2014 Program Progress Clean Air Interstate Rule, Acid Rain Program, and Former NOX Budget Trading Program


2014 Program Progress
Clean Air Interstate Rule, Acid Rain Program,
and Former NOx Budget Trading Program
Affected Units
Emission Reductions
Program Basics
Emission Controls & Monitoring
Air Quality
Program Compliance
Acid Deposition
Market Activity
Ecosystem Response
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2014 Program Progress - Clean Air Interstate Rule, Acid Rain Program,
and Former NOx Budget Trading Program
https://www3.epa.gov/airmarkets/progress/reports/index.html
Executive Summary
This report summarizes annual progress through 2014 under the Acid Rain Program (ARP), the N0X
Budget Trading Program (NBP), and the Clean Air Interstate Rule (CAIR). Progress under the Cross-State
Air Pollution Rule (CSAPR), which went into effect in 2015, is not currently covered in this report, as it
presents data from years prior to CSAPR implementation.
A cornerstone of effective emission reduction programs is transparency and data availability. This report
highlights data on emissions, compliance, and environmental effects that EPA systematically collects.
The success of these programs is highlighted through substantial reductions in power sector emissions
of S02 and NOx and improvements in air quality and the environment.
Contents
Executive Summary	1
2014 ARP and CAIR at a Glance	5
Chapter 1: Program Basics	6
Analysis and Background Information	6
Acid Rain Program	6
NOx Budget Trading Program	6
Clean Air Interstate Rule	6
Cross-State Air Pollution Rule	7
Cross-State Air Pollution Rule Update	7
Next Steps to Address Interstate Air Pollution Transport	7
Key Points	8
Acid Rain Program (ARP)	8
NOx Budget Trading Program (NBP)	8
Clean Air Interstate Rule (CAIR)	8
Cross-State Air Pollution Rule (CSAPR)	8
Cross-State Air Pollution Rule Update (CSAPR Update)	9
More Information	9
Chapter 2: Affected Units	13
Analysis and Background Information	13
Key Points	13
Acid Rain Program (ARP)	13
Clean Air Interstate Rule (CAIR)	13
Executive Summary	1
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More Information	13
Chapter 3: Emission Reductions	16
Analysis and Background Information	16
Key Points	16
S02 Emission Trends	16
S02 State-by-State Emissions	17
S02 Emission Rates	17
More Information	17
Analysis and Background Information	22
Key Points	22
Annual N0X Trends	22
Annual N0X State-by-State Emissions	22
Annual N0X Emission Rates	22
More Information	23
Analysis and Background Information	28
Key Points	28
Ozone Season N0X Trends	28
Ozone Season N0X State-by-State Emissions	28
Ozone Season N0X Emission Rates	29
More Information	29
Chapter 4: Emission Controls and Monitoring	34
Analysis and Background Information	34
Continuous Emission Monitoring Systems (CEMS)	34
S02 Controls	34
N0X Controls	34
Key Points	34
ARP and CAIR S02 Program Controls	34
CAIR N0X Annual Program Controls	35
CAIR N0X Ozone Season Program Controls	35
More Information	35
Chapter 5: Program Compliance	39
Analysis and Background Information	39
Key Points	39
ARP and CAIR S02 Programs	39
Executive Summary
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CAIR N0X Annual Program	39
CAIR N0X Ozone Season Program	40
More Information	40
Chapter 6: Market Activity	44
Analysis and Background Information	44
Transaction Types and Volumes	44
Allowance Markets	44
Key Points	45
Transaction Types and Volumes	45
2014 Allowance Prices	45
More Information	45
Chapter 7: Ambient Air Quality	48
Analysis and Background Information	48
Sulfur Dioxide	48
Nitrogen Oxides	48
Key Points	48
National S02 Air Quality	48
Regional Changes in Air Quality	49
More Information	49
References	49
Analysis and Background Information	52
Ozone Standards	52
Regional Trends in Ozone	52
