POWER SECTOR PROGRAMS
PROGRESS REPORT
Affected Units
Program Compliance
Acid Deposition
Emission Reductions
Market Activity
Ecosystem Response
Program Basics
Emission Controls & Monitoring
Air Quality
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Executive Summary
Under the Clean Air Act, EPA implements several regulations that affect power plants, including the Acid
Rain Program (ARP), the Cross-State Air Pollution Rule (CSAPR) and CSAPR Update, and the Mercury and
Air Toxics Standards (MATS). These programs require fossil fuel-fired electric generating units to reduce
emissions of sulfur dioxide (S02), nitrogen oxides (N0X), and hazardous air pollutants (including mercury
(Hg)) to protect human health and the environment. This reporting year marks the third year of CSAPR
implementation, the twenty-second year of ARP, and the first year of MATS implementation in which
the majority of sources were required to report emissions for the full year. This report summarizes
annual progress through 2017, highlighting data that EPA systematically collects on emissions for all
three programs, on compliance, and environmental effects for ARP and CSAPR. Transparency and data
availability are a hallmark of these programs, and a cornerstone of their success.
Sulfur dioxide, nitrogen oxides, and hazardous air pollutants, including mercury, are fossil fuel
combustion byproducts that impact public health and the environment. S02 and NOx, and their sulfate
and nitrate byproducts, are transported and deposited as acid rain at levels harmful to sensitive
ecosystems in many areas of the country. These pollutants also contribute to the formation of fine
particles (sulfates and nitrates) and ground level ozone that are associated with significant human
health effects and regional haze. Atmospheric mercury deposition accumulates in fish to levels of
concern for human health and the health of fish-eating wildlife.
The Acid Rain Program, CSAPR, CSAPR Update and MATS have delivered substantial reductions in power
sector emissions of S02, NOx, and hazardous air pollutants, along with significant improvements in air
quality and the environment. In addition to the demonstrated reductions achieved by the power sector
emission control programs described in this report, S02, NOx, and hazardous air pollutant emissions
have declined steadily in recent years due to a variety of power industry trends that are expected to
continue.
2017 ARP, CSAPR and MATS at a Glance
• Annual S02 emissions:
CSAPR - 0.8 million tons (91 percent below 2005)
ARP -1.3 million tons (92 percent below 1990)
• Annual NOx emissions:
CSAPR - 0.6 million tons (73 percent below 2005)
ARP -1.0 million tons (84 percent below 1990)
• CSAPR ozone season NOx emissions: 300,000 tons (53 percent below 2005)
• Compliance: 100 percent compliance for power plants in the market-based ARP and CSAPR
allowance-trading programs.
• Emissions reported under MATS:
Mercury - 4 tons (86 percent below 2010)
Acid gases - 4,831 tons (96 percent below 2010)
Non-mercury metals - 221 tons (81 percent below 2010)
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• Ambient particulate sulfate concentrations: The eastern United States has shown substantial
improvement, decreasing 33 to 71 percent between 2000-2002 and 2015-2017.
• Ozone NAAQS attainment: Based on 2015-2017 data, all 92 areas in the East originally
designated as nonattainment for the 1997 ozone NAAQS are now meeting the standard.
• PM2.5 NAAQS attainment: Based on 2015-2017 data, 36 of the 39 areas in the East originally
designated as nonattainment for the 1997 PM2.5 NAAQS are now meeting the standard (one
area has incomplete data).
• Wet sulfate deposition: All areas of the eastern United States have shown significant
improvement with an overall 64 percent reduction in wet sulfate deposition from 2000-2002 to
2015-2017.
• Levels of acid neutralizing capacity (ANC): This indicator of recovery improved (i.e., increased)
significantly from 1990 levels at lake and stream monitoring sites in the Adirondack region, New
England and the Catskill mountains.
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Executive Summary
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Contents
Executive Summary 2
2017 ARP, CSAPR and MATS at a Glance 2
Chapter 1: Program Basics 10
Highlights 10
Acid Rain Program (ARP): 1995 - present 10
Cross-State Air Pollution Rule (CSAPR): 2015 - present 11
Cross-State Air Pollution Rule Update (CSAPR Update): 2017 - present 11
CSAPR and CSAPR Update Budgets 11
Mercury and Air Toxics Standards (MATS) 11
Background Information 12
Power Sector Trends 12
Acid Rain Program 12
NOx Budget Trading Program 13
Clean Air Interstate Rule 13
Cross-State Air Pollution Rule 13
Cross-State Air Pollution Rule Update 14
Cross-State Air Pollution Rule Close-Out 14
Mercury and Air Toxics Standards 14
More Information 14
Figures 16
Chapter 2: Affected Units 19
Highlights 19
Acid Rain Program (ARP) 19
Cross-State Air Pollution Rule (CSAPR) 19
Mercury and Air Toxics (MATS) 19
Background Information 19
More Information 19
Figures 21
Chapter 3: Emission Reductions 23
Sulfur Dioxide (SO2) 23
Highlights 23
Overall Results 23
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S02 Emission Trends 23
S02 State-by-State Emissions 23
S02 Emission Rates 24
Background Information 24
More Information 24
Figures 25
Annual Nitrogen Oxides 29
Highlights 29
Overall Results 29
Annual N0X Emissions Trends 29
Annual N0X State-by-State Emissions 29
Annual N0X Emission Rates 29
Background Information 30
More Information 30
Figures 31
Ozone Season Nitrogen Oxides 35
Highlights 35
Overall Results 35
Ozone Season NOx Emissions Trends 35
Ozone Season NOx State-by-State Emissions 35
Ozone Season NOx Emission Rates 35
Background Information 36
More Information 36
Figures 37
Mercury and Air Toxics 41
Highlights 41
Overall Results 41
Mercury and Hazardous Air Pollutant Emission Trends 41
Reducing Mercury Emissions from Coal-Fired Power Plants Since 2010 41
Decreasing Coal-Fired Generation 42
Controlling Mercury Emissions at Coal-Fired EGUs 42
Contents
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Background Information 42
More Information 43
Figures 44
Chapter 4: Emission Controls and Monitoring 47
Highlights 47
ARP and CSAPR S02 Program Controls and Monitoring 47
CSAPR N0X Annual Program Controls and Monitoring 47
CSAPR N0X Ozone Season Program Controls and Monitoring 47
MATS Controls and Monitoring 47
Background Information 48
Continuous Emission Monitoring Systems (CEMS) 48
S02 Emission Controls 48
N0X Emission Controls 48
Hazardous Air Pollutant Controls 48
More Information 49
Figures 50
Chapter 5: Program Compliance 60
Highlights 60
ARP S02 Program 60
CSAPR S02 Group 1 Program 60
CSAPR S02 Group 2 Program 60
CSAPR NOx Annual Program 60
CSAPR NOx Ozone Season Group 1 Program 61
CSAPR NOx Ozone Season Group 2 Program 61
Background Information 61
More Information 61
Figures 62
Chapter 6: Market Activity 68
Highlights 68
Transaction Types and Volumes 68
2017 Allowance Prices 68
Background Information 68
Transaction Types and Volumes 68
Allowance Markets 69
Contents
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More Information
Figures
Chapter 7: Air Quality
Sulfur Dioxide and Nitrogen Oxides Trends
Highlights
National S02 Air Quality
Regional Changes in Air Quality
Background Information
Sulfur Dioxide
Nitrogen Oxides 73
More Information 73
References 73
Figures 74
Ozone 76
Highlights 76
Changes in 1-Hour Ozone during Ozone Season 76
Trends in Rural 8-Hour Ozone 76
Changes in 8-Hour Ozone Concentrations 76
Changes in Ozone Nonattainment Areas 76
Background Information 77
Ozone Standards 77
Regional Trends in Ozone 77
Meteorologically-Adjusted Daily Maximum 8-Hour Ozone Concentrations 78
Changes in Ozone Nonattainment Areas 78
More Information 78
References 78
Figures 80
Particulate Matter 85
Highlights 85
PM Seasonal Trends 85
Changes in PM2.5 Nonattainment 85
Background Information 85
Particulate Matter Standards 86
Changes in PM2.5 Nonattainment Areas 86
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More Information 86
References 86
Figures 88
Chapter 8: Acid Deposition 90
Highlights 90
Wet Sulfate Deposition 90
Wet Inorganic Nitrogen Deposition 90
Regional Trends in Total Deposition 90
Background Information 90
Acid Deposition 90
Monitoring Networks 91
More Information 91
References 91
Figures 92
Chapter 9: Ecosystem Response 95
Ecosystem Health 95
Highlights 95
Regional Trends in Water Quality 95
Ozone Impacts on Forests 95
Background Information 96
Acidified Surface Water Trends 96
Surface Water Monitoring Networks 97
Forest Health 97
More Information 97
References 97
Figures 98
Critical Loads Analysis 101
Highlights 101
Critical Loads and Exceedances 101
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Background Information 101
More Information 101
References 102
Figures 103
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Chapter 1: Program Basics
The Acid Rain Program (ARP), the Cross-State Air Pollution Rule (CSAPR), and the CSAPR Update are
implemented through cap and trade programs designed to reduce emissions of sulfur dioxide (S02) and
nitrogen oxides (N0X) from covered power plants. Established under Title IV of the 1990 Clean Air Act
Amendments, the Acid Rain Program was a landmark nationwide cap and trade program, with a goal of
reducing the emissions that cause acid rain. The undisputed success of the program in achieving
significant emission reductions in a cost-effective manner led to the application of the market-based cap
and trade tool for other regional environmental problems, namely interstate air pollution transport, or
pollution from upwind emission sources that impacts air quality in downwind areas. The interstate
transport of pollution can make it difficult for downwind states to meet health-based air quality
standards for regional pollutants, particularly PM2.5 and ozone. EPA first employed trading to address
regional criteria pollution in the NOx Budget Trading Program (NBP), which helped northeastern states
address the interstate transport of NOx emissions causing ozone pollution in northeastern states. Next,
NBP was effectively replaced by the ozone season NOx program under the Clean Air Interstate Rule
(CAIR), which required further summertime NOx emission reductions from the power sector, and also
required annual reductions of NOx and S02 to address PM2.5 transport. In response to a court decision on
CAIR, CSAPR replaced CAIR beginning in 2015 and continued to reduce annual S02 and NOx emissions, as
well as seasonal NOx emissions, to facilitate attainment of the fine particle and ozone NAAQS. Most
recently, implementation of CSAPR Update began in 2017. CSAPR Update further reduces seasonal NOx
emissions to help states attain and maintain a newer ozone National Ambient Air Quality Standards
(NAAQS).
The Mercury and Air Toxics Standards (MATS) set limits on emissions of hazardous air pollutants from
covered power plants. EPA published the final standards in February 2012, and the compliance
requirements generally went into effect in April 2015, with extensions for some plants until April 2016
and a small number until April 2017. As such, 2017 is the first full year for which the vast majority of
sources covered by MATS have reported emissions data to the EPA.
Highlights
Acid Rain Program (ARP): 1995 - present
• ARP began in 1995 and covers fossil fuel-fired power plants across the contiguous United States.
ARP was established under Title IV of the 1990 Clean Air Act Amendments and is designed to
reduce S02 and NOx emissions, the primary precursors of acid rain.
• The ARP's market-based S02 cap and trade program sets an annual cap on the total amount of
S02 that may be emitted by covered electricity generating units (EGUs) throughout the
contiguous U.S. The final annual S02 emissions cap was set at 8.95 million tons in 2010, a level of
about one-half of the emissions from the power sector in 1980.
• NOx reductions under ARP are achieved through a rate-based approach that applies to a subset
of coal-fired EGUs.
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Cross-State Air Pollution Rule (CSAPR): 2015 - present
• CSAPR addresses regional interstate transport of fine particle and ozone pollution for the 1997
ozone and PM25 NAAQS and the 2006 PM25 NAAQS. In 2015, CSAPR required a total of 28
eastern states to reduce S02 emissions, annual NOx emissions and/or ozone season NOx
emissions. Specifically, CSAPR required reductions in annual emissions of S02 and NOx from
power plants in 23 eastern states and reductions of NOx emissions during the ozone season
from power plants in 25 eastern states.
• CSAPR includes four separate cap and trade programs to achieve these reductions: CSAPR S02
Group 1 and Group 2 trading programs, CSAPR NOx Annual trading program, and CSAPR NOx
Ozone Season Group 1 trading program.
Cross-State Air Pollution Rule Update (CSAPR Update): 2017 - present
• CSAPR Update was developed to address regional interstate transport for the 2008 ozone
NAAQS and to respond to the July 2015 court remand of certain CSAPR ozone season
requirements.
• Starting in May 2017, CSAPR Update began further reducing ozone season NOx emissions from
power plants in 22 states in the eastern U.S.
• CSAPR Update achieves these reductions through the CSAPR NOx Ozone Season Group 2 trading
program. The total CSAPR Update budget equals the sum of the individual state budgets for
those states included in the program. The CSAPR Update budget is set at 316,464 tons in 2017.
CSAPR and CSAPR Update Budgets
• The total CSAPR and CSAPR Update budget for each of the five trading programs equals the sum
of the individual state budgets for those states affected by each program. In 2017, some original
CSAPR budgets tightened, particularly in the S02 Group 1 program. Also, CSAPR Update replaced
the original CSAPR ozone season NOx program for most states. The total budget for each
program was set at the following level in 2017:
o S02 Group 1 - 1,372,631 tons
o S02 Group 2 - 597,579 tons
o NOx Annual - 1,069,256 tons
o NOx Ozone Season Group 1 - 24,041 tons1
o NOx Ozone Season Group 2 - 316,464 tons
Mercury and Air Toxics Standards (MATS)
• EPA announced standards to limit mercury, acid gases, and other toxic pollution from power
plants in December 2011 (published in February 2012). EPA provided the maximum 3-year
compliance period so sources were generally required to comply no later than April 16, 2015.
Some sources obtained a one-year extension from their state permitting authority, allowed
under the CAA, and so, were required to comply with the final rule by April 16, 2016.
^he CSAPR NOx Ozone Season Group 1 program applies only to sources in Georgia.
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• Units subject to MATS must comply with emission rate limits for certain hazardous air pollutants
(or surrogates). There are several ways to demonstrate compliance, including the use of
continuous monitoring or through periodic measurement of emissions. Some units may choose
to demonstrate compliance through periodic performance tests.
• This 2017 progress report only provides data from affected sources that submitted hourly
emissions data in 2017. Units not reporting data (e.g. those monitoring using periodic testing)
are not included in this report.
Background Information
Power Sector Trends
The widespread and dramatic emission reductions in the power sector over the last few decades have
come about from several factors, including changes in markets for fuels and electricity as well as
regulatory programs. While most coal-fired electricity generation comes from sources with state of the
art emission controls, broad industry shifts from coal-fired generation to gas-fired generation as well as
increases in zero-emitting generation sources also have reduced power sector emissions. Market
factors, reduced electricity demand, and policy and regulatory efforts have resulted in a notable change
in the last decade to the country's overall generation mix as natural gas and renewable energy
generation increased while coal-fired generation decreased.
Looking ahead, the price of natural gas is expected to remain low for the foreseeable future as
improvements in drilling technologies and techniques continue to reduce the cost of extraction. In
addition, the existing fleet of coal-fired EGUs is aging and there are very few new coal-fired generation
projects under development. With a continued (but reduced) tax credit and declining capital costs, solar
capacity is projected to grow through 2050, while tax credits that phase out for plants entering service
through 2024 provide incentives for new wind capacity in the near-term. Some power generators have
announced that they expect to continue to change their generation mix away from coal-fired generation
and toward natural-gas fired generation, renewables, and more deployment of energy efficiency
measures. All of these factors, in total, have resulted in declining power sector emissions in recent years,
a trend that is expected to continue going forward.
