America's smoggiest cities

NEW YORK (CNNMoney.com) -- Los Angeles ranks as the smoggiest city in the United States, according to an annual report card released Tuesday by the American Lung Association. It leads the nation in all three major air pollution categories, short-term particle pollution, year-round particle pollution and ozone pollution.

The report did offer some good news. Ozone levels have lessened nationwide, on average. And particulates, the most dangerous form of air pollution, have decreased west of the Mississippi. They did increase in the East.

The decrease in ozone came principally from success in reducing auto and truck emissions, the report said. The increase in soot in eastern air was attributed to a jump in electricity generated by heavy polluting power plants.

"The increased particle pollution in the East is a particularly troubling trend, because exposure to particle pollution can not only take years off your life, it can threaten your life immediately," said Terri E. Weaver, the American Lung Association Chair, in a press release.

Pittsburgh had the second highest levels of both short-term and year-round particulate pollution among cities. Others in the top 10 for both lists were Bakersfield, Calif., Birmingham, Ala., Detroit and Cleveland.

The cities with the worst ozone levels, besides Los Angeles, were clustered in California's Central Valley and other Sun Belt locales. Bakersfield was second, followed by Visalia and Fresno.

Houston was the worst non-California city, coming in at fifth on the ozone list, and New York, which checked in at No. 10, was the lone northern town to crack the top 10.

The cleanest cities were mostly smaller metropolises located in otherwise wide-open spaces.

For short-term particulates, Amarillo, Tex., was the cleanest, followed by Bismarck, North Dakota and Cheyenne, Wyoming. For long-term particulates, it was Cheyenne, Santa Fe and Honolulu.

The city with the lowest ozone levels was Ames, Iowa with Bellingham, Washington and Bloomington, Ill., second and third.

The Miami metro area finished in the top 25 cleanest in both long- and short-term particulate levels, the biggest city (more than 5 million residents) to accomplish that feat. Portland, Ore., with more than 2 million people, was the biggest city in the top 25 for least ozone pollution.