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 Zapata County, Texas, and

Zavala County, Texas, give the percentage contributions from specific air pollution sources.  The Zapata County Seat is Zapata, Texas, and the Zavala County Seat is Crystal City, Texas.