Acid Rain Program
Title IV of the 1990 Clean Air Act Amendments established ARP to address acid deposition nationwide by
reducing annual S02 and NOx emissions from fossil fuel-fired power plants. In contrast to traditional
command and control regulatory methods that establish specific emissions limitations, the ARP S02
program introduced a landmark allowance trading system that harnessed the economic incentives of
the market to reduce pollution. This market-based cap and trade program was implemented in two
phases. Phase I began in 1995 and affected the most polluting coal-burning units in 21 eastern and
midwestern states. Phase II began in 2000 and expanded the program to include other units fired by
coal, oil, and gas in the contiguous U.S. Under Phase II, Congress also tightened the annual S02
emissions cap, with a permanent annual cap set at 8.95 million allowances starting in 2010. The NOx
program has a similar results-oriented approach and ensures program integrity through measurement
and reporting. However, it does not cap NOx emissions, nor does it utilize an allowance trading system.
Instead, ARP NOx program provisions apply boiler-specific NOx emission limits - or rates - in pounds per
million British thermal units (Ib/mmBtu) on certain coal-fired boilers. There is a degree of flexibility,
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however. Units under common control can comply through the use of emission rate averaging plans,
subject to requirements ensuring that the total mass emissions from the units in an averaging plan do
not exceed the total mass emissions the units would have emitted at their individual emission rate
limits.
NOx Budget Trading Program
NBP was a market-based cap and trade program created to reduce N0X emissions from power plants
and other large stationary combustion sources during the summer ozone season to address regional air
pollution transport that contributes to the formation of ozone in the eastern United States. The
program, which operated during the ozone seasons from 2003 to 2008, was a central component of the
NOx State Implementation Plan (SIP) Call, promulgated in 1998, to help states attain the 1997 ozone
NAAQS. All 21 jurisdictions (20 states plus Washington, D.C.) covered by the NOx SIP Call opted to
participate in NBP. In 2009, CAIR's NOx ozone season program began, effectively replacing NBP to
continue achieving ozone season NOx emission reductions from the power sector.
Clean Air Interstate Rule
CAIR required 25 eastern jurisdictions (24 states plus Washington, D.C.) to limit annual power sector
emissions of S02 and NOx to address regional interstate transport of air pollution that contributes to the
formation of fine particulates. It also required 26 jurisdictions (25 states plus Washington, D.C.) to limit
power sector ozone season NOx emissions to address regional interstate transport of air pollution that
contributes to the formation of ozone during the ozone season. CAIR used three separate market-based
cap and trade programs to achieve emission reductions and to help states meet the 1997 ozone and fine
particle NAAQS.
EPA issued CAIR on May 12, 2005 and the CAIR federal implementation plans (FIPs) on April 26, 2006. In
2008, the U.S. Court of Appeals for the DC Circuit remanded CAIR to the Agency, leaving existing CAIR
programs in place while directing EPA to replace them as rapidly as possible with a new rule consistent
with the Clean Air Act. The CAIR NOx ozone season and NOx annual programs began in 2009, while the
CAIR S02 program began in 2010. As discussed below, CAIR was replaced by CSAPR in 2015.
Cross-State Air Pollution Rule
EPA issued CSAPR in July 2011, requiring 28 states in the eastern half of the United States to significantly
improve air quality by reducing power plant emissions that cross state lines and contribute to fine
particle and summertime ozone pollution in downwind states. CSAPR required 23 states to reduce
annual S02 and NOx emissions to help downwind areas attain the 2006 and/or 1997 annual PM2.5
NAAQS. CSAPR also required 25 states to reduce ozone season NOx emissions to help downwind areas
attain the 1997 ozone NAAQS. CSAPR divides the states required to reduce S02 emissions into two
groups (Group 1 and Group 2). Both groups were required to reduce their S02 emissions in Phase I. All
Group 1 states, as well as some Group 2 states, were required to make additional reductions in S02
emissions in Phase II in order to eliminate their significant contribution to air quality problems in
downwind areas.
CSAPR was scheduled to replace CAIR starting on January 1, 2012. However, the timing of CSAPR's
implementation was affected by D.C. Circuit actions that stayed and then vacated CSAPR before
implementation. On April 29, 2014, the U.S. Supreme Court reversed the D.C. Circuit's vacatur, and on
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October 23, 2014, the D.C. Circuit granted EPA's motion to lift the stay and shift CSAPR compliance
deadlines by three years. Accordingly, CSAPR Phase I implementation began on January 1, 2015,
replacing CAIR, and CSAPR Phase II began January 1, 2017.
Cross-State Air Pollution Rule Update
On September 7, 2016, EPA finalized an update to CSAPR ozone season program by issuing the CSAPR
Update. This rule addresses the summertime ozone pollution in the eastern U.S. that crosses state lines
and will help downwind states and communities meet and maintain the 2008 ozone NAAQS. In May
2017, CSAPR Update began further reducing ozone season NOx emissions from power plants in 22 states
in the eastern U.S.
Cross-State Air Pollution Rule Close-Out
Under the Clean Air Act's "good neighbor" provision (section 110(a)(2)(D)(i)(l)), upwind states that
contribute significantly to nonattainment or interfere with maintenance of NAAQS in downwind areas
must implement emission reductions through a state implementation plan (SIP) or, in the absence of an
approved SIP, a federal implementation plan (FIP). When issuing the CSAPR Update in September 2016,
EPA found that, while it would result in meaningful, near-term reductions in ozone pollution that crosses
state lines, the CSAPR Update may not be sufficient to fully address all covered states' good neighbor
obligations with respect to the 2008 ozone NAAQS. However, based on additional analysis conducted
after issuance of the rule, EPA determined in December 2018 that the emission reductions required by
the CSAPR Update in fact would fully address all covered states' good neighbor obligations with respect
to this NAAQS. As a result, the covered states do not need to submit SIPs to establish additional
emission reduction requirements beyond the existing CSAPR Update requirements to further reduce
transported ozone under the 2008 ozone NAAQS. Likewise, EPA has no obligation to establish additional
emission reduction requirements for this purpose.
Mercury and Air Toxics Standards
On December 16, 2011, the EPA announced final standards to reduce emissions of toxic air pollutants
from new and existing coal- and oil-fired electric utility steam generating units (EGUs) in all 50 states and
U.S. territories. MATS established technology-based emission rate standards that reflect the level of
hazardous air pollutant (HAP) emissions that had been achieved by the best-performing sources. These
HAPs include mercury (Hg), non-mercury metals (such as arsenic (As), chromium (Cr), and nickel (Ni)),
and acid gases, including hydrochloric acid (HCI) and hydrofluoric acid (HF). EPA provided the maximum
3-year compliance period so sources were generally required to comply no later than April 16, 2015.
Some sources obtained a one-year extension from their state permitting authority, allowed under the
CAA, and so, were required to comply with the final rule by April 16, 2016.
More Information
• Acid Rain Program (ARP) https://www.epa.gov/airmarkets/acid-rain-program
• Interstate Air Pollution Transport https://www.epa.gov/airmarkets/interstate-air-pollution-
transport
• Cross-State Air Pollution Rule (CSAPR) https://www.epa.gov/csapr
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• Cross-State Air Pollution Rule Update (CSAPR Update) https://www.epa.gov/airmarkets/final-
cross-state-air-pollution-rule-update
• Cross-State Air Pollution Rule Close-Out (CSAPR Close-Out)
https://www.epa.gov/airmarkets/final-csapr-close-out
• Clean Air Interstate Rule (CAIR)
https://archive.epa.gov/airmarkets/programs/cair/web/html/index.html
• N0X Budget Trading Program (NBP) / N0X SIP Call https://www.epa.gov/airmarkets/nox-budget-
trading-program
• National Ambient Air Quality Standards (NAAQS) https://www.epa.gov/criteria-air-pollutants
• EPA's Clean Air Market Programs https://www.epa.gov/airmarkets/programs
• Emissions Trading https://www.epa.gov/emissions-trading-resources
• MATS https://www.epa.gov/mats
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Figures
History of the ARP. NBP, CAIR, CSAPR and MATS
2015-MATS begins
I
2010 - Full implementation of the ARP
I
MATS
1995 -ARP
PHASE 1 BEGINS
2000 - ARP
PHASE 2 BEGINS
ARP
1990-Clean Air Act
Amendments
establish Title IV ARP
Acid Rain Program (ARP)
NOx Budget Trading Program (NBP)
Clean Air Interstate Rule (CAIR)
Cross-State Air Pollution Rule (CSAPR)
Mercury and Air Toxics Standards (MATS)
NBP
2003 - NBP begins
(additional states added
in 2004 and 2007)
2009 - CAIR NOx ozone season and
NOx annual programs begin,
replacing NBP in most states
2010 - CAIR S02 program begins
CAIR
CSAPR
2015 -CSAPR S02.
NOx annual, and
NOxozone programs
begin, replacing CAIR
2017 - CSAPR Update begins
Source: EPA, 2019
Figure 1. History of the ARP, NBP, CAIR, CSAPR and MATS
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% ^
Map of Cross-State Air Pollution Rule Implementation for 2017
~ CSAPR States controlled for both fine particles (S02 and annual N0X) and ozone (ozone season NO*) -17 states
¦ CSAPR States controlled for fine particles only (S02 and annual N0X) - 4 states
~ CSAPR States controlled for ozone only (ozone season N0X) - 5 states
M Georgia is covered by CSAPR for both fine particles (S02 and annual NOx) and ozone (ozone season NO*) -1 state
The ARP covers sources in the lower 48 states.
The MATS covers sources in all 50 states and US territories.
Source: EPA, 2019
Figure 2, Map of Cross-State Air Pollution Rule Implementation for 2017
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Electricity Generation from ARP-Affeeted Power Plants, 2005-2017
3000
2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017
¦ Coal ¦ Gas ¦ Oil Other
Noses:
• There is a amount of generation from "OS" or fueSs. The data for these foeJs a not easfiy vstole on the fuS chart. To more dearty see the generator! data for these fuels, use the interactive features of the figure: cfcefc on
the sexes in the legend to turn off the blue and orange categories of fwets (labeled "Co*" and "Gas") and turn on the green and yetow categories of fuels (labeled "OiT and "Other"i
Source: ER
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Chapter 2: Affected Units
The Acid Rain Program (ARP), the Cross-State Air Pollution Rule's (CSAPR) sulfur dioxide (S02) and
nitrogen oxides (N0X) emission reduction programs, apply to large electricity generating units (EGUs)
that burn fossil fuels to generate electricity for sale. The Mercury and Air Toxics Standards only cover
large EGUs that burn coal or oil to generate electricity for sale. This is the primary reason that this report
includes less units for MATS. This section covers units affected in 2017.
Highlights
Acid Rain Program (ARP)
• In 2017, ARP S02 requirements applied to 3,383 fossil fuel-fired combustion units at 1,195
facilities across the country; 657 units at 295 facilities were subject to the ARP NOx program.
Cross-State Air Pollution Rule (CSAPR)
• In 2017, there were 2,287 affected EGUs at 712 facilities in the CSAPR S02 program. Of those,
1,805 (79 percent) were also covered by ARP.
• In 2017, there were 2,287 affected EGUs at 712 facilities in the CSAPR NOx annual program and
2,623 affected EGUs at 837 facilities in the CSAPR NOx ozone season program. Of those, 1,805
(79 percent) and 2,124 (81 percent), respectively, were also covered by ARP.
Mercury and Air Toxics (MATS)
• The Mercury and Air Toxics Standards (MATS) set limits on the emissions of hazardous air
pollutants from coal- and oil-fired electric utility steam generating units (EGUs) in all 50 states
and U.S. territories. MATS is issued under section 112 of the Clean Air Act and requires units to
conduct testing and submit emissions data to EPA periodically. EPA is including a summary of
the mercury data submitted by affected sources in this report.
• In 2017, 530 units at 235 facilities reported hourly mercury emissions to EPA under MATS.
Background Information
In general, ARP; the CSAPR S02, NOx annual, and NOx ozone season trading programs; apply to large
EGUs - boilers, turbines, and combined cycle units - that burn fossil fuel, serve generators with
nameplate capacity greater than 25 megawatts, and produce electricity for sale. MATS appl ies only to
coal- and oil-fired steam generating EGUs (i.e., utility boilers). It does not apply to turbines, combined
cycle units, or to natural gas-fired utility boilers. These EGUs include a range of unit types, including
units that operate year-round to provide baseload power to the electric grid, as well as units that
provide power only on peak demand days. The ARP NOx program applies to a subset of these units that
are older and historically coal-fired.
More Information
• Acid Rain Program (ARP) https://www.epa.gov/airmarkets/acid-rain-program
• Cross-State Air Pollution Rule (CSAPR) https://www.epa.gov/csapr
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Chapter 2: Affected Units
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Mercury and Air Toxics Standards (MATS) https://www.epa.gov/mats
Chapter 2: Affected Units
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Figures
Affected Units in CSAPR and ARP, 2017
4k
3.383
2,287
2,287
657
ARP NO, Program ARP SO* Program CSAPR SOs and NO, Annual Programs CSAPR NO, Ozone Season Program
¦ Coal EGUs ¦ Gas EGUs ¦ Oil EGUs ¦ Other Fuel EGUs ¦ Unclassified EGUs
Notes:
• "Unclassified" units have not submitted a fuel type in the* monitoring plan and did not report emissions.
• "OVW futi r»)M » units tMt bum w*it*. wood. pttfoJtum cokt. tift-d«nvtd fuel. »tc.
Source: EWV, 2019
Figure 1. Affected Units in CSAPR and ARP, 2017
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Affected Units in CSAPR and ARP, 2017
Coal
S75
666
503
503
Gas
80
2,562
1,498
1,498
Oil
0
117
249
249
Other
2
29
37
37
Unclassified
0
9
0
0
Total Units
657
3,383
2,287
2,287
Notes:
• Unclassified" units have no! submitted a fuel type m fitetr rrcofsitorasg pEan arxj && not report emissions.
• "Oth*r" fi*l to units that burn wut*. wood. ptWOlMm cek«, w*-d*riv*d fu*t tic
Source EPA, 2019
Figure 2. Affected Units in CSAPR and ARP, 2017
Chapter 2: Affected Units
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Chapter 3: Emission Reductions
The Acid Rain Program (ARP) and Cross-State Air Pollution Rule (CSAPR) programs significantly reduced
sulfur dioxide (S02), annual nitrogen oxides (N0X), and ozone season N0X emissions from power plants.
Most of the emission reductions since 2005 occurred in response to the Clean Air Interstate Rule (CAIR),
which was replaced by CSAPR in 2015. The Mercury and Air Toxics Standards (MATS) set limits on the
emissions of hazardous air pollutants from coal- and oil-fired electric utility steam generating units
(EGUs) and have been one of the reasons for reductions in those emissions since 2010. This section
covers changes in emissions at units affected by CSAPR, ARP, and MATS between 2017 and previous
years.
Highlights
Overall Results
• Under the ARP, CAIR, and now CSAPR, power plants have significantly lowered S02 emissions
while electricity generation has remained relatively stable since 2000.
• These emission reductions are a result of an overall increase in the environmental efficiency at
affected sources as power generators installed controls, switched to lower emitting fuels, or
otherwise reduced their S02 emissions. These trends are discussed further in Chapter 1.
SO2 Emission Trends
• ARP: Units in ARP emitted 1.3 million tons of S02 in 2017, well below the ARP's statutory annual
cap of 8.95 million tons. ARP sources reduced emissions by 14.4 million tons (92 percent) from
1990 levels and 15.9 million tons (92 percent) from 1980 levels.
• CSAPR and ARP: In 2017, the third year of operation of the CSAPR S02 program, sources in both
the CSAPR S02 annual program and ARP together reduced S02 emissions by 14.4 million tons (92
percent) from 1990 levels (before implementation of ARP), 9.9 million tons (88 percent) from
2000 levels (ARP Phase II), and 8.9 million tons (87 percent) from 2005 levels (before
implementation of CAIR and CSAPR). All ARP and CSAPR sources together emitted a total of 1.3
million tons of S02 in 2017.
• CSAPR: Annual S02 emissions from sources in the CSAPR S02 program alone fell from 8.1 million
tons in 2005 to 0.8 million tons in 2017, a 91 percent reduction. In 2017, S02 emissions were
about 1.2 million tons below the regional CSAPR emission budgets (0.7 million in Group 1 and
0.5 million in Group 2); the CSAPR S02 annual program's 2017 regional budgets are 1,372,631
and 597,579 tons for Group 1 and Group 2, respectively.
