oversight

Air Emissions and Electricity Generation at U.S. Power Plants

Published by the Government Accountability Office on 2012-04-18.

Below is a raw (and likely hideous) rendition of the original report. (PDF)

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. 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. 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. 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. 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


    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.

                                      GAO-12-545R Air Emissions and Electricity Generation at U.S. Power Plants
established in 1977. 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.” 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. 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). 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,



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, 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.


Page 2                          GAO-12-545R Air Emissions and Electricity Generation at U.S. Power Plants
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




Page 3                       GAO-12-545R Air Emissions and Electricity Generation at U.S. Power Plants
emissions from all sources nationwide. 9 Electricity generation was also responsible for 39
percent of carbon dioxide emissions from all sources in 2009. 10 Units in the Southeast, South
Central, and Great Lakes regions produced most of the electricity and emissions from fossil fuel
units. (See encls. 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. 11
For example, sulfur dioxide and nitrogen oxides contribute to the formation of fine particles, and
nitrogen oxides contribute to the formation of ozone. 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. 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. 14



9
 EPA, National Emissions Inventory Air Pollutant Emissions Trends Data, “Current Emissions Trends
Summaries,” accessed October 2011, 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
  GAO-02-709 and GAO, Air Quality: Information on Tall Smokestacks and Their Contribution to
Interstate Transport of Air Pollution, 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
    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).


Page 4                         GAO-12-545R Air Emissions and Electricity Generation at U.S. Power Plants
Figure 1: Sample Layout of Emissions Controls at a Coal Power Plant




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. 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.




15
  EPA, Integrated Planning Model, “TR Base Case v.4.10,” accessed April 2, 2012,
http://www.epa.gov/airmarkets/progsregs/epa-ipm/BaseCasev410.html#documentation.


Page 5                       GAO-12-545R Air Emissions and Electricity Generation at U.S. Power Plants
Table 1: Summary of Emissions Control Equipment Used at Electricity Generating Units

    Pollutant         Control equipment         How it works                                 Removal efficiency

    Sulfur dioxidea   Flue gas                  Wet flue gas desulfurization units inject a Wet flue gas desulfurization units can
                      desulfurization unit      liquid sorbent, such as limestone, into the remove 80-99 percent of sulfur dioxide.
                      (commonly referred to     flue gas to form a wet solid that can be
                      as a “scrubber”)          disposed of or sold.                        Dry flue gas desulfurization units can
                                                                                            remove 70-95 percent of sulfur dioxide.
                                                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.

    Nitrogen oxides   Combustion control        Coal combustion conditions are adjusted These technologies can reduce
                      technologies, such as     to inhibit the formation of nitrogen oxides. formation of nitrogen oxides by 40-
                      low-nitrogen-oxides                                                    45 percent.
                      burnersb

                      Postcombustion            Selective catalytic reduction units inject   Selective catalytic reduction units can
                      controls, such as         ammonia into flue gas to form nitrogen       remove 70-95 percent of nitrogen
                      selective catalytic       and water and use a catalyst to enhance      oxides.
                      reduction and selective   the reaction.
                      noncatalytic reduction                                                 Selective noncatalytic reduction units
                      units                     Selective noncatalytic reduction units       can remove 30-75 percent of nitrogen
                                                also inject ammonia but do not use a         oxides.
                                                catalyst.

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.


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 fig. 2). Units that began operating after 1978 were responsible
for the remainder of the emissions and electricity production. 16




16
 Of the 3,443 fossil fuel electricity generating units we assessed, 1,485 were older units, and 1,958 were
newer units.


Page 6                                 GAO-12-545R Air Emissions and Electricity Generation at U.S. Power Plants
Figure 2: Share of Total Electricity and Emissions per Unit of Electricity Generated by Fossil Generating
Units in 2010




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.


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




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.




Page 7                                  GAO-12-545R Air Emissions and Electricity Generation at U.S. Power Plants
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




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.


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 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.




Page 8                                 GAO-12-545R Air Emissions and Electricity Generation at U.S. Power Plants
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




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.

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.




Page 9                                 GAO-12-545R Air Emissions and Electricity Generation at U.S. Power Plants
Figure 6: Carbon Dioxide Emissions per Unit of Electricity Generated by Fossil Fuel Generating Units in 2010,
by Decade Unit Began Operating




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.

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.




