This is the accessible text file for GAO report number GAO-12-545R entitled 'Air Emissions and Electricity Generation at U.S. Power Plants' which was released on May 18, 2012. This text file was formatted by the U.S. Government Accountability Office (GAO) to be accessible to users with visual impairments, as part of a longer term project to improve GAO products' accessibility. Every attempt has been made to maintain the structural and data integrity of the original printed product. Accessibility features, such as text descriptions of tables, consecutively numbered footnotes placed at the end of the file, and the text of agency comment letters, are provided but may not exactly duplicate the presentation or format of the printed version. The portable document format (PDF) file is an exact electronic replica of the printed version. We welcome your feedback. Please E-mail your comments regarding the contents or accessibility features of this document to Webmaster@gao.gov. This is a work of the U.S. government and is not subject to copyright protection in the United States. It may be reproduced and distributed in its entirety without further permission from GAO. Because this work may contain copyrighted images or other material, permission from the copyright holder may be necessary if you wish to reproduce this material separately. GAO-12-545R: United States Government Accountability Office: Washington, DC 20548: April 18, 2012: The Honorable Sheldon Whitehouse: Chairman: Subcommittee on Oversight: Committee on Environment and Public Works: United States Senate: Subject: Air Emissions and Electricity Generation at U.S. Power Plants: Dear Mr. Chairman: The United States depends on a variety of fuels to generate electricity, including fossil fuels (coal, natural gas, and oil), nuclear power, and renewable sources. Power plants that burn fossil fuels provide about 70 percent of U.S. electricity, but they also produce substantial amounts of harmful air emissions.[Footnote 1] In particular, electricity generating units at fossil fuel power plants are among the largest emitters of sulfur dioxide and nitrogen oxides, which have been linked to respiratory illnesses and acid rain, as well as of carbon dioxide, the primary greenhouse gas contributing to climate change.[Footnote 2] Of the three fossil fuels, coal is the most widely used fuel in the United States, providing about 45 percent of electricity in 2010, followed by natural gas, which provided about 24 percent.[Footnote 3] Coal plays a critical role in the reliability of the electricity grid, especially in certain geographic areas, but coal-fired units also generally emit more air pollution than units burning natural gas or oil. Under the Clean Air Act, the Environmental Protection Agency (EPA) establishes national ambient air quality standards for six pollutants that states are primarily responsible for attaining.[Footnote 4] States attain these standards, in part, by regulating emissions of these pollutants from certain stationary sources, such as electricity generating units. Numerous Clean Air Act requirements apply to electricity generating units, including New Source Review (NSR), a permitting process established in 1977.[Footnote 5] Under NSR, owners of generating units must obtain a preconstruction permit that establishes emission limits and requires the use of certain pollution control technologies. NSR applies to (1) generating units built after August 7, 1977, and (2) to existing generating units--regardless of the date built--that seek to undertake a "major modification," a physical or operational change that would result in a significant net increase in emissions of a regulated pollutant. Units built before August 7, 1977, are not required to undergo NSR unless they undertake a major modification. For the purposes of this report, we refer to units that began operation in or before 1978--the first full year after NSR was established--as "older units" and those that began operating after 1978 as "newer units."[Footnote 6] In limiting NSR's requirements to facilities built or undertaking major modifications after August 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 percent 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, we reported that older fossil fuel electricity generating units emitted air pollution at higher rates than newer units.[Footnote 7] This report responds in part to your request for information on electricity generation and emissions at U.S. electricity generating units and the implementation of NSR. Our objective is to provide information on how older fossil fuel electricity generating units compare with newer units in terms of their air emissions and electricity generation. To respond to this objective, we reviewed selected data elements in the Ventyx Velocity Suite EV Market-Ops database. This proprietary database contains consolidated energy and emissions data from EPA, the Energy Information Administration (EIA), and other sources. Specifically, we analyzed how older plants compare with newer plants in their emissions, energy production, location, and fuel type. We reviewed energy and emissions data from calendar year 2010. We reviewed data from units that (1) listed a fossil fuel (coal, natural gas, or oil) as a primary fuel; (2) generated electricity in 2010; and (3) had a net summer capacity greater than 25 megawatts, making them subject to EPA emissions monitoring and reporting requirements. In all, we examined the characteristics of 3,443 electricity generating units--1,485 older units and 1,958 newer units. We focused our analysis on power plant emissions of three regulated pollutants: sulfur dioxide (as a proxy for sulfur oxides), nitrogen oxides, and carbon dioxide (a greenhouse gas).[Footnote 8] To assess the reliability of the Ventyx data, we reviewed existing documentation about the data and the system that produced them, interviewed Ventyx staff who were knowledgeable about the data, and consulted with EPA and EIA agency officials knowledgeable in energy issues. We determined the Ventyx data to be sufficiently reliable for the purpose of this report. We conducted this performance audit from February 2012 to April 2012 in accordance with generally accepted government auditing standards. Those standards require that we plan and perform the audit to obtain sufficient, appropriate evidence to provide a reasonable basis for our findings and conclusions based on our audit objectives. We believe that the evidence obtained provides a reasonable basis for our findings and conclusions based on our audit objectives. Results in Brief: Older electricity generating units--those that began operating in or before 1978--provided 45 percent 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 percent of sulfur dioxide emissions, 64 percent of nitrogen oxides emissions, and 54 percent of carbon dioxide emissions from fossil fuel units. For each unit of electricity generated, older units collectively emitted about 3.6 times as much sulfur dioxide, 2.1 times as much nitrogen oxides, and 1.3 times as much carbon dioxide as newer units. The difference in emissions between older units and their newer counterparts may be attributed to a number of factors. First, 93 percent 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 sulfur dioxide, twice as much carbon dioxide and over five times as much nitrogen oxides per unit of electricity, largely because coal contains more sulfur and carbon than natural gas. 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 sulfur dioxide emissions from electric power generation--approximately 26 percent of older units used controls for sulfur dioxide, compared with 63 percent of newer units. Controls for nitrogen oxide emissions were more common among all types of fossil fuel units, but these controls vary widely in their effectiveness. Among older units, 14 percent had installed selective catalytic reduction (SCR) equipment, the type of control capable of reducing the greatest amount of nitrogen oxides emissions, compared with 33 percent of newer units. In addition, approximately 38 percent of older units did not have any controls for nitrogen oxides, compared with 6 percent 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 electricity generating sector, particularly in certain regions of the United States. Background: The efficient and reliable operation of the electricity industry is critical to the health of the U.S. economy. Residential consumers rely on electricity to power their households, and electricity is a key input for businesses that produce trillions of dollars in products and services. Domestic energy production also provides U.S. jobs and supports economic growth. Plentiful, reliable, and relatively inexpensive fossil fuels have been a mainstay of the U.S. electricity mix. The electricity generating sector is also a major contributor to air emissions in the United States. Based on emissions data published by EPA, in 2010, fuel combustion by electric utilities was responsible for about 65 percent of sulfur dioxide emissions and 16 percent of nitrogen oxides emissions from all sources nationwide.[Footnote 9] Electricity generation was also responsible for 39 percent of carbon dioxide emissions from all sources in 2009.