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 Hays County, Texas, and

Hemphill County, Texas, give the percentage contributions from specific air pollution sources.  The Hays County Seat is San Marcos, Texas, and the Hemphill County Seat is Canadian, Texas.