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 Pipestone County, Minnesota, and

Polk County, Minnesota, give the percentage contributions from specific air pollution sources.  The Pipestone County Seat is Pipestone, Minnesota, and the Polk County Seat is Crookston, Minnesota.