SO2 State-by-State Emissions
• CSAPR and ARP: From 1990 to 2017, annual S02 emissions from sources in ARP and the CSAPR
S02 program dropped in 46 states plus Washington, D.C. by a total of 14.4 million tons. In
Sulfur Dioxide (SO2)
Chapter 3: Emission Reductions - Sulfur Dioxide (S02)
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contrast, annual S02 emissions increased in two states (Idaho and Vermont) by a combined total
of 7 tons from 1990 to 2017.
• CSAPR: All 22 states (16 states in Group 1 and 6 states in Group 2) had emissions below their
CSAPR allowance budgets, collectively by about 1.2 million tons.
SO2 Emission Rates
• The average S02 emission rate for units in ARP or CSAPR S02 program fell to 0.12 pounds per
million British thermal units (Ib/mmBtu). This indicates an 84 percent reduction from 2005 rates,
with the majority of reductions coming from coal-fired units.
• Emissions have decreased dramatically since 2005, due in large part to greater use of control
technology on coal-fired units and increased generation at natural gas-fired units that emit very
little S02 emissions.
Background Information
S02 is a highly reactive gas that is generated primarily from coal-fired power plants. In addition to
contributing to the formation of fine particle pollution (PM2.5), S02 emissions are linked with a number
of adverse effects to human health and ecosystems.
The states with the highest emitting sources in 1990 have generally seen the greatest S02 emission
reductions under ARP, and this trend continued under CAIR and CSAPR. Most of these states are located
in the Ohio River Valley and are upwind of the areas ARP and CSAPR were designed to protect.
Reductions under these programs have provided important environmental and health benefits over a
large region.
More Information
• Power Plant Emission Trends https://www.epa.gov/airmarkets/power-plant-emission-trends
• Air Markets Program Data (AMPD) https://ampd.epa.gov/ampd/
• Acid Rain Program (ARP) https://www.epa.gov/airmarkets/acid-rain-program
• Cross-State Air Pollution Rule (CSAPR) https://www.epa.gov/csapr
• Sulfur Dioxide (SO?) Pollution https://www.epa.gov/so2-pollution
• Particulate Matter (PM) Pollution https://www.epa.gov/pm-pollution
• Power Profiler https://www.epa.gov/energy/power-profiler
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Chapter 3: Emission Reductions - Sulfur Dioxide (S02)
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Figures
SO: Emissions from CSAPR and ARP Sources, 1980-2017
20
H nil
1980 1990 1995 2000 2005 2010 2015 2017
¦ ARP ¦ ARP and CSAPR ¦ CSAPR not ARP ARP not CSAPR
Nc*es:
¦ SCt values are shewn as millions of tons.
• For CSAPR un«t« not m the ARP. the 2015 annual SO» emissions were app&ed retroactivity for each pre-CSAPR year foBowmg the year m which the unit te®am operating
~ There are a imjl number of sources m CSAPR but not in ARP Emtsssns from these sources compose about 1 percent of total emissions a^ are not eas-iiy vesfcie on the fui chart
Source: Efi^. 2019
Figure 1. SO2 Emissions from CSAPR and ARP Sources, 1980-2017
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State-by-State SO: Emissions from CSAPR and ARP Sources, 1990-2017 SO: Emissions (thousand tons)
600
SOO
CSAPR states controlled for fine particles
1990 SOi emissions (tons)
2000 2005 2017
¦ Alabama
• SO? values rt shown as tons.
Source- EfVV 2019
Figure 2. State-by-State SO2 Emissions from CSAPR and ARP Sources, 1990-2017
Chapter 3: Emission Reductions - Sulfur Dioxide (S02)
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CSAPR and ARP SO: Emissions Trends, 2017
SO? Emissions (thousand tons)
SO* Rate (Ib/mmBtu)
Primary Fuel
2000
2005
2010
2017
2000
2005
2010
2017
Coal
10,708
9,835
5,051
1,316
1.04
0.95
0.53
0.14
Gas
108
91
19
8
0.06
0.03
0.01
0.03
Oil
384
292
28
2
0.73
0.70
0.19
0.11
Other
1
4
22
12
0.20
0.27
0.57
0.10
Total / Average
11,201
10,222
5,120
1,338
0.88
0.75
039
0.09
Noses:
• The data shown here reflect totals for those facilities required to comply with each program in each respective year Ths mea^s that CSAPR-onity SO: program fac4ties are not included m the SO; emissions data pro? to 2015.
• Fuel type represents primary fuel type; units might combust more than ooe fuel,
• Totals may not reflect the sum of individual rews -;u* jo rounding.
• The emisson fate reflects the emissions (pounds) pe* unit of heat input (mmBtu) foe e3Ch fuel category The total SO-, emission rate m eaeh ©okimn of the tab* is not cumulative and doe not equal the amhmette mean of the four fuel-
specific rates. The total for each year indicates the average rate across all units in the program because each facility influences the annual emission rate in proportion to its heat input, and heat input is unevenly districted across tfte fuel
categories.
• Unless otherwise noted, £PA data are current as of Way 20!9, and may differ from past or future reports as a result of resubmissions by sources a«d oagoMt data quality assurance activct«*s
Source: EPA, 2019
Figure 4. CSAPR and ARP S02 Emissions Trends, 2017
Chapter 3: Emission Reductions - Sulfur Dioxide (S02)
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Annual Nitrogen Oxides
Highlights
Overall Results
• Annual N0X emissions have declined dramatically under the ARP, CAIR, and CSAPR programs,
with the majority of reductions coming from coal-fired units. These reductions have occurred
while electricity generation has remained relatively stable since 2000.
• These emission reductions are a result of an overall increase in the environmental efficiency at
affected sources as power generators installed controls, ran their controls year-round, switched
to lower emitting fuels, or otherwise reduced their NOx emissions. These trends are discussed
further in Chapter 1.
• Other programs - such as regional and state NOx emission control programs - also contributed
significantly to the annual NOx emission reductions achieved by sources in 2017.
Annual NOx Emissions Trends
• ARP: Units in the ARP NOx program emitted 1.0 million tons of NOx emissions in 2017. Sources
reduced emissions by 7.1 million tons from the projected level in 2000 without ARP, over three
times the program's NOx emission reduction objective.
• CSAPR and ARP: In 2017, the third year of operation of the CSAPR NOx annual program, sources
in both the CSAPR NOx annual program and ARP together emitted 1.1 million tons, a reduction
of 5.4 million tons (84 percent reduction) from 1990 levels, 4.1 million tons (79 percent
reduction) from 2000, and 2.7 million tons (71 percent reduction) from 2005 levels.
• CSAPR: Emissions from CSAPR NOx annual program sources alone were 586,000 tons in 2017.
This is about 1.6 million tons (73 percent) lower than in 2005 and 480,000 tons (45 percent)
below the CSAPR NOx annual program's 2017 regional budget of 1,069,256 tons.
Annual NOx State-by-State Emissions
• CSAPR and ARP: From 1990 to 2017, annual NOx emissions in ARP and the CSAPR NOx program
dropped in 47 states plus Washington, D.C. by a total of approximately 5.4 million tons. In
contrast, annual emissions increased in one state (Idaho) by 200 tons from 1990 to 2017.
• CSAPR: Twenty-one states had emissions below their CSAPR 2017 allowance budgets,
collectively by 480,000 tons. A single state (Missouri) exceeded its 2017 budget by 950 tons.
Annual NOx Emission Rates
• In 2017, the CSAPR and ARP average annual NOx emission rate was 0.10 Ib/mmBtu, a 64 percent
reduction from 2005.
• Emissions have decreased dramatically since 2005, due in large part to greater use of control
technology, primarily on coal-fired units, and increased generation at natural gas-fired units that
emit less NOx emissions than coal-fired units.
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Chapter 3: Emission Reductions-Annual Nitrogen Oxides (NOx)
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Background Information
Nitrogen oxides (N0X) are made up of a group of highly reactive gases that are emitted from power
plants and motor vehicles, as well as other sources. N0X emissions contribute to the formation of
ground-level ozone and fine particle pollution, which cause a variety of adverse health effects.
More Information
• Power Plant Emission Trends https://www.epa.gov/airmarkets/power-plant-emission-trends
• Air Markets Program Data (AMPD) https://ampd.epa.gov/ampd/
• Acid Rain Program (ARP) https://www.epa.gov/airmarkets/acid-rain-program
• Cross-State Air Pollution Rule (CSAPR) https://www.epa.gov/csapr
• Nitrogen Oxides (N0X) Pollution https://www.epa.gov/no2-pollution
• Particulate Matter (PM) Pollution https://www.epa.gov/pm-pollution
• Power Profiler https://www.epa.gov/energy/power-profiler
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Chapter 3: Emission Reductions-Annual Nitrogen Oxides (N0X)
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% pRo^s°
Figures
Annual NQx Emissions from CSAPR and ARP Sources, 1990-2017
¦ ARP ¦ ARP and CSAPR ¦ ARP, not CSAPR CSAPR. not ARP
Noses:
• NO. values are shown as mikms of torts.
* For CSAPR utwts not m the ARP. the 2015 annual NO, tmisstofts were retroactively for «acfc cxe-CSAPR yea* foOowir-j the ye*- m the unit began operating.
- T>*r* are a imjl number of sources m CSAPR but not m ARP Ermssoa* from these sources compete about '¦ peoett of tota* emtss»ns and are not eas-tfy visible on the fu» chart.
Source: EPA, 2019
Figure 1. Annual NOx Emissions from CSAPR and ARP Sources, 1990-2017
Chapter 3: Emission Reductions-Annual Nitrogen Oxides (NOx)
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State-by-State Annual NO* Emissions from CSAPR and ARP Sources,
1990-2017
NOx Emissions (thousand tons)
CSAPR states controlled for Tine particles
1990 NO. emissions (tons)
1990 2000 2005 2017
¦ Alabama
Source: ER^, 2019
Figure 2. State-by-State Annual NOx Emissions from CSAPR and ARP Sources, 1990-
2017
Chapter 3: Emission Reductions-Annual Nitrogen Oxides (NOx)
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CSAPR arid ARP Annual NOx Emissions Trends, 2017
NO* Emissions
thousand tons)
NOx Rate (Ib/mmBtu)
Primary Fuel
2000
2005
2010
2017
2000
2005
2010
2017
Coal
4,587
3,356
1,896
918
0.44
0.32
0.20
0.14
Gas
355
167
142
131
0.18
0.06
0.04
0.03
Oil
162
104
20
4
0.31
0.25
0.13
0.11
Other
2
6
5
7
0.24
0.42
0.13
0.10
Total / Average
5,106
3,633
2,063
1,060
0.40
0.27
0.16
0.09
Notes:
• The oata shown here reflect totals for those facSties requred to oompJy with each program ir. each respective year This means thai CSAPR-oeriy annual NO, program fac&tess are not nvcAjcJed for each fuel category The total annual NO* emission rate in each column of the Uble ts not cumulative and does not equal the arithmetic mean of the four
fuel-specific rates. The total for each year mdaates the average rate across all units in the program because each facSty influences the annual emission rate in proportion to As heat input, and heat input e uneventy distributed across the
fuel categories
¦ Unless otheros* noted. EPA data are cuneni as of May 201$. and may drffer from past or future reports as a resuft of resubmissions by sources and or^omg data quality assurance activities.
Source: EPA. 2019
Figure 4. CSAPR and ARP Annual NOx Emissions Trends, 2017
Chapter 3: Emission Reductions - Annual Nitrogen Oxides (NOx)
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Ozone Season Nitrogen Oxides
Highlights
Overall Results
• Ozone season N0X emissions have declined dramatically under ARP, NBP, CAIR, and CSAPR
programs.
• States with the highest emitting sources of ozone season N0X emissions in 2000 have seen the
greatest reductions under the CSAPR NOx ozone season program. Most of these states are in the
Ohio River Valley and are upwind of the areas CSAPR was designed to protect. Reductions by
sources in these states have resulted in important environmental and human health benefits
over a large region.
• These reductions have occurred while electricity generation has remained relatively stable since
2000. These trends are discussed further in Chapter 1.
• Other programs—such as regional and state NOx emission control programs—also contributed
significantly to the ozone season NOx emission reductions achieved by sources in 2017.
Ozone Season NOx Emissions Trends
• Units in the CSAPR NOx ozone season program emitted 300,000 tons in 2017
o A reduction of 1.7 million tons (85 percent) from 1990,
o 1.0 million tons lower (76 percent reduction) than in 2000 (before implementation of
NBP),
o 350,000 tons lower (53 percent reduction) than in 2005 (before implementation of
CAIR), and
o 87,000 tons lower (22 percent reduction) than in 2015.
• In 2017, CSAPR NOx ozone season program emissions were 11 percent below the regional
emission budget of 340,505 tons (24,041 tons for Group 1 and 316,464 tons for Group 2).
Ozone Season NOx State-by-State Emissions
• Between 2005 and 2017, ozone season NOx emissions from CSAPR sources fell in every state
participating in the CSAPR NOx ozone season program.
• Seventeen states had emissions below their CSAPR 2017 allowance budgets, collectively by
about 43,000 tons. Six states (Arkansas, Ohio, Tennessee, Texas, West Virginia, and Wisconsin)
exceeded their 2017 budgets by about 3,900 tons combined.
Ozone Season NOx Emission Rates
• In 2017, the average NOx ozone season emission rate fell to 0.08 Ib/mmBtu for CSAPR ozone
season program states and 0.09 Ib/mmBtu nationally. This represents a 50 and 56 percent
reduction, respectively, from 2005 emission rates, with the majority of reductions coming from
coal-fired units.
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Chapter 3: Emission Reductions - Ozone Season Nitrogen Oxides (NOx)
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• Emissions have decreased dramatically since 2005, due in large part to greater use of control
technology, primarily on coal-fired units, and increased generation at natural gas-fired units,
which emit less NOx emissions than coal-fired units.
Background Information
Nitrogen oxides (NOx) are made up of a group of highly reactive gases that are emitted from power
plants and motor vehicles, as well as other sources. NOx emissions contribute to the formation of
ground-level ozone and fine particle pollution, which cause a variety of adverse human health effects.
The CSAPR NOx ozone season program was established to reduce interstate transport during the ozone
season (May 1 - September 30), the warm summer months when ozone formation is highest, and to
help eastern U.S. counties attain the 1997 ozone standard.
More Information
• Power Plant Emission Trends https://www.epa.gov/airmarkets/power-plant-emission-trends
• Air Markets Program Data (AMPD) https://ampd.epa.gov/ampd/
• Cross-State Air Pollution Rule (CSAPR) https://www.epa.gov/csapr
• Pollution from Nitrogen Oxides (N0X) https://www.epa.gov/no2-pollution
• Pollution from Ozone https://www.epa.gov/ozone-pollution
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Chapter 3: Emission Reductions - Ozone Season Nitrogen Oxides (N0X)
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Figures
Ozone Season NO* Emissions from CSAPR Sources, 2005-2017
.£ 0.5
CSAPR Update Ozone Season NO. Budget (2017)
¦ CSAPR
- NO, values ate shown as nrifcos of tons.
• For CSAPR u?wJs not in the ARP. the 2015 ozone season NQ« emisswns were appfied retroacfovety for each pre-CSAPR yeat following the year in wNch the unit began operating
• There are * smaa number of sources m CSAPR but not n ARP. Emission* from these sources comprise about 1 percent of total emissions artf are not easily vaoie or. the fu* chart
Source: EPA, 2019
Figure 1. Ozone Season NOx Emissions from CSAPR Sources, 2005-2017
Chapter 3: Emission Reductions - Ozone Season Nitrogen Oxides (NOx)
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State-by-State Ozone Season NOx Emissions from CSAPR Sources,
2000-2017
NOx Emissions (thousand tons)
CSAPR states controlled for ozone
@ 2000 NO* emissions (tons)
2000 2005 2015 2017
¦ Alabama
NoJes:
* The 2003 and 2005 ozone season values re?v»ct data that *ere reported uftde* other programs. For fatties that were not covered by another program and did not report 2030 of 2005 emissions. then reported emsstons for 2015 *
substituted.
