WASHINGTON Pittsburgh, a former steel-making center once known for its sooty skies, is the worst U.S. city for short-term particle pollution, the American Lung Association announced on Thursday.
It was the first time a city outside California topped any of the association's three lists for different kinds of pollution in its annual "State of the Air" report.
Greater Los Angeles was listed as the worst city for ground-level ozone -- also known as smog -- and year-round particle pollution. Pittsburgh had the second-worst year-round particle pollution, the association said.
The shift occurred because Los Angeles took action to clean up particle pollution, the kind of tiny bits that can be inhaled and lodge in the lungs, the association's Janice Nolen said in a telephone interview.
In Pittsburgh, the biggest source of particle pollution is a steel plant in nearby Clareton, Nolen said. There are plans to reduce that kind of pollution in Pittsburgh, but because the report uses data from 2004 to 2006, those changes are not evident in the current report, she said.
Overall, the report found 42 percent of U.S. residents, or nearly 125 million people, lived in counties with unhealthy levels of either ozone or particle pollution.
"We had seen some real improvement in a lot of areas in the first part of this century, but now we're seeing a leveling-off," Nolen said.
The earlier improvement was due in part to measures put in place to clean air pollution from power plants in the eastern United States, she said.
But other factors are pushing up pollution levels, including more electricity generation and an increase in the distances traveled by polluting vehicles, according to Nolen.
"Those kinds of things can add pollution and can make it harder to clean up the pollution that's already there," she said.
Ozone -- a gas that forms when sunlight reacts with emissions from motor vehicles, factories and power plants -- irritates the respiratory tract and can cause asthma attacks, coughing, wheezing, chest pain and premature death, the report said.
Short-term particle pollution, which affects over 81 million U.S. residents, involves sharp, brief rises in the level of sooty particles in the air, lasting from hours to several days. Those episodes can increase the risk of heart attacks, strokes and emergency-room visits for asthma and cardiovascular disease, and can increase the risk of early death.
Long-term particle pollution involves lower levels of pollution over longer periods of time, which can increase risk of hospitalization for asthma, damage lungs and increase the risk of premature death.
More information is available online at www.lungusa.org.
(Editing by Peter Cooney)