"The State of the Air," a report by the American Lung Association, lists both the cleanest city -- Santa Fe, N.M. -- and most polluted areas -- all in California. Los Angeles-Long Beach-Riverside in California had the worst air pollution for ozone, Bakersfield-Delano in California, ranked No. 1 for short-term particle pollution and annual particle pollution, as well.
"This report shows that air pollution remains a serious health threat to too many Californians," Jane Warner, president and chief executive officer of the American Lung Association in California, said in a statement.
"'State of the Air 2012' shows that we're making real and steady progress in the fight for clean air, but unhealthy levels of air pollution still exist, putting the health of millions Californians at risk."
The worse the air quality in an area, the more risk there is for asthma attacks, heart attacks and premature death, Warner said.
As in previous years, California cities once again dominated lists for the top 10 most polluted areas in the nation for ozone (smog) and short-term and annual particle pollution.
Despite these poor rankings, many California cities continue to show improvements, including reductions in unhealthy ozone and particulate pollution -- particularly in Los Angeles.