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 Perkins County, Nebraska, and

Phelps County, Nebraska, give the percentage contributions from specific air pollution sources.  The Perkins County Seat is Grant, Nebraska, and the Phelps County Seat is Holdrege, Nebraska.