POWER SECTOR PROGRAMS
PROGRESS REPORT
Air Quality Acid Deposition
Affected Communities Ecosystem Response
Program Basics Emission Reductions Program Compliance
Affected Units Emission Controls & Monitoring Market Activity
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2021 Power Sector Programs - Progress Report
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Executive Summary
Part 1, Program Implementation, Compliance, and Emissions Trends, released in July, 2022, covers
program basics, and provides annual updates on pollution controls, monitoring methods, and changes
in emissions. Part 2, Environmental Results and Affected Communities, covers the air quality and
ecosystem response to these reductions, and also features a new section on community impacts.
Under the Clean Air Act, EPA implements regulations to reduce emissions from power plants, including
the Acid Rain Program (ARP), the Cross-State Air Pollution Rule (CSAPR), the CSAPR Update, the Revised
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 (NOx), and
hazardous air pollutants including mercury (Hg) to protect human health and the environment. This
reporting year marks the seventh year of CSAPR implementation, the fifth year of the CSAPR Update
implementation, the first year of Revised CSAPR Update implementation, the twenty-seventh year of
the ARP, and the fifth year of MATS implementation. This report summarizes annual progress through
2021, highlighting data that EPA systematically collects on emissions for all power plant programs and
on compliance for the ARP and the CSAPR programs. Commitment to transparency and data availability
is a hallmark of these programs and a cornerstone of their success.
S02, NOx, and hazardous air pollutants (HAPs), including mercury, are fossil fuel combustion byproducts
that affect public health and the environment. S02 and NOx, and their sulfate and nitrate byproducts,
are transported downwind and deposited as acid rain which can be 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 offish-eating wildlife.
The ARP, CSAPR, CSAPR Update, Revised 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 requirement of the power sector
emission control programs described in this report, a variety of power industry trends have contributed
to further declines of S02, NOx, and hazardous air pollutant emissions.
EPA data in this report are current as of March 2023 and reflects 2021 data. Data may differ from past or
future reports because of data resubmissions by sources and ongoing data quality assurance activities.
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2021 Program Implementation, Compliance, and Emissions Trends
at a Glance
Annual S02 emissions:
CSAPR - 592,000 tons (93 percent below 2005)
ARP - 936,000 tons (94 percent below 1990)
Annual NOx emissions:
CSAPR - 440,000 tons (80 percent below 2005)
ARP - 763,000 tons (85 percent below 2000)
CSAPR ozone season NOx emissions: 242,000 tons (46 percent below 2015)
Compliance: 100 percent compliance for in the market-based ARP and CSAPR emissions trading
programs
Emissions reported under MATS:
Mercury - 3.0 tons (90 percent below 2010)
2021 Environmental Results at a Glance
Ambient particulate sulfate concentrations: The eastern United States has shown substantial
improvement, decreasing 76 to 79 percent from 2000-2002 to 2019-2021.
Ozone NAAQS attainment: Based on 2019-2021 data, 19 of the 22 areas in the East originally
designated as nonattainment for the 2008 ozone NAAQS are now meeting the standard, while
the remaining three areas have shown improvement.
PM2.5 NAAQS attainment: Based on 2019-2021 data, all 16 areas in the East originally
designated as nonattainment for the 2006 24-hour PM2.5 NAAQS are now meeting the standard.
Affected communities: Program evaluation through an environmental justice lens shows more
disadvantaged people living near power plants with higher emissions, and a greater overall
emission reduction trend in areas of potential environmental justice concern.
Wet sulfate deposition: All areas of the eastern U.S. have shown significant improvement with
an overall 71 percent reduction in wet sulfate deposition from 2000-2002 to 2019-2021.
Levels of acid neutralizing capacity (ANC): This indicator of aquatic ecosystem 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
2021 Program Implementation, Compliance, and Emissions Trends at a Glance 3
2021 Environmental Results at a Glance 3
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
Revised Cross-State Air Pollution Rule Update (Revised CSAPR Update): 2021 - present 11
CSAPR, CSAPR Update, and Revised CSAPR Update Budgets 12
Mercury and Air Toxics Standards (MATS) 12
Background Information 12
Power Sector Trends 12
Acid Rain Program 13
NOx Budget Trading Program 13
Clean Air Interstate Rule 14
Cross-State Air Pollution Rule 14
Cross-State Air Pollution Rule Update 14
Revised Cross-State Air Pollution Rule Update 15
Mercury and Air Toxics Standards 15
More Information 15
Figures 17
Chapter 2: Regulated Emissions Sources 20
Highlights 20
Acid Rain Program (ARP) 20
Cross-State Air Pollution Rule (CSAPR) 20
Mercury and Air Toxics (MATS) 20
Background Information 20
More Information 21
Figures 22
Chapter 3: Emission Reductions 24
Sulfur Dioxide (SO2) 24
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Highlights 24
Overall Results 24
S02 Emission Trends 24
S02 State-by-State Emissions 24
S02 Emission Rates 25
Background Information 25
More Information 25
Figures 26
Annual Nitrogen Oxides 30
Highlights 30
Overall Results 30
Annual NOx Emissions Trends 30
Annual NOx State-by-State Emissions 30
Annual NOx Emission Rates 30
Background Information 31
More Information 31
Figures 32
Ozone Season Nitrogen Oxides 36
Highlights 36
Overall Results 36
Ozone Season NOx Emissions Trends 36
Ozone Season NOx State-by-State Emissions 36
Ozone Season NOx Emission Rates 36
Background Information 37
More Information 37
Figures 38
Mercury 42
Highlights 42
Overall Results 42
Mercury and Hazardous Air Pollutant Emission Trends 42
Background Information 42
More Information 42
Figures 43
Chapter 4: Emission Controls and Monitoring 45
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Highlights 45
ARP and CSAPR S02 Program Controls and Monitoring 45
CSAPR N0X Annual Program Controls and Monitoring 45
CSAPR N0X Ozone Season Program Controls and Monitoring 45
MATS Controls and Monitoring 46
Background Information 46
Continuous Emission Monitoring Systems (CEMS) 46
S02 Emission Controls 46
N0X Emission Controls 46
Hazardous Air Pollutant Controls 46
More Information 47
Figures 48
Chapter 5: Program Compliance 56
Highlights 56
ARP S02 Program 56
CSAPR S02 Group 1 Program 56
CSAPR S02 Group 2 Program 56
CSAPR N0X Annual Program 56
CSAPR N0X Ozone Season Group 1 Program 57
CSAPR N0X Ozone Season Group 2 Program 57
CSAPR N0X Ozone Season Group 3 Program 57
Background Information 57
More Information 58
Figures 59
Chapter 6: Market Activity 66
Highlights 66
Transaction Types and Volumes 66
2021 Allowance Prices 66
Background Information 67
Transaction Types 67
Allowance Markets 67
More Information 68
Figures 69
Chapter 7: Air Quality 71
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Sulfur Dioxide and Nitrogen Oxides Trends
Highlights
National S02 Air Quality
Regional Changes in Air Quality
Background Information
Sulfur Dioxide
Nitrogen Oxides 72
More Information 72
References 72
Figures 73
Ozone 75
Highlights 75
Ozone Season Changes in 1-Hour Ozone 75
Annual Trends in Rural 8-Hour Ozone 75
Ozone Season Changes in 8-Hour Ozone Concentrations 75
Changes in Ozone Nonattainment Areas 75
Background Information 76
Ozone Standards 76
Regional Trends in Ozone 76
Meteorologically-Adjusted Daily Maximum 8-Hour Ozone Concentrations 77
Changes in Ozone Nonattainment Areas 77
More Information 78
References 78
Figures 79
Particulate Matter 84
Highlights 84
Particulate Matter Seasonal Trends 84
Changes in PM2.5 Nonattainment 84
Background Information 84
PM Standards 85
Changes in PM2.5 Nonattainment Areas 85
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More Information 85
References 85
Figures 87
Chapter 8: Affected Communities 89
Highlights 89
People Living Near Power Plants 89
Emissions Affecting People Living Near Power Plants 90
Emissions Trends: 2014-2021 91
Conclusion 91
Background Information 92
More Information 92
References 93
Figures 95
Chapter 9: Acid Deposition 99
Highlights 99
Wet Sulfate Deposition 99
Wet Inorganic Nitrogen Deposition 99
Regional Trends in Total Deposition 99
Background Information 100
Acid Deposition 100
Monitoring Networks 100
More Information 101
References 101
Figures 102
Chapter 10: Ecosystem Response 105
Ecosystem Health 105
Highlights 105
Regional Trends in Water Quality 105
Ozone Impacts on Forests 105
Background Information 106
Acidified Surface Water Trends 106
Surface Water Monitoring Networks 107
Forest Health 107
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More Information 107
References 107
Figures 108
Critical Loads Analysis Ill
Highlights Ill
Critical Loads and Exceedances Ill
Background Information Ill
More Information Ill
References 112
Figures 113
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Chapter 1: Program Basics
The Acid Rain Program (ARP), the Cross-State Air Pollution Rule (CSAPR), the CSAPR Update, and the
Revised CSAPR Update are implemented through trading programs1 designed to reduce emissions of
sulfur dioxide (S02) and nitrogen oxides (N0X) from power plants. Established under Title IV of the 1990
Clean Air Act Amendments, the ARP was a landmark nationwide emissions trading program, with a goal
of reducing the emissions that cause acid rain. The success of the program in achieving significant
emission reductions in a cost-effective manner led to the application of the market-based emissions
trading 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 makes it difficult for downwind states to meet health-based air quality standards
for regional pollutants, particularly fine particulates (PM2.5) and ozone. EPA first employed trading to
address regional 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,
the NBP was effectively replaced by the ozone season N0X program under the Clean Air Interstate Rule
(CAIR), which required further summertime N0X emission reductions from the power sector, and also
required annual reductions of NOx and S02 emissions 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 ozone season NOx emissions, to facilitate attainment of the 1997 annual PM2.5, the
2006 24-hour PM2.5, and the 1997 8-hour ozone National Ambient Air Quality Standards (NAAQS).
Implementation of the CSAPR Update began in 2017. The CSAPR Update further reduces ozone season
NOx emissions to help states attain and maintain a newer ozone NAAQS established in 2008.
Implementation of the Revised CSAPR Update began in 2021 and resolves 21 states' outstanding
interstate transport obligations for the 2008 ozone NAAQS. Most recently, in February 2022, the EPA
proposed additional reductions in ozone-forming emissions of NOx to facilitate attainment and
maintenance of the more stringent 2015 ozone NAAQS.
The Mercury and Air Toxics Standards (MATS) set limits on emissions of hazardous air pollutants from
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, 2021 is the fifth full year for which most sources covered by MATS
have reported emissions data to the EPA.
Highlights
Acid Rain Program (ARP): 1995 - present
The ARP began in 1995 and covers fossil fuel-fired power plants across the contiguous United
States. The 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.
1 These emissions trading programs are also known as "allowance trading programs" or "cap-and-trade" programs.
Chapter 1: Program Basics
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The ARP's market-based S02 emissions trading program sets an annual cap on the total amount
of S02 that may be emitted by power plants 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 the ARP are achieved through a rate-based approach that applies to a
subset of coal-fired power plants.
Cross-State Air Pollution Rule (CSAPR): 2015 - present
CSAPR addresses regional interstate transport of fine particle (PM2.5) and ozone pollution for the
1997 ozone and PM2.5 NAAQS and the 2006 PM2.5 NAAQS. In 2015, 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, covering 28 states in
all.
CSAPR includes four separate emissions trading programs to achieve these reductions: the
CSAPR S02 Group 1 and Group 2 trading programs, the CSAPR NOx Annual trading program, and
the CSAPR NOx Ozone Season Group 1 trading program.
Cross-State Air Pollution Rule Update (CSAPR Update): 2017 - present
The 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.
As of May 2017, the CSAPR Update began further reducing ozone season NOx emissions from
power plants in 22 states in the eastern U.S.
The CSAPR Update achieves these reductions through the CSAPR NOx Ozone Season Group 2
trading program.
Revised Cross-State Air Pollution Rule Update (Revised CSAPR Update): 2021 -
present
The Revised CSAPR Update was developed to resolve 21 states' outstanding interstate transport
obligations for the 2008 ozone NAAQS and to respond to the September 2019 court remand of
the 2016 CSAPR Update.
Beginning in June 2021, further emission reductions were required at power plants in 12 of the
21 states for which the CSAPR Update was previously found to be only a partial remedy. These
reductions are based on optimization of existing, already-installed selective catalytic reduction
(SCR) and selective non-catalytic reduction (SNCR) controls beginning in the 2021 ozone season,
and installation or upgrade of enhanced NOx combustion controls beginning in the 2022 ozone
season. EPA will also adjust these 12 states' ozone season emission budgets through 2024 to
incentivize the continued use of these control technologies.
The Revised CSAPR Update achieves these reductions through the CSAPR NOx Ozone Season
Group 3 trading program.
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CSAPR, CSAPR Update, and Revised CSAPR Update Budgets
The total CSAPR, CSAPR Update, and Revised CSAPR Update budget for each of the six trading
programs equals the sum of the individual state budgets for those states affected by each
program. The CSAPR Update replaced the original CSAPR ozone season N0X program for most
states. Most recently, the Revised CSAPR Update replaced the CSAPR Update ozone season N0X
program for twelve states. The total budget for each program was set at the following level in
2021:
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 tons2
o NOx Ozone Season Group 2 - 143,408 tons3
o NOx Ozone Season Group 3 - 131,430 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.
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 progress report only provides data from affected sources that submitted hourly emissions
data in 2021. Mercury emissions data are not available for 79 low emitting electric generating
units.
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.4 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, modest demand growth, and policy and regulatory efforts have resulted in a notable
2 Since the start of CSAPR Update in 2017, the CSAPR NOx Ozone Season Group 1 program applies only to sources in Georgia.
3 Since the start of Revised CSAPR Update in 2021, the CSAPR Update Group 2 program applies only to sources in ten states.
4 EIA, Annual Energy Outlook 2022.
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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.
While the current and near-term expectations for natural gas prices are higher than recent historical
levels, the price of natural gas is expected to decline to lower levels in the medium and long term.3 In
addition, the existing fleet of coal-fired power plants continues to age. 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 2023 provide incentives for new wind capacity in the
near-term.5 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.6 All these factors, in total, have resulted in
declining power sector emissions in recent years, a trend that is expected to continue.
Acid Rain Program
Title IV of the 1990 Clean Air Act Amendments established the 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 emissions trading system that harnessed the economic
incentives of the market to reduce pollution. This market-based emissions trading program was
implemented in two phases. Phase I began in 1995 and affected the most polluting units, largely coal-
fired, 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 emissions
trading system. Instead, the 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, however. Units under common control, which are owned or operated by the same
company, can comply using 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
The NBP was a market-based emissions trading program created to reduce NOx 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 1979 ozone
NAAQS. All 21 jurisdictions (20 states plus Washington, D.C.) covered by the NOx SIP Call opted to
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3 EIA, Annual Energy Outlook 2022.
5 EIA, Annual Energy Outlook 2021.
6 EIA, "Corporate Goal Case Using Annual Energy Outlook 2021".
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participate in the NBP. In 2009, the CAIR's N0X ozone season program began, effectively replacing the
NBP to continue achieving ozone season N0X 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
emissions trading 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 the 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 U.S. to significantly improve
air quality by reducing power plant emissions that travel across 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 24-hour PM25 NAAQS and/or the 1997
annual PM25 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
October 23, 2014, the D.C. Circuit granted EPA's motion to lift the stay and shift the 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 the CSAPR ozone season program by issuing the
CSAPR Update. This rule addressed summertime ozone pollution in the eastern U.S. that crosses state
lines in order to help downwind states and communities meet and maintain the 2008 ozone NAAQS. In
May 2017, the CSAPR Update began further reducing ozone season NOx emissions from power plants in
22 states in the eastern U.S. When issuing the CSAPR Update, EPA found that while the rule would result
in meaningful, near-term reductions in ozone pollution that crosses state lines, the rule might not be
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sufficient to fully address all covered states' good neighbor obligations7 with respect to the 2008 ozone
NAAQS. In December 2018, based on additional analysis conducted after issuance of the rule, EPA
published a determination 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.
In September 2019, the D.C. Circuit upheld the CSAPR Update in most respects but remanded the rule to
EPA to address the court's holding that the rule unlawfully allowed upwind states' significant
contribution to downwind air quality problems to continue beyond downwind states' deadlines for
attaining the NAAQS. Relatedly, in October 2019, the court vacated EPA's December 2018 determination
that the CSAPR Update fully addressed covered states' good neighbor obligations with respect to the
2008 ozone NAAQS.
