(KRON) — California is home to some of the cities with the worst air pollution in the nation, according to the latest State of the Air report from the American Lung Association.

“Millions of Americans are still breathing unhealthy air,” the ALA says. More than one in three Americans currently live in areas with unhealthy levels of air pollution, the report states.

The report lays out two types of air pollution: particle pollution and ozone pollution. Particle pollution is a mixture of tiny bits of solids and liquids in the air that we breathe. Ozone pollution, often referred to as smog, is a result of pollutants “cooking” together in the sunlight and chemically reacting to form ozone. Sometimes this pollutant is referred to as “ground level ozone” to help distinguish it from the ozone that protects us from the sun.

People of color are carrying a larger share of the unhealthy air burden than their white counterparts according to the report. Nearly 54% of the 120 million people who live in counties that failed to meet at least one air quality measurement are people of color.

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Bakersfield ranked as the metropolitan area with the worst short-term particle pollution, and it tied with Visalia, both in the Central Valley. However, Los Angeles is the city with the worst ozone pollution in the nation, as it has been for all but one of the past 24 years.

(Photo by Mario Tama/Getty Images)

Most Polluted Cities by Year-Round Particle Pollution

(Some cities in the study were tied, they are reflected in the list above.)

What are the factors contributing to pollution on the West Coast? Particle pollution can come from factories, gasoline and diesel-powered vehicles and equipment. Wood stoves and residential fireplaces can also contribute to particle pollution. Wildfires have contributed greatly to the growing number of days and locations that navigate unhealthy levels of particle pollution. An expert tells KRON4 that wildfires are most often sparked by people, and populations, particularly in places along the Wildland Urban Interface, are growing. These growing populations could mean a higher likelihood of wildfires and poor air quality.

Most Polluted Cities by Ozone

The State of the Air report also describes the health effects of breathing polluted air. Research has shown that particle pollution is connected to increased mortality in infants and an increase in hospital admission for cardiovascular disease and chronic obstructive pulmonary disease. It has also been shown to be connected to the increased severity of asthma attacks and hospitalization for asthma among children.

Ozone pollution can be just as dangerous. According to recent research, short-term exposure to ozone, even at low levels, likely increases the risk of premature death, especially for older adults. Those most at risk from ozone pollution include pregnant people and their fetuses, children, anyone age 65 or older or people with existing lung disease.

As for metropolitan areas with the cleanest air, five can be found on the East Coast. They are listed below in alphabetical order:

  • Asheville-Marion-Brevard, NC
  • Bangor, ME
  • Greenville-Kinston-Washington, NC
  • Lincoln-Beatrice, NE
  • Rochester-Batavia-Seneca Falls, NY
  • Urban Honolulu, HI
  • Wilmington, NC