Bakersfield, Calif., had the worst particle pollution over a 24-hour period, and the Phoenix area had the worst year-round. Alexandria, La., had the lowest level of particle pollution over a 24-hour period, and Cheyenne, Wyo., had the lowest year-round.
Fargo and Wahpeton, N.D., and Lincoln, Nev., emerged as the cleanest cities overall.
The report, based on 2006-2008 figures, credited cleaner diesel engines and controls on coal-fired power plants for decreasing pollution such as soot and dust. However, the report estimates that nearly 30 million people live in areas with chronic levels of pollution, so that even when levels are relatively low, people can be exposed to particles that will increase the risk of asthma, lung damage and premature death.
About 24 million people live in 18 counties with unhealthy levels of ozone, short-term particle pollution and year-round particle pollution, the report said, adding that new research shows the risk of health problems from pollution may be worse than once thought, especially for infants and children.
The two biggest air pollution threats in the United States are ozone and particle pollution, the Lung Association said. Others include carbon monoxide, lead, nitrogen dioxide, sulfur dioxide and a variety of toxic substances.
For the first time, the association included people living in poverty as one of its at-risk groups, reasoning that people with lower income levels face higher pollution risks.