[Footnote 10] Units in the Southeast, South Central, and Great Lakes regions produced most of the electricity and emissions from fossil fuel units. (See enclosures I through IV for additional information on the location of generating units, their electricity production, and their emissions.) As we have previously reported, sulfur dioxide and nitrogen oxides have been linked to a variety of health and environmental concerns, and carbon dioxide has been linked to climate change.[Footnote 11] For example, sulfur dioxide and nitrogen oxides contribute to the formation of fine particles, and nitrogen oxides contribute to the formation of ozone.[Footnote 12] Fine particles have been linked to premature death, aggravated asthma, and chronic bronchitis, and ozone can inflame lung tissue and increase susceptibility to bronchitis and pneumonia. In addition to affecting health, sulfur dioxide and nitrogen oxides reduce visibility and contribute to acid rain, which harms aquatic life and degrades forests. These emissions affect local air quality, and they can also travel hundreds of miles to affect the air quality of downwind states. In addition, the accumulation of carbon dioxide in the atmosphere is linked to increases in air and ocean temperatures, which could threaten coastal areas with rising sea levels, alter agricultural productivity, and increase the intensity and frequency of floods and tropical storms. Emissions controls can help reduce the emissions from generating units by either limiting their formation or capturing them after they are formed.[Footnote 13] At coal-fired units, emissions controls are generally installed in a boiler, where coal is burned, or the duct work that connects the boiler to a smokestack. Figure 1 shows some of the pollution controls that may be used at coal power plants, including flue gas desulfurization units--known as scrubbers--to control sulfur dioxide emissions, fabric filters or electrostatic precipitators to control particulate matter, and selective catalytic reduction (SCR) or selective noncatalytic reduction (SNCR) units to control nitrogen oxides emissions. According to a 2010 EPA report, the development of effective and commercially viable carbon dioxide controls for coal-fired electricity generating units has received significant attention, but some of these technologies are still in the research and development phase, and most are not yet commercially viable.[Footnote 14] Figure 1: Sample Layout of Emissions Controls at a Coal Power Plant: [Refer to PDF for image: illustration] Depicted on the illustration: Coal supply: Smokestack: SCR or SNCR: Fabric filter or ESP: FGD: Boiler: Turbine and generator: Electricity: Legend: ESP = electrostatic precipitators. FGD = flue gas desulfurization unit. SCR = selective catalytic reduction unit. SNCR = selective noncatalytic reduction unit. Sources: GAO analysis of information from Electric Power Research Institute and Tennessee Valley Authority. [End of figure] The reduction in emissions from the use of emissions controls can be substantial, as shown in table 1. Used commercially since the early 1970s, scrubbers are the most common technology for reducing sulfur dioxide emissions, and are capable of removing up to 99 percent of sulfur dioxide emissions. Commercially available low-nitrogen-oxide burners and SCRs are among the more common nitrogen oxide control technologies, with SCRs able to reduce these emissions by more than 90 percent. The installation of emissions controls can also be expensive. According to EPA, a typical coal unit with a capacity of 700 megawatts could incur from $269 million to $329 million to install a scrubber and from $108 million to $129 million to install an SCR, plus operating and maintenance costs.[Footnote 15] Additionally, emissions controls can require additional electricity from the unit to operate, which reduces the amount of electricity available to be used by customers. Table 1: Summary of Emissions Control Equipment Used at Electricity Generating Units: Pollutant: Sulfur dioxide[A]; Control equipment: Flue gas desulfurization unit (commonly referred to as a "scrubber"); How it works: Wet flue gas desulfurization units inject a liquid sorbent, such as limestone, into the flue gas to form a wet solid that can be disposed of or sold. Dry flue gas desulfurization units inject a dry sorbent, such as lime, into the flue gas to form a solid by- product that is collected and removed; Removal efficiency: Wet flue gas desulfurization units can remove 80- 99 percent of sulfur dioxide. Dry flue gas desulfurization units can remove 70-95 percent of sulfur dioxide. Pollutant: Nitrogen oxides; Control equipment: Combustion control technologies, such as low- nitrogen-oxides burners[B]; How it works: Coal combustion conditions are adjusted to inhibit the formation of nitrogen oxides; Removal efficiency: These technologies can reduce formation of nitrogen oxides by 40-45 percent. Pollutant: Nitrogen oxides; Control equipment: Postcombustion controls, such as selective catalytic reduction and selective noncatalytic reduction units; How it works: Selective catalytic reduction units inject ammonia into flue gas to form nitrogen and water and use a catalyst to enhance the reaction. Selective noncatalytic reduction units also inject ammonia but do not use a catalyst; Removal efficiency: Selective catalytic reduction units can remove 70- 95 percent of nitrogen oxides. Selective noncatalytic reduction units can remove 30-75 percent of nitrogen oxides. Source: GAO. [A] Another approach to reducing sulfur dioxide emissions from a coal- fired electricity generating unit is for a plant to switch from using coal with a higher sulfur content to coal with a lower sulfur content or to blend higher-sulfur coal with lower-sulfur coal. [B] Low-nitrogen-oxides burners can be used in conjunction with postcombustion controls for nitrogen oxides. [End of table] Older Fossil Fuel Units Produce More Emissions and Less Electricity Than Newer Units: In general, older electricity generating units, which run primarily on coal, produce more emissions than newer units, and at higher rates per unit of electricity. Much of this difference can likely be attributed to a greater reliance on coal among older units. In addition, fewer older units have installed emissions controls, and older units are generally less efficient at converting fuel to electricity. Nonetheless, some older units play an important role in providing reliable electricity to certain U.S. regions. Older Units Emit More Than Newer Units: In 2010, older fossil fuel electricity generating units--those that began operating in or by 1978--produced a disproportionate share of emissions for the electricity they produced. Specifically, older units generated 45 percent of the electricity from fossil fuel units in 2010 but emitted 75 percent of sulfur dioxide emissions, 64 percent of nitrogen oxides emissions, and 54 percent of carbon dioxide emissions (see figure 2). Units that began operating after 1978 were responsible for the remainder of the emissions and electricity production. [Footnote 16] Figure 2: Share of Total Electricity and Emissions per Unit of Electricity Generated by Fossil Generating Units in 2010: [Refer to PDF for image: stacked horizontal bar graph] Electricity generation: Older units (units that began operating in or before 1978): 45%; Newer units (units that began operating after 1978): 55%. Sulfur dioxide emissions: Older units (units that began operating in or before 1978): 75%; Newer units (units that began operating after 1978): 25%. Nitrogen oxides emissions: Older units (units that began operating in or before 1978): 64%; Newer units (units that began operating after 1978): 36%. Carbon dioxide emissions: Older units (units that began operating in or before 1978): 54%; Newer units (units that began operating after 1978): 46%. Source: GAO analysis of Ventyx data. Note: Chart reflects older and newer generating units that use coal, natural gas, and oil. Older generating units are mostly coal fired, whereas newer generating units rely more heavily on natural gas. [End of figure] Older units produced emissions at a higher rate than newer units in 2010; that is, they produced more emissions per unit of electricity they generated. As shown in figure 3, for each megawatt-hour of electricity generated, older units, on average, emitted about 3.6 times as much sulfur dioxide as newer units, about 2.1 times as much nitrogen oxides, and about 1.3 times as much carbon dioxide. Figure 3: Emissions per Unit of Electricity Generated in 2010: [Refer to PDF for image: vertical bar graph] Carbon dioxide emissions rate (tons/MWh): Older units (units that began operating in or before 1978): 1.0; Newer units (units that began operating after 1978): 0.8 Nitrogen oxides Carbon dioxide emissions rate (lbs/MWh): Older units (units that began operating in or before 1978): 2.1; Newer units (units that began operating after 1978): 1.0. Sulfur dioxides Carbon dioxide emissions rate (lbs/MWh): Older units (units that began operating in or before 1978): 6.2; Newer units (units that began operating after 1978): 1.7. Legend: lbs/MWh: pounds per