D.C., along with much of Maryland and Northern Virginia, is getting failing grades in an annual report on air quality.
The American Lung Association says "positive air quality trends" continue, but air quality remains poor in America's most-polluted cities. Officials credit the protection of the Clean Air Act for continued cleanup of coal-fired power plants, and a reduction of emissions from diesel engines and large vehicles.
The group's annual State of the Air report gives the D.C. area a grade of F when it comes to unhealthy levels of ozone air pollution. The Lung Association calls the nation's air quality standards "woefully outdated."
Santa Fe, New Mexico ranks as the cleanest city in America, while Los Angeles tops the list of most ozone-polluted cities.