Revised Cross-State Air Pollution Rule Update
On March 15, 2021, EPA finalized the Revised CSAPR Update to resolve 21 states' outstanding interstate
transport obligations for the 2008 ozone NAAQS. Based on EPA's analysis, the Agency determined that
additional emission reductions relative to the CSAPR Update were necessary for 12 of the 21 states.
These reductions were based on optimization of existing, already-installed controls beginning in the
2021 ozone season, and installation or upgrade of state-of-the-art NOx combustion controls beginning in
the 2022 ozone season. This rulemaking also adjusted these 12 states' ozone season emission budgets
through 2024 to incentivize the continued use of these control technologies. The rule became effective
on June 29, 2021.
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 power plants 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, as allowed under the CAA, and thus
were required to comply with the final rule by April 16, 2016.
More Information
Acid Rain Program (ARP) https://www.epa.gov/acidrain/acid-rain-program
Interstate Air Pollution Transport https://www.epa.gov/interstate-air-pollution-transport
Cross-State Air Pollution Rule (CSAPR) https://www.epa.gov/csapr
Cross-State Air Pollution Rule Update (CSAPR Update) https://www.epa.gov/airmarkets/final-
cross-state-air-pollution-rule-update
7 "Good neighbor" obligations refer to provisions in the Clean Air Act that require upwind states to reduce the emissions that
affect downwind states' ability to attain or maintain NAAQS.
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Revised CSAPR Update https://www.epa.gov/csapr/revised-cross-state-air-pollution-rule-update
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
Mercury and Air Toxics Standards (MATS) https://www.epa.gov/stationary-sources-air-
pollution/mercury-and-air-toxics-standards
EIA Annual Energy Outlook https://www.eia.gov/outlooks/aeo
Corporate Goal Case Using Annual Energy Outlook 2021
https://www.eia.gov/outlooks/aeo/corporate goal/
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Chapter 1: Program Basics
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Figures
1990 - Clean Air Act
Amendments
establishTitle IV ARP
History of the ARP, NBP, CAIR, CSAPR, and MATS
2015 - MATS begins
I
2010 - Full implementation of the ARP
I
1995-ARP
PHASE 1 BEGINS
2000-ARP
PHASE 2 BEGINS
ARP
MATS
NBP
2003 - SIP Call 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 SO;,
NOx annual, and
NOx ozone programs
begin, replacing CAIR
2017 - CSAPR Update begins
2021 - Revised CSAPR Update begins
Source: EPA, 2022
Figure 1. History of the ARP, NBP, CAIR, CSAPR, and MATS
Chapter 1: Program Basics
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Map of CSAPR Implementation, 2021
CSAPR (SO2 and annual NOx)
CSAPR NOx Ozone Season Group 2
CSAPR NOx Ozone Season Group 1
CSAPR NOx Ozone Season Group 3
Notes:
The ARP covers sources in all of the lower 48 states.
To more clearly see the states included in the "CSAPR (SO2 and annual NO.)" program, use the interactive features of the figure: click on the boxes in the legenc
to turn off the pink, orange, and green categories (labeled "CSAPR NOx Ozone Season").
Source: EPA, 2022
Figure 2. Map of CSAPR Implementation for 2021
Notes:
The ARP covers sources in all of the lower 48 states.
To more clearly see the states included in the "CSAPR (S02 and annual NO*)" program, use the interactive features of the
figure: click on the boxes in the legend to turn off the pink, orange, and green categories (labeled "CSAPR N0X Ozone Season")
Chapter 1: Program Basics
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Electricity Generation from ARP- and CSAPR-Affected Power Plants, 2005-2021
c 2000
o
E
c
o
fo 1000
cu
O
IMIMM
"J 2,678 2,658 2,652 2,657 2,649
2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021
Coal Gas
Oil
Other
Notes:
There is a small amount of generation from "Oil" or "Other" fuels. The data for these fuels is not easily visible on the full chart. To more clearly see the generation
data for these fuels, use the interactive features of the figure: click on the boxes in the legend to turn off the blue and orange categories of fuels (labeled "Coal" and
"Gas") and turn on the green and yellow categories of fuels (labeled "Oil" and "Other").
Source: EPA, 2022
Figure 3. Electricity Generation from ARP- and CSAPR-Affected Power Plants, 2005-2021
Notes:
There is a small amount of generation from "Oil" or "Other" fuels. The data for these fuels is not easily visible on the full
chart. To more clearly see the generation data for these fuels, use the interactive features of the figure: click on the boxes in
the legend to turn off the blue and orange categories of fuels (labeled "Coal" and "Gas") and turn on the green and yellow
categories of fuels (labeled "Oil" and "Other").
Chapter 1: Program Basics
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Chapter 2: Regulated Emissions Sources
The Acid Rain Program (ARP) and the Cross-State Air Pollution Rule's (CSAPR)1 sulfur dioxide (S02) and
nitrogen oxides (N0X) emission reduction programs apply to large power plants that burn fossil fuels to
generate electricity for sale. The Mercury and Air Toxics Standards (MATS) only cover large power plants
that burn coal or oil to generate electricity for sale and excludes gas-fired units, resulting in fewer units
in MATS than in the ARP and CSAPR.
Highlights
Acid Rain Program (ARP)
In 2021, the ARP S02 requirements applied to 3,243 fossil fuel-fired units at 1,150 power plants
across the country; 493 units at 227 power plants were subject to the ARP NOx program.
Cross-State Air Pollution Rule (CSAPR)
In 2021, there were 2,125 regulated emissions sources at 665 power plants in the CSAPR S02
programs. Of those, 1,713 (81 percent) were also covered by the ARP.
In 2021, there were 2,125 regulated emissions sources at 665 power plants in the CSAPR NOx
annual program and 2,499 regulated emissions sources at 799 power plants in the CSAPR NOx
ozone season programs. Of those, 1,713 (81 percent) and 2,079 (83 percent), respectively, were
also covered by the 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 in all 50 states and U.S.
territories. MATS was issued under section 112 of the Clean Air Act. EPA is including a summary
of the mercury data submitted by affected sources in this report.
In 2021, 406 units at 186 power plants reported hourly mercury emissions to EPA under MATS.
Background Information
In general, the ARP and CSAPR programs (CSAPR, CSAPR Update, and the Revised CSAPR Update) apply
to large electricity generating units - 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 applies only to coal- and oil-fired steam generating units (i.e., utility boilers). MATS does not apply
to combustion turbines, combined cycle units, or to natural gas-fired utility boilers. The power plants
affected by these programs 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.
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1 CSAPR refers to the CSAPR, the CSAPR Update, and the Revised CSAPR Update programs.
Chapter 2: Regulated Emissions Sources
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More Information
Acid Rain Program (ARP) https://www.epa.gov/acidrain/acicl-rain-program
Cross-State Air Pollution Rule (CSAPR) https://www.epa.gov/csapr
Mercury and Air Toxics Standards (MATS) https://www.epa.gov/stationary-sources-air-
pollution/mercury-and-air-toxics-standards
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Chapter 2: Regulated Emissions Sources
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PRO^
Figures
Regulated Emissions Sources in CSAPR and ARP, 2021
4
ARP NOx Program ARP SO2 Program CSAPR NOx Annual CSAPR NOx Ozone Season CSAPR SO2 Annual
Program Program Programs
ฆ Coal EGUs ฆ Gas EGUs ฆ Oil EGUs ฆ Other Fuel EGUs ฆ Unclassified EGUs
Notes:
"Unclassified" units have not submitted a fuel type in their monitoring plan and did not report emissions.
"Other fuel units" include units that combusted primarily wood, waste, or other non-fossil fuel (which also boost mercury and HCI removal by ACI and DSI).
Source: EPA, 2022
Figure 1. Regulated Emissions Sources in CSAPR and ARP, 2021
Notes:
"Unclassified" units have not submitted a fuel type in their monitoring plan and did not report emissions.
"Other fuel units" include units that combusted primarily wood, waste, or other non-fossil fuel (which also boost mercury and
HCI removal by ACI and DSI).
Chapter 2: Regulated Emissions Sources
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Regulated Emissions Sources in CSAPR and ARP, 2021
Coal EGUs
410
487
351
352
351
Gas EGUs
81
2,641
1,525
1,948
1,525
Oil EGUs
0
83
216
164
216
Other Fuel EGUs
2
27
33
24
33
Unclassified EGUs
0
5
0
11
0
Total Units
493
3,243
2,125
2,499
2,125
Notes:
"Unclassified" units nave not submitted a fuel type in their monitoring plan and did not report emissions
"Otner fuel units" include units that combusted primarily wood, waste, or other non-fossil fuel (which also boost mercury and HCI removal by ACI and DSI).
Source EPA. 2022
Last updated 04/2022
Figure 2. Regulated Emissions Sources iri CSAPR and ARP, 2021
Notes:
"Unclassified" units have not submitted a fuel type in their monitoring plan and did not report emissions.
"Other fuel units" include units that combusted primarily wood, waste,, or other non-fossil fuel (which also boost mercury and
HCI removal by ACI and DSI).
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Chapter 2: Regulated Emissions Sources
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Chapter 3: Emission Reductions
The Acid Rain Program (ARP) and Cross-State Air Pollution Rule (CSAPR) programs1 significantly reduced
sulfur dioxide (S02), annual nitrogen oxides (N0X), and ozone season N0X emissions from power plants.
The Mercury and Air Toxics Standards (MATS) set limits on the emissions of hazardous air pollutants
from coal and oil burning power plants and have led to reductions in those emissions since 2010. This
section covers changes in emissions at power plants affected by CSAPR, ARP, and MATS between 2021
and previous years.
Sulfur Dioxide (SO2)
Highlights
Overall Results
Under the ARP, CAIR, and CSAPR, power plants have significantly lowered S02 emissions while
electricity generation from power plants in these programs has remained relatively stable since
2000.
These emission reductions are a result of an overall increase in the environmental effectiveness
at affected sources as electric 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 the ARP emitted 936,000 tons of S02 in 2021, well below the ARP's statutory
annual cap of 8.95 million tons. The ARP sources reduced emissions by 14.8 million tons (94
percent) from 1990 levels and 16.3 million tons (95 percent) from 1980 levels.
CSAPR and ARP: In 2021, the seventh year of operation of the CSAPR S02 program, sources in
both the CSAPR S02 annual programs and the ARP together reduced S02 emissions by 14.8
million tons (94 percent) from 1990 levels (before implementation of the ARP), 10.3 million tons
(92 percent) from 2000 levels (ARP Phase II), and 9.3 million tons (91 percent) from 2005 levels
(before implementation of the CAIR and the CSAPR). All ARP and CSAPR sources together
emitted a total of 942,000 tons of S02 in 2021.
CSAPR: Annual S02 emissions from sources in the CSAPR S02 programs fell from 7.7 million tons
in 2005 to 592,000 tons in 2021 (93 percent). In 2021, S02 emissions were about 1.4 million tons
below the regional CSAPR emission budgets (0.85 million in Group 1 and 0.52 million in Group
2); the CSAPR S02 annual programs' 2021 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 2021, annual S02 emissions from sources in the ARP and the
CSAPR S02 program dropped in 46 states plus Washington, D.C. by a total of 14.8 million tons. In
1 CSAPR refers to the CSAPR, the CSAPR Update, and the Revised CSAPR Update programs.
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Chapter 3: Emission Reductions - Sulfur Dioxide (SO2)
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contrast, annual S02 emissions increased in two states (Idaho and Vermont) by a combined total
of 13 tons from 1990 to 2021.
CSAPR: All 22 states (16 states in Group 1 and 6 states in Group 2) had emissions below their
CSAPR allowance budgets, collectively by 1.4 million tons.
SO2 Emission Rates
The average S02 emission rate for units in the ARP or CSAPR S02 program fell to 0.09 pounds per
million British thermal units (Ib/mmBtu). This indicates an 88 percent reduction from 2005 rates,
with most 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 acid rain and fine particle (PM2.5) pollution, 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 the ARP, and this trend continued under CAIR and CSAPR. Most of these states are in
the Ohio River Valley and are upwind of the areas the 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
Power Sector Emissions, Operations, and Environmental Data
https://www.epa.gov/airmarkets/data-resources
Acid Rain Program (ARP) https://www.epa.gov/acidrain/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 (SO2)
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+L PRO^
Figures
SO2 Emissions from CSAPR and ARP Sources, 1980-2021
ฃ 15
ui 10
CSAPR SO2 Phase 2 Budget (2017 and beyond)
1980
1990
1995
2000
2005
2010
2015
2020
2021
ARP pre-CSAPR ฆ ARP and CSAPR ฆ CSAPR not ARP I ARP not CSAPR
Notes:
SO2 values are shown as millions of tons.
The data shown here reflect totals for those units required to comply with each program in each respective year. This means that the CSAPR-only SO2 program
units are not included in the SO2 data prior to 2015.
There are a small number of sources in CSAPR but not in the ARP. Emissions from these sources comprise about 1 percent of total emissions and are not easily
visible on the full chart.
Source: EPA, 2022
Figure 1. SO2 Emissions from CSAPR and ARP Sources, 1980-2021
Notes:
S02 values are shown as millions of tons.
The data shown here reflect totals for those units required to comply with each program in each respective year. This means
that the CSAPR-only S02 program units are not included in the S02 data prior to 2015.
There are a small number of sources in CSAPR but not in the ARP. Emissions from these sources comprise about 1 percent of
total emissions and are not easily visible on the full chart.
Chapter 3: Emission Reductions - Sulfur Dioxide (SO2)
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State-by-State SOz Emissions from CSAPR and ARP Sources,
1990-2021
SO2 Emissions (tons)
ฆ CSAPR states controlled for fine particles
# 1990 SO2 emissions (tons)
e reflect totals for these units required to comply with each program in each respective year. This means that the CSAPR-only SCh progra
I
2000 2010
ฆ Alabama
e not included in the SO2 data prior to 2015.
Source: El*. 2022
Figure 2. State-by-State SO2 Emissions from CSAPR and ARP Sources, 1990-2021
Notes:
The data shown here reflect totals for those units required to comply with each program in each respective year. This means
that the CSAPR-only S02 program units are not included in the S02 data prior to 2015.
Chapter 3: Emission Reductions - Sulfur Dioxide (SO2)
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Comparison of SO2 Emissions and Generation for CSAPR and ARP Sources, 2000-2021
SOz Emissions
2000 2001 2002 2003 2004 200S 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021
I Coal
Gas
Oil
Other
Generation
2000 2001 2002 2003 2004 200S 2006 2007 200B 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021
i Coal
Gas
Oil
Other
Notes:
~ The data shcrwn here reflect totals for those units required to comply with each program in each respective year. This means that the CSAPR-only SOi program units are not
included in the SQz data prior to 2015.
~ Fuel type represents primary fuel type; units might combust more than one fuel.
Source: EFft. 2022
Figure 3. Comparison of SO2 Emissions and Generation for CSAPR and ARP Sources,
2000-2021
Notes:
The data shown here reflect totals for those units required to comply with each program in each respective year. This means
that the CSAPR-only S02 program units are not included in the S02 data prior to 2015.
Fuel type represents primary fuel type; units might combust more than one fuel.
Chapter 3: Emission Reductions - Sulfur Dioxide (SO2)
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CSAPR and ARP SO: Emissions Trends, 2021
SOi Emissions (thousand tons) SO> Rate (Ib/mmBtu)
2021
0.19
0.00
0.06
0.10
0.09
Notes
The data shown herฎ reflect totals lor those units required to comply with each program m each respective year This means that the CSAPR-only SO: program units are not included m the SOi emissions data prior to 2015
Fuel type represents primary fuel type, units might combust more than ono fuel
Totals may not lefled the sum of individual rows due to rounding
The emission rate reflects the emissions (pounds) per unit of heat input (mmBtu) for each fuel category The total SO; emission rate in each column of I ho table is not cumulative and does not equal the arithmetic mean of the tour tuel-
spoalic rates The total for each year indicates the average rate across aN units in the program because each unit influences the annual omission rate m proportion to its heat input, and heal input is unevenly distnbuted across the fuel
categories
Source: EPA. 2022
Figure 4. CSAPR and ARP SO2 Emissions Trends, 2000-2021
Notes:
The data shown here reflect totals for those units required to comply with each program in each respective year. This means
that the CSAPR-only S02 program units are not included in the S02 emissions data prior to 2015.
Fuel type represents primary fuel type; units might combust more than one fuel.
Totals may not reflect the sum of individual rows due to rounding.
The emission rate reflects the emissions (pounds) per unit of heat input (mmBtu) for each fuel category. The total S02
emission rate in each column of the table is not cumulative and does not equal the arithmetic mean of the four fuel-specific
rates. The total for each year indicates the average rate across all units in the program because each unit influences the annual
emission rate in proportion to its heat input, and heat input is unevenly distributed across the fuel categories.
