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 Fergus County, Montana, and

Flathead County, Montana, give the percentage contributions from specific air pollution sources.  The Fergus County Seat is Lewistown, Montana, and the Flathead County Seat is Kalispell, Montana.