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 McLean County, North Dakota, and

Mercer County, North Dakota, give the percentage contributions from specific air pollution sources.  The McLean County Seat is Washburn, North Dakota, and the Mercer County Seat is Stanton, North Dakota.