American Lung Association, State of the Air

"State of the Air" is the American Lung Association's annual national air quality "report card." It uses the most recent air pollution data, compiled by the U.S. Environmental Protection Agency (EPA), for the two most widespread types of pollution—ozone (smog) and particle pollution (PM2.5, also known as soot). The report grades counties and ranks cities and counties based on their scores for ozone, year-round particle pollution and short-term particle pollution levels. Since 2000, the American Lung Association has analyzed data from official air quality monitors to compile the "State of the Air" report.