The U.S. Environmental Protection Agency (EPA) lowered by 20% the National Ambient Air Quality Standards for fine particle pollution (PM2.5), from 15 micrograms to 12 micrograms per cubic meter averaged over a year. The EPA did not change the standard for coarse particle pollution (PM10), which remains at 150 micrograms averaged over a 24-hour period.
The small soot particles come from a variety of man-made and natural sources, including diesel tailpipe emissions, smokestacks and fires. The agency’s new PM2.5 standard is approximately one-thirtieth the width of a human hair. The EPA is concerned that once in the bloodstream or lungs, the particles can cause aggravated asthma and other respiratory and heart ailments. The agency estimates that 66 of the nation’s 3,033 counties will be found in violation of the new standard when the EPA updates its nonattainment designations around 2015. States would then have five years to meet the revised standard. The EPA contends that many counties will not need to take any additional actions to comply with the rule as long as other air pollution rules the EPA is pursuing are implemented as scheduled. These actions include diesel emissions limits for off-road vehicles and installation of new pollution-abatement equipment at oil refineries, power plants and some large-scale manufacturing facilities.
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