megawatt-hour. tons/MWh: tons per megawatt-hour. Source: GAO analysis of Ventyx data. Note: Chart reflects older and newer generating units that use coal, natural gas, and oil. Older generating units are mostly coal-fired, whereas newer generating units rely more heavily on natural gas. [End of figure] Emissions from fossil fuel units in 2010 varied widely, depending on the decade in which the unit began operating. In aggregate, the oldest units produced the most emissions, and more recently built units produced the least emissions (see fig. 4). For example, units that began operating in the 1960s generated 12 percent of electricity in 2010, but also produced 26 percent of sulfur dioxide emissions, 21 percent of nitrogen oxides emissions, and 15 percent of carbon dioxide emissions in that year. In comparison, units that began operating in the 2000s produced over twice as much electricity (26 percent) in 2010, but a much lower share of emissions--1 percent of sulfur dioxide, 3 percent of nitrogen oxides, and 15 percent of carbon dioxide. Figure 4: Share of Total Electricity and Emissions Produced by Fossil Fuel Generating Units in 2010, by Decade Unit Began Operating: [Refer to PDF for image: vertical bar graph] Age of unit (decade began operating): 1950s; Electricity generation: 7.1%; Carbon dioxide emissions: 8.66%; Nitrogen dioxide emissions: 12.98%; Sulfur dioxide emissions: 22.01%. Age of unit (decade began operating): 1960s; Electricity generation: 12.83%; Carbon dioxide emissions: 15.14%; Nitrogen dioxide emissions: 21.19%; Sulfur dioxide emissions: 26.62%. Age of unit (decade began operating): 1970s; Electricity generation: 27.97%; Carbon dioxide emissions: 32.66%; Nitrogen dioxide emissions: 33.13%; Sulfur dioxide emissions: 29.21%. Age of unit (decade began operating): 1980s; Electricity generation: 18.66%; Carbon dioxide emissions: 22.5%; Nitrogen dioxide emissions: 24.92%; Sulfur dioxide emissions: 19.14%. Age of unit (decade began operating): 1990s; Electricity generation: 5.94%; Carbon dioxide emissions: 4.86%; Nitrogen dioxide emissions: 4.05%; Sulfur dioxide emissions: 1.45%. Age of unit (decade began operating): 2000s; Electricity generation: 26.43%; Carbon dioxide emissions: 15.1%; Nitrogen dioxide emissions: 3.1%; Sulfur dioxide emissions: 0.61%. Source: GAO analysis of Ventyx data. Note: Chart reflects generating units that use coal, natural gas, and oil. Older generating units are mostly coal-fired, whereas newer generating units rely more heavily on natural gas. [End of figure] As shown in figure 5, units that began operating more recently are more likely to have comparatively lower emissions rates. In 2010, units that began operating in the 1970s or later generally emitted substantially less sulfur dioxide and nitrogen oxides for each unit of electricity they generated. For example, units built in the 1960s emitted an average of 7.8 pounds of sulfur dioxide and 2.5 pounds of nitrogen oxides per megawatt-hour of electricity generated, whereas units built in the 2000s emitted an average of 0.1 pounds of sulfur dioxide and 0.2 pounds of nitrogen oxides per megawatt-hour. Figure 5: Emissions of Sulfur Dioxide and Nitrogen Oxides per Unit of Electricity Generated by Fossil Fuel Generating Units in 2010, by Decade Unit Began Operating: [Refer to PDF for image: vertical bar graph] Emissions rate in lbs/MWh: Age of unit (decade began operating): 1950s; Nitrogen dioxide emissions rate: 11.6; Sulfur dioxide emissions rate: 2.8. Age of unit (decade began operating): 1960s; Nitrogen dioxide emissions: 7.8; Sulfur dioxide emissions: 2.5. Age of unit (decade began operating): 1970s; Nitrogen dioxide emissions: 3.9; Sulfur dioxide emissions: 1.8. Age of unit (decade began operating): 1980s; Nitrogen dioxide emissions: 3.8; Sulfur dioxide emissions: 2.0. Age of unit (decade began operating): 1990s; Nitrogen dioxide emissions: 0.9; Sulfur dioxide emissions: 1.6. Age of unit (decade began operating): 2000s; Nitrogen dioxide emissions: 0.1; Sulfur dioxide emissions: 0.2. Source: GAO analysis of Ventyx data. Note: Chart reflects generating units that use coal, natural gas, and oil. Older generating units are mostly coal-fired, whereas newer generating units rely more heavily on natural gas. [End of figure] Carbon dioxide emissions rates have also declined among newer units in the last several decades, although to a smaller extent. As shown in figure 6, units that began operating in the 1980s emitted an average of 2,160 pounds of carbon dioxide per unit of electricity in 2010, a decline of around one percent compared to units that began operating in the 1950s. In contrast, units that began operating after the 1980s had substantially lower carbon dioxide emissions rates, on average. For example, units that began operating in the 2000s emitted carbon dioxide at a rate of 1,016 pounds per megawatt-hour, about 53 percent less than units that began operating in the 1980s. Figure 6: Carbon Dioxide Emissions per Unit of Electricity Generated by Fossil Fuel Generating Units in 2010, by Decade Unit Began Operating: [Refer to PDF for image: vertical bar graph] Carbon dioxide emissions rate in lbs/MWh: Age of unit (decade began operating): 1950s; Carbon dioxide emissions rate: 2,169. Age of unit (decade began operating): 1960s; Carbon dioxide emissions rate: 2,098. Age of unit (decade began operating): 1970s; Carbon dioxide emissions rate: 2,076. Age of unit (decade began operating): 1980s; Carbon dioxide emissions rate: 2,144; Age of unit (decade began operating): 1990s; Carbon dioxide emissions rate: 1,454. Age of unit (decade began operating): 2000s; Carbon dioxide emissions rate: 1,016. Source: GAO analysis of Ventyx data. Legend: lbs/MWh = pounds per megawatt-hour. Note: Chart reflects generating units that use coal, natural gas, and oil. Older generating units are mostly coal-fired, whereas newer generating units rely more heavily on natural gas. [End of figure] As discussed below, we identified three reasons why older units may emit more than newer units: (1) older units are more likely to use coal, (2) older units are less likely to have installed emissions controls, and (3) older units are generally less efficient. Older Units Are Mostly Fueled by Coal, and Newer Units Rely More on Natural Gas: The difference in emissions between older and newer units is likely due, in part, to significant changes in the fuels used to generate electricity--in particular, a shift from coal to natural gas. Compared with coal, natural gas produces substantially lower emissions per unit of electricity generated, largely because natural gas contains less sulfur and carbon. This disparity is most apparent with sulfur dioxide emissions, as shown in figure 7. On average, coal-fired units--both older and newer--produced over 90 times as much sulfur dioxide emissions per unit of electricity as natural gas-fired units in 2010. Compared to natural gas-fired units, coal-fired units also produced over twice as much carbon dioxide and over five times as much nitrogen oxides per unit of electricity in 2010. Figure 7: Emissions per Unit of Electricity Generated by Fossil Fuel Generating Units in 2010, by Type of Fuel: [Refer to PDF for image: vertical bar graph] Emissions rate in tons/MWh: Carbon dioxide emissions rate: Coal: 1.08; Natural gas: 0.49. Emissions rate in lbs/MWh: Nitrogen oxides emissions rate: Coal: 2.08; Natural gas: 0.36. Sulfur dioxide emissions rate: Coal: 5.50; Natural gas: 0.06. Source: GAO analysis of Ventyx data. Legend: lbs/MWh = pounds per megawatt-hour. tons/MWh = tons per megawatt-hour. [End of figure] Older generating units are much more likely than newer units to use coal as a primary fuel. In 2010, coal-fired units accounted for about 93 percent of electricity from older units and 47 percent of electricity from newer units. While other fossil fuels, particularly oil, played an important role in electricity generation in the late 1960s and 1970s, many of these units have since been retired, a development likely attributable to rising oil prices.[Footnote 17] In addition, between 1978 and 1987, the Powerplant and Industrial Fuel Use Act of 1978 (Fuel Use Act) restricted construction of new power plants using oil or natural gas as a primary energy source. Since the 1990s, natural gas has played a much larger role in electricity generation (see fig. 8). After the 1987 repeal of provisions in the Fuel Use Act, use of natural gas by the electric power sector increased by more than 240 percent.[Footnote 18] As we have previously reported, factors contributing to the rise of natural gas include the comparatively low levels of emissions produced by natural gas units and a long period of low natural gas prices in the 1990s.