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 Sanilac County, Michigan, and

Schoolcraft County, Michigan, give the percentage contributions from specific air pollution sources.  The Sanilac County Seat is Sandusky, Michigan, and the Schoolcraft County Seat is Manistique, Michigan.