Page 10                                  GAO-12-545R Air Emissions and Electricity Generation at U.S. Power Plants
Figure 7: Emissions per Unit of Electricity Generated by Fossil Fuel Generating Units in 2010, by Type of Fuel




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. 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. 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. 19 After
rising in the early 2000s, natural gas prices have again fallen in recent years, a trend that may



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, GAO-06-420T
(Washington, D.C.: Feb. 13, 2006).


Page 11                          GAO-12-545R Air Emissions and Electricity Generation at U.S. Power Plants
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




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.




Page 12                         GAO-12-545R Air Emissions and Electricity Generation at U.S. Power Plants
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




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. 20




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.


Page 13                          GAO-12-545R Air Emissions and Electricity Generation at U.S. Power Plants
Figure 10: Use of Sulfur Dioxide Emissions Controls among Older and Newer Coal-Fired Generating Units in
2010




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.




Page 14                         GAO-12-545R Air Emissions and Electricity Generation at U.S. Power Plants
Figure 11: Sulfur Dioxide Emissions from Controlled and Uncontrolled Coal-Fired Generating Units in 2010




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.




Page 15                         GAO-12-545R Air Emissions and Electricity Generation at U.S. Power Plants
Table 2: Controls for Nitrogen Oxides in Fossil Fuel Electricity Generating Units: Removal Efficiency and
Extent of Use in 2010

 Category                  Control type                                   Number of older units         Number of newer units

 1                         None                                                               564                            116

 2                         Selective noncatalytic reduction, low
                           nitrogen-oxides burners, and others                                708                          1,204

 3                         Selective catalytic reduction (SCR)                                213                            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.


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




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.


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


Page 16                                       GAO-12-545R Air Emissions and Electricity Generation at U.S. Power Plants
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. 21 Conversely, some uncontrolled units may be limited in their ability to install certain
types of emissions controls if these controls are not required. 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.” 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. 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.


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.


Page 17                         GAO-12-545R Air Emissions and Electricity Generation at U.S. Power Plants
Figure 13: Average Efficiency (Heat Rate) of Fossil Fuel Units in 2010, by Decade Unit Began Operating




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.

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. 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.




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).


Page 18                                  GAO-12-545R Air Emissions and Electricity Generation at U.S. Power Plants
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 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,




David C. Trimble
Director, Natural Resources and Environment




Frank Rusco
Director, Natural Resources and Environment


Enclosures - 4




Page 19                       GAO-12-545R Air Emissions and Electricity Generation at U.S. Power Plants
 Enclosure I

   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

                                              Electricity
                         Number of           generation      Carbon dioxide     Nitrogen oxide      Sulfur dioxide
State                        units      (megawatt-hours)    emissions (tons)   emissions (tons)   emissions (tons)
Alabama                         88           100,961,300         84,828,993             63,336            204,195

Arizona                         63            74,817,174         60,732,544             60,524             36,445

Arkansas                        30            40,295,345         36,271,855             37,783             67,084

California                     179            80,854,400         36,929,068              4,467                226

Colorado                        58            45,728,202         44,826,939             54,088             45,391

Connecticut                     39            12,497,043           8,526,856             2,783              1,955

Delaware                        15             5,489,585           4,318,918             4,330             14,496

District of Columbia             2               207,916            220,765                373                874

Florida                        246           188,566,114        135,313,627             79,759            144,829

Georgia                        141            95,973,778         87,569,772             60,580            218,906

Idaho                            7             1,566,178            693,069                113                  3

Illinois                       196            97,862,368        107,058,198             77,063            220,077

Indiana                        126           120,785,560        124,321,920            121,844            414,638

Iowa                            48            41,249,495         45,296,689             44,796            104,389

Kansas                          48            35,758,838         39,757,268             48,938             45,251

Kentucky                        96            96,980,846        101,053,094             93,040            270,045

Louisiana                       70            70,221,777         52,344,198             47,153            102,263

Maine                           11             7,902,550           3,953,551               719                821

Maryland                        46            26,381,736         27,999,389             19,434             29,946

Massachusetts                   48            31,174,655         19,787,576              8,181             36,892

Michigan                        96            76,833,143         74,272,141             79,566            242,409

Minnesota                       45            31,496,681         32,900,506             29,911             41,076

Mississippi                     57            40,802,413         30,624,811             29,773             54,696

Missouri                       102            77,566,300         83,182,289             58,288            235,368

Montana                         12            18,752,877         21,356,366             21,728             19,896

Nebraska                        29            23,688,902         26,402,103             37,402             64,184

