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 Oliver County, North Dakota, and

Pembina County, North Dakota, give the percentage contributions from specific air pollution sources.  The Oliver County Seat is Center, North Dakota, and the Pembina County Seat is Cavalier, North Dakota.