Meteorologically-Adjusted Daily Maximum 8-Hour Ozone Concentrations	52
Changes in Ozone Nonattainment Areas	53
Key Points	53
Changes in 1-Hour Ozone during Ozone Season	53
Trends in Rural Ozone	53
Changes in 8-Hour Ozone Concentrations	53
Changes in Ozone Nonattainment Areas	53
More Information	54
References	54
Analysis and Background Information	59
Particulate Matter Standards	59
Changes in PM2.5 Nonattainment Areas	59
Executive Summary
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Key Points	60
PM Seasonal Trends	60
Changes in PM2 5 Nonattainment	60
More Information	60
References	60
Chapter 8: Acid Deposition	64
Analysis and Background Information	64
Acid Deposition	64
Monitoring Networks	64
Key Points	65
Wet Sulfate Deposition	65
Wet Inorganic Nitrogen Deposition	65
Regional Trends in Deposition	65
More Information	65
References	65
Chapter 9: Ecosystem Response	69
Analysis and Background Information	69
Acidified Surface Water Trends	69
Monitoring Networks	70
Key Points	70
Regional Trends in Water Quality	70
More Information	70
References	70
Analysis and Background Information	73
Key Points	73
Critical Loads and Exceedances	73
More Information	73
References	74
Executive Summary	4

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2014 Program Progress - Clean Air Interstate Rule, Acid Rain Program,
and Former NOx Budget Trading Program
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2014 ARP and CAIR at a Glance
•	CAIR and ARP annual S02 emissions:
3.2 million tons (69 percent below 2005)
•	CAIR and ARP annual NOx emissions:
1.7 million tons (54 percent below 2005)
•	CAIR ozone season NOx emissions:
450,000 tons (44 percent below 2005)
•	Perfect compliance:
100 percent of covered facilities in the ARP and CAIR programs were in compliance
•	Ambient particulate sulfate concentrations: decreased 64 to 68 percent in observed regions (from
1989-1991 to 2012-2014)
•	Wet sulfate deposition: Northeast and Mid-Atlantic states saw the greatest improvement (69
percent reduction) from 1989-1991 to 2012-2014
•	Levels of acid neutralizing capacity (ANC): increased in Adirondack Mountains and Northern
Appalachian Plateau lake and stream monitoring sites
Executive Summary
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Chapter 1: Program Basics
The Acid Rain Program (ARP) and the Clean Air Interstate Rule (CAIR) are cap and trade programs
designed to reduce emissions of sulfur dioxide (S02) and nitrogen oxides (N0X) from covered power
plants. Both programs were in effect in 2014. The ARP covers power plants across the contiguous United
States, while CAIR covered power plants in the East. The N0X Budget Trading Program (NBP) operated
from 2003 to 2008 in the eastern United States during the ozone season (May 1 - September 30) and
was replaced by CAIR in 2009. In 2015, EPA's Cross-State Air Pollution Rule (CSAPR) replaced CAIR.
Analysis and Background Information
Acid Rain Program
Title IV of the 1990 Clean Air Act (CAA) Amendments established the ARP to address acid deposition
nationwide by reducing S02 and annual NOx emissions from coal-fired power plants. In contrast to
traditional command and control regulatory methods that establish specific emissions limitations, the
ARP S02 program introduced a novel allowance trading system that harnessed the incentives of the
market to reduce pollution. This market-based cap and trade program was implemented in two phases.
Phase I began in 1995 and affected the most polluting coal-burning units in 21 eastern and Midwestern
states. Phase II began in 2000 and expanded the program to include other units fired by coal, oil, and
gas. Under Phase II, EPA 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 as the S02 program does, nor does it utilize an allowance 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.
