SUPPLEMENTARY INFORMATION:

Two sections of the Clean Air Act (CAA or the Act) govern the establishment and revision of the NAAQS. Section 108 directs the Administrator to identify and list certain air pollutants and then issue “air quality criteria” for those pollutants. 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 such pollutant in the ambient air . . .” (CAA section 108(a)(2)). Under section 109 of the Act, the EPA is then to establish primary (health-based) and secondary (welfare-based) NAAQS for each pollutant for which the EPA has issued air quality criteria. Section 109(d)(1) of the Act requires periodic review and, if appropriate, revision of existing air quality criteria. Revised air quality criteria are to reflect advances in scientific knowledge on the effects of the pollutant on public health and welfare. Under the same provision, the EPA is also to periodically review and, if appropriate, revise the NAAQS, based on the revised air quality criteria.

The Act additionally requires appointment of an independent scientific review committee that is to periodically review the existing air quality criteria and NAAQS and to recommend any new standards and revisions of existing criteria and standards as may be appropriate (CAA section 109(d)(2)(A)-(B)). Since the early 1980s, the requirement for an independent scientific review committee has been fulfilled by the Clean Air Scientific Advisory Committee (CASAC).

The EPA's overall plan for this review is presented in the Integrated Review Plan for the Secondary National Ambient Air Quality Standards for Ecological Effects of Oxides of Nitrogen, Oxides of Sulfur and Particulate Matter (IRP).^[1] As described in the IRP, the EPA has prepared the Integrated Science Assessment (ISA) for Oxides of Nitrogen, Oxides of Sulfur and Particulate Matter Ecological Criteria (U.S. EPA, 2020), drafts of which were released in March 2017 and June 2018 for public comment and review by the CASAC.^[2] A draft of the PA was also reviewed by the CASAC (88 FR 17572, March 23, 2023; 88 FR 45414, July 17, 2023). The final PA reflects consideration of the advice and comments from the CASAC on the draft PA, as well as public comments. The PA serves to “bridge the gap” between the scientific and technical information in the 2020 ISA and any air quality, exposure, and risk analyses available in this review, and the judgments required of the Administrator in determining whether to retain or revise the existing secondary ambient air quality standards for NO_2, SO₂ and PM. The final PA document will be available on EPA's website at https://www.epa.gov/​naaqs/​nitrogen-dioxideno2-and-sulfur-dioxide-so2-secondaryair-quality-standards. The document briefly described here does not represent and should not be construed to represent any final EPA policy, viewpoint, or determination.

89 FR 2223