[Footnote 19] After rising in the early 2000s, natural gas prices have again fallen in recent years, a trend that may influence decisions about the future composition of the fleet of generating units, with the potential for retirements of older coal-fired units and the construction of new natural gas units. In 2010, natural gas units accounted for approximately one-third of the electricity generated by fossil fuel units. Most of this natural- gas-based generation--about 78 percent--came from units that began operating in 2000 or later. Conversely, most coal-based generation-- about 66 percent--came from units that have been operating more than 30 years. Figure 8: Electricity Generation from Fossil Fuel Generating Units in 2010, by Decade Unit Began Operating and Fuel Type: [Refer to PDF for image: stacked vertical bar graph] Electricity generated in MWh in millions: Age of unit (decade began operating): Before 1950; Oil: 2; Natural gas: 0; Coal: 0. Age of unit (decade began operating): 1950s; Oil: 184; Natural gas: 11; Coal: 0. Age of unit (decade began operating): 1960s; Oil: 321; Natural gas: 31; Coal: 2. Age of unit (decade began operating): 1970s; Oil: 720; Natural gas: 44; Coal: 7. Age of unit (decade began operating): 1980s; Oil: 498; Natural gas: 15; Coal: 1. Age of unit (decade began operating): 1990s; Oil: 66; Natural gas: 90; Coal: 0. Age of unit (decade began operating): After 2000; Oil: 68; Natural gas: 686; Coal: 1. Source: GAO analysis of Ventyx data. Legend: MWh + megawatt-hours. [End of figure] Nonetheless, coal-fired units, both older and newer, remain both a key source of electricity and a significant source of emissions. As shown in figure 9, coal-fired units generated 67 percent of electricity from fossil fuel units in 2010, but also produced 99 percent of sulfur dioxide emissions, 92 percent of nitrogen oxides emissions, and 82 percent of carbon dioxide emissions from fossil fuel units in that year. Figure 9: Electricity Generation and Emissions from Coal-Fired Units in 2010, as a Percentage of Total Generation and Emissions from Fossil Fuel Generating Units: [Refer to PDF for image: vertical bar graph] Electricity generation: 67%; Carbon dioxide emissions: 82%; Nitrogen oxides emissions: 92%; Sulfur dioxide emissions: 99%. Source: GAO analysis of Ventyx data. [End of figure] Older Units Are Less Likely to Use Emissions Controls: Another likely reason that older units have higher aggregate emissions is that many older units have not installed emissions controls. Over the last several decades, the electricity generating industry has employed a number of technologies to comply with NSR and other state and federal air quality regulations. Some of the most common and effective technologies include flue gas desulfurization unit systems, or "scrubbers," to control sulfur dioxide and SCRs to control nitrogen oxides. Regarding the use of controls for sulfur dioxide in 2010, 63 percent of newer coal-fired units--those that began operating after 1978--had installed controls (see fig. 10). In contrast, 26 percent of older, coal-fired units had installed sulfur dioxide controls.[Footnote 20] Figure 10: Use of Sulfur Dioxide Emissions Controls among Older and Newer Coal-Fired Generating Units in 2010: [Refer to PDF for image: 2 pie-charts] Older coal-fired units: coal-fired united that began operating in or before 1978: Without controls: 74%; With controls: 26%. Newer coal-fired units: coal-fired united that began operating after 1978: Without controls: 37%; With controls: 63%. Source: GAO analysis of Ventyx data. [End of figure] Older coal-fired units without sulfur dioxide controls were responsible for the majority of sulfur dioxide emissions from fossil fuel units in 2010. Specifically, older coal-fired units without sulfur dioxide control equipment generated about 18 percent of electricity while producing 55 percent of sulfur dioxide emissions. As shown in figure 11, older coal-fired units without sulfur dioxide controls accounted for 2.8 million tons of sulfur dioxide emissions, nearly three times as much as older units with sulfur dioxide controls. Among those coal-fired units without sulfur dioxide controls, the majority (88 percent) were older units. Figure 11: Sulfur Dioxide Emissions from Controlled and Uncontrolled Coal-Fired Generating Units in 2010: [Refer to PDF for image: vertical bar graph] Emissions in thousands of tons: With Sulfur dioxide controls: Newer units (units that began operating after 1978): 651. Older units (units that began operating in or before 1978): 1,005. Without Sulfur dioxide controls: Newer units (units that began operating after 1978): 2,840; Older units (units that began operating in or before 1978): 614. Source: GAO analysis of Ventyx data. [End of figure] The use of controls for nitrogen oxides is more widespread than for sulfur dioxide, although the effectiveness of these controls at removing nitrogen oxides varies widely. For purposes of our analysis, we classified controls for nitrogen oxides into three categories, as shown in table 2. Overall, older units were less likely than newer units to use controls for nitrogen oxides. Among older units, 38 percent had no controls for nitrogen oxides, compared with 6 percent of newer units. Older units were also less likely to have installed SCR controls, the most effective category of control for nitrogen oxides: about 14 percent of older units had such controls, compared with 33 percent of newer units. Table 2: Controls for Nitrogen Oxides in Fossil Fuel Electricity Generating Units: Removal Efficiency and Extent of Use in 2010: Category: 1; Control type: None; Number of older units: 564; Number of newer units: 116. Category: 2; Control type: Selective noncatalytic reduction, low nitrogen-oxides burners, and others; Number of older units: 708; Number of newer units: 1,204. Category: 3; Control type: Selective catalytic reduction (SCR); Number of older units: 213; Number of newer units: 638. Source: GAO analysis of Ventyx data. Note: Units in categories 2 and 3 may have installed multiple nitrogen oxides controls; no units in category 2, however, had installed an SCR. [End of table] As shown in figure 12, older units collectively emitted nitrogen oxides at higher rates than newer units. For example, older units without any nitrogen oxides controls emitted an average of 3.5 pounds of nitrogen oxides per megawatt-hour of electricity generated in 2010, approximately twice the rate as newer units. Figure 12: Emissions Rates of Nitrogen Oxides for Older and Newer Fossil Fuel Generating Units in 2010, by Type of Control for Nitrogen Oxides: [Refer to PDF for image: vertical bar graph] Nitrogen oxides emissions in lbs/MWh: No control: Newer units (units that began operating after 1978): 1.7. Older units (units that began operating in or before 1978): 3.5. Non-SCR control: Newer units (units that began operating after 1978): 1.8; Older units (units that began operating in or before 1978): 2.8. SCR: Newer units (units that began operating after 1978): 0.4; Older units (units that began operating in or before 1978): 1.1. Source: GAO analysis of Ventyx data. Legend: SCR = selective catalytic reduction unit. lbs/MWh = pounds per megawatt-hour. Note: "Non-SCR" refers to any other emissions control other than an SCR (see category 2 in table 2). Chart reflects generating units that use coal, natural gas, and oil. Older generating units are mostly coal fired, whereas newer generating units rely more heavily on natural gas. [End of figure] The increased use of emissions controls over time may be attributable, in part, to the Clean Air Act requirements such as NSR and the Acid Rain Program. The Acid Rain Program, created by the Clean Air Act Amendments of 1990, established a cap on the amount of sulfur dioxide that may be emitted by electricity generating units nationwide. According to EPA officials, both NSR and the Acid Rain Program have contributed to more widespread use of emissions controls. In addition, EPA has recently finalized regulations that may prompt generating unit owners to (1) retrofit older units with emissions controls or (2) retire units that are not cost-effective to retrofit.[Footnote 21] Conversely, some uncontrolled units may be limited in their ability to install certain types of emissions controls if these controls are not required.[Footnote 22] Older Units Are Generally Less Efficient Than Newer Units: The average efficiency with which electricity generating units produce electricity has improved over time, which has likely contributed to lower collective emissions among newer units. Generating efficiency is often measured by the total heat (fuel) required to generate each unit of electricity, known as a "heat rate."[Footnote 23] More efficient units require less fuel to produce the same amount of electricity, generally resulting in lower emissions and fuel costs. A number of factors can affect a unit's efficiency, including its design, its operation, the choice of fuel, the use of emission controls, and the environmental conditions in which the unit operates. For example, some types of coal are more efficient than others because they have lower ash and water content. Emissions controls can also reduce a unit's efficiency because some electricity must be used to operate the controls. As shown in figure 13, the operating efficiency of generating units built before 1950 is much lower than newer generating units. On average, in 2010, units that began operating in 2000 or later were approximately 46 percent more efficient than units that began operating before 1950. In addition to a greater reliance on coal, many older units only operate periodically, during times of peak electricity demand, which decreases their efficiency relative to units that operate on a more continuous basis.