Special Report

The 10 Most Polluted Cities in America

5. Modesto-Merced, Calif.
> Year-round particle pollution rank: 5th worst
> Ozone pollution rank: 7th worst
> Adults with asthma: 49,029
> Population: 784,031

The Modesto metro area’s pollution problem is not limited to year-round particle pollution. Stanislaus County, which is part of the metro area, had an average of 21.2 high ozone days and 29.2 high particle pollution days, both receiving a failing grade from the ALA. The number of high particle pollution days increased in the Modesto area from the previous period as well. Like many of America’s most polluted cities, Modesto is located in the Central Valley region of California. In addition to causing significant farming problems, the drought has worsened the metro area’s pollution problem by keeping the pollution in the air. Part of the area’s drought may be attributable to the “Ridiculously Resilient Ridge” — a massive high-pressure ridge west of the region currently blocking storms coming in from the Pacific and naturally filtering the air.

4. Los Angeles-Long Beach, Calif.
> Year-round particle pollution rank: 4th worst
> Ozone pollution rank: the worst
> Adults with asthma: 1.2 million
> Population: 18.2 million

Although Los Angeles recorded its lowest levels of particle pollution, the area is still among the most polluted in the country. The metro area, which has more than 18 million residents, had an average of 77.5 days of high ozone levels, the highest in the country, and 25.2 days of high particle pollution days. The area received F grades in both measures from the ALA. Recently, the California Department of Environmental Protection released its first ever list of census areas most burdened by pollution in hopes that it will pressure local politicians to clean up the worst affected regions, including Los Angeles. The high number of residents with respiratory diseases is also likely of concern. More than 1.6 million residents suffered from asthma and more than 625,000 residents suffered from COPD.

3. Bakersfield, Calif.
> Year-round particle pollution rank: 3rd worst
> Ozone pollution rank: 3rd worst
> Adults with asthma: 52,552
> Population: 856,158

Although still one of the worst polluted metro areas in the country, Bakersfield moved up from the most polluted area last year to the third most polluted in the most recent report. Kern County, which makes up the Bakersfield metro area, had an average of 78.5 days of high ozone levels and 33.3 days of high particle pollution, both of which received a failing grade from the ALA. In late 2012, the San Joaquin Valley Air Pollution Control District passed an air pollution control plan with the goal of meeting federal EPA standards by 2019. EPA projections from that year show that only seven counties — all in California — were expected to fail emissions tests in 2020, including three in the Central Valley: Kern, Tulare and Merced.

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2. Visalia-Porterville-Hanford, Calif.
> Year-round particle pollution rank: 9th worst
> Ozone pollution rank: 2nd worst
> Adults with asthma: 36,397
> Population: 603,341

The Visalia metro area improved to its lowest levels of year-round particle pollution since last year, but air pollution in general remained a major problem. The Visalia metro area, which consists of Tulare County, had an average of 88.7 high ozone days per year, worse than all but two other U.S. counties. The county also had an average of seven high particle pollution days per year, enough to earn a failing grade from the ALA. Out of a population of roughly 600,000, more than 50,000 adults and nearly 20,000 children suffered from asthma.

1. Fresno-Madera, Calif.
> Year-round particle pollution rank: the worst
> Ozone pollution rank: 4th worst
> Adults with asthma: 68,342
> Population: 1.1 million

The Fresno metro area overtook Bakersfield as the most polluted metro area in the country in the ALA’s report. The two counties in the metro area, Madera and Fresno, were the nation’s worst and second-worst for year-round particle pollution. The air pollution got so severe this past winter that school and city officials would actually raise red flags throughout the city to warn students and parents when the air outside was dangerous to breathe, according to the Los Angeles Times. Out of its 1.1 million residents, nearly 100,000 suffered from asthma. Exhaust from agricultural operations, the area’s topography and smog drifting in from San Francisco and Sacramento all contributed to the air pollution.