The Environmental Protection Agency (EPA) is proposing to strengthen its national ambient air quality standards (NAAQS) for particulate matter (PM) by lowering the primary annual PM2.5 standard level. The proposal retains the current primary standards for 24-hour PM2.5 and 24-hour PM10. EPA also proposes revisions to the Air Quality Index (AQI) and monitoring requirements for the PM NAAQS. Comments due 60 days after publication in the Federal Register.

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