIP submittal, the state may provide a ‘‘certification’’ sp ecifying that certain existing provisions in the SIP are adequate. Although the term ‘‘certification’’ does not appear in the CAA as a type of infrastructure SIP submittal, the EPA sometimes uses the term in the context of infrastructure SIPs, by policy an d convention, to refer to a state’s SIP submission. If a state determines that its existing EPA

- approved SIP provisions are adequate in light of the revised O 3 NAAQS with respect to a given infrastructure SIP element (or sub

- element), then the state may ma ke a ”certification” that the existing SIP contains provisions that address those*** E.O. 12866 Review

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Page 529 of 647 requirements of the specific section 110(a)(2) infrastructure elements. In the case of a certification, the submittal does not have to include another copy of the relevant pr ovision (e.g., rule or statute) itself. Rather, the submittal may provide citations to the already SIP

- approved state statutes, regulations, or non

- regulatory measures, as appropriate, which meet the relevant CAA requirement. Like any other SIP submittal, such certification can be made only after the state has provided reasonable notice and opportunity for public hearing. This ‘‘reasonable notice and opportunity for public hearing’’ requirement for infrastructure SIP submittals appears at section 110(a), an d it comports with the more general SIP requirement at section 110(l) of the CAA. Under the EPA’s regulations at 40 CFR part 51, if a public hearing is held, an infrastructure SIP submittal must include documentation by the state that the public hearing wa s held in accordance with the EPA’s procedural requirements for public hearings. See 40 CFR part 51, appendix V, paragraph 2.1(g), and 40 CFR 51.102. 4. Nonattainment Area Requirements Part D of the CAA describes the various program requirements that app ly to states with nonattainment areas for different NAAQS. Section 182 (found in subpart 2 of part D) includes the SIP requirements that govern the O 3 program, and supplements the more general nonattainment area requirements in sections 172 and 173. Under section 182, states generally are required to submit attainment demonstration SIPs within 3 or 4 years of the effective date of area designations by the EPA, depending on the classification of the area. These plans need to show how the nonattainment area w ill attain the primary O 3 standard ‘‘as expeditiously as practicable,’’ but no later than within the relevant time frame from the effective date of designations associated with the classification of the area.*** E.O. 12866 Review

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Page 530 of 647 Section 181(a)(1) of the CAA establishes clas sification categories for areas designated nonattainment for the primary O 3 NAAQS. These categories range from “Marginal,” the lowest
O 3 classification with the fewest requirements associated with it, to “Extreme,” the highest classification with the most required programs. Areas with worse O 3 problems are given more time to attain the NAAQS and more associated emission control requirements. Pursuant to previous O 3 NAAQS reviews the EPA set the secondary NAAQS equal to the primary NAAQS. Thus, previous impl ementation programs for O 3 standards did not include a separate classification threshold methodology for the secondary NAAQS. For this NAAQS review, which may result in a secondary standard different in form and level compared to the primary standard, the EPA is considering methodologies for establishing the air

- quality based thresholds for assigning the section 181 classifications to areas out of attainment with a secondary O 3 NAAQS. Any such methods would be proposed for comment if the EPA finalizes a dis tinct secondary NAAQS. The re are two main EPA rule making s relating to implementation of the 2008 O 3 NAAQS. In May 2012, the EPA issued the final Classification s Rule (77 FR 30160; May 21, 2012). The Classifications Rule detailed the classifications approa ch, established attainment deadlines and revoked the 1997 O 3 NAAQS for purposes of transportation conformity. In June 2013, the EPA proposed a SIP Requirements Rule (78 FR 34178; June 6, 2013) to provide rules and guidance to states regarding development o f SIPs to attain the 2008 O 3 NAAQS. The EPA believes that the overall framework and policy approach of the proposed SIP Requirements Rule for the 2008 O 3 NAAQS provides an effective and appropriate template for the general approach states would follow in p lanning for attainment of a revised primary O 3 standard. The EPA intends to develop and propose a new SIP Requirements Rule that will address, to the extent necessary, any new*** E.O. 12866 Review

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Page 531 of 647 implementation requirements that would result from any revised O 3 NAAQS. The EPA intends to propose this implementation rule within 1 year after the revised O 3 NAAQS are promulgated, and finalize the implementation rule by no later than the time the area designations process is finalized (approximately 2 years after promulgation of th e O 3 NAAQS). In general, when developing an attainment plan the state begins with the evaluation of the air quality improvements the nonattainment area can expect in the future due to ‘‘on the books’’ existing federal, state, and local emission reduction measures. The state then must conduct a further assessment of relevant NO X and VOC emission sources in the nonattainment area, and the additional reasonably available control measures (RACM) and reasonably available control technology (RACT) that can be im plemented by these sources, in determining how soon the area can attain the standard. Under section 172(c)(1) of the CAA as interpreted by the EPA, attainment demonstrations must include a RACM analysis showing that no additional reasonably available measu res could be adopted and implemented such that the SIP could specify an attainment date that is 1 or more years earlier. The evaluation of these potential emissions reductions and associated air quality improvement is commonly performed with sophisticated air quality modeling tools. Given that
O 3 concentrations are affected both by regionally

- transported O 3 and O 3 precursor emissions and emissions of precursors from local sources in the nonattainment area (e.g., industrial sources, EGUs, and on

- road mobile sources), the EPA recommends the use of regional grid

- based models (such as CMAQ and CAMx) to develop O 3 attainment strategies. Although , as described above, the EPA projects significant improvements in O 3 concentrations regionally resulting from a number of ongoing emission reduction programs already in place (e.g., mobile source engine and fuel standards and regulations for power plants ) and from a number of recently promulgated*** E.O. 12866 Review

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Page 532 of 647 rules such as the Cross State Air Pollution Rule (76 FR 48208, August 8, 2011), the Mercury and Air Toxics Standards rule (77 FR 9304, February 16, 2012) and the Tier 3 rule (79 FR 23414; April 28, 2014) that will result in VOC and NO X reductions from many geographically dispersed sources, local reductions of direct O 3 precurso rs can also result in important health benefits. States must also ensure that a nonattainment area will make ‘‘reasonable further progress’’ (RFP) in accordance with subpart 2 of the CAA from the time of the nonattainment designation to its attainment da te. The amount of RFP required is based on the classification of the nonattainment area. Under the approach outlined in the proposed SIP Requirements Rule for the 2008 O 3 NAAQS, areas designated nonattainment and classified as Moderate would generally be r equired to reduce emissions by 15 % over the first six years after the effective date of designations. Areas classified higher than Moderate would be required to produce additional emission reductions after this 6

- year period for an area that average 3 % re ductions per year. All RFP and attainment plans must also include contingency measures which would apply without significant delay in the event the area fails to attain by its attainment date or meet RFP milestones. The EPA expects that the same general a pproach for determining attainment of the previous 1997 and 2008 8

- hour O 3 primary standards by the attainment deadline would be followed for determining attainment with any revised primary O 3 standard. Attainment would be evaluated based on the 3 most rec ent years of certified, complete, and quality

- assured air quality data in the nonattainment area. Areas are able to obtain up to two 1

- year attainment date extensions provided under section 181 under certain circumstances. Under previous 8

- hour O 3 NAAQS ru les, an area whose design value based on the most recent 3 years of data exceeds the standard could receive a 1

- year attainment date extension if the air quality concentration for the*** E.O. 12866 Review

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Page 533 of 647 third year alone does not exceed the level of the standard. Similarly, a n area that has received a
1

- year extension could receive a second 1

- year extension if the average of the area’s air quality concentration in the ‘‘extension year’’ and the previous year does not exceed the level of the
standard. B. Implementing a Distinc t Secondary O 3 NAAQS , i f One is Established In each of the previous O3 NAAQS reviews the secondary standard was set equal to the primary standard. As discussed in section IV above, the EPA is proposing to revise the level of the current secondary standard to a level within the range proposed for the primary standard. The EPA is also soliciting comment on the alternative approach of revising the secondary standard to a cumulative, seasonal, concentration

- weighted form based on the
W126 index.
If the EPA we re to establish a distinct secondary standard, there would be unique implementation issues to consider . These could include issues related to, but not limited to, PSD implementation, nonattainment area classification thresholds, attainment planning, and

co nformity demonstrations. These issues would be addressed in future implementation rules and guidance, as necessary. The EPA solicits comments on the specific kinds of implementation

related issues (with examples, where possible) that air agencies and affec ted sources would face if a separate and distinct secondary standard is established.
C. Designation of Areas After the EPA establishes or revises a NAAQS, the CAA directs the EPA and the states to take steps to ensure that the new or revised NAAQS is met. One of the first steps, known as the initial area designations, involves identifying areas of the country that either do not meet the new or revised NAAQS along with the nearby areas that contribute to the violations.*** E.O. 12866 Review

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Page 534 of 647 Section 107(d)(1) of the CAA provid es that, "By such date as the Administrator may reasonably require, but not later than 1 year after promulgation of a new or revised national ambient air quality standard for any pollutant under section 109, the Governor of each state shall * * * submit to the Administrator a list of all areas (or portions thereof) in the state" that designates those areas as nonattainment, attainment, or unclassifiable. The EPA must then promulgate the area designations according to a specified process, including procedure s to be followed if the EPA intends to modify a recommendation. The CAA defines an area as nonattainment if it is violating the NAAQS or if it is contributing to a violation in a nearby area. Section 107(d)(1)(B)(i) further provides, "Upon promulgation o r revision of a national ambient air quality standard, the Administrator shall promulgate the designations of all areas (or portions thereof) * * * as expeditiously as practicable, but in no case later than 2 years from the date of promulgation of the new or revised national ambient air quality standard. Such period may be extended for up to one year in the event the Administrator has insufficient information to promulgate the designations.” In certain contexts, w ith respect to the NAAQS, the term “promulga tion” has been interpreted by the courts to be signature and widespread dissemination of a final NAAQS rule. 248 By no later than 120 days prior to promulgating area designations, the EPA is required to notify states of any intended modifications to their rec ommendations that the EPA may deem necessary. States then have an opportunity to demonstrate why any proposed modification is inappropriate. Whether or not a state provides a recommendation, the EPA must timely promulgate the designation that the Agency de ems appropriate. While section 107 of the CAA specifically addresses states, the EPA intends to follow the same process for tribes to the extent practicable, pursuant to CAA section 301(d) regarding tribal

248 American Petroleum Institute v. Costle , 609 F.2d 20 (D.C. Cir. 1979)*** E.O. 12866 Review

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Page 535 of 647 authority and the Tribal Authority Rule (63 FR 7254, February 12, 1998). To provide clarity and consistency in doing so, the EPA issued a 2011 guidance memorandum on working with tribes during the designation process. 249 As discussed in sections II and IV, the EPA is proposing to revise both the primary and secondary O 3 NAAQS, which currently are identical 8

- hour standards that were set at 0.075 ppm in the 2008 NAAQS rule (73 FR 16436; March 27, 2008). If the EPA revises the primary and secondary O 3 NAAQS based on this proposal, the EPA intends to comple te designations for both NAAQS following the standard 2

- year process discussed above. The EPA is required to sign the final rule for this O 3 NAAQS review no later than October 1, 2015 under a court

- ordered deadline . In accordance with section 107(d)(4) of the CAA, state Governors (and tribes, if they choose) should submit their initial designation recommendations for a revised primary and secondary NAAQS no later than 1 year after promulgation of any revised O 3 NAAQS (for example, by October 1, 2016 if the EPA promulgates such NAAQS on October 1, 2015.) If the EPA intends to modify any state recommendation, the EPA would notify the appropriate state Governor (or tribal leader) no later than 120 days prior to making final designation decisions. A state or tri be that believes the modification is inappropriate would then have the opportunity to demonstrate to EPA why it believes its original recommendation (or a revised recommendation) is more appropriate. The EPA would take any additional input into account in making the final designation decisions.

249 Memorandum titled, “Guidance to Regions for Working with Tribes during the National Ambient Air Quality Standards (NAAQS) Designations Process,” from Stephen D. Page, Director, Office of Air Quality Planning and Standards to Regional Air Directors, Region s I

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Page 536 of 647 Consistent with previous designations, the EPA intends to use area

- specific multi

- factor analyses to support area boundary decisions for any revised primary or secondary O 3 standards. Historically, the EPA has evaluated information related to the following factors for designations: air quality data, emissions

- related data, meteorology, geography/topography, and jurisdictional boundaries. The EPA solicits comment related to establishing area designation boundarie s for the proposed revised primary and secondary NAAQS, including any relevant technical information that should be considered by the EPA and the extent to which different considerations may be relevant to establishing boundaries for a distinct secondary N AAQS. As noted earlier, t he EPA intends to issue designation guidance to the states shortly after the promulgation of any revised
O 3 NAAQS to provide information on the designation process and to assist states in developing their recommendations. The EPA i nvites preliminary comment on all aspects of the designation process at this time, which the EPA will consider in developing that guidance.
D. Prevention of Significant Deterioration and Nonattainment New Source Review Program s for the Proposed Revised Pri mary O 3 NAAQS and the Proposed Secondary O 3 NAAQS The CAA, at parts C and D of title I, contains new source review (NSR) requirements that constitute preconstruction review and permitting programs applicable to new major stationary sources and major modifications of existing major sources. The preconstruc tion review of each new major source and major modification generally applies on a pollutant

specific basis, and the requirements that apply for each pollutant generally depend on whether the area is designated as attainment (or unclassifiable) or nonattai nment for that pollutant. For the O 3 NAAQS, in areas designated attainment and unclassifiable, the Prevention of Significant Deterioration (PSD) requirements under part C apply. In nonattainment areas for O 3 , the NNSR*** E.O. 12866 Review

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Page 537 of 647 requirements under part D apply. Colle ctively, those two sets of permit requirements are commonly referred to as the “major NSR programs.” Until areas are designated for the proposed revised O 3 NAAQS, the NSR provisions applicable under an area’s designation for the 2008 NAAQS (including any applicable anti

backsliding requirements) would continue to apply. See 40 CFR 51.166(i)(2) and 52.21(i)(2). When the new designations for any revised O 3 NAAQS are effective they generally will serve to determine whether the PSD or nonattainment NSR program applies. 1. Prevention of Significant Deterioration (PSD) The statutory requirements for a PSD permit program set forth under part C (sections 160 through 169 of the CAA) are addressed by the EPA’s PSD regulations found at 40 CFR 51.166 (minimum require ments for an approvable SIP) and 40 CFR 52.21 (federal PSD permit program for areas lacking an EPA

- approved PSD program in the applicable SIP and for lands owned by the federal government and tribal lands). Both sets of regulations already apply to O 3 . See 40 CFR 51.166(b)(23), (49); 40 CFR 52.21(b)(23), (50).

. Among other things, in attainment and unclassifiable areas, the PSD program requires a new major stationary source or a major modification to an existing major source to apply best available control technology (BACT) for each applicable pollutant and to conduct an air quality impact analysis to demonstrate that the proposed source or project will not cause or contribute to a violation of any NAAQS or PSD increment ( see CAA section 165(a)(3)

- (4), 40 CF R 51.166(j)

- (k), 40 CFR 52.21(j)

- (k)). PSD requirements may also include, in appropriate cases, an analysis of potential adverse impacts on*** E.O. 12866 Review

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Page 538 of 647 Class I areas ( see CAA sections 162 and 165). 250 These existing requirements of the PSD program will remain applicabl e to O 3 and the demonstration required under 51.166(k) and 52.21(k) will apply to any revised O 3 NAQS when such NAAQS become effective, except to the extent that a pending permit application is subject to the grandfathering provision that the EPA is
propos ing in this rule. To address ambient O 3 impacts of VOC and NO X precursor emissions from individual stationary sources, Appendix W to 40 CFR part 51 currently directs states to consult with the applicable EPA Regional Office to determine the appropriate te chniques on a case

- by

- case basis, which may or may not involve the use of air quality models, for evaluating whether a PSD source causes or contributes to a violation of the O 3 NAAQS. 40 CFR part 51, Appendix W, section 5.2.1.c. At present, the EPA is eval uating the models and techniques available to address atmospheric chemistry of O 3 formation in assessing such single source impacts, and as part of that evaluation has conducted discussions of such tools with the regulatory modeling community. Consistent w ith its commitment to engage in a rulemaking process to determine whether updates to Appendix W in 40 CFR part 51 are warranted, 251 the EPA is planning to propose a rulemaking in the spring of 2015 to consider whether to update Appendix W. If the EPA conclud es that it is technically and scientifically appropriate, it will propose appropriate regulatory updates to Appendix W as part of that rulemaking and may also make related updates to technical guidance,

250 Congress established certain Class I areas in section 162(a) of the CAA, including international parks, national wilderness areas, and national parks that meet certain criteria. Such Class I areas, known as mandatory federal Cla ss I areas, are afforded special protection under the CAA. In addition, states and tribal governments may establish Class I areas within their own political jurisdictions to provide similar special air quality protection. 251 See Letter from Gina McCarthy, A ssistant Administrator, to Robert Ukeiley, at 1 (Jan. 4, 2012), available at http://www.epa.gov/scram001/10thmodconf/review_material/Sierra _Club_Petition_OAR

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Page 539 of 647 as appropriate. In the meantime, in order to demonstr ate that a proposed source or modification does not cause or contribute to a violation of the applicable O 3 NAAQS, PSD permit applicants would follow the current provisions in Appendix W until any revisions to them are in effect. For PSD, a “major station ary source” is one with the potential to emit 250 tons per year (TPY) or more of any regulated NSR pollutant, unless the new or modified source is classified under a list of 28 source categories contained in the statutory definition of “major emitting
faci lity” in section 169(1) of the CAA. For those 28 source categories, a “major stationary source” is one with the potential to emit 100 TPY or more of any regulated NSR pollutant. A “major modification” is a physical change or a change in the method of opera tion of an existing major stationary source that results first, in a significant emissions increase of a regulated NSR pollutant at a project, and second, in a significant net emissions increase of that pollutant at the

source. 252 See 40 CFR 51.166(b)(2)(i), 40 CFR 52.21(b)(2)(i). The EPA’s regulations define the term “regulated NSR pollutant” to include “[a]ny pollutant for which a [NAAQS] has been promulgated and any pollutant identified [in EPA regulations] as a constituent or pre cursor to such pollutant.” 40 CFR 51.166(b)(49); 40 CFR 52.21(b)(50). These regulations identify VOC and NO X as precursors to O 3 in all attainment and unclassifiable areas. 40 CFR 51.166(b)(49)(i)(a); 40 CFR 52.21(b)(50)(i)(a). Thus, for O 3 , the PSD progra m currently requires the review and control of emissions of VOC and NO X , as applicable, as precursors of O 3 .

252 As explained in 40 CFR 52.21(a)(2)(iv)(a) and 51.166(a)(7)(iv)(a), “[t]he proj ect is not a major modification if it does not cause a significant emissions increase. If the project causes a significant emissions increase, then the project is a major modification only if it also results in a significant net emissions increase.” The PS D regulations at 40 CFR 51.166(a)(7) and 52.21(a)(2) also explain in more detail the two

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Page 540 of 647 As noted above, section 165(a)(3) of the CAA and the implementing PSD regulations require the owner or operator of a proposed facility to, among other things, demonstrate that “emissions from construction or operation of such facility will not cause, or contribute to, air pollution in excess of any ... national ambient air quality standard in any air control region.” See also 40 CFR 51.166(k), 40 CFR 52.21(k). The EPA has interpreted this requirement to include any NAAQS that is in effect as of the date a permit is issued, unless it has grandfathered permit applications from the requirement to demonstrate that the proposed facility does not cause or

c ontribute to a violation of the new or revised NAAQS. 253 S ee, e.g. , 73 FR 28321, 28324, 28340 (May 16, 2008); 78 FR 3253 (Jan. 15, 2013). Memorandum from Stephen D. Page, Director, Office of Air Quality Planning & Standards, “Applicability of the Federal Pre vention of Significant Deterioration Permit Requirements to New and Revised National Ambient Air Quality Standards” (April 1, 2010). Consistent with this interpretation, any revised O 3 NAAQS finalized through this rulemaking will need to be addressed by PS D permit applicants and permitting authorities, in permits issued on or after the date when the revised NAAQS become effective, unless the permit application has been grandfathered through rulemaking, as described below in this proposal.

