Smog over downtown Los Angeles: LA residents could be at risk for lung cancer thanks to the city's pollution, the third-worst in the country.

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eople who have never smoked yet live in areas with high pollution levels have a 20 percent higher risk of dying from lung cancer than those who live in areas with cleaner air, according to a new study from the Harvard School of Public Health. The study's authors suspect that the "fine particles" in air pollution might be to blame, corroborating similar reports from China linking coal heating with elevated lung cancer rates. Here's what you should know:

What did researchers find?
Out of 180,000 nonsmokers the researchers tracked over 26 years, 1,100 died from lung cancer. The researchers controlled for external factors, such as secondhand smoke and exposure to radon, and discovered that people in U.S. cities with more pollutants had a discernibly higher risk than those in places with cleaner air. 

How did researchers figure out pollution rates?
They matched their subjects' zip codes with air pollution data. That gave them an estimate of each person's exposure to pollution, measured in micrograms of particles per cubic meter of air. The researchers determined that for every 10 added units of air pollution exposure, a person's risk of lung cancer rose by 15 to 27 percent. But smokers are still much more susceptible to lung cancer than nonsmokers, with an increased risk described as "20-fold."

Could I be at risk?
More research is necessary to establish a concrete link. But scientists know which cities in the United States have the thickest air pollution. Bakersfield, Calif., has the worst air pollution in the United States. There's a three-way tie for second place between Mesa, Glendale, and Phoenix, Ariz. California's Los Angeles region comes in third. 

Sources: Reuters, Philly Magazine, State Column, The Atlantic