Source: EftV 2019
Figure 2. State-by-State Ozone Season NOx Emissions from CSAPR Sources, 2000-2017
Chapter 3: Emission Reductions - Ozone Season Nitrogen Oxides (NOx)
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% pro^0y sources and or^ data quality assurance aci>vrt*s
Source: EPA. 2019
Figure 3. Comparison of Ozone Season NOx Emissions and Generation for CSAPR
Sources, 2000-2017
Chapter 3: Emission Reductions - Ozone Season Nitrogen Oxides (NOx)
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CSAPR Ozone Season NO* Emissions Trends, 2017
Ozone Emissions (thousand tons)
Ozone Rate (U>/mmBtu)
Primary Fuel
2000
2005
2010
2017
2000
2005
2010
2017
Coal
1,926
1,117
821
389
0.43
0.25
0.19
0.13
Gas
195
95
78
69
0.19
0.06
0.04
0.03
Oil
79
53
13
2
0.31
0.25
0.13
0.10
Other
1
2
2
3
0.21
0.39
0.11
0.08
Total / Average
2,201
1,267
915
463
0.38
0.20
0.15
0.09
Notes:
• The data stow here reflect totals for those facities reqwred to oompty with each program «n each respective year This means that CSAPR NQs ozone season only program facifttes are not included m the ozone seasori NO, emssons
date poor to 2015.
• Fuel typt represents primary fuel type, units ra«jht combust iw» than on* fuel
• Tetais may not reflect the sum of individual rows due to rounding
• The emission rate reflects the emissions (pounds) per unit of heat input (mmSta) for each fuel category. The total NO* ozone season emission rate in each column of tne table is not emwbfivc ana does not equal the arithmetic mean of
the four fuel-specsf*: rates. The total for each year indicates the average rate across an uiwts in the program because each facity influences the arvmiaJ emission rate m proportion to its heat input, and heat input is unevenly jfistrftuted
ict»i the fuel categor**.
• Unless oth«r«se noted. data are current u of Way 2019. and may tfiffe* from pujt or future reports as a result of resubmissions by sources and ongoing data quatty assurance activities
Source: EPA. 2019
Figure 4. CSAPR Ozone Season NOx Emissions Trends, 2017
Chapter 3: Emission Reductions - Ozone Season Nitrogen Oxides (NOx)
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Mercury and Air Toxics
Highlights
Overall Results
• Mercury and other hazardous air pollutant (HAP) emissions have declined significantly since
2010 estimates. These emission reductions were driven by the installation of new pollution
controls and enhancements of existing pollution controls that reduce multiple pollutants.
Emissions have also decreased due to operational changes, such as fuel switching and increased
generation at natural gas-fired units that emit very little mercury and HAP. These trends are
discussed in Chapter 1.
• Other programs - such as regional and state S02 and NOx emission control programs - also
contributed to the mercury and other HAP emission reductions achieved by covered sources in
2017.
Mercury and Hazardous Air Pollutant Emission Trends
• Compared to 20101, units covered under MATS in 2017 emitted
o 25 fewer tons of mercury (86% reduction),2
o 120,877 fewer tons of acid gases (96% reduction),3 and
o 949 fewer tons of non-mercury metals (81% reduction).4
Reducing Mercury Emissions from Coal-Fired Power Plants Since 2010
Over the past decade, the power sector has undergone significant changes in the mix of generating
sources (e.g., coal, gas, and renewables), as well as in the prevalence of pollution control technologies.
These changes have led to substantial decreases in mercury emissions, from about 29 tons in 2010 to 4
tons in 2017. These drivers are explained in more detail below.
1 Emissions from 2010 are estimated as described in Memorandum: Emissions Overview: Hazardous Air
Pollutants in Support of the Final Mercury and Air Toxics Standard. EPA-454/R-11-014. November
2011; Docket ID No. EPA-HQ-OAR-2009-0234-19914.
2 Certain units did not report from January-May 2017. Also, data do not include emissions from low
emitting electric generating units (LEEs). Mercury emissions from 87 LEEs are estimated to be 326
pounds. Emissions from 24 additional LEEs are not available.
3 Most coal- and oil- fired EGUs report emissions of S02 as a surrogate to demonstrate compliance with
standards for the acid gas HAP. The EPA used those S02 emissions to estimate emission of the acid gas
HAP (hydrogen chloride and hydrogen fluoride).
4 Most coal- and oil- fired EGUs report emissions of filterable particulate matter (fPM) as a surrogate to
demonstrate compliance with standards for the non-mercury metal HAP. The EPA used those fPM
emissions to estimate emission of the non-mercury metal HAP (e.g., lead, arsenic, selenium, etc.).
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Chapter 3: Emission Reductions - Mercury and Air Toxics
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Decreasing Coal-Fired Generation
Coal-fired EGUs are the main source of mercury emissions in the power sector, so reductions in the
amount of generation from coal will have an impact on power sector mercury emissions. Reductions in
coal-fired generation at the EGU-level can occur in a number of ways: decreased utilization of an existing
EGU, retirement of an EGU, or conversion from coal to other fuels with lower or no mercury emissions.
The following trends in coal-fired generation since 2010 have contributed to the observed reduction of
mercury emissions:
• Electricity generation from all coal-fired EGUs decreased by approximately one-third between
2010 and 2017.
• In 2010, nearly 10 percent of electricity generation from coal-fired EGUs was from 259 units that
have since retired.
• In addition, 74 EGUs that were coal-fired in 2010 have been converted to burn natural gas or
other fuel sources (which do not emit as much mercury as coal).
Controlling Mercury Emissions at Coal-Fired EGUs
Coal-fired EGUs have also installed post-combustion pollution control technologies, like activated carbon
injection (ACI) and flue-gas desulfurization (FGD), to comply with air quality regulatory programs. ACI
controls are designed to specifically capture mercury, while FGD are designed to reduce sulfur dioxide
(S02) and other acid gases, but, in certain situations, can also capture mercury effectively. These
technologies can work independently or in combination with other technologies to improve mercury
control. Circulating fluidized bed (CFB) boilers can also reduce emissions of S02 through the addition of
lime or limestone during the combustion process or downstream using a dry sorbent injection system.
The following trends in pollution control technology have contributed to the observed reduction of
mercury emissions:
• Half of all electricity generation from coal-fired EGUs in 2010 was from units that had installed a
post-combustion control device, like ACI or FGD; in 2017, that share increased to more than 90
percent.
• Generation from coal-fired EGUs that had no post-combustion pollution control technology
declined 91 percent between 2010 and 2017.
• In 2010, only 4 percent of coal generation was from units that reported using ACI; in 2017, that
share increased to nearly 40 percent.
Background Information
Hazardous air pollutants (HAPs) emitted by power plants include mercury, acid gases (e.g., HCI, HF), non-
mercury metallic toxics (e.g., arsenic, nickel, and chromium) and organic HAPs (e.g., formaldehyde,
dioxin/furan). Exposure to these pollutants at certain concentrations and durations can increase chances
of cancer and immune system damage, along with neurological, reproductive, developmental,
respiratory, and other health problems.
In 2011, EPA issued MATS, establishing national emission standards for mercury and other hazardous air
pollutants for new and existing coal- and oil-fired power plants. The standards were finalized under
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Chapter 3: Emission Reductions - Mercury and Air Toxics
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section 112 of the 1990 Clean Air Act amendments. The MATS emission standards were established
using data from a 2010 information collection request (ICR) that was sent to selected coal- and oil- fired
EGUs.
More Information
• Air Markets Program Data (AMPD) https://ampd.epa.gov/ampd/
• MATS https://www.epa.gov/mats
• HAPs https://www.epa.gov/haps
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Chapter 3: Emission Reductions - Mercury and Air Toxics
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Figures
Mercury and Hazardous Air Pollutant Emissions from MATS Sources, 2010 and 2017
I Hg
I Acid Gases
] Hon Hq Metals
Notes:
• Data do not mcijde emissions from low emitting electro generating units (LEEs) Mercury emissions from 87 LEEs ate estimated to be 329 pounds. Emissions from 24 addrtcnal LEEs a?e not available.
• There is a smai amount of generate from "Kg* and "Non-Hg Metals' 1>* data for these emissions «s not eauiy vts<&* on the lu> chart. To more clearty tee tf* generate data for ffi«M emissions, use the interactive features of the
figure, cbck on the boxes m the legend to turn of# the orange category (labeled "Ac>3 Gases") an3 turn on the blue a«d green cate$o?*s (labeled "Hg* and "Non-Hg Uetalj")
Source: EPA, 2019
Figure 1, Mercury and Hazardous Air Pollutant Emissions from MATS Sources, 2010 and
2017
Mercury and Hazardous Air Pollutant Emissions from MATS Sources, 2010 and 2017
¦ Hg
Notes:
• Data do not include emissions from low emitting eiectnc generating units (LEEs). Mercury emissions from 87 LEEs are estimated to be 32© pounds. Emissions from 24 addtonaJ LEEs are not availabte.
• There is a sma* amount of generation from "Hg* and "Non-Hg Metals' The data for these emissions «s not easily vtsibfe on the fui chart. To more dearly see the generation data for these emissions, use the interactive features of the
figure cbck on the boxes in the fcgend to turn off the orange category (labeled "Add Gases") and turn on the blue amd green categories (labeled "Hg* and "Non-Hg Metals").
Source: ERA, 2019
Chapter 3: Emission Reductions — Mercury and Air Toxics
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Mercury and Hazardous Air Pollutant Emission Trends, 2017
Pollutant
2010 Emissions (tons)
2017 Emissions (tons)
Reduction (%)
Hg
29
4
86%
Acid Gases
125,708
4,831
96%
Non-Hg Metals
1,170
221
81%
Organic HAP
Not Available
<3
Not Available
Notes:
- Daw do not mcfcde •rmmons from low mining •KKtnc units (lEEs). Mefewy *m«s«o«s from 87 lEEs vt est»matea to b* 329 pourtfs. Emissions from 24 a«Si»flai LEEs *• nw avaHaWt.
• MATS units covV rt^pesi yp to two one-year compkanoe extensions under the Units under tfits extersofl we not required to report emissions and comply **tt> I he standards until Aprt of 2017.
Source: ERA, 2019
Figure 2. Mercury and Hazardous Air Pollutant Emission Trends, 2017
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I Fuel Conversion ¦ CF8 and No Post-Combustion Controls ¦ ACI Both FGO and ACI ¦ FGD
Source: EB*. 2019
Figure 3. US Coal Generation (MWh), 2010 versus 2017
Chapter 3: Emission Reductions - Mercury and Air Toxics
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Chapter 4: Emission Controls and Monitoring
Many sources opted to install control technologies to meet the Acid Rain Program (ARP) and Cross-State
Air Pollution Rule (CSAPR) emission reduction targets. A wide range of controls is available to help
reduce emissions. Affected units under the Mercury and Air Toxics Standards (MATS) also have several
options for reducing hazardous air pollutants, and have some flexibility in how they monitor emissions.
These programs hold sources to high standards of accountability for emissions. Accurate and consistent
emissions monitoring data is critical to ensure program results. Most emissions from affected sources
are measured by continuous emission monitoring systems (CEMS).
Highlights
ARP and CSAPR SO2 Program Controls and Monitoring
• Units with advanced flue gas desulfurization (FGD) controls (also known as scrubbers) accounted
for 76 percent of coal-fired units and 83 percent of coal-fired electricity generation, measured in
megawatt hours, or MWh, in 2017.
• In 2017, 30 percent of CSAPR units (including 100 percent of coal-fired units) monitored S02
emissions using CEMS. Ninety-nine percent of S02 emissions were measured by CEMS.
CSAPR NOx Annual Program Controls and Monitoring
• Seventy-nine percent of fossil fuel-fired generation (as measured in megawatt hours, or MWh)
was produced by units with advanced pollution controls (either selective catalytic reduction
[SCR] or selective non-catalytic reduction [SNCR]).
• In 2017, the 298 coal-fired units with advanced add-on controls (either SCRs or SNCRs)
generated 77 percent of coal-fired electricity. At oil- and natural gas-fired units, SCR- and SNCR-
controlled units produced 82 percent of generation.
• In 2017, 69 percent of CSAPR units (including 100 percent of coal-fired units) monitored NOx
emissions using CEMS. Ninety-nine percent of NOx emissions were measured by CEMS.
CSAPR NOx Ozone Season Program Controls and Monitoring
• Seventy-one percent of all the fossil fuel-fired generation (as measured in megawatt hours, or
MWh) was produced by units with advanced pollution controls (either SCRs or SNCRs).
• In 2017, 278 units with advanced add-on controls (either SCR or SNCR) accounted for 71 percent
of coal-fired generation. At oil- and natural gas-fired units, SCR- and SNCR-controlled units
produced 71 percent of generation.
• In 2017, 75 percent of CSAPR units (including 100 percent of coal-fired units) monitored ozone
season NOx emissions using CEMS. Ninety-nine percent of ozone season NOx emissions were
measured by CEMS.
MATS Controls and Monitoring
• In 2017, 530 units at 235 facilities reported continuous mercury emissions data to EPA under
MATS. Fifty-six percent of MATS units reporting mercury emissions and 44 percent of the
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electricity generation at MATS reporting units used activated carbon injection (ACI), a mercury-
specific pollution control method to reduce mercury emissions and S02.
• About 78 percent of units that reported continuous mercury emissions data (or 87 percent of
the total electricity generation from units that reported data) reported the use of advanced
controls, such as wet scrubbers, dry scrubbers, or ACI, to reduce hazardous air pollutant
emissions in 2017. These controls also reduce other pollutants, including S02. Some oil-fired
units are able to meet the MATS emission limits through the use of particulate matter (PM)
controls such as electrostatic precipitators (ESPs) or fabric filters (FFs).
Background Information
Continuous Emission Monitoring Systems (CEMS)
EPA has developed detailed procedures codified in federal regulations (40 CFR Part 75) to ensure that
sources monitor and report emissions with a high degree of precision, reliability, accuracy, and
timeliness. Sources are required to use CEMS or other approved methods to record and report pollutant
emissions data. Sources conduct stringent quality assurance tests of their monitoring systems to ensure
the accuracy of emissions data and to provide assurance to market participants that a ton of emissions
measured at one facility is equivalent to a ton measured at a different facility. EPA conducts
comprehensive electronic and field data audits to validate the reported data. While some units with low
levels of S02 and N0X emissions are allowed to use other approved monitoring methods, the vast
majority of S02 and N0X emissions are measured by CEMS.
Under MATS measurement regulations (40 CFR part 63), affected units can continuously measure
emissions using CEMS for mercury, S02, HCI, PM, and HF, or sorbent traps for Hg. Some qualifying units
with low emissions can conduct periodic stack tests in lieu of continuous monitoring.
SO2 Emission Controls
Sources in ARP and the CSAPR S02 program have a number of S02 emission control options available.
These include switching to low sulfur coal or natural gas, employing various types of FGDs, or, in the
case of fluidized bed boilers, injecting limestone into the furnace. FGDs - also known as scrubbers - on
coal-fired electricity generating units are the principal means of controlling S02 emissions and tend to be
present on the highest generating coal-fired units.
NOx Emission Controls
Sources in ARP and the CSAPR NOx annual and ozone season programs have a variety of options by
which to reduce NOx emissions, including advanced post-combustion controls such as SCR or SNCR, and
combustion controls, such as low NOx burners.
Hazardous Air Pollutant Controls
Sources in MATS have a number of options available to reduce hazardous air pollutants (HAPs), including
mercury, PM (a surrogate for toxic non-mercury metals), HCI, HF, and other acid gases. Sources can
improve operation of existing controls, add pollution controls, and switch fuels (including coal blending).
Specific pollution control devices that reduce mercury and HCI include wet FGDs (scrubbers), activated
carbon injection (ACI), dry sorbent injection (DSI), and fabric filters.