253 In the past the EPA has asserted the discretion to take such grandfat hering action, under appropriate circumstances, either by rulemaking or through a case

- by

- case determination for a specific permit application . The United States Court of Appeals for the Ninth Circuit recently vacated a decision by the EPA to issue an indi vidual PSD permit grandfathering a permit applicant from certain requirements. In light of that decision, the EPA is no longer asserting authority to grandfather permit applications on a case

- by

- case basis. Sierra Club v. EPA , Case No. 11

- 73342 (9th Cir., Aug. 12, 2014). However, in the same opinion the court also stated that it did “not doubt, or express any opinion on, the EPA’s traditional authority to employ formal rulemaking to implement grandfathering” and distinguished that authority from the permit

specific grandfathering at issue in the case before it. Id. , Slip. Op. at 23, n.7 & 23

- 26. Thus, the EPA does not interpret this opinion to limit its authority to grandfather through rulemaking, but rather believes that the decision offers support for such authority.*** E.O. 12866 Review

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Page 541 of 647 Because the comp lex chemistry of ozone formation poses significant challenges for the assessing the impacts of individual stationary sources on ozone formation, the EPA’s judgment has been that it was not technically sound to designate a specific air quality model that mu st be used in the PSD permitting process to make this demonstration for ozone. 254 The EPA has explained that sources must make the demonstration required under CAA section 165(a)(3) and the implementing regulations, that this demonstration necessarily involv es an analysis, and has established a process to determine on a case

- by

- case basis, in consultation with the appropriate EPA Regional Office, what analytical techniques should be used to assess the impact of an individual source. 255 40 CFR Part 51, Appendix W, Section 5.2.1.c. The EPA has, however, granted a petition from Sierra Club requesting, among other things, that it initiate rulemaking to designate air quality models for ozone, and consistent with that petition grant, has been going through a process t o evaluate potential updates to Appendix W. 256 While that process is underway, individual sources should continue to follow the existing procedures to determine what method is appropriate to use to evaluate their impacts on ozone formation. The PSD rules in 40 CFR 51.166(i)(2) and 52.21(i)(2) contain an exemption for particular pollutants from the PSD requirements if the owner or operator of the source demonstrates that the area in which the facility is located is designated as nonattainment for that pollutan t under CAA section 107. Thus, new major sources and modifications will generally be subject to the PSD program requirements for O 3 if they are locating in an area that does not have a current nonattainment designation under CAA section 107 for O 3 . As expl ained in the recent

254 Letter from Gina McCarthy, Assistant Administrator, to Robert Ukeiley, at 2 (Jan. 4, 2012), available at http://www. epa.gov/ scram001/10thmodconf/review_material/Sierra _Club_Petition_OAR

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Page 542 of 647 proposal for the implementation rule for the 2008 O 3 NAAQS, references to historical nonattainment designations for a revoked standard should not be viewed as current “nonattainment designation[s] under CAA § 107” within the meaning of 40 CFR 51.166(i)(2) and 52.21(i)(2) and, therefore, do not trigger the exemption from PSD requirements that would otherwise result from those provisions. 78 FR 34216 (June 6, 2013). a. PSD Grandfathering Provision Recognizing that some PSD applications m ay have already been submitted and could be in the review process when a revised O 3 NAAQS becomes effective, the EPA is proposing a transition plan that would enable certain PSD applications to make the demonstration that the proposed project will not caus e or contribute to a violation of any NAAQS with respect to the O 3 NAAQS that were in effect when the application was submitted, rather than the revised O 3 NAAQS, if any is finalized. 257 The EPA is proposing and taking comment on adding a grandfathering provision to EPA’s regulations at 40 CFR 51.166 and 52.21 that would apply specifically to two categories of PSD permit applications that are pending when the EPA issues the revised O 3 NAAQ S: (1) applications for which the reviewing authority has formally determined that the application is complete on or before the signature date of the revised NAAQS; and (2) applications for which the reviewing authority has first published a public notice that a draft permit or preliminary

257 The proposed grandfathering provision is intended to apply to pending PSD permit applications that meet one or both of the specified criteria and that are for sources locating in areas where PSD continues to apply with respect to O 3 at the t ime the permit is issued

. The proposed grandfathering provision is not intended to apply to sources locating i n areas where NNSR applies at the time of permit issuance (for example, if the area had been designated as attainment for ozone when the permit ap plication was submitted but was subsequently designated as nonattainment for ozone and that nonattainment designation would be in effect when the permit would be issued). For such sources, the permit application must be resubmitted in accordance with the applicable NNSR requirements.*** E.O. 12866 Review

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Page 543 of 647 determination has been prepared before the effective date of the revised NAAQS. These two categories are proposed because some states do not do completeness determinations as part of their permit process

. As explained a bove, the EPA interprets the CAA and implementing PSD regulations at 40 CFR 52.21(k)(1) and 51.166(k)(1) to require that PSD permit applications must include a demonstration that new major sources and major modifications will not cause or contribute to a

v iolation of any NAAQS that is in effect as of the date the PSD permit is issued. Thus, if the EPA revises the O 3 NAAQS, any proposed new source or modification with a PSD permit application pending at the time the revised O 3 NAAQS takes effect would be exp ected to conduct an analysis to demonstrate that it does not cause or contribute to a violation of that NAAQS, absent some type of transition provision exempting the application from that requirement. This demonstration, as noted above, should be completed in consultation with the applicable EPA Regional Office. Nevertheless, the Agency has previously recognized that the CAA provides discretion for the EPA to grandfather PSD permit applications from requirements that become applicable while the application s are pending (45 FR 52683, August 7, 1980; 52 FR 24672, July 1, 1987; 78 FR 3086, January 15, 2013). As discussed in more detail in these referenced actions, section 165(a)(3) of the CAA requires that a permit applicant demonstrate that its proposed proje ct will not cause or contribute to a violation of any NAAQS. At the same time, section 165(c) of the CAA requires that a PSD permit be granted or denied within 1 year after the permitting authority determines the application for such permit to be complete. In addition, section 301 of the CAA authorizes the Administrator “to prescribe such regulations as are necessary to carry out his functions under this chapter.” When read in combination, these three provisions of the CAA*** E.O. 12866 Review

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Page 544 of 647 provide the EPA with the discretio n to issue regulations to grandfather pending permit applications from having to address a revised NAAQS where necessary to achieve both CAA objectives to protect the NAAQS and to avoid delays in processing PSD permit applications. Moreover, in a recent op inion the U.S. Court of Appeals for the Ninth Circuit recognized the EPA’s traditional exercise of grandfathering authority through rulemaking and indicated that this approach was consistent with statutory requirement to “enforce whatever regulations are i n effect at the time the agency makes a final decision” because it involved identifying “an operative date, incident to setting the new substantive standard, and the grandfathering of pending permit applications was explicitly built into the new regulation s.” Sierra Club v. EPA , Case No. 11

- 73342, Slip. Op. at 26 (Aug. 12, 2014). In the EPA’s most recent adoption of a grandfathering provision for PSD, it adopted a provision for PM 2.5 that provides a reasonable transition for implementing certain new PSD

re quirements related to the 2012 PM 2.5 NAAQS for pending permit applications that have met certain criteria. As finalized, the PM 2.5 grandfathering provision included the same two categories of permit applications that today are being proposed for O 3 . See 40 CFR 51.166(i)(10) and 52.21(i)(11). In the rulemaking adding the grandfathering provision for the PM 2.5 NAAQS, the EPA also provided a detailed rationale and legal basis for including the grandfathering provision in the PSD program. See 78 FR 3087 at 3253

- 59 (January 15, 2013); see also 77 FR 39023

- 24 (June 29, 2012). When the PM 2.5 NAAQS grandfathering provision was originally proposed, the EPA provided for only one category of pending PSD applications

— applications for which the reviewing authority has published a public notice on the draft permit prior to the effective date of the revised PM 2.5 NAAQS. A majority of the commenters supported the adoption of a*** E.O. 12866 Review

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Page 545 of 647 grandfathering provision but some responded that a grandfathering milestone based on the submitta l of a complete application would be more appropriate in order to avoid significant burdens associated with having to withdraw an application. These commenters pointed out the significant level of effort, resources and time involved in preparing all of the information necessary for a complete permit application. They claimed that it would be unfair to establish grandfathering milestones beyond the complete application date because the processes and timeframe involved in generating the draft permit or prelim inary determination materials and publishing the public notice are largely out of the control of the permit applicant and vary from agency to agency. Based on this and other pertinent information provided by the commenters, the EPA concluded in that rulem aking that it should add an additional grandfathering milestone to avoid substantial additional burden and delay for permit applications that have reached a stage in the review process by which significant resources have been expended to complete PSD analy ses and demonstrations that would have to be redone to address the revised NAAQS. Accordingly, the EPA adopted a grandfathering provision for the PM 2.5 NAAQS in the final rule that included two milestones for establishing grandfathering eligibility. The EP A believes that these considerations and this rationale also apply to pending PSD permit applications that would be affected by a revised O 3 NAAQS. Accordingly, the EPA is proposing to apply these same two milestones in this proposed rulemaking for the rev ised O 3 NAAQS. The proposed grandfathering provision does not apply to any applicable PSD requirements related to O 3 other than the requirement to demonstrate that the proposed source does not cause or contribute to a violation of any revised O 3 NAAQS. Sources with projects qualifying under the grandfathering provision will be required to apply BACT to all applicable*** E.O. 12866 Review

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Page 546 of 647 pollutants, demonstrate that the project emissions will not cause or contribute to a violation of the existing O 3 NAAQS, and addres s any Class I area and additional O 3 related impacts in accordance with the PSD regulatory requirements. For the reasons provided both herein and in the prior EPA actions referenced above, the EPA proposes to amend the federal PSD permitting regulations at 40 CFR 52.21 to add the described grandfathering provision for the proposed O 3 NAAQS revision. Specifically, the proposed provision provides that qualifying new sources and modifications seeking PSD permits under 40 CFR 52.21 shall not be required to de monstrate that their proposed emissions will not cause or contribute to a violation of the revised O 3 NAAQS, but instead must demonstrate that their proposed emissions will not cause or contribute to a violation of the O 3 NAAQS in effect on the date the re viewing authority determines the permit application complete or the date the public notice on the draft permit or preliminary determination is first published, depending on which prong of the grandfathering provision is applicable for that source. See prop osed 40 CFR 52.21(i)(12). For sources subject to the PSD program under section 52.21, it should be noted that the EPA intends for a source that satisfies either milestone in the proposed revisions to section 52.21(i) to be grandfathered from this requireme nt if those revisions are finalized. Accordingly, if a particular source does not qualify under the first milestone based on a complete application, it may qualify under the second milestone based on the issuance of a public notice. Conversely, a

source ma y qualify for grandfathering under the first milestone, even if it does not satisfy the second. As explained below, states with EPA

- approved PSD programs in their SIPs would have additional flexibility for implementing the proposed grandfathering provision to the extent that any alternative approach is at least as stringent as the federal provision.*** E.O. 12866 Review

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Page 547 of 647 The EPA also proposes that states that issue PSD permits under a SIP

- approved PSD permit program should have discretion to “grandfather” pending PSD permits in the same manner under these same circumstances. Therefore, the EPA is proposing to revise its rules at 40 CFR 51.166 to provide a comparable exemption applicable to SIP

- approved PSD programs, although such states are under no obligation to grandfather. See proposed 40 CFR 51.166(i)(11). The EPA recognizes that such states interested in grandfathering PSD sources for ozone will not have time to revise their rules and submit them to the EPA for approval into the SIP, since the need to grandfather sources will occur immediately upon the effective date of the revised O 3 NAAQS. As explained in an earlier rulemaking, the EPA believes that states implementing a
SIP

- approved PSD program have the discretion to allow grandfathering consistent with the grandfathering p rovision contained in the federal rule provisions, even in the absence of an express grandfathering provision in their state rules, if the particular state’s laws and regulations may be interpreted to provide such discretion. See 78 FR 3086 at 3258.
Becaus e state SIPs cannot be less stringent than federal requirements, the states’ discretion must be limited to applying grandfathering consistent with the federal rule provisions for ozone. However, we believe that such consistent application affords states wi th ample flexibility for implementing the provision. Accordingly, a state may elect to apply both milestones or it may elect to rely solely upon one of the milestones for grandfathering PSD permits for ozone. For example, in states that do not issue a form al completeness determination, the complete application milestone would not serve any practical purpose for grandfathering a PSD source, so the state may choose not to use this milestone. These states may elect to rely solely upon the public notice milesto ne, regardless of whether it issues formal completeness determinations. However, the EPA anticipates that once a decision is made concerning either the*** E.O. 12866 Review

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Page 548 of 64 7 use of both milestones or only one, states will apply the provision consistently to all PSD permit appli cations that would qualify under the elected milestone(s). The EPA seeks comments on all aspects of the proposed grandfathering provisions under either 40 CFR 52.21 or 51.166 as they would apply to exempt certain pending PSD permit applications from having to address the revised O 3 NAAQS. b. PSD Screening Tools The EPA has historically allowed the use of screening tools to help facilitate the implementation of the NSR program by reducing the source’s burden and streamlining the permitting process for circumstances where pollutant emissions or ambient impacts coul d be considered de minimis . For example, the EPA has established significant emission rates or SERs that are used to determine when the NSR requirements should be applied to a particular new or modified source with regard to each regulated NSR pollutant. S ee 40 CFR 51.166(b)(23) and 52.21(b)(23). For O 3 , the EPA established a separate SER in these regulations of 40 tpy for emissions of each O 3 precursor -- VOC and NO X . For PSD, these SER values for VOC and NO X are used to determine when the proposed major sou rce or major modification must complete PSD review for that precursor, including complying with BACT for that precursor and completing the appropriate air quality analyses associated with the proposed emissions increase of that precursor. Another key scr eening tool commonly used for PSD is the significant impact level (SIL). This particular tool is used to determine the extent to which an ambient impact analysis must be completed for the applicable pollutant. The EPA has not established a SIL for O 3 . T he PSD regulations currently state that “[n]o de minimis air quality level is provided for ozone. However,
any net emissions increase of 100 tons per year or more of [ VOC ] or [ NO X ] subject to PSD*** E.O. 12866 Review

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Page 549 of 647 would be required to perform an ambient impact analysis , includ ing the gathering of ambient air quality data. ” 258 The EPA intends to consider whether it is appropriate to make any revisions to the PSD regulations related to the screening tools for O 3 in a separate rulemaking that will specifically address various imple mentation issues for O 3 . However, there are no such revisions being proposed in today’s rulemaking. Until any rulemaking to amend existing regulations is completed, permitting decisions should continue to be based on the existing 40 TPY SER for O 3 precurso rs ( NO X and VOC) in existing regulations. Further decisions regarding the need for an analysis to assess the impact of an individual source on the O 3 NAAQS and the method of analysis depend on the nature of the source and its emissions, and, as noted above , should be determined in consultation with the EPA Regional Office on a case

- by

- case basis in accordance with section 5.2.1.c. of Appendix W to 40 CFR part 51. c. Other PSD Transition Issues As explained earlier in this section, the EPA anticipates that the existing O 3 air quality in some areas will no longer be in attainment of the primary O 3 standard when it is revised, and that these areas will be designated as “nonattainment” at a later date consistent with the designation process set forth for O 3 un der the CAA. However, until such nonattainment designation occurs,

258 Th is language is contained in a footnote in the PSD regulations at 40 CFR 51.166(i)(5)(i) and 52.21(i)(5)(i) and it ha s not been revisited by the EPA since the issuance of the 8

- hour ozone NAAQS. These values do not reflect a categorical conclusion by EPA that sources emitting less than 100 tpy of VOCs or NO X will not cause or contribute to a violation of the current (or any revised) ozone NAAQS, nor does it reflect a conclusion that such sources should be categorically exclu ded from the requirement for an ambient impact analysis. Instead, the EPA recommends consultation with the appropriate EPA Regional Office in accordance with section 5.2.1.c of Appendix W when a review of an application for a new source or modification inv olves emissions less than 100 tpy of either ozone precursor. See Letter from Gina McCarthy, Assistant Administrator, to Robert Ukeiley, at 4 (Jan. 4, 2012), available at http://www. epa.gov/ scram001/10thmodconf/review_material/Sierra _Club_Petition_OAR

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Page 550 of 647 proposed new major sources or major modifications located in any area designated attainment or unclassifiable for the 2008 O 3 NAAQS will continue to be required to obtain a PSD permit. 259
Thi s raises the question as to how a source can be issued a PSD permit in light of known existing ambient violations of the revised NAAQS. Section 165(a)(3)(B) of the CAA requires that a proposed source may not construct unless it demonstrates that it will not cause or contribute to a violation of any NAAQS. This statutory requirement is implemented through a provision contained in the PSD regulations at 40 CFR 51.166(k) and 52.21(k). If a source cannot make this demonstration or if its initial air quality i mpact analysis shows that the source’s impact does cause or contribute to a violation, a PSD permit may not be issued until that adverse impact is mitigated. 260 The PSD regulations, however, do not explicitly specify remedial actions that a prospective sourc e can take to address such a situation. Nevertheless, the EPA has historically recognized in regulations and through other actions that sources applying for PSD permits may utilize offsets as part of the required PSD demonstration under the CAA section 165 (a)(3)(B), even though the PSD provisions of the Clean Air Act do not expressly reference offsets, in contrast to the NNSR provisions of the
Act. 261

259 Any proposed major stationary source or major modification for O 3 that does not receive its PSD permit by the effective date of a new nonattainment designation for the area where the source would locate would then be required to satisfy all of the applicable NNSR preconstruction permit requirements for O 3 . 260 See, e.g ., Stephen D. Page, Director, Office of Air Quality Planning and Standards, to Regional Air Division Directors, “Guidance Concerning Implementation of the 1

- hour SO2 NAAQS for th e Prevention of Significant Deterioration Program,” (August 23, 2010); 44 FR 3278 (January 16, 1979). 261 See , e.g., In re Interpower of New York, Inc ., 5 E.A.D. 130, 141 (EAB 1994) (describing an EPA Region 2 PSD permit that relied in part on offsets to dem onstrate the source would not cause or contribute to a violation of the NAAQS). 52 FR 24698 (July 1, 1987) ; 78 FR 3261

- 62 (Jan. 15, 2013)

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Page 551 of 647 The EPA has looked to the procedures contained in a separate set of regulations at 40 CFR 51.165(b) to guide the process by which a source that is located in an area designated as attainment or unclassifiable for a NAAQS, but that is determined to cause or contribute to a violation of that NAAQS in any area, can use offsets to mitigate its adverse impact on the NAAQS and ultimately meet the PSD demonstration requirement under the CAA section 165(a)(3)(B) and the implementing regulations. 262 Section 51.165(b) states that plans shall include a preconstruction review permit program (or its equivalent) to satisfy the requirements of CAA section 110(a)(2)(D)(i) for major sources and major modifications, and that the program shall apply to any major stationary source or major modification locating in an area designated attainment or unclassifiable for any NAAQS, when th at source would cause or contribute to a NAAQS violation. 263 Paragraph (b)(3) of that regulation provides that the required permit program may include a provision allowing a proposed major source or major modification to reduce the impact of its emissions on air quality by obtaining sufficient emissions reductions to, at a minimum, compensate for its adverse ambient impact where the source or modification would otherwise cause or contribute to a violation of any NAAQS. Although section 51.165(b) refers explic itly to CAA section 110(a)(2)(D)(i), which now addresses transport issues, but not CAA section 165(a)(3)(B), the

262 78 FR 3261 (January 15, 2013); Stephen D. Page, Director, Office of Air Quality Planning and Standards, to Regional Air Division Directors, “Guidance Concerning Implementation of the 1

