Older electricity generating units—those that began operating in or before 1978—provided 45% of electricity from fossil fuel units in 2010 but produced a disproportionate share of emissions, both in aggregate and per unit of electricity generated.
Overall, in 2010, older units contributed 75% of SO2 emissions, 64% of NOx emissions, and 54% of CO2 emissions from fossil fuel units, said a new Government Accountability Office report released May 18. The report itself is dated April 18 and was submitted by GAO to Sen. Sheldon Whitehouse, D-R.I., Chairman of the Subcommittee on Oversight of the Senate Committee on Environment and Public Works. Whitehouse has been a particularly aggressive supporter of new air initiatives, including The U.S. Environmental Protection Agency’s new Mercury and Air Toxics Standards (MATS).
For each unit of electricity generated, older units collectively emitted about 3.6 times as much SO2, 2.1 times as much NOx, and 1.3 times as much CO2 as newer units. The difference in emissions between older units and their newer counterparts may be attributed to a number of factors.
- First, 93% of the electricity produced by older fossil fuel units in 2010 was generated by coal-fired units. Compared with natural gas units, coal-fired units produced over 90 times as much SO2, twice as much CO2 and over five times as much NOx per unit of electricity, GAO noted.
- Second, fewer older units have installed emissions controls, which reduce emissions by limiting their formation or capturing them after they are formed. Among coal-fired units—which produce nearly all SO2 emissions from electric power generation—about 26% of older units used controls for SO2, compared with 63% of newer units. Controls for NOx were more common among all types of fossil fuel units, but these controls vary widely in their effectiveness. Among older units, 14% had installed selective catalytic reduction (SCR) equipment, the type of control capable of reducing the greatest amount of NOx emissions, compared with 33% of newer units. In addition, about 38% of older units did not have any controls for NOx, compared with 6% of newer units.
- Third, lower emissions among newer units may be attributable in part to improvements in the efficiency with which newer units convert fuel into electricity.
“Nonetheless, older units remain an important part of the U.S. electricity generating sector,” GAO noted. “In 2010, older units were responsible for 45 percent of total electricity production from fossil fuel units. In certain regions, older units played a more significant role in providing electricity. For example, in the Mid-Atlantic and Great Lakes regions, older units generated 64 percent and 70 percent, respectively, of electricity coming from fossil fuel units. Some older units also provide services that help ensure the reliable flow of electricity to certain regions; for example, some older units may be used to help restart the electricity system in the event of a blackout.”
Report prompted by New Source Review inquiry
The GAO report responds in part to a Congressional request for information on electricity generation and emissions at U.S. electricity generating units and the implementation of New Source Review (NSR).
Under the Clean Air Act (CAA), the U.S. Environmental Protection Agency establishes national ambient air quality standards for six pollutants that states are primarily responsible for attaining. States attain these standards, in part, by regulating emissions of these pollutants from certain stationary sources, such as electricity generating units. Numerous CAA requirements apply to electricity generating units, including NSR, a permitting process established in 1977. Under NSR, owners of generating units must obtain a preconstruction permit that establishes emission limits and requires the use of certain pollution control technologies.
In limiting NSR’s requirements to facilities built or undertaking major modifications after Aug. 7, 1977, Congress allowed existing facilities to defer installation of pollution controls until they made a major modification, with the expectation that over time all facilities would either install such equipment or shut down, thereby lowering overall emissions. According to EPA data, 1,485 older units (43% of fossil fuel units) were still in operation in 2010. Some research suggests that many of these older units continue to operate without emissions controls, and in June 2002, GAO reported that older fossil fuel electricity generating units emitted air pollution at higher rates than newer units.
Notable is that new EPA air rules, like MATS and the Cross-State Air Pollution Rule, are now forcing many of those older coal plants to be shut.