Special Report

The 10 Most Polluted Cities in America

7. San Jose-San Francisco-Oakland, CA
> Average year-round particle pollution:
13.8 ug/M3
> People with asthma: 744,481
> Population: 8,469,854
> High ozone days per year: 8.8

The San Francisco Bay Area, which includes the cities of Oakland and San Jose, has the third-largest combined population at risk of illness due to air pollution, at close to 8.5 million. The metro area reported the most days with high particle pollution on record because of the addition of San Joaquin county to the region. The county was the only one in the metro area to fail the ALA’s test for ozone levels and short- and long-term particle pollution. San Joaquin county had an average of 54 days a year in either orange-level conditions, which are unhealthy for people with sensitive respiratory tracts, or in red conditions, which are unhealthy for everyone.

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6. El Centro, CA
> Average year-round particle pollution:
14.3 ug/M3
> People with asthma: 15,439
> Population: 176,584
> High ozone days per year: 16.2

Like many of the most polluted metro areas in California, El Centro residents suffer from high levels of both ozone and particle pollution. Located in Imperial County, El Centro residents have experienced an average of 16 high-ozone days a year, which is sixth-worst in the country. Known more commonly as smog, high ozone levels occur when fumes from burning fossil fuels are exposed to sunlight. Prolonged exposure to high ozone levels can exacerbate existing respiratory conditions and contribute to early death. More than 15,000 El Centro residents live with asthma, and 5,700 adult residents have been diagnosed with COPD.

5. Los Angeles-Long Beach, CA
> Average year-round particle pollution:
15.1 ug/M3
> People with asthma: 1,607,111
> Population: 18,351,929
> High ozone days per year: 117.7

Los Angeles port’s cargo volume this past July was the highest ever in its over 100-year history. According to the EPA, high traffic through the port creates higher emissions that contribute to poor air quality throughout the region. High concentrations of power plants, including numerous oil and gas, petroleum, and electricity plants, release tens of millions of metric tons of carbon emissions each year. While the area is among the nation’s most polluted, Los Angeles reported its lowest pollution levels since the ALA started producing this report. Still, in Los Angeles, residents have experienced an average of 117.7 days of high ozone levels each year, the most of any U.S. metropolitan area.

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4. Modesto-Merced, CA
> Average year-round particle pollution:
15.7 ug/M3
> People with asthma: 69,027
> Population: 788,719
> High ozone days per year: 22.3

Modesto residents have experienced an average of 22 high ozone days per year. Only seven metro areas in the country had a greater number of high ozone days. Located almost directly in the center of California’s Central Valley, an area surrounded on three sides by mountains that limit wind and annual rainfall, polluted air stagnates in Modesto. The city was one of six in the country that failed to meet federal air quality standards and where particle pollution worsened since last year’s report. Nearly 70,000 Modesto residents suffer from asthma, and over 25,000 area adults have been diagnosed with COPD.