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US EPA proposes to tighten ambient PM2.5 standard

7 January 2023

The US Environmental Protection Agency (EPA) issued a proposed rule to strengthen the national ambient air quality standard (NAAQS) for fine particulate matter (PM2.5).

The EPA’s proposal will specifically take comment on strengthening the primary (health-based) annual PM2.5 standard from the current level of 12 μg/m3 to a level between 9 and 10 μg/m3. The agency will also take comment on the full range—between 8 and 11 μg/m3—included in the latest report by the EPA Clean Air Scientific Advisory Committee’s (CASAC).

The agency proposed to retain the primary 24-hour PM2.5 standard of 35 μg/m3, while taking comment on revising this level to as low as 25 μg/m3.

The EPA also proposed to revise other aspects related to the PM standards—such as monitoring requirements and the Air Quality Index (AQI).

The NAAQS standards for PM were last reviewed in 2020, under the prior US administration, when the EPA decided to retain the existing standards for PM2.5 and PM10. In June 2021, the EPA announced that it would reexamine the PM standards. The PM standards were last strengthened in 2012.

The World Health Organization (WHO) air quality guideline for ambient PM2.5, adopted in 2021, is 5 μg/m3. The prior WHO guideline for PM2.5 was 10 μg/m3.

The EPA will accept public comment for 60 days after the proposal is published in the Federal Register.

Source: US EPA