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Primary Fuel
Coal
Gas
Oil
Other
Total I Average
10,708
108
384
1
11,201
9,835
91
292
4
10,222
5,052
19
28
22
5,120
I
II
0.06
0.73
0.23
0.88
0.03
0.70
0.27
0.75
0.01
0.19
0.57
0.39
0.00
0.04
0.17
0.08
Chapter 3: Emission Reductions - Sulfur Dioxide (SO2)
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Annual Nitrogen Oxides
Highlights
Overall Results
Annual N0X emissions have declined dramatically under the ARP, CAIR, and CSAPR programs,
with most 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 2021.
Annual NOx Emissions Trends
ARP: Units in the ARP NOx program emitted 763,000 tons of NOx emissions in 2021. Sources
reduced emissions by 7.3 million tons from the projected level in 2000 without the ARP, over
three times the program's NOx emission reduction objective.
CSAPR and ARP: In 2021, the seventh year of operation of the CSAPR NOx annual program,
sources in both the CSAPR NOx annual program and the ARP together emitted 779,000 tons, a
reduction of 5.6 million tons (88 percent reduction) from 1990 levels, 4.4 million tons (85
percent reduction) from 2000, and 2.9 million tons (79 percent reduction) from 2005 levels.
CSAPR: Emissions from the CSAPR NOx annual program sources were 440,000 tons in 2021. This
is about 1.7 million tons (80 percent) lower than in 2005 and 629,000 tons (59 percent) below
the CSAPR NOx annual program's 2021 regional budget of 1,069,256 tons.
Annual NOx State-by-State Emissions
CSAPR and ARP: From 1990 to 2021, annual NOx emissions in the ARP and the CSAPR NOx
program dropped in 47 states plus Washington, D.C. by a total of approximately 5.6 million tons.
In contrast, annual emissions increased in one state (Idaho) by 428 tons from 1990 to 2021.
CSAPR: 21 of 22 states had emissions below their CSAPR 2021 allowance budgets, collectively by
632,000 tons. One state (Missouri) exceeded its 2021 state level budget by 2,623 tons. For more
information about Program Compliance, see the Program Compliance chapter.
Annual NOx Emission Rates
In 2021, the ARP and CSAPR average annual NOx emission rate was 0.07 Ib/mmBtu, a 73 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 per unit of electricity 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
Power Sector Emissions, Operations, and Environmental Data
https://www.epa.gov/airmarkets/data-resources
Acid Rain Program (ARP) https://www.epa.gov/acidrain/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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Figures
Annual NO* Emissions from CSAPR and ARP Sources, 1990-2021
2.5
CSAPR Annual NOx Phase 2 Budget (2017 and beyond)
1990
2000
2005
2010
2015
2020
2021
ARP pre-CSAPR ฆ ARP and CSAPR ฆ CSAPR not ARP I ARP not CSAPR
Notes:
NOx values are shown as millions of tons.
The data shown here reflect totals for those units required to comply with each program in each respective year. This means that the CSAPR-only NO. program
units are not included in the NOx data prior to 2015.
There are a small number of sources in CSAPR but not in the ARP. Emissions from these sources comprise about 1 percent of total emissions and are not easily
visible on the full chart.
Source: EPA, 2022
Figure 1. Annual NOx Emissions from CSAPR and ARP Sources, 1990-2021
Notes:
NOx values are shown as millions of tons.
The data shown here reflect totals for those units required to comply with each program in each respective year. This means
that the CSAPR-only NOx program units are not included in the NOx data prior to 2015.
There are a small number of sources in CSAPR but not in the ARP. Emissions from these sources comprise about 1 percent of
total emissions and are not easily visible on the full chart.
Chapter 3: Emission Reductions - Annual Nitrogen Oxides (NOx)
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% pro^ฐ
State-by-State Annual NOx Emissions from CSAPR and ARP
Sources, 1990-2021
NO* Emissions (tons)
CSAPR states controlled for fine particles
1990 NOx emissions (tons)
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Comparison of Annual NO* Emissions and Generation for CSAPR and ARP Sources, 2000-2021
NOx Emissions
2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021
ฆ Coal ฆ Gas ฆ Oil Other
Generation
2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021
ฆ Coal ฆ Gas ฆ Oil Other
Notes:
~ The data shown here for the annual programs reflect totals for those units required to comply with each program in each respective year This means that the CSAPR NO. annual program
units are not included in the annual NO. emissions data prior to 2015.
~ Fuel type represents primary fuel type; units might combust more than one fuel.
Source: EFft. 2022
Figure 3. Comparison of Annual NOx Emissions and Generation for CSAPR and ARP
Sources, 2000-2021
Notes:
The data shown here for the annual programs reflect totals for those units required to comply with each program in each
respective year. This means that the CSAPR NOx annual program units are not included in the annual NOx emissions data prior
to 2015.
Fuel type represents primary fuei type; units might combust more than one fuel.
Chapter 3: Emission Reductions - Annual Nitrogen Oxides (NOx)
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CSAPR and ARP Annual NO* Emissions Trends, 2021
NOx Emissions (thousand tons)
NOx Rate (Ib/mmBtu)
Primary Fuel
2000
2005
2010
2020
2021
2000
2005
2010
2020
2021
Coal
4,587
3,356
1,896
569
624
0.44
0.32
0.20
0.14
0.13
Gas
355
167
142
160
146
0.18
0.06
0.04
0.03
0.03
Oil
162
104
20
2
3
0.31
0.25
0.13
0.10
0.20
Other
2
6 5
6
6
0.26
0.42
0.14
0.09
0.08
Total / Average
5,104
3,633
2,063
737
779
0.40
0.27
0.16
0.07
0.07
Notes
The data shown here rafted totals (or Ihose units reqwrod to comply with each program m each respective year This means that the CSAPR only annual NO. program units are not included in the NO. emissions data prior to 2015
Fuel type represents primary fuel type units might combust more than one fuel
Totals may not reflect the sum of individual rows due to rounding
The omission rate reflects the emissions (pounds) per unit of heat input (mmBlu) for each fliol category The total annual NO. emission rate in each column of tho table is not cumulative and does not equal the anthmetic mean of the four
fuel-spoofปc rates The total for each year indicates the average 'ate across an units in the program because each unit influences the annual emission rote m proportion to its heat input, and heat input is unevenly distnbuted across the fuel
categories
Source; EPA, 2022
Figure 4. CSAPR and ARP Annual NOx Emissions Trends, 2000-2021
Notes:
The data shown here reflect totals for those units required to comply with each program in each respective year. This means
that the CSAPR-only annual NO* program units are not included in the NOx emissions data prior to 2015.
Fuel type represents primary fuel type; units might combust more than one fuel.
Totals may not reflect the sum of individual rows due to rounding.
The emission rate reflects the emissions (pounds) per unit of heat input (mmBtu) for each fuel category. The total annual NOx
emission rate in each column of the table is not cumulative and does not equal the arithmetic mean of the four fuel-specific
rates. The total for each year indicates the average rate across all units in the program because each unit influences the annua!
emission rate in proportion to its heat input, and heat input is unevenly distributed across the fuei categories.
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Ozone Season Nitrogen Oxides
Highlights
Overall Results
Ozone season N0X emissions have declined dramatically under the ARP, NBP, CAIR, and CSAPR
programs.1
States with the highest emitting sources of ozone season N0X emissions in 2000 have seen the
greatest reductions under the CSAPR NOx ozone season programs. 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 2021.
Ozone Season NOx Emissions Trends
ARP: Units in the ARP program emitted 351,000 tons of ozone season NOx emissions in 2021.
Sources reduced emissions by 1.8 million tons (84 percent) from the 2000 ozone season and
920,000 tons (72 percent) from the 2005 ozone season.
CSAPR: In 2021, units covered under the CSAPR NOx ozone season programs (Groups 1, 2, and 3)
emitted 242,000 tons, a reduction of 210,000 (46%) since 2015.
In 2021, the CSAPR NOx ozone season program emissions were 19 percent below the regional
emission budget of 298,879 tons (24,041 tons for Group 1, 143,408 tons for Group 2, and
131,430 tons for Group 3).
Ozone Season NOx State-by-State Emissions
Between 2005 and 2021, ozone season NOx emissions from the CSAPR sources fell in every state
participating in the CSAPR NOx ozone season program.
20 states had emissions below their CSAPR 2021 allowance budgets, collectively by about
62,000 tons. Three states (Illinois, Missouri, and Pennsylvania) exceeded their 2021 state level
budgets by about 5,400 tons total.
Ozone Season NOx Emission Rates
In 2021, the average NOx ozone season emission rate fell to 0.07 Ib/mmBtu for the CSAPR ozone
season program states and 0.07 Ib/mmBtu nationally. This represents a 63 and 66 percent
reduction, respectively, from 2005 emission rates, with the majority of reductions coming from
coal-fired units.
1 CSAPR refers to the CSAPR, the CSAPR Update, and the Revised CSAPR Update programs.
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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 per unit of electricity 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 of air pollution
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. The CSAPR Update NOx ozone
season program was similarly established to help eastern U.S. counties attain the 2008 ozone standard.
On March 15, 2021, EPA finalized the Revised CSAPR Update to further reduce NOx emissions from
power plants in 12 states. The rule responded to a September 2019 ruling by the United States Court of
Appeals for the D.C. Circuit, Wisconsin v. EPA, which remanded the 2016 CSAPR Update to EPA for failing
to fully eliminate significant contribution to nonattainment and interference with maintenance of the
2008 ozone NAAQSfrom these states by downwind areas' attainment dates.
More Information
Power Plant Emission Trends https://www.epa.gov/airmarkets/power-plant-emission-trends
Power Sector Emissions, Operations, and Environmental Data
https://www.epa.gov/airmarkets/data-resources
Cross-State Air Pollution Rule (CSAPR) https://www.epa.gov/csapr
Pollution from Nitrogen Oxides (NOx) 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 and ARP Sources, 2005-2021
o 2
i/)
Q) 0
CSAPR Ozone Season NOx Program Budget (2018 and beyond)
2000
2005
2010
2015
2020
2021
ARP pre-CSAPR ฆ ARP and CSAPR ฆ CSAPR not ARP I ARP not CSAPR
Notes:
NOx values are shown as millions of tons.
The data shown here reflect totals for those units required to comply with each program in each respective year. This means that the CSAPR-only ozone season
NOx program units are not included in the ozone season NOซ data prior to 2015.
There are a small number of sources in CSAPR but not in the ARP. Emissions from these sources comprise about 1 percent of total emissions and are not easily
visible on the full chart.
Source: EPA, 2022
Figure 1. Ozone Season NOx Emissions from CSAPR and ARP Sources, 2000-2021
Notes:
N0X values are shown as millions of tons.
The data shown here reflect totals for those units required to comply with each program in each respective year. This means
that the CSAPR-only ozone season N0X program units are not included in the ozone season N0X data prior to 2015.
There are a small number of sources in CSAPR but not in the ARP. Emissions from these sources comprise about 1 percent of
total emissions and are not easily visible on the full chart.
Chapter 3: Emission Reductions - Ozone Season Nitrogen Oxides (NOx)
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+L PRO^
State-by-State Ozone Season NO* Emissions from CSAPR and Ozone Season NOx Emissions (tons)
ARP Sources, 2000-2021
CSAPR states controlled for ozone
ฎ 2000 Ozone season NO> emissions (tons) h A|a
is for these units required to comply with each program in each respective year. This means that the CSAPR-only ozone season NO. program units are not included ir
Figure 2. State-by-State Ozone Season NOx Emissions from CSAPR and ARP Sources,
2000-2021
Notes:
The data shown here reflect totals for those units required to comply with each program in each respective year. This means
that the CSAPR-only ozone season NOx program units are not included in the ozone season NOx data prior to 2015.
Chapter 3: Emission Reductions - Ozone Season Nitrogen Oxides (NOx)
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% pro^ฐ
g Comparison of Ozone Season NO* Emissions and Generation for CSAPR and ARP Sources, 2000-2021
2 Ozone Season NO* Emissions
c
g 3
I
o
N
o
ฆ Coal ฆ Gas ฆ! Oil Other
Generation
1000
o i 1 1 1 1 1 1 i I I i i i 1 1 i i 1
2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021
ฆ Coal ฆ Gas ฆ Oil Other
Notes:
The data shown here for the ozone season program reflect totals for those units required to comply with each program in each respective year This means that the CSAPR NO. ozone
season only program units are not included in the ozone season NO. emissions data prior to 2015.
Fuel type represents primary fuel type; units might combust more than one fuel
Source: EW. 2022
Figure 3. Comparison of Ozone Season NOx Emissions and Generation for CSAPR and
ARP Sources, 2000-2021
Notes:
The data shown here for the ozone season program reflect totals for those units required to comply with each program in
each respective year. This means that the CSAPR NOx ozone season only program units are not included in the ozone season
NOx emissions data prior to 2015.
Fuel type represents primary fuel type; units might combust more than one fuel.
Chapter 3: Emission Reductions - Ozone Season Nitrogen Oxides (NOx)
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CSAPR and ARP Ozone Season NOx Emissions Trends, 2021
Ozone Season NO* Emissions (
thousand tons)
Ozone Season NOx Rate (Ib/mmBtu)
Primary Fuel
2000
2005
2010
2020
2021
2000
2005
2010
2020
2021
Coat
1,926
1,117
821
253
282
0.43
0.25
0.19
0.13
0.12
Gas
196
96
79
85
73
0.19
0.07
0.04
0.03
0.03
Oil
78
52
12
1
1
0.31
0.25
0.13
0.09
0.13
Other
1
2
2
2
3
0.25
0.40
0.11
0.08
0.09
Total / Average
2,201
1,267
914
341
359
0.38
0.20
0.15
0.07
0.07
Notes
The data shown here reflect totals for those units required to comply with each program in each respective year This means that the CSAPR NO. ozone season only program units are not mcluded in the ozone season NO. emissions data
poor to 2015.
Fuel type represents pnmary fuel type, units might combust more than one fuel
Totals may not reflect the sum of individual rows due to rounding
The emission rate reflects the emissions (pounds) per unit of heat input (mmBtu) for each fuel category The total NO. ozone season emission rate in each column of the table is not cumulative and does not equal the arithmetic mean of the
four fuel-specific rales The total for each year indicates the average rale across an units in the program because each unit influences the annual emission rate in proportion to its heat *K>ut and neat input is unevenly distributed across the
fuel categories
Source: EPA. 2022
Figure 4. CSAPR Ozone Season NOx Emissions Trends, 2000-2021
Notes:
The data shown here reflect totals for those units required to comply with each program in each respective year. This means
that the CSAPR NOx ozone season only program units are not included in the ozone season NOx emissions data prior to 2015.
Fuel type represents primary fuel type; units might combust more than one fuel.
Totals may not reflect the sum of individual rows due to rounding.
The emission rate reflects the emissions (pounds) per unit of heat input (mmBtu) for each fuel category. The total NOx ozone
season emission rate in each column of the table is not cumulative and does not equal the arithmetic mean of the four fuel-
specific rates. The total for each year indicates the average rate across all units in the program because each unit influences the
annual emission rate in proportion to its heat input, and heat input is unevenly distributed across the fuel categories.
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Chapter 3: Emission Reductions - Ozone Season Nitrogen Oxides (NOx)
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Mercury
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 other HAPs. 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
2021.
Mercury and Hazardous Air Pollutant Emission Trends
Compared to 20101, units covered under MATS in 2021 emitted 26 fewer tons of mercury (90%
reduction).
Background Information
Hazardous air pollutants (HAPs) emitted by power plants include mercury, acid gases (e.g., hydrochloric
acid, hydrofluoric acid), 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 neurological and developmental effects, cancer, and reproductive,
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
section 112 of the Clean Air Act. The MATS emission standards were established using data from a 2010
information collection request that was sent to selected coal and oil burning power plants.
More Information
Power Sector Emissions, Operations, and Environmental Data
https://www.epa.gov/airmarkets/data-resources
Mercury and Air Toxics Standards (MATS) https://www.epa.gov/stationary-sources-air-
pollution/mercury-and-air-toxics-standards
Hazardous Air Pollutants (HAPs) https://www.epa.gov/haps
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.
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Chapter 3: Emission Reductions - Mercury
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Figures
40
Mercury Emissions from MATS Sources, 2010-2021
30
20
10
2010
2017
2018
2019
2020
2021
I Hg
Notes:
Mercury emissions data are not available for 79 low emitting electricity generating units (LEEs).
Source: EPA, 2022
Figure 1. Mercury Emissions from MATS Sources, 2010-2021
Notes:
Mercury emissions data are not available for 79 low emitting electricity generating units (LEEs).
