High levels of soot, also known as fine particulate air pollution, have once again placed Pittsburgh high on a list of polluted cities.

A report by the U.S. Public Interest Research Group, released yesterday by PennEnvironment and other environmental and health groups, ranked Pittsburgh first nationwide among large metropolitan areas for violations of the Environmental Protection Agency's 24-hour standard for fine particulates, which are harmful to the heart and lungs.

The study also ranked Pittsburgh second among large cities for annual soot pollution levels.

Soot is nothing new for Pittsburgh. Allegheny County is one of 22 counties statewide that must develop plans to reduce airborne particulates by 2010. High readings at county monitoring stations, particularly one located downwind from the U.S. Steel Clairton coke works, last year landed Pittsburgh on Self magazine's list of cities with "unhealthiest hearts," and earned a grade of F on the American Lung Association's annual State of the Air report.

Environmentalists have decried the EPA's decision last month not to tighten its soot pollution standards, despite recommendations by its staff scientists and science advisers.