Oil pumps stand at the Chevron Corp. Kern River oil field in Bakersfield, Calif. on March 29, 2011.
Bloomberg/Getty Images
By Justin Worland
April 29, 2015
TIME Health
For more, visit TIME Health.

More than 40% of Americans live in a place with unhealthy air quality, according to a new report from the American Lung Association. But, when it comes to how bad that air pollution can get, there’s a real range.

Los Angeles, which has some of the most polluted air in the country, experiences unhealthy levels of particle pollution for the equivalent of nearly a month out of each year and unhealthy ozone pollution for the equivalent of more than two months annually. Six cities, all much smaller in size, went an entire year without an unhealthy day of either.

Particle pollution refers to the toxic exhaust emitted by processes like smoking or driving a car, and ozone pollution refers to an invisible substance present in smog. Exposure to either pollutant can exacerbate breathing problems and increase residents’ chance of developing cancer.

People most harmed by air pollution include those with cardiovascular diseases, diabetes and asthma, as well as children and the elderly. The report also notes that great disparities in risk exist even within cities. People who live close to highways or busy roads, for instance, are at increased risk, and overall, low socioeconomic status is associated with exposure to poorer air quality.

The report offers a few guidelines for individuals to manage pollution, like avoiding high-traffic areas, but the report also suggests a more top-level approach to public health: strengthening clean-air regulation.

Here are the U.S. cities with the most ozone pollution in 2015:

1. Los Angeles-Long Beach, CA
2. Visalia-Porterville-Hanford, CA
3. Bakersfield, CA
4. Fresno-Madera, CA
5. Sacramento-Roseville, CA
6. Houston-The Woodlands, TX
7. Dallas-Fort Worth, TX-OK
8. Modesto-Merced, CA
9. Las Vegas-Henderson, NV-AZ
10. Phoenix-Mesa-Scottsdale, AZ

The six cities without any days of unhealthy ozone or particle pollution are Bismarck, N.D.,Cape Coral-Fort Myers-Naples, Fla., Elmira-Corning, N.Y., Fargo-Wahpeton, N.D.-Minn., Rapid City-Spearfish, S.D. and Salinas, Calif.

Los Angeles-Long Beach, CA

Pier G, foreground, sits idle at the Port of Long Beach in Long Beach, Calif., Dec. 3, 2012.
Tim Rue—Bloomberg/Getty Images

Los Angeles has topped the list of the most ozone-polluted cities in 15 out of the last 16 American Lung Association reports. And though the city has actually reduced the total annual days of ozone pollution, there was still an unhealthy level of ozone still for more than two months.

Visalia-Porterville-Hanford, CA

Canadian geese fly over a tumbleweed-covered fallow field at sunrise on Feb. 5, 2014 near Visalia, California.
David McNew—Getty Images

The number of days of unhealthy ozone levels in Visalia, a Central California metropolitan area of more than 600,000 people, declined to the lowest level in the 2015 report.

Bakersfield, CA

Oil pumps stand at the Chevron Corp. Kern River oil field in Bakersfield, Calif., March 29, 2011.
Ken James—Bloomberg/Getty Images

Mountains that surround Bakersfield on three sides trap pollution in this central California city.

Fresno-Madera, CA

The downtown Fresno skyline with heavy haze is seen, Jan. 17, 2014.
Craig Kohlruss—MCT/Getty Images

Fresno, another city in central California, is home to the greatest number of at-risk people, according to the report.

Sacramento-Roseville, CA

California’s capital city is home to more than 200,000 people with asthma, including 50,000 children.

Houston-The Woodlands, TX

A boat passes a refinery standing along the Houston Ship Channel in Houston, Texas, Jan. 30, 2014.
Scott Dalton—Bloomberg/Getty Images

Houston, home to a significant number of heavy industry companies, has instituted a number of policies in recent years that have actually improved air quality.

Dallas-Fort Worth, TX

A 150-foot derrick towers over traffic along Interstate 35W, left, positioned on a natural gas well site on Dec. 17, 2008 in Fort Worth, Texas.
Robert Nickelsberg—Getty Images

The Dallas metropolitan area had an average of 16 days of unhealthy ozone pollution each year, according to the report.

Modesto-Merced, CA

Modesto is yet another Central California city to fail pollution standards.

Las Vegas-Henderson, NV

The M Resort in Henderson, Nev. on May 21, 2012.
Steve Marcus—AP

Las Vegas has hundreds of thousands of at-risk residents, including more than 175,000 people with asthma.

Phoenix-Mesa-Scottsdale, AZ

Morning view from the top of Piestawa Peak looking Southeast over Scottsdale, Paradise Valley, and Phoenix, Ariz.
Tim McGuire—Corbis

Phoenix, a newcomer to the top-ten list, saw reduced air quality in recent years.


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