- hour SO2 NAAQS for the Prevention of Significant Deterioration Program,” (August 23, 2010). 263 The definition of “major stationary source” and “major modification” in this regulation is b ased on the respective definitions in the NNSR regulations at 40 CFR 51.165(a), which are more inclusive than the respective PSD definitions, but clearly include major sources covered by the PSD requirements.*** E.O. 12866 Review

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Page 552 of 647 EPA has previously explained that 51.165(b) may also be interpreted to apply to the section 165(a)(3)(B) demonstration based on the regulatory history. 78 FR 3262, n. 256. 264 Generally, the offset needed to compensate for a proposed source’s adverse impact would be determined by the ability of any particular emissions reduction to mitigate the source’s adverse impact at the location of the violati on. As long as the emissions reduction or offset can be shown to compensate for the source’s adverse impact, there is no implied requirement that the amount of the emissions reduction be equal to or greater than the proposed emissions increase.
See 44 FR 3278 (January 16, 1979) (“Although full emissions offsets are not required, such a source must obtain emissions offsets sufficient to compensate for it air quality impact where the violation occurs.”) In previous discussions of the use of emission s offsets to help make the demonstration required under CAA section 165(a)(3)(B), the EPA has explained that any emissions used for PSD purposes must meet applicability criteria that are at least as stringent as the offset criteria set forth in the NNSR re quirements for offsets under 40 CFR 51.165(a)(3). See 78 FR 3262. The

264 Briefly, in 1980, the EPA had determined that the statutory requirements under CAA section 165(a)(3)(B), taken together with the requirements of CAA section 110(a)(2)(D) required all major sources locating outside a nonattainment area but causing or contributing to a NAAQS violation to reduce the imp act on air quality so as to assure attainment and maintenance of the NAAQS. 45 FR 31310 (May 13, 1980). In a footnote, the EPA further indicated that this offset requirement must apply to sources causing or contributing to a newly discovered NAAQS violatio n until the area is designated nonattainment. See 45 FR 31310 (May 13, 1980). In the 1980 rule, the EPA adopted section 51.18(k), which was later renumbered section 51.165(b). The EPA revised 51.165(b) to expressly authorize an offset program to meet the r equirements of CAA section 110(a)(2)(D)(i), but this provision may also be interpreted to apply to section 165(a)(3)(B), consistent with the EPA’s reading of section 51.18(k) in 1980. It is also worth noting that at the time of these rules, before the 1990 CAA amendments, section 110(a)(2)(D) required each state to have “a permit or equivalent program for any major emitting facility...to assure (i) that national air quality standards are achieved and maintained....”*** E.O. 12866 Review

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Page 553 of 647 EPA continues to believe that these criteria provide the most appropriate criteria for determining the creditability of PSD offsets. d. PSD for a Distinct Secondary Standard , if One is E stablished As noted above, the CAA requires that proposed new major stationary sources and major modifications demonstrate that their emissions increases will not cause or contribute to a violation of any NAAQS, which includes the primary and secondary NA AQS. For O 3 , the existing primary and secondary NAAQS are defined in the same form and at the same level. As described earlier in this preamble, the Administrator is proposing to revise the level of the current secondary standard within the range proposed for the primary standard of 70 to 65 ppb

. In addition, among other things, the Agency is seeking comment on the alternative approach of revising the secondary standard to establish a distinct O 3 secondary standard . If the Agency were to finalize a secondar y standard that differs from the primary standard, PSD permit applicants would be required to provide an analysis that specifically addresses the revised secondary standard and make the necessary showing of compliance with that standard, as well as any

rev ised primary standard. Moreover, if such a secondary standard is expressed in a distinctly different form than the primary standard, the required analysis for making the compliance demonstration would need to be consistent with that form. Should the Admin istrator decide to establish a distinct secondary NAAQS for O 3 , the
EPA would consider whether the approaches put forth in any regulatory updates to Appendix W and associated guidance, as noted in this preamble above, are sufficient for making the necessa ry compliance demonstration for that standard for purposes of PSD. If appropriate, the EPA may consider establishing a surrogacy policy that would allow a source to make the PSD

- required demonstration of compliance with a distinct secondary O 3 NAAQS solely through a*** E.O. 12866 Review

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Page 554 of 647 demonstration of compliance with the primary NAAQS.[ INSERT CITE ]. Therefore, the EPA expects that projects subject to the revised ozone NAAQS could generally move forward consistent with the PSD program requirements and NNSR program requirement s as subject to the revised primary and secondary ozone NAAQS. The EPA seeks comment on this potential approach as well as any other options that should be considered for showing compliance with any revised primary and secondary O 3 NAAQS. 2. Nonattainment New Source Review
P art D of title I of the CAA includes preconstruction review and permitting requirements for new major stationary sources and major modifications when they locate in areas designated nonattainment for a particular pollutant. As explained in section VII.D.1 of this preamble, the relevant part D requirements are typically referred to as the NNSR program. The EPA’s regulations for the N NSR programs are contained in 40 CFR 51.165, 52.24 and part 51, Appendix S

. For example, the EPA has develo ped minimum program requirements for an NNSR program that is approvable in a SIP, and those requirements, which include requirements for O 3 , are contained in 40 CFR 51.165. In addition, 40 CFR part 51, Appendix S contains requirements constituting an interim NNSR program. This program governs NNSR permitting in nonattainment areas that lack a SIP

- approved NNSR permitting program, and applies during the time between the date of the relevant designation and the date that EPA approves into the SIP a
NNSR program. 265 This program is commonly known as the Emissions Offset Interpretative Rule, and is applicable to O 3 as well. 266

265 See Appendix S, Part I; 40 CFR 52.24(k). 266 As appropriate, certain NNSR requirements under 40 CFR 51.165 or Appendix S can also apply to sources and modifications located in areas that are designated attainment or unclassifiable in the Ozone Transport Region. See, e.g., CAA 184(b)(2), 40 C.F.R. 52.24(k).*** E.O. 12866 Review

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Page 555 of 647 As with PSD, the NNSR requirements apply on a pollutant

- specific basis. However, in nonattainment areas NNSR applies only to nonattai nment pollutants, that is, pollutants for which an area is designated nonattainment on the date when the permit is issued. As explained in section VII.D.1 in this preamble, prior to the designation of areas for any revised O 3 NAAQS, applicability of either PSD or NNSR for O 3 to a proposed major new or modified source will depend on an area’s current designations with regard to the O 3 NAAQS. Accordingly, a major stationary source or major modification proposing to locate in an area currently designated
nonat tainment for the 2008 O 3 NAAQS must satisfy the NNSR permit requirements for O 3 . The EPA is not proposing any new or revised NNSR requirements in this proposal. As explained in section VII.A.2 of this preamble, the CAA requires that area designations for n ew or revised NAAQS be addressed subsequent to the effective date of such new or revised NAAQS. The EPA anticipates that the area designation process for any revised O 3 NAAQS will be completed within 2 years after the revised NAAQS become effective. Accord ingly, any revisions to the existing NNSR requirements for O 3 will be proposed at a later date consistent with the designation process for any revised O 3 NAAQS. The EPA will also at the same time propose any necessary revisions to the NNSR requirements und er Appendix S so that states will be able to issue NNSR permits for the revised O 3 NAAQS on and after the effective date of designations of new nonattainment areas for O 3 until such time that their own NNSR program is approved as part of their SIP, where t he state does not already have an approved NNSR program applicable to O 3 . This section provides an explanation of some of the key requirements of the NNSR program as it currently applies to O 3 . For NNSR, “major stationary source” is generally defined

as a source with the potential to emit at least 100 tpy of the pollutant for which the area is designated nonattainment. In some cases, however, the CAA and the NNSR regulations define*** E.O. 12866 Review

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Page 556 of 647 “major stationary source” for NNSR in terms of a lower rate dependent on the pollutant. For ozone, in addition to the general threshold level of 100 tpy, lower major source thresholds have been defined for O 3 nonattainment areas based on the stringency of the area’s classification. The NNSR program requires the review and control of emissions of both VOC and NOx as precursors of ozone, and both are reviewed separately in accordance with the applicable major source threshold. For example, the threshold for O 3 nonattainment areas classified as Serious is 50 tpy both VOC and NOx. See 40 CFR 51.165(a)(1)(iv)(A)( 1 )( i ) and (a)(1)(iv)(A)( 2 )( iv ), respectively. As explained earlier in section VII.D.1 of this preamble, a major modification is a physical change or change in the method of operation of an existing major stationary source that results in both a significant emissions increase, and a significant net emissions increase. To determine whether an emissions increase is significant, the NNSR rules define significant emissions rates or SERs for each applicable pollutant. The SER for VOC is 40 tpy, as is the SER for NOx. See 40 CFR 51.165(a)(1)(x)(A). It should be noted that there are additional more stringent criteria that must be considered in determining a major modification in nonattainment areas classified as Serious, Severe or Extreme for O 3 . See 40 CFR 51.165(a)(1)(x)( B), (C) and (E). New major stationary sources and major modifications for O 3 must comply with the lowest achievable emissions rate (LAER) as defined in the CAA and NNSR rules, as well as perform ing other analyses as required under section 173 of the CAA

. In addition, appropriate emissions reductions, known as emissions offsets, must be secured to offset the proposed emissions increase of the precursors that trigger NNSR for O 3 . The appropriate emissions offset needed for a particular source will depend upo n the classification for the O 3 nonattainment area*** E.O. 12866 Review

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Page 557 of 647 in which the source or modification will locate. Generally, the ratio of the total emissions reduction to the emissions increase is at least 1:1; however, more stringent ratios apply to O 3 nonattainment ar eas according to the area classification. See , e.g., 40 CFR 51.165(a)(9) and 40 CFR Part 51, App. S, IV.G.2.
E. Transportation and General Conformity Programs 1. What are T ransportation and G eneral C onformity? Conformity is required under CAA section 176 (c) to ensure that federal actions are consistent with (“conform to”) the purpose of the SIP. Conformity to the purpose of the SIP means that federal activities will not cause new air quality violations, worsen existing violations, or delay timely attainme nt of the relevant NAAQS or interim reductions and milestones. Conformity applies to areas that are designated nonattainment, and those nonattainment areas redesignated to attainment with a CAA section 175A maintenance plan after 1990 (“maintenance areas”)

. The EPA’s Transportation Conformity Rule (40 CFR 51.390 and Part 93, subpart A) establishes the criteria and procedures for determining whether transportation activities conform to the SIP. These activities include adopting, funding or approving transp ortation plans, transportation improvement programs (TIPs) and federally supported highway and transit projects. For further information on conformity rulemakings, policy guidance and outreach materials, see the EPA’s website at http://www.epa.gov/otaq/sta teresources/transconf/index.htm

. The EPA may issue future transportation conformity guidance as needed to implement a revised
O 3 NAAQS. With regard to general conformity, the EPA first promulgated general conformity regulations in November 1993. (40 CFR p art 51, subpart W, 40 CRF part 93, subpart B)*** E.O. 12866 Review

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Page 558 of 647 Subsequently the EPA finalized revisions to the general conformity regulations on April 5, 2010. (75 FR 17254

- 17279) Besides ensuring that federal actions not covered by the transportation conformity rule will not interfere with the SIP, the general conformity program also fosters communications between federal agencies and state/local air quality agencies, provides for public notification of and access to federal agency conformity determinations and allows for air quality review of individual federal actions. More information on the general conformity program is available at http://www.epa.gov/air/genconform/

. 2. Why I s the EPA D iscussing T ransportation and G eneral C onformity in this P roposed
R ulemaking? The EPA is discussing transportation and general conformity in this proposed O 3 NAAQS rulemaking in order to provide affected parties with information on when and how conformity must be implemented after nonattainment areas are designated for a revised O 3 NAAQ S. The information presented here is consistent with existing conformity regulations and statutory provisions that are not addressed by this O 3 NAAQS rulemaking. Affected parties would include state and local transportation and air quality agencies, metrop olitan planning organizations (MPOs), and federal agencies including the U.S. Department of Transportation (DOT), the U.S. Department of Defense, the U.S. Department of Interior and the U.S. Department of Agriculture. 3. When W ould T ransportation and G eneral C onformity A pply to A reas D esignated
N onattainment for a R evised O 3 NAAQS , if One is Established ? Transportation and general conformity apply one year after the effective date of nonattainment designations for a revised O 3 NAAQS. This is because CA A section 176(c)(6) provides a 1

- year grace period from the effective date of initial designations for any revised*** E.O. 12866 Review

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Page 559 of 647 NAAQS before transportation and general conformity apply in areas newly designated nonattainment for a specific pollutant and NAAQS. 4. Will T ransportation and G eneral C onformity A pply to a D istinct S econdary O 3 NAAQS, if
O ne is E stablished? CAA section 176(c)(1)(A) states that conformity to a SIP means “conformity to an implementation plan’s purpose of eliminating or reducing the severity a nd number of violations of the national ambient air quality standards and achieving expeditious attainment of such standards...” In other words, because the CAA refers to the NAAQS without distinguishing between them, conformity applies to both the primary and secondary NAAQS for all criteria pollutants. Therefore, if a distinct secondary O 3 NAAQS is established, both transportation and general conformity will apply in any areas designated nonattainment for such a NAAQS. Current transportation and general conformity regulations already apply to such a secondary NAAQS, and nothing in this proposal affects those transportation and general conformity requirements. The EPA will consider the need to issue additional guidance concerning the implementation of tran sportation and general conformity in areas designated nonattainment for a distinct secondary O 3 NAAQS, if one is established

. 5. What I mpact W ould the I mplementation of a R evised O 3 NAAQS H ave on a S tate’s
T ransportation and/or G eneral C onformity SIP?
I f the EPA revises the O 3 NAAQS, but does not make specific changes to its transportation or general conformity regulations , then states should not need to revise their transportation and/or general conformity SIPs. The EPA is not proposing any changes to its transportation or general conformity regulations. While we are not proposing any revisions to the general conformity regulatio ns at this time, we recommend, when areas develop SIPs for a*** E.O. 12866 Review

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Page 560 of 647 revised O 3 NAAQS, that state and local air quality agencies work with federal agencies with large facilities that are subject to the general conformity regulations to establish an emissions budge t for those facilities in order to facilitate future conformity determinations under the conformity regulations. Such a budget could be used by federal agencies in determining conformity or identifying mitigation measures if the budget level is included an d identified in the SIP. Finally, states with new nonattainment areas may also need to revise conformity SIPs in order to ensure the state regulations apply in any newly designated areas if the existing SIP does include current conformity provisions.
If this is the first time that transportation conformity will apply in a state, such a state is required by the statute and EPA regulations to submit a SIP revision that addresses three specific transportation conformity requirements that address consultation procedures and written commitments to control or mitigation measures associated with conformity determinations for transportation plans, TIPs or projects. (40 CFR 51.390) Additional information and guidance can be found in the EPA’s “Guidance for Developi ng Transportation Conformity State Implementation Plans” ( http://www.epa.gov/otaq/stateresources/transconf/policy/420b09001.pdf ). F. How Background O 3 Is Addressed in C A A Implementation Provisions 1. Introduction
T he EPA and state, local and tribal air agencies, need to determine how to most effectively and efficiently use the CAA’s various provisions to provide required public health and welfare protection from the harm ful effects of O 3 . In most cases, reducing man

- made emissions of NO X and VOCs will reduce O 3 formation and provide additional health and welfare protection. The EPA recognizes, however, that “background” O 3 levels, which can be significant*** E.O. 12866 Review

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Page 561 of 647 in some areas on some days, may present a challenge to air agencies in preparing clean air plans.
T hat is, O 3 and O 3 - forming pollution from natural and international sources could prevent ambient levels from reaching attainment levels in locations where the impacts of suc h sources are large relative to the impact of controllable man

- made sources of NO X and VOC emissions within the U.S., especially in locations with few remaining untapped opportunities for local emission reductions. The term “background” is often used gener ically and the lack of specificity can lead to confusion as to what sources are being considered. The PA provides three specific definitions of background O 3 : natural background, North American background, and United States background. Natural background (NB) is defined as the O 3 that would exist in the absence of any manmade O 3 precursor emissions. North American background (NAB) is defined as that O 3 that would exist in the absence of any manmade O 3 precursor emissions from North America. U.S. background (USB) is defined as that O 3 that would exist in the absence of any manmade emissions inside the United States. Because background O 3 is difficult to measure, air quality modeling is conducted to estimate NA, NAB, and USB. The PA identifies several key fi ndings related to background O 3 . First, background O 3 can comprise a considerable fraction of total seasonal mean O 3 across the U.S. Studies have estimated that seasonal mean USB 8

- hour ozone values across U.S. locations varied between 25
to 50 ppb in 2007 (USEPA, 2014c , Figure 211 ) . The largest seasonal average values of background are modeled to occur at locations in the intermountain western U.S. and the highest daily USB levels are highest in the spring and early summer seasons . Second, the modeling ind icates that U.S. anthropogenic emission sources are the dominant contributor to the majority of modeled O 3 exceedances of the NAAQS across the U.S. This conclusion is based on results*** E.O. 12866 Review

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Page 562 of 647 that indicate background contributions are generally similar on high O 3 days as on all other O 3 days. As a result, the proportional influence of background sources tends to be lower on high ozone days. Third, while the majority of modeled O 3 exceedances have local and regional emissions as their primary cause, there can be eve nts where O 3 levels approach or exceed the concentration levels being proposed in this notice (i.e., 60

- 70 ppb) in large part due to background sources. These cases of high USB levels on high O 3 days typically result from stratospheric intrusions of O 3 , wi ldfire O 3 plumes, or long

- range transport of O 3 from sources outside the U.S. In most locations, these events are relatively infrequent and the CAA contains provisions that can be used to help deal with certain events, including providing varying degrees

o f regulatory relief for air agencies and potential regulated entities. Regulatory relief associated with U.S. background O 3 may include: 267

 Relief from designation as a nonattainment area (through exclusion of data affected by exceptional events)

 Relief from the more stringent requirements of higher nonattainment area classifications (through treatment as a rural transport area; through exclusion of data affected by exceptional events; or through international transport provisions)

 Relief from adop ting more than reasonable controls to demonstrate attainment (through international transport provisions) None of these relief mechanisms are completely burden

- free, meaning they all require some level of assessment or demonstration by a state and/or EPA to legally invoke. In no case

267 Note that the relief mechanisms discussed here do not include the CAA’s interstate transport provisions found in sections 110(a)(2)(D) and 126. The interstate transport provisions are intended to address the cross

- sta te transport of O 3 and O 3 precursor emissions from man

- made sources within the continental U.S. rather than background O 3 as it is defined in this section.*** E.O. 12866 Review

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Page 563 of 647 does the CAA authorize a blanket exclusion from the basic application of an air quality management regime because an area is significantly impacted by background O 3 . While any prediction of the exact nature of future implement ation challenges associated with alternative prospective standards is inherently uncertain, there is no question that, as the levels of alternative prospective standards are lowered, background will represent increasingly larger fractions of total O 3 level s and may subsequently complicate efforts to attain these standards. For a prospective standard of 70 ppb, the EPA does not believe that background O 3 would create significant implementation

- related challenges at locations throughout the U.S. and prevent

a ttainment of the NAAQS. However, as the levels of prospective standards are lowered, the areas that would most likely need to use the relief mechanisms discussed in this section as part of attaining the lower prospective levels are rural locations in the w estern U.S., consistent with the previously mentioned locations where we have estimated the largest seasonal average values of background occur. The remainder of this section discusses these relief mechanisms and the methods associated with legally invokin g them. These relief mechanisms depend on distinguishing background O 3 by the following types of drivers: routine natural emissions, non

routine natural events and international emissions. The EPA welcomes comment on any of these issues related to O 3 backg round and implementation. 2. Exceptional Events Exclusions A state can request and the EPA can agree to exclude data associated with event

influenced exceedances or violations of a NAAQS, including the proposed O 3 NAAQS, provided the event meets the statu tory requirements in section 319 of the CAA:

 The event “affects air quality.”