Nevada                          37            28,136,479         17,222,084             10,812              7,889

New Hampshire                    7             8,069,450           5,899,639             4,612             36,833

New Jersey                     107            30,081,377         19,995,676              9,937             15,270

New Mexico                      35            34,294,657         32,657,348             60,256             16,570

New York                       165            63,663,802         41,687,271             28,311             47,488




 Page 20                             GAO-12-545R Air Emissions and Electricity Generation at U.S. Power Plants
Enclosure I


                                                            Electricity
                                    Number of              generation      Carbon dioxide        Nitrogen oxide          Sulfur dioxide
State                                   units         (megawatt-hours)    emissions (tons)      emissions (tons)       emissions (tons)
North Carolina                              104             78,576,396         76,242,017                   53,390                120,254

North Dakota                                 11             28,269,255         33,609,781                   54,744                124,096

Ohio                                        135            126,505,558        125,054,961                 104,871                 572,110

Oklahoma                                     66             60,394,162         49,876,813                   71,434                 85,135

Oregon                                        8             19,280,743         10,875,349                    9,729                 15,696

Pennsylvania                                123            143,267,035        125,643,066                 134,169                 411,216

Rhode Island                                  8              7,094,295           3,504,392                     578                       18

South Carolina                               71             48,054,008         44,815,737                   28,123                 94,641

South Dakota                                  8              3,255,521           3,765,854                  12,433                 12,589

Tennessee                                    85             45,166,515         46,449,221                   31,239                118,723

Texas                                       284            318,045,099        255,708,493                 145,798                 461,754

Utah                                         26             39,211,138         37,005,962                   61,415                 21,598

Virginia                                     97             42,773,143         35,584,177                   38,300                 93,385

Washington                                   13             17,402,607         14,560,232                   11,980                  2,651

Wisconsin                                    84             46,382,410         49,753,419                   33,082                109,158

West Virginia                                50             79,543,178         79,135,925                   53,757                109,028

Wyoming                                      21             42,829,664         49,382,465                   60,902                 64,849
Total                                      3,443          2,754,711,668      2,448,972,387              2,105,844               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.




Page 21                                            GAO-12-545R Air Emissions and Electricity Generation at U.S. Power Plants
  Enclosure II

   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
                                                                Carbon dioxide    Nitrogen oxides    Sulfur dioxide
                                                  Electricity
State                Number of units                            emissions rate     emissions rate   emissions rate
                                           generation (MWh)
                                                                   (tons/MWh)           (lbs/MWh)        (lbs/MWh)
Alabama                          88              100,961,300              0.84               1.25             4.05
Arizona                          63               74,817,174              0.81               1.62             0.97
Arkansas                         30               40,295,345              0.90               1.88             3.33
California                      179               80,854,400              0.46               0.11             0.01
Colorado                         58               45,728,202              0.98               2.37             1.99
Connecticut                      39               12,497,043              0.68               0.45             0.31
Delaware                         15                5,489,585              0.79               1.58             5.28
District of
Columbia                          2                  207,916              1.06               3.59             8.41
Florida                         246              188,566,114              0.72               0.85             1.54
Georgia                         141               95,973,778              0.91               1.26             4.56
Idaho                             7                1,566,178              0.44               0.14             0.00
Illinois                        196               97,862,368              1.09               1.57             4.50
Indiana                         126              120,785,560              1.03               2.02             6.87
Iowa                             48               41,249,495              1.10               2.17             5.06
Kansas                           48               35,758,838              1.11               2.74             2.53
Kentucky                         96               96,980,846              1.04               1.92             5.57
Louisiana                        70               70,221,777              0.75               1.34             2.91
Maine                            11                7,902,550              0.50               0.18             0.21
Maryland                         46               26,381,736              1.06               1.47             2.27
Massachusetts                    48               31,174,655              0.63               0.52             2.37
Michigan                         96               76,833,143              0.97               2.07             6.31
Minnesota                        45               31,496,681              1.04               1.90             2.61
Mississippi                      57               40,802,413              0.75               1.46             2.68
Missouri                        102               77,566,300              1.07               1.50             6.07
Montana                          12               18,752,877              1.14               2.32             2.12
Nebraska                         29               23,688,902              1.11               3.16             5.42
Nevada                           37               28,136,479              0.61               0.77             0.56
New Hampshire                     7                8,069,450              0.73               1.14             9.13
New Jersey                      107               30,081,377              0.66               0.66             1.02
New Mexico                       35               34,294,657              0.95               3.51             0.97
New York                        165               63,663,802              0.65               0.89             1.49




