The 10 Most Polluted Cities in America

10. Cleveland-Akron-Canton, OH

> Average year-round particle pollution: 12.5 ug/M3

> People with asthma: 339,464

> Population: 3,501,538

> High ozone days per year: 10.8

Home to more than 3.5 million people, the Cleveland metro area has some of the most polluted air in the country. Cleveland was actually one of five cities that yielded its lowest yearly average particle pollution in the ALA’s 2015 report. Despite the improvement, the metropolitan area still had a much higher than acceptable level of particle pollution. Particle pollution is often the byproduct of the burning of fossil fuels in such places as factories, power plants, and personal vehicles. Manufacturing activity — a long time major economic engine in the Cleveland area — has certainly contributed to the city’s poor air quality. Nearly 340,000 Cleveland residents suffer from asthma, and 232,000 area adults have been diagnosed with COPD. Especially vulnerable to pollution related health risks are the area’s more than 1.3 million residents younger than 18 or older than 65.

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9. Pittsburgh-New Castle-Weirton, PA-OH-WV

> Average year-round particle pollution: 13.4 ug/M3

> People with asthma: 256,406

> Population: 2,659,937

> High ozone days per year: 12.5

During the golden age of steel production in Pittsburgh, the area was one of the most polluted cities in the United States. By many accounts, between the factories and the smoke from the coal that was used to heat residents’ homes, the sky was black with smoke before 9 a.m. every morning. While Pittsburgh is a much less industrial city today and the air quality has improved somewhat, the city remains one of the most polluted cities in the country. According to Nolen, the biggest source of pollution in the area is the U.S. Steel plant. The city received failing grades in ozone pollution as well as in long-term and short-term particle pollution. More than a quarter of a million Pittsburgh residents have asthma, a condition which can be exacerbated by air pollution.

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8. Cincinnati-Wilmington-Maysville, OH-KY-IN

> Average year-round particle pollution: 13.6 ug/M3

> People with asthma: 213,812

> Population: 2,196,629

> High ozone days per year: 12.2

Like most cities with high particle pollution, the Cincinnati metro area also has a problem with severe ozone pollution. The greater Cincinnati area has been under several air quality advisories this summer due to dangerously high ozone levels. Similar to California’s Central Valley, high traffic volumes in the Cincinnati area contribute to high pollution levels. In addition, the city is located in a valley, which, like the mountains surrounding Central Valley, helps trap emissions.