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More Information
• Power Plant Emission Trends https://www.epa.gov/airmarkets/power-plant-emission-trends
• Air Markets Program Data (AMPD) https://ampd.epa.gov/ampd/
• Emissions Monitoring https://www.epa.gov/airmarkets/emissions-monitoring
• Plain English guide to 40 CRF Part 75 https://www.epa.gov/airmarkets/plain-english-guide-part-
75-rule
• Continuous Emission Monitoring Systems (CEMS) https://www.epa.gov/emc/emc-continuous-
emission-monitoring-systems
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Figures
SO: Emissions Controls in the ARP and CSAPR SO: Program, 2017
Generation (million MWh) by SO: Emission Control
Type
Generation by Number of Units with and without SO:
Emission Controls
¦ CFBw'limestone ¦ Coalwi'FGD ¦ CFB w/limestone ¦ Coalw/FCD
¦ Coal and Oil w.'o post- ¦ Coal and Oil w o post-
combustion controls combustion controls
Notes
• Dve » round«g. percentages shown may not add up to 100%.
• "FGD" refers to Floe-gas desulfurization; "Other" fuel refers to units that burn waste, wood, petroleum coke, tire-derived fuel, etc.: "Unknown" is counted as uncontrolled.
- Emissions data coflected and reported uswg CEMS.
• c^A data in ttas f>guf# v* current as of October 2018. and may differ from past or future reports as a result of resubimssttris by souroes and ongos^g data quality assurance activities.
• There e a smal amount of generation from units with "Other* controls or "Unknown* controls. The data for these units s not easily visiMe on the full c#art. To mere dearly see the generate data for these units, especaJy for 0< and
Other fuel types. use the interactive features of the figure' cfeck on the boxes in the legend to turn off the blue 3rsd green categories of control types (labeled "FGD" and "UneontfoJed") and tan on the orange and yefiow categories of
control types (labeled "Othe*' and "Unknown").
• The acronyms represent the two control types FGD ti flwe-gas desvMursation, and CFB « Circulating fluidaed bed
Source: EPA. 2019
Figure 1. SO2 Emissions Controls in the ARP and CSAPR SO2 Program, 2017
Chapter 4: Emission Controls and Monitoring
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CSAPR SO: Program Monitoring Methodology, 2017
Monitoring Methodology by Number of Units, 2017 Monitoring Methodology by SO: Emissions, 2017
Gas Units w/CEMS
Oil Units w/CEMS
Other Units w/CEMS
; Coal Units w/CEMS
I Gas Units w/o CEMS
Oil Units w/oCEMS
I Other Units w/o CEMS
Notes:
• Percent totais may not aW uo to 100 percenl due to roun&og.
• "Oshtf fu*l inolud* uftitt tfw 0©mt>uJ!*3 pftmifity wsttft. ot »lh*f ron?©»H fw*l,
Gas Units w/CEMS
Oil Units wj'CEMS
Other Units w/CEMS
Coal Units w/CEMS
Gas Units w/o CEMS
Oil Units w/oCEMS
Other Units w/o CEMS
Source: EPA, 2019
Figure 2. CSAPR SO2 Program Monitoring Methodology, 2017
Chapter 4: Emission Controls and Monitoring
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CSAPR NOx Annual Program Monitoring Methodology, 2017
Monitoring Methodology by Number of Units, 2017 Monitoring Methodology by NOx Emissions, 2017
Gas Units w/CEMS
Oil Units w/CEMS
Other Units w/CEMS
Coal Units w/CEMS
I Gas Units w/oCEMS
Oil Units wto CEMS
I Other Units wto CEMS
I Gas Units w/CEMS
Oil Units w/CEMS
Other Units wCEMS
I Coal Units w/CEMS
Gas Units w/oCEMS
Oil Units w/o CEMS
I Other Units w/o CEMS
* Percent totais may not add op to 100 pecens due to rowing.
. "Othtf oflJts" tooludt uftas Shit prfotffy cx otbtr nonlotU fuf
Source; EPA, 2019
Figure 4. CSAPR NOx Annual Program Monitoring Methodology, 2017
Chapter 4: Emission Controls and Monitoring
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NOx Emissions Controls in CSAPR NO* Ozone Season Program, 2017
Generation (million MWh) by NOx Emission Control
Type
Generation by Number of Units with and without NOx
Emission Controls
Combustion Only
SNCR
Other
SCR
Uncontrolled
Combustion Only
SNCR
Other
SCR
Uncontrolled
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CSAPR NOx Ozone Season Program Monitoring Methodology, 2017
Monitoring Methodology by Number of Units, 2017 Monitoring Methodology by Ozone Emissions, 2017
! Gas Units w/CEMS
Oil Units w/CEMS
Other Units w/CEMS
I Coal Units w/CEMS
Gas Units w/o CEMS
Oil Units w/o CEMS
I Other Units w/o CEMS
I Gas Units w/CEMS
Oil Units w/CEMS
Other Units w/CEMS
I Coal Units w/CEMS
Notes:
• P*fC*nt touts rnty not up to 100 pWMftt to rounding
• futl u*Wi Cut oombusttfl pnmarty wood, *Mtt. Of othtf nonfotsfl fu*l *lso boost mtrcory and HCI by ACl and DSI)
Gas Units w/o CEMS
Oil Units w/o CEMS
Other Units w/o CEMS
Source: Efiflk, 2019
Figure 6. CSAPR NOx Ozone Season Program Monitoring Methodology, 2017
Chapter 4: Emission Controls and Monitoring
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Mercury Controls at MATS-Aftected Sources, 2017
Mercury Controls on MATS Covered Units (units) Mercury Controls on MATS Covered Units (MWh)
FGD
Both FGD & ACI
CFB & No Post-Combustion
Controls
I FGD
Both FGD & ACI
CFB & No Post-Combustion
Controls
• Ems s ions -lata effected and reported usftq CEMS
• E?A data m Was figure are eunent as of October 2018.
• Tries dJU i« from UATS-a! ftctM sourcw thii su&nvittw ho«rty tm!S.sons ii'-i » SPA Units not rt®orting data (eg iNjs* mentoring usir-g pwiod»s listing) M not inciu«*3 «i this report
Figure 7. Mercury Controls at MATS-Affected Sources, 2017
Source: em. 2019
Chapter 4: Emission Controls and Monitoring
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Mercury Compliance and Monitoring Methods used by Units Reporting Hourly Data under MATS, 2017
Reporting Hourly data
Compliance Method (# of Units)
Monitoring Method
Number of reporting
units
Number of reporting
facilities
Electrical Output
Heat input Sorbent Trap
CEMS
CEMS and Sorbent Trap
530
235
160
370 232
255
43
NOW*:
• Emissions data cotectw and reported using CEMS
• EFA data this figure are current as of October 2018,
• This data ce ttwugh methods other than eontmyously ro©*to«ed emissions.
Source: EM, 2019
Figure 8. Mercury Compliance and Monitoring Methods used by Units Reporting Hourly
Data under MATS, 2017
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Acid Gas Controls at MATS-Affected Sources, 2017
Acid Gas Controls on MATS Covered Units (units)
Acid Gas Controls on MATS Covered Units (MWh)
I OSI
I Wet Scrubbers
I Other controls
Dry Scrubbers
Hon Con trolled
I OSI
I Wet Scrubbers
Dry Scrubbers
Non-Controlled
Note:
- Emissions data coaecteS and reported using CEMS
• ERA data in this figure are cyfreri as of October 2018.
• This data ts from MATS-a'fecled sources that submitted hourly emesioas data to EFA and does rw? show complete data from an MATS-affected sources because rrany sources received compfcance extensons or those to denwnstrate
eoffipJaifto* Hwo^jh method* other than ooaGftsousty mofWor»d emotioos
Source: EBk. 2019
Figure 9. Acid Gas Controls at MATS-Affected Sources, 2017
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Acid Gas Compliance and Monitoring Methods used by Units Reporting Hourly Data under MATS, 2017
Reporting Hourly data
Compliance Method (• of Units)
Monitoring Method
Add Gas
Number of reporting
units
Number of reporting
facilities
Electrical Output
Heat Input
CIMS
HCl
4
3
1
3
4
S02 as a surrogate for HCl
354
168
6
348
354
Nch#*:
• Emissions oata cofectsa ana reporteo using CEMS
¦ EFA data in the figure are current as of October 2018.
• Thts data is from UATS-aH feeted sources that submitted hourly emssons data to tFA aid does not show complete data from a® UAJS-affected sources because many sources received compliance extensions or c£ose to demonstrate
sompMftc* through method! other thin c©ftWioou*fy moMo^a env»»©n»
Source: EF&, 2019
Figure 10. Acid Gas Compliance and Monitoring Methods used by Units Reporting Hourly
Data under MATS, 2017
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Chapter 5: Program Compliance
This section shows how the Acid Rain Program (ARP) and Cross-State Air Pollution Rule (CSAPR)
allowances were used for compliance under the allowance trading programs in 2017. In contrast to ARP
and CSAPR, MATS is issued under section 112 of the Clean Air Act and is not an allowance trading
program.
Highlights
ARP SO2 Program
• The reported 2017 S02 emissions by ARP sources totaled 1,318,755 tons.
• Over 47 million S02 allowances were available for compliance (9 million vintage 2017 and nearly
38 million banked from prior years).
• EPA deducted just over 1.3 million allowances for ARP compliance. After reconciliation, over 46
million ARP S02 allowances were banked and carried forward to the 2018 ARP compliance year.
• All ARP S02 facilities were in compliance in 2017 (holding sufficient allowances to cover their S02
CSAPR SO2 Group 1 Program
• The reported 2017 S02 emissions by CSAPR Group 1 sources totaled 653,658 tons.
• Over 4.2 million S02 Group 1 allowances were available for compliance.
• EPA deducted over 653,000 allowances for CSAPR S02 Group 1 compliance. After reconciliation,
over 3.6 million CSAPR S02 Group 1 allowances were banked and carried forward to the 2018
compliance year.
• All CSAPR S02 Group 1 facilities were in compliance in 2017 (holding sufficient allowances to
cover their S02 emissions).
CSAPR SO2 Group 2 Program
• The reported 2017 S02 emissions by CSAPR Group 2 sources totaled 99,739 tons.
• Over 1.5 million S02 Group 2 allowances were available for compliance.
• EPA deducted just under 100,000 allowances for CSAPR S02 Group 2 compliance. After
reconciliation, over 1.4 million CSAPR S02 Group 2 allowances were banked and carried forward
to the 2018 compliance year.
• All CSAPR S02 Group 2 facilities were in compliance in 2017 (holding sufficient allowances to
cover their S02 emissions).
CSAPR NOx Annual Program
• The reported 2017 annual NOx emissions by CSAPR sources totaled 585,855 tons.
• Over 1.8 million NOx Annual allowances were available for compliance.
emissions .
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• EPA deducted just under 586,000 allowances for CSAPR N0X Annual compliance. After
reconciliation, almost 1.3 million CSAPR NOx Annual allowances were banked and carried
forward to the 2018 compliance year.
• One facility was out of compliance with the CSAPR NOx Annual program and had 44 tons of
excess emissions.
CSAPR NOx Ozone Season Group 1 Program
• The reported 2017 ozone season NOx emissions by CSAPR sources totaled 7,136 tons.
• Over 42,000 NOx Ozone Season Group 1 allowances were available for compliance.
• EPA deducted over 7,000 allowances for CSAPR NOx Ozone Season Group 1 compliance. After
reconciliation, over 35,000 CSAPR NOx Ozone Season Group 1 allowances were banked.
• All CSAPR NOx Ozone Season Group 1 facilities were in compliance (holding sufficient allowances
to cover their NOx emissions).
CSAPR NOx Ozone Season Group 2 Program
• The reported 2017 ozone season NOx emissions by CSAPR sources totaled 294,468 tons.
• Just under 412,000 NOx Ozone Season Group 2 allowances were available for compliance.
• EPA deducted over 294,000 allowances for CSAPR NOx Ozone Season Group 2 compliance. After
reconciliation, over 117,000 CSAPR NOx Ozone Season Group 2 allowances were banked.
• All CSAPR NOx Ozone Season Group 2 facilities were in compliance (holding sufficient allowances
to cover their NOx emissions).
Background Information
The year 2017 was the third year of compliance for the CSAPR S02 (Group 1 and Group 2), NOx Annual
and NOx Ozone Season Group 1 programs, while it was the first year of compliance for the CSAPR NOx
Ozone Season Group 2 program. Each program has its own distinct set of allowances, which cannot be
used for compliance with the other programs (e.g., CSAPR S02 Group 1 allowances cannot be used to
comply with the CSAPR S02 Group 2 Program).
The compliance summary emissions number cited in "Highlights" may differ slightly from the sums of
emissions used for reconciliation purposes shown in the "Allowance Reconciliation Summary" figures
because of variation in rounding conventions, changes due to resubmissions by sources, and compliance
issues at certain units. Therefore, the allowance totals deducted for actual emissions in those figures
differ slightly from the number of emissions shown elsewhere in this report.
More Information
• Allowance Markets https://www.epa.gov/airmarkets/allowance-markets
• Air Markets Business Center https://www.epa.gov/airmarkets/business-center
• Air Markets Program Data (AMPD) https://ampd.epa.gov/ampd/
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• Emissions Trading https://www.epa.gov/emissioris-tradirig-resources
Figures
Acid Rain Program S02 Program Allowance Reconciliation Summary, 2017
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Cross-State Air Pollution Rule S02 Group 1 Program Allowance Reconciliation Summary, 2017
Held by Affected Facility Accounts
3,656,070
Total Allowances Held (2015 - 2017 Vintage) 4,263,345
Held by Other Accounts (General,
State Holding and Non-Affected
Facility Accounts)
607,275
Allowances Deducted for Cross-State Air Pollution Rule 653,650
S02 Group 1 Program
Penalty Allowance Deductions 0
Held by Affected Facility Accounts
3,002,420
Banked Allowances 3,609,695
Held by Other Accounts (General,
State Holding and Non-Affected
Facility Accounts)
607,275
CSAPR S02 Group 1 Program Compliance Results
Reported Emissions (tons)
653,658
Compliance issues, rounding and report resubmission adjustments (tons) -8
Emissions not covered by allowances (tons)
0
Total allowances deducted for emissions 653,650
Notes:
• Compliance emissions data may vary from other report sections as a result of variation in rounding conventions, changes due to resubmissions by sources, or allowance compliance issues at certain units.
- Reconciliation and compliance data are current as of June 2018 and subsequent allowance deduction adjustments and penalties are not reflected.
Source: EPA. 2019
Figure 2. Cross-State Air Pollution Rule SO2 Group 1 Program Allowance Reconciliation
Summary, 2017
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Cross-State Air Pollution Rule S02 Group 2 Program Allowance Reconciliation Summary, 2017
Held by Affected Facility Accounts
1.186,746
Total Allowances Held (2015 - 2017 Vintage) 1,554,461
Held by Other Accounts (General,
State Holding and Non-Affected
Facility Accounts)
367,715
Allowances Deducted for Cross-State Air Pollution Rule 99,724
S02 Group 2 Program
Penalty Allowance Deductions 0
Held by Affected Facility Accounts
1,087,022
Banked Allowances 1,454,737
Held by Other Accounts (General,
State Holding and Non-Affected
Facility Accounts)
367,715
CSAPR S02 Group 2 Program Compliance Results
Reported Emissions (tons)
99,739
Compliance issues, rounding and report resubmission adjustments (tons)
-15
Emissions not covered by allowances (tons)
0
Total allowances deducted for emissions 99,724
Notes:
• Compliance emissions data may vary from other report sections as a result of variation in rounding conventions, changes due to resubmissions by sources, or allowance compliance issues at certain units.
- Reconciliation and compliance data are current as of June 2018 and subsequent allowance deduction adjustments and penalties are not reflected.
Source: EPA. 2019
Figure 3. Cross-State Air Pollution Rule SO2 Group 2 Program Allowance Reconciliation
Summary, 2017
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Cross-State Air Pollution Rule N0X Annual Program Allowance Reconciliation Summary. 2017
Held by Affected Facility Accounts
1.604,243
Total Allowances Held (2015-2017 Vintage) 1,852,814
Held by Other Accounts (General,
State Holding and Non-Affected
Facility Accounts)
248.571
Allowances Deducted for Cross-State Air Pollution Rule 585,869
NOx Annual Program
Penalty Allowance Deductions (2018 Vintage) 88
Held by Affected Facility Accounts
1.018,374
Banked Allowances 1,266.945
Held by Other Accounts (General,
State Holding and Non-Affected
Facility Accounts)
248,571
CSAPR NOx Annual Program Compliance Results
Reported Emissions (tons)
585,855
Compliance issues, rounding and report resubmission adjustments (tons)
58
Emissions not covered by allowances (tons)
-44
Total allowances deducted for emissions 585,869
Notes:
• Compliance emissions data may vary from other report sections as a result of variation in rounding conventions, changes due to resubmissions by sources, or allowance compliance issues at certain units.
