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EIA: SO2 and NOx emissions last year were at lowest level since 1990

From the February 28, 2013 issue of Public Power Daily

Originally published February 28, 2013

By Robert Varela
Editorial Director

Emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx) from the electric power sector in 2012 declined to their lowest level since the passage of the Clean Air Act Amendments of 1990, the Energy Information Administration said Feb. 27. The decline in emissions is due primarily to three factors, EIA said: an increasing number of coal-fired units retrofitted with flue-gas desulfurization, or scrubbers; coal plants switching to lower-sulfur coal; and use of selective catalytic reduction, selective noncatalytic reduction or low-NOx burners to limit NOx emissions. In recent years the decreased use of coal for electric power generation because of cheaper natural gas has also played a significant role in the SO2 and NOx emissions declines, EIA said. 

The decline in SO2 and NOx emissions began soon after enactment of the 1990 Clean Air Act Amendments, which established a national cap-and-trade program for SO2 and required other controls for NOx emissions from fossil-fueled electric power plants, EIA said. Because coal-fired units accounted for a large share of SO2 and NOx emissions, the program provided an economic incentive for coal-fired power plants to reduce emissions by installing pollution control systems, burning lower-sulfur coal, or, for high-emitting plants, dispatching less electricity. 

In 2005, the Environmental Protection Agency developed the Clean Air Interstate Rule, a cap-and-trade program intended to reduce SO2 and NOx emissions in the eastern half of the United States, EIA said. While that rule and several proposed alternatives have been challenged in the courts, 91 GW of coal-fired power capacity was retrofitted with flue-gas desulfurization scrubbers between 2005 and 2011. By the end of 2011, 60 percent of the U.S. coal fleet had scrubbers installed, and 67 percent had installed either selective catalytic reduction or selective noncatalytic reduction, the agency said. 

Additional state requirements and settlements under the Clean Air Act's New Source Review program also contributed to the increases in coal plant environmental retrofits, EIA said. The Mercury and Air Toxics Standards, issued in 2011 and set to take effect in 2015, do not directly regulate SO2 or NOx but the standards should lead coal-fired power plants to install equipment that further limits SO2 emissions, the agency said. 

The reduction in SO2 and NOx emissions through the late 2000s was primarily the result of coal plants employing strategies to reduce emissions, not a reduction in the use of coal overall, EIA said. In fact, coal generation set record highs in 2007 when significant SO2 reduction was already under way. However, since late 2008, two major contributors of declining SO2 and NOx emissions have been: historically low natural gas prices, which have contributed to shifting some generation from coal to natural gas; and lower overall generation from coal in 2012.


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