SO2 emissions from power plants down 73% in US in 2006-2015: EIA

From 2014 to 2015 SO2 emissions fell 26% “the largest annual drop in percentage terms in the previous decade” it said.

EIA identified several factors which contributed to lower SO2 emissions, including changes in the electricity generation mix.
Electricity generation from coal fell 14% from 2014 to 2015. “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” EIA said.

Secondly, to comply with the federal Mercury and Air Toxics (MATS) rule, several coal and oil-fired plants installed pollution control equipment, EIA said.
Plants had to comply by April 15, 2015, or for some plants that received one-year extensions, by April 15, 2016. Two types of pollution control technologies installed for MATS compliance that also reduced SO2 emissions are dry sorbet injection systems (DSI) and flue gas desulfurization (FGD) systems or scrubbers, EIA added.
Between December 2014 and April 2016, DSI systems were installed on 15 GW of coal capacity, and FGD scrubbers were installed on 12 GW of coal capacity. During 2015, these plants burned 18% less coal than in 2014 and reduced their SO2 emissions by 49%, it said.

Thirdly, there was a “lower utilization of the most-polluting plants,” as plants that produce more than two metric tons of SO2 per million KWh of electricity generation were used less often in 2015.

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