Air Pollution US
iOS iPhone Weather
Air Pollution US is for current and forecasted air quality for hundreds of US cities. The app uses data from the AirNow program.
If you are especially sensitive to air quality or are near harmful pollution levels, you can know not to exercise that day, keep outdoor time to a minimum, or a wear a respiratory breathing mask.
App uses free data provided by the United States Environmental Protection Agency--AirNow.
Important update: bug fixes, and I added a disclaimer.