In response to a court order, the U.S. Environmental Protection Agency (EPA) has finalized an update to its national air quality standards for fine particulate material (PM2.5), setting the annual health standard at 12 micrograms per cubic meter. The update has no effect on the existing daily standard for PM2.5 or the existing daily standard for coarse particles (PM10).

By 2020, 99% of U.S. counties are projected to meet revised health standard without any additional actions. It is expected that fewer than 10 counties in the United States will need to consider any local actions to reduce fine particle pollution in order to meet the new standard by 2020, as required by the Clean Air Act.

The Clean Air Act requires EPA to review its air quality standards every five years to determine whether the standards should be revised. The law requires the agency to ensure the standards are “requisite to protect public health with an adequate margin of safety” and “requisite to protect the public welfare.” A federal court required EPA to issue final standard by December 14, because the agency did not meet its five-year legal deadline for reviewing the standards.

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