LOS ANGELES -- Six in 10 Americans - about 175 million people - are living in places where air pollution often reaches dangerous levels, despite progress in reducing particle pollution, the American Lung Association said in a report released Wednesday.
The Los Angeles area had the nation's worst ozone pollution.
The report examined fine particulate matter over 24-hour periods and as a year-round average. Bakersfield, Calif., had the worst short-term particle pollution, and the Phoenix-Mesa-Scottsdale area of Arizona had the worst year-round particle pollution.
The U.S. cities with the cleanest air were Fargo, N.D., Wahpeton, N.D., and Lincoln, Neb.
The report is accurate, but it doesn't show how far California has come, said Dimitri Stanich, a spokesman for the California Air Resources Board.
"More than 45 percent of the days in the 1990 ozone season were considered very unhealthy (in the South Coast area). Today, 45 percent of the days are clean, more than double the number of clean days during 1990."
"So while we are still not meeting the federal air quality standards, the concentrations that Californians are exposed to are coming down dramatically," he said.
In Arizona, Benjamin H. Grumbles, the state's environmental quality director, issued a statement objecting to the methodology used in the report.
"This finding came about because of one lonely air quality monitor near the cowtown area of western Pinal County, nearly 40 miles and across the mountains from downtown Phoenix," he said. He also called the data outdated, saying pollution levels have improved since 2008.
He said the state recognizes that the Phoenix area has significant air pollution problems, and "we're making some progress on dust and ozone in the Phoenix area, but not enough and not as quickly as we'd like."
The report, based on 2006-08 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 California Air Resources Board has tripled its estimates of premature deaths in California from particle pollution to 18,000 a year, the report said. Stanich said those numbers were taken from 2008 documents and were in the process of being updated now. He said he expected new numbers in about a month.
Freeways remain high-risk areas for everyone, the study said, increasing the risk of heart attack, allergies, premature births and infant deaths.
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.