[Footnote 24] While some energy efficiency technologies are available for application to existing units, the biggest efficiency gains result from the substitution of old units with new, more efficient units. Some natural gas units constructed in the last two decades, for example, are capable of achieving heat rates below 7,000 million British thermal units (Btu) per kilowatt-hour, which is substantially lower than the averages highlighted in figure 13. Figure 13: Average Efficiency (Heat Rate) of Fossil Fuel Units in 2010, by Decade Unit Began Operating: [Refer to PDF for image: vertical bar graph] Age of unit (decade began operating): Before 1950; Heat rate (mmBTU/KWh): 14,827. Age of unit (decade began operating): 1950s; Heat rate (mmBTU/KWh): 10,865. Age of unit (decade began operating): 1960s; Heat rate (mmBTU/KWh): 10,600. Age of unit (decade began operating): 1970s; Heat rate (mmBTU/KWh): 10,313. Age of unit (decade began operating): 1980s; Heat rate (mmBTU/KWh): 10,553. Age of unit (decade began operating): 1990s; Heat rate (mmBTU/KWh): 10,053. Age of unit (decade began operating): After 2000; Heat rate (mmBTU/KWh): 8,076. Source: GAO analysis of Ventyx data. Legend: mmBTU: million British thermal units. KWh: kilowatt-hours. Note: A British thermal unit (Btu) is a standard unit of measurement used to denote the amount of heat energy in fuels. A lower heat rate indicates a higher level of efficiency. Chart reflects generating units that use coal, natural gas, and oil. Older generating units are mostly coal fired, whereas newer generating units rely more heavily on natural gas. [End of figure] Nonetheless, older units remain an important part of the U.S. electricity generating sector. 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.[Footnote 25] 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. Agency Comments: We provided a draft of this report to EPA and the Department of Energy for their review and comment. EPA and the Department of Energy provided technical comments, which we have incorporated as appropriate. As agreed with your office, unless you publicly announce the contents of this report earlier, we plan no further distribution until 30 days from the report date. At that time, we will send copies to the appropriate congressional committees, the Administrator of EPA, the Secretary of Energy, and other interested parties. In addition, the report will be available at no charge on the GAO website at [hyperlink http://www.gao.gov]. If you or your staff have any questions about this report, please contact David Trimble at (202) 512-3841 or trimbled@gao.gov or Frank Rusco at (202) 512-3841 or ruscof@gao.gov. Contact points for our Offices of Congressional Relations and Public Affairs may be found on the last page of this report. GAO staff who made key contributions to this report were Michael Hix (Assistant Director), Ellen W. Chu, Philip Farah, Cindy Gilbert, Mitchell Karpman, Jessica Lemke, Jon Ludwigson, Nancy Meyer, Mick Ray, and Jeanette Soares. Sincerely yours, Signed by: David C. Trimble: Director, Natural Resources and Environment: Signed by: Frank Rusco: Director, Natural Resources and Environment: Enclosures - 4: [End of section] Electricity-generation and Aggregate Emissions from Fossil Fuel Electricity Generating Units in 2010, By State: Table 3 presents, by state, data on fossil fuel units' electricity generation and aggregate emissions of sulfur dioxide, nitrogen oxides, and carbon dioxide in 2010. Table 3: Electricity and Emissions from Fossil Fuel Electricity Generating Units in 2010, by State: State: Alabama; Number of units: 88; Electricity generation (megawatt-hours): 100,961,300; Carbon dioxide emissions (tons): 84,828,993; Nitrogen oxide emissions (tons): 63,336; Sulfur dioxide emissions (tons): 204,195. State: Arizona; Number of units: 63; Electricity generation (megawatt-hours): 74,817,174; Carbon dioxide emissions (tons): 60,732,544; Nitrogen oxide emissions (tons): 60,524; Sulfur dioxide emissions (tons): 36,445. State: Arkansas; Number of units: 30; Electricity generation (megawatt-hours): 40,295,345; Carbon dioxide emissions (tons): 36,271,855; Nitrogen oxide emissions (tons): 37,783; Sulfur dioxide emissions (tons): 67,084. State: California; Number of units: 179; Electricity generation (megawatt-hours): 80,854,400; Carbon dioxide emissions (tons): 36,929,068; Nitrogen oxide emissions (tons): 4,467; Sulfur dioxide emissions (tons): 226. State: Colorado; Number of units: 58; Electricity generation (megawatt-hours): 45,728,202; Carbon dioxide emissions (tons): 44,826,939; Nitrogen oxide emissions (tons): 54,088; Sulfur dioxide emissions (tons): 45,391. State: Connecticut; Number of units: 39; Electricity generation (megawatt-hours): 12,497,043; Carbon dioxide emissions (tons): 8,526,856; Nitrogen oxide emissions (tons): 2,783; Sulfur dioxide emissions (tons): 1,955. State: Delaware; Number of units: 15; Electricity generation (megawatt-hours): 5,489,585; Carbon dioxide emissions (tons): 4,318,918; Nitrogen oxide emissions (tons): 4,330; Sulfur dioxide emissions (tons): 14,496. State: District of Columbia; Number of units: 2; Electricity generation (megawatt-hours): 207,916; Carbon dioxide emissions (tons): 220,765; Nitrogen oxide emissions (tons): 373; Sulfur dioxide emissions (tons): 874. State: Florida; Number of units: 246; Electricity generation (megawatt-hours): 188,566,114; Carbon dioxide emissions (tons): 135,313,627; Nitrogen oxide emissions (tons): 79,759; Sulfur dioxide emissions (tons): 144,829. State: Georgia; Number of units: 141; Electricity generation (megawatt-hours): 95,973,778; Carbon dioxide emissions (tons): 87,569,772; Nitrogen oxide emissions (tons): 60,580; Sulfur dioxide emissions (tons): 218,906. State: Idaho; Number of units: 7; Electricity generation (megawatt-hours): 1,566,178; Carbon dioxide emissions (tons): 693,069; Nitrogen oxide emissions (tons): 113; Sulfur dioxide emissions (tons): 3. State: Illinois; Number of units: 196; Electricity generation (megawatt-hours): 97,862,368; Carbon dioxide emissions (tons): 107,058,198; Nitrogen oxide emissions (tons): 77,063; Sulfur dioxide emissions (tons): 220,077. State: Indiana; Number of units: 126; Electricity generation (megawatt-hours): 120,785,560; Carbon dioxide emissions (tons): 124,321,920; Nitrogen oxide emissions (tons): 121,844; Sulfur dioxide emissions (tons): 414,638. State: Iowa; Number of units: 48; Electricity generation (megawatt-hours): 41,249,495; Carbon dioxide emissions (tons): 45,296,689; Nitrogen oxide emissions (tons): 44,796; Sulfur dioxide emissions (tons): 104,389. State: Kansas; Number of units: 48; Electricity generation (megawatt-hours): 35,758,838; Carbon dioxide emissions (tons): 39,757,268; Nitrogen oxide emissions (tons): 48,938; Sulfur dioxide emissions (tons): 45,251. State: Kentucky; Number of units: 96; Electricity generation (megawatt-hours): 96,980,846; Carbon dioxide emissions (tons): 101,053,094; Nitrogen oxide emissions (tons): 93,040; Sulfur dioxide emissions (tons): 270,045. State: Louisiana; Number of units: 70; Electricity generation (megawatt-hours): 70,221,777; Carbon dioxide emissions (tons): 52,344,198; Nitrogen oxide emissions (tons): 47,153; Sulfur dioxide emissions (tons): 102,263. State: Maine; Number of units: 11; Electricity generation (megawatt-hours): 7,902,550; Carbon dioxide emissions (tons): 3,953,551; Nitrogen oxide emissions (tons): 719; Sulfur dioxide emissions (tons): 821. State: Maryland; Number of units: 46; Electricity generation (megawatt-hours): 26,381,736; Carbon dioxide emissions (tons): 27,999,389; Nitrogen oxide emissions (tons): 19,434; Sulfur dioxide emissions (tons): 29,946. State: Massachusetts; Number of units: 48; Electricity generation (megawatt-hours): 31,174,655; Carbon dioxide emissions (tons): 19,787,576; Nitrogen oxide emissions (tons): 8,181; Sulfur dioxide emissions (tons): 36,892. State: Michigan; Number of units: 96; Electricity generation (megawatt-hours): 76,833,143; Carbon dioxide emissions (tons): 74,272,141; Nitrogen oxide emissions (tons): 79,566; Sulfur dioxide emissions (tons): 242,409. State: Minnesota; Number of units: 45; Electricity generation (megawatt-hours): 31,496,681; Carbon dioxide emissions (tons): 32,900,506; Nitrogen oxide emissions (tons): 29,911; Sulfur dioxide emissions (tons): 41,076. State: Mississippi; Number of units: 57; Electricity generation (megawatt-hours): 40,802,413; Carbon dioxide emissions (tons): 30,624,811; Nitrogen oxide emissions (tons): 29,773; Sulfur dioxide emissions (tons): 54,696. State: Missouri; Number of units: 102; Electricity generation (megawatt-hours): 77,566,300; Carbon dioxide emissions (tons): 83,182,289; Nitrogen oxide emissions (tons): 58,288; Sulfur dioxide emissions (tons): 235,368. State: Montana; Number of units: 12; Electricity generation (megawatt-hours): 18,752,877; Carbon dioxide emissions (tons): 21,356,366; Nitrogen oxide emissions (tons): 21,728; Sulfur dioxide emissions (tons): 19,896. State: Nebraska; Number of units: 29; Electricity generation (megawatt-hours): 23,688,902; Carbon dioxide emissions (tons): 26,402,103; Nitrogen oxide emissions (tons): 37,402; Sulfur