America's 10 Dirtiest Cities

The American Lung Association, in its report State Of The Air 2010, finds seven California metropolitan areas with air quality bad enough that they make it on the list of the Top 10 Dirtiest Cities in America. The 20 million people in these cities are at higher risk of asthma and chronic bronchitis.

No. 1: Bakersfield, Calif. 
Population: 800,000
Short-term particle pollution rank: 1
Year-round particle pollution rank: 2
Ozone pollution rank: 2
Hot, dusty and surrounded by California's San Joaquin Valley oil fields, Bakersfield has all the ingredients for the worst air in the nation

No. 2: Los Angeles-Long Beach-Riverside, Calif. 
Population: 17.8 million
Short-term particle pollution rank: 4
Year-round particle pollution rank: 3
Ozone pollution rank: 1
University of Calgary researchers found in 2008 that salty coastal air mixed with sunshine and pollutants helps create unexpectedly high levels of ground-level ozone.

No. 3: Fresno-Madera, Calif. 
Population: 1.1 million
Short-term particle pollution rank: 2
Year-round particle pollution rank: 6
Ozone pollution rank: 4
Cars, agriculture, petroleum and mega-dairies all contribute to the brown haze that hangs over the San Joaquin Valley.

No. 4: Visalia-Porterville, Calif. 
Population: 430,000
Short-term particle pollution rank: 8
Year-round particle pollution rank: 3
Ozone pollution rank: 3
Proximity to the giant trees of Sequoia National Park isn't enough to clean Visalia's smoggy San Joaquin Valley air.

No. 5: Hanford-Corcoran, Calif. 
Population: 150,000
Short-term particle pollution rank: 10
Year-round particle pollution rank: 8
Ozone pollution rank: 6
Hundreds of aircraft based at the giant Naval Air Station in nearby Lemoore doesn't help Hanford'sair quality.

No. 6: Phoenix-Mesa-Scottsdale, Ariz.

Population: 4.3 million

Short-term particle pollution rank: 14

Year-round particle pollution rank: 1

Ozone pollution rank: 11

Asthmatics used to flock to Phoenix for clean air. Yet today the Valley of the Sun's inversion layer traps pollutants, creating the city's "Brown Cloud."

No. 7: Birmingham-Hoover-Cullman, Ala.

Population: 1.2 million

Short-term particle pollution rank: 5

Year-round particle pollution rank: 7

Ozone pollution rank: 19

Three old coal-fired power plants contribute to high levels of sulfur dioxide, nitrogen oxide, soot and mercury around Birmingham.

No. 8: Modesto, Calif.

Population: 511,000

Short-term particle pollution rank: 9

Year-round particle pollution rank: 14

Ozone pollution rank: 22

Home to the largest winery in the world, operated by E&J Gallo, which also runs world's largest wine bottle factory here.

No. 9: Sacramento-Arden-Arcade-Yuba City, Calif./Nev.

Population: 2.4 million

Short-term particle pollution rank: 6

Year-round particle pollution rank: n/a

Ozone pollution rank: 5

Sacramento incentivizes residents to trade in gasoline lawn mowers for electric ones, diesel-powered trucks for hybrid ones and old wood stoves for new ones.

No. 10: Pittsburgh-New Castle, Pennsylvania

Population: 2.4 million

Short-term particle pollution rank: 3

Year-round particle pollution rank: 5

Ozone pollution rank: n/a

One-hundred seventy-five million Americans live in counties with unhealthy air.