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 St. Charles County, Missouri, and

St. Clair County, Missouri, give the percentage contributions from specific air pollution sources.  The St. Charles County Seat is Saint Charles, Missouri, and the St. Clair County Seat is Osceola, Missouri.