SUPPLEMENTARY INFORMATION:

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 https://www.epa.gov/​naaqs).

EPA has established NAAQS for six criteria pollutants. In conducting periodic reviews of the air quality criteria and NAAQS, EPA reviews the scientific basis for these standards by preparing an Integrated Science Assessment (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 10, 2021, the EPA announced its decision to reconsider the 2020 p.m. NAAQS final action, available at: https://www.epa.gov/​newsreleases/​epa-reexamine-health-standards-harmful-soot-previous-administration-left-unchanged. The EPA also announced that, as a part of the reconsideration, a supplement to the Integrated Science Assessment (ISA) for Particulate Matter (PM), which was finalized in December 2019, would be developed. The “Supplement to the 2019 Integrated Science Assessment for Particulate Matter (External Review Draft)” was released for public comment and review by the CASAC on September 30, 2021 ( https://cfpub.epa.gov/​ncea/​isa/​recordisplay.cfm?​deid=​352823).

The CASAC PM panel met at a virtual public meeting on November 17-19, 2021, to review the draft Supplement to the 2019 p.m. ISA (86 FR 52673, September 22, 2021). A virtual public meeting was then held on February 25, 2022-March 4, 2022, and during this meeting on February 28, 2022, the chartered CASAC considered the CASAC PM Panel's draft letter to the Administrator on the draft Supplement to the 2019 p.m. ISA. This meeting was announced in the Federal Register on January 7, 2022 (87 FR 958). Subsequently, on March 18, 2022, the chartered CASAC provided a consensus letter of their review to the Administrator of the EPA ( https://casac.epa.gov/​ords/​sab/​f?​p=​113:0:9895873668768:APPLICATION_​PROCESS=​REPORT_​DOC:::REPORT_​ID:1093). The EPA has considered comments by the chartered CASAC and by the public in preparing this final Supplement to the 2019 p.m. ISA.

87 FR 22207