The explanation for the disparity between Maryland's leadership in reducing CO2 while it continues to produce filthy air rests, in part, with its aged, uncontrolled coal-fired power plants. Over half of those plants operate without modern pollution controls for nitrogen oxides — the precursor to ozone — and six of the 13 are in the bottom 20 percent of East Coast emitters of sulfur dioxide (SO2). EPA studies of our air attribute 44 percent of Maryland's sulfur dioxide emissions and 14 percent of nitrogen dioxide to coal plants. The burning of coal also releases toxic heavy metals including lead, mercury and arsenic, which can seriously affect the nervous system, heart, kidneys, bones and reproductive organs. While some Maryland coal power plants have state-of-the-art pollution-cutting technology, others have yet to invest in this expensive equipment. Two such plants, located in the Baltimore area, are the C.P. Crane and H.A. Wagner coal power plants.