Anannual report of airpollutant emissions from the 100 largest U.S. power producers found that sulfurdioxide, nitrogen oxide and mercury emissions have dropped since 1990, whilecarbon dioxide emissions have increased.
Congresspassed major amendments to the Clean Air Act in 1990, triggering reductions incertain pollutants released in the process of generating electricity. Asemissions have plummeted, total generation and GDP have increased, according tothe report, "Benchmarking Air Emissions of the 100 Largest Electric PowerProducers in the United States." SO2 and NOx emissions have dropped 80%and 75%, respectively, since the passage of the amendments. Emissions rates permegawatt-hour of SO2 dropped by 85%, NOx by 81% and carbon dioxide by 16% in2014 compared with 1990.
However,overall carbon emissions were 14% higher among the top 100 power producers in2014 compared with 1990, but dropped by 12% between 2008 and 2014 as low-costnatural gas and renewable energy generation pushed coal out of the market andthe industry ramped up energy efficiency measures.
Thereport, a joint effort of Ceres, the Natural Resources Defense Council,Calpine Corp.,Entergy Corp.,Exelon Corp. and Bankof America, was prepared by M.J. Bradley & Associates LLC.
Mercuryemissions from coal-fired power plants have been cut by more than a half since2000. Since the bulk of the U.S. fleet of coal-fired generation is now subjectto the U.S. EPA's Mercury and Air Toxics Standards, those emissions areexpected to continue to decline. The mercury emissions rate has also declinedby 44% since 2000.
Thetop 100 power companies, based on each company's 2014 generation output,generated 85% of all electric power in the U.S. Similar to the results of the2015 edition of thereport, a relatively small amount of the top generators are responsible for thehighest concentration of emissions. A quarter of SO2 and mercury emissions camefrom just two utilities, while a quarter of all NOx and carbon was emitted byfour utilities.
Thereport ranked generators in terms of total generation in megawatt-hours, totalemissions and emission rates per unit of electricity output. Measuring powerproduction, Duke Energy Corp.topped the list at 245 million MWh, followed by Southern Co. at 190.9 million MWh, and at 183 million MWh.
However,when tons of emissions are factored in, American Electric Power Co. Inc. is ranked number onefor all four pollutants studied, as well as for most coal-fired generationoverall. Duke is ranked number two for NOx and carbon dioxide; , which isreferred to as Energy Future Holdings in the report, is number two for mercury;NRG Energy Inc. isnumber two for SO2 and three for mercury; and Southern Co. is number three forSO2, NOx and carbon dioxide.
Texasleads the country with the most CO2 emissions, at 263.3 million tons in 2014,followed by Florida at 119 million tons and Indiana at 114.1 million tons.Vermont, Idaho and Maine had the lowest amount of CO2 emissions in 2014.