dioxide emissions (tons): 64,184. State: Nevada; Number of units: 37; Electricity generation (megawatt-hours): 28,136,479; Carbon dioxide emissions (tons): 17,222,084; Nitrogen oxide emissions (tons): 10,812; Sulfur dioxide emissions (tons): 7,889. State: New Hampshire; Number of units: 7; Electricity generation (megawatt-hours): 8,069,450; Carbon dioxide emissions (tons): 5,899,639; Nitrogen oxide emissions (tons): 4,612; Sulfur dioxide emissions (tons): 36,833. State: New Jersey; Number of units: 107; Electricity generation (megawatt-hours): 30,081,377; Carbon dioxide emissions (tons): 19,995,676; Nitrogen oxide emissions (tons): 9,937; Sulfur dioxide emissions (tons): 15,270. State: New Mexico; Number of units: 35; Electricity generation (megawatt-hours): 34,294,657; Carbon dioxide emissions (tons): 32,657,348; Nitrogen oxide emissions (tons): 60,256; Sulfur dioxide emissions (tons): 16,570. State: New York; Number of units: 165; Electricity generation (megawatt-hours): 63,663,802; Carbon dioxide emissions (tons): 41,687,271; Nitrogen oxide emissions (tons): 28,311; Sulfur dioxide emissions (tons): 47,488. State: North Carolina; Number of units: 104; Electricity generation (megawatt-hours): 78,576,396; Carbon dioxide emissions (tons): 76,242,017; Nitrogen oxide emissions (tons): 53,390; Sulfur dioxide emissions (tons): 120,254. State: North Dakota; Number of units: 11; Electricity generation (megawatt-hours): 28,269,255; Carbon dioxide emissions (tons): 33,609,781; Nitrogen oxide emissions (tons): 54,744; Sulfur dioxide emissions (tons): 124,096. State: Ohio; Number of units: 135; Electricity generation (megawatt-hours): 126,505,558; Carbon dioxide emissions (tons): 125,054,961; Nitrogen oxide emissions (tons): 104,871; Sulfur dioxide emissions (tons): 572,110. State: Oklahoma; Number of units: 66; Electricity generation (megawatt-hours): 60,394,162; Carbon dioxide emissions (tons): 49,876,813; Nitrogen oxide emissions (tons): 71,434; Sulfur dioxide emissions (tons): 85,135. State: Oregon; Number of units: 8; Electricity generation (megawatt-hours): 19,280,743; Carbon dioxide emissions (tons): 10,875,349; Nitrogen oxide emissions (tons): 9,729; Sulfur dioxide emissions (tons): 15,696. State: Pennsylvania; Number of units: 123; Electricity generation (megawatt-hours): 143,267,035; Carbon dioxide emissions (tons): 125,643,066; Nitrogen oxide emissions (tons): 134,169; Sulfur dioxide emissions (tons): 411,216. State: Rhode Island; Number of units: 8; Electricity generation (megawatt-hours): 7,094,295; Carbon dioxide emissions (tons): 3,504,392; Nitrogen oxide emissions (tons): 578; Sulfur dioxide emissions (tons): 18. State: South Carolina; Number of units: 71; Electricity generation (megawatt-hours): 48,054,008; Carbon dioxide emissions (tons): 44,815,737; Nitrogen oxide emissions (tons): 28,123; Sulfur dioxide emissions (tons): 94,641. State: South Dakota; Number of units: 8; Electricity generation (megawatt-hours): 3,255,521; Carbon dioxide emissions (tons): 3,765,854; Nitrogen oxide emissions (tons): 12,433; Sulfur dioxide emissions (tons): 12,589. State: Tennessee; Number of units: 85; Electricity generation (megawatt-hours): 45,166,515; Carbon dioxide emissions (tons): 46,449,221; Nitrogen oxide emissions (tons): 31,239; Sulfur dioxide emissions (tons): 118,723. State: Texas; Number of units: 284; Electricity generation (megawatt-hours): 318,045,099; Carbon dioxide emissions (tons): 255,708,493; Nitrogen oxide emissions (tons): 145,798; Sulfur dioxide emissions (tons): 461,754. State: Utah; Number of units: 26; Electricity generation (megawatt-hours): 39,211,138; Carbon dioxide emissions (tons): 37,005,962; Nitrogen oxide emissions (tons): 61,415; Sulfur dioxide emissions (tons): 21,598. State: Virginia; Number of units: 97; Electricity generation (megawatt-hours): 42,773,143; Carbon dioxide emissions (tons): 35,584,177; Nitrogen oxide emissions (tons): 38,300; Sulfur dioxide emissions (tons): 93,385. State: Washington; Number of units: 13; Electricity generation (megawatt-hours): 17,402,607; Carbon dioxide emissions (tons): 14,560,232; Nitrogen oxide emissions (tons): 11,980; Sulfur dioxide emissions (tons): 2,651. State: Wisconsin; Number of units: 84; Electricity generation (megawatt-hours): 46,382,410; Carbon dioxide emissions (tons): 49,753,419; Nitrogen oxide emissions (tons): 33,082; Sulfur dioxide emissions (tons): 109,158. State: West Virginia; Number of units: 50; Electricity generation (megawatt-hours): 79,543,178; Carbon dioxide emissions (tons): 79,135,925; Nitrogen oxide emissions (tons): 53,757; Sulfur dioxide emissions (tons): 109,028. State: Wyoming; Number of units: 21; Electricity generation (megawatt-hours): 42,829,664; Carbon dioxide emissions (tons): 49,382,465; Nitrogen oxide emissions (tons): 60,902; Sulfur dioxide emissions (tons): 64,849. Total: Number of units: 3,443; Electricity generation (megawatt-hours): 2,754,711,668; Carbon dioxide emissions (tons): 2,448,972,387; Nitrogen oxide emissions (tons): 2,105,844; Sulfur dioxide emissions (tons): 5,157,306. Source: GAO presentation of Ventyx data. Note: As with most of the other data presented in this report, we limited our analysis to those units that (1) list a fossil fuel as a primary fuel, (2) have a net summer capacity greater than 25 megawatts, and (3) produced power in 2010. No reported electricity production or emissions were reported from fossil fuel units in Alaska, Hawaii, or Vermont. [End of table] [End of section] Electricity Generation and Emissions Rates from Fossil Fuel Electricity Generating Units in 2010, by State: Table 4 presents, by state, data on fossil fuel units' electricity generation and emissions rates in 2010. Table 4: Electricity Generation and Emissions Rates from Fossil Fuel Electricity Generating Units in 2010, by State: State: Alabama; Number of units: 88; Electricity generation (MWh): 100,961,300; Carbon dioxide emissions rate (tons/MWh): 0.84; Nitrogen oxides emissions rate (lbs/MWh): 1.25; Sulfur dioxide emissions rate (lbs/MWh): 4.05. State: Arizona; Number of units: 63; Electricity generation (MWh): 74,817,174; Carbon dioxide emissions rate (tons/MWh): 0.81; Nitrogen oxides emissions rate (lbs/MWh): 1.62; Sulfur dioxide emissions rate (lbs/MWh): 0.97. State: Arkansas; Number of units: 30; Electricity generation (MWh): 40,295,345; Carbon dioxide emissions rate (tons/MWh): 0.90; Nitrogen oxides emissions rate (lbs/MWh): 1.88; Sulfur dioxide emissions rate (lbs/MWh): 3.33. State: California; Number of units: 179; Electricity generation (MWh): 80,854,400; Carbon dioxide emissions rate (tons/MWh): 0.46; Nitrogen oxides emissions rate (lbs/MWh): 0.11; Sulfur dioxide emissions rate (lbs/MWh): 0.01. State: Colorado; Number of units: 58; Electricity generation (MWh): 45,728,202; Carbon dioxide emissions rate (tons/MWh): 0.98; Nitrogen oxides emissions rate (lbs/MWh): 2.37; Sulfur dioxide emissions rate (lbs/MWh): 1.99. State: Connecticut; Number of units: 39; Electricity generation (MWh): 12,497,043; Carbon dioxide emissions rate (tons/MWh): 0.68; Nitrogen oxides emissions rate (lbs/MWh): 0.45; Sulfur dioxide emissions rate (lbs/MWh): 0.31. State: Delaware; Number of units: 15; Electricity generation (MWh): 5,489,585; Carbon dioxide emissions rate (tons/MWh): 0.79; Nitrogen oxides emissions rate (lbs/MWh): 1.58; Sulfur dioxide emissions rate (lbs/MWh): 5.28. State: District of Columbia; Number of units: 2; Electricity generation (MWh): 207,916; Carbon dioxide emissions rate (tons/MWh): 1.06; Nitrogen oxides emissions rate (lbs/MWh): 3.59; Sulfur dioxide emissions rate (lbs/MWh): 8.41. State: Florida; Number of units: 246; Electricity generation (MWh): 188,566,114; Carbon dioxide emissions rate (tons/MWh): 0.72; Nitrogen oxides emissions rate (lbs/MWh): 0.85; Sulfur dioxide emissions rate (lbs/MWh): 1.54. State: Georgia; Number of units: 141; Electricity generation (MWh): 95,973,778; Carbon dioxide emissions rate (tons/MWh): 0.91; Nitrogen oxides emissions rate (lbs/MWh): 1.26; Sulfur dioxide emissions rate (lbs/MWh): 4.56. State: Idaho; Number of units: 7; Electricity generation (MWh): 1,566,178; Carbon dioxide emissions rate (tons/MWh): 0.44; Nitrogen oxides emissions rate (lbs/MWh): 0.14; Sulfur dioxide emissions rate (lbs/MWh): 0.00. State: Illinois; Number of units: 196; Electricity generation (MWh): 97,862,368; Carbon dioxide emissions rate (tons/MWh): 1.09; Nitrogen oxides emissions rate (lbs/MWh): 1.57; Sulfur dioxide emissions rate (lbs/MWh): 4.50. State: Indiana; Number of units: 126; Electricity generation (MWh): 120,785,560; Carbon dioxide emissions rate (tons/MWh): 1.03; Nitrogen oxides emissions rate (lbs/MWh): 2.02; Sulfur dioxide emissions rate (lbs/MWh): 6.87. State: Iowa; Number of units: 48; Electricity generation (MWh): 41,249,495; Carbon dioxide emissions rate (tons/MWh): 1.10; Nitrogen oxides emissions rate (lbs/MWh): 2.17; Sulfur dioxide emissions rate (lbs/MWh): 5.06. State: Kansas; Number of units: 48; Electricity generation (MWh): 35,758,838; Carbon dioxide emissions rate (tons/MWh): 1.11; Nitrogen oxides emissions rate (lbs/MWh): 2.74; Sulfur dioxide emissions rate (lbs/MWh): 2.53. State: Kentucky; Number of units: 96; Electricity generation (MWh): 96,980,846; Carbon