Annual emissions of sulfur dioxide and nitrogen oxides in the U.S. power sector dropped by 88 percent and 76 percent, respectively, between their peaks in 1997 and 2017, according to a Dec. 11 report from the U.S. Energy Information Administration.

• Coal’s share of generation declined to 30 percent in 2017 from more than 50 percent in 1997, while natural gas and renewables grew to nearly 50 percent from 26 percent over the same period.
• Compliance with environmental rules was instrumental in cutting emissions, with most of the reductions occurring in the 27 states regulated under the Cross-State Air Pollution Rule — states which accounted for over 80 percent of coal-based generation and national sulfur and nitrogen oxide emissions in 1997.
• To comply with the Mercury and Air Toxics Standards, with an April 2015 initial deadline, electric generators installed scrubbers or dry sorbent injection equipment, which also removes sulfur and nitrogen oxides in addition to the targeted pollutants.