- Reconciliation and compliance data are current as of June 2018 and subsequent allowance deduction adjustments and penalties are not reflected.
Source: EPA. 2019
Figure 4. Cross-State Air Pollution Rule NOx Annual Program Allowance Reconciliation
Summary, 2017
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Cross-State Air Pollution Rule NOx Ozone Season Program Group 1 Allowance Reconciliation Summary, 2017
Held by Affected Facility Accounts
28.552
Total Allowances Held (2015 - 2017 Vintage) 42,554
Held by Other Accounts (General,
State Holding and Non-Affected
Facility Accounts)
14,002
Allowances Deducted for Cross-State Air Pollution Rule 7,093
NOx Ozone Season Program Group 1
Penalty Allowance Deductions 0
Held by Affected Facility Accounts
21,459
Banked Allowances 35,461
Held by Other Accounts (General,
State Holding and Non-Affected
Facility Accounts)
14,002
CSAPR NOx Ozone Season Program Group 1 Compliance Results
Reported Emissions (tons)
7,136
Compliance issues, rounding and report resubmission adjustments (tons)
-43
Emissions not covered by allowances (tons)
0
Total allowances deducted for emissions 7,093
Notes:
• Compliance emissions data may vary from other report sections as a result of variation in rounding conventions, changes due to resubmissions by sources, or allowance compliance issues at certain units.
- Reconciliation and compliance data are current as of June 2018 and subsequent allowance deduction adjustments and penalties are not reflected.
Source: EPA. 2019
Figure 5. Cross-State Air Pollution Rule NOx Ozone Season Program Group 1 Allowance
Reconciliation Summary, 2017
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Cross-State Air Pollution Rule NOx Ozone Season Program Group 2 Allowance Reconciliation Summary, 2017
Held by Affected Facility Accounts
382,255
Total Allowances Held (2017 Vintage) 411,931
Held by Other Accounts (General,
State Holding and Non-Affected
Facility Accounts)
29,676
Allowances Deducted for Cross-State Air Pollution Rule 294,488
NOx Ozone Season Program Group 2
Penalty Allowance Deductions 0
Held by Affected Facility Accounts
87,767
Banked Allowances 117,443
Held by Other Accounts (General,
State Holding and Non-Affected
Facility Accounts)
29,676
CSAPR NOx Ozone Season Program Group 2 Compliance Results
Reported Emissions (tons)
294,468
Compliance issues, rounding, and report resubmission adjustments (tons)
20
Emissions not covered by allowances (tons)
0
Total allowances deducted for emissions 294,488
Notes:
• Compliance emissions data may vary from other report sections as a result of variation in rounding conventions, changes due to resubmissions by sources, or allowance compliance issues at certain units.
- Reconciliation and compliance data are current as of June 2018 and subsequent allowance deduction adjustments and penalties are not reflected.
Source: EPA. 2019
Figure 6. Cross-State Air Pollution Rule NOx Ozone Season Program Group 2 Allowance
Reconciliation Summary, 2017
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Chapter 6: Market Activity
Cap and trade programs allow participants to independently determine their best compliance strategy.
Participants that reduce their emissions below the number of allowances they hold may trade
allowances, sell them, or bank them for use in future years. While ARP and CSAPR are cap and trade
programs, MATS is not a market-based program; therefore this section does not report on market
activity for MATS.
Highlights
Transaction Types and Volumes
• In 2017, more than 970,000 allowances were traded across all five of the CSAPR trading
• Just under one-quarter of the transactions within the CSAPR programs were between distinct
organizations. In 2017, over 6 million ARP allowances were traded, the majority (67 percent)
between related organizations.
2017 Allowance Prices1
• ARP S02 allowance prices averaged less than $1 per ton in 2017.
• CSAPR S02 Group 1 allowance prices started 2017 at $5.25 per ton and ended 2017 at $2.13 per
ton.
• CSAPR S02 Group 2 allowance prices started 2017 at $5.25 per ton and ended 2017 at $2.63 per
ton.
• CSAPR NOx annual program allowances started 2017 at $6 per ton and ended 2017 at $2 per
ton.
• CSAPR NOx ozone season program allowances started 2017 at $525 per ton and ended 2017 at
$175 per ton.2
Background Information
Transaction Types and Volumes
Allowance transfer activity includes two types of transfers: EPA transfers to accounts and private
transactions. EPA transfers to accounts include the initial allocation of allowances by states or EPA, as
well as transfers into accounts related to set-asides. This category does not include transfers due to
allowance retirements. Private transactions include all transfers initiated by authorized account
representatives for any compliance or general account purposes.
1 Allowance prices as reported by SNL Finance, 2017.
2 These prices reflect CSAPR Update ozone season NOx allowances. In October 2017, EPA published an update to the CSAPR
ozone season allowance trading programs. On October 23rd, 2017, most CSAPR ozone season NOx allowances were
converted to CSAPR Update ozone season NOx allowances.
programs.
Chapter 6: Market Activity
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To better understand the trends in market performance and transfer history, EPA classifies private
transfers of allowance transactions into two categories:
• Transfers between separate and unrelated parties (distinct organizations), which may include
companies with contractual relationships (such as power purchase agreements), but excludes
parent-subsidiary types of relationships.
• Transfers within a company or between related entities (e.g., holding company transfers
between a facility compliance account and any account held by a company with an ownership
interest in the facility).
While all transactions are important to proper market operation, EPA follows trends in transactions
between distinct economic entities with particular interest. These transactions represent an actual
exchange of assets between unaffiliated participants, which reflect companies making the most of the
cost-minimizing flexibility of emission trading programs. Companies accomplish this by finding the
cheapest emission reductions not only among their own generating assets, but across the entire
marketplace of power generators.
Allowance Markets
The 2017 emissions were below emission budgets for the Acid Rain Program (ARP) and for all five Cross-
State Air Pollution Rule (CSAPR) programs. As a result, CSAPR allowance prices were well below the
marginal cost for reductions projected at the time of the final rule, and are subject, in part, to downward
pressure from the available banks of allowances.
More Information
• Allowance Markets https://www.epa.gov/airmarkets/allowance-markets
• Air Markets Business Center https://www.epa.gov/airmarkets/business-center
• Air Markets Program Data (AMPD) https://ampd.epa.gov/ampd/
• Emissions Trading https://www.epa.gov/emissions-trading-resources
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Figures
2017 Allowance Transfers under CSAPR and ARP
Transactions Conducted
Allowa nces Transferred
Share of Program's Allowances Transferred
Related (%) Distinct (%)
ARPSOi
718
6,622,116
67%
33%
CSAPR SOj Group 1
355
304,224
85%
15%
CSAPR SO: Group 2
137
173,046
84%
16%
CSAPR NOx Annual
800
388,382
68%
32%
CSAPR NO* Ozone Season Group 1
18
13,239
100%
0%
CSAPR NOx Ozone Season Group 2
490
92,804
53%
47%
Notes:
• The breakout between distinct and related organisations is not an exact value as relationships are often difficult to categorae ri a simpie bifurcated manner EFA's analyses s conservative and the "Distinct Or^arsatops" percentage ss
tttefy higher.
• Percentilej may not add up to 100% due to rouftd«g.
Source: Efifc, 2019
Figure 1, 2017 Allowance Transfers under CSAPR and ARP
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% pro^0e* for
these items, use the interacts* features of the figure: cbc* on the imes »nthe legend to turn off the yeto* category (labeled "CSAPR Update NO, Seasonal"} and ictep an of the other legend items on.
Source: 5NL Financtal, 2019
Figure 2. Allowance Spot Price (Prompt Vintage), January-December 2017
Chapter 6: Market Activity
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Chapter 7: Air Quality
The Acid Rain Program (ARP) and Cross-State Air Pollution Rule (CSAPR) were designed to reduce sulfur
dioxide (S02) and nitrogen oxides (N0X) emissions from power plants. These pollutants contribute to the
formation of ground-level ozone and particulate matter, which cause a range of serious health effects
and degrade visibility in many American cities and scenic areas, including National Parks. The dramatic
emission reductions achieved under these programs have improved air quality and delivered significant
human health and ecological benefits across the United States.
To evaluate the impact of emission reductions on air quality, scientists and policymakers use data
collected from long-term national air quality monitoring networks. These networks provide information
on a variety of indicators useful for tracking and understanding temporal trends in regional air quality.
Sulfur Dioxide and Nitrogen Oxides Trends
Highlights
National SO2 Air Quality
• Based on EPA's air trends data, the national average of S02 annual mean ambient
concentrations decreased from 11.8 parts per billion (ppb) to 1.0 ppb (92 percent) between
1980 and 2017.
• The two largest single-year reductions (over 20 percent) occurred in the first year of the ARP,
between 1994 and 1995, and between 2008 and 2009, just prior to the start of the CAIR S02
program.
Regional Changes in Air Quality
• Average ambient S02 concentrations declined in the eastern United States following
implementation of the ARP and other emission reduction programs. Regional average
concentrations declined 91 percent from the 1989-1991 to the 2015-2017 observation periods.
• Ambient particulate sulfate concentrations have decreased since the ARP was implemented,
with average concentrations decreasing by 44 to 78 percent in observed regions from 1989-
1991 to 2015-2017.
• Average annual ambient total nitrate concentrations declined 55 percent from 1989-1991 to
2015-2017 in the eastern United States, with the most significant decreases occurring after
2002 coinciding with the implementation of the NOx Budget Trading Program and CAIR.
Background Information
Sulfur Dioxide
Sulfur oxides are a group of highly reactive gases that can travel long distances in the upper atmosphere
and predominantly exist as sulfur dioxide (S02). The primary source of S02 emissions is fossil fuel
combustion at power plants. Smaller sources of S02 emissions include industrial processes, such as
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extracting metal from ore, as well as the burning of high sulfur-containing fuels by locomotives, large
ships, and non-road equipment. S02 emissions contribute to the formation of fine particle pollution
(PM2.5) and are linked with adverse effects on the respiratory system.1 In addition, particulate sulfate
degrades visibility and, because sulfur compounds are typically acidic, can harm ecosystems when
deposited.
Nitrogen Oxides
Nitrogen oxides are a group of highly reactive gases including nitric oxide (NO) and nitrogen dioxide
(N02). In addition to contributing to the formation of ground-level ozone and PM2.5, N0X emissions are
linked with adverse effects on the respiratory system.2,3 N0X also reacts in the atmosphere to form nitric
acid (HNO3) and particulate ammonium nitrate (NH4NO3). HN03 and N03, reported as total nitrate, can
also lead to adverse health effects and, when deposited, cause damage to sensitive ecosystems.
Although the ARP and CSAPR programs have significantly reduced N0X emissions (primarily from power
plants) and improved air quality, emissions from other sources (such as motor vehicles and agriculture)
contribute to total nitrate concentrations in many areas. Ambient nitrate levels can also be affected by
emissions transported via air currents over wide regions.
More Information
• Clean Air Status and Trends Network (CASTNET) https://www.epa.gov/castnet
• Air Quality System (AQS) https://www.epa.gov/aqs
• National Ambient Air Quality Standards (NAAQS) https://www.epa.gov/criteria-air-pollutants
• Sulfur Dioxide (SO?) Pollution https://www.epa.gov/so2-pollution
• Nitrogen Oxides (NOx) Pollution https://www.epa.gov/no2-pollution
• EPA's Clean Air Market Programs https://www.epa.gov/airmarkets/programs
• EPA's 2019 National Air Quality Trends Report https://www.epa.gov/air-trends
References
1. Katsouyanni, K., Schwartz, J., Spix, C., Touloumi, G., Zmirou, D., Zanobetti, A., Wojtyniak, B.,
Vonk, J.M., Tobias, A., Ponka, A., Medina, S., Bacharova, L., & Anderson, H.R. (1996). Short term
effects of air pollution on health: a European approach using epidemiologic time series data: the
APHEA protocol. J. of Epidemiol Community Health, 50: S12-S18.
2. Peel, J.L., Tolbert, P.E., Klein, M., Metzger, K.B., Flanders, W.D., Todd, K., Mulholland, J.A., Ryan,
P.B., & Frumkin, H. (2005). Ambient air pollution and respiratory emergency department visits.
Epidemiology, 16: 164-174.
3. Hong, C., Goldberg, M.S., Burnett, R.T., Jerrett, M., Wheeler, A.J., & Villeneuve, P.J. (2013) Long-
term exposure to traffic-related air pollution and cardiovascular mortality. Epidemiology, 24:
35-43.
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Figures
National SO: Air Quality Trend, 1980-2017
c 25
A)
u
c
0
H 20
c
a>
3
1
c
ro
| 10
% PRO^S°
1960 1965 1990 1995 2000 2005 2010 2015
Average Concentration 90S of sites have concentrations below this line •— 10% of sites have concentrations below this line
Noies
• DjU bM*d on suit, local, «.«d ESA monitomQ »>t»» wf»cA 1't tocat#<3 p«njiUy m urfcjfl art**.
Source: ERA, 2019
Figure 1. National SO2 Air Quality Trend, 1980-2017
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Regional Changes in Air Quality
Measurement
Region
Annual Average,
2000-2002
Annual Average,
2015-2017
Percent Change
Number of Sites
Mid-Atlantic
4.8
1.4
-71
13
Midwest
4.3
1.4
-67
16
North Central
1.3
0.70
¦46
2.0
Ambient Particulate Sulfate
Northeast
2.6
0.80
-69
6.0
Concentration (|ig/m3)
Pacific
0.82
0.55
-33
5.0
Rocky Mountain
0.66
0.40
-39
10
South Central
2.9
1.5
-48
2.0
Southeast
4.2
1.3
•69
12
Mid-Atlantic
8.0
1.0
-88
13
Midwest
6.8
1.1
-84
16
North Central
1.0
0.S0
-50
2.0
Ambient Sulfur Dioxide
Northeast
3.4
0.60
-82
6.0
Concentration (ug/m3)
Pacific
0.37
0.34
-8.0
5.0
Rocky Mountain
0.48
0.29
-40
10
South Central
1.1
0.60
-45
2.0
Southeast
3.4
0.50
-85
12
Mid-Atlantic
3.0
1A
-53
13
Midwest
4.1
2.0
-51
16
North Central
1.2
0.80
-33
2.0
Ambient Total Nitrate
Northeast
1.9
0.90
-53
6.0
Concentration (ng/m3)
Pacific
1.8
0.90
•50
5.0
Rocky Mountain
0.78
0.48
-38
10
South Central
1.5
0.90
-40
2.0
Southeast
2.3
1.1
-52
12
Notes:
• AvtfSQtS jrt tit mw Of *11 Srtw in * r*3*an th»j «** m*t th* oo^0l«t*fl*»* OMVtWA for 2000 » 2002 m*y from Mt: rtportl.
Source: Efifc, 2019
Figure 2. Regional Changes in Air Quality
Chapter 7: Air Quality-Sulfur Dioxide and Nitrogen Oxides Trends
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Ozone
Highlights
Changes in 1-Hour Ozone during Ozone Season
• There was an overall regional reduction in ozone levels between 2000-2002 and 2015-2017,
with a 19 percent reduction in the highest (99th percentile) ozone concentrations in CSAPR
states.
• Results demonstrate how NOx emission reduction policies have affected 1-hour ozone
concentrations in the eastern United States - the region that the policies were designed to
target.
Trends in Rural 8-Hour Ozone
• From 2015 to 2017, rural ozone concentrations averaged 65 ppb in CSAPR states, a decrease of
25 ppb (27 percent) from the 1990 to 2002 period.
• The Autoregressive Integrated Moving Average (ARIMA) model shows how the reductions in
rural ozone concentrations compare with the implementation of the NBP in 2003 (two-year 14
ppb reduction from 2002) and the start of the CAIR NOx Ozone Season program in 2009 (two-
year 7 ppb reduction from 2007).