NOx Budget Trading Program
The NBP was a market-based cap and trade program created to reduce NOx emissions from power
plants and other large combustion sources during the summer ozone season to address regional air
pollution transport that contributes to the formation of smog (ozone) in the eastern United States. The
program was a central component of the NOx State Implementation Plan (SIP) Call, promulgated in
1998, to help states meet the 1997 ozone air quality standard (known as the National Ambient Air
Quality Standard, or NAAQS). All 21 states (20 states plus Washington, D.C.) covered by the NOx SIP Call
participated in the NBP, which operated during the ozone season from 2003 to 2008. In 2009, CAIR's
NOx ozone season program began, effectively replacing the NBP to continue achieving ozone season NOx
emission reductions from the power sector.
Clean Air Interstate Rule
CAIR required 28 eastern states (27 states plus Washington, D.C.) to make reductions in S02 and NOx
emissions that contribute to unhealthy levels of fine particulate matter (soot) and ozone pollution in
downwind states. CAIR required 25 eastern states (24 states plus Washington, D.C.) to limit annual
power sector emissions of NOx and S02 to address regional transport that contributes to the formation
of fine particulates. It also required 26 states (25 states plus Washington, D.C.) to limit power sector
ozone season NOx emissions to address regional transport of air pollution that contributes to the
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formation of ozone during the ozone season. Similar to the ARP, CAIR used three separate market-based
cap and trade programs to achieve emission reductions and to help states meet the 1997 ozone and fine
particle NAAQS.
The CAIR N0X ozone season and annual programs began in 2009, while the CAIR S02 program began in
2010. The CSAPR replaced CAIR starting on January 1, 2015.
Cross-State Air Pollution Rule
EPA issued the CSAPR in July 2011, requiring 28 states in the eastern half of the United States to
significantly improve air quality by reducing power plant emissions that cross state lines and contribute
to fine particle and summertime ozone pollution in other states. The CSAPR requires 23 states to reduce
annual S02 and NOx emissions to help downwind areas attain the 2006 24-hour and/or 1997 annual fine
particle NAAQS. Twenty-five states are required to reduce ozone season NOx emissions to help
downwind areas attain the 1997 8-hour ozone NAAQS. The final CSAPR divides the states required to
reduce S02 emissions into two groups (Group 1 and Group 2). Both groups must reduce their S02
emissions in Phase I. Group 1 states must make additional reductions in S02 emissions for Phase II in
order to eliminate their significant contribution to air quality problems in downwind areas.
The CSAPR was scheduled to replace CAIR starting on January 1, 2012. However, the timing of the
CSAPR's implementation was affected by D.C. Circuit actions that stayed and then vacated the 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 January 1,
2015, with Phase II to begin in 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 addresses the summertime transport of ozone pollution in the eastern U.S. that
crosses state lines and will help downwind states and communities meet and maintain the 2008 ozone
NAAQS. Starting in May 2017, the CSAPR Update will further reduce ozone season emissions of NOx
from power plants in 22 states in the eastern U.S.
Next Steps to Address Interstate Air Pollution Transport
The final CSAPR Update will result in meaningful, near-term reductions in ozone pollution that crosses
state lines. While the CSAPR Update is focused on the 2008 standard, emission reductions achieved
under this final rule will also help states attain and maintain the strengthened 2015 ozone NAAQS.
However, it is likely that, after implementation of this rule, some upwind states will need to make
additional reductions to address transport of ozone pollution. The EPA will continue to look at the
availability, cost-effectiveness, and timing of emissions reductions beyond 2017 for potential inclusion in
a future transport rule.
In its 2015 ozone NAAQS implementation memo, the EPA noted that the Clean Air Act's "good neighbor"
provision for the 2015 ozone NAAQS can also be addressed in a timely fashion using the 4-step CSAPR
framework. The agency intends to provide information regarding the early analytical steps of the CSAPR
Chapter 1: Program Basics
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framework for the 2015 NAAQS in fall of 2016. In addition, EPA will continue supporting efforts across
the United States that reduce S02 and NOx emissions by implementing existing programs; finalizing
pending rules; and working with regional, state, and local air quality planners to evaluate the need for
complementary clean air actions.
