The U.S. Environmental Protection Agency (EPA) intends to tighten the National Ambient Air Quality Standards for fine particle pollution (PM2.5), while retaining the existing standard for coarse particle pollution (PM10). The small particles of soot come from a variety of man-made and natural sources, including vehicles, smokestacks and fires. The agency is under a court order to update the PM standards. The agency has proposed lowering the PM2.5 standard from 15 micrograms per cubic meter averaged over a year to a range of 12.0 to 13.0 micrograms (approximately one-thirtieth the width of a human hair).
The EPA based its decision on concern that once in the bloodstream or lungs, the particles can cause aggravated asthma and other respiratory and heart ailments. The agency contends 99% of the country will meet the new standard without taking any additional actions as long as other air pollution rules the EPA is pursuing are implemented as scheduled. Those actions would require oil refiners, power plants and some large-scale manufacturers to install pollution-abatement upgrades.
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