 The event “is not reasonably controllable or preventable.”*** E.O. 12866 Review

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Page 564 of 647  The event is “caused by human activity that is unlikely to recur at a particular location or [is] a natural event.” 268 The EPA’s implementing regulations , the 2007 Exceptional Events Rule, further specify that states must provide evidence that: 269

 “There is a clear causal relationship between the measurement under consideration and the event that is claimed to have affected the air quality in the area;”

 “The event is associated with a measured concentration in excess of normal historical fluctuations, including background;” and

 “There would have been no exceedance or violation but for the event.” The ISA contains discussion s of natural events that may contribute to O 3 or O 3 precursors. These include stratospheric O 3 intrusion and wildfire events

. 270 As indicated above, to satisfy the exceptional event requirements and to qualify for data exclusion under the Exceptional Events Rule, a state must develop and submit evidence addressing each of the identified criteria. The extent to which a stratospheric O 3 intrusion event or a wildfire event contribute to O 3 levels can be uncertain, and in most cases requires detailed investigation and analysis to adequately determine

.

268 A natural event is further described in 40 CFR 50.1(k) as “an event in which human activity plays little or no direct causal role.” 269 See 72 Federal Register 13560 (March 22, 2007), 40 CFR Part 50.1, 40 CFR Part 50.14 and 40 CFR Part 51.930. 270 The preamble to the Exceptional Events Rule (72 FR 13560, March 22, 2007) identifies both stratospheric O 3 intrusions and wildfires as natural events that could also qualify as exceptional events under the CAA and Exceptional Event Rule criteria. Note that O 3 resulting from routine natural emissions from vegetation, microbes, animals and lightning are not excep tional events authorized for exclusion under the section 319 of the CAA.*** E.O. 12866 Review

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Page 565 of 647 Strong stratospheric O 3 intrusion events, most prevalent at high elevation sites during winter or spring, can be identified based on measurements of low relative humidity, evidence of deep atmospheric m ixing, and a low ratio of carbon monoxide to O 3 based on ambient
measurements. Accurately d etermin ing the extent of weaker intrusion events remains challenging. 271 Although states have submitted only a few exceptional event demonstrations for stratospheric O 3 intrusion, the EPA recently approved a demonstration from Wyoming for a June 2012 stratospheric O 3 event. 272 While stratospheric O 3 intrusions can increase monitored ground

- level ambient O 3 concentrations, w ildfire plumes can either suppress or enhance O 3 depending upon a variety of factors including fuel type, combustion stage , plume chemistry, aerosol effects, meteorological conditions and distance from the fire (Jaffe and Widger, 2012). As such, determining the impact of wildfire emissions on specific O 3 observations is challenging. The EPA has, however, recently approved two exceptional event demonstrations that successfully used a variety of analytical tools (e.g ., regression modeling, back trajectories, satellite imagery, etc.) to support the exclusi on of O 3 data affected by large fires

. 273 The first example involved wildfires affecting 1

- hour O 3 levels in Sacramento, California in 2008. The second example involved large scale prescribed fires in the Flint Hills area of Kansas in 2011

. While the EPA doe s not include the O 3 effects of prescribed fires with in the definition of U.S. background because they are not natural, the physical conditions of these prescribed fires may resemble large natural wildfires on the same type of landscape.

271 See ISA page 3

- 34 272 See www.epa.gov/ttn/analysis/exevents.htm 273 See examples of O 3 - related exceptional event submissions at www.epa.gov/ttn/analysis/exevents.htm*** E.O. 12866 Review

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Page 566 of 647 Because of previously expressed stakeholder feedback regarding implementation of the Exceptional Events Rule and specific stakeholder concerns regarding the analyses that can be used to support O 3 - related exceptional event demonstrations, the EPA intends to propose

r evisions to the Exceptional Events Rule in a future notice and comment rulemaking effort and will solicit public comment at that time. Additionally, t he EPA intends to develop guidance to address implementing the Exceptional Events Rule criteria for fires that could affect ambient O 3 concentrations. 3. Rural Transport Areas CAA section 182(h) authorizes the EPA Administrator to determine that an area designated nonattainment can be treated as a rural transport area. In accordance with the statute,
a nonat tainment area may qualify for this determination if it meets the following criteria:

 The area does not contain emissions sources that make a significant contribution to monitored O 3 concentrations in the area, or in other areas; and

 The area does not inclu de and is not adjacent to a Metropolitan Statistical Area

. 274
H istorically , the EPA has recognized few nonattainment areas under this statutory provision. 275 The EPA has not finalized separate written guidance to further elaborate on the interpretation of thes e CAA qualification criteria. However, the EPA developed draft guidance in 2005 that explains the kinds of technical analyses that states could use to establish that transport

274 Note that the EPA interprets the rural transport provisions of section 182(h) would not apply to an O 3 monitor that is located in a relatively rural l ocation, but is heavily influenced by short

range upwind contributions from a nearby urbanized area. The EPA will work closely with states to determine whether a particular monitor violating the NAAQS is considered to be affiliated with a nearby urban area , or is an isolated rural area monitor. 275 For the 1979 1

- hour O 3 standard Essex County, New York, and Smyth County, Virginia (White Top Mountain) were recognized by the EPA as rural transport areas.*** E.O. 12866 Review

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Page 567 of 647 of O 3 and/or O 3 precursors into the area is so overwhelming that the contributio n of local emissions to an observed 8

- hour O 3 concentration above the level of the NAAQS is relatively minor and determine that emissions within the area do not make a significant contribution to the
O 3 concentrations measured in the area or in other areas

. 276 An area that qualifies for treatment as a rural transport area is deemed to have fulfilled all
O 3 - related planning and control requirements if it meets the CAA’s requirements for areas classified Marginal, which is the lowest classification specified i n the CAA. Therefore, a state would not need to develop an attainment plan or an attainment demonstration for such an area or adopt the various mandatory measures required in nonattainment areas classified as Moderate or above . The only requirements that w ould apply, regardless of the level of O 3 air quality, would be NNSR (at the Marginal major source threshold and offset ratio), conformity requirements associated with a nonattainment designation, and the emission inventory and source emission
statement re quirements. 4. International Transport CAA section 179B recognizes the possibility that certain nonattainment areas may be heavily impacted by O 3 or O 3 precursor emissions from international sources beyond the regulatory jurisdiction of the state

. The EP A’s science review suggests that the influence of international sources on U.S. O 3 levels will be largest in locations that are in the immediate vicinity of an international border with Canada or Mexico, but other locations can also potentially be affected when conditions are favorable for long

- range transport. 277 Sec tion 179B

276 The draft EPA guidance document titled “Criteria For Assessing Whether an Ozone Nonattainment Area is Affected by Overwhelming Transport” (draft 6

- 29

- 05) was not finalized and did not specifically address the provisions of CAA section 182(h). The draft gu idance can be viewed at www.epa.gov/scram001/guidance/guide/owt_guidance_07

- 13

- 05.pdf 277 ISA (U.S. EPA , 2013 , p. 3

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Page 568 of 647 allows states to consider in their attainment demonstrations whether an area might have met the
O 3 NAAQS by the attainment date “but for” emissions contributing to the area originating outside the United States. If a state is unable to demonstrate attainment in such an area after adopting all reasonably available control measures (RACM, including RACT, as required by CAA section 182(b)), the EPA can nonetheless approve the CAA

- required s tate attainment plan and demonstration using the authority in section 179B. When the EPA approves this type of attainment plan, states avoid potential sanctions and federal implementation plans (FIPs), and there would be no adverse consequence for a find ing that the area failed to attain the NAAQS by the relevant attainment date. For example, the area would not be reclassified to the next highest classification or required to implement a section 185 penalty fee program. Section 179B authority does not a llow the EPA to avoid designating an area as nonattainment or for the area to be classified with a lower classification than is indicated by actual air quality. Generally, monitoring data influenced by international transport may not be excluded from regul atory determinations, unless the data are influenced by an excludable exceptional event. Section 179B also does not provide for any relaxation of mandatory emissions control measures (including contingency measures) or the prescribed emissions reductions

n ecessary to achieve reasonable further progress (RFP). The EPA’s guidance on ‘but for’ demonstrations involving international emissions indicates that states may want to consider conducting air quality modeling using O 3 episodes that do not involve intern ational transport of emissions (see guidance document entitled “Criteria for Assessing the Role of Transported O 3 /Precursors in O 3 Nonattainment Areas” 278 ), running the

278 EPA

- 450/4

- 91

- 015, May 1991.*** E.O. 12866 Review

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Page 569 of 647 model with boundary conditions that reflect general U.S. background concentrations, and analyzing monitoring data if a dense network has been established. Additional information that may be helpful at nonattainment areas abutting international borders could include evaluating changes in O 3 with changes in wind direction at monitors near the b order, and comparing emissions on both sides of the border. States are encouraged to consult with their EPA Regional Office to establish appropriate technical requirements for these analyses. The EPA has used section 179B authority previously to approve a ttainment plans for Mexican border areas in El Paso, TX (O 3 , PM10, and CO plans); Nogales, AZ (PM10 plan); and Imperial Valley, CA (PM10 plan). The 1

- hour O 3 attainment plan for El Paso, TX was approved by EPA as sufficient to demonstrate attainment of the NAAQS by the Moderate classification deadline of November 15, 1996, taking into account “but for” international emissions sources in Ciudad Juárez, Mexico (69 FR 32450, June 10, 2004). The state’s demonstration included airshed modeling using only the U.S

. emissions data because emissions data from Ciudad Juárez were not available.
VIII. Statutory and Executive Order Reviews
A. National Technology Transfer and Advancement Act Section 12(d) of the National Technology Transfer and Advancement Act of 1995 (NTTAA), Public Law No. 104

- 113, §12(d) (15 U.S.C. 272 note) directs the EPA to use voluntary consensus standards in its regulatory activities unless to do so would be inconsistent with applicable law or otherwise impractical. V oluntary consensus standards are technical standards (e.g., materials specifications, test methods, sampling procedures, and business practices) that are developed or adopted by voluntary consensus standards bodies. The NTTAA*** E.O. 12866 Review

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Page 570 of 647 directs the EPA to provide Congress, through OMB, explanat ions when the Agency decides not to use available and applicable voluntary consensus standards. This proposed rulemaking involves environmental monitoring and measurement

c onsistent with the Agency’s Performance Based Measurement System (PBMS) . The EPA
pro pose s not to require the use of specific, prescribed analytical methods. Rather, the Agency plans to allow the use of any method that meets the pr escribed performance criteria. Ambient air concentrations of ozone are currently measured by the Federal refer ence method (FRM) in 40 CFR part 50, Appendix D (Measurement Principle and Calibration Procedure for the Measurement of Ozone in the Atmosphere) or by Federal equivalent methods (FEM) that meet the requirements of 40 CFR part 53. Procedures are available i n part 53 that allow for the approval of an FEM for O 3 that is similar to the FRM. Any method that meets the performance criteria for a candidate equivalent method may be approved for use as an FEM. This approach is consistent with EPA’s PBMS. The PBMS app roach is intended to be more flexible and cost

effective for the regulated community; it is also intended to encourage innovation in analytical technol ogy and improved data quality. The EPA is not precluding the use of any method, whether it constitutes a voluntary consensus standard or not, as long as it meets the specified performance criteria.
B. Paperwork Reduction Act The information collection requirements in this proposed rule have been submitted for approval to the Office of Management and Budget (O MB) under the Paperwork Reduction Act, 44 U.S.C. 3501 et seq. The Information Collection Request (ICR) document prepared by EPA has been assigned EPA ICR No. XXXX

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Page 571 of 647 The information collected and reported under 40 CFR part 58 is needed to determine compliance with the NAAQS, to characterize air quality and associated health and ecosystems impacts, to develop emission control strategies, and to measure progress for the ai r pollution
program. We are proposing to extend the length of the required O 3 monitoring season in 33 states and propose that the revised O 3 monitoring seasons become effective on January 1 , 2017. We are also proposing revisions to the PAMS monitoring requirements that reduce the number of required PAMS sites while improving spatia l coverage, and proposing to require states with O 3

non - attainment areas to develop an enhanced monitoring plan as part of the PAMS requirements. For areas currently designated as nonattainment for O 3 based on the 2008 NAAQS, we propose that these areas co mply with the PAMS requirements by June 1, 2017. For new areas designated based on a revised NAAQS, if finalized, we propose that those areas comply with the PAMS requirements by January 1, 2019.
T he annual average reporting burden for the collection under 40 CFR part 58 (averaged over the first 3 years of this ICR) for XXX respondents is estimated to increase by a total of XX l abor hours per year with an increase of $XX per year . Burden is defined at 5 CFR 1320.3(b ). State, local, and tribal entities are e ligible for state assistance grants provided by the Federal government under the CAA which can be used for related activities. The proposal for a new FRM in 40 CFR part 50 and revisions to the O 3 FEM procedures for testing performance characteristics in 40 CFR part 53 does not add any additional information collection requirements. An agency may not conduct or sponsor, and a person is not required to respond to, a collection of information unless it displays a curre ntly valid OMB control number. The OMB

con trol numbers for EPA’s regulations in 40 CFR are listed in 40 CFR part 9.*** E.O. 12866 Review

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Page 572 of 647 To comment on the Agency’s need for this information, the accuracy of the provided burden estimates, and any suggested methods for minimizing respondent burden, EPA has establishe d a public docket for this rule, which includes this ICR, under Docket ID number EPA

HQ

- OAR

- 2008

- 0699. Subm it any comments related to the ICR to EPA and OMB . Send comments to the EPA at the air and Radiation Docket and Information Center Docket in the EPA Docket Center (EPA/DC), EPA West, Room 3334, 1301 Constitution Ave. NW.,Washington DC. The Docket Center Public Reading Room is open from 8:30 a.m. to 4:30 p.m., Monday through Friday, excluding legal holidays. The telephone number for the Reading Room is (202) 566

- 1744, and the telephone number for the Air and Radiation Docket and Information Center Docket is (202) 56

- 1742. An electronic version of the public docket is available at www.regulations.gov

. Send commen ts to OMB at the Office of Information and Regulatory Affairs, Office of Management and Budget, 725 17th Street, NW, Washington, DC 20503, Attention: Desk Office for EPA. Since OMB is required to make a decision concerning the ICR between 30 and 60 days af ter [Insert date of publication in the Federal Register.], a comment to OMB is best assured of having its full effect if OMB receives it by [Insert date 30 days after publ ication in the Federal Register ]. The final rule will respond to any OMB or public co mments on the information collection requirements contained in this proposal.
C. Regulatory Flexibility Act The Regulatory Flexibility Act (RFA) generally requires an agency to prepare a regulatory flexibility analysis of any rule subject to notice and c omment rulemaking requirements under the Administrative Procedure Act or any other statute unless the agency certifies that the rule will not have a significant economic impact on a substantial number of*** E.O. 12866 Review

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Page 573 of 647 small entities. Small entities include small busines ses, small organizations, and small governmental jurisdictions. For purposes of assessing the impacts of today’s proposed rule on small entities, small entity is defined as: (1) a small business that is a small industrial entity as defined by the Small
Bus iness Administration’s (SBA) regulations at 13 CFR 121.201; (2) a small governmental jurisdiction that is a government of a city, county, town, school district or special district with a population of less than 50,000; and (3) a small organization that is any not

- for

- profit enterprise which is independently owned and operated and is not dominant in its field. After considering the economic impacts of today's proposed rule on small entities, I certify that this action will not have a significant economic im pact on a substantial number of small entities. The reason is that this proposed rule will not impose any requirements on small entities. Rather, this rule establishes national standards for allowable concentrations of O 3 in ambient air as required by section 109 of the CAA. See also American Trucking Associations v.
EPA , 175 F. 3d at 1044

- 45 (NAAQS do not have significant impacts upon small entities because NAAQS themselves impose no regulations upon small entities). Sim ilarly, the proposed revisions to 40 CFR part 58 address the requirements for states to collect information and report compliance with the NAAQS and will not impose any requirements on small entities. Similarly, the addition of a new FRM in 40 CFR part 50 and revisions to the FEM procedures for testing in 40 CFR part 53 will not impose any requirements on small entities.
D. Unfunded Mandates Reform Act Title II of the Unfunded Mandates Reform Act of 1995 (UMRA), Public Law 104

- 4 , establishes requirements for f ederal agencies to assess the effects of their regulatory actions on

s tate, local, and t ribal governments and the private sector. Under section 202 of the UMRA, the*** E.O. 12866 Review

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Page 574 of 647 EPA generally must prepare a written statement, including a cost

- benefit analysis, for proposed and final rules with “f

ederal mandates” that may result in exp enditures to state, local, and t ribal governments, in the aggregate, or to the private sector, of $100 million or more in any 1 year. Before promulgating an EPA rule for which a writt en statement is needed, section 205 of the UMRA generally requires the EPA to identify and consider a reasonable number of regulatory alternatives and to adopt the least costly, most cost

- effective or least burdensome alternative that achieves the objectiv es of the rule. The provisions of section 205 do not apply when they are inc onsistent with applicable law. Moreover, section 205 allows the EPA to adopt an alternative other than the least costly, most cost

- effective or least burdensome alternative if the Administrator publishes with the final rule an explanation why that alternative was not adopted. Before the EPA establishes any regulatory requirements that may significantly or uniquely affect small governments, incl uding t ribal governments, it must have developed under section 203 of the UMRA a small government agency plan. The plan must provide for notifying potentially affected small governments, enabling officials of affected small governments to have meaningful and timely input in the development of t he EPA regulat ory proposals with significant f ederal intergovernmental mandates, and informing, educating, and advising small governments on compliance with the regulatory requirements. Today’s proposed rule contains no f ederal mandates (under the regulat ory provision s of Title II of the UMRA) for state, local, or t ribal gov ernments or the private sector. The proposed rule imposes no new expendit ure or enforceable duty on any state, local or t ribal governments or the private sector, and the EPA has determi ned that this proposed rule contains no regulatory requirements that might significantly or uniquely affect small governments. Furthermore, as indicated previously, in setting a NAAQS the EPA cannot consider the economic or*** E.O. 12866 Review

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Page 575 of 647 technological feasibility of att aining ambient air quality standards, although such factors may be considered to a degree in the development of s tate plans to implement the standards. See also American Trucking Associations v. EPA , 175 F. 3d at 1043 (noting that because the EPA is preclu ded from considering costs of implementation in establishing NAAQS, preparation of a Regulatory Impact Analysis (RIA) pursuant to the Unfunded Mandates Reform Act would not furnish any information which the court could consider in reviewing the NAAQS).
Th e proposed revisions to 40 CFR part 58 do not contain a Federal mandate that may result in expenditures of $100 million or more for state, local, and tribal governments, in the aggregate, or the private sector in any o ne year. The addition of a new FRM in 40 CFR part 50 and revisions to the FEM procedures for testing performance in 40 CFR part 53 will not result in associated cost because it does not add any new requirements or require state, local, tribal governments to change or add monitoring methods. Accordingly, the EPA has determined that the provisions of sections 202, 203, and 205 of the UMRA do not apply to this propos al

. The EPA acknowledges, however, that any corresponding revisions to associated SIP requirements, 40 CFR part 51, might result i n such effects. Accordingly, EPA will address, as appropriate, unfunded mandates if and when it proposes any revisions to 40 CFR parts 51.
E. Executive Order 12866: Regulatory Planning and Review Under section 3(f)(1) of Executive Order (EO) 12866 (58 FR 51735, October 4, 1993), the O 3 NAAQS action is an “economically significant regulatory action” because it is likely to have an annual effect on the economy of $100 million or more. Accordingly, the EPA submitted this action to the Office of Management an d Budget (OMB) for review under EO 12866 and any changes made in response to OMB recommendations have been documented in the docket for*** E.O. 12866 Review

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Page 576 of 647 this action. In addition, the EPA prepared this RIA of the potential costs and benefits associated with this action. Thi s analysis is contained in the document, Regulatory Impact Analysis for the
O 3 NA AQS , Month, 2014

