DES MOINES, Iowa — The U.S. Environmental Protection Agency warned Tuesday that two eastern Iowa counties are exceeding pollution standards.

Scott and Muscatine counties are violating short-term, fine-particle emissions requirements under the National Ambient Air Quality Standard, the EPA wrote in a letter to Gov. Chet Culver sent on Tuesday.

Air monitors in both counties have detected levels of air pollution that are slightly higher than acceptable levels, said EPA spokesman David Bryan.

If the counties cannot prove they are in compliance by Oct. 20, he said, the EPA may designate the counties as “pollution nonattainment areas,” which would require the state and the EPA to cooperate on an emissions reduction plan.

“We give the state of Iowa credit, they’ve already begun to contact major emitters like factories and grain elevators in the area and are working with them to come up with some control strategies to begin to eliminate the problem,” he said.

Officials with the Iowa Department of Natural Resources said they disagree with the EPA’s findings and will respond before October. The DNR contends the areas that are potentially in violation of clean air standards are much smaller than the EPA has detailed, DNR Director Rich Leopold said in a statement.

“We’re continuing to collect and analyze data to provide EPA with more up to date information,” he said. “Meanwhile we will continue to work with industry and the citizens of Scott and Muscatine counties toward the common goal of clean air.

Fine particle pollution is one of the most significant barriers to clean air and is a primary cause of smog. It can also linger in the air for long periods and potentially cause heath problems.