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 Morton County, North Dakota, and

Mountrail County, North Dakota, give the percentage contributions from specific air pollution sources.  The Morton County Seat is Mandan, North Dakota, and the Mountrail County Seat is Stanley, North Dakota.