. A copy of the analysis is available in the RIA docket (EPA

- HQ

OAR

- 2013

- 0169 ) and the analysis is briefly summarized here. The RIA estimates the costs and

mon etized human health and welfare benefits of attaining four alternative O 3 NAAQS nationwide. Specifically, the RIA examines the alternatives of 60 ppb, 65 ppb, 70 ppb, and 75 ppb. The RIA contains illustrative analyses that consider a limited number of emissions control scenarios that states and Regional Planning Organizations might implement to achieve these alternative O 3 NAAQS. However, the CAA and judicial decisions make c lear that the economic and technical feasibility of attaining ambient standards are not to be considered in setting or revising NAAQS, although such factors may be considered in the development of s tate plans to implement the standards. Accordingly, althou gh an RIA has been prepared, the results of the RIA have not been considered in issuing this proposed rule.
F. Executive Order 12898: Federal Actions to Address Environmental Justice in Minority Populations and Low

- Income Populations Executive Order 12898 (59 FR 7629 (Feb. 16, 1994)) establishes federal executive policy on environmental justice. Its main provision directs federal agencies, to the greatest extent practicable and permitted by law, to make environmental justice part of their mission by identif ying and addressing, as appropriate, disproportionately high and adverse human health or environmental effects of their programs, policies, and activities on minority populations and low

income populations in the United States. The EPA has determined tha t this proposed rule will not have disproportionately high and adverse human health or environmental effects on minority or low

- income populations because it*** E.O. 12866 Review

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Page 577 of 647 increases the level of environmental protection for all affected populations without having any di sproportionately high and adverse human health or environmental effects on any population, including any minority or low

- income population. The proposed rule , if finalized, will establish uniform national standards for O 3 air pollution.
G. Executive Order 13045: Protection of Children from Environmental Health & Safety Risks Executive Order 13045, “Protection of Children from Environmental Health Risks and Safety Risks” (62 FR 19885, April 23, 1997) applies to any rule that: (1) is determined to be “econo mically significant” as defined under Executive Order 12866, and (2) concerns an environmental health or safety risk that the EPA has reason to believe may have a disproportionate effect on children. If the regulatory action meets both criteria, the Agency must evaluate the environmental health or safety effects of the planned rule on children, and explain why the planned regulation is preferable to other potentially effective and reasonably feasible alternatives considered by the Agency. This proposed rule is subject to Executi ve Order 13045 because it is an economically significant regulatory action as defined by Executive Order 12866, and we believe that the environmental health risk addressed by this action may have a disproportionate effect on children. The proposed rule will establish uniform national ambient air quality standards for O 3 ; these standards are designed to protect public health with an adequate margin of safety, as required by CAA section 109. However, the protection offered by these stand ards may be especially important for children because children, especially children with asthma, along with other at

- risk population s 279 such as all people with lung disease and people active outdoors, are

279 As used here and s imilarly throughout this document, the term population refers to p eople having a quality or characteristic in common, including a specific pre

- existing illness or a specific age or life stage.*** E.O. 12866 Review

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Page 578 of 647 potentially susceptible to health effects resulting from O 3 exposure. Because children are considered a n at

- risk lifestage , we have carefully evaluated the environmental health effects of exposure to O 3 pollution among children. Discussions of the results of the evaluation of the scientific evidence, policy considerations, and the exposure and risk assessments pertaining to children are contained in sections II. B and II. C of this preamble.
H. Executive Order 13132: Federalism Executive Order 13132, entitled “Federalism” (64 FR 43255, August 10, 1999), requires EPA to develop an accountable process to ensure “meaningful and timely input by s tate and local officials in the development of regulatory policies that have federalism implications.” “Policies that have f

ederalism implications” are defined in the Executive Order to include regulations that have “sub stantial direct effects on the s tates, on the relationship between the national government and the s tates, or on the distribution of power and responsibilities among the various levels of government.” This proposed rule does not have federalism implications. It will not have sub stantial direct effects on the s tates, on the relationship between the national government and the s tates, or on the distribution of power and r esponsibilities among the various levels of government, as specified in Executive Order 13132. The rule does not alter the relationship between the f ederal government and the s tates regarding the establishment and implementation of air quality improvement programs as codified in the CAA. Under section 109 of the CAA, the EPA is mandated to establish NAAQS; however, CAA section 116 preserves the rights of s tates to establish more stringent requirements if deemed necessary by a s tate. Furthermore, this propos ed rule does not impact CAA section 107 which establishes that the s tates have primary responsibility for implementation of the NAAQS. Finally, as noted in section E (above) on*** E.O. 12866 Review

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Page 579 of 647 UMRA, this rule does n ot impose significant costs on s tate, local, or t ribal go vernments or the private sector. Thus, Executive Order 13132 does not apply to this rule. However, as also noted in section D (above) on UMRA, EPA recognizes that s tates will have a substantial interest in this rule and any corresponding revisions to assoc iated SIP requirements and air quality surveillance requirements, 40 CFR part 51 and 40 CFR part 58, respectively. Therefore, in the spirit of Executive Order 13132, and consistent with the EPA policy to promote communications between the EPA and s tate and local governments, the EPA specifically solicits comment on this proposed rule from s tate and local officials.
I

. Executive Order 13175: Consultation and Coordination with Indian Tribal Governments Executive Order 13175, entitled “Consultation and Coordination with Indian Tribal Governments” (65 FR 67249, November 9, 2000), requires the EPA to develop an accountable process to ensure “meaningful and timely input by tribal officials in the development of regulatory policies that have tribal implications.” This rule concerns the establishment of O 3 NAAQS , establishes an additional FRM, revises FEM procedures for testing, and revises air quality surveillance requirements . T he Tribal Authority Rule gives t ribes the opportunity to develop and implement CAA programs such as the O 3 NAAQS, but it leaves to the discretion of the t ribe whether to develop these programs and which programs, or appropriate elements of a program, they will adopt. This proposed rul e does not have t ribal implications, as specified in Executive Order 13175. It does not have a substantial direct effect on on e or more Indian Tribes, since t ribes are not obligated to adopt or implement any NAAQS. In addition, t ribes are not obligated to conduct ambient monitoring for O 3 or to adopt the ambient monitoring requirements of 40 CFR part 58. Thus, Executive Order 13175 does not apply to this rule.*** E.O. 12866 Review

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Page 580 of 647 Although Executive Order 13175 does not apply to this rule, the EPA contacted tribal environmental professionals during the development of the this proposal. The EPA staff participated in the regularly scheduled Tribal Air call sponsored by the National Tribal Air Association during the [ season ] of 2014 as the proposal was under development. The EPA
sp ecifically solicits additional comm ent on this proposed rule from t ribal officials.
J. Executive Order 13211: Actions that Significantly Affect Energy Supply, Distribution or Use This proposed rule is not a “significant energy action” as defined in Executi ve Order 13211, “Actions Concerning Regulations That Significantly Affect Energy Supply, Distribution, or U se” (66 FR 28355 (May 22, 2001)) because in the Agency’s judgment it is not likely to have a significant adverse effect on the supply, distribution, or use of energy. The purpose of this rule is to establish revised NAAQS for O 3 , establish an additional FRM, revise FEM procedures for testing, and revises air quality surveillance requirements . The rule does not prescribe specific pollution control strat egies by which these ambient standards and monitoring revisions will be met. Such strategies will be developed by s tates on a case

- by

- case basis, and the EPA cannot predict whether the control options selected by s tates will include regulations on energy suppliers, distributors, or users. Thus, the EPA concludes that this rule is not likely to have any adverse energy effects and does not constitute a significant energy action as defined in Executive Order 13211.
Re ferences Abt Associates, Inc. (1995). Ozone NAAQS benefits analysis: California crops. Report to U.S. EPA, July

. Adams, W. C. (2006) Comparison of chamber 6.6 hour exposures to 0.04

- 0.08 ppm ozone via square - wave and triangular profiles on pulmonary resp onses. Inhalation Toxicol. 18: 127

- 136. http://dx.doi.org/10.1080/08958370500306107*** E.O. 12866 Review

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Page 581 of 647 Adams, WC. (2003). Comparison of chamber and face mask 6.6

- hour exposure to 0.08 ppm ozone via square

- wave and triangular profiles on pulmonary responses. Inhal Toxicol 1 5: 265

- 281. Adams, WC. (2002). Comparison of chamber and face

- mask 6.6

- hour exposures to ozone on pulmonary function and symptoms responses. Inhal Toxicol 14: 745

- 764. http://dx.doi.org/10.1080/08958370290084610 Adams, P. F.; Hendershot, G. E.; Marano, M . A. (1999) Current estimates from the National Health Interview Survey, 1996. Hyattsville, MD: U.S. Department of Health and Human Services, Public Health Service, National Center for Health Statistics; DHHS publication no. (PHS) 99

- 1528. (Vital and healt h statistics: v. 10, data from the National Health Survey, no. 200). Available: http://www.cdc.gov/nchs/products/pubs/pubd/series/sr10/pre

- 200/pre

- 200.htm [12 March, 2001]. Adamson, I; Prieditis, H. (1995). Response of mouse lung to carbon deposition durin g injury and repair. Environmental Health Perspectives. 103: 1: 72

- 76. Akbari, H. (2002) Shade trees reduce building energy use and CO2 emissions from power plants. Environmental Pollution 116 (2002) S119

– S126 Alexeeff, SE; Litonjua, AA; Suh, H; Sparrow, D; Vokonas, PS; Schwartz, J. (2007). Ozone exposure and lung function: Effect modified by obesity and airways hyperresponsiveness in the VA Normative Aging Study. Chest 132: 1890

- 1897. http://dx.doi.org/10.1378/chest.07

- 1126 Alexis, NE; Lay, JC; Hazucha, M; Harris, B; Hernandez, ML; Bromberg, PA; Kehrl, H; Diaz

Sanchez, D; Kim, C; Devlin, RB; Peden, DB. (2010). Low

- level ozone exposure induces airways inflammation and modifies cell surface phenotypes in healthy humans. Inhal Toxicol 22: 593

- 600. Alexis, N; Urch, B; Tarlo, S; Corey, P; Pengelly, D; O'Byrne, P; Silverman, F. (2000). Cyclooxygenase metabolites play a different role in ozone

- induced pulmonary function decline in asthmatics compared to normals. Inhal Toxicol 12: 1205

- 1224. Andersen, CP; Wilson, R; Plocher, M; Hogsett, WE. (1997). Carry

- over effects of ozone on root growth and carbohydrate concentrations of ponderosa pine seedlings. Tree Physiol 17: 805

- 811. ATS (American Thoracic Society). (2000). What constitutes an adverse health effect of air pollution? Am. J. Respir. Crit. Care Med. 161: 665

- 673. ATS (American Thoracic Society). (1991). Lung function testing: selection of reference values and interpretive strategies. Am. Rev. Respir. Dis. 144: 1202

- 1218.*** E.O. 12866 Review

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Page 582 of 647 ATS (American Thoracic Society). (1985 ) Guidelines as to what constitutes an adverse respiratory health effect, with special reference to epidemiological studies of air pollution. Am. Rev. Respir. Dis. 131: 666

- 668. Avol, EL; Trim, SC; Little, DE; Spier, CE; Smith, MN; Peng, RC; Linn, WS; Hackney, JD; Gross, KB; D'Arcy, JB; Gibbons, D; Higgins, ITT. (1990). Ozone exposure and lung function in children attending a southern California summer camp. In Proceedings of the 83rd A&WMA Annual Meeting. Pittsburgh, PA: Air & Waste Management Association. Balmes, JR; Chen, LL; Scannell, C; Tager, I; Christian, D; Hearne, PQ; Kelly, T; Aris, RM. (1996). Ozoneinduced decrements in FEV1 and FVC do not correlate with measures of infl ammation. Am J Respir Crit Care Med 153: 904

- 909. Barraza

- Villarreal, A; Sunyer, J; Hernandez

- Cadena, L; Escamilla

- Nunez, MC; Sienra

- Monge, JJ; Ramirez

- Aguilar, M; Cortez

- Lugo, M; Holguin, F; Diaz

- Sanchez, D; Olin, AC; Romieu, I. (2008). Air pollution, air way inflammation, and lung function in a cohort study of Mexico City schoolchildren. Environ Health Perspect 116: 832

- 838. http://dx.doi.org/10.1289/ehp.10926 Basha, MA; Gross, KB; Gwizdala, CJ; Haidar, AH; Popovich, J, Jr. (1994). Bronchoalveolar lavage n eutrophilia in asthmatic and healthy volunteers after controlled exposure to ozone and filtered purified air. Chest 106: 1757

- 1765. Bell, ML; Peng, RD; Dominici, F. (2006). The exposure

- response curve for ozone and risk of mortality and the adequacy of cur rent ozone regulations. Environ Health Perspect 114: 532

- 536. Berhane, K; Zhang, Y; Linn, WS; Rappaport, EB; Bastain, TM; Salam, MT; Islam, T; Lurmann, F; Gilliland, FD. (2011). The effect of ambient air pollution on exhaled nitric oxide in the Children's Health Study. Eur Respir J 37: 1029

- 1036. http://dx.doi.org/10.1183/09031936.00081410 Berry, M; Lioy, PJ; Gelperin, K; Buckler, G; Klotz, J. (1991). Accumulated exposure to ozone and measurement of health effects in children and counselors at two summer c amps. Environ Res 54: 135

- 150. Betzelberger, AM; Gillespie, KM; McGrath, JM; Koester, RP; Nelson, RL; Ainsworth, EA. (2010). Effects of chronic elevated ozone concentration on antioxidant capacity, photosynthesis and seed yield of 10 soybean cultivars. Pla nt Cell Environ 33: 1569

- 1581. http://dx.doi.org/10.1111/j.1365

- 3040.2010.02165.x Blomberg, A; Mudway, IS; Nordenhall, C; Hedenstrom, H; Kelly, FJ; Frew, AJ; Holgate, ST; Sandstrom, T. (1999). Ozone

- induced lung function decrements do not correlate with ea rly airway inflammatory or antioxidant responses. Eur Respir J 13: 1418

- 1428. Bloom B, Cohen RA, Freeman G. (2011). Summary health statistics for U.S. children: National Health Interview Survey, 2010. National Center for Health Statistics. Vital Health Sta t 10(250). http://www.cdc.gov/nchs/data/series/sr_10/sr10_250.pdf*** E.O. 12866 Review

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Page 583 of 647 Bosson, J; Stenfors, N; Bucht, A; Helleday, R; Pourazar, J; Holgate, ST; Kelly, FJ; Sandstrom, T; Wilson, S; Frew, AJ; Blomberg, A. (2003). Ozone

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- Ozone. An Interim Repo rt of the U.S. EPA Global Change Research Program. U.S Environmental Protection Agency, Washington, DC. EPA/600/R

– 07/094. U.S. EPA (2007). Review of the National Ambient Air Quality Standards for Ozone: Policy Assessment of Scientific and Technical Inform ation, OAQPS Staff Paper. EPA

- 452/R

07

- 007

. U.S. EPA (2006 a ). Air Quality Criteria for Ozone and Related Photochemical Oxidants (2006 Final). U.S. Environmental Protection Agency, Washington, DC. EPA/600/R

- 05/004aF

cF. March 2006. Available at: http://www.epa.gov/ttn/naaqs/standards/ozone/s_o3_cr_cd.html U.S. EPA (2006b). Ecological Benefits Assessment Strategic Plan. EPA

- 240

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- 001. Office of Administrator, Washington, D.C. Available at http://yosemite.epa.gov/ee/epa/eed.nsf/webpages/ecologbenefitsplan.html*** E.O. 12866 Review

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Page 601 of 647 U.S. EPA (1996). Air quality criteria for ozone and related photochemical oxidants [EPA Report]. (EPA/600/P

- 93/004aF, cF). U.S. Environmental Protection Agency, Re search Triangle Park, NC. U.S. EPA (1992)

. Summary of selected new information on effects of ozone on health and vegetation: supplement to 1986 air quality criteria for ozone and other photochemical oxidants. Research Triangle Park, NC: Office of Health an d Environmental Assessment, Environmental Criteria and Assessment Office; EPA report no. EPA/600/8

- 88/105F. Available from: NTIS, Springfield, VA; PB92

- 235670

. U.S. EPA (1989)

. Review of the National Ambient Air Quality Standards for Ozone: Policy Assessment of Scientific and Technical Information. OAQPS Staff Paper. Office of Air Quality Planning and Standards, Research Triangle Park, NC. the National Ambient Air Quality Stand ards for Ozone: Policy Assessment of Scientific and Technical Information. OAQPS Staff Paper. Office of Air Quality Planning and St U.S. EPA (1986). Air quality criteria for ozone and other photochemical oxidants [EPA Report]. (EPA

- 600/8

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- 020aF

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- 020eF). Research Triangle Park, NC. http://www.ntis.gov/search/product.aspx?ABBR=PB87142949 U.S. EPA (1978). Air quality criteria for ozone and other photochemical oxidants [EPA Report]. (EPA/600/8

- 78/004). Washington, D.C. US Forest Service, Nati onal Park Service, and U.S. Fish and Wildlife Service. 2010. Federal land managers’ air quality related values work group (FLAG): phase I report

— revised (2010). Natural Resource Report NPS/NRPC/NRR

— 2010/232. National Park Service, Denver, Colorado. http://www.nature.nps.gov/air/Pubs/pdf/flag/FLAG_2010.pdf West, JJ; Fiore, AM; Horowitz, LW; Mauzerall, DL. (2006). Global health benefits of mitigating ozone pollution with methane emission controls. PNAS 103: 3988

- 3993. http://dx.doi.org/10.1073/pnas.0600201103 Ulmer, C; Kopp, M; Ihorst, G; Frischer, T; Forster, J; Kuehr, J. (1997). Effects of ambient ozone exposures during the sprin g and summer of 1994 on pulmonary function of schoolchildren. Pediatr Pulmonol 23: 344

- 353. http://dx.doi.org/10.1002/(SICI)1099

- 0496(199705)23:5<344::AID

- P PUL6>3.0.CO;2

- K Vagaggini, B; Cianchetti, S; Bartoli, M; Ricci, M; Bacci, E; Dente, FL; Di Franco, A; Paggiaro, P. (2007). Prednisone blunts airway neutrophilic inflammatory response due to ozone exposure in asthmatic subjects. Respiration 74: 61

- 58. http://dx.doi.org/10.1159/000096078 Vagaggini, B; Taccola, M; Clanchetti, S; Carnevali, S; Bartoli, ML; Bacci, E; Dente, FL; Di Franco, A; Giannini, D; Paggiaro, PL. (2002). Ozone exposure increases eosino philic airway response induced by previous allergen challenge. Am J Respir Crit Care Med 166: 1073

- 1077. Vagaggini, B; Taccola, M; Conti, I; Carnevali, S; Cianchetti, S; Bartoli, ML; Bacci, E; Dente, FL; Di Franco, A; Giannini, D; Paggiaro, PL. (2001). Bud esonide reduces neutrophilic*** E.O. 12866 Review

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Page 602 of 647 but not functional airway response to ozone in mild asthmatics. Am J Respir Crit Care Med 164: 2172

- 2176. Vedal, S.; Brauer, M.; White, R.; Petkau, J. (2003) Air pollution and daily mortality in a city with low levels of pollut ion. Environ. Health Perspect. 111: 45

– 51. Villeneuve, PJ; Chen, L; Rowe, BH; Coates, F. (2007). Outdoor air pollution and emergency department visits for asthma among children and adults: A case

- crossover study in northern Alberta, Canada. Environ Health Global Access Sci Source 6: 40. http://dx.doi.org/10.1186/1476

- 069X

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- 40 Ward, DJ; Roberts, KT; Jones, N; Harrison, RM; Ayres, JG; Hussain, S; Walters, S. (2002). Effects of daily variation in outdoo r particulates and ambient acid species in normal and asthmatic children. Thorax 57: 489

- 502. http://dx.doi.org/10.1136/thorax.57.6.489 Wells, B. (2014) Comparison of Ozone Metrics Considered in Cur rent NAAQS Review. Memorandum to the Ozone NAAQS Review Docket, EPA