  Page 22                              GAO-12-545R Air Emissions and Electricity Generation at U.S. Power Plants
 Enclosure II


                                                                             Carbon dioxide         Nitrogen oxides         Sulfur dioxide
                                                               Electricity
State                        Number of units                                 emissions rate          emissions rate        emissions rate
                                                        generation (MWh)
                                                                                (tons/MWh)                (lbs/MWh)             (lbs/MWh)
North Carolina                               104               78,576,396               0.97                     1.36                     3.06
North Dakota                                  11               28,269,255               1.19                     3.87                     8.78
Ohio                                         135              126,505,558               0.99                     1.66                     9.04
Oklahoma                                      66               60,394,162               0.83                     2.37                     2.82
Oregon                                         8               19,280,743               0.56                     1.01                     1.63
Pennsylvania                                 123              143,267,035               0.88                     1.87                     5.74
Rhode Island                                   8                7,094,295               0.49                     0.16                     0.01
South Carolina                                71               48,054,008               0.93                     1.17                     3.94
South Dakota                                   8                3,255,521               1.16                     7.64                     7.73
Tennessee                                     85               45,166,515               1.03                     1.38                     5.26
Texas                                        284              318,045,099               0.80                     0.92                     2.90
Utah                                          26               39,211,138               0.94                     3.13                     1.10
Virginia                                      97               42,773,143               0.83                     1.79                     4.37
Washington                                    13               17,402,607               0.84                     1.38                     0.30

West Virginia                                 50               79,543,178               0.99                     1.35                     2.74
Wisconsin                                     84               46,382,410               1.07                     1.43                     4.71
Wyoming                                       21               42,829,664               1.15                     2.84                     3.03
Total                                       3,443           2,754,711,668                   -                        -                       -
 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.




 Page 23                                            GAO-12-545R Air Emissions and Electricity Generation at U.S. Power Plants
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. 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 elecricity from fossil fuel units.
Figure 14: Geographic Distribution of Electricity Generation from Fossil Fuel Electricity Generating Units,
2010




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).


Page 24                          GAO-12-545R Air Emissions and Electricity Generation at U.S. Power Plants
Enclosure III

Figure 15: Geographic Distribution of Sulfur Dioxide Emissions from Fossil Fuel Electricity Generating Units,
2010




Page 25                          GAO-12-545R Air Emissions and Electricity Generation at U.S. Power Plants
Enclosure III

Figure 16: Geographic Distribution of Nitrogen Oxides Emissions from Fossil Fuel Electricity Generating
Units, 2010




Page 26                         GAO-12-545R Air Emissions and Electricity Generation at U.S. Power Plants
Enclosure III

Figure 17: Geographic Distribution of Carbon Dioxide Emissions from Fossil Fuel Electricity Generating
Units, 2010




Page 27                         GAO-12-545R Air Emissions and Electricity Generation at U.S. Power Plants
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

                                                                  Decade unit began operating
                                          1950s          1960s           1970s         1980s         1990s          2000s
 Number of units                            415            382             683           232           404          1,249
 Electricity generation
 (MWh, in thousands)                    195,561        353,497          770,451       513,904       163,507       728,165
 Net summer capacity
 (MW)                                    52,130         93,570          177,014        83,160        52,967       241,798
 Carbon dioxide
 emissions (tons, in
 thousands)                             212,070        370,819          799,849       551,016       118,900       369,887
 Carbon dioxide
 emissions rate
 (lbs/MWh)                                2,169          2,098            2,076         2,144         1,454         1,016
 Nitrogen oxides
 emissions (lbs)                        273,290        446,312          697,687       524,769        85,282        65,186
 Nitrogen oxides
 emissions rate
 (lbs/MWh)                                  2.79           2.53            1.81          2.04          1.04          0.18
 Sulfur dioxide
 emissions (lbs)                       1,135,001      1,372,766       1,506,432       987,113        74,822        31,368
 Sulfur dioxide
 emissions (lbs/MWh)                      11.61            7.77            3.91          3.84          0.92          0.09
Source: GAO analysis of Ventyx data.


Legend

lb = pound
MWh = megawatt-hour




(361383)




Page 28                                      GAO-12-545R Air Emissions and Electricity Generation at U.S. Power Plants
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