Key Points
Acid Rain Program (ARP)
• The ARP covers fossil fuel-fired power plants across the contiguous United States and sets annual
emission requirements for S02 and NOx, the primary precursors of acid rain.
• The market-based S02 cap and trade program sets a permanent cap on the cumulative amount of
S02 that may be emitted by electricity generating units (EGUs). The final annual S02 cap is set at 8.95
million tons, 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 EGUs.
NOx Budget Trading Program (NBP)
• The NBP was a cap and trade program that operated from 2003 to 2008, requiring NOx emission
reductions from affected power plants and industrial units in 21 eastern states (20 states plus
Washington D.C.) during the ozone season.
• In 2009, the CAIR NOx ozone season program replaced the NBP to continue ozone season NOx
emission reductions from the power sector.
Clean Air Interstate Rule (CAIR)
• CAIR required 28 eastern states (27 states plus Washington, D.C.) to reduce power sector S02 and/or
NOx emissions to address regional interstate transport for the 1997 fine particle pollution (PM2.5)
and ozone NAAQS. CAIR required reductions in annual emissions of S02 and NOxfrom power plants
in 25 eastern states (24 states plus Washington, D.C.) and reductions of NOx emissions during the
ozone season from 26 eastern states (25 states plus Washington, D.C.).
• CAIR included three separate cap and trade programs to achieve the required reductions: the CAIR
S02 trading program, the CAIR NOx annual trading program, and the CAIR NOx ozone season trading
• A December 2008 court decision kept the requirements of CAIR in place temporarily but directed
EPA to issue a new rule to address interstate transport. The CSAPR replaced CAIR starting on January
Cross-State Air Pollution Rule (CSAPR)
• The CSAPR was developed in response to the December 2008 court decision on CAIR and replaced
CAIR starting on January 1, 2015.
program.
1, 2015.
Chapter 1: Program Basics
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•	The CSAPR addresses regional interstate transport of fine particle and ozone pollution for the 1997
ozone and PM2.5 NAAQS and the 2006 PM2.5 NAAQS. The CSAPR requires a total of 28 eastern states
to reduce S02 emissions, annual NOx emissions and/or ozone season NOx emissions.
•	The CSAPR includes four separate cap and trade programs to achieve these reductions: the CSAPR
NOx annual trading program, the CSAPR NOx ozone season trading program, and the CSAPR S02
Group 1 and Group 2 trading programs.
Cross-State Air Pollution Rule Update (CSAPR Update)
•	On September 7, 2016, EPA finalized an update to the Cross-State Air Pollution Rule ozone season
program by issuing the CSAPR Update.
•	Starting in May 2017, the CSAPR Update will further reduce ozone season NOx emissions from
power plants in 22 states in the eastern U.S.
•	The CSAPR Update achieves these reductions through an ozone season NOx cap and trade program.
•	The CSAPR Update responds to the July 2015 remand of certain CSAPR budgets and updates the
CSAPR ozone season program to help downwind states and communities meet and maintain the
2008 ozone NAAQS.
