The following air emission charts show the emissions from our fossil fuel fired power plants over the prior several years. The trend indicates that the NOx and Sulfur Dioxide (SO2) rates have decreased over the past several years as a result of the voluntary installation of additional pollution controls at our coal-fired power plants. Also, due to the retirement of Four Corners Units 1, 2 and 3 in 2013 and to the retirement of Cholla Unit 2 in 2015, emissions of criteria pollutants are trending downward.