Slide #4: The Four Foes of Clean Air

The four main pollutants emitted by coal-fired power plants are sulfur dioxide (SOX), nitrogen oxides (NOx), mercury, and carbon dioxide. These four are not the only pollutants that coal-fired power plants emit, but they create the biggest air quality problems facing America.

Sulfur Dioxide (SOX)

Coal contains sulfur in varying quantities, depending on the type. SOX is created when sulfur reacts with oxygen in the combustion process. Coal-fired power plants are responsible for 10 million tons of SOX emissions per year, about two-thirds of the U.S. total.

Nitrogen Oxides (NOx)

Burning any fuel at a high temperature will result in formation of NOx. Coal-fired power plants are responsible for about 4.5 million tons of NOx emissions per year, about one-fourth of the U.S. total.

Mercury

Mercury is a naturally occurring element and some of the mercury in the environment comes from natural sources. But human activities release mercury in quantities that may exceed natural inputs by a 2 to 1 margin. Coal-fired power plants are responsible for an estimated 45 tons of mercury emissions per year, roughly one-third of the total human-caused mercury emissions in the U.S.

Carbon Dioxide

Carbon dioxide is an unavoidable byproduct of burning carbon-based fuels. Each year, human activity in the U.S. puts about 5.8 billion metric tons of carbon dioxide into the atmosphere. About one-third of those carbon emissions come from generating electricity, and most of the power sector's emissions come from coal-fired power plants.

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