More Information
•	Acid Rain Program (ARP) https://www.epa.gov/airmarkets/acid-rain-program
•	Clean Air Interstate Rule (CAIR)
https://archive.epa.gov/airmarkets/programs/cair/web/html/index.html
•	NOx Budget Trading Program (NBP) / NOx SIP Call https://www.epa.gov/airmarkets/nox-budget-
trading-program
•	Cross-State Air Pollution Rule (CSAPR) https://www3.epa.gov/airtransport/CSAPR/index.html
•	Cross-State Air Pollution Update Rule https://www.epa.gov/airmarkets/final-cross-state-air-
pollution-rule-update
•	National Ambient Air Quality Standards (NAAQS) https://www.epa.gov/criteria-air-pollutants
•	Learn more about EPA's Clean Air Market Programs https://www.epa.gov/airmarkets/programs
•	Learn more about emissions trading https://www.epa.gov/emissions-trading-resources
Chapter 1: Program Basics
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Figures
History of ARP, NBP, CAIR, and CSAPR
2010 - Full implementation of the ARP
1995-ARP
PHASE 1 BEGINS
2000 -ARP
PHASE 2 BEGINS
ARP
1990 - Clean Air Act
Amendments
establish Title IV ARP
Acid Rain Program (ARP)
NOx Budget Trading Program (NBP)
Clean Air Interstate Rule (CAIR)
Cross-State Air Pollution Rule (CSAPR)
NBP
CAIR
T
2003- NBP begins
(additional states added
in 2004 and 2007)
2009 - CAIR NOx ozone season and
NO,, annual programs begin,
replacing NBP in most states
CSAPR
2015 - CSAPR S02,
NO,, annual, and
NO,, ozone programs
begin, replacing CAIR
2010 - CAIR S02 program begins
Source EPA, 2016
Figure 1. History of ARP, NBP, CAIR, and CSAPR
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Program Map of ARP, NBP, and CA1R States
J CAIR states only controlled for both fine particles (S02 and annual NQX)
and ozone (ozone season NOx) - 23 sfafes
~ CAIR states controlled for fine particles only (S02 and annual NOx) - 25 states
CAIR states controlled for ozone only (ozone season NOx) - 26 states
The ARP covers sources in the lower 48 states.
Figure 2. Program Map of ARP, NBP, and CAIR States
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Chapter 1: Program Basics
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Program Map of Cross-State Air Pollution Rule States
States controlled for both fine particles (S02 and annual NOx)
and ozone (ozone season NO*) — 20 states
States controlled for fine particles only (S02 and annual N0>:) — 3 states
States controlled for ozone only (ozone season NOx) — 5 states
States not covered by the Cross-State Air Pollution Rule
Figure 3. Large Map of Cross-State Air Pollution Rule
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Chapter 1: Program Basics
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Chapter 2: Affected Units
Under the Acid Rain Program (ARP) and Clean Air Interstate Rule (CAIR) sulfur dioxide (S02) and nitrogen
oxides (N0X) annual programs, emission reductions generally apply to large electricity generating units
(EGUs)—boilers, turbines, and combined cycle units- that burn fossil fuels to generate electricity for
sale. The CAIR N0X ozone season program included EGUs and, in some states, large industrial units that
burn fossil fuels and have been carried over from the N0X Budget Trading Program (NBP). This section
covers units affected in 2014, and does not include programs not being implemented in 2014 (NBP and
Cross-State Air Pollution Rule [CSAPR]).
Analysis and Background Information
The ARP affects EGUs with an output capacity greater than 25 megawatts that burn coal, oil, or gas, as
well as all new EGUs. The ARP NOx program affects boilers mostly at coal-fired power plants.
The CAIR S02 and NOx annual programs generally applied to large EGUs that burned fossil fuels to
generate electricity for sale. EGUs in the CAIR programs covered a range of unit types, including units
that operated year-round to provide baseload power to the electric grid, as well as units that provided
power only on peak demand days.
In addition to including large EGUs that generated electricity for sale, the CAIR NOx ozone season
program included some other fossil fuel-fired facilities that were carried over from the NBP. Such
facilities may include large industrial units, such as boilers and turbines at heavy manufacturing facilities
(including paper mills, petroleum refineries, and iron and steel production facilities). These units also
included some fossil fuel-fired steam plants at institutions such as large universities or hospitals.
Key Points
Acid Rain Program (ARP)
• In 2014, the ARP S02 requirements applied to 3,597 fossil fuel-fired combustion units at 1,239
facilities across the country; 845 units at 351 facilities were subject to the ARP NOx program.
Clean Air Interstate Rule (CAIR)
• In 2014, there were 3,199 affected EGUs at 926 facilities in the CAIR S02 program. Of those, 2,529
(79 percent) were also covered by the ARP.
