The 20 Dirtiest Cities in the U.S.

On the state level, California regulations on carbon emissions such as a cap-and-trade programs, and reducing vehicle emissions should help improve the air quality in its cities.

Further improvements will be made at the federal level as well. The Environmental Protection Agency's expected rules on power plants will lead to companies either retrofitting plants with new technology, or closing power plants altogether, reports Christopher Helman.

Data from The American Lung Association's State of the Air 2011 report was used to compile this list.