dioxide emissions rate (tons/MWh): 1.04; Nitrogen oxides emissions rate (lbs/MWh): 1.92; Sulfur dioxide emissions rate (lbs/MWh): 5.57. State: Louisiana; Number of units: 70; Electricity generation (MWh): 70,221,777; Carbon dioxide emissions rate (tons/MWh): 0.75; Nitrogen oxides emissions rate (lbs/MWh): 1.34; Sulfur dioxide emissions rate (lbs/MWh): 2.91. State: Maine; Number of units: 11; Electricity generation (MWh): 7,902,550; Carbon dioxide emissions rate (tons/MWh): 0.50; Nitrogen oxides emissions rate (lbs/MWh): 0.18; Sulfur dioxide emissions rate (lbs/MWh): 0.21. State: Maryland; Number of units: 46; Electricity generation (MWh): 26,381,736; Carbon dioxide emissions rate (tons/MWh): 1.06; Nitrogen oxides emissions rate (lbs/MWh): 1.47; Sulfur dioxide emissions rate (lbs/MWh): 2.27. State: Massachusetts; Number of units: 48; Electricity generation (MWh): 31,174,655; Carbon dioxide emissions rate (tons/MWh): 0.63; Nitrogen oxides emissions rate (lbs/MWh): 0.52; Sulfur dioxide emissions rate (lbs/MWh): 2.37. State: Michigan; Number of units: 96; Electricity generation (MWh): 76,833,143; Carbon dioxide emissions rate (tons/MWh): 0.97; Nitrogen oxides emissions rate (lbs/MWh): 2.07; Sulfur dioxide emissions rate (lbs/MWh): 6.31. State: Minnesota; Number of units: 45; Electricity generation (MWh): 31,496,681; Carbon dioxide emissions rate (tons/MWh): 1.04; Nitrogen oxides emissions rate (lbs/MWh): 1.90; Sulfur dioxide emissions rate (lbs/MWh): 2.61. State: Mississippi; Number of units: 57; Electricity generation (MWh): 40,802,413; Carbon dioxide emissions rate (tons/MWh): 0.75; Nitrogen oxides emissions rate (lbs/MWh): 1.46; Sulfur dioxide emissions rate (lbs/MWh): 2.68. State: Missouri; Number of units: 102; Electricity generation (MWh): 77,566,300; Carbon dioxide emissions rate (tons/MWh): 1.07; Nitrogen oxides emissions rate (lbs/MWh): 1.50; Sulfur dioxide emissions rate (lbs/MWh): 6.07. State: Montana; Number of units: 12; Electricity generation (MWh): 18,752,877; Carbon dioxide emissions rate (tons/MWh): 1.14; Nitrogen oxides emissions rate (lbs/MWh): 2.32; Sulfur dioxide emissions rate (lbs/MWh): 2.12. State: Nebraska; Number of units: 29; Electricity generation (MWh): 23,688,902; Carbon dioxide emissions rate (tons/MWh): 1.11; Nitrogen oxides emissions rate (lbs/MWh): 3.16; Sulfur dioxide emissions rate (lbs/MWh): 5.42. State: Nevada; Number of units: 37; Electricity generation (MWh): 28,136,479; Carbon dioxide emissions rate (tons/MWh): 0.61; Nitrogen oxides emissions rate (lbs/MWh): 0.77; Sulfur dioxide emissions rate (lbs/MWh): 0.56. State: New Hampshire; Number of units: 7; Electricity generation (MWh): 8,069,450; Carbon dioxide emissions rate (tons/MWh): 0.73; Nitrogen oxides emissions rate (lbs/MWh): 1.14; Sulfur dioxide emissions rate (lbs/MWh): 9.13. State: New Jersey; Number of units: 107; Electricity generation (MWh): 30,081,377; Carbon dioxide emissions rate (tons/MWh): 0.66; Nitrogen oxides emissions rate (lbs/MWh): 0.66; Sulfur dioxide emissions rate (lbs/MWh): 1.02. State: New Mexico; Number of units: 35; Electricity generation (MWh): 34,294,657; Carbon dioxide emissions rate (tons/MWh): 0.95; Nitrogen oxides emissions rate (lbs/MWh): 3.51; Sulfur dioxide emissions rate (lbs/MWh): 0.97. State: New York; Number of units: 165; Electricity generation (MWh): 63,663,802; Carbon dioxide emissions rate (tons/MWh): 0.65; Nitrogen oxides emissions rate (lbs/MWh): 0.89; Sulfur dioxide emissions rate (lbs/MWh): 1.49. State: North Carolina; Number of units: 104; Electricity generation (MWh): 78,576,396; Carbon dioxide emissions rate (tons/MWh): 0.97; Nitrogen oxides emissions rate (lbs/MWh): 1.36; Sulfur dioxide emissions rate (lbs/MWh): 3.06. State: North Dakota; Number of units: 11; Electricity generation (MWh): 28,269,255; Carbon dioxide emissions rate (tons/MWh): 1.19; Nitrogen oxides emissions rate (lbs/MWh): 3.87; Sulfur dioxide emissions rate (lbs/MWh): 8.78. State: Ohio; Number of units: 135; Electricity generation (MWh): 126,505,558; Carbon dioxide emissions rate (tons/MWh): 0.99; Nitrogen oxides emissions rate (lbs/MWh): 1.66; Sulfur dioxide emissions rate (lbs/MWh): 9.04. State: Oklahoma; Number of units: 66; Electricity generation (MWh): 60,394,162; Carbon dioxide emissions rate (tons/MWh): 0.83; Nitrogen oxides emissions rate (lbs/MWh): 2.37; Sulfur dioxide emissions rate (lbs/MWh): 2.82. State: Oregon; Number of units: 8; Electricity generation (MWh): 19,280,743; Carbon dioxide emissions rate (tons/MWh): 0.56; Nitrogen oxides emissions rate (lbs/MWh): 1.01; Sulfur dioxide emissions rate (lbs/MWh): 1.63. State: Pennsylvania; Number of units: 123; Electricity generation (MWh): 143,267,035; Carbon dioxide emissions rate (tons/MWh): 0.88; Nitrogen oxides emissions rate (lbs/MWh): 1.87; Sulfur dioxide emissions rate (lbs/MWh): 5.74. State: Rhode Island; Number of units: 8; Electricity generation (MWh): 7,094,295; Carbon dioxide emissions rate (tons/MWh): 0.49; Nitrogen oxides emissions rate (lbs/MWh): 0.16; Sulfur dioxide emissions rate (lbs/MWh): 0.01. State: South Carolina; Number of units: 71; Electricity generation (MWh): 48,054,008; Carbon dioxide emissions rate (tons/MWh): 0.93; Nitrogen oxides emissions rate (lbs/MWh): 1.17; Sulfur dioxide emissions rate (lbs/MWh): 3.94. State: South Dakota; Number of units: 8; Electricity generation (MWh): 3,255,521; Carbon dioxide emissions rate (tons/MWh): 1.16; Nitrogen oxides emissions rate (lbs/MWh): 7.64; Sulfur dioxide emissions rate (lbs/MWh): 7.73. State: Tennessee; Number of units: 85; Electricity generation (MWh): 45,166,515; Carbon dioxide emissions rate (tons/MWh): 1.03; Nitrogen oxides emissions rate (lbs/MWh): 1.38; Sulfur dioxide emissions rate (lbs/MWh): 5.26. State: Texas; Number of units: 284; Electricity generation (MWh): 318,045,099; Carbon dioxide emissions rate (tons/MWh): 0.80; Nitrogen oxides emissions rate (lbs/MWh): 0.92; Sulfur dioxide emissions rate (lbs/MWh): 2.90. State: Utah; Number of units: 26; Electricity generation (MWh): 39,211,138; Carbon dioxide emissions rate (tons/MWh): 0.94; Nitrogen oxides emissions rate (lbs/MWh): 3.13; Sulfur dioxide emissions rate (lbs/MWh): 1.10. State: Virginia; Number of units: 97; Electricity generation (MWh): 42,773,143; Carbon dioxide emissions rate (tons/MWh): 0.83; Nitrogen oxides emissions rate (lbs/MWh): 1.79; Sulfur dioxide emissions rate (lbs/MWh): 4.37. State: Washington; Number of units: 13; Electricity generation (MWh): 17,402,607; Carbon dioxide emissions rate (tons/MWh): 0.84; Nitrogen oxides emissions rate (lbs/MWh): 1.38; Sulfur dioxide emissions rate (lbs/MWh): 0.30. State: West Virginia; Number of units: 50; Electricity generation (MWh): 79,543,178; Carbon dioxide emissions rate (tons/MWh): 0.99; Nitrogen oxides emissions rate (lbs/MWh): 1.35; Sulfur dioxide emissions rate (lbs/MWh): 2.74. State: Wisconsin; Number of units: 84; Electricity generation (MWh): 46,382,410; Carbon dioxide emissions rate (tons/MWh): 1.07; Nitrogen oxides emissions rate (lbs/MWh): 1.43; Sulfur dioxide emissions rate (lbs/MWh): 4.71. State: Wyoming; Number of units: 21; Electricity generation (MWh): 42,829,664; Carbon dioxide emissions rate (tons/MWh): 1.15; Nitrogen oxides emissions rate (lbs/MWh): 2.84; Sulfur dioxide emissions rate (lbs/MWh): 3.03. Total: Number of units: 3,443; Electricity generation (MWh): 2,754,711,668; Carbon dioxide emissions rate (tons/MWh): [Empty]; Nitrogen oxides emissions rate (lbs/MWh): [Empty]; Sulfur dioxide emissions rate (lbs/MWh): [Empty]. Source: GAO presentation of Ventyx data. Legend: Lb = pound: MWh = megawatt-hour: Note: As with most of the other data presented in this report, we limited our analysis to those units that (1) list a fossil fuel as a primary fuel, (2) have a net summer capacity greater than 25 megawatts, and (3) produced power in 2010. No reported electricity production or emissions were reported from fossil fuel units in Alaska, Hawaii, or Vermont. [End of table] [End of section] Enclosure III: Energy and Emissions from U.S. Fossil Fuel Electricity Generating Units, by Location in 2010: Figures 14,15, 16, and 17 show the location of electricity generating units and the amount of electricity, sulfur dioxide, nitrogen oxides, and carbon dioxide they produced in 2010. Units in the Great Lakes, South Central, and Southeast regions produced most of the emissions.