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10 most polluted cities

These 10 cities had the highest level of year-round pollution and some of the highest incidences of heart and lung issues as well, according to the American Lung Association's annual report.

8. Pittsburgh

most polluted cities pittsburgh
  • Population: 2.5 million
  • Cardiovascular cases: 705,000
  • Rank among ozone-polluted cities: 24

The air in this steel town was once so polluted with coal and coke soot that streetlights were sometimes turned on at high noon. Now, much of Pittsburgh's pollution comes from Ohio, West Virginia and further west, according to Neil Donahue, who studies transport pollution at Carnegie Mellon University.

While coal-burning power plants strung for hundreds of miles along the Ohio River are still a problem, many plants can switch back and forth between coal and natural gas. So when gas prices drop, as they did last year, the plants rely more heavily on that cleaner-burning fuel, which accounts for some of the city's improved air quality.

With its deep valleys, however, Pittsburgh's topography works against it, especially during the hazy days of summer, according to Donahue. That's when warm blankets of air bottle up pollution in the city's deep river valleys for days at a time.

Source: American Lung Association's State of the Air 2013 report
1. Ranking is based on year-round particle pollution. This is in the air we breathe and consists of such things as dust, metals, smoke, exhaust, pollen and acids, like nitrates and sulfates. 2. The data for cardiovascular disease includes all cases in a given city whether they were caused by air pollution or not. Air pollution puts those with cardiovascular disease at a higher risk of health issues. 3. Ozone is created when a chemical or fossil fuel, like coal or gasoline, is partially burned and the unburned hydrocarbons, when combined with ultraviolet light, form a gas that is very corrosive to lungs.
  @CNNMoney - Last updated April 24 2013 12:33 PM ET

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