• In 2014, there were 3,199 affected EGUs at 926 facilities in the CAIR NOx annual program and 3,126
EGUs and industrial units at 914 facilities in the CAIR NOx ozone season program.
More Information
• Acid Rain Program (ARP) https://www.epa.gov/airmarkets/acid-rain-program
• Clean Air Interstate Rule (CAIR)
https://archive.epa.gov/airmarkets/programs/cair/web/html/index.html
Chapter 2: Affected Units
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Figures
4k
I 3K
Affected Units in CAIR and ARP Programs, 2014
£L
c 2k
<
O"
2
CC
<
O 1k
Ok
3,597
845
ARP NO Program
ARP SO Program
3,199
CAIR NO, Annual
Program
3,126
¦ Coal EG Us Gas EGUs Unclassified EGUs Oil EGUs
Notes:
•	'Unclassified* unite have not submitted a fuel type in (hBir monitonng plan and d«J no* report emisakins.
•	'Other" 1uel refers to units that bum waste, wood, petroleum coke, tire-derived fuel. etc.
CAIR NO^ Ozone
Season Program
Industrial Units
3.199
CAIR S0; Program
Other Fuel EGUs
Source: EPA. 2016
Notes:
Unclassified" units have not submitted a fuel type in their monitoring plan and did not report emissions.
Other" fuel refers to units that burn waste, wood, petroleum coke, tire-derived fuel, etc.
Figure 1. Affected Units in CAIR and ARP Programs, 2014
Chapter 2: Affected Units
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Affected Units in the CAIR and ARP Programs, 2014
Fuel
ARP NOx
Program
ARPSO,
Program
CAIR NOx
Annual
Program
CAIR NOj.
Ozone Season
Program
CAIR S02
Program
Coal EGUs
816
929
757
701
757
Gas EGUs
25
2480
2019
1730
2019
Oil EGUs
0
151
381
467
381
Industrial Units
0
0
0
186
0
Unclassified EGUs
0
9
4
1
4
OtherEGUs
4
28
38
41
38
Total Units
845
3597
3199
3126
3199
Notes:
•	"Unclassified" units have not submitted a fuel type in their monitoring plan and did not report emissions.
•	"Other" fuel refers to units that burn waste., wood, petroleum coke, tire-derived fuel, etc.
Source EPA, 2016
Notes:
•	"Unclassified" units have not submitted a fuei type in their monitoring pian and did not report emissions.
•	"Other" fuel refers to units that burn waste, wood, petroleum coke, tire-derived fuel, etc.
Figure 2. Affected Units in the CAIR and ARP Programs, 2014
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Chapter 2: Affected Units
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Chapter 3: Emission Reductions
The Acid Rain Program (ARP) and Clean Air Interstate Rule (CAIR) programs significantly reduced sulfur
dioxide (S02), annual nitrogen oxides (N0X), and ozone season N0X emissions. These reductions
occurred while electricity demand (measured as heat input) remained relatively stable, indicating that
the emission reductions were not driven by decreased electric generation.
These emission reductions are a result of an overall increase in the environmental efficiency of these
sources as power generators installed controls, ran their controls year-round, switched to lower
emitting fuels, or otherwise reduced their S02 and N0X emissions while meeting relatively steady
electricity demand. Most of the emission reductions since 2005 are from early reduction incentives and
stricter emission cap levels under CAIR.
S02 is a highly reactive gas that is generated primarily from the burning of fossil fuels at power plants. In
addition to contributing to the formation of fine particle pollution (PM25), S02 is 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. Most of these states are located in the
Ohio River Valley and are upwind of the areas the ARP and CAIR were designed to protect. Reductions
under the ARP and CAIR have provided important environmental and health benefits over a large region.
Key Points
S02 Emission Trends
• ARP: Units in the ARP emitted 3.1 million tons of S02 in 2014, well below the ARP's statutory annual
cap of 8.95 million tons. ARP sources reduced emissions by 12.6 million tons (80 percent) from 1990
levels and 14.1 million tons (82 percent) from 1980 levels.
