America's Most Polluted Cities Revealed

Los Angeles, a habitual offender on the most polluted cities lists, was rated the most polluted city by ozone and year-round for particle pollution.

"Particulate pollution is a major killer in the United States," Edelman said. "Exposure to particle pollution increases the chance for lung cancer and may explain, at least in part, lung cancer in non-smoking individuals. … The more we study the more we learn and frankly the more difficult and terrifying it seems to be exposed to these high levels of pollution."

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For the first time, Pittsburgh scored poorly in short-term particle pollution, overtaking habitual offender Los Angeles. Pittsburgh also came in second on the list of most polluted cities for year-round particle pollution.

George Leikauf, a professor of environmental health at the School of Public Health at the University of Pittsburgh, found the results of the study only "a little surprising."

The Washington, D.C. and Baltimore Areas appeared on the most polluted lists for both ozone pollution and short-term particle pollution.

"We knew that the eastern seaboard has had trouble with particulate matter. It's still a problem," Leikauf said. "I'm not an apologist for Pittsburgh. … Particulate has been associated with more deaths than ozone. If you had to pick your poison, you'd rather have ozone than particulate matter."

Although much of the country may have a stereotype of Pittsburgh as a blue collar, steel mill town, Leikauf says that's no longer the case. According to him, more than 80 percent of western Pennsylvania's particulate matter actually drifts from Ohio power plants.

"It turns out we don't have very many steel mills at all anymore," Leikauf said. "These are fine particles. They stay suspended in the air. You can detect them in the Antarctic. In fact, some of California's air pollution is coming from China."