Chapter 3: Emission Reductions - Mercury
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State-by-State Mercury Emissions from MATS Sources,
2018-2021
Mercury Emissions (lbs)
Notes:
Data do not inclL
Data for Alaska a
2018 Mercury Emissions (lbs)
>missions from low emitting electric generating units (LEEs).
jt displayed on the map above. They are available in the Data Download.
Source: El*. 2022
Notes:
Figure 2. State-by-State Mercury Emissions from MATS Sources, 2021
Data do not include emissions from low emitting electric generating units (LEEs).
Data for Alaska are not displayed on the map above. They are available in the Data Download.
Chapter 3: Emission Reductions - Mercury
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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.1 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 are critical to ensure program results and accountability. 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 71 percent of coal-fired units and 81 percent of coal-fired electricity generation, measured in
megawatt hours, or MWh, in 2021.
In 2021, 20 percent of the 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
Eighty-one percent of fossil fuel-fired generation was produced by units with advanced add-on
controls (either selective catalytic reduction [SCR] or selective non-catalytic reduction [SNCR]).
In 2021, the 236 coal-fired units with advanced add-on controls (either SCRs or SNCRs)
generated 78 percent of coal-fired electricity. At oil- and natural gas-fired units, SCR- and SNCR-
controlled units produced 84 percent of electricity generation.
In 2021, 67 percent of the CSAPR units (including 100 percent of coal-fired units) monitored NOx
emissions using CEMS. Ninety-seven percent of NOx emissions were measured by CEMS.
CSAPR NOx Ozone Season Program Controls and Monitoring
Seventy-three percent of all the fossil fuel-fired generation was produced by units with
advanced add-on controls (either SCRs or SNCRs).
In 2021, 213 units with advanced add-on controls (either SCR or SNCR) accounted for 71 percent
of coal-fired electricity generation. At oil- and natural gas-fired units, SCR- and SNCR-controlled
units produced 75 percent of electricity generation.
In 2021, 73 percent of the CSAPR units (including 100 percent of coal-fired units) monitored
ozone season NOx emissions using CEMS. Ninety-seven percent of ozone season NOx emissions
were measured by CEMS.
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1 CSAPR refers to the CSAPR, the CSAPR Update, and the Revised CSAPR Update programs.
Chapter 4: Emission Controls and Monitoring
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MATS Controls and Monitoring
In 2021, forty-six percent of the MATS units reporting mercury emissions and 52 percent of the
electricity generation at the MATS reporting units used activated carbon injection (ACI), a
mercury-specific pollution control method to reduce mercury emissions and S02.
About 81 percent of units that reported continuous mercury emissions data (or 82 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 2021. These controls also reduce other pollutants, including S02. Some oil-fired
units can 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 quantity of
emissions measured at one facility is equivalent to the same quantity measured at a different facility.
EPA conducts comprehensive electronic and desk data audits to validate the reported data. While some
units with low levels of S02 or NOx emissions are allowed to use other approved monitoring methods,
the vast majority of S02 and NOx emissions are measured by CEMS.
Affected units have a variety of monitoring options, but most use either CEMS or sorbent traps for
mercury (Hg). Some qualifying units with low emissions can conduct periodic stack tests in lieu of
continuous monitoring.
SO2 Emission Controls
Sources in the ARP or the CSAPR S02 programs 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 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 the ARP or the CSAPR NOx annual and ozone season programs have a variety of options by
which to reduce NOx emissions, including advanced add-on 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).
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Specific pollution control devices that reduce mercury and HCI include wet FGDs, activated carbon
injection (ACI), dry sorbent injection (DSI), and fabric filters.
More Information
Power Plant Emission Trends https://www.epa.gov/airmarkets/power-plant-emission-trends
Power Sector Emissions, Operations, and Environmental Data
https://www.epa.gov/airmarkets/data-resources
Emissions Monitoring https://www.epa.gov/airmarkets/emissions-monitoring-and-reporting
Plain English guide to 40 CFR 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
SO2 Emissions Controls in the ARP and CSAPR SO2 Program, 2021
Generation (million MWh) by SO2 Emission Control Type Percentage of Units with and without
lonn SO2 Emission Controls
I CFB w/limestone
Coal and Oil w/o post-
combustion controls
/ CFB w/limestone
/ 8%
I CFB w/limestone
Coal and Oil w/o post-
combustion controls
Notes:
Due to rounding, percentages shown may not add up to 100%.
The acronyms represent the two control types. FGD is flue-gas desulfurization, and CFB is circulating fluidized bed.
Source: EM. 2022
Figure 1. SO2 Emissions Controls in the ARP and CSAPR SO2 Program, 2021
Notes:
Due to rounding, percentages shown may not add up to 100%.
The acronyms represent the two control types. FGD is flue-gas desulfurization, and CFB is circulating fluidized bed.
Chapter 4: Emission Controls and Monitoring
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CSAPR SO2 Program Monitoring Methodology, 2021
Monitoring Methodology by Number of Units, 2021 Monitoring Methodology by SO2 Emissions, 2021
Other Units w/o CEM
0%
Other Units w/CEMS.
Oil Units w/CEM!
Gas Units w/CEMS
Units w/CEMS
Gas Units w/o CEMS
.%
Oil Units w/CEMS
0%
Oil Units w/o CEMS
0%
Other Units w/CEMS
I 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
Gas Units w/o CEMS
Oil Units w/o CEMS
I Other Units w/o CEMS
Notes:
This figure displays CSAPR units which reported SO2 emissions in 2021, with a breakdown by SCb monitoring methodology and primary fuel type group (coal, gas, oi
Among these. 418 units monitored SCb using CEMS, and 354 are coal-fired units.
Percent totals may not add up to 100 percent due to rounding.
"Other fuel units" include units that combusted primarily wood, waste, or other non-fcesil fuel (which also bocet mercury and MCI removal by ACI and DSI).
d other). The total number of CSAPR units that reported SO: emissions in 2021 was 2,125.
Source: EFA. 2022
Figure 2. CSAPR SO2 Program Monitoring Methodology, 2021
Notes:
This figure displays CSAPR units which reported S02 emissions in 2021, with a breakdown by S02 monitoring methodology and
primary fuel type group (coal, gas, oil, and other). The total number of CSAPR units that reported S02 emissions in 2021 was
2,125. Among those, 418 units monitored S02 using CEMS, and 354 are coal-fired units.
Percent totals may not add up to 100 percent due to rounding.
"Other fuel units" include units that combusted primarily wood, waste, or other non-fossil fuel (which also boost mercury and
HCI removal by ACI and DSI).
Chapter 4: Emission Controls and Monitoring
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NO. Emissions Controls in CSAPR NO. Annual Program, 2021
Generation (million MWh) by NOx Control Type
Percentage of Units with and without
NOx Emission Controls
I Combustion Only
I SNCR
Other
Notes:
Due to rounding, percentages shown may not add up to 100%.
"SCR" refers to selective catalytic reduction: "SNCR" fuel refers t<
as waste, wood, petroleum coke, or tire-derived fuel.
Emissions data collected and reported using CEMS.
"Other fuel units" include units that combusted primarily wood,
I SCR
Uncontrolled
I Combustion Only
I SNCR
Other
catalytic reduction: "Combustion Only" refers to low NO. burners, combustion modification/fuel reburning, or overfire
other non-fcssil fuel (which also boost mercury and HCI removal by ACI and DSI).
I SCR
Uncontrolled
d "Other" fuel refers to units that bi
Source: EM. 2022
Figure 3. NOx Emissions Controls in CSAPR NOx Annual Program, 2021
Notes:
Due to rounding, percentages shown may not add up to 100%.
"SCR" refers to selective catalytic reduction; "SNCR" fuel refers to selective non-catalytic reduction; "Combustion Only" refers
to low NOx burners, combustion modification/fuel reburning, and/or overfire air; and "Other" fuel refers to units that burn fuels
such as waste, wood, petroleum coke, or tire-derived fuel.
"Other fuel units" include units that combusted primarily wood, waste, or other non-fossil fuel (which also boost mercury and
HCI removal by ACI and DSI).
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CSAPR NO. Annual Program Monitoring Methodology, 2021
Monitoring Methodology by Number of Units, 2021
Monitoring Methodology by N0ซ Emissions, 2021
Other Units w/o CEMS
0%
Other Units w/CEMS.
2%
Oil Units w/o CEMS.
9%
Oil Units w/CEMS.
Gas Units w/o CEMS-
Gas Units w/CEMS
10%
Gas Units w/o CEMS
2%
Oil Units w/CEMS
_ _ Oil Units w/o CEMS
Other Units w/CEMS
Other Units w/o CEMS
I Gas Units w/CEMS
I Oil Units w/CEMS
] Other Units w/CEMS
I Coal Units w/CEMS
I Gas Units w/o CEMS
Oil Units w/o CEMS
I Other Units w/o CEMS
I Gas Units w/CEMS
I Oil Units w/CEMS
] Other Units w/CEMS
I Coal Units w/CEMS
I Gas Units w/o CEMS
Oil Units w/o CEMS
I Other Units w/o CEMS
Notes:
This figure displays CSAPR uni
Among those, 1,417 units monib
Percent totals may not add up
"Other fuel units" include unil
> which reported N0> emissions in 2021, with a breakdown by NO. monitoring methodology and primary fuel type group (c
red NO. using CEMS. and 351 a re cca I -fi red units,
o 100 percent due to rounding.
; that com busted primarily wood, waste, or other non-fcssil fuel (which also boost mercury and HCI removal by AG and DSI)
it reported N0> emiss
Figure 4. CSAPR NOx Annual Program Monitoring Methodology, 2021
Notes:
This figure displays CSAPR units which reported NOx emissions in 2021, with a breakdown by NOx monitoring methodology
and primary fuel type group (coal, gas, oil, and other). The total number of CSAPR units that reported NOx emissions in 2021
was 2,125. Among those, 1,417 units monitored NOx using CEMS, and 351 are coal-fired units.
Percent totals may not add up to 100 percent due to rounding.
"Other fuel units" include units that combusted primarily wood, waste, or other non-fossil fuel (which also boost mercury and
HCI removal by ACI and DSI).
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NOx Emissions Controls in CSAPR NOx Ozone Season Program, 2021
Generation (million MWh) by NO> Emission Control Type
Percentage of Units with and without
NOx Emission Controls
Uncontrolled-
Combustion Only
I Combustion Only
SNCR
Other
I SCR
Uncontrolled
I Combustion Only
SNCR
Other
] SCR
Uncontrolled
Notes:
Due to rounding, percentages shown may not add up to 100%.
"SCR" refers to selective catalytic reduction: "SNCR" fuel refers to selective non-catalytic reduction: "Combustion Only" refers to low NO. burners, combustion modification/fuel reburning, and/or overfire air; and "Other" fuel refers to units that burn fuels such
as waste, wood, petroleum coke, and tire-derived fuel.
"Other fuel units" include units that combusted primarily wood, waste, or other non-fossil fuel (which also boost mercury and HCI removal by AC I and DSI).
There is a small amount of generation from units with "Other" controls and from "Uncontrolled" units. The data for these units is not easily visible on the full chart, "b more clearly see the generation data for these units, especially for Uncontrolled and Other
fuel types, use the interactive features of the figure: click on the boxes in the legend to turn off the blue, dark orange, and green categories of control types (labeled "Combustion Only," "SCR," and "SNCR") and turn on the yellow and light orange
categories of control types (labeled "Uncontrolled" "Other").
Source: Em, 2022
Figure 5. NOx Emissions Controls in the CSAPR NOx Ozone Season Program, 2021
Notes:
Due to rounding, percentages shown may not add up to 100%.
"SCR" refers to selective catalytic reduction; "SNCR" fuel refers to selective non-catalytic reduction; "Combustion Only" refers
to low NOx burners, combustion modification/fuel reburning, and/or overfire air; and "Other" fuel refers to units that burn fuels
such as waste, wood, petroleum coke, and tire-derived fuel.
"Other fuel units" include units that combusted primarily wood, waste, or other non-fossil fuel (which also boost mercury and
HCI removal by ACI and DSI).
There is a small amount of generation from units with "Other" controls and from "Uncontrolled" units. The data for these
units is not easily visible on the full chart. To more clearly see the generation data for these units, especially for Uncontrolled
and Other fuel types, use the interactive features of the figure: click on the boxes in the legend to turn off the blue, dark
orange, and green categories of control types (labeled "Combustion Only," "SCR," and "SNCR") and turn on the yellow and light
orange categories of control types (labeled "Uncontrolled" "Other").
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CSAPR NOx Ozone Season Program Monitoring Methodology, 2021
Monitoring Methodology by Number of Units, 2021 Monitoring Methodology by Ozone Emissions, 2021
Coal Units w/CEMS
14%
Other Units w/o CEMS
0%
Other Units w/CEM!
1%
Oil Units w/o CEMS
5%
Oil Units w/CEM!
1%
Gas Units w/o CEMS--^"
21%
ฆ Gas Units w/CEMS
ฆ Oil Units w/CEMS
ฆ Other Units w/CEMS I
ฆ Coal Units w/CEMS
Notes:
This figure displays CSAPR units which reported ozone season NO
Among those, 1,8X6 units monitored NO. using CEMS, and 352 are
Percent totals may not add up to 100 percent due to rounding.
I Gas Units w/o CEMS
Oil Units w/o CEMS
I Other Units w/o CEMS
s in 2021, with a breakdown by ozone se
I Gas Units w/CEMS
Oil Units w/CEMS
I Other Units w/CEMS
I Coal Units w/CEMS
Gas Units w/CEMS
3%
Gas Units w/o CEMS
3%
Oil Units w/CEMS
0%
, Oil Units w/o CEMS
0%
Other Units w/CEMS
1%
Other Units w/o CEMS
0%
I Gas Units w/o CEMS
Oil Units w/o CEMS
I Other Units w/o CEMS
in NO. monitoring methodology and primary fuel type group (coal, gas, oil, and other). The total number of CSAPR units that reported ozone se
ry and HCI removal by ACI and DSI).
Source: EM, 2022
Figure 6. CSAPR NOx Ozone Season Program Monitoring Methodology, 2021
Notes:
This figure displays CSAPR units which reported ozone season NOx emissions in 2021, with a breakdown by ozone season NOx
monitoring methodology and primary fuel type group (coal, gas, oil, and other). The total number of CSAPR units that reported
ozone season NOx emissions in 2021 was 2,499. Among those, 1,816 units monitored NOx using CEMS, and 352 are coal-fired
units.
Percent totals may not add up to 100 percent due to rounding.
"Other fuel units" include units that combusted primarily wood, waste, or other non-fossil fuel (which also boost mercury and
HCI removal by ACI and DSI).
Chapter 4: Emission Controls and Monitoring
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PRO^
Mercury Controls at MATS-Affected Sources, 2021
Mercury Controls on MATS Covered Units (units) Mercury Controls on MATS Covered Units (MWh)
CFB & No Post-Combustion Controls
I FGD
Both FGD & ACI
I ACI
CFB & No Post-
Combustion Controls
I FGD
Both FGD & ACI
I ACI
CFB & No Post-
Combustion Controls
Notes:
Percent totals may not add up to 100 percent due to rounding.
This data is from the MATS-affected sources that submitted hourly er
oEM. Units not reporting data (e.g. these monitoring using periodic testing) are not included in this report.
Source: Eป, 2022
Figure 7. Mercury Controls at MATS-Affected Sources, 2021
Notes:
Percent totals may not add up to 100 percent due to rounding.
This data is from the MATS-affected sources that submitted hourly emissions data to EPA. Units not reporting data (e.g., those
monitoring using periodic testing) are not included in this report.
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Mercury Compliance and Monitoring Methods used by Units Reporting Hourly Data under MATS, 2021
Reporting Hourly Data
Compliance Method (# of Units)
Monitoring Method
Number of
reporting units
Number of reporting
facilities
Electrical Output
Heat Input
SorbentTrap
CEMS
CEMS and Sorbent Trap
405
186
115
290
177
187
41
Notes
This data ts from the MATS-affecttd sources that submitted hourly emissions data to EPA and does not show complete data hom ail the MATS-affected sources because many sources received compliance extensions or chose to
demonstrate compliance through methods other than continuously monitored emissions
Source: EPA. 2022
Last updated: 05/2022
Figure 8. Mercury Compliance and Monitoring Methods used by Units Reporting Hourly
Data under MATS, 2021
Notes:
This data is from the MATS-affected sources that submitted hourly emissions data to EPA and does not show complete data
from all the MATS-affected sources because many sources received compliance extensions or chose to demonstrate
compliance through methods other than continuously monitored emissions.
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Chapter 5: Program Compliance
Compliance for the Acid Rain Program (ARP) and each of the Cross-State Air Pollution Rule (CSAPR)1
trading programs is assessed on an annual basis. Each regulated facility must hold an amount of
allowances equal to or greater than its emissions for the relevant compliance period. Historically, these
programs have had exceptionally high rates of compliance. This performance continued in 2021 as 100%
of the facilities in each of these programs held sufficient allowances to cover their emission obligations.
