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 La Plata County, Colorado, and

Lake County, Colorado, give the percentage contributions from specific air pollution sources.  The La Plata County Seat is Durango, Colorado, and the Lake County Seat is Leadville, Colorado.