Abstract: The Environmental Protection Agency (EPA) compiles data on emission tonnages of air pollutants for US counties.  US Air Quality Gradebook ("AirGrades") emission gradesheets compare emission densities, in tons per square mile per year, for all measured counties in the

United States.  This gradesheet shows South Dakota emission grades for Pennington-Ziebach counties.  Grading A-F is on the bell curve, comparing the more than 3,000 US counties having EPA data on air pollution emissions.