• Five of the six lowest observed annual ozone concentrations were between 2013 and 2017.
Ozone season NOx emissions fell steadily under CAIR and continued to drop after
implementation of CSAPR in 2015. In addition, implementation of the mercury and air toxics
standards (MATS), which began in 2015, achieves co-benefit reductions of NOx emissions.
Changes in 8-Hour Ozone Concentrations
• The average reduction in both urban and rural ozone concentrations (not adjusted for weather)
in the CSAPR NOx Ozone Season program region from 2000-2002 to 2015-2017 was about 10
ppb (18 percent).
• The average reduction in the meteorologically-adjusted ozone concentrations in the CSAPR NOx
Ozone Season program region from 2000-2002 to 2015-2017 was about 11 ppb (20 percent).
Changes in Ozone Nonattainment Areas
• Ninety-two of the 113 areas originally designated as nonattainment for the 1997 8-hour ozone
National Ambient Air Quality Standard (NAAQS) (0.08 ppm) are in the eastern United States and
are home to about 122 million people.1 These nonattainment areas were designated in 2004
using air quality data from 2001 to 2003.2
o Based on data from 2015 to 2017, 91 of the eastern ozone nonattainment areas now
show concentrations below the level of the 1997 standard, while the remaining area
had incomplete data.
• Twenty-two of the 46 areas originally designated as nonattainment for the 2008 8-hour ozone
NAAQS (0.075 ppm) are in the eastern United States and are home to about 80 million people.
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These nonattainment areas were designated in 2012 using air quality data from 2008 to 2010 or
2009 to 2011.
o Based on data from 2015-2017, 73 percent (16 areas) of the eastern ozone
nonattainment areas now show concentrations below the level of the 2008 standard.
While six areas continue to show concentrations above the 2008 standard, four of those
areas made progress toward meeting the standard in the 2015-2017 period. It is
reasonable to conclude that ozone season NOx emission reductions from the NBP, CAIR,
and CSAPR have significantly contributed to these improvements in ozone air quality.
• Effective August 3, 2018, EPA designated 52 areas nonattainment for the 2015 8-hour ozone
standard based on air quality data from 2014-2016 or 2015-2017. Twenty-two of the 52 areas
are in the eastern United States and are home to 76 million people.
Background Information
Ozone pollution - also known as smog - forms when NOx and volatile organic compounds (VOCs) react
in the presence of sunlight. Major anthropogenic sources of NOx and VOC emissions include electric
power plants, motor vehicles, solvents, and industrial facilities. Meteorology plays a significant role in
ozone formation and hot, sunny days are most favorable for ozone production. For ozone, EPA and
states typically regulate NOx emissions during the summer when sunlight intensity and temperatures are
highest.
Ozone Standards
In 1979, EPA established NAAQS for 1-hour ozone at 0.12 parts per million (ppm), or 124 parts per billion
(ppb). In 1997, a more stringent 8-hour ozone standard of 0.08 ppm (84 ppb) was finalized, revising the
1979 standard. CSAPR was designed to help downwind states in the eastern United States achieve the
1997 ozone NAAQS. Based on extensive scientific evidence about ozone's effects on public health and
welfare, EPA strengthened the 8-hour ozone standard to 0.075 ppm (75 ppb) in 2008, and further
strengthened the 8-hour NAAQS for ground-level ozone to 0.070 ppm (70 ppb) in 2015. EPA revoked the
1-hour ozone standard in 2005 and also recently revoked the 1997 8-hour ozone standard in 2015.
Regional Trends in Ozone
EPA investigated trends in daily maximum 8-hour ozone concentrations measured at rural Clean Air
Status and Trends Network (CASTNET) monitoring sites within the CSAPR NOx ozone season program
region and in adjacent states. Rural ozone measurements are useful in assessing the impacts on air
quality resulting from regional NOx emission reductions because they are typically less affected by local
sources of NOx emissions (e.g., industrial and mobile) than urban measurements. Reductions in rural
ozone concentrations are largely attributed to reductions in regional NOx emissions and transported
ozone.
The Autoregressive Integrated Moving Average (ARIMA) model is an advanced statistical analysis tool
used to visualize the trend in regional ozone concentrations following implementation of various
programs geared toward reducing ozone season NOx emissions. To show the shift in the highest daily
ozone levels, EPA modeled the average of the 99th percentile of the daily maximum 8-hour ozone
concentrations measured at CASTNET sites (as described above).
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Meteorologically-Adjusted Daily Maximum 8-Hour Ozone Concentrations
Meteorologically-adjusted ozone trends provide additional insight on the influence of CSAPR NOx Ozone
Season program emission reductions on regional air quality. EPA retrieved daily maximum 8-hour ozone
concentration data from CASTNET and daily meteorology data from the National Weather Service for 78
urban areas and 37 rural CASTNET monitoring sites located in the CSAPR N0X Ozone Season program
region. EPA uses these data in a statistical model to account for the influence of weather on seasonal
average ozone concentrations at each monitoring site.3,4
Changes in Ozone Nonattainment Areas
The majority of ozone season N0X emission reductions in the power sector after 2003 are attributable to
the NBP, CAIR, and CSAPR. As power sector emissions are an important component of the NOx emission
inventory, it is reasonable to conclude that the reduction in ozone season NOx emissions from these
programs have significantly contributed to improvements in ozone concentrations and attainment of
the 1997 ozone health-based air quality standard.
Emission reductions under these power sector programs have helped many areas in the eastern United
States reach attainment for the 2008 ozone NAAQS. However, several areas continue to be out of
attainment with the 2008 ozone NAAQS, and additional ozone season NOx emission reductions are
needed to attain that standard as well as the strengthened ozone standard that was finalized in 2015.
In order to help downwind states and communities meet and maintain the 2008 ozone standard, EPA
finalized the CSAPR Update in September 2016 to address the transport of ozone pollution that crosses
state lines in the eastern United States. Implementation began in May 2017 to further reduce ozone
season NOx emissions from power plants in 22 states in the eastern US.
More Information
• Clean Air Status and Trends Network (CASTNET) https://www.epa.gov/castnet
• Air Quality System (AQS) https://www.epa.gov/aqs
• National Ambient Air Quality Standards (NAAQS) https://www.epa.gov/criteria-air-pollutants
• Ozone Pollution https://www.epa.gov/ozone-pollution
• Nitrogen Oxides (NOx) Pollution https://www.epa.gov/no2-pollution
• Nonattainment Areas https://www.epa.gov/green-book
• EPA's Clean Air Market Programs https://www.epa.gov/airmarkets/programs
• EPA's 2019 National Air Quality Trends Report https://www.epa.gov/air-trends
References
1. U.S. Census. (2010).
2. 40 CFR Part 81. Designation of Areas for Air Quality Planning Purposes.
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3. Cox, W.M. & Chu, S.H. (1996). Assessment of interannual ozone variation in urban areas from a
climatological perspective. Atmospheric Environment, 30 (16): 2615-2625.
4. Camalier, L., Cox, W.M., & Dolwick, P. 2007. The effects of meteorology on ozone in urban areas
and their use in assessing ozone trends. Atmospheric Environment, 41(33): 7127-7137.
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% pRo^s°
Figures
Percent Change in the Highest Values (99th percentile) of 1-hour Ozone Concentrations during the Ozone Season,
2000-2002 versus 2015-2017
Notes:
• Data are from State and Local Air Monitoring Stations (SLAMS) AOS and CASTNET monitoring sites with two or more years of data within each three-year monitoring period.
• The 99* percentile represents ate highest 1% of hcurty ozone measurements at a gwen monitor
Source: EPA, 2019
Figure 1. Percent Change in the Highest Values (99th percentile) of 1-hour Ozone
Concentrations during the Ozone Season, 2000-2002 versus 2015-2017
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Seasonal Average of 8-Hour Ozone Concentrations in CSAPR States, Unadjusted and Adjusted for Weather
7J
2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017
¦I Unadjusted concentrations ¦ Adjusted concentrations
Notes.
• 3-Hour daily maximum ozone concentrator data from EFA's AOS and cfaiy meteorology data from the National Weather Service *®fe retrieved foe 78 urban areas and 37 rural CASTNET monitoring stes located in the CSAPR NO* ozone
season program reg>on.
• For a monitor to S* included *> tfws trends anatyse*i day
Source: ERA, 2019
Figure 3. Seasonal Average of 8-Hour Ozone Concentrations in CSAPR States,
Unadjusted and Adjusted for Weather
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Particulate Matter
Highlights
PM Seasonal Trends
• The Air Quality System (AQS) includes average PM2.5 concentration data for 244 sites located in
the CSAPR S02 and annual NOx program region. Trend lines in PM2.5 concentrations show
decreasing trends in both the warm months (April to September) and cool months (October to
March) unadjusted for the influence of weather.
• The seasonal average PM2.5 concentrations have decreased by about 47 and 46 percent in the
warm and cool season months, respectively, between 2000 and 2017.
Changes in PM2.5 Nonattainment
• 36 of the 39 designated nonattainment areas for the 1997 annual average PM2.5 NAAQS are in
the eastern United States and are home to about 75 million people.1,2 The nonattainment areas
were designated in January 2005 using 2001 to 2003 data.
o Based on data gathered from 2015 to 2017, 35 of these eastern areas originally
designated nonattainment show concentrations below the level of the 1997 PM2.5
standard (15 ng/m3), indicating improvements in PM2.5 air quality. One area has
incomplete data.
• Given that power sector emissions are an important component of the S02 and annual NOx
emission inventory and that the majority of power sector S02 and annual NOx emission
reductions occurring after 2003 are attributable in part to the ARP, NBP, CAIR, and CSAPR, it is
reasonable to conclude that these emission reduction programs have significantly contributed
to these improvements in PM2.5 air quality.
Background Information
Particulate matter—also known as soot, particle pollution, or PM—is a complex mixture of extremely
small particles and liquid droplets. Particle pollution is made up of a number of components, including
acid-forming nitrate and sulfate compounds, organic compounds, metals, and soil or dust particles. Fine
particles (defined as particulate matter with aerodynamic diameter < 2.5 pim, and abbreviated as PM2.5)
can be directly emitted or can form when gases emitted from power plants, industrial sources,
automobiles, and other sources react in the air.
Particle pollution—especially fine particles—contains microscopic solids or liquid droplets so small that
they can get deep into the lungs and cause serious health problems. Numerous scientific studies have
linked particle pollution exposure to a variety of problems, including the following: premature death;
increased respiratory symptoms, such as irritation of the airways, coughing, or difficulty breathing;
decreased lung function; aggravated asthma; development of chronic bronchitis; irregular heartbeat;
and nonfatal heart attacks.3,4,5
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Particulate Matter Standards
The CAA requires EPA to set NAAQS for particle pollution. In 1997, EPA set the first standards for fine
particles at 65 micrograms per cubic meter (ng/m3) measured as the three-year average of the 98th
percentile for 24-hour exposure, and at 15 ng/m3 for annual exposure measured as the three-year
annual mean. EPA revised the air quality standards for particle pollution in 2006, tightening the 24-hour
fine particle standard to 35 ng/m3 and retaining the annual fine particle standard at 15 ng/m3. In
December 2012, EPA strengthened the annual fine particle standard to 12 ng/m3.
CSAPR was promulgated to help downwind states in the eastern United States achieve the 1997 annual
average PM2.5 NAAQS and the 2006 24-hour PM2.5 NAAQS; therefore, analyses in this report focus on
those standards.
Changes in PM2.5 Nonattainment Areas
In the eastern US, recent data indicate that no areas are violating the 1997 or 2006 PM2.5 NAAQS. One
area in the eastern US (Allegheny County, PA) is violating the 2012 annual PM2.5 NAAQS. The majority of
S02 and annual NOx emission reductions in the power sector that occurred after 2003 are attributable to
the ARP, NBP, CAIR, and CSAPR. As power sector emissions are an important component of the S02 and
annual NOx emission inventory, it is reasonable to conclude that these emission reduction programs
have significantly contributed to these improvements in PM2.5 air quality.
More Information
• Clean Air Status and Trends Network (CASTNET) https://www.epa.gov/castnet
• Air Quality System (AQS) https://www.epa.gov/aqs
• National Ambient Air Quality Standards https://www.epa.gov/criteria-air-pollutants
• Particulate Matter (PM) Pollution https://www.epa.gov/pm-pollution
• Sulfur Dioxide (SO?) Pollution https://www.epa.gov/so2-pollution
• Nitrogen Oxides (NOx) Pollution https://www.epa.gov/no2-pollution
• Nonattainment Areas https://www.epa.gov/green-book
• EPA's Clean Air Market Programs https://www.epa.gov/airmarkets/programs
• EPA's 2019 National Air Quality Trends Report https://www.epa.gov/air-trends
References
1. 40 CFR Part 81. Designation of Areas for Air Quality Planning Purposes.
2. U.S. Census. (2010).
3. Dockery, D.W., Speizer F.E., Stram, D.O., Ware, J.H., Spengler, J.D., & Ferris Jr., B.G. (1989).
Effects of inhalable particles on respiratory health of children. American Review of Respiratory
Disease 139: 587-594.
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4. Schwartz, J. & Lucas, N. (2000). Fine particles are more strongly associated than coarse particles
with acute respiratory health effects in school children. I 11: 6-10.
5. Bell, M.L., Dominici, F., Ebisu, K., Zeger, S.L., & Samet, J.M. (2007). Spatial and temporal variation
in PM2.5 chemical composition in the United States for health effects studies. Environmental
Health Perspectives 115: 989-995.
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Chapter 8: Acid Deposition
Acid deposition, commonly known as "acid rain/' is a broad term referring to the mixture of wet and dry
deposition from the atmosphere containing higher than normal amounts of sulfur and nitrogen-
containing acidic pollutants. The precursors of acid deposition are primarily the result of emissions of
sulfur dioxide (S02) and nitrogen oxides (N0X) from fossil fuel combustion; however, natural sources,
such as volcanoes and decaying vegetation, also contribute a small amount.
Highlights
Wet Sulfate Deposition
• All areas of the eastern United States have shown significant improvement, with an overall 64
percent reduction in wet sulfate deposition from 2000-2002 to 2015-2017.
• Between 2000-2002 and 2015-2017, the Northeast and Mid-Atlantic experienced the largest
reductions in wet sulfate deposition of 71 percent and 70 percent, respectively.
• A reduction in S02 emissions and consequent decrease in the formation of sulfates that are
transported long distances have resulted in reduced sulfate deposition in the Northeast. The
sulfate reductions documented in the region, particularly across New England and portions of
New York, were also affected by lowered S02 emissions in eastern Canada.1
Wet Inorganic Nitrogen Deposition
• Wet deposition of inorganic nitrogen decreased an average of 21 percent in the Mid-Atlantic
and 33 percent in the Northeast but increased 13 percent in the Rocky Mountain region from
2000-2002 to 2015-2017. Increases in wet deposition of inorganic nitrogen in the Rocky
Mountain region are attributed to a 57 percent increase in wet deposition of reduced nitrogen
(NH4+) between 2000 and 2017.
• Reductions in nitrogen deposition recorded since the early 1990s have been less pronounced
than those for sulfur. Emissions from other source categories (e.g., mobile sources, agriculture,
and manufacturing) contribute to air concentrations and deposition of nitrogen.
Regional Trends in Total Deposition
• The reduction in total sulfur deposition (wet plus dry) has been of similar magnitude to that of
wet deposition with an overall average reduction of 69 percent from 2000-2002 to 2015-2017.
• Decreases in dry and total inorganic nitrogen deposition have generally been greater than that
of wet deposition, with average reductions of 28 percent and 21 percent, respectively. In
contrast, wet deposition from inorganic nitrogen decreased by an average of 10 percent from
2000-2002 to 2015-2017.
Background Information
Acid Deposition
As S02 and NOx gases react in the atmosphere with water, oxygen, and other chemicals, they form acidic
compounds that are deposited to the earth's surface in the form of wet and dry acid deposition.
