Since 1997, an increasing fraction of electric power in the U.S. has been generated from natural gas. Here, we use data from continuous emissions monitoring systems (CEMS), which measure emissions at the stack of most U.S. electric power generation units, to investigate how this switch affected the emissions of CO2, NOx and SO2. Per unit of energy produced, natural gas power plants equipped with combined cycle technology emit on average 44% of the CO2 compared with coal power plants. As a result of the increased use of natural gas, CO2 emissions from U.S. fossil-fuel power plants were 23% lower in 2012 than they would have been, if coal had continued to provide the same fraction of electric power as in 1997. In addition, natural gas power plants with combined cycle technology emit less NOx and far less SO2 per unit energy produced than coal power plants. The increased use of
natural gas has therefore led to emissions reductions of NOx (40%) and SO2 (44%), in addition to those obtained from the implementation of emissions control systems on coal power plants. These benefits to air quality and climate should be weighed against the increase in emissions of methane,
volatile organic compounds and other trace gases that are associated with the production, processing, storage and transport of natural gas.
Over the last decade the increased use of natural gas power plants with combined cycle technology has significantly decreased the atmospheric emissions of CO2, NOx and SO2 associated with electric power generation in the U.S. Further reductions in these emissions can follow by converting a larger fraction of U.S. electric power production to natural gas, and by ensuring that all natural gas power plants are equipped with the latest combined cycle technology. These results illustrate some of the advantages to both climate and air quality that result from the switch from coal to natural gas.
These advantages must be considered in the perspective of the environmental impacts of natural gas production including methane and hydrocarbon leakage to the atmosphere that await more comprehensive quantification.