September 16, 2022

Final Policy Assessment for Particulate Matter NAAQS

In May 2022, EPA released its Policy Assessment for the Reconsideration of the NAAQS for Particulate Matter (PM). [87 FR 31965] Similar to the draft policy assessment on ozone released in April 2022 (see previous article), this final policy assessment “bridges the gap” between previous assessments and more recent scientific and quantitative technical information. Specifically, the agency is reviewing previous recommendations based on 2019 Integrated Science Assessment for Particulate Matter (2019 ISA) and 2020 Policy Assessment (2020 PA) in light of the more recent information in the 2022 ISA Supplement. In essence, the policy implications of the 2019 ISA have been reassessed, and EPA policymakers will use this information to decide whether to retain the existing PM NAAQS. It is notable that the 2020 PA suggested reducing the primary annual PM_2.5 standard based on evidence indicating the standard was inadequate to protect public health. However, EPA’s December 2020 decision resulted in no changes to the PM_2.5 and PM₁₀ standards.

The 2022 final policy assessment sits at 685 pages, much of which is an analysis of the relevant scientific data. Five chapters provide this information:

Chapter 1 reviews the CAA statutory requirements for establishing and reviewing NAAQS and the history of the PM NAAQS. Starting with the regulation of total suspended particles (TSP) in 1971, EPA changed the indicator from TSP to PM₁₀ in 1987 to focus on inhalable particles small enough to penetrate the thoracic region of the respiratory tract. The 1997 review saw the establishment of PM_2.5 standards, creating different primary and secondary standards for coarse particulate matter (PM₁₀) and fine particulate matter (PM_2.5). Since the original 1971 TSP standards, EPA has consistently faced reconsiderations, court challenges, and petitions for judicial review by the regulated community and interest groups.
Chapter 2 reviews the available information on PM-related emissions, atmospheric chemistry, particle size distribution, monitoring, and air quality. Unlike some criteria pollutants such as lead, PM readily occurs from both natural and anthropogenic courses. While PM occurs from stationary sources like fuel combustion and construction/demolition, as well as mobile sources on the nation’s highways, the largest sources of PM₁₀ and PM_2.5 emissions are wildfires and dust. When not controlled via emission control equipment (e.g., a baghouse), PM is typically suspended in the lower troposphere for a few hours to a few weeks before being deposited via rain, snow, gravitational settling, or surface collision.
Chapters 3 and 4 evaluate the policy implications of the current technical information regarding the primary, health-based standards for PM_2.5 and PM_10, respectively. Several decades-worth of evidence indicate the relationship between short- and long-term PM exposure and morbidity/mortality. These chapters explain the technical literature and data, concluding the primary PM₁₀ standard seems to be adequate. On the other hand, the primary annual PM_2.5 standard may warrant strengthening, and the policy assessment specifically discusses options for a 16.6-33.3% strengthening of the PM_2.5 standard.
Chapter 5 focuses on welfare impacts from the secondary PM standards. While the current secondary PM standards are deemed adequate, the policy assessment highlights areas for future research on the effects of PM on public welfare. These issues include visibility impacts and preferences, climate impacts (e.g., radiative forcing), improved modeling, and materials degradation.

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