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 Otoe County, Nebraska, and

Pawnee County, Nebraska, give the percentage contributions from specific air pollution sources.  The Otoe County Seat is Nebraska City, Nebraska, and the Pawnee County Seat is Pawnee City, Nebraska.