[Footnote 26] Specifically, in 2010, units in these regions accounted for 69 percent of the sulfur dioxide, 59 percent of nitrogen oxides, and 63 percent of the carbon dioxide emitted from older units nationwide in 2010 and generated 62 percent of the electricity from fossil fuel units. Figure 14: Geographic Distribution of Electricity Generation from Fossil Fuel Electricity Generating Units, 2010: [Refer to PDF for image: illustrated U.S. map] Depicted on the map: Electricity generation, in megawatt hours, by location: 10,000,000 to 27,000,000; 4,000,000 to 10,000,000; 1,000,000 to 4,000,000; 0 to 1,000,000. Source: GAO analysis of Ventyx data. [End of figure] Figure 15: Geographic Distribution of Sulfur Dioxide Emissions from Fossil Fuel Electricity Generating Units, 2010: [Refer to PDF for image: illustrated U.S. map] Depicted on the map: Sulfur dioxide emissions, in tons, by location: 35,000 to 135,000; 11,000 to 35,000; 1,000 to 11,000; 0 to 1,000. Source: GAO analysis of Ventyx data. [End of figure] Figure 16: Geographic Distribution of Nitrogen Oxides Emissions from Fossil Fuel Electricity Generating Units, 2010: [Refer to PDF for image: illustrated U.S. map] Depicted on the map: Nitrogen oxides emissions, in tons, by location: 10,500 to 38,900; 4,200 to 10,500; 900 to 4,200; 0 to 900. Source: GAO analysis of Ventyx data. [End of figure] Figure 17: Geographic Distribution of Carbon Dioxide Emissions from Fossil Fuel Electricity Generating Units, 2010: [Refer to PDF for image: illustrated U.S. map] Depicted on the map: Carbon dioxide emissions, in tons, by location: 10,500,000 to 25,400,000; 4,200,000 to 10,500,000; 900,000 to 4,200,000; 0 to 900,000. Source: GAO analysis of Ventyx data. [End of figure] [End of section] Enclosure IV: Energy and Emissions from U.S. Fossil Fuel Electricity Generating Units in 2010, by Decade Unit Began Operating: Table 5 presents data on fossil fuel units' electricity generation, aggregate emissions, capacity, and emissions per unit of electricity generated, based on the decade the unit began operating. Table 5: Electricity Generation and Emissions in 2010, by Decade Unit Began Operating: Number of units; Decade unit began operating: 1950s: 415; 1960s: 382; 1970s: 683; 1980s: 232; 1990s: 404; 2000s: 1,249. Electricity generation (MWh, in thousands); Decade unit began operating: 1950s: 195,561; 1960s: 353,497; 1970s: 770,451; 1980s: 513,904; 1990s: 163,507; 2000s: 728,165. Net summer capacity (MW); Decade unit began operating: 1950s: 52,130; 1960s: 93,570; 1970s: 177,014; 1980s: 83,160; 1990s: 52,967; 2000s: 241,798. Carbon dioxide emissions (tons, in thousands); Decade unit began operating: 1950s: 212,070; 1960s: 370,819; 1970s: 799,849; 1980s: 551,016; 1990s: 118,900; 2000s: 369,887. Carbon dioxide emissions rate (lbs/MWh); Decade unit began operating: 1950s: 2,169; 1960s: 2,098; 1970s: 2,076; 1980s: 2,144; 1990s: 1,454; 2000s: 1,016. Nitrogen oxides emissions (lbs); Decade unit began operating: 1950s: 273,290; 1960s: 446,312; 1970s: 697,687; 1980s: 524,769; 1990s: 85,282; 2000s: 65,186. Nitrogen oxides emissions rate (lbs/MWh); Decade unit began operating: 1950s: 2.79; 1960s: 2.53; 1970s: 1.81; 1980s: 2.04; 1990s: 1.04; 2000s: 0.18. Sulfur dioxide emissions (lbs); Decade unit began operating: 1950s: 1,135,001; 1960s: 1,372,766; 1970s: 1,506,432; 1980s: 987,113; 1990s: 74,822; 2000s: 31,368. Sulfur dioxide emissions (lbs/MWh); Decade unit began operating: 1950s: 11.61; 1960s: 7.77; 1970s: 3.91; 1980s: 3.84; 1990s: 0.92; 2000s: 0.09. Source: GAO analysis of Ventyx data. Legend: lb = pound: MWh = megawatt-hour: [End of table] [End of section] Footnotes: [1] Fossil fuels are responsible for nearly all emissions of carbon dioxide, sulfur dioxide, and nitrogen oxides from power plants. [2] An electricity generating unit consists of any combination of an electricity generator, reactor, boiler, combustion turbine, or other equipment operated together to produce electrical power. A power plant is a facility with one or more generating units, together with other equipment used to produce electric power. [3] Oil is used to a very limited extent, providing less than 1 percent of electricity in 2010. [4] EPA has set national ambient air quality standards for six pollutants, termed "criteria" pollutants: carbon monoxide, lead, nitrogen oxides, ozone, particulate matter, and sulfur oxides. [5] This report focuses solely on fossil fuel electricity generating units, although NSR also applies to certain other major stationary sources of air pollution, such as other industrial facilities. [6] We used 1978 as the cutoff date for our analysis--instead of August 7, 1977--because 1978 was the first full year after NSR's establishment, and our analysis reports only annual data. [7] GAO, Air Pollution: Emissions from Older Electricity Generating Units, [hyperlink, http://www.gao.gov/products/GAO-02-709] (Washington, D.C.: June 12, 2002). Note: This report defines "older units" as those fossil fuel generating units that began operation before 1972. [8] Regulated pollutants are sulfur oxides; nitrogen oxides; other criteria pollutants; and, since January 2, 2011, greenhouse gases. [9] EPA, National Emissions Inventory Air Pollutant Emissions Trends Data, "Current Emissions Trends Summaries," accessed October 2011, [hyperlink, http://www.epa.gov/ttn/chief/trends/index.html#tables]. [10] EPA, Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990- 2009, EPA-430-R-11-005 (Washington, D.C.: Apr. 15, 2011). [11] [hyperlink, http://www.gao.gov/products/GAO-02-709] and GAO, Air Quality: Information on Tall Smokestacks and Their Contribution to Interstate Transport of Air Pollution, [hyperlink, http://www.gao.gov/products/GAO-11-473] (Washington, D.C.: May 11, 2011). [12] Sulfur dioxide and nitrogen oxides can transform into fine particles in the atmosphere. Fine particles are a subset of particulate matter, a regulated pollutant. Ozone, also a regulated pollutant, forms when nitrogen oxides react with volatile organic compounds (chemicals that are emitted as gases from natural sources, such as trees, as well as from anthropogenic sources, such as motor vehicles) in the presence of heat and sunlight. [13] [hyperlink, http://www.gao.gov/products/GAO-11-473]. [14] EPA, Office of Air and Radiation, Available and Emerging Technologies for Reducing Greenhouse Gas Emissions from Coal-Fired Electric Generating Units (Research Triangle Park, NC: October 2010). [15] EPA, Integrated Planning Model, "TR Base Case v.4.10," accessed April 2, 2012, [hyperlink, http://www.epa.gov/airmarkets/progsregs/epa- ipm/BaseCasev410.html#documentation]. [16] Of the 3,443 fossil fuel electricity generating units we assessed, 1,485 were older units, and 1,958 were newer units. [17] In 2010, oil-fired units (both older and newer) accounted for less than one percent of electricity from fossil fuel units. [18] The 240 percent increase refers to 1987 through 2009. See Energy Information Administration, Annual Energy Review 2010, DOE/EIA- 0384(2010) (Washington, D.C.: October 2011). [19] GAO, Natural Gas: Factors Affecting Prices and Potential Impacts on Consumers, [hyperlink, http://www.gao.gov/products/GAO-06-420T] (Washington, D.C.: Feb. 13, 2006). [20] We limited this analysis to coal-fired units because these units are responsible for nearly all (99 percent) of sulfur dioxide emissions from fossil fuel units. [21] These regulations include the Cross-State Air Pollution Rule-- which limits sulfur dioxide and nitrogen oxides emissions from a number of states that contribute significantly to nonattainment of or interference with maintenance of certain national ambient air quality standards in downwind states--and National Emissions Standards for Hazardous Air Pollutants from Coal-and Oil-Fired Electric Utility Steam Generating Units, also known as the Mercury and Air Toxics Standards, which establish emissions limitations on mercury and other pollutants. Both regulations are being challenged in court. [22] In many states, public utility commissions are responsible for approving the rates (or prices) electric utilities charge their customers and ensuring they are reasonable. As part of approving rates, these commissions approve such utility investments as emissions controls and, as a result, may consider whether specific technologies are reasonable. These commissions generally require some demonstration that the investment is prudent. [23] Heat rate is a measurement used in the energy industry to calculate how efficiently an electricity generator uses heat energy. It is expressed as the number of British thermal units (Btu) of heat required to produce a kilowatt hour of energy. A lower heat rate signifies greater efficiency. [24] Generating units that undergo frequent startups use comparatively large amounts of fuel and may be less efficient than units that operate continuously. [25] These regions correspond to Environmental Protection Agency (EPA) Region 3 (Delaware, District of Columbia, Maryland, Pennsylvania, Virginia, and West Virginia) and Region 5 (Illinois, Indiana, Michigan, Minnesota, Ohio, and Wisconsin). [26] These regions correspond to Environmental Protection Agency (EPA) Region 5 (Illinois, Indiana, Michigan, Minnesota, Ohio, and Wisconsin); Region 6 (Arkansas, Louisiana, New Mexico, Oklahoma, and Texas); and Region 4 (Alabama, Florida, Georgia, Kentucky, Mississippi, North Carolina, South Carolina, and Tennessee). [End of section] GAO’s Mission: The Government Accountability Office, the audit, evaluation, and investigative arm of Congress, exists to support Congress in meeting its constitutional responsibilities and to help improve the performance and accountability of the federal government for the American people. GAO examines the use of public funds; evaluates federal programs and policies; and provides analyses, recommendations, and other assistance to help Congress make informed oversight, policy, and funding decisions. GAO’s commitment to good government is reflected in its core values of accountability, integrity, and reliability. 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