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 Ogemaw County, Michigan, and

Ontonagon County, Michigan, give the percentage contributions from specific air pollution sources.  The Ogemaw County Seat is West Branch, Michigan, and the Ontonagon County Seat is Ontonagon, Michigan.