WASHINGTON, Feb. 8, 2017 - Sulfur dioxide (SO2) emissions produced in the generation of electricity at power plants in the U.S. declined by 73 percent from 2006 to 2015, according to data from the Energy Information Administration (EIA).

The reduction is much larger than the decrease in coal-fired electricity generation over that period, which was 32 percent.

From 2014 to 2015, the most recent year with complete power plant emissions data, SO2 emissions fell 26 percent.

EIA says this is the largest annual drop in percentage terms in the previous decade.

Nearly all electricity-related SO2 emissions are associated with coal-fired generation, the agency notes.

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SO2 emissions chartEIA says that several factors have contributed to lower SO2 emissions:

  • Changes in the electricity generation mix. Electricity generation from coal fell 14 percent from 2014 to 2015, the data show. The agency says this drop was mostly offset by an increase in electricity generation from natural gas, but because natural gas has only trace amounts of sulfur, the net effect resulted in fewer SO2 emissions.
  • Installation of environmental equipment. To comply with the federal Mercury and Air Toxics (MATS) rule, several coal and oil-fired plants installed pollution control equipment. Plants had to comply by April 15, 2015, or for some plants that received one-year extensions, by April 15, 2016. During 2015, EIA says these plants burned 18 percent less coal than in 2014 and reduced their SO2 emissions by 49 percent.
  • Lower utilization of the most-polluting plants. Different coal-fired plants produce SO2 at different rates. The data show that plants that produce more than two metric tons of SO2 per million kilowatt-hours of electricity generation were used less often in 2015.

EIA notes that Ohio, Indiana, and Kentucky had the highest SO2 emissions rates in 2014, but each state experienced substantial decreases in 2015. These states were among the top five states to retire coal capacity during 2015, EIA says, collectively retiring more than one-third of all retired coal-fired capacity in 2015.