The information below details how the ARP and CSAPR allowances were used for compliance under the
emissions trading programs in 2021. In contrast to the ARP and CSAPR,1 the Mercury and Air Toxics
Standards (MATS) rule is issued under section 112 of the Clean Air Act and is not an emissions trading
program.
Highlights
ARP SO2 Program
All ARP SO? facilities were in compliance in 2021, holding sufficient allowances to cover their S02
emissions.
ARP sources reported total S02 emissions of 935,750 tons in 2021.
EPA deducted 935,703 allowances for compliance with the ARP. After reconciliation, over 71
million ARP S02 allowances remain unused and were banked.
CSAPR SO2 Group 1 Program
All CSAPR SO? Group 1 facilities were in compliance in 2021, holding sufficient allowances to
cover their S02 emissions.
CSAPR S02Group 1 sources reported total S02 emissions of 518,858 tons in 2021.
EPA deducted 518,867 allowances for the CSAPR S02 Group 1 compliance. After reconciliation,
about 6.6 million CSAPR S02 Group 1 allowances remain unused and were banked.
CSAPR SO2 Group 2 Program
All CSAPR SO? Group 2 facilities were in compliance in 2021, holding sufficient allowances to
cover their S02 emissions.
CSAPR S02Group 2 sources reported total S02 emissions of 73,572 tons in 2021.
EPA deducted 73,565 allowances for the CSAPR S02 Group 2 compliance. After reconciliation,
about 3.4 million CSAPR S02 Group 2 allowances remain unused and were banked.
CSAPR NOx Annual Program
All CSAPR NOx Annual Program facilities were in compliance in 2021, holding sufficient
allowances to cover their NOx emissions.
1 CSAPR refers to the CSAPR, the CSAPR Update, and the Revised CSAPR Update programs.
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CSAPR annual N0X sources reported total N0X emissions of 440,051 tons in 2021.
EPA deducted 440,184 allowances for the CSAPR NOx Annual Program compliance. After
reconciliation, about 3.4 million CSAPR NOx Annual Program allowances remain unused and
were banked.
CSAPR NOx Ozone Season Group 1 Program
All CSAPR NOx Ozone Season Group 1 facilities were in compliance in 2021, holding sufficient
allowances to cover their NOx emissions.
CSAPR NOx Ozone Season Group 1 sources reported total ozone season NOx emissions of 6,150
tons in 2021.
EPA deducted 6,154 allowances for the CSAPR NOx Ozone Season Group 1 compliance. After
reconciliation, over 105,000 CSAPR NOx Ozone Season Group 1 allowances remain unused and
were banked.
CSAPR NOx Ozone Season Group 2 Program
All CSAPR NOx Ozone Season Group 2 facilities were in compliance in 2021, holding sufficient
allowances to cover their NOx emissions.
CSAPR NOx Ozone Season Group 2 sources reported total ozone season NOx emissions of
121,838 tons in 2021.
EPA deducted 121,877 allowances for the CSAPR NOx Ozone Season Group 2 compliance. After
reconciliation, over 157,000 CSAPR NOx Ozone Season Group 2 allowances remain unused and
were banked.
Based on preliminary calculations, in 2021, Missouri units covered by the CSAPR Ozone Season
NOx Group 2 Program reported emissions exceeding the state's assurance level, triggering the
assurance provisions. Emissions in Missouri exceeded the state's assurance level by 1,289 tons,
resulting in the surrender of 2,578 additional allowances.2
CSAPR NOx Ozone Season Group 3 Program
All CSAPR NOx Ozone Season Group 3 facilities were in compliance for 2021, holding sufficient
allowances to cover NOx emissions.
CSAPR NOx Ozone Season Group 3 sources reported total ozone season NOx emissions of
114,293 tons in 2021.
EPA deducted over 114,337 allowances for the CSAPR NOx Ozone Season Group 3 compliance.
After reconciliation, about 30,000 CSAPR NOx Ozone Season Group 3 allowances remain unused
and were banked.
Background Information
The year 2021 was the seventh 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 fifth year of compliance for the
2 See 87 Fed. Reg. 42459.
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CSAPR N0X Ozone Season Group 2 program and the first year of compliance for the CSAPR N0X Ozone
Season Group 3 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). Each CSAPR trading program contains "assurance provisions" to
guarantee that each covered state achieves the required emissions reductions. If a state's covered units
exceed the state's assurance level under the specific trading program, then the state must surrender
two allowances for each ton of emissions exceeding the assurance level.
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 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
Clean Air Markets Program Data (CAMPD) https://campd.epa.gov
Emissions Trading https://www.epa.gov/emissions-trading-resources
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Figures
ARP SOj Program Allowance Reconciliation Summary, 2021
Total Allowances Held (1995-2021 Vintage)
72,424,252
Held by Affected Facility Accounts
Held by Other Accounts (General and Non-Affected Facility Accounts)
42,606,024
29,818,228
Allowances Deducted for ARP Compliance*
935,703
Penalty Allowance Deduction
0
Banked Allowances
71,488,549
Held by Affected Facility Accounts
Held by Other Accounts (General and Non-Affected Facility Accounts)
41,670,321
29,818,228
* Includes allowances deducted from opt-in for reduced utilization.
Acid Rain Program Compliance Results
Reported Emissions (tons) 935,750
Rounding and compliance issues (tons) -47
Emissions not covered by allowances (tons) 0
Total allowances deducted for emissions 935,703
Notes:
Compliance emissions data may vary from other report sections as a result of variation in rounding conventions or allowance compliance issues at certain units.
Reconciliation and compliance data are current as of May 2022 and subsequent allowance deduction adjustments and penalties are not reflected.
Source EPA, 2022
Figure 1. ARP SO2 Program Allowance Reconciliation Summary, 2021
Notes:
Compliance emissions data may vary from other report sections as a result of variation in rounding conventions or allowance
compliance issues at certain units.
Reconciliation and compliance data are current as of May 2022 and subsequent allowance deduction adjustments and
penalties are not reflected.
Chapter 5: Program Compliance
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CSAPR SO2 Group 1 Program Allowance Reconciliation Summary, 2021
Total Allowances Held (2015-2021 Vintage)
7,168,328
Held by Affected Facility Accounts
Held by Other Accounts (General, State Holding, and Non-Affected Facility Accounts)
5,491,118
1,677,210
Allowances Deducted for CSAPR SO; Group 1 Program
518,867
Penalty Allowance Deduction
0
Banked Allowances
6,649,461
Held by Affected Facility Accounts
Held by Other Accounts (General, State Holding, and Non-Affected Facility Accounts)
4,972,251
1,677,210
CSAPR SO; Group 1 Program Compliance Results
Reported Emissions (tons)
518,858
Rounding and compliance issues (tons)
9
Emissions not covered by allowances (tons)
0
Total allowances deducted for emissions 518,867
Notes
Compliance emissions data may vary from other report sections as a result of variation m rounding conventions or allowance compliance issues at certain units
Reconciliation and compliance data are current as of May 2022 and subsequent allowance deduction adjustments and penalties are not reflected
Source: EPA, 2022
Figure 2. CSAPR SO2 Group 1 Program Allowance Reconciliation Summary, 2021
Notes:
Compliance emissions data may vary from other report sections as a result of variation in rounding conventions or allowance
compliance issues at certain units.
Reconciliation and compliance data are current as of May 2022 and subsequent allowance deduction adjustments and
penalties are not reflected.
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CSAPR SO2 Group 2 Program Allowance Reconciliation Summary, 2021
Total Allowances Held (2015-2021 Vintage)
3,536,164
Held by Affected Facility Accounts
Held by Other Accounts (General, State Holding, and Non-Affected Facility Accounts)
2,770,959
765,205
Allowances Deducted for CSAPR SO: Group 2 Program
73,565
Penalty Allowance Deduction
0
Banked Allowances
3,462,599
Held by Affected Facility Accounts
2,697,394
Held by Other Accounts (General, State Holding, and Non-Affected Facility Accounts)
765,205
CSAPR SO2 Group 2 Program Compliance Results
Reported Emissions (tons)
73,572
Rounding and compliance issues (tons)
-7
Emissions not covered by allowances (tons)
0
Total allowances deducted for emissions 73,565
Notes:
ฆ Compliance emissions daia may vary from other report sections as a result of variation in rounding conventions or allowance compliance issues at certain units
Reconciliation and compliance data are current as of May 2022 and subsequent allowance deduction adjustments and penalties are not reflected
Source. EPA, 2022
Figure 3. CSAPR NOx Annual Program Allowance Reconciliation Summary, 2021
Notes:
Compliance emissions data may vary from other report sections as a result of variation in rounding conventions or allowance
compliance issues at certain units.
Reconciliation and compliance data are current as of May 2022 and subsequent allowance deduction adjustments and
penalties are not reflected.
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CSAPR NOx Annual Program Allowance Reconciliation Summary, 2021
Total Allowances Held (2015-2021 Vintage)
3,889,515
Held by Affected Facility Accounts
Held by Other Accounts (General, State Holding, and Non-Affected Facility Accounts)
3,058,849
830,666
Allowances Deducted for CSAPR NOx Annual Program
440,184
Penalty Allowance Deduction
0
Banked Allowances
3,449,331
Held by Affected Facility Accounts
Held by Other Accounts (General, State Holding, and Non-Affected Facility Accounts)
2,618,665
830,666
CSAPR NOx Annual Program Compliance Results
Reported Emissions (tons)
440,051
Rounding and compliance issues (tons)
133
Emissions not covered by allowances (tons)
0
Total allowances deducted for emissions 440,184
Notes:
Compliance emissions data may vary from other report sections as a result of variation in rounding conventions or allowance compliance issues at certain units
Reconciliation and compliance data are current as of May 2022 and subsequent allowance deduction adjustments and penalties are not reflected
Source: EPA, 2022
Figure 4. CSAPR NOx Annual Program Allowance Reconciliation Summary, 2021
Notes:
Compliance emissions data may vary from other report sections as a result of variation in rounding conventions or allowance
compliance issues at certain units.
Reconciliation and compliance data are current as of May 2022 and subsequent allowance deduction adjustments and
penalties are not reflected.
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CSAPR NO* Ozone Season Group 1 Program Allowance Reconciliation Summary, 2021
Total Allowances Held (2015-2021 Vintage)
112,024
Held by Affected Facility Accounts
Held by Other Accounts (General, State Holding, and Non-Affected Facility Accounts)
49,727
62,297
Allowances Deducted for CSAPR NOx Ozone Season Group 1 Program
6,154
Penalty Allowance Deduction
0
Banked Allowances
105,870
Held by Affected Facility Accounts
Held by Other Accounts (General, State Holding, and Non-Affected Facility Accounts)
43,573
62,297
CSAPR NOx Ozone Season Group 1 Program Compliance Results
Reported Emissions (tons) 6,150
Rounding and compliance issues (tons) 4
Emissions not covered by allowances (tons) 0
Total allowances deducted for emissions 6,154
Notes:
Compliance emissions data may vary from other report sections as a result of variation in rounding conventions or allowance compliance issues at certain units
Reconciliation and compliance data are current as of May 2022 and subsequent allowance deduction adjustments and penalties are not reflected
Source: EPA, 2022
Figure 5. CSAPR NOx Ozone Season Program Group 1 Allowance Reconciliation
Summary, 2021
Notes:
Compliance emissions data may vary from other report sections as a result of variation in rounding conventions or allowance
compliance issues at certain units.
Reconciliation and compliance data are current as of May 2022 and subsequent allowance deduction adjustments and
penalties are not reflected.
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CSAPR N0X Ozone Season Group 2 Program Allowance Reconciliation Summary, 2021
Total Allowances Held (2017-2021 Vintage)
279,237
Held by Affected Facility Accounts
Held by Other Accounts (General, State Holding, and Non-Affected Facility Accounts)
217,834
61,403
Allowances Deducted for CSAPR NOx Ozone Season Group 2 Program
121,877
Penalty Allowance Deduction
0
Banked Allowances
157,360
Held by Affected Facility Accounts
Held by Other Accounts (General, State Holding, and Non-Affected Facility Accounts)
95,957
61,403
CSAPR N0X Ozone Season Group 2 Program Compliance Results
Reported Emissions (tons) 121,838
Rounding and compliance issues (tons) 39
Emissions not covered by allowances (tons) 0
Total allowances deducted for emissions 121,877
Notes:
Compliance emissions data may vary from other report sections as a result of variation In rounding conventions or allowance compliance issues a! certain units
Reconciliation and compliance data are current as of May 2022 and subsequent allowance deduction adjustments and penalties are nol reflected
Source: EPA, 2022
Figure 6. CSAPR NOx Ozone Season Program Group 2 Allowance Reconciliation
Summary, 2021
Notes:
Compliance emissions data may vary from other report sections as a result of variation in rounding conventions or allowance
compliance issues at certain units.
Reconciliation and compliance data are current as of May 2022 and subsequent allowance deduction adjustments and
penalties are not reflected.
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CSAPR NOx Ozone Season Group 3 Program Allowance Reconciliation Summary, 2021
Total Allowances Held (2021 Vintage)
143,837
Held by Affected Facility Accounts
Held by Other Accounts (General, State Holding, and Non-Affected Facility Accounts)
140,108
3,729
Allowances Deducted for CSAPR NOx Ozone Season Group 3 Program
114,337
Penalty Allowance Deduction
0
Banked Allowances
29,500
Held by Affected Facility Accounts
Held by Other Accounts (General, State Holding, and Non-Affected Facility Accounts)
25,771
3,729
CSAPR NOx Ozone Season Group 3 Program Compliance Results
Reported Emissions (tons) 114,293
Rounding and compliance issues (tons) 44
Emissions not covered by allowances (tons) 0
Total allowances deducted for emissions 114,337
Notes
Compliance emissions data may vary from other report sections as a result of variation In rounding conventions or allowance compliance Issues at certain units
Reconciliation and compliance data are currenl as of May 2022 and subsequent allowance deduction adjustments and penalties are not reflected
Source: EPA, 2022
Figure 7. CSAPR NOx Ozone Season Program Group 3 Allowance Reconciliation
Summary, 2021
Notes:
Compliance emissions data may vary from other report sections as a result of variation in rounding conventions or allowance
compliance issues at certain units.
Reconciliation and compliance data are current as of May 2022 and subsequent allowance deduction adjustments and
penalties are not reflected.
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Chapter 6: Market Activity
Emissions trading 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 the Acid Rain Program (ARP) and the
Cross-State Air Pollution Rule (CSAPR)1 are emissions trading programs, Mercury and Air Toxics Standard
(MATS) is not a market-based program; therefore, this section does not discuss MATS.
Highlights
Transaction Types and Volumes
In 2021, more than 550,000 allowances were traded across all six of the CSAPR trading
programs.
Thirty-six percent of the transactions within the CSAPR programs were between distinct
organizations.
In 2021, over 3 million ARP allowances were traded.
Twenty-six percent of the transactions within the ARP were between distinct organizations.
2021 Allowance Prices2
The ARP S02 allowance prices averaged less than $1 per ton in 2021.
The CSAPR S02 Group 1 allowance prices started and ended 2021 at $1.56 per ton.
The CSAPR S02 Group 2 allowance prices started and ended 2021 at $2.31 per ton.
The CSAPR NOx annual program allowances started 2021 at $2.00 per ton and ended 2021 at
$2.50 per ton.
The CSAPR NOx ozone season Group 1 program allowances started 2021 at $2.00 per ton and
ended 2021 at $2.50 per ton.
The CSAPR NOx ozone season Group 2 program allowances started 2021 at $200 per ton and
ended 2021 at $166 per ton.3
1 CSAPR refers to the CSAPR, the CSAPR Update, and the Revised CSAPR Update programs.
2 Allowance prices as reported by S&P Global Market Intelligence, 2022.
3 The CSAPR NOx Ozone Season Group 2 program was established by the CSAPR Update in October 2016. The program originally
covered 22 states, and currently covers 10 states, including Alabama, Arkansas, Iowa, Kansas, Mississippi, Missouri,
Oklahoma, Tennessee, Texas, and Wisconsin.
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The CSAPR N0X ozone season Group 3 program allowances started in March 2021 at $3,000 per
ton and ended 2021 at $3,175 per ton.1
Background Information
Transaction Types
Allowance transfers are the movement of allowances between allowance holding accounts. There are
generally two types of transfers, those initiated by the EPA 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. Private transactions include all transfers initiated by authorized account
representatives for any compliance or general account purposes. The market activity analysis is based
on private transactions.
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 2021 emissions were below emission budgets for the ARP and for all six CSAPR programs. As a
result, the allowance prices for most of the CSAPR programs 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.
