New England's power grid operator says emissions of sulfur dioxide and nitrogen oxides by electricity generators have decreased dramatically since 2001.
ISO New England says emissions of sulfur dioxide fell 60 percent and emissions of nitrogen oxides dropped 52 percent between 2001 and 2011.
The ISO says emission controls on power plants have helped. But it says the decline is mainly due to increased use of natural gas-fired generators, which are more efficient and have fewer emissions than oil- and coal-fired generators.
As of 2011, natural gas accounted for 52 percent of the region's energy production, up from 15 percent in 2000. Oil accounted for less than 1 percent of energy production, down from 22 percent in 2000. Coal has fallen from 18 percent to 6 percent during that time.
This program aired on December 10, 2012. The audio for this program is not available.