California cities rank at the top of the list of the areas with the worst air pollution, according to the American Lung Association's "State of the Air" report for 2015.

Los Angeles-Long Beach ranked first on the list of highest pollution by ozone, while Fresno-Madera ranked at the top of the list by year round particle pollution and short-term particle pollution. This year's report has shown improvement over a year ago, said Harold Wimmer, the association's national president and chief executive.

"This year's report shows encouraging progress, evidence of the success of our long fight for cleaner, healthier air for all Americans," Wimmer said. "Paired with that progress is evidence of troubling challenges."

After Los Angeles, areas with the highest ozone levels include Visalia-Porterville-Hanford, Calif.; Bakersfield, Calif.; Fresno-Madera; Sacramento-Roseville, Calif.; Houston-The Woodlands, Texas; Dallas-Fort Worth; Modesto-Merced, Calif.; Las Vegas-Henderson; and Phoenix-Mesa-Scottsdale.

Areas with the highest year round particle pollution after Fresno include Bakersfield, Visalia, Modesto, Los Angeles, El Centro (Calif.), San Jose-San Francisco-Oakland, Cincinnati-Wilmington-Maysville, Pittsburgh-New Castle (Ohio)-Weirton (W. Va.), and Cleveland-Akron-Canton.

Areas with the highest short-term particle pollution after Fresno include Bakersfield, Visalia, Modesto, Los Angeles, San Jose, Salt Lake City-Provo-Orem, Logan (Utah and Idaho), and Fairbanks (Alaska).

For the full list of areas with the worst air pollution, click here. For a full list of areas with the least air pollution, click here.