1 The CSAPR NOx Ozone Season Group 3 program was established under the Revised CSAPR Update in April 2021 and covers 12
states, including Illinois, Indiana, Kentucky, Louisiana, Maryland, Michigan, New Jersey, New York, Ohio, Pennsylvania,
Virginia, and West Virginia.
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More Information
Allowance Markets https://www.epa.gov/airmarkets/allowance-markets
Air Markets Business Center https://www.epa.gov/airmarkets/business-center
Clean Air Markets Program Data (CAMPD) https://campd.epa.gov
Emissions Trading https://www.epa.gov/emissions-trading-resources
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Figures
2021 Allowance Transfers under CSAPR and ARP
Transactions Conducted
Allowances Transferred
Share of Program's Allowances Transferred
Related (%) Distinct (%)
ARP SO:
517
3,113,196
40%
60%
CSAPR SO: Group 1
169
201,086
68%
32%
CSAPR SO: Group 2
45
84,085
90%
10%
CSAPR NOx Annual
341
96,831
78%
22%
CSAPR NOx Ozone Season Group 1
28
4,248
99%
1%
CSAPR NOx Ozone Season Group 2
914
165,068
57%
43%
CSAPR NOx Ozone Season Group 3
109
9,923
49%
51%
Notes
The breakout between distinct and related organizations is not an exact value as relationships are often difficult to categorize in a simple bifurcated manner EPA's analysis is conservative and the "Distinct Organizations- percentage is likely higher
Percentages may not acw up to 100% due to roundmg
Source EPA, 2022
Last updated 05/2022
Figure 1. 2021 Allowance Transfers under CSAPR and ARP
Notes:
The breakout between distinct and related organizations is not an exact value as relationships are often difficult to categorize
in a simple bifurcated manner. EPA's analysis is conservative and the "Distinct Organizations" percentage is likely higher.
Percentages may not add up to 100% due to rounding.
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PRO"**-
Allowance Spot Price (Prompt Vintage), January-December 2021
$4000
v $2000
J ^
$0
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan
CSAPR S02 Group 1 CSAPR SO2 Group 2 CSAPR NO. Annual
CSAPR NO. Ozone Season Group 1 CSAPR NO. Ozone Season Group 2 CSAPR NO. Ozone Season Group 3
Notes:
Prompt vintage is the vintage for the "current" compliance year.
The CSAPR Update Rule, published October 2016, created two geographically distinct state trading groups: Group 1, comprised only of Georgia, and Group 2. originally comprised of 22
states. The Revised CSAPR Update, published April 2021, created a third trading group, moving 12 states from Group 2 to Group 3. The allowance prices for Group 1. Group 2. and Group 3 are
shown.
There is a small value for the allowance price for "CSAPR SO* Group 1", "CSAPR SOj Group 2", "CSAPR NO. Annual", and "CSAPR NO. Ozone Season Group 1". The data for these items is
not easily visible on the full chart. To more clearly see the allowance price for these items, use the interactive features of the figure: click on the lines in the legend to turn off the purple and
organge categories (labeled "CSAPR NO. Ozone Season Group 2" and "CSAPR NO. Ozone Season Group 3") and keep all of the other legend items on.
Source: S&P Global Market Intelligence, 2022
Figure 2. Allowance Spot Price (Prompt Vintage), January-December 2021
Notes:
Prompt vintage is the vintage for the "current" compliance year.
The CSAPR Update Rule, published October 2016, created two geographically distinct state trading groups: Group 1,
comprised only of Georgia, and Group 2, originally comprised of 22 states. The Revised CSAPR Update, published April 2021,
created a third trading group, moving 12 states from Group 2 to Group 3. The allowance prices for Group 1, Group 2, and Group
3 are shown.
There is a small value for the allowance price for "CSAPR S02 Group 1", "CSAPR S02 Group 2", "CSAPR NOx Annual", and
"CSAPR NOx Ozone Season Group 1". The data for these items is not easily visible on the full chart. To more clearly see the
allowance price for these items, use the interactive features of the figure: click on the lines in the legend to turn off the purple
and orange categories (labeled "CSAPR NOx Ozone Season Group 2" and "CSAPR NOx Ozone Season Group 3") and keep all of
the other legend items on.
Chapter 6: Market Activity
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Chapter 7: Air Quality
The Acid Rain Program (ARP), N0X Budget Trading Program (NBP), Clean Air Interstate Rule (CAIR), Cross-
State Air Pollution Rule (CSAPR), and CSAPR Update 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 12.0 parts per billion (ppb) to 0.7 ppb (94 percent) between
1980 and 2021.
Since the first year of the ARP, three years have seen reductions of greater than 20 percent:
1994-1995 (22 percent); 2008-2009 (21 percent); and 2014-2015 (23 percent).
Regional Changes in Air Quality
Regional average ambient S02 concentrations declined in the eastern U.S. by 95 percent from
the 1989-1991 observation period to the 2019-2021 observation period.
Average ambient particulate sulfate concentrations have decreased by 49 to 84 percent in
observed regions from 1989-1991 to 2019-2021.
Average annual ambient total nitrate concentrations declined 59 percent from 1989-1991 to
2019-2021 in the eastern U.S., with the most significant decreases occurring after 2002,
coinciding with the implementation of the NOx Budget Trading Program, followed by CAIR,
CSAPR, and CSAPR Update.
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
extracting metal from ore, as well as the burning of high sulfur-containing fuels by locomotives, large
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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 nitrate (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 (N0X) Pollution https://www.epa.gov/no2-pollution
EPA's Power Sector Programs https://www.epa.gov/power-sector/power-sector-programs
EPA's 2021 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 SO2 Air Quality Trend, 1980-2021
35
30
25
.2! ~ 20
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<
15
10
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1980 1985 1990 1995 2000 2005 2010 2015 2020
Average Concentration 90% of sites have concentrations below this line
10% of sites have concentrations below this line
Notes:
Data based on state, local, and EPA monitoring sites which are located primarily in urban areas.
Source: EPA, 2022
Figure 1. National SO2 Air Quality Trend, 1980-2021
Notes:
Data based on state, local, and EPA monitoring sites which are located primarily in urban areas.
Chapter 7: Air Quality-Sulfur Dioxide and Nitrogen Oxides Trends
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% pro^ฐ
Regional Changes in Air Quality
Measurement
Region
Annual Average, 2000-
2002
Annual Average, 2019-
2021
Percent Change
Number of Sites
Mid-Atlantic
4.8
1
-79
13
Midwest
4.3
1.1
-74
16
North Central
1.3
0.6
-54
2
Ambient Particulate Sulfate
Northeast
2.6
0.6
-77
6
Concentration (ng/m3)
Pacific
0.8
0.5
-37
5
Rocky Mountain
0.7
0.4
-45
10
South Central
2.9
1.2
-59
2
Southeast
4.2
1
-76
12
Mid-Atlantic
8
1
-88
13
Midwest
6.8
0.6
-91
16
North Central
1
0.4
-60
2
Ambient Sulfur Dioxide
Northeast
3.4
0.3
-91
6
Concentration (ug/m3)
Pacific
0.4
0.2
-35
5
Rocky Mountain
0.5
0.2
-60
10
South Central
1.1
0.4
-64
2
Southeast
3.4
0.3
-91
12
Mid-Atlantic
3
1.2
-60
13
Midwest
4.1
1.8
-56
16
North Central
1.2
0.8
-33
2
Ambient Total Nitrate
Northeast
1.9
0.8
-58
6
Concentration (ng/m3)
Pacific
1.8
0.9
-50
5
Rocky Mountain
0.8
0.5
-38
10
South Central
1.5
0.9
-40
2
Southeast
2.3
0.9
-61
12
Averages are Ihe arithmetic mean of all sues in a region that were present ana mei the completeness criteria in both averaging periods.Thus, average concentrations for 2000 to 2002 may differ from past reports.
Data are from CASTNET monitoring sites which are typically located away from stationary emissions sources. Percent diange is calculated from the base period of 2000-2002 to coincide with the deposition changes In Chapter 8.
5 1:" - r : I . .' ; r .! I v sigi ! r r ' ! i: -1 j ฆ r. Soil ' i i : =r: i !;i; re" ]> ! nod .i: it::c i ir ' J':: :r. lr
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Ozone
Highlights
Ozone Season Changes in 1-Hour Ozone
There was an overall regional reduction in ozone levels between 2000-2002 and 2019-2021,
with a 25 percent reduction in the highest (99th percentile) ozone concentrations in CSAPR and
CSAPR Update states.
Results demonstrate how NOx emission reduction policies have benefitted 1-hour ozone
concentrations in the eastern U.S. - historically, the region that the ozone policies were
designed to target.
Annual Trends in Rural 8-Hour Ozone
From 2019 to 2021, rural ozone concentrations averaged 61 ppb in CSAPR states, a decrease of
28 ppb (31 percent) from the 1990 to 2002 average period.
The Autoregressive Integrated Moving Average (ARIMA) model shows how the reductions in
rural ozone concentrations correlate with the implementation of the NBP in 2003 and the CAIR
NOx Ozone Season program in 2009. There was a 10 ppb reduction in 03 from 2002 to 2004 and
a 6 ppb reduction in 03 from 2007 to 2009.
Eight of the nine lowest observed annual ozone concentrations were between 2013 and 2021.
Ozone season NOx emissions fell steadily under CAIR and continued to drop after
implementation of CSAPR in 2015 and CSAPR Update in 2017. In addition, implementation of the
mercury and air toxics standards (MATS), which began in 2015, achieves co-benefit reductions of
NOx emissions.
Ozone Season Changes in 8-Hour Ozone Concentrations
The average reduction in seasonal mean ozone concentrations in the CSAPR Update region from
2000-2002 to 2019-2021 was about 10 ppb (19 percent), while the average reduction in the
98th percentile concentrations was about 23 ppb (26 percent) before adjusting for weather-
related effects.
The average reduction in the meteorologically-adjusted seasonal mean ozone concentrations in
the CSAPR Update region from 2000-2002 to 2019-2021 was about 11 ppb (21 percent), while
the average reduction in the 98th percentile concentrations was about 21 ppb (24 percent) after
adjusting for weather-related effects.3
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 U.S. and are home
to about 131 million people.1 These nonattainment areas were designated in 2004 using air
quality data from 2001 to 2003.2
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Based on data from 2019 to 2021, 89 of the eastern ozone nonattainment areas now
show concentrations below the level of the 1997 standard, while the remaining three
areas 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 U.S. and are home to about 80 million people.1 These
nonattainment areas were designated in 2012 using air quality data from 2008 to 2010 or 2009
to 2011.2
Based on data from 2019 to 2021, 86 percent (19 areas) of the eastern ozone
nonattainment areas now show concentrations below the level of the 2008 standard,
while the remaining three areas have shown progress toward meeting the standard. It is
reasonable to conclude that ozone season NOx emission reductions from the NBP, CAIR,
CSAPR, and CSAPR Update have significantly contributed to these improvements in
ozone air quality.
Twenty-two of the 52 areas originally designated as nonattainment for the 2015 8-hour ozone
NAAQS (0.070 ppm) are in the eastern U.S. and are home to about 85 million people.1 These
nonattainment areas were designated in 2018 using air quality data from 2014 to 2016 or 2015
to 2017.2
Based on data from 2019 to 2021, nine of the 22 eastern ozone nonattainment areas
now show concentrations below the level of the 2015 standard, and an additional 10
areas have made progress toward meeting the standard.
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 U.S. 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. Finalized in 2016, the CSAPR
Update was designed to help downwind states meet and maintain the 2008 ozone NAAQS. EPA 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 more 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 states requiring ozone season
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reductions under CSAPR and CSAPR Update, as well as in adjacent states. Rural ozone measurements
are useful in assessing the impacts on air quality resulting from regional N0X emission reductions
because they are typically less affected by local sources of N0X emissions (e.g., industrial and mobile)
than urban measurements. Reductions in rural ozone concentrations are largely attributed to reductions
in regional N0X 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 N0X 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).
Meteorologically-Adjusted Daily Maximum 8-Hour Ozone Concentrations
Variations in weather conditions play an important role in determining ozone concentrations. Ozone is
more readily formed on warm, sunny days when the air is stagnant. Conversely, ozone production is
more limited when it is cloudy, cool, rainy, or windy. EPA uses statistical models to adjust for the
variability in seasonal ozone concentrations due to weather to provide a more accurate assessment of
the underlying trend in ozone caused by emissions.
Meteorologically-adjusted ozone trends provide additional insight on the influence of CSAPR N0X Ozone
Season program and CSAPR Update emission reductions on regional air quality. EPA retrieved daily
maximum 8-hour ozone concentration data from the Air Quality System (AQS) and daily meteorology
data from the National Weather Service for 386 ozone monitoring sites located in the CSAPR Update
region. EPA uses these data in statistical models to account for the influence of weather on seasonal
average and 98th percentile ozone concentrations at each monitoring site.3
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, CSAPR, and CSAPR Update. 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 U.S.
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 U.S. Implementation began in May 2017 to further reduce ozone season NOx
emissions from power plants in 22 states in the eastern U.S. Starting June 2021, further emission
reductions were required under the Revised CSAPR Update at power plants in 12 of the 21 CSAPR
Update states.
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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 (N0X) Pollution https://www.epa.gov/no2-pollution
Nonattainment Areas https://www.epa.gov/green-book
EPA's Power Sector Programs https://www.epa.gov/power-sector/power-sector-programs
EPA's 2021 National Air Quality Trends Report https://www.epa.gov/air-trends
References
1. U.S. Census. (2020).
2. 40 CFR Part 81. Designation of Areas for Air Quality Planning Purposes.
3. Wells, B. et al. (2021). Improved Estimation of Trends in U.S. Ozone Concentrations Adjusted for
Interannual Variability in Meteorological Conditions. Atmospheric Environment, 248 (2021):
118234.
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V
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Figures
Percent Change in the Highest Values (99th percentile) of 1-hour Ozone Concentrations during the Ozone Season.
2000-2002 versus 2019-2021
' o* 0 n A*
Ao :$vvp".-o MF
. - O
-
U .
% .
CASTNET Sites
AQS Site
99th Percentile
(% change)
M<-20
H-19--15
ฆI-14--10
f il -9 - -5
I i-4-0
I-5
II-15
ฆI 16-20
H>20
Notes:
Data are from State and Local Air Monitoring Stations (SLAMS) AQS and CASTNET monitoring sites with two or more years of data within each three-year monitoring period.
The 99" percentile represents the highest 1% of hourly ozone measurements at a given monitor
Source: EPA, 2022
Figure 1. Percent Change in the Highest Values (99th percentile) of 1-hour Ozone
Concentrations during the Ozone Season, 2000-2002 versus 2019-2021
Notes:
Data are from State and Local Air Monitoring Stations {SLAMS) AQS and CASTNET monitoring sites with two or more years
of data within each three-year monitoring period.
The 99th percentile represents the highest 1% of hourly ozone measurements at a given monitor.
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Shifts in 8-Hour Seasonal Rural Ozone Concentrations in CSAPR N0X Ozone Season and CSAPR Update Regions,
1990-2021
1990 2000 2010 2020
# Actual Predicted 95% Confidence Interval
Notes:
Ozone concentration data are an average of the 99"' percentile of the 8-hour daily maximum ozone concentrations measured at rural CASTNET sites that meet completeness criteria and are located
in or adjacent to the CSAPR NO, Ozone Season and CSAPR Update regions.
Source: EPA, 2022
Figure 2. Shifts in 8-Hour Seasonal Rural Ozone Concentrations in CSAPR NOx Ozone
Season and CSAPR Update Regions, 1990-2021
Notes:
Ozone concentration data are an average of the 99th percentile of the 8-hour daily maximum ozone concentrations
measured at rural CASTNET sites that meet completeness criteria and are located in or adjacent to the CSAPR NOx
ozone season program region.
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Seasonal Average of 8-Hour Ozone Concentrations in CSAPR and CSAPR Update States,
Unadjusted and Adjusted for Weather
2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021
| Unadjusted concentrations (seasonal mean)| Adjusted concentrations (seasonal mean)
Unadjusted concentrations (98th percentile) Adjusted concentrations (98th percentile)
Notes:
8-Hour daily maximum ozone concentration data from EPA's AQS and daily meteorology data from the National Weather Service were retrieved for 390 ozone
monitoring sites in the CSAPR Update region.
For a monitor to be included in this trends analysis, it had to provide complete and valid data for 75 percent of the days in the May to September period, for each
of the years from 2000 to 2015. In urban areas with more than one monitoring site, the highest observed ozone concentration in the area was used for each day.
