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 yesterday.

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 area of Arizona had the worst year-round particle pollution.

The US 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, he said. “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He also called the data outdated, saying pollution levels have improved since 2008.

“We’re making some progress on dust and ozone in the Phoenix area, but not enough and not as quickly as we’d like,’’ he said.

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.

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