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Integrated Science Assessment for Ozone and Related Photochemical Oxidants

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Environmental Protection Agency (EPA).


Notice of availability.


The Environmental Protection Agency (EPA) is announcing the availability of a final document titled, “Integrated Science Assessment for Ozone and Related Photochemical Oxidants (Final)” (EPA/600/R-20/012). The document was prepared by the Center for Public Health and Environmental Assessment (CPHEA) within EPA's Office of Research and Development (ORD) as part of the review of the primary (health-based) and secondary (welfare-based) ozone national ambient air quality standards (NAAQS) and represents an update of the 2013 Integrated Science Assessment (ISA) for ozone and related photochemical oxidants. The ISA, in conjunction with additional technical and policy assessments, provides the basis for EPA's decisions on the adequacy of the current NAAQS and the appropriateness of possible alternative standards.


The document will be available on or about April 24, 2020.


The “Integrated Science Assessment for Ozone and Related Photochemical Oxidants (Final)” will be available primarily via the internet on EPA's Integrated Science Assessment for Ozone page at​isa/​integrated-science-assessment-isa-ozone-and-related-photochemical-oxidants or the public docket at, Docket ID: EPA-HQ-ORD-2018-0274. A limited number of CD-ROM copies will be available. Contact Ms. Marieka Boyd by phone: 919-541-0031; fax: 919-541-5078; or email: to request a CD-ROM, and please provide your name, your mailing address, and the document title, “Integrated Science Assessment for Ozone and Related Photochemical Oxidants (Final)” to facilitate processing of your request.

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For technical information, contact Dr. Thomas Luben, CPHEA; phone: 919-541-5762; fax: 919-541-1818; or email:

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I. Information About the Document

Section 108(a) of the Clean Air Act directs the Administrator to identify certain air pollutants which, among other things, “cause or contribute to air pollution which may reasonably be anticipated to endanger public health or welfare”; and to issue air quality criteria for them. The air quality criteria are 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 . . . .”. Under section 109 of the Act, EPA is then to establish NAAQS for each pollutant for which EPA has issued criteria. Section 109(d)(1) of the Act subsequently requires periodic review and, if appropriate, revision of existing air quality criteria to reflect advances in scientific knowledge on the effects of the pollutant on public health or welfare. EPA is also required to review and, if appropriate, revise the NAAQS, based on the revised air quality criteria (for more information on the NAAQS review process, see​naaqs).

EPA has established NAAQS for six criteria pollutants. Presently the EPA is reviewing the air quality criteria and NAAQS for photochemical oxidants and ozone; ozone is the current indicator for this NAAQS. Periodically, EPA reviews the scientific basis for these standards by preparing an ISA (formerly called an Air Quality Criteria Document). The ISA provides the scientific basis for EPA's decisions, in conjunction with additional technical and policy assessments, on the adequacy of the current NAAQS and the appropriateness of possible alternative standards. The Clean Air Scientific Advisory Committee (CASAC), an independent science advisory committee whose review and advisory functions are mandated by Section 109(d)(2) of the Clean Air Act, is charged (among other things) with independent scientific review of the EPA's air quality criteria.

On June 26, 2018 (83 FR 29785), EPA formally initiated its current review of the air quality criteria for the health and welfare effects of ozone and related photochemical oxidants and the primary (health-based) and secondary (welfare-based) ozone NAAQS, requesting the submission of scientific and policy-relevant information on specified topics. This information was incorporated into EPA's “Integrated Review Plan for the Review of the Ozone National Ambient Air Quality Standards (External Review Draft),” which was available for public comment (83 FR 55163) and discussion by the CASAC via publicly accessible teleconference consultation (83 FR 55528). The final “Integrated Review Plan for the Review of the Ozone National Ambient Air Quality Standards” was posted to the EPA website in August 2019 (​naaqs/​ozone-o3-air-quality-standards).

In the development of the draft ISA, webinar workshops were held on October 29 and 31, 2018, and November 1 and 5, 2018, to discuss initial draft materials with invited EPA and external scientific experts (83 FR 53472). The input received during these webinar workshops aided in the development of the materials presented in the “Integrated Science Assessment for Ozone and Related Photochemical Oxidants (External Review Draft)”, which was released on September 19, 2019 (84 FR 50836) and is available at:​ncea/​isa/​recordisplay.cfm?​deid=​344670. The CASAC met at a public meeting on December 3-6, 2019 (84 FR 58713), to review the draft Ozone ISA. A public teleconference was then held on February 11, 2020 for CASAC to review their draft letter to the Administrator on the draft ISA. This meeting was announced in the Federal Register on January 27, 2020 (85 FR 4656). Subsequently, on February 19, 2020, the CASAC provided a letter of their review to the Administrator of the EPA, available at:​sab/​sabproduct.nsf/​264cb1227d55e02c85257402007446a4/​F228E5D4D848BBED85258515006354D0/​$File/​EPA-Start Printed Page 21850CASAC-20-002.pdf. The letter from the CASAC, as well as public comments received on the draft Ozone ISA, can be found in Docket ID No. EPA-HQ-ORD-2018-0274.

The Administrator responded to the CASAC's letter on the External Review Draft of the Ozone ISA on April 1, 2020, and the letter is available at:​sab/​sabproduct.nsf/​LookupWebProjectsCurrentCASAC/​F228E5D4D848BBED85258515006354D0/​$File/​EPA-CASAC-;​20-002+​Response.pdf. Administrator Wheeler's letter to the CASAC indicated the Agency will “incorporate the CASAC's comments and recommendations, to the extent possible, and create a final Ozone ISA so that it may be available to inform a proposed decision on any necessary revisions of the NAAQS by spring 2020.” The consensus CASAC comments on the draft Ozone ISA (February 19, 2020) recommended that the Draft Ozone ISA would benefit from: (1) Critical review, synthesis, and discussion of available scientific evidence; (2) reassessment of causality determinations and rationale for some new and altered causality determinations; and (3) consultation with outside experts on high-level, over-arching process aspects related to ISA development and consideration of causality. In consideration of these comments while preparing the Final Ozone ISA, the EPA added new text and clarified existing text in the Preface and in Appendix 10 to more clearly articulate how scientific evidence is identified, evaluated and summarized in the ISA, revised the causality determination for long-term ozone exposure and metabolic effects, and will take steps to both identify methods for improving the ISA process and to solicit outside expertise on best practices for making causality determinations from multiple lines of evidence. Additionally, the EPA focused on addressing those comments that contributed to improving clarity, could be addressed in the near-term, and identified errors in the draft Ozone ISA. Lastly, Administrator Wheeler noted, “for those comments and recommendations that are more substantial or cross-cutting and which cannot be fully addressed in this timeframe, [the Agency will] develop a plan to incorporate these changes into future Ozone ISAs as well as ISAs for other criteria pollutant reviews.”

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Dated: April 14, 2020.

Wayne Cascio,

Director, Center for Public Health and Environmental Assessment.

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[FR Doc. 2020-08333 Filed 4-17-20; 8:45 am]