Source: EPA, 2022
Figure 3. Seasonal Average of 8-Hour Ozone Concentrations in CSAPR and CSAPR
Update States, Unadjusted and Adjusted for Weather
Notes:
8-Hour daily maximum ozone concentration data from EPA's AQS and daily meteorology data from the National Weather
Service were retrieved for 78 urban areas and 37 rural CASTNET monitoring sites located in the CSAPR NOx ozone
season program region.
For a monitor to be included in this trends analysis, it had to provide complete and valid data for 75 percent of the days in
the May to September period, for each of the years from 2000 to 2020. In urban areas with more than one
monitoring site, the highest observed ozone concentration in the area was used for each day.
Seasonal mean ozone values indicate the average ozone concentrations across the U.S. The 98th percentile ozone values
show the highest ozone concentrations across the U.S. NOx reductions are generally effective in reducing these peak
ozone levels in all regions of the U.S.
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Changes in 1997 Ozone NAAQS Nonattainment Areas in CSAPR Region, 2001-2003 (Original Designations)
versus 2019-2021
Source: EPA, 2022
Figure 4. Changes in 1997 Ozone NAAQS Nonattainment Areas in CSAPR Region,
2001-2003 (Original Designations) versus 2019-2021
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Changes in 2008 Ozone NAAQS Nonattainment Areas, 2008-2010 (Original Designations) versus 2018-2021
Source: EPA, 2022
Figure 5. Changes in 2008 Ozone NAAQS Nonattainment Areas,
2008-2010 (Original Designations) versus 2019
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Particulate Matter
Highlights
Particulate Matter Seasonal Trends
The Air Quality System (AQS) includes average PM2.5 concentration data for 127 sites located in
the CSAPR S02 and annual N0X 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 39 and 46 percent in the
warm and cool season months, respectively, between 2000 and 2021.
Changes in PM2.5 Nonattainment
Thirty six of the 39 designated nonattainment areas for the 1997 annual average PM2.5 NAAQS
are in the eastern U.S. and are home to about 79 million people.1,2 The nonattainment areas
were designated in January 2005 using 2001 to 2003 data.
Based on data gathered from 2019 to 2021, 35 of these eastern areas originally designated
nonattainment have concentrations below the level of the 1997 PM2.5 standard (15.0 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 matteralso known as soot, particle pollution, or PMis a complex mixture of extremely
small particles and liquid droplets. Particle pollution is made up of several 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 pollutionespecially fine particlescontains 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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PM 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 15.0 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 15.0 ng/m3. In
December 2012, EPA strengthened the annual fine particle standard to 12.0 ng/m3.
CSAPR was promulgated to help downwind states in the eastern U.S. 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 U.S., recent data indicate that no areas are violating the 1997, 2006, or 2012 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
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 Power Sector Programs https://www.epa.gov/power-sector/power-sector-programs
EPA's 2021 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. (2020).
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.
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.
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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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Figures
PM2.5 Seasonal Trends, 2000-2021
c
o
20
Q_
0
2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021
Cool season Warm season
Notes:
For a PM2.5 monitoring site to be included in the trends analysis, it had to meet all of the following criteria: 1) each site-year quarterly mean concentration value
had to encompass at least 11 or more samples, 2) all four quarterly mean values had to be valid for a given year (i.e., meet criterion #1), and 3) all 22 years of
site-level seasonal means had to be valid for the given site (i.e. meet criteria #1 and #2).
Annual "cool" season mean values for each site-year were computed as the average of the first and fourth quarterly mean values. Annual "warm" season mean
values for each site-year were computed as the average of the second and third quarterly mean values. For a given year, all of the seasonal mean values for the
monitoring sites located in the CSAPR region were then averaged together to obtain a single year (composite) seasonal mean value.
Notes:
For a PM2.5 monitoring site to be included in the trends analysis, it had to meet all of the following criteria: 1) each site-
year quarterly mean concentration value had to encompass at least 11 or more samples, 2) all four quarterly mean
values had to be valid for a given year (i.e., meet criterion #1), and 3) all 22 years of site-level seasonal means had to
be valid for the given site (i.e. meet criteria #1 and #2).
Annual "cool" season mean values for each site-year were computed as the average of the first and fourth quarterly mean
values. Annual "warm" season mean values for each site-year were computed as the average of the second and third
quarterly mean values. For a given year, all of the seasonal mean values for the monitoring sites located in the CSAPR
region were then averaged together to obtain a single year (composite) seasonal mean value.
Source: EPA, 2022
Figure 1. PM2.5 Seasonal Trends, 2000-2021
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Changes in 1997 Annual PM2B NAAQS Nonattainment Areas in CSAPR States, 2001-2003 (Original Designations)
versus 2019-2021
Source: EPA, 2022
Figure 2. Changes in the 1997 Annual PM2.5 NAAQS Nonattainment Areas in CSAPR
States, 2001-2003 (Original Designations) versus 2019-2021
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Chapter 8: Affected Communities
Regulatory programs implemented under the Clean Air Act to reduce emissions in the power
sector have delivered substantial air quality improvements since the first nationwide program
was implemented decades ago.1 However, fossil fuel-fired power plants continue to be a
leading source of ozone- and particulate-forming pollution, impacting our communities, lands,
and waterways.
Environmental hazards can be inequitably distributed in the United States, with people of color
and low-income populations consistently bearing a disproportionate burden of environmental
pollution in some areas.2 Further, climate change impacts human health through increasing
concentrations of ambient air pollutants, including ground-level ozone.3 In this chapter of the
Progress Report, we examine the results of the EPA's power sector programs through an
environmental justice lens to better understand the impacts of those programs on changes in
emissions at plants located near disadvantaged communities.
We draw on detailed air emissions data that EPA collects from power plants across the country to
provide three types of analyses.4 First, we estimate the U.S. population living within three miles of a
fossil-fired power plant and characterize the demographics in those areas.5 Second, we compare 2021
emissions from plants located near areas of potential environmental justice (EJ) concern to emissions
from all other plants. Lastly, we present emission trends associated with these plants from 2014, prior to
implementation of the Cross-State Air Pollution Rule (CSAPR), through 2021. These analyses rely on
approaches established by EPA's environmental justice screening and mapping tools, including
EJScreen, which provides a nationally consistent approach for combining environmental and
demographic indicators to highlight places that may have higher environmental burdens and vulnerable
populations.
This chapter focuses on the people who live within three miles of the power plants regulated
under EPA's Acid Rain Program (ARP) and three CSAPR programs.6 At this time, it does not
consider other pollution sources which may contribute to a disproportionate environmental
burden for some people, nor does it consider the people who live more than three miles from
each plant and who may be affected by air pollution from these facilities.
Highlights
People Living Near Power Plants
Proximity analysis is a frequently used approach to examine impacts on people who reside in
areas that may be affected by a pollution source. In 2021, over 1,200 fossil fuel-fired power
plants were covered under the ARP and CSAPR programs. Of the 329.3 million people in the
contiguous U.S. (excluding Alaska, Hawaii, Puerto Rico and other U.S. territories), 10 percent
live within three miles of one or more of these power plants.7 Most of that population (greater
than 8 percent) live near a plant fueled by natural gas. Less than 2 percent live near other types
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of fossil fuel-fired facilities, such as coal-fired or oil-fired power plants, which are typically
higher-emitting (see Figure 1).
The federal government has long recognized the heightened vulnerability of people of color and
low-income8 individuals to environmental pollutants. EPA compared the percentages of people
of color and low-income populations living within three miles of these power plants to the
national average and found that there is a greater percentage of people of color and low-
income individuals living near power plants than in the rest of the country on average.
According to 2020 census data, on average, the U.S. population is comprised of 40 percent
people of color and 30 percent low-income individuals. In contrast, the population living near
fossil fuel-fired power plants is comprised of 53 percent people of color and 34 percent low-
income individuals. For higher-emitting coal plants, the average population of people of color
and low-income is slightly higher than the national average percentages. Figure 2 summarizes
the percentages and national percentiles9 for people of color and low-income populations.
The rest of this chapter takes a closer look at the emissions associated with plants that are
located near areas of potential EJ concern. In the following analyses, those plants include any
that are located within three miles of at least one census block group10 where the population is
characterized by either a relatively high11 people of color or low-income population, based on
data available in EPA's EJScreen. As shown in Figure 1. 886 power plants (72 percent) were
located near areas of potential EJ concern in 2021.12
Emissions Affecting People Living Near Power Plants
This section focuses on 2021 sulfur dioxide (SO2) and nitrogen oxide (NOx) emissions from
plants located near areas of potential EJ concern. Sulfur dioxide is a highly reactive gas that is
generated primarily from coal-fired power plants. In addition to contributing to the formation
of acid rain and fine particle pollution, SO2 emissions are linked to many adverse human health
effects. Nitrogen oxide emissions contribute to the formation of ground-level ozone and fine
particle pollution, which cause a variety of adverse health effects, including decreased lung
function, aggravated asthma, and premature death.
The majority of the 2021 electricity generation from all ARP and CSAPR power plants comes
from plants located near areas of potential EJ concern (63 percent). A measure of power plant
output, like electricity generation (i.e., the amount of electricity produced), may often be more
informative than comparing the number of plants and can give a sense of scale to comparisons
between different groups of plants or when comparing changes across time periods. This group
of plants is also responsible for a larger share of emissions near areas of potential EJ concern:
53 percent of SO2 emissions and 54 percent of annual and ozone season (May 1-September 30)
NOx emissions (see Figure 3).
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Emissions Trends: 2014-2021
EPA analyzed emission trends between 2014 and 2021 for the ARP and CSAPR power plants. During this
time, the percent reduction in total net S02 and NOx emissions was greater at the group of plants
located near areas of potential EJ concern than for all other plants. On average, S02 emission reductions
decreased by 67 percent at the plants located near areas of potential EJ concern, compared to a 55
percent reduction from all other plants. Annual NOx and ozone season NOx emissions decreased by 46
percent and 41 percent, respectively, from plants near areas of potential EJ concern. This is slightly
greater than the percent reduction in those pollutants at all other plants, where annual NOx emissions
decreased by 43 percent and seasonal NOx emissions decreased by 36 percent (see Figure 4).
Conclusion
This chapter of the Progress Report combines publicly available emissions data with
information in EJScreen and contributes to our understanding of the relationship between the
power sector and nearby areas of potential EJ concern. The intent of this report is to focus on
emissions at the fossil-fired power plants in the contiguous U.S. which are covered by EPA's
regulatory programs developed to reduce acid rain and cross-state transport of particulate
matter and ozone and relate those emissions to nearby areas. It does not yet consider the
aggregate of all pollutants affecting these areas. Additionally, unlike EPA's regulatory analyses,
this chapter does not consider the ability of emissions to travel more than three miles and
combine with other pollutants. These considerations are important to evaluating the full impact
of the fossil-fuel fired power plants in the U.S.
The chapter provides a first step toward that evaluation and consists of three analyses:
First, EPA looked within three miles of each power plant regulated under EPA's ARP and CSAPR
programs and found that 10 percent of people in the contiguous U.S. live within three miles of a
power plant. These are mostly gas-fired power plants, with less than 2 percent of the
population living near coal- or oil-fired plants. Compared to the national average, the
population living near power plants is characterized by a higher percentage people of color and
low-income population.
Next, looking carefully at each census block group within a three-mile radius, EPA found that
most of these power plants are located nearby at least one area of potential EJ concern.13
These plants were responsible for 53 percent of SO2 emissions and 54 percent of both annual
and ozone season NOx emissions in 2021.
Finally, the third analysis found that aggregate emission trends between 2014 and 2021 show a
greater percent reduction in pollutants from plants located near areas of potential EJ concern,
compared to all other ARP and CSAPR plants. Specifically, SO2 emissions decreased by 67
percent at the plants located near areas of potential EJ concern, compared to a 55 percent
reduction from all other plants. Annual NOx and ozone season NOx emissions decreased by 46
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percent and 41 percent, respectively, from plants near areas of potential EJ concern. At all
other plants annual NOx emissions decreased by 43 percent and ozone season NOx emissions
decreased by 36 percent.
While EPA's programs have been effective in achieving overall emissions reductions, there is
clearly more to do, both to address the adverse health outcomes and environmental harms
associated with power plant emissions and, importantly, to advance the fair distribution of air
quality and human health benefits from EPA's emission reduction programs. We are dedicated
to continuous progress toward these goals. EPA will continue to assess the results of existing
and future power plant emissions reduction programs through a demographic lens. Future
analyses will build upon the findings presented in this chapter.
EPA invites your feedback. We would like to make this work accessible and useful to as many
people as possible and welcome your ideas about how to do so. The data informing these
analyses can be found here. We also encourage you to explore our tools, such as Power Plants
and Neighboring Communities, and access the wealth of additional public data, interactive
maps, graphs, and other resources available through our website.
Background Information
EPA conducted three analyses:
1. People living near power plants - EPA mapped the power plants in the contiguous U.S.,
estimated the U.S. population living within three miles of a power plant, and identified
areas of potential EJ concern using two demographic indicators: people of color and
low-income. EPA defined an area as being of potential EJ concern if, on average, either
or both indicators showed a population greater than or equal to the 80th percentile on a
national basis.
2. Emissions affecting people living near power plants - Drawing on detailed 2021 air
emissions data collected from power plants across the country, EPA compared
emissions from plants located near areas of potential EJ concern to emissions from all
other plants.
3. Emissions trends: 2014-2021 - Looking at the time period from 2014, prior to
implementation of CSAPR, through 2021, EPA compared emission trends from power
plants located near areas of potential EJ concern to emissions trends from all other
plants.
More Information
Environmental Justice Screening and Mapping Tool (EJ Screen) https://www.epa.gov/eiscreen
Power Plants and Neighboring Communities https://www.epa.gov/power-sector/power-plants-
and-neighboring-communities
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Power Sector Emissions, Operations, and Environmental Data https://epa.gov/power-
sector/data-tools
References
1. For more information about reductions in emissions and improved air quality, see the emissions
reductions chapter of the Progress Report.
2. See, for example, Cole, L. W., & Foster, S. R. (2001). From the ground up: Environmental racism
and the rise of the environmental justice movement (Vol. 34). NYU Press; Jbaily, A., Zhou, X., Liu,
J., Lee, T. H., Kamareddine, L., Verguet, S., & Dominici, F. (2022). Air pollution exposure
disparities across U.S. population and income groups. Nature, 601(7892), 228-233; and Liu, J.,
Clark, L. P., Bechle, M. J., Hajat, A., Kim, S. Y., Robinson, A. L., ... & Marshall, J. D. (2021).
Disparities in air pollution exposure in the United States by race/ethnicity and income, 1990-
2010. Environmental Health Perspectives, 129(12), 127005.
3. Nolte, C.G., Dolwick, P.D., Fann, N., Horowitz, L.W., Naik, V., Pinder, R.W., Spero, T.L., Winner,
D.A., Ziska, L.H. (2018a). Air Quality. In Impacts, Risks, and Adaptation in the United States:
Fourth National Climate Assessment, Volume II, U.S. Global Change Research Program,
Washington, DC.
4. The most recent annual emissions data are from 2021.
5. U.S. Census. (2020).
6. These are power plants that combust fossil fuels to generate electricity and emit air pollution.
CSAPR refers to the Cross-State Air Pollution Rule (CSAPR), the CSAPR Update, and the Revised
CSAPR Update programs.
7. It is important to note that the impacts of power plant emissions are not limited to a three-mile
radius. Because pollution can travel over long distances from a power plant, the impacts of both
potential increases and decreases in power plant emissions can be felt many miles away,
meaning that the air quality in a community can be due to far-distant sources as well as those
sited within a community. Still, being aware of the characteristics of communities closest to
power plants is a starting point in understanding the potential sources of pollution that may
impact a community and how changes in a power plant's air emissions may affect the air quality
experienced by some of those already vulnerable to environmental burdens.
8. EJScreen defines people of color as the percent of individuals in a block group who list their
racial status as a race other than white alone and/or list their ethnicity as Hispanic or Latino (all
people other than non-Hispanic white-alone individuals). The word "alone" in this case indicates
that the person is of a single race, not multiracial. EJScreen defines low-income as the percent of
a block group's population in households where the household income is less than or equal to
twice the federal "poverty level."
9. Percentiles are a way to see how areas of interest compare to everywhere else in the United
States. The national percentile indicates what percent of the U.S. population has an equal or
lower value, e.g., a lower percent of people of color or low-income population.
10. Census block groups are statistical divisions of census tracts and are generally defined as
containing between 600 and 3,000 people.
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11. In this report, we define "relatively high" to include percentile values greater than or equal to
the 80th percentile on a national basis. This threshold is applied here as a starting point for the
purpose of identifying geographic areas that may warrant further consideration, analysis, or
outreach. The application of this threshold in this report is not intended to determine the
existence or absence of EJ concerns or designate an area as an "EJ community." Rather, the
intent of this report is to provide screening level analysis.
