Abstract: The Environmental Protection Agency (EPA) compiles data on emission tonnages of air pollutants for US counties.  US Air Quality Gradebook ("AirGrades") source sheets such as this one for Arapahoe County, Colorado, and

Archuleta County, Colorado, give the percentage contributions from specific air pollution sources.  The Arapahoe County Seat is Littleton, Colorado, and the Archuleta County Seat is Pagosa Springs, Colorado.