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Under the Clean Air Act Amendments of 1977, EPA is required to review and if appropriate revise the air quality criteria for the primary (health-based) and secondary (welfare-based) national ambient air quality standards (NAAQS) every 5 years. On December 18, 2020, the EPA published a final decision retaining the NAAQS for particulate matter (PM), which was the subject of several petitions for reconsideration as well as petitions for judicial review. As directed in Executive Order 13990, "Protecting Public Health and the Environment and Restoring Science to Tackle the Climate Crisis,” signed by President Biden on January 20, 2021, EPA is undertaking a reconsideration of the December 2020 decision to retain the PM NAAQS because the available scientific evidence and technical information indicate that the current standards may not be adequate to protect public health and welfare, as required by the Clean Air Act. As part of this reconsideration, EPA developed a Supplement to the 2019 PM Integrated Science Assessment (ISA) and a Policy Assessment to take into account the most up-to-date science on public health impacts of PM and engaged with the chartered Clean Air Scientific Advisory Committee (CASAC) and a newly-constituted expert CASAC PM panel. The notice of proposed rulemaking was signed on January 5, 2023, and a final rule will be issued in fall 2023. EPA proposed to revise the level of the primary annual PM2.5 standard from its current level of 12 µg/m3 to within the range of 9-10 µg/m3. EPA proposed to retain all other PM NAAQS, including the primary and secondary 24-hour PM2.5 standards, the primary and secondary 24-hour PM10 standards, and the secondary annual PM2.5 standard. EPA also proposed revisions to the Air Quality Index (AQI) and monitoring network requirements.

Statement of Need: Under the Clean Air Act Amendments of 1977, EPA is required to review and if appropriate revise the air quality criteria and national ambient air quality standards (NAAQS) every 5 years. On December 18, 2020, EPA published a final rule retaining the NAAQS for particulate matter, without revision. On June 10, 2021, EPA announced that it is reconsidering the December 2020 decision on the air quality standards for PM.

Summary of the Legal Basis: Under the Clean Air Act Amendments of 1977, EPA is required to review and if appropriate revise the air quality criteria and the primary (health-based) and secondary (welfare-based) national ambient air quality standards (NAAQS) every 5 years.

Alternatives: The main alternative for the Administrator’s decision on the review of the national ambient air quality standards for particulate matter is whether to retain or revise the existing standards.

Anticipated Costs and Benefits: When the Agency proposes revisions to the standards, the Agency prepares a Regulatory Impact Analysis (RIA) to provide the public with illustrative estimates of the potential costs and health and welfare benefits of attaining the revised standards. However, the Clean Air Act makes clear that the economic and technical feasibility of attaining standards are not to be considered in setting or revising the NAAQS, although such factors may be considered in the development of state plans to implement the standards.

Risks: The reconsideration builds on the review completed in 2020, which included the preparation by EPA of an Integrated Review Plan, an Integrated Science Assessment, and a Policy Assessment, which includes a risk/exposure assessment, with opportunities for review by the EPA's Clean Air Scientific Advisory Committee (CASAC) and the public. These documents informed the Administrator's final decision to retain the PM standards in 2020. As a part of the reconsideration, EPA prepared a Supplement to the 2019 PM Integrated Science Assessment and a Policy Assessment, which was reviewed at a public meeting by the CASAC. These documents informed the Administrator’s proposed decisions on whether to revise the PM NAAQS, and the Administrator's final decisions on whether to revise the PM NAAQS will take into consideration these documents, CASAC advice, and public comment on the proposed decision.