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 Genesee County, Michigan, and

Gladwin County, Michigan, give the percentage contributions from specific air pollution sources.  The Genesee County Seat is Flint, Michigan, and the Gladwin County Seat is Gladwin, Michigan.