This is an archived article and the information in the article may be outdated. Please look at the time stamp on the story to see when it was last updated.

(NEXSTAR) – The World Health Organization announced this week that 99% of the world’s population breathes poor-quality air, that when inhaled over time can cause cardiovascular and respiratory disease.

While cities in the developing world have the worst air quality, according to the WHO, pollution is still a problem in American cities. There are chronic sources of air pollution, like vehicle traffic on busy highways, as well as seasonal issues, like smoke from wildfires.

The American Lung Association tracks air pollution in U.S. cities., and California cities dominate its list of unhealthiest places.

The group’s annual report uses data from the Environmental Protection Agency on the presence of two types of pollutants: ozone (or smog) and particulate matter. Particulate matter has many sources, such as transportation, power plants, agriculture, fires and industry – as well as from natural sources like desert dust.

Using the EPA data, the report ranks the most and least polluted metro areas. On the list of 10 most polluted cities, California metro areas take up seven spots.

The California cities with the highest amount of ozone pollution (or smog) are:

  1. Los Angeles-Long Beach
  2. Bakersfield
  3. Visalia
  4. Fresno-Madera-Hanford
  5. Sacramento-Roseville
  6. San Diego-Chula Vista-Carlsbad
  7. San Jose-San Francisco-Oakland
  8. El Centro
  9. Chico
  10. Redding-Red Bluff

The cities with the worst year-round particle pollution are:

  1. Bakersfield
  2. Fresno-Madera-Hanford
  3. Visalia
  4. Los Angeles-Long Beach
  5. San Jose-San Francisco-Oakland
  6. El Centro
  7. Sacramento-Roseville
  8. Redding-Red Bluff

“Particulate matter, especially PM2.5, is capable of penetrating deep into the lungs and entering the bloodstream, causing cardiovascular, cerebrovascular (stroke) and respiratory impacts,” WHO said. “There is emerging evidence that particulate matter impacts other organs and causes other diseases as well.”

The American Lung Association also keeps track of which cities have the least air pollution. Only one California city ranked among the list of top 25 cities with the least amount of particle pollution: Salinas in Monterey County.

The ten U.S. cities with the cleanest air, free of particle pollution are:

  1. Urban Honolulu, Hawaii
  2. Kahului-Wailuku-Lahaina, Hawaii
  3. Cheyenne, Wyoming
  4. Wilmington, North Carolina
  5. Casper, Wyoming
  6. St. George, Utah
  7. Bellingham, Washington
  8. Elmira-Corning, New York
  9. Sioux Falls, South Dakota
  10. Duluth, Minnesota/Wisconsin

The Associated Press contributed to this report.