Despite many cleanup efforts, more than half of Americans – particularly those in California – are still exposed to potentially dangerous air pollution, according to the American Lung Association’s annual report.

Los Angeles remains the nation’s smoggiest city, according to the American Lung Assocation’s annual survey of air quaity.

CAPTIONBy Nick Ut, APLos Angeles remains the nation’s smoggiest city, followed by Bakersfield, Calif., says “State of the Air 2010.” Of the 10 smoggiest metro areas, eight are in California. The two exceptions are Houston, Texas, and Charlotte, N.C. The report says smog or ozone can trigger coughing and asthma attacks.

In contrast, two of the five cities with the least smog are in North Dakota: Bismarck and Fargo. The other three: Brownsville, Texas; Couer d’Alene, Idaho; and Duluth, Minn.

The annual report also looks at particulate pollution – or soot – at short-term and year-round levels, based on Environmental Protection Agency data for 2006, 2007 and 2008. How does your area rank? Just type your ZIP code into the report’s website.

At least half of the 10 cities with the most soot are in California. The dirtiest, on the short-term scale, is Phoenix, followed by Bakersfield and Los Angeles. Year-round, Bakersfield has the most particle pollution, followed by Fresno, Calif., and Pittsburgh.

Much progress has been made in the last year, according to the report, which says 20 of the sootiest cities year-round improved their annual averages. Also, 14 of the 25 smoggiest cities made gains.

Still, it says, more that 175 million people or 58% of the U.S. population breathe potentially dangerous air.

“More needs to be done,” said Mary H. Partridge, the national board chair of the American Lung Association , in releasing the report.

The short-term soot levels of seven of the dirtiest cities got worse in the last year. This list includes Phoenix, Provo, Utah, and five California cities: Bakersfield, Fresno-Madera, Visalia-Porterville, Modesto and Stockton.