U.S. cities with the cleanest air

Getty ImagesGetty ImagesBy Lynne Peeples

Forty years after the Clean Air Act, more people are breathing easier. "In general, we've seen tremendous improvement in air quality," says Jonathan M. Samet, MD, director of the Institute for Global Health at the University of Southern California, in Los Angeles.

But some air is cleaner than others. Here are the 5 cities with the cleanest air, according to the American Lung Association's annual report, which looks at levels of ozone and particulates, which are tiny particles that can get lodged in your lungs.

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Cheyenne, Wyo.
Population: 88,854

Cheyenne is the clear winner: It has the lowest level of year-round PM 2.5 particulates, tiny lung invaders about 1/30th the width of a human hair. Cheyenne's small size may help; fewer cars travel the roads, and vehicles are a key source of PM 2.5 (and ozone).

Wyoming's capital also has fewer short-term spikes in 24-hour particle pollution. "When exposure peaks, you can have an increased risk of hospitalization for asthma or a heart attack," notes Joel Kaufman, MD, director of the Occupational and Environmental Medicine Program at the University of Washington, in Seattle.

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Santa Fe, N.M.
Population: 188,210

Popular for both its art galleries and clean air, it may come as no surprise that a Santa Fe artist recently unveiled a sculpture that measures particulate air pollution.

The city's growing population cares about air quality too. There are strict rules that limit wood burning, a source of particulates. (The area has more than 1.5 million acres of national forest.)

Santa Fe is one of only 20 U.S. cities the ALA looked at with consistently safe ozone levels. (While the atmosphere's ozone protects us from the sun's rays, ground-level ozone is a pollutant.)

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Bismarck, N.D.
Population: 106,286

Bismarck has some of the lowest year-round particulate levels of all U.S. cities (it comes in at number 11) and ozone levels below what is considered dangerous.

North Dakota's capital is protected from pollutants due to a relatively remote location and the fact that it's not downwind of other cities. Although its winters make it one of the coldest U.S. cities, the low temperatures keep ozone at bay.

Its citizens care also helped establish the Bismarck Tobacco Free Coalition to promote a smoke-free environment.

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Great Falls, Mont.
Population: 82,178

It's a good thing that the small and relatively remote city of Great Falls enjoys clean air, given how much time its residents probably spend outdoors taking advantage of the area's natural beauty.

The city continues to work hard to maintain that quality standard, recently fending off a major coal-fired power-plant project (another major PM 2.5 offender).

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Honolulu
Population: 907,574

Honolulu is well-known as a popular vacation destination. But it can be a vacation for the lungs too, as it has some of the nation's lowest levels of both ozone and particulates.

Due to Honolulu's isolation in the Pacific Ocean, Dr. Kaufman suggests that it generally remains safe from the long-range transport of pollution. Particles that result from burning coal, for example, can travel great distances, but few are likely to reach Honolulu, some 2,000 miles off the mainland.

Large amounts of rain, adds Dr. Samet, also help.

Keep reading: Health.com: 10 U.S. Cities With the Cleanest Air