Reporter Dina Cappiello found shockingly high levels of toxic air pollutants in neighborhoods around Houston and Southeast Texas. According to the American Lung Association, Los Angeles, Pittsburgh, Bakersfield, and Birmingham also rank among the cities with the most air pollution.

Which cities have the cleanest air? Cheyenne, Wyoming tops the list, followed by Santa Fe, New Mexico; Honolulu, Hawaii; and Great Falls, Montana.

>> Worried about your town? Find out if the EPA is tracking toxic releases in your zip code. Check out the Air Quality Index for local air quality conditions and forecasts.