- HQ

- OAR

- 2008

- 0699 Wittig, VE; Ainsworth, EA; Long, SP. (2007). To what extent do current and projected increases in surface ozone affect photosynthesis and stomatal conductance of trees? A meta

analytic review of the last 3 decades of experiments [Review]. Plant Cell Environ 30: 1150

- 1162. http://dx.doi.org/10.1111/j.1365

- 3040.2007.01717.x Wittig, VE; Ainsworth, EA; Naidu, SL; Karnosky, DF; Long, SP. (2009). Quantifying the impact of curr ent and future tropospheric ozone on tree biomass, growth, physiology and biochemistry: A quantitative meta

- analysis. Global Change Biol 15: 396

- 424. http://dx.doi.org/10.1111/j.1365

- 2486.2008.01774.x Wolff, G.T. (1995) Letter to EPA Administrator Carol Br owner: “CASAC Closure on the Primary Standard Portion of the Staff Paper for Ozone” EPA

- SAB

- CASAC

- LTR

- 96

- 002, November 30, 1995. Wong, CM; Vichit

- Vadakan, N; Vajanapoom, N; Ostro, B; Thach, TQ; Chau, PY; Chan, EK; Chung, RY; Ou, CQ; Yang, L; Peiris, JS; Th omas, GN; Lam, TH; Wong, TW; Hedley, AJ; Kan, H; Chen, B; Zhao, N; London, SJ; Song, G; Chen, G; Zhang, Y; Jiang, L; Qian, Z; He, Q; Lin, HM; Kong, L; Zhou, D; Liang, S; Zhu, Z; Liao, D; Liu, W; Bentley, CM; Dan, J; Wang, B; Yang, N; Xu, S; Gong, J; Wei, H ; Sun, H; Qin, Z. (2010). Part 5. Public health and air pollution in Asia (PAPA): A combined analysis of four studies of air pollution and mortality. In Public Health and Air Pollution in Asia (PAPA): Coordinated Studies of Short

- Term Exposure to Air Pollu tion and Daily Mortality in Four Cities (pp. 377

- 418). Boston, MA: Health Effects Institute. http://pubs.healtheffects.org/view.php?id=348 Wong, CM; Yang, L; Thach, TQ; Chau, PY; Chan, KP; Thomas, GN; Lam, TH; Wong, TW; Hedley, AJ; Peiris, JS. (2009). Mod ification by influenza on health effects of air pollution in Hong Kong. Environ Health Perspect 117: 248

- 253. http://dx.doi.org/10.1289/ehp.11605*** E.O. 12866 Review

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Page 603 of 647 Woodwell, D. A.; Cherry, D. K. (2004) National Ambulatory Medical Care Survey: 2002 summary. Hyattsville, MD: National Center for Health Statistics; DHHS publication no. (PHS) 2004

- 1250. (Advance data from vital and health statistics; no. 346). Available: http://www.cdc.gov/nchs/data/ad/ad346.pdf [3 August, 2005] Xia, Y; Tong, H. (2006). Cumulative effects of air pollution on public health. Stat Med 25: 3548

- 3559. http://dx.doi.org/10.1002/sim.2446 Zanobetti, A; Schwartz, J. (2011). Ozone and survival in four cohorts with potentially predisposing diseases. Am J Respir Crit Care Med 184: 836

- 841. http://dx.doi.org /10.1164/rccm.201102

- 0227OC Zanobetti, A; Schwartz, J. (2008a). Is there adaptation in the ozone mortality relationship: A multi

- city case

- crossover analysis. Environ Health 7: 22. http://dx.doi.org/10.1186/1476

- 069X

- 7

- 22 Zanobetti, A; Schwartz, J. (2008b). Mortality displacement in the association of ozone with mortality: An analysis of 48 cities in the United States. Am J Respir Crit Care Med 177: 184

- 189. http://dx.doi.org/10.1164/rccm.200706

- 823OC Zanobetti, A; Schwartz, J. (2006). Air pollution and emergency admissions in Boston, MA. J Epidemiol Community Health 60: 890

- 895. http://dx.doi.org/10.1136/jech.2005.039834*** E.O. 12866 Review

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Page 604 of 647 Page X of Y

– O 3 NAAQS Proposed Rule List of Subjects 40 CFR Part 50 Environmental protection, Air pollution control, Carbon monoxide, Lead, Nitrogen dioxide, Ozone, Particulate matter, Sulfur oxides. 40 CFR Part 51 Environmental protecti on, Administrative practices and procedures, Air pollution control, Intergover nmental relations. 40 CFR Part 52 Environmental Protection, Administrative practices and procedures, Air pollution control, Incorporation by reference, Intergovernmental relations. 40 CFR Part 53 [to be filled in] 40 CFR Part 58 Environmental protection, Administrative practice and procedure, Air pollution control, Intergovernmental relations, Reporting and recordkeeping requirements

________________________________ Dated:

_________________________________ Gina McCarthy , Administrator

For the reasons set forth in the preamble, chapter I of title 40 of the Code of Federal Regulations is proposed to be amended as follows:*** E.O. 12866 Review

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Page 605 of 647 **************************** E.O. 12866 Review

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Page 606 of 647 PART 50

– NATIONAL PRIMARY AND SECONDARY AMBIENT AIR QUALITY STANDARDS 1. The authority citation for part 50 continues to read as follows: Authority: 42 U.S.C. 7401 et seq.
2. The language in §50.14(c)(2)(vi) is revised to read as follows and Table 2 is inserted. § 50.14 Treatment of air quality monitoring data influenced by exceptional events.
* * * * * (c) *** (2) *** (iii) Flags placed on data as being due to an exceptional event together with an initial description of the event shall be submitted to EPA not later than July 1 st of the calendar year following the year in which the flagged meas urement occurred, except as allowed under paragraph (c)(2)( vi) of this section. (iv) [Reserved] (v) [Reserved] (vi) Table 1 identifies the data submission process for new or revised NAAQS , beginning with the 2015 Ozone NAAQS

. Th is process shall apply to th ose data that will or may influence the initial designation of areas for any new or revised NAAQS. W hen EPA sets a NAAQS for a new pollutant or revises the NAAQS for an existing pollutant, it may revise or set a new schedule for flagging exceptional event data, providing initial data descriptions and providing detailed data documentation in AQS for the initial designations of areas for those NAAQS.

Table 1 . Schedule for Exceptional Event Flagging and Documentation Submission for Data to be Used in Initial Area Designations*** E.O. 12866 Review

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Page 607 of 647 Exceptional Event / Regulatory

Action Exceptional Event Deadline Schedule d

Exceptional event data flagging and initial description deadline for data years 1, 2 and 3 a If state and tribal recommendations for the new/revised NAAQS are due August through January, then the flagging and initial description deadline will be the July 1 prior to the recommendation deadline. If state and tribal recommendations for the new/revise d NAAQS are due February through July, then the flagging and initial description deadline will be the January 1 prior to the recommendation deadline. Exceptional event demonstration submittal deadline for data years 1, 2 and 3 a No later than the date that state and tribal recommendations are due to EPA

Exceptional event data flagging, initial description, and exceptional event demonstration submittal deadline for data year 4 b and potential data year 5 c By the last day of the month that is 1 year and 7 months after promulgation of a new or revised NAAQS, unless either option a or b applies. a. If the EPA follows a 3 year designation schedule, the deadline is 2 years and 7 months after promulgation of a new or revised NAAQS. b. I f the EPA notifies the state/tribe via Federal Register notice, letter or guidance that it intends to complete the initial area designations process according to a schedule other than a 2 year or 3 year timeline, the deadline is 5 months prior to the date of final designations decisions

. a Where data years 1, 2, and 3 are those years expected to be considered in state and tribal recommendations b Where data year 4 is the additional year of data that the EPA may consider when it makes final area designation s for the new/revised NAAQS under a 2

- year designations schedule.
c Where data year 5 is the additional year of data that the EPA may consider when it makes final area designations for the new/revised NAAQS under an extended designations schedule. d The date by which air agencies must certify their ambient air quality monitoring data in AQS is annually on May 1 of the year following the year of data collection. EPA cannot require air agencies to certify data prior to this date. In some cases, however, air agencies may choose to certify a prior year's data in advance of May 1 of the following year, particularly if EPA has indicated its intent to promulgate final designations in the months of May, June, July or August. Exceptional event flagging, initial des cription, and demonstration deadlines for "early certified" data will follow the deadlines for "year 4" and “year 5” data.*** E.O. 12866 Review

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Page 608 of 647 (3 ) Submission of demonstrations

. (i) Except as allowed under paragraph (c)(2)(vi) of this section, a State that has flagged data as being due to an exceptional event and is requesting exclusion of the affected measurement data shall, after notice and opportunity for public comment, submit a demonstration to justify data exclusion to EPA not later than th e lesser of, 3 years following the end of the calendar quarter in which the flagged concentration was recorded or, 12 months prior to the date that a regulatory decision must be made by EPA. A State must submit the public comments it received along with it s demonstration to EPA. (ii) [Reserved] (iii) [Reserved]

***** 3 . Section 50. 19 is added to read as follows: § 50. 19 National primary and secondary ambient air quality standards for ozone. (a) The level of the national 8

- hour primary ambient air quality standard for ozone (O 3 ) is (0.065

- 0.070 ) parts per million (ppm), daily maximum 8

- hour average, measured by a reference method based on appendix D to this part and designated in accordance with part 53 of this chapter or an equivalent method designated in accordance with part 53 of this chapter. (b) The 8

- hour primary O 3 ambient air quality standard is met at an ambient air quality monitoring site when the 3

- year average of the annual fourth

- highest daily maximum 8

- hour average O 3 concentration is less than or equal to (0.065

- 0.070 ) ppm, as determined in accordance with appendix U to this part. (c) The level of the national secondary ambient air quality standard for O 3 is (0.065

- 0.070 ) ppm , daily maximum 8

- hour average, measured by a reference method based on appendix D to this*** E.O. 12866 Review

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Page 609 of 647 part and designated in accordance with part 53 of this chapter or an equivalent method designated in accordance with part 53 of this chapter. (d) The 8

- hour secondary O 3 ambient air quality standard is met at an ambient air quality monitoring site when the 3

- year average of the annual fourth

- highest daily maximum 8

- hour average O 3 concentration is less than or equal to (0.065

- 0.070 ) ppm, as determined in accordance with appendix U to this part.

***** The EPA p roposes to revise Appendix D to part 50 of this chapter to read as follows: Appendix D to Part 50

— Reference Measurement Principle and Calibration Procedure for the Measurement of Ozone in the Atmosphere (Chemiluminescence Method)
1.0 Applicability

. 1.1 T his chemiluminescence method provides reference measurements of the concentration of ozone (O 3 ) in ambient air for determining compliance with the national primary and secondary ambient air quality standards for O 3 as specified in 40 CFR part 50. This
auto mated method is applicable to the measurement of ambient O 3 concentrations using continuous (real

- time) sampling and analysis. Additional quality assurance procedures and guidance are provided in 40 CFR part 58, appendix A, and in Reference 14.
2.0 Measure ment Principle

. 2.1 This reference method is based on continuous automated measurement of the
i ntensity of the characteristic chemiluminescence released by the gas phase reaction of O 3 in sampled air with either ethylene (C 2 H 4 ) or nitric oxide (NO) gas. An ambient air sample stream and a specific flowing concentration of either C 2 H 4 (ET

- CL method) or NO (NO

- CL method) are mixed in a measurement cell, where the resulting chemiluminescence is quantitatively measured*** E.O. 12866 Review

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Page 610 of 647 by a sensitive photo

- detector. References 8

- 11 describe the chemiluminescence measurement principle.
2.2 The measurement system is calibrated by referencing the instrumental chemiluminescence measurements to certified O 3 standard concentrations generated in a dynamic flow system and assayed by phot ometry to be traceable to a National Institute of Standards and Technology (NIST) standard reference photometer for O 3 (see Section 4, Calibration Procedure, below).
2.3 An analyzer implementing this measurement principle is shown schematically in Figure 1. Designs implementing this measurement principle must include : an appropriately designed mixing and measurement cell; a suitable quantitative photometric measurement system with adequate sensitivity and wave length specificity for O 3 ; a pump, flow contro l, and sample conditioning system for sampling and drying the ambient air and moving it into and through the measurement cell; a means to supply, meter, and mix a constant, flowing stream of either C 2 H 4 or NO gas of fixed concentration with the sample air flow in the measurement cell; suitable electronic control and measurement processing capability; and other associated apparatus as may be necessary. The analyzer must be designed and constructed to provide accurate, repeatable, and continuous measurements of O 3 concentrations in ambient air, with measurement performance that meets the requirements specified in subpart B of part 53 of this chapter.
2.4 An analyzer implementing this measurement principle and calibration procedure will be considered a federal reference method (FRM) only if it has been designated as a reference method in accordance with part 53 of this chapter

. 2.5 Sampling considerations

. The use of a particle filter on the sample inlet line of a chemiluminescence O 3 FRM analyzer is required to prevent buildup of particulate matter in the*** E.O. 12866 Review

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Page 611 of 647 measurement cell and inlet components. This filter must be changed weekly (or at least often as specified in the manufacturer’s operation/instruction manual) , and the sample inlet system used with the analyzer must be kept clean, to avoid loss of O 3 in the O 3 sample air prior to the concentration measurement.
3.0 Interferences

. 3.1 Except as described in 3.2 below , the chemiluminescence measurement system is inherently free of significant interferences from othe r pollutant substances that may be present in ambient air.
3.2 A small sensitivity to variations in the humidity of the sample air is minimized by a sample air dryer. Potential loss of O 3 in the inlet air filter and in the air sample handling components of the analyzer and associated exterior air sampling components due to buildup of airborne particulate matter is minimized by filter replacement and cleaning of the other inlet components. 4.0 Calibration Procedure

. 4.1 Principle

. The calibration procedure i s based on the photometric assay of O 3 concentrations in a dynamic flow system. The concentration of O 3 in an absorption cell is determined from a measurement of the amount of 254 nm light absorbed by the sample. This determination requires knowledge of (1 ) the absorption coefficient (α) of O 3 at 254 nm, (2) the optical path length ( l ) through the sample, (3) the transmittance of the sample at a nominal wavelength of 254 nm, and (4) the temperature (T) and pressure (P) of the sample. The transmittance is de fined as the ratio I/I 0 , where I is the intensity of light which passes through the cell and is sensed by the detector when the cell contains an O 3 sample, and I 0 is the intensity of light which passes through the cell and is sensed by the detector when the cell contains zero air.*** E.O. 12866 Review

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Page 612 of 647 It is assumed that all conditions of the system, except for the contents of the absorption cell, are identical during measurement of I and I 0 . The quantities defined above are related by the Beer

Lambert absorption law,
Transmit ance = I I 0 = e − α cl (1)
where: α = absorption coefficient of O 3 at 254 nm = 308 ±4 atm−1 cm−1 at 0 °C and 760
torr, 1, 2, 3, 4, 5, 6, 7

c = O 3 concentration in atmospheres, and
l = optical path length in cm.
A stable O 3 generator is used to produce O 3 concentrations over the required calibration concentration range. Each O 3 concentration is determined from the measurement of the transmittance (I/I 0 ) of the sample at 254 nm with a photometer of path length l and calculated from the equation,

c ( atm ) = − 1

α l ( ln I I 0 ) (2a)

or

c ( ppm ) = − 10 6

α l ( ln I I 0 )

. (2b)
The calculated O 3 concentrations must be corrected for O 3 losses, which may occur in the photometer, and for the temperature and pressure of the sample.
4.2 Applicability. This procedure is applicable to the c alibration of ambient air
O 3 analyzers, either directly or by means of a transfer standard certified by this procedure. Transfer standards must meet the requirements and specifications set forth in Reference 12.*** E.O. 12866 Review

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Page 613 of 647 4.3 Apparatus. A complete UV calibration s ystem consists of an O 3 generator, an output port or manifold, a photometer, an appropriate source of zero air, and other components as
necessary. The configuration must provide a stable O 3 concentration at the system output and allow the photometer to acc urately assay the output concentration to the precision specified for the photometer (4.3.1). Figure 2 shows a commonly used configuration and serves to illustrate the calibration procedure, which follows. Other configurations may require appropriate varia tions in the procedural steps. All connections between components in the calibration system downstream of the O 3 generator must be of glass, Teflon, or other relatively inert materials. Additional information regarding the assembly of a UV photometric cali bration apparatus is given in Reference 13. For certification of transfer standards which provide their own source of
O 3 , the transfer standard may replace the O 3 generator and possibly other components shown in Figure 2; see Reference 12 for guidance.
4.3 .1 UV photometer. The photometer consists of a low

- pressure mercury discharge lamp, (optional) collimation optics, an absorption cell, a detector, and signal

- processing electronics, as illustrated in Figure 2. It must be capable of measuring the transmitta nce, I/I 0 , at a wavelength of 254 nm with sufficient precision such that the standard deviation of the concentration measurements does not exceed the greater of 0.005 ppm or 3% of the concentration. Because the low

- pressure mercury lamp radiates at several wavelengths, the photometer must incorporate suitable means to assure that no O 3 is generated in the cell by the lamp, and that at least 99.5% of the radiation sensed by the detector is 254 nm radiation. (This can be readily achieved by prudent selection of optical filter and detector response characteristics.) The length of the light path through the absorption cell must be known with an accuracy of at least 99.5%. In addition, the cell and associated plumbing must be designed to*** E.O. 12866 Review

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Page 614 of 647 minimize loss of O 3 from contact with cell walls and gas handling components. See Reference 13 for additional information.
4.3.2 Air flow controllers. Air flow controllers are dev ices capable of regulating air flows as necessary to meet the output stability and photometer precisio n requirements.
4.3.3 Ozone generator. The ozone generator used must be capable of generating stable levels of O 3 over the required concentration range.
4.3.4 Output manifold. The output manifold must be constructed of glass, Teflon, or other relatively in ert material, and should be of sufficient diameter to insure a negligible pressure drop at the photometer connection and other output ports. The system must have a vent designed to insure atmospheric pressure in the manifold and to prevent ambient air from entering the manifold. 4.3.5 Two

- way valve. A m anual or automatic two

- way valve, or other means is used to switch the photometer flow between zero air and the O 3 concentration.
4.3.6 Temperature indicator. A device to indicate temperature must be used tha t is

a ccurate to ±1 °C. 4.3.7 Barometer or pressure indicator. A device to indicate barometric pressure must be used that is a ccurate to ±2 torr.
4.4 Reagents. 4.4.1 Zero air. The zero air must be free of contaminants which would cause a detectable response from the O 3 analyzer, and it must be free of NO, C 2 H 4 , and other species which react with O 3 . A procedure for generating suitable zero air is given in Reference 13. As shown in Figure 2, the zero air supplied to the photometer cell for the I 0 refe rence measurement must be derived from the same source as the zero air used for generation of the O 3 concentration to be*** E.O. 12866 Review

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Page 615 of 647 assayed (I measurement). When using the photometer to certify a transfer standard having its own source of O 3 , see Reference 12 for gui dance on meeting this requirement. 4.5 Procedure. 4.5.1 General operation. The calibration photometer must be dedicated exclusively to use as a calibration standard. It must always be used with clean, filtered calibration gases, and never used for ambient air sampling. A number of advantages are realized by locating the calibration photometer in a clean laboratory where it can be stationary, protected from the physical shock of transportation , operated by a responsible analyst, and used as a common standard for all field calibrations via transfer standards. 4.5.2 Preparation. Proper operation of the photometer is of critical importance to the accuracy of this procedure. Upon initial operation of the photometer, the following steps must be carried out with al l quantitative results or indications recorded in a chronological record, either in tabular form or plotted on a graphical chart. As the performance and stability record of the photometer is established, the frequency of these steps may be reduced to be consistent with the documented stability of the photometer and the guidance provided in Reference 12