12. In this example, for an area to be in the 80th percentile nationwide means that the percent
people of color and/or low-income within that block group is higher than 80 percent of all block
groups across the country. In other words, the percent people of color and/or low income in the
area is significantly higher than average.
13. Again, in this report, an "area of potential EJ concern" is defined as a census block group where
the population is characterized by either a relatively high people of color or low-income
population. It does not take the number of people living within the block group into account.
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Figures
Map of Power Plants Covered by EPA's ARP and CSAPR Programs
Legend
Power Plants
Plants located near
communities with EJ concerns
Filters
Y Plants Near Potential EJ
Y Coal-fired Plants
"Y Gas-fired Plants
Y Oil-fired Plants
Y Other fuel-fired Plants
Layers
<ฃ> Power Plants
3-mile Buffer
People of Color
<&> Census Block
Group
a
CANADA
Q
Guadalajara
Esri, Garmin, FAO, NOAA, USGS, EPA | U.S. Environmental Protection'Agency, Office of Air and Radiation (OAR)
Click here to view the map fullscreen.
( 1,234 Plants )
Powered by Esri
Source: EPA. 2023
Figure 1. Map of Power Plants Covered by EPA's ARP and CSAPR Programs
Notes:
Click the image above to open the interactive version of the figure.
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% pro^ฐ
Comparative Percentages of People of Color and Low-Income Populations Within Three Miles of a Power Plant,
2021
National
Percentage
All Plants
Coal
Gas
Oil
Other Fuel
53%
31%
54%
46%
49%
People of Color
40%
(64th)
(68th)
(51")
(69th)
(66th)
Low Income
30%
34%
(60th)
33%
(59th)
34%
(60th)
35%
(61st)
45%
(74th)
Notes.
Percentiles are shown in parentessis
Percentiles are a way to see how areas of interest compare to everywhere else in the United States The national percentile indicates what percent of the U S population has an equal or lower value e g a lower percent of people of color or
low-income population.
Source: EPA. 2023
Figure 2. Comparative Percentages of People of Color and Low-Income Populations
Within Three Miles of a Power Plant
Notes:
Percentiles are shown in parenthesis.
Percentiles are a way to see how areas of interest compare to everywhere else in the U.S. The national percentile indicates
what percent of the U.S. population has an equal or lower value, e.g., a lower percent of people of color or low-
income population.
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Comparative 2021 Generation and Emissions
Power Plant Generation, 2021
2,500,000
37%
63%
Power Plant Emissions, 2021
Ozone Season NO*
Near Areas of Potential EJ Concern
Other Areas
Near Areas of Potential EJ Concern
Other Areas
Source: Eป. 2023
Figure 3. Comparative 2021 Generation and Emissions
Chapter 8: Affected Communities
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Changes in Power Plant Emissions, 2014-2021
20
-5%
-20
-40
-43%
-46%
pR0^ฐ
-41%
-67%
-80
Generation SO2 NOx Ozone Season NO*
Other Areas ฆ Near Areas of Potential EJ Concern
Figure 4. Changes in Power Plant Emissions, 2014-2021
Source: EPA, 2023
Chapter 8: Affected Communities
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Chapter 9: 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 71
percent reduction in wet sulfate deposition from 2000-2002 to 2019-2021.
Between 2000-2002 and 2019-2021, the Northeast and Mid-Atlantic experienced a 77 percent
reduction in wet sulfate deposition.
S02 emissions reductions and the 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 25 percent in the Mid-Atlantic
and 32 percent in the Northeast but increased in the Mountain and Central regions from 2000-
2002 to 2019-2021. Increases in wet deposition of inorganic nitrogen in the Rocky Mountain
and Central regions are attributed to 36 and 34 percent increases in wet deposition of reduced
nitrogen (NH4+), respectively, between 2000 and 2021.
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,
biomass burning, and manufacturing) contribute to air concentrations and deposition of
nitrogen.
Regional Trends in Total Deposition
The reduction in total sulfur deposition (wet plus dry) in the eastern U.S. has been of similar
magnitude to that of wet deposition with an overall average reduction of 82 percent from 2000-
2002 to 2019-2021.
Decreases in oxidized nitrogen (NOx) have generally been greater than that of reduced nitrogen
(NHx) deposition. Total oxidized nitrogen deposition decreased 59 percent in the east. In
contrast, total deposition of reduced nitrogen increased by an average of 46 percent in the east
from 2000-2002 to 2019-2021.
Chapter 9: Acid Deposition
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Background Information
Acid Deposition
As S02 and N0X gases react in the atmosphere with water, oxygen, and other pollutants, they form
acidic compounds that are deposited to the earth's surface in the form of wet and dry deposition.
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 forms of precipitation) has decreased in much of the eastern U.S. 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 regulated
sources contribute to changes in air concentrations and deposition of oxidized, reduced, and organic
forms 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. In 2021,
CASTNET operated 100 regional sites throughout the contiguous U.S., 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 U.S., 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 Maps and regional trends provided in this chapter were
produced using the measurement-model fusion method developed by NADP's Total Deposition Science
Committee. Briefly, CASTNET and NADP/NTN data are combined with modeled deposition results from
EPA's Community Multiscale Air Quality Model (CMAQ) to produce gridded estimates of total
deposition. The deposition values provided in this report have been updated using CMAQv5.3.2,
incorporating the state of the science input data for emissions, meteorology, and air quality over the
timeseries (2002-2019).3 Improvements to the model have resulted in significant changes to the
modeled deposition (e.g., reduced dry nitrogen deposition, non-measured oxidized nitrogen deposition).
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More Information
Acid Rain https://www.epa.gov/acidrain
Clean Air Status and Trends Network (CASTNET) https://epa.gov/castnet
EPA's Air QUAIity TimE Series (EQUATES) for the Community Multi-Scale Air Quality Modeling
System (CMAQ) https://www.epa.gov/cmaq/equates
National Atmospheric Deposition Program (NADP) https://nadp.slh.wisc.edu/
References
1. Government of Canada, Environment Canada. (2018). 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.
3. Appel, K.W., Bash, J.O., Fahey, K.M., Foley, K.M., Gilliam, R.C., Hogrefe, C., Hutzell, W.T., Kang,
D., Mathur, R., Murphy, B.N., Napelenok, S.L., Nolte, C.G., Pleim, J.E., Pouliot, G.A., Pye, H.O.T.,
Ran, L., Roselle, S.J., Sarwar, G., Schwede, D.B., Sidi, F.I., Spero, T.L., and Wong, D.C. The
Community Multiscale Air Quality (CMAQ) model versions 5.3 and 5.3.1: system updates and
evaluation, Geosci. Model Dev., 14, 2867-2897, https://doi.org/10.5194/gmd-14-2867-2021,
2021.
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Figures
Figure 1. Three-Year Average of Total Sulfur Deposition
Source: CASTNET/CMAQ/NADP
USEPA, 2022
Three-Year Average of Total Sulfur Deposition
2000-2002 2019-2021
Total S
(kg-S/ha)
-8
-10
i12
14
16
18
>20
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Source: CASTNET/CMAQ/NADP
USEPA, 2022
Three-Year Average of Total Nitrogen Deposition
2000-2002 2019-2021
Total N
(kg-N/ha)
Figure 2. Three-Year Average of Total Nitrogen Deposition
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RegionalTrends in Deposition - Nitrogen RegionalTrends in Deposition - Sulfur
So., ซ'FM, 7(133
Figure 3. Regional Trends in Deposition
Notes:
Averages are the arithmetic mean of all spatial grids in a region for each time period.
Chapter 9: Acid Deposition
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Chapter 10: 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 NOx 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 NOx
emission reduction programs provides information about the effect of reduced NOx emissions and
ozone concentrations on forested areas.
Between 1990 and 2021, 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 2021, streams in the central Appalachian region have
experienced mixed results due in part to their soils and geology. Only 64 percent of monitored
streams show lower sulfate concentrations (and statistically significant trends), while 4 percent
show increased sulfate concentrations.
Nitrate concentrations and trends are highly variable and many sites do not show consistent
improving trends between 1990 and 2021, despite reductions in NOx emissions and inorganic
nitrogen deposition.
In 2021, levels of acid neutralizing capacity (ANC), a key indicator of aquatic ecosystem recovery
from acidification, have increased significantly from 1990 in lake and stream sites in the
Adirondack Mountains, New England, and the Catskill mountains. In the central Appalachian
region, sites with increasing ANC remain low at 14 percent.
Ozone Impacts on Forests
Between 2000-2002 and 2019-2021, the area in the eastern U.S. with combined biomass loss >
2 percent, 5 percent, and 10 percent for the forest decreased from 35 percent to 4.5 percent,
8.7 percent to 0.5 percent, and 1.7 percent to 0.1 percent, respectively, for seven tree species
combined - black cherry, yellow poplar, sugar maple, eastern white pine, Virginia pine, red
maple, and quaking aspen. This is an improvement of over 90 percent.
Ecosystem Health
Highlights
Regional Trends in Water Quality
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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 U.S. with significant biomass loss decreased from 17.0
percent to 4 percent for black cherry, and from 5.6 percent to 0 percent for yellow poplar
between 2000-2002 and 2019-2021.
For the period 2019-2021, total land area in the eastern U.S. 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 6.9 percent for the period of 2000-2002.
While this change in biomass loss cannot be exclusively attributed to the implementation of the
NBP, CAIR, CSAPR, CSAPR Update, and Revised CSAPR Update, 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 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 availability and stored sulfate in the soils means
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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 the LTM
program which provides information on the impacts of acidic deposition on otherwise pristine lakes and
streams. This program is designed to track changes in surface water chemistry in the four regions
sensitive to acid rain in the eastern U.S.: 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, and other
environmental stressors. 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 commercial and ecologically
important forest tree species throughout the U.S.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 U.S. 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/power-sector/monitoring-surface-water-
chemistry
Acid Rain https://www.epa.gov/acidrain/
Ozone W126 Index https://www.epa.gov/air-qualitv-analysis/ozone-wl26-index
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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Figures
Long-term Monitoring Program Sites and Trends, 1990-2020
LTM lakes LTM streams
Notes:
Trends are significant at the 95 percent confidence interval (p < 0.05).
Base cations are calculated as the sum of calcium, magnesium, potassium, and sodium ions.
Trends are determined by multivariate Mann-Kendall tests.
Source: EPA, 2021
Figure 1. Long-term Monitoring Program Sites and Trends, 1990-2021
Notes:
Trends are significant at the 95 percent confidence interval (p < 0.05).
Base cations are calculated as the sum of calcium, magnesium, potassium, and sodium ions.
Trends are determined by multivariate Mann-Kendall tests.
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Regional Trends in Sulfate, Nitrate, ANC, and Base Cations at Long-term Monitoring Sites, 1990-2021
Water Bodies
Region
Covered
% of Sites with Improving
Sulfate Trend
% of Sites with Improving
Nitrate Trend
% of Sites with
Improving ANC Trend
% of Sites with Improving
Base Cations Trend
Adirondack Mountains 58 lakes in NY*
98%
86%
88%
91%
26 lakes in ME and
New England
VT
100%
8%
77%
65%
Catskitls/ N. 9 streams in NY
Appalachian Plateau and PA"
78%
56%
67%
89%
Central Appalachians 70 streams in VA
64%
79%
14%
47%
Notes
Trends are determined by multivanate Mann-Kendall tests
Trends are significant at the 95 percent confidence interval (p < 0.05)
DOC is not routinely measured m Central Appalachian streams
Sum of Base Cations calculated as (Ca*Mg*K*Na)
" Data for Adirondack lakes from 1992
" Data for PA streams m N Appalachian Plateau is only through 2015
Source: EPA, 2023
Figure 2. Regional Trends in Sulfate, Nitrate, ANC, and Base Cations at Long-term
Monitoring Sites, 1990-2021
Notes:
Trends are determined by multivariate Mann-Kendaii tests
Trends are significant at the 95 percent confidence interval (p < 0.05)
DOC is not routinely measured in Central Appalachian streams
Sum of Base Cations calculated as (Ca+Mg+K+Na)
* Data for Adirondack lakes from 1992
** Data for PA streams in N. Appalachian Plateau is only through 2015
Chapter 10: Ecosystem Response - Ecosystem Health
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Estimated Black Cherry, Yellow Poplar, Sugar Maple, Eastern White Pine, Red Maple, and Quaking Aspen
Biomass Loss Due to Ozone Exposure, 2000-2002 versus 2019-2021
2000-2002
2019-2021
Notes:
Biomass loss was calculated by incorporating each tree's C-R jCauchy-Riemann) functions with the three-month, 12-hour W126 exposure metric
The W126 exposure metric is a cumulative exposure index that is biologically based and emphasized hourly ozone concentrations taken from 2000-2021 data.This evaluation incorporated
the W126 method which measures cumulative ozone exposures during the growing season when daytime ozone concentrations are the highest and plant growth is most likely to be affected.
Source: EPA, 2023
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 2019-2021
Biomass loss was calculated by incorporating each tree's C-R (Cauchy-Riemann) 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 2000-2020 data. This evaluation incorporated the W126 method which measures
cumulative ozone exposures during the growing season when daytime ozone concentrations are the highest and
plant growth is most likely to be affected.
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Critical Loads Analysis
Highlights
Critical Loads and Exceedances
For the period from 2019 to 2021, 5.8 percent of the 7,869 studied lakes and streams still
received levels of combined total sulfur and nitrogen deposition exceeding their calculated
critical load. This is an 84 percent improvement over the period from 2000 to 2002 when 38
percent of all studied lakes and streams exceeded their calculated critical load.
Emission reductions achieved between 2000 and 2021 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 for the period of 2019 to
2021 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 are negatively impacting 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 combined 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 7,869 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/power-sector/monitoring-surface-water-
chemistrv
National Acid Precipitation Assessment Program (NAPAP) Report to Congress
https://nv.water.usgs.gov/proiects/NAPAP/
Chapter 10: Ecosystem Response - Critical Loads Analysis
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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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Sites that do not Exceed the Critical Load
C Sites At or Near the Critical Load
Sites that F.xceed the Critical Load
Notes:
Surfaoe water samples from the represented lakes and streams compiled from surface monitoring programs, such as National Surface Water Survey (NSWS). Environmental Monitoring and Assessment
Program IEMAP), Wadeable Stream Assessment (WSA), National Lake Assessment I NLA). Temporally Integrated Monitoring of Eoosystems ITlMEl, Long Term Monitoring ILTM), and other water quality
monitoring programs
Steady state exceedances calculated in units of meq/nv/yr
Source: EPA, 2023
Figure 1. Lake and Stream Exceedances of Estimated Critical Loads for Total
Nitrogen and Sulfur Deposition, 2000-2002 versus 2019-2021
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Figures
Lake and Stream Exceedances of Estimated Critical Loads forTotal Nitrogen and Sulfur Deposition,
2000-2002 versus 2019-2021
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), National Lake Assessment (NLA), Temporally Integrated Monitoring of Ecosystems (TIME),
Long Term Monitoring (LTM), and other water quality monitoring programs.
Steady state exceedances calculated in units of meq/m2/yr.
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Critical Load Exceedances by Region, 2000-2002 versus 2019-2021
Water Bodies in Exceedance of Critical Load
Region
Number of Water
Bodies Modeled
2000
-2002
2019-
ฆ2021
Percent
Reduction
Number of Sites
Percent of Sites
Number of Sites
Percent of Sites
New England
(CT, MA, ME, NH, Rl, VT)
2,309
548
24%
101
4%
82%
Adirondack
(NY)
1,581
688
44%
151
10%
78%
Northern Mid-Atlantic
(NY, NJ, PA)
1,200
351
29%
32
3%
91%
Southern Mid-Atlantic
(KY, MD, VA, WV)
1,840
1000
54%
94
5%
91%
Southern Appalachian Mountains
(AL, GA, SC, TN)
939
364
39%
80
9%
78%
Total Units
7,869
2,951
38%
458
5.8%
84%
Notes
Surface water samples from me represented laKes ami streams complied from surface monitoring programs, such as National Surface water Survey (NSWS), Environmental Monitoring and Assessment Program (EMAP). wadeawe Stream
Assessment (WSA), National Lake Assessment (NLA). Temporally Integrated Monitoring of Ecosystems (TIME). Long Term Monitoring (LTM), and other water quality monitoring programs
Steady slate exceedances calculated m units of meq/m2/year
Source. EPA. 2023
Figure 2. Critical Load Exceedances by Region, 2000-2002 versus 2019-2021
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), National Lake Assessment (NLA), Temporally Integrated Monitoring of Ecosystems (TIME),
Long Term Monitoring (LTM), and other water quality monitoring programs.
Steady state exceedances calculated in units of meq/m2/yr.
Chapter 10: Ecosystem Response - Critical Loads Analysis
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