Charleston, W.Va. (AP) -- The U.S. Environmental Protection Agency says four West Virginia counties don't meet federal standards for tiny soot particles.
Brooke, Hancock, Kanawha and Putnam Counties are among 31 areas EPA says fail to meet the 24-hour standard for fine particulate matter.
The pollution particles are no bigger than 2.5 micrometers -- one-30th the diameter of a human hair.
Particulate matter is emitted by power plants, factories and motor vehicles.
It can aggravate asthma and lead to increased health problems, including heart attacks and premature death.
EPA says the West Virginia Department of Environmental Protection must develop a plan to correct the problem within three years.
A DEP spokesman did not immediately return a call seeking comment.
(Copyright 2009 by the Associated Press. All rights reserved.)
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