. 4.5.2.1 Instruction manual . C arry out all set up and adjustment procedures or checks as described in the operation or instruction manual associated with t he photometer. 4.5.2.2 System check . C heck the photometer system for integrity, leaks, cleanliness, proper flow rates, etc. Service or replace filters and zero air scrubbers or other consumable materials, as necessary. 4.5.2.3 Linearity

. Verify that the ph otometer manufacturer has adequately established that the linearity error of the photometer is less than 3%, or test the linearity by dilution as follows: Generate and assay an O 3 concentration near the upper range limit of the system or appropriate*** E.O. 12866 Review

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Page 616 of 647 calibr ation scale for the instrument , then accurately dilute that concentration with zero air and re

assay it. Repeat at several different dilution ratios. Compare the assay of the original concentration with the assay of the diluted concentration divided by the dilution ratio, as follows
E = A 1 − A 2 / R

A 1 × 100% (3)
where: E = linearity error, percent
A 1 = assay of the original concentration
A 2 = assay of the diluted concentration R = dilution ratio = flow of original concentration divided by the total flow The l inearity error must be less than 5%. Since the accuracy of the measured flow

- rates will affect the linearity error as measured this way, the test is not necessarily conclusive. Additional information on verifying linearity is contained in Reference 13. 4.5 .2.4 Inter

- comparison . T he photometer must be inter

- compared annually , either directly or via transfer standards, with a NIST standard reference photometer (SRP) or calibration photometers used by other agencies or laboratories. 4.5.2.5 Ozone losses

. Some portion of the O 3 may be lost upon contact with the photometer cell walls and gas handling components. The magnitude of this loss must be determined and used to correct the calculated O 3 concentration. This loss must not exceed 5%. Some guidelines for quan titatively determining this loss are discussed in Reference 13. 4.5.3 Assay of O 3 concentrations. The operator must carry out the following steps to properly assay O 3 concentrations. 4.5.3.1 Allow the photometer system to warm up and stabilize.*** E.O. 12866 Review

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Page 617 of 647 4.5.3.2 Ver ify that the flow rate through the photometer absorption cell, F, allows the cell to be flushed in a reasonably short period of time (2 liter/min is a typical flow). The precision of the measurements is inversely related to the time required for flushing, since the photometer drift error increases with time. 4.5.3.3 E nsure that the flow rate into the output manifold is at least 1 liter/min greater than the total flow rate required by the photometer and any other flow demand connected to the manifold. 4.5.3. 4 E nsure that the flow rate of zero air, Fz, is at least 1 liter/min greater than the flow rate required by the photometer. 4.5.3.5 With zero air flowing in the output manifold, actuate the two

- way valve to allow the photometer to sample first the manifold zero air, then Fz. The two photometer readings must be equal (I = I 0 ).
Note: In some commercially available photometers, the operation of the two

- way valve and various other operations in section 4.5.3 may be carried out automatically by the photometer.
4 .5.3.6 Adjust the O 3 generator to produce an O 3 concentration as needed. 4.5.3.7 Actuate the two

- way valve to allow the photometer to sample zero air until the absorption cell is thoroughly flushed and record the stable measured value of Io. 4.5.3.8 Actuat e the two

- way valve to allow the photometer to sample the O 3 concentration until the absorption cell is thoroughly flushed and record the stable measured value of I. 4.5.3.9 Record the temperature and pressure of the sample in the photometer absorption cel l. (See Reference 13 for guidance.)*** E.O. 12866 Review

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Page 618 of 647 4.5.3.10 Calculate the O 3 concentration from equation 4. An average of several determinations will provide better precision. [ O 3 ] OUT = (

− 1

α l ln I I 0 ) ( T 273 ) ( 760 P ) × 10 6

L (4)
where: [O 3 ] OUT = O 3 concentration, ppm α = absorption coefficient of O 3 at 254 nm = 308 atm−1 cm−1 at 0° C and 760 torr
l = optical path length, cm T = sample temperature, K P = sample pressure, torr L = correction factor for O 3 losses from 4.5.2.5 = (1−fraction of O 3 lost).
Note: Some commercial photometers may automatically evaluate all or part of equation
4. It is the operator's responsibility to verify that all of the information required for equation 4 is obtained, either automatically by the photometer or manually. For “automatic” photometers which evalu ate the first term of equation 4 based on a linear approximation, a manual correction may be required, particularly at higher O 3 levels. See the photometer instruction manual and Reference 13 for guidance. 4.5.3.11 Obtain additional O 3 concentration standa rds as necessary by repeating steps 4.5.3.6 to 4.5.3.10 or by Option 1. 4.5.4 Certification of transfer standards. A transfer standard is certified by relating the output of the transfer standard to one or more O 3 calibration standards as determined accord ing to section 4.5.3. The exact procedure varies depending on the nature and design of the transfer standard. Consult Reference 12 for guidance.*** E.O. 12866 Review

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Page 619 of 647 4.5.5 Calibration of ozone analyzers. Ozone analyzers must be calibrated as follows, using O 3 standards obtaine d directly according to section 4.5.3 or by means of a certified transfer standard. 4.5.5.1 Allow sufficient time for the O 3 analyzer and the photometer or transfer standard
to warm

- up and stabilize. 4.5.5.2 Allow the O 3 analyzer to sample zero air until a stable response is obtained and then adjust the O 3 analyzer's zero control. Offsetting the analyzer's zero adjustment to +5% of scale is recommended to facilitate observing negative zero drift (if any). Record the stable zero air response as “Z”.
4.5.5.3 Generate an O 3 concentration standard of approximately 80% of the desired upper range limit (URL) of the O 3 analyzer. Allow the O 3 analyzer to sample this O 3 concentration standard until a stable response is obtained. 4.5.5.4 Adjust the O 3 analyzer's span control to obtain the desired response equivalent to the calculated standard concentration. Record the O 3 concentration and the corresponding analyzer response. If substantial adjustment of the span control is necessary, recheck the zero and span adjustmen ts by repeating steps 4.5.5.2 to 4.5.5.4. 4.5.5.5 Generate additional O 3 concentration standards (a minimum of 5 are recommended) over the calibration scale of the O 3 analyzer by adjusting the O 3 source or by Option 1. For each O 3 concentration standard, record the O 3 concentration and the corresponding analyzer response. 4.5.5.6 Plot the O 3 analyzer responses (vertical or Y

- axis) versus the corresponding
O 3 standard concentrations (horizontal or X

- axis). Compute the linear regression slope and*** E.O. 12866 Review

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Page 620 of 647 intercept a nd plot the regression line to verify that no point deviates from this line by more than 2 percent of the maximum concentration tested. 4.5.5.7 Option 1: The various O 3 concentrations required in steps 4.5.3.11 and 4.5.5.5 may be obtained by dilution of th e O 3 concentration generated in steps 4.5.3.6 and 4.5.5.3. With this option, accurate flow measurements are required. The dynamic calibration system may be modified as shown in Figure 3 to allow for dilution air to be metered in downstream of the
O 3 genera tor. A mixing chamber between the O 3 generator and the output manifold is also required. The flow rate through the O 3 generator (Fo) and the dilution air flow rate (FD) are measured with a flow or volume standard that is traceable to a NIST flow or volume calibration standard

. Each O 3 concentration generated by dilution is calculated from: [ O 3 ] ′ OUT = [ O 3 ] OUT ( F O F O + F D ) (5)
where: [O 3 ]′ OUT = diluted O 3 concentration, ppm
FO = flow rate through the O 3 generator, liter/min
FD = diluent air flow rate, liter/min
Note: Additional information on calibration and pollutant standards is provided in Section 12 of Reference 14. 5.0 Frequency of Calibration

. 5.1 The frequency of calibration, as well as the number of points necessary to establish the calibration curve, and the frequency of other performance checking will vary by analyzer; however, the minimum frequency, acceptance criteria, and subsequent actions are specified in Appendix D of Reference 14: Measurement Quality Objectives and Validation Templates. The
user's quality control program shall provide guidelines for initial establishment of these variables*** E.O. 12866 Review

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Page 621 of 647 and for subsequent alteration as operational experience is accumulated. Manufacturers of analyzers should include in their instruction/operation manuals informat ion and guidance as to these variables and on other matters of operation, calibration, routine maintenance, and quality control.
6.0 References 1. E.C.Y. Inn and Y. Tanaka, “Absorption coefficient of Ozone in the Ultraviolet and Visible Regions”, J. Opt. Soc. Am., 43, 870 (1953). 2. A. G. Hearn, “Absorption of Ozone in the Ultraviolet and Visible Regions of the Spectrum”, Proc. Phys. Soc. (London), 78, 932 (1961). 3. W. B. DeMore and O. Raper, “Hartley Band Extinction Coefficients of Ozone in the Gas Phase and in Liquid Nitrogen, Carbon Monoxide, and Argon”, J. Phys. Chem., 68, 412 (1964). 4. M. Griggs, “Absorption Coefficients of Ozone in the Ultraviolet and Visible Regions”, J. Chem. Phys., 49, 857 (1968). 5. K. H. Becker, U. Schurath, and H. Seitz, “Ozon e Olefin Reactions in the Gas Phase. 1. Rate Constants and Activation Energies”, Int'l Jour. of Chem. Kinetics, VI, 725 (1974). 6. M. A. A. Clyne and J. A. Coxom, “Kinetic Studies of Oxy

- halogen Radical Systems”, Proc. Roy. Soc., A303, 207 (1968).
7. J. W. Simons, R. J. Paur, H. A. Webster, and E. J. Bair, “Ozone Ultraviolet Photolysis. VI. The Ultraviolet Spectrum”, J. Chem. Phys., 59, 1203 (1973). 8. Ollison, W.M.; Crow, W.; Spicer, C.W. “Field testing of new

- technology ambient air ozone monitors.” J. Air Waste Manage. Assoc., 63 (7), 855

- 863 (2013).*** E.O. 12866 Review

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Page 622 of 647 9. Parrish, D.D.; Fehsenfeld, F.C. “Methods for gas

- phase measurements of ozone, ozone precursors and aerosol precursors.” Atmos. Environ., 34 (12

- 14), 1921

- 1957(2000). 10. Ridley, B.A.; Grahek, F.E.; Walega, J.G. “A small, high

- sensitivity, medium

response ozone detector suitable for measurements from light aircraft.” J. Atmos. Oceanic Technol., 9 (2), 142

- 148(1992). 11. Boylan, P., Helmig, D., and Park, J.H. “Characterization and mitigation of water vapor eff ects in the measurement of ozone by chemiluminescence with nitric oxide.” Atmos. Meas. Tech. 7, 1231

- 1244 (2014). 12. Transfer Standards for Calibration of Ambient Air Monitoring Analyzers for Ozone, EPA publication number EPA

- 454/B

- 13

- 004, October 2013. E PA, Office of Air Quality Planning and Standards, Research Triangle Park, NC 27711. [Available at www.epa.gov/ttnamti1/files/ambient/qaqc/OzoneTransferStandard Guidance.pdf .] 13. Technical Assistance Document for the Calibration of Ambient Ozone Monitors, EPA publication number EPA

- 600/4

- 79

- 057, September, 1979. [ A vailable at www.epa.gov/ttnamti1/files/ambient/criteria/4

- 79

- 057.pdf .] 14. QA Handbook for Air Pollution Measurement Systems

— Volume II. Ambient Air Quality Monitoring Program. EPA

- 454/B

- 13

- 003, May 2013. [Available at http://www.epa.gov/ttnamti1/files/ambient/pm25/qa/QA

- Handbook

- Vol

- II.pdf .]*** E.O. 12866 Review

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Page 623 of 647 Figure 1. Gas

- phase chemiluminescence analyzer schematic diagram , where PMT means photomultiplier tube.*** E.O. 12866 Review

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Page 624 of 647 Figure 2. Schematic diagram of a typical UV photometric calibration system.*** E.O. 12866 Review

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Page 625 of 647 Figure 3. Schematic diagram of a typical UV photometric calibration system (Option 1).*** E.O. 12866 Review

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Page 626 of 647 Appendix U to Part 50 is added to read as follows: Appendix U to Part 50
-- Interpretation of the Primary and Secondary National Ambient Air Quality Standards for Ozone
1. General (a) This appendix explains the data handling conventions and computations necessary for determining whether the primary and secondary national ambient air quality standards (NAAQS) for ozone (O 3 ) specified in §50.19 are met at an ambient O 3 air quality monitoring site. Data reporting, data handling, and computation procedures to be used in making comparisons between reported O 3 concentrations and the levels of the O 3 NAAQS are specified in the foll owing sections. (b) Whether to exclude, retain, or make adjustments to the data affected by exceptional events, including wildfires, stratospheric O 3 intrusions, or other natural events, is determined by the requirements under §§50.1, 50.14 and 51.930. (c) The terms used in this appendix are defined as follows:
8

- hour average refers to the moving average of eight consecutive hourly O 3 concentrations measured at a site, as explained in section 3 of this appendix. Annual fourth

- highest daily maximum refers to the fourth highest value measured at a site during a particular year. Collocated monitors refers to the instance of two or more O 3 monitors operating at the same site. Daily maximum 8

- hour average O 3 concentration refers to the maximum calculated 8

- hour

a verage value measured at a site on a particular day, as explained in section 3 of this appendix.*** E.O. 12866 Review

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Page 627 of 647 Design value refers to the metric ( i.e. , statistic) that is used to compare ambient O 3 concentration data measured at a site to the NAAQS in order to determine compliance, as explained in section 4 of this appendix. Minimum data completeness requirements refer to the amount of data that a site is required to collect in order to make a valid determination that the site is meeting the NAAQS.
Monitor refers to a physical instrument used to measure ambient O 3 concentrations.
O 3 monitoring season refers to the span of time within a year when individual s tates are required to measure ambient O 3 co ncentrations, as listed in Appendix D to part 58 of this chapter.
Site refers to an ambient O 3 air quality monitoring site. Site data record refers to the set of hourly O 3 concentration data collected at a site for use in comparisons with the NAAQS.
Year refers to calendar year.
2. Selection of Data for use in Comparisons with the Primary and Secondary Ozone NAAQS (a) All valid hourly O 3 concentration data collected using a federal reference method specified in Appendix D to this part, or an equivalent me thod designated in accordance with part 53 of this chapter, meeting all applicable requirements in part 58 of this chapter, and submitted to EPA’s Air Quality System (AQS) database, or otherwise available to EPA, shall be used in design value calculations. Data not meeting these requirements shall not be used in design value calculations. (b ) All design value calculations shall be implemented on a site

- level basis. If data are reported to EPA from collocated monitors, those data shall be combined into a si ngle site data record as follows: (i) The monitoring agency may designate one monitor as the primary monitor for the site. If a primary monitor has not been designated by the monitoring agency, the monitor with*** E.O. 12866 Review

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Page 628 of 647 the largest number of hourly O 3 concentration s reported for the year shall be designated as the primary monitor. (ii) Hourly O 3 concentration data from a collocated monitor shall be substituted into the site data record whenever a valid hourly O 3 concentration is not obtained from the primary monitor . In the event that hourly O 3 concentration data are available for two or more collocated monitors, the hourly concentration data for those monitors shall be averaged and substituted into the site data record. (c ) In certain circumstances, including but no t limited to site closures or relocations, data from two nearby sites may be combined into a single site data record for the purpose of calculating a valid design value. The appropriate Regional Administrator may approve such combinations after taking into consideration factors such as distance between sites, spatial and temporal patterns in air quality, local emissions and meteorology, jurisdictional boundaries, and terrain features. 3. Data Reporting and Data Handling Conventions (a) Hourly average O 3 con centrations shall be reported in parts per million (ppm) to the third decimal place, with additional digits to the right of the third decimal place truncated. Each hour shall be identified using local standard time (LST). (b) Moving 8

- hour averages shall b e computed from the hourly O 3 concentration data for each hour of the year and shall be stored in the first, or start, hour of the 8

- hour period. An 8

- hour average shall be considered valid if at least 6 of the hourly concentrations for the 8

- hour period

a re available. In the event that only 6 or 7 hourly concentrations are available, the 8

- hour average shall be computed on the basis of the hours available, using 6 or 7 as the divisor. In addition, in the event that 5 or fewer hourly concentrations are avai lable, the 8

- hour average shall be*** E.O. 12866 Review

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Page 629 of 647 considered valid if, after substituting zero for the missing hourly concentrations, the resulting 8

- hour average is greater than the level of the NAAQS. The 8

- hour averages shall be reported to three decimal places, with additional digits to the right of the third decimal place truncated. Hourly O 3 concentrations that have been approved under §50.14 as having been affected by exceptional events shall be counted as missing or unavailable in the calculation of 8

- hour
average s. (c) The daily maximum 8

- hour average O 3 concentration for a given day is the highest of the 17 consecutive 8

- hour averages beginning with the 8

- hour period from 7:00 AM to 3:00 PM and ending with the 8

- hour period from 11:00 PM to 7:00 AM (i.e., the 8

- h our averages for 7:00 AM to 11:00 PM). Daily maximum 8

- hour average O 3 concentrations shall be determined for each day with ambient O 3 monitoring data, including days outside the O 3 monitoring season if those data are available. (d) A daily maximum 8

- hour average O 3 concentration shall be considered valid if valid 8

- hour averages are available for at least 13 of the 17 consecutive 8

- hour periods starting from 7:00 AM to 11:00 PM. In addition, in the event that fewer than 13 valid 8

- hour averages are availab le, a daily maximum 8

- hour average O 3 concentration shall also be considered valid if it is greater than the level of the NAAQS. Hourly O 3 concentrations that have been approved under §50.14 as having been affected by exceptional events shall be included w hen determining whether these criteria have been met. (e) The primary and secondary O 3 design value statistic is the annual fourth

- highest daily maximum 8

- hour O 3 concentration, averaged over three years, expressed in parts per million. The fourth

- highest daily maximum 8

- hour O 3 concentration for each year shall be determined based only on days meeting the validity criteria in 3(d). The 3

- year average shall be computed*** E.O. 12866 Review

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Page 630 of 647 using the three most recent, consecutive years of ambient O 3 monitoring data. Design valu es shall be reported to three decimal places, with additional digits to the right of the third decimal place truncated.
4. Comparisons with the Primary and Secondary Ozone NAAQS (a) The primary and secondary national ambient air quality standards for O 3 ar e met at an ambient air quality monitoring site when the 3

- year average of the annual fourth

- highest daily maximum 8

- hour average O 3 concentration (i.e., the design value) is less than or equal to (0.065

– 0.070) ppm. (b) A design value greater than the le vel of the NAAQS is always considered to be valid. A design value less than or equal to the level of the NAAQS must meet minimum data completeness requirements in order to be considered valid. These requirements are met for a 3

- year period at a site if val id daily maximum 8

- hour average O 3 concentrations are available for at least 90% of the days within the O 3 monitoring season, on average, for the 3

- year period, with a minimum of at least 75% of the days within the O 3 monitoring season in any one year. (c) When computing whether the minimum data completeness requirements have been met, meteorological or ambient data may be sufficient to demonstrate that meteorological conditions on missing days were not conducive to concentrations above the level of the NAA QS. Missing days assumed less than the level of the NAAQS are counted for the purpose of meeting the minimum data completeness requirements, subject to the approval of the appropriate Regional Administrator. (d) Comparisons with the primary and secondary O 3 NAAQS are demonstrated by examples 1 and 2 as follows: Example 1: Site Meeting the Primary and Secondary O 3 NAAQS*** E.O. 12866 Review

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Page 631 of 647 Year Percent valid days within O 3 monitoring

season 1st highest

daily max 8

- hour O 3 (ppm) 2nd highest

daily max 8

- hour O 3 (ppm) 3rd highest

daily max 8

- hour O 3 (ppm) 4th highest

daily max 8

- hour O 3 (ppm) 5th highest

daily max 8

- hour O 3 (ppm)
2014 100 0.082 0.080 0.075 0.069 0.068
2015 96 0.074 0.073 0.065 0.062 0.060
2016 98 0.070 0.069 0.067 0.066 0.060 Average 98 0.065
As shown in Example 1, this site meets the primary and secondary O 3 NAAQS because the 3

