The U.S. Environmental Protection Agency has delayed issuing its final soot designations for the Pittsburgh region and other areas in 22 states across the country that regularly experience unhealthy levels of airborne particles.

The designations, which ultimately will require tighter emissions controls from soot-producing sources like power plants, industry and diesel vehicles, were scheduled for release last week, but instead will be rolled out Dec. 13, still in time to meet the statutory end of the year deadline.

"The EPA has decided to work out the interstate transport rule first so it pushed the soot designations back," said Darrell Stern, head of the Allegheny County Health Department's air monitoring program, who participated in a conference call with EPA representatives Wednesday. "Transport is a big problem for Western Pennsylvania so it will be interesting to see how the EPA will try to control it."

Twenty-two Pennsylvania counties, including Allegheny, Beaver, Butler, Westmore- land, Washington, Armstrong, Greene, Indiana and Mercer, do not meet the 1997 federal standards for health-harmful soot, according to preliminary designations announced by the EPA in June.

The new federal standard, which takes effect in February, counts fine particles that are less than 2.5 micrometers in size, about one-fiftieth the size of a human hair. Studies have shown that those tiny particles are breathed deeply into the lungs and can cause premature death, a variety of respiratory diseases, decreased lung function and increased hospital and emergency room visits.

Much of the region's soot problem is blown in on prevailing westerly winds from utilities and industries in the Ohio River valley.

After the designations take effect in February, states will have until 2007 to put together plans to reduce soot emissions in those areas, and reach attainment of those standards in 2009.

Complicating the planning to reduce soot is the Clean Air Interstate Rule, which attempts to limit the emission and transport of gases that form soot. CAIR requires transport controls in 2010.

The EPA may be considering bringing the soot and CAIR cleanup requirements into alignment by delaying implementation of the soot standards, but Jayme Graham, head planner at the health Department's Air Quality Division, said that would be a mistake.

"It makes more sense to do it the other way -- move up the control dates for power plants in the interstate transport rule," Graham said.