The US Environmental Protection Agency (EPA) announced that it will reconsider the previous administration’s decision to retain the particulate matter (PM) National Ambient Air Quality Standards (NAAQS) (earlier post), which were last strengthened in 2012.

EPA is reconsidering the December 2020 decision because it says that 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.

EPA sets both an annual and a 24-hour standard for fine particles (PM_2.5). These standards work together to protect the public from harmful health effects from both long- and short-term fine particle exposures.

• The current annual standard (in place since 2012) is 12.0 μg/m₃. An area meets the standard if the three-year average of its annual average PM_2.5 concentration is less than or equal to the level of the standard.

• The current 24-hour standard is 35 μg/m³ (in place since 2006). An area meets the 24-hour standard if the 98^th percentile of the yearly distribution of 24-hour PM_2.5 concentrations, averaged over three years, is less than or equal to 35 μg/m³.

Scientific evidence shows that long- and short-term exposures to fine particles (PM_2.5) can harm people’s health, leading to heart attacks, asthma attacks, and premature death. A number of recent studies have examined relationships between COVID and air pollutants, including PM, and potential health implications.

While some PM is emitted directly from sources such as construction sites, unpaved roads, fields, smokestacks or fires, most particles form in the atmosphere as a result of complex reactions of chemicals such as sulfur dioxide and nitrogen oxides, which are pollutants emitted from power plants, industrial facilities and vehicles.

EPA’s 2020 Policy Assessment concluded that the scientific evidence and information support revising the level of the annual standard for the PM NAAQS to below the current level of 12 micrograms per cubic meter while retaining the 24-hour standard. The agency also received numerous petitions for reconsideration as well as lawsuits challenging the December 2020 final action.

EPA will develop a supplement to the 2019 Final Integrated Science Assessment (ISA) that will take into account the most up-to-date science, including new studies in the emerging area of COVID-related research.

This supplement will be reviewed at a public meeting by the chartered Clean Air Scientific Advisory Committee (CASAC), supported by a particulate matter review panel of scientific experts on the health and welfare impacts of PM. The CASAC and the PM panel will also review a revised policy assessment and formulate advice to the Administrator. As with all reviews, the public will have opportunities to comment on these documents during the CASAC review process, as well as to provide input during the rulemaking through the public comment process and public hearings on any proposed decision.

EPA expects to issue a proposed rulemaking in Summer 2022 and a final rule in Spring 2023. In accordance with Executive Orders and guidance, the agency will be considering environmental justice during the rulemaking process.