Georgia Power's Plant Scherer learned the answer during a project that aimed to halve the NOx emissions from three units, only one of which fires PRB coal. Test results confirmed that overfire air can reduce formation of the pollutant while keeping increases in CO and unburned carbon to a minimum. And a comparison of the test results at Scherer with those from another plant in the Southern Company fleet confirms that coal composition has a significant impact on NOx emissions, and NOx emissions from boilers burning PRB coal are independent of boiler size.