Chapter 8: Acid Deposition
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Long-term monitoring network data show significant improvements in the primary indicators of acid
deposition. For example, wet sulfate deposition (sulfate that falls to the earth through rain, snow, and
other precipitation) has decreased in much of the eastern United States due to S02 emission reductions
achieved through implementation of the Acid Rain Program (ARP), the Clean Air Interstate Rule (CAIR)
and the Cross-State Air Pollution Rule (CSAPR). Some of the most dramatic reductions have occurred in
the mid-Appalachian region, including Maryland, New York, West Virginia, Virginia, and most of
Pennsylvania. Along with wet sulfate deposition, precipitation acidity, expressed as hydrogen ion (H+ or
pH) concentration, has also decreased by similar percentages.
Reductions in nitrogen deposition compared to the early 1990s have been less pronounced than those
for sulfur. As noted earlier, emissions from source categories other than ARP and CSAPR sources
contribute to changes in air concentrations and deposition of nitrogen.
Monitoring Networks
The Clean Air Status and Trends Network (CASTNET) provides long-term monitoring of regional air
quality to determine trends in atmospheric concentrations and deposition of nitrogen, sulfur, and ozone
in order to evaluate the effectiveness of national and regional air pollution control programs. CASTNET
now operates more than 90 regional sites throughout the contiguous United States, Alaska, and Canada.
Sites are located in areas where urban influences are minimal.
The National Atmospheric Deposition Program/National Trends Network (NADP/NTN) is a nationwide,
long-term network tracking the chemistry of precipitation. The NADP/NTN provides concentration and
wet deposition data on hydrogen ion (acidity as pH), sulfate, nitrate, ammonium, chloride, and base
cations. The NADP/NTN has grown to more than 250 sites spanning the United States, Canada, Puerto
Rico, and the Virgin Islands.
Together, these complementary networks provide long-term data needed to estimate spatial patterns
and temporal trends in total deposition.2
More Information
• Acid Rain https://www.epa.gov/acidrain
• Clean Air Status and Trends Network (CASTNET) https://epa.gov/castnet
• National Atmospheric Deposition Program (NADP) http://nadp.slh.wisc.edu/
References
1. Government of Canada, Environment Canada. (2017). Canada-United States Air Quality
Agreement Progress Report 2016. ISSN: 1910-5223: Cat. No.: En85-1E-PDF.
2. Schwede, DB and Lear, GG. (2014). A novel hybrid approach for estimating total deposition in
the United States. Atmosphere Environment 92: 207-220.
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USEPA, 2019
Figure 1. Three-Year Total Sulfur Deposition
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Chapter 9: Ecosystem Response
Acidic deposition resulting from sulfur dioxide (S02) and nitrogen oxides (N0X) emissions may negatively
affect the biological health of lakes, streams, forests, grasslands, and other ecosystems in the United
States. Trends in measured chemical indicators allow scientists to determine whether water bodies are
improving and heading towards recovery or if they are still acidifying. Assessment tools, such as critical
loads analysis, provide a quantitative estimate of whether decreases in acidic deposition levels of sulfur
and nitrogen resulting from S02 and N0X emission reductions are sufficient to protect aquatic resources.
Ground-level ozone is an air pollutant that can impact ecological systems like forests, altering a plant's
health and leading to changes in individual tree growth (e.g., biomass loss) and to the biological
community. Analyzing the biomass loss of certain trees before and after implementation of N0X
emission reduction programs provides information about the effect of reduced N0X emissions and
ozone concentrations on forested areas.
• Between 1990 and 2017, improved lake and stream health was demonstrated by significant
decreasing trends in sulfate concentrations in water at all long-term monitoring (LTM) program
lake and stream monitoring sites in New England, the Adirondacks, and the Catskill mountains.
• On the other hand, between 1990 and 2017, streams in the central Appalachian region have
experienced mixed results due in part to their soils and geology. Only 45 percent of monitored
streams show lower sulfate concentrations (and statistically significant trends), while 8 percent
show increased sulfate concentrations.
• Nitrate concentrations and trends are highly variable and many sites do not show improving
trends between 1990 and 2017, despite reductions in NOx emissions and inorganic nitrogen
• In 2017, levels of acid neutralizing capacity (ANC), a key indicator of aquatic ecosystem recovery,
have increased significantly from 1990 in lake and stream sites in the Adirondack Mountains,
New England, and the Catskill mountains. In the Appalachians, sites with increasing ANC remain
low at 21 percent, reflecting a 3 percent increase from 2016.
Ozone Impacts on Forests
• Between 2000-2002 and 2015-2017, the area in the eastern United States with significant
forest biomass loss (>2% biomass loss) decreased from 34 percent to 5.7 percent for seven tree
species combined - black cherry, yellow poplar, sugar maple, eastern white pine, Virginia pine,
red maple, and quaking aspen.
Ecosystem Health
Highlights
Regional Trends in Water Quality
deposition.
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• For black cherry and yellow poplar individually (the tree species most sensitive to ground-level
ozone), the total land area in the eastern United States with significant biomass loss decreased
from 15 percent to 5.2 percent for black cherry, and from 3 percent to 0 percent for yellow
poplar between 2000-2002 and 2015-2017.
• For the period 2015-2017, total land area in the eastern United States with significant biomass
loss for the remaining five species combined (red maple, sugar maple, quaking aspen, Virginia
pine, and eastern white pine) is now zero. This is in contrast to 3.4% for the period of 2000-
2002.
• While this change in biomass loss cannot be exclusively attributed to the implementation of the
NBP, CAIR, and CSAPR, it is likely that NOx ozone season emission reductions achieved under
these programs, and the corresponding decreases in ozone concentration, contributed to this
environmental improvement.
Background Information
Acidified Surface Water Trends
Acidified precipitation can impact lakes and streams by mobilizing toxic forms of aluminum from soils,
(particularly in clay rich soils) and/or by lowering the pH of the water, harming fish and other aquatic
wildlife. In a healthy well-buffered lake or stream, decreased acid deposition would be reflected by
decreasing trends in surface water acidity. Four chemical indicators of aquatic ecosystem response to
emission changes are presented here: trends in sulfate and nitrate anions, acid neutralizing capacity
(ANC), and sum of base cations. Improvement in surface water status is generally indicated by
decreasing concentration of sulfate and nitrate anions and increasing base cations and ANC. The
following is a description of each indicator:
• Sulfate is the primary anion in most acid-sensitive waters and has the potential to acidify
surface waters (lower the pH) and leach base cations and toxic forms of aluminum from soils,
leaving soils depleted of their ability to neutralize acidic inputs.
• Nitrate has the potential to acidify surface waters. However, nitrogen is an important nutrient
for plant and algae growth, and most of the nitrogen inputs from deposition are quickly taken
up by plants and algae, leaving less in surface waters.
• ANC is a key indicator of ecosystem recovery and is a measure of overall buffering capacity of
surface waters against acidification; it indicates the ability to neutralize strong acids that enter
aquatic systems from deposition and other sources.
• Base cations neutralize both sulfate and nitrate anions, thereby preventing surface water
acidification. Base cation availability is largely a function of underlying geology, soil type, and the
vegetation community. Surface waters with fewer base cations are more susceptible to
acidification.
In the central Appalachian region, some watersheds have depleted, base cation-poor soils which have
also accumulated and stored sulfate over the past decades of high sulfate deposition. As a result, the
substantial decrease in acidic deposition has not yet resulted in comparably lower sulfate
concentrations in many of the monitored Appalachian streams. A combination of low base cation
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availability and stored sulfate in the soils means that stream sulfate concentrations in some areas are
not changing, or may be increasing, as the stored sulfate slowly bleeds out without adequate base
cation concentrations to neutralize sulfate anions.1
Surface Water Monitoring Networks
In collaboration with other federal and state agencies and universities, EPA administers a monitoring
program that provides information on the impacts of acidic deposition on otherwise pristine lakes and
streams: the Long-term Monitoring (LTM) program. This program is designed to track changes in surface
water chemistry in the four regions sensitive to acid rain in the eastern United States: New England, the
Adirondack Mountains, the Northern Appalachian Plateau, and the central Appalachians (the Valley,
Ridge, and Blue Ridge geologic provinces).
Forest Health
Ground-level ozone is one of many air pollutants that can alter a plant's health and ability to reproduce
and can make the plant more susceptible to disease, insects, fungus, harsh weather, etc. These impacts
can lead to changes in the biological community, both in the diversity of species and in the health, vigor,
and growth of individual species. As an example, many studies have shown that ground-level ozone
reduces the health of many commercial and ecologically important forest tree species throughout the
United States.2,3 By looking at the distribution and abundance of seven sensitive tree species and the
level of ozone at particular locations, it is possible to estimate reduction in growth - or biomass loss -
for each species. The EPA evaluated biomass loss for seven common tree species in the eastern United
States that have a higher sensitivity to ozone (black cherry, yellow poplar, sugar maple, eastern white
pine, Virginia pine, red maple, and quaking aspen) to determine whether decreasing ozone
concentrations are reducing biomass loss in forest ecosystems.
More Information
• Surface water monitoring at EPA https://www.epa.gov/airmarkets/clean-air-markets-
monitoring-surface-water-chemistrv
• Acid Rain https://www.epa.gov/acidrain/
References
1. Burns, D.A., Lynch, J. A., Cosby, B.J., Fenn, M.E., & Baron, J.S. (2011). National Acid Precipitation
Assessment Program Report to Congress 2011: An Integrated Assessment U.S. EPA, National
Science and Technology Council, Washington, D.C.: 114 p
2. Chappelka, A.H. & Samuelson, L.J. (1998). Ambient ozone effects on forest trees of the eastern
United States: A review. New Phytologist 139: 91-108.
3. Ollinger, S.V., Aber, J.D., & Reich, P.B. (1997). Simulating ozone effects on forest productivity:
interactions among leaf-canopy and stand-level processes. Ecological Applications 7(4), 1237-
1251.
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Estimated Black Cherry. Yellow Poplar. Sugar Maple, Eastern White Pine, Virginia Pine, Red Maple, and Quaking Aspen
Biomass Loss Due to Ozone Exposure, 2000-2002 versus 2015-2017
2000 - 2002
2015-2017
Biomass (% Loss)
>1%
1 to 3%
3 to 6%
6 to 9%
¦ > 9% Max = 11.7%
Notes:
* Biomass loss was calculated by incorporating each tree's C-R functions with the three-month, 12-hour W126 exposure metric.
• The W126 exposure metric is a cumulative exposure index that is biologically based and emphasizes hourly ozone concentrations taken from 2000-2017 data.
Source: EPA, 2019
Figure 3, Estimated Black Cherry, Yellow Poplar, Sugar Maple, Eastern White Pine,
Virginia Pine, Red Maple, and Quaking Aspen Biomass Loss Due to Ozone Exposure,
2000-2002 versus 2015-2017
Chapter9: Ecosystem Response - Ecosystem Health
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Critical Loads Analysis
Highlights
Critical Loads and Exceedances
• For the period from 2015 to 2017, seven percent of all studied lakes and streams still received
levels of combined total sulfur and nitrogen deposition exceeding their calculated critical load.
This is an 80 percent improvement over the period from 2000 to 2002 when 37 percent of all
studied lakes and streams exceeded their calculated critical load.
• Emission reductions achieved between 2000 and 2017 have contributed and will continue to
contribute to broad surface water improvements and increased aquatic ecosystem protection
across the five LTM regions along the Appalachian Mountains.
• Based on this analysis, current sulfur and nitrogen deposition loadings in 2017 still exceed levels
required for recovery of some lakes and streams, indicating that some additional emission
reductions are necessary for some acid-sensitive aquatic ecosystems along the Appalachian
Mountains to recover and be protected from acid deposition.
Background Information
A critical loads analysis is an assessment used to provide a quantitative estimate of whether acid
deposition levels resulting from S02 and NOx emissions are sufficient to protect ecosystem health. The
analysis here focuses on aquatic biological resources. If acidic deposition is less than the calculated
critical load, harmful ecological effects (e.g., reduced reproductive success, stunted growth, loss of
biological diversity) are not expected to occur, and ecosystems damaged by past exposure are expected
to eventually recover.1
Lake and stream waters having an ANC value greater than 50 neq/L are classified as having a moderately
healthy aquatic biological community; therefore, this ANC concentration is often used as a goal for
ecological protection of surface waters affected by acidic deposition. In this analysis, the critical load
represents the amount of sulfur and nitrogen that could be deposited annually to a lake or stream and
its watershed and still support a moderately healthy aquatic ecosystem (i.e., having an ANC greater than
50 pieq/L). Surface water samples from 6,275 lakes and streams along acid-sensitive regions of the
Appalachian Mountains and some adjoining northern coastal plain regions were collected through a
number of water quality monitoring programs. Critical load exceedances were calculated using the
Steady-State Water Chemistry model.2,3
More Information
• Surface water monitoring at EPA https://www.epa.gov/airmarkets/monitoring-surface-water-
chemistrv
• National Acid Precipitation Assessment Program (NAPAP) Report to Congress
https://nv.water.usgs.gov/proiects/NAPAP/
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References
1. Dupont,J., Clair, T.A., Gagnon, C., Jeffries, D.S., Kahl, J.S., Nelson, S.J., & Peckenham, J.M. (2005).
Estimation of critical loads of acidity for lakes in the northeastern United States and eastern
Canada. Environmental Monitoring and Assessment, 109:275-291.
2. Sullivan, T.J., Cosby, B.J., Webb, J.R., Dennis, R.L., Bulger, A.J., & Deviney, Jr. F.A. (2007).
Streamwater acid-base chemistry and critical loads of atmospheric sulfur deposition in
Shenandoah National Park, Virginia. Environmental Monitoring and Assessment, 137: 85-99.
3. Nilsson, J. & Grennfelt, P. (Eds) (1988). Critical loads for sulphur and nitrogen. UNECE/Nordic
Council workshop report, Skokloster, Sweden. Nordic Council of Ministers: Copenhagen.
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Figures
Lake and Stream Exceedances of Estimated Critical Loads for Total Nitrogen and Sulfur Deposition,
2000-2002 versus 2015-2017
• lh»t rvsw So IVM the crfUdi k>.*J compared lo WX-Z002
• IM *xcm4 th* tntkai kn4
ww ncMiM n* cneui M
Notes:
* Surface water samples from the represented lakes and streams complied from surface monitoring programs, such as National Surface Water Survey (NSWS), Environmental Monitoring and Assessment
Program (EMAP). Wadeable Stream Assessment (WSA). Nations! Lake Assessment (NLA). Temporally Integrated Monitoring of Ecosystems (TIME), Long Term Monitoring (LTM). and other water quality
monitoring programs
• Steady stat* «*ceedances calculated in units of meqrtnVyr.
Source: EPA, 2019
Figure 1. Lake and Stream Exceedances of Estimated Critical Loads for Total
Nitrogen and Sulfur Deposition, 2000-2002 versus 2015-2017
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Critical Load Exceedances by Region, 2000-2002 versus 2015-2017
Water Bodies in Exceedance of Critical Load
Region
N u m ber of Water
Bodies Modeled
2000-2002
2015-2017
Percent
Reduction
Number of Sites
Percent of Sites
Number of Sites
Percent of Sites
New England
(CT, MA, ME, NH, RI,VT)
2,195
580
26%
121
6%
79%
Adirondack
(NY)
312
163
S2%
37
12%
77%
Northern Mid-Atlantic
(NY, NJ, PA)
1,14$
301
26%
44
4%
85%
Southern Mid-Atlantic
(KY,MD,VA,WV)
1,740
968
56%
198
11%
77%
Southern Appalachian Mountains
(AL, GA, SC, TN)
882
298
34%
70
8%
76%
Total Units
6,275
2,310
37%
470
7%
80%
Notes:
• Surface water samples from the represented takes and streams compiled from surface monitoring programs, such as National Surface Water Survey (N'SWS). Environmental Mor-itormg and Assessment Program (EMAP). WadeaMe
Stream Assessment (WSA), National Lake Assessment (NLA}. Temporary integrated Mexttomj of Ecosystems (TIME). Lorg Term Uonrtowg (LTM). arxj ottse* water quality mofmemrg programs.
• Steady sute txc««irc« cafeylated in units of maqtar/yr.
Source: Ef20t9
Figure 2. Critical Load Exceedances by Region, 2000-2002 versus 2015-2017
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