Allegheny County and Western Pennsylvania will have to do a better job reducing health-harmful airborne soot, according to a study released yesterday by the U.S. Environmental Protection Agency.

The national study shows that fine-particulate pollution has been reduced by about 10 percent across the country in the five years the material has been monitored. But levels in Western Pennsylvania, which are among the highest in the Eastern part of the country, have remained relatively stable, said Judy Katz, air protection director for EPA's regional office in Philadelphia.

The study doesn't order any changes, but by the end of the year the agency is expected to release a list of areas not in compliance and require them to develop improvement plans. A preliminary report in June included 22 counties in Pennsylvania, including Allegheny and nine others in this area.

The EPA ordered monitoring of fine particulate pollution in 1999 because it has been associated with serious health problems, like aggravating asthma and contributing to chronic bronchitis and heart conditions.

The agency set the acceptable level of fine particulates at 15 micrograms per cubic meter of air. It calls the particles PM2.5, referring to particles 2.5 micrometers or smaller, about one-thirtieth the thickness of the average human hair.

Katz said Western Pennsylvania in general remained stable at a microgram or two above the acceptable level in data collected from 1999 through 2003. She said about half of the pollution comes from coal-fired utility plants and other industrial sites in neighboring states to the west.

"We still have a long way to go, particularly in the Pittsburgh area," Katz said. "I think the Pittsburgh area is impacted particularly by [upwind] power plants."

The EPA expects to begin addressing that problem nationally next year with new rules controlling emissions of fine particulates. The rules will be similar to those for acid rain reduction, which require plants to improve their emissions or buy credits from other facilities that do meet the standards.

But Katz said communities in Western Pennsylvania also should take additional measures to reduce fine particulate pollution. Those could include restrictions on industries as well as rules to limit idling of diesel-powered vehicles or equip them to reduce pollution.

Guillermo Cole, spokesman for the Allegheny County Health Department, said the Board of Health already has taken some steps locally and is expected to take additional steps next year. In October, rules went into effect limiting how long school buses could be left idling and the department is working to expand that rule to all diesel-powered vehicles.

Cole said Allegheny County's figures show the amount of fine particulates has gone down, but not for three consecutive years as EPA would require for compliance. He expects the county to be listed as out of compliance when the EPA releases its list in the next two weeks.

Cole said county figures for 10 sites in continuous operation put particulates at 16.04 micrograms in 2000; 16.53 in 2001; 15.08 in 2002; 15.65 in 2003; and 14.49 through the first nine months this year. He attributed the lower figure this year to the high amount of rain, which removes particles from the air.

The highest areas are monitoring sites in North Braddock and Liberty, near U.S. Steel's Edgar Thomson Plant and Clairton Coke Works, respectively.

"To be sure, there will need to be provisions developed for cutting back on pollution in our area, but there will have to be help from the federal government to deal with sources [upwind]," Cole said.

Once the EPA lists counties not in compliance, the county and state will have three years to develop an improvement plan. If approved, the plan would take effect in 2010, unless the area seeks a five-year waiver.