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 Weld County, Colorado, and

Yuma County, Colorado, give the percentage contributions from specific air pollution sources.  The Weld County Seat is Greeley, Colorado, and the Yuma County Seat is Wray, Colorado.