- year average of the annual fourth

- highest daily maximum 8

- hour average O 3 concentrations ( i.e. , 0.065666 ppm, truncated to 0.065 ppm) is less than or equal to (0.065

– 0.070) ppm. The minimum data completeness requirements are also met because the average percent of days within the O 3 monitoring season with valid ambient monitoring data is greater than 90%, and no single year has less than 75% data completeness. Example 2: Site Fail ing to Meet the Primary and Secondary O 3 NAAQS

Year Percent valid days within O 3 monitoring

season 1st highest

daily max 8

- hour O 3 (ppm) 2nd highest

daily max 8

- hour O 3 (ppm) 3rd highest

daily max 8

- hour O 3 (ppm) 4th highest

daily max 8

- hour O 3 (ppm) 5th highest

daily max 8

- hour O 3 (ppm)
2014 96 0.085 0.080 0.079 0.074 0.072
2015 74 0.084 0.083 0.072 0.071 0.068
2016 98 0.083 0.081 0.081 0.075 0.074*** E.O. 12866 Review

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Page 632 of 647 Average 89 0.073 As shown in Example 2, this site fails to meet the primary and secondary O 3 NAAQS because the 3

- year average of the annual fourth

- highest daily maximum 8

- hour average O 3 concentrations ( i.e. , 0.073333 ppm, truncated to 0.073 ppm) is greater than (0.065

– 0.070) ppm, even though the annual data completeness is less than 75% in one year a nd the 3

- year average data completeness is less than 90%. PART 51

— REQUIREMENTS FOR PREPARATION, ADOPTION, AND SUBMITTAL OF IMPLEMENATION PLANS [XX]. The authority citation for part 51 continues to read as follows: Authority : 23 U.S.C. 101; 42 U.S.C. 7401

- 7 671q. Subpart I

– [Amended] [XX]. Section 51.166 is amended by adding paragraph (i)(11) to read as follows: § 51.166 Prevention of significant deterioration of air quality
* * * * * (i) * * * (11) The plan may provide that the requirements of paragraph (k)(1) of this section shall not apply to a stationary source or modification with respect to the national ambient air quality standards for ozone in effect on [INSERT EFFECTIVE DATE OF FI NAL RUL E ] if: (i) The reviewing authority has determined a permit application subject to this section to be complete on or before [INSERT SIGNATURE DATE OF FINAL RULE ]. Instead, the requirements in paragraph (k)(1) of this section shall apply with respect to the national ambient air quality standards for ozone in effect at the time the reviewing authority determined the permit application to be complete; or*** E.O. 12866 Review

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Page 633 of 647 (ii) The reviewing authority has first published before [INSERT EFFECTIVE DATE OF
FINAL RULE ] a public notic e of a preliminary determination or draft permit for the permit application subject to this section. Instead, the requirements in paragraph (k)(1) of this section shall apply with respect to the national ambient air quality standards for ozone in effect at the time of first publication of a public notice on the preliminary determination.
* * * * * PART 52

— APPROVAL AND PROMULGATION OF IMPLEMENTATION PLANS [XX]. The authority citation for part 52 continues to read as follows: Authority: 42 U.S.C. 7401 et seq
. [XX]. Section 52.21 is amended by adding paragraph (i)(12) to read as follows: § 52.21 Prevention of significant deterioration of air quality.
* * * * * (i) * * * (12) The requirements of paragraph (k)(1) of this section shall not apply to a stationary source or modification with respect to the national ambient air quality standards for ozone in effect on [INSERT EFFECTIVE DATE OF FI NAL RULE ] if: (i) The Administrator has determined a permit application subject to this section to be complete on or befor e [INSERT SIGNATURE DATE OF FI NAL RULE ]. Instead, the requirements in paragraph (k)(1) of this section shall apply with respect to the national ambient air quality standards for ozone in effect at the time the Administrator determined the permit applicatio n to be complete; or (ii) The Administrator has first published before [INSERT EFFECTIVE DATE OF
FINAL RULE ] a public notice that a preliminary determination or draft permit subject to this*** E.O. 12866 Review

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Page 6 34 of 647 section has been prepared. Instead, the requirements in paragraph (k)(1) of this section shall apply with respect to the national ambient air quality standards for ozone in effect on the date the Administrator first published a public notice that a draft permit has been prepared.

* * * * *

* * * * * The EPA proposes to revise p art 53 as follows:
In s ubpart A,
1. Revise § 53.14(c) to read: Within 90 calendar days after receiving a report under paragraph (a) of this section, the Administrator will take one or more of the following actions: 2. Remove section (i) from § 53.9

. In s ubpart B, 1. Revise paragraph §53.23(e)(vi) to read as follows: Precision: Variation about the mean of repeated measurements of the same pollutant concentration, denoted as the standard deviation expressed as a percentage of the upper range limit s

. 280
2. Revise and Tables B

- 1 and B

- 3 to read as follows:

280 NO 2 precision in Table B

- 1 is also changed to percent to agr ee with the calculation specified in 53.23(e)(10)(vi).*** E.O. 12866 Review

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Page 635 of 647 Table B

- 1 to Subpart B of Part 53

— Performance Limit Specifications for Automated Methods

Performance parameter Units 1 SO 2 O 3 CO NO 2 (Std. range) Definitions and

test procedures Std. range 3 Lower

r ange 2,3 Std.

range 3 Lower

range 2,3 Std.

range 3 Lower range 2,3 1. Range ppm 0

- 0.5 <0.5 0

- 0.5 <0.5 0

- 50 <50 0

- 0.5 Sec. 53.23(a). 2. Noise ppm 0.001 0.0005 0.001 0.0005 0.2 0.1 0.005 Sec. 53.23(b). 3. Lower detectable limit ppm 0.002 0.001 0.003 0.001 0.4 0.2 0.010 Sec. 53.23(c). 4. I nterference equivalent Each interferent Total, all interferents ppm ppm ±0.005

--- 4±0.005

--- ±0.005

--- ±0.005

--- ±1.0

--- ±0.5

--- ±0.02

0.04 Sec. 53.23(d).

Sec. 53.23(d). 5. Zero drift, 12 and 24 hour ppm ±0.004 ±0.002 ±0.004 ±0.002 ±0.5 ±0.3 ±0.02 Sec. 53.23(e). 6. Span drift, 24 hour 20% of upper range limit 80% of upper range limit Percent Percent ---

±3.0 ---

±3.0 ---

±3.0 ---

±3.0 ---

±2.0 --- ±2.0 ±20.0

±5.0 Sec. 53.23(e)

Sec. 53.23(e). 7. Lag time Minutes 2 2 2 2 2.0 2.0 20 Sec. 53.23(e). 8. Rise time Minutes 2 2 2 2 2.0 2.0 15 Sec. 53.23(e). 9. Fall time Minutes 2 2 2 2 2.0 2.0 15 Sec. 53.23(e). 10. Precision 20 % of upper range limit 80 % of upper range limit Percent 5
Percent 5 ---

2

--- 2 ---

2

--- 2 ---

2

--- 2 ---

2

--- 2 --

1.0

--- 1.0 --- 1.0

--- 1.0 4

6 Sec. 53.23(e).

Sec. 53.23(e). Sec. 53.23(e). Sec. 53.23(e). 1. To convert from parts per million (ppm) to μg/m 3 at 25 °C and 760 mm Hg, multiply by M/0.02447, where M is th e molecular weight of the gas. Percent means percent of the upper measurement range limit. 2

. Tests for interference equivalent and lag time do no t need to be repeated for any lower range provided the test for the standard range shows that the lower range specification (if applicable) is met for each of these test parameters. 3

. For candidate analyzers having automatic or adaptive time constants or smoothing filters, describe their functional nature, and describe and conduct suitable tests to demonstrate their function aspects and verify that performances for calibration, noise , lag, rise, fall times, and precision are within specifications under all applicable conditions. For candidate analyzers with operator

- selectable*** E.O. 12866 Review

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Page 636 of 647 time constants or smoothing filters, conduct calibration, noise, lag, rise, fall times, and precision tests at the highest an d lowest settings that are to be included in the FRM or FE M designation. 4

. For nitric oxide interference for the SO 2 UVF method, interference equivalent is ±0.0003 ppm for the lower range. 5

. Standard deviation expressed as percent of the URL.*** E.O. 12866 Review

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Page 637 of 647 Table B

- 3 to Subpart B of Part 53

— Interferent Test Concentration, 1 Parts per Million Pollutant Analyzer type Hydro chloric acid Ammo nia Hydrogen sulfide Sulfur dioxide Nitrogen dioxide Nitric oxide Carbon dioxide
E th ylene

O zone m - Xy lene Water vapor Carbon mon

oxide Methane Ethane Naphthalene

SO 2 Ultraviolet fluorescence 5 0.1 4 0.14 0 .5 0 .5 0 .5 0 .2 20,000 6 0.05 SO 2 Flame photometric 0.01 4 0.14 750 3 20,000 50 SO 2 Gas chromatography 0.1 4 0.14 750 3 20,000 50

SO 2 Spectrophotometric

- wet chemical (pararosanaline) 0.2 0.1 0.1 4 0.14 0 .5 750 0 .5

SO 2 Electrochemical 0.2 0.1 0.1 4 0.14 0 .5 0 .5 0 .2 0 .5 3 20,000 SO 2 Conductivity 0.2 0.1 4 0.14 0 .5 750 SO 2 Spectrophotometric

- gas phase, including DOAS 4 0.14 0 .5 0 .5 0. 2

O 3 Ethylene chemiluminescene 3 0.1 750 4 0.08 3 20,000

O 3 NO

chemiluminescene 3 0.1 0.5 750 0.08 20,000

O 3 Electrochemical 3 0.1 0 .5 0.5 0.08*** E.O. 12866 Review

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Page 638 of 647 O 3 Spectrophotometric

- wet chemical (potassium iodide) 3 0.1 0 .5 0.5 0.5 0.08

O 3 Spectrophotometric

- gas phase, including ultraviolet absorption and DOAS 0 .5 0.5 0 .5 0.08 0 .02 20,000

CO Non

- dispersive Infrared 750 20,000 4 10

CO Gas chromatography with flame ionization detector 20,000 4 10 0.5

CO Electrochemical 0 .5 0 .2 20,000 4 10 CO Catalytic combustion

- thermal detection 0.1 750 0 .2 20,000 4 10 5.0 0.5

CO IR fluorescence 750 20,000 4 10 0.5 CO Mercury replacement

- UV photometric 0 .2 4 10 0.5

NO 2 Chemiluminescent 3 0.1 0 .5 4 0.1 0 .5 20,000 NO 2 Spectrophotometric

- wet chemical (azo

- dye reaction) 0 .5 4 0.1 0 .5 750 0 .5*** E.O. 12866 Review

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Page 639 of 647 1

. Concentrations of interferents listed must be prepared and controlled to ±10 percent of the stated value. 2

. Analyzer types not listed will be considered by the Administrator as special cases. 3

. Do not mix with the pollutant. 4

. Concentration of pollutant used for test. These pollutant concentrations must be prepared to ±10 percent of the stated value. 5

. If candidate method utilizes an elevated

- temperature scrubber for removal of aromatic hydrocarbons, perform this interference test. 6

. If naphthalene test concentration cannot be accurately quantified, remove the scrubber, use a test concentration that causes a full scale response, reattach the scrubber, and evaluate response for interference.

3. Revise f

igure B

- 5 i s revised to correct a minor inconsistency in the “Calculation s ” column for the two “ Precision ” rows to change “% URL” to % Standard Deviation. Figure B

- 5 is revised to read as follows:

CALCULATION OF ZERO DRIFT, SPAN DRIFT, AND PRECISION Applicant____________________________________________________________ Date_________________________ Analyzer____________________________________________________________ Pollutant_____________________

TEST PARAMETERS CALCULATIONS TEST DAY (n) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

SPAN DRIFT 12

HOUR 12 ZD = C max − C

min

24 HOUR Z = ( L 1 + L 2 ) / 2

24 ZD = Z

n − Z n − 1 NO 2 Electrochemical 0.2 3 0.1 0.5 4 0.1 0 .5 750 0 .5 20,000 50 NO 2 Spectrophotometric

- gas phase 3 0.1 0.5 4 0.1 0 .5 0 .5 20,000 50*** E.O. 12866 Review

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Page 640 of 647 24 ZD = Z

n ′

− Z n − 1 ′

SPAN DRIFT 24

HOUR S

n = 1 6 ∑ P i 12

i = 7 SD n = S

n − S n − 1 S n − 1 × 100%

SD n = S

n − S n − 1 ′ S n − 1 ′ × 100%

PREC

ISION 20%

URL ( P 20 ) P 20 = % STANDARD

DEVIATION OF (P 1 ...P 6 ) 80% URL ( P 80 ) P 8 0 = % STANDARD

DEVIATION OF (P 7 ...P 12 )

Figure B

- 5. Form for calculating zero drift, span drift, and precision (§ 53.23(e)).*** E.O. 12866 Review

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Page 641 of 647 In subpart C,
1. Revise paragraph §53.32(g)(1)(iii) is to read as follows: The measurements shall be made in the sequence specified in table C

- 2 of this subpar t. The EPA proposes to amend part 58 as follows: In subpart E, 1. Remove figure E

- 2 PART 58

-- [ Amended ] 1. The authority citation for part 58 continues to read as follows: Authority: 42 U.S.C. 7403, 7410, 7601(a), 7611, and 7619.
In s ubpart B

– [Amended]
2. Section §58.10 is amended by adding paragraph (a)(10) and (a)(11) to read as follows: §58.10 Annual monitoring network plan and periodic assessment.
* * * * * (a)(10) The annual monitoring network plan shall provide for the required O 3 sites to be
ope rating on the first day of the applicable required O 3 monitoring season in effect on January 1, 2017 as listed in Table D

- 3 of appendix D of this part. (a)(11) The annual monitoring network plan shall include the E nhanced Monitoring Plan (EMP) for areas de signated as O 3 nonattainment , as required under 40 CFR part 58 Appendix D, section 5(f) beginning with the annual monitoring plans due on July 1, 2016.
* * * * * 3. Section §58.13 is amended by adding paragraph (g) and (h) to read as follows: §58.13 Mo nitoring network completion.
* * * * **** E.O. 12866 Review

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Page 642 of 647 (g) The O 3 monitors required under appendix D, section 4.1 of this part must operate on the first day of the applicable required O 3 monitoring season in effect January 1, 2017. (h) The Photochemical Assessment Monitoring sites required under 40 CFR part 58 Appendix D, section 5(a) must be physically established and operating under all of the requirements of this part, including the requirements of appendix A, C, D, an d E of this part, no later than June 1, 2017, or two years following designation as O 3 nonattainment.
* * * * *
4

. Appendix D to part 58 is amended by revising section 4.1(i) as follows: Appendix D to part 58

— Network Design Criteria for Ambient Air Quality Monitoring:
* * * * *
4.1 ( i ) Since O 3 levels decrease significantly in the colder parts of the year in many areas, O 3 is required to be monitored at SLAMS monitoring sites only during the “ozone sea son” as described below in Table D

– 3 of this appendix . These ozone seasons are also identified in the AQS fil es on a state

- by

- state basis. Deviations from the O 3 monitoring season must be approved by the EPA Regional Administrator. These requests will be r eviewed by Regional Administrators taking into consideration , at a minimum, the frequency of out

- of

- season O 3 NAAQS exceedances , as well as occurrences of the Moderate air quality index level and regional consistency

. Any deviations based on the Regional A dministrator’s waiver of requirements must be described in the annual monitoring network plan and updated in AQS. Changes to the O 3 monitoring season requirements in Table D

- 3 revoke any previously approved Regional Administrator waivers for affected state s. Requests for monitoring season waivers must be accompanied by relevant supporting information. Information on how to analyze O 3 data to support a change to the O 3 season in support of the 8

- hour standard for a specific state can be*** E.O. 12866 Review

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Page 643 of 647 found in footnote ref

erence 8 to this appendix. O 3 monitors at NCore stations are required to be operated on a year

- round basis ( January to December )

. Table D

- 3 to Appendix D of part 58. Ozone Monitoring Season by state. 281

State Begin M onth End Month Alabama March October Alaska April October Arizona January December Arkansas March November California January December Colorado January December Connecticut March September Delaware March October District of Columbia March October Florida January December Georgia March October Hawaii January December Idaho April September Illinois March October Indiana March October Iowa March October
Kansas March October Kentucky March October

281 The required O 3 monitoring season for NCore stations is January through December.*** E.O. 12866 Review

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Page 644 of 647 Louisiana (Northern) AQCR 019,022 March October

Louisiana (Southern) AQCR 106 January December Maine April September Maryland March October Massachusetts March September Michigan March October Minnesota March October Mississippi March October Missouri March October
Montana April September Nebraska March October Nevada January December New Hampshire March September New Jersey March October New Mexico January December New York March October North Carolina March October North Dakota March September Ohio March October Oklahoma March November Oregon May September Pennsylvania March October Puerto Rico January December*** E.O. 12866 Review

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Page 645 of 647 Rhode Island March September South Carolina March October South Dakota March October
Tennessee March October
Texas (Northern) AQCR 022, 210, 211, 212, 215, 217, 218 March November

Texas (Southern) AQCR 106, 153, 213, 214, 216 January December

Utah January December
Vermont April September Virginia March October Washington May September West Virginia March October Wisconsin March October 15 Wyoming January September American Samoa January December Guam January December Virgin Islands January December

* * * * * 5

. Appendix D to part 58 is amended by revising section 5, Network Design for Photochemical Assessment Monitoring Stations (PAMS) and Enhanced Ozone Monitoring, as follows:*** E.O. 12866 Review

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Page 646 of 647 (a) State and local monitoring agencies are required to collect and report the following PAMS measurements at each NCore site required under paragraph 3(a) of this appendix located in an area designated as nonattainment for O 3 . (b) PAMS measur ements include: (1) Hourly averaged speciated volatile organic compounds (VOCs), (2) 8 3

- hour averaged carbonyls daily, (3) Hourly averaged O 3 , (4) Hourly averaged nitrogen oxide (NO), nitrogen dioxide (NO 2 ), and total reactive nitrogen (NO y ),

(5) Hourly averaged 3 meter ambient temperature, (6) Hourly vector

- averaged 10 meter wind direction, (7) Hourly averaged 10 meter wind speed, (8) Hourly average atmospheric pressure, (9) Hourly averaged relative humidity, and (10) Hourly averaged mixing

- height. (c) The EPA Regional Administrator may grant a waiver to allow the collection of required PAMS measurements at an alternative location where the monitoring agency can demonstrate that the alternative location will provide representative data useful for regional or national scale modeling and the tracking of trends in O 3 precursors. (d) The EPA Regional Administrator may also grant a waiver to allow representative meteorological data from nearby monitoring stations to be used to meet the requirement s to collect temperature, wind direction, wind speed, atmospheric pressure, relative humidity, or*** E.O. 12866 Review

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Page 647 of 647 hourly averaged mixing height where the monitoring agency can demonstrate the data is collected in a manner consistent with EPA quality requirements for these measurements. (e) At a minimum, the monitoring agency shall collect the required PAMS measurements during the months of June, July, and August. (f) States with O 3 nonattainment areas are required to develop and implement an Enhanced Monitoring Plan (EMP) detailing enhanced O 3 and O 3 precursor monitoring activities to be performed which is subject to review and approval by the EPA Regional Administrator. The EMP will include monitoring activities deemed important to understanding the O 3 problems in the stat e. Such activities may include, but are not limited to, the following: (1) Additional O 3 monitors beyond the minimally required under paragraph 4.1 of this appendix, (2) Additional NO X or NO y monitors beyond those required under 4.3 of this appendix, (3) Additional speciated VOC measurements including data gathered during different periods other than required under paragraph 5(e) of this appendix, or locations other than those required under paragraph 5(a) of this appendix, and (4) Enhanced upper air measu rements of meteorology or pollution concentrations.