Many metro areas around the country, including Baltimore-Washington, have made improvements in air quality in the last year, but half the nation still has unhealthy level of air pollution, according to the annual State of the Air report from the American Lung Association.

The bad air that some 154.5 million people breathe contains ozone (smog) or particle pollution (soot) from smokestacks and tailpipes that can cause early death, asthma exacerbations, coughing and wheezing, heart attacks, strokes and emergency room visits.

The good news, the lung association said, was that in the last year all metro area surrounding the 25 cities most polluted by ozone showed improvement – Baltimore-Washington-Northern Virginia, with 8.4 million people, is No. 14 on this list, up a spot from last year. And all but two of the 25 cities most polluted with year-round particle pollution improved. Only 11, however, of those most polluted by short-term spokes in particle pollution saw improvement.

“State of the Air tells us that the progress the nation has made cleaning up coal-fired power plants, diesel emissions and other pollution sources has drastically cut dangerous pollution from the air we breathe,” said Charles D. Connor, American Lung Association president and chief executive. “We owe our cleaner air to the Clean Air Act.”

The lung association decried efforts in Congress to weaken the act, which the Environmental Protection Agency credits with saving more than 160,000 lives last year.

The group used the color-coated air quality index that warns the public of bad air quality days used by the EPA. It considers ozone and particle pollution, the most widespread types of air pollution. The data in the report, which can be found at stateoftheair.org, is from 2007-2009.
The cleanest cities were Honolulu and Santa Fe-Espanola, N.M. Most of the dirtiest were cities in California, lead by Bakersfield and Los Angeles-Riverside.

In Maryland, Baltimore City and Garrett County were the only two areas without a failing grade for high ozone days. And only Harford and Frederick made the list of cleanest counties for short-term particle pollution.