The Environmental Protection Agency (EPA) proposes to retain the current National Ambient Air Quality Standards (NAAQS) for fine particulate matter (particles with a diameter of ≤2.5 μm [PM2.5]) — that is, levels not exceeding an annual average of 12 μg per cubic meter and a 24-hour average of 35 μg per cubic meter.1 The current NAAQS were set in 2012 on the basis of a scientific review that was largely completed in 2010.2 At that time, available epidemiologic evidence, supported by toxicologic evidence and a risk assessment conducted by EPA staff, indicated that annual exposure to PM2.5 caused premature death at ambient concentrations as low as 11 μg per cubic meter. However, on the basis of more recent evidence, as described below, exposure to ambient PM2.5 at the levels of the current standards is estimated by the EPA to be responsible for tens of thousands of premature deaths in the United States each year.3

 

 

NOMAD [CC BY 2.0 (https://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons

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