• CAIR and ARP: In 2014, the fourth year of operation of the CAIR S02 program, sources in both the
CAIR S02 annual program and the ARP together reduced S02 emissions by 12.6 million tons (80
percent) from 1990 levels (before implementation of the ARP), 8.1 million tons (72 percent) from
2000 levels (ARP Phase II), and 7.1 million tons (69 percent) from 2005 levels (before
implementation of CAIR). All ARP and CAIR sources together emitted a total of 3.2 million tons of
S02 in 2014.
• CAIR: Annual S02 emissions from sources in the CAIR S02 program alone fell from 9.1 million tons in
2005 to 2.7 million tons in 2014, a 71 percent reduction. Between 2013 and 2014, S02 emissions fell
48,000 tons (2 percent) and were about 970,000 tons below the regional CAIR emission budget.
Sulfur Dioxide (SO2)
Analysis and Background Information
Chapter 3: Emission Reductions - Sulfur Dioxide (SO2)
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S02 State-by-State Emissions
•	CAIR and ARP: From 1990 to 2014, annual S02 emissions in the ARP and the CAIR S02 program
dropped in 43 states (42 states plus Washington, D.C.) by a total of approximately 12.6 million tons.
In contrast, annual S02 emissions increased in five states (Arkansas, Idaho, Nebraska, Oregon, and
Vermont) by a combined total of 20,000 tons from 1990 to 2014.
•	CAIR:- In 2014, seventeen states (16 states plus Washington, D.C.) had emissions below their CAIR
allowance budgets, collectively by about 1.1 million tons. Another six states exceeded their 2014
budgets by a combined total of about 140,000 tons, indicating that, on an aggregate basis, sources
within those states covered a portion of their emissions with allowances banked from earlier years,
transferred from an out-of-state account, or purchased from the market.
S02 Emission Rates
•	In 2014, the average S02 emission rate for units in the ARP and CAIR S02 program fell to 0.25
Ib/mmBtu. This indicates a 71 percent reduction from 2000 rates, with the majority of reductions
coming from coal-fired units.
•	Although heat input has remained steady over the past 14 years, emissions have decreased
dramatically since 2000, indicating an improvement in emission rate at the sources. This is 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.
More Information
•	Visit EPA's Power Plant Emission Trends site for the most up-to-date emissions and control data for
sources in CAIR and the ARP https://www3.epa.gov/airmarkets/progress/datatrends/index.html
•	Air Markets Program Data (AMPD) https://ampd.epa.gov/ampd/
•	Acid Rain Program (ARP) https://www.epa.gov/airmarkets/acid-rain-program
•	Clean Air Interstate Rule (CAIR)
https://archive.epa.gov/airmarkets/programs/cair/web/html/index.html
•	Learn more about sulfur dioxide (S02) https://www.epa.gov/so2-pollution
•	Learn more about particulate matter (PM) https://www.epa.gov/pm-pollution
Chapter 3: Emission Reductions - Sulfur Dioxide (SO2)
17

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and Former NOx Budget Trading Program
https://www3.epa.gov/airmarkets/progress/reports/iridex.html
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Figures
Subtopic: Sulfur Dioxide (SO2)
20
15
£
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S02 Emissions from CAIR and ARP Sources, 1980-2014
1980
1990
1995
2000
2005

2010
CAIR SO., program budget
2013
2014
ARP ARP and CAIR CAIR, not ARP ARP, not CAIR
Notes:
- For CAIR units not in the ARP. 1he 2(X>9 annual S03 emissions were applied retroactively for each pre-CAIR year following the year in which the unit began operating.
• There are a small number of sources in CAIR but not in ARP. Emsaons from tftese sources comprise about 1 percent of total ernissK^ns and are not easily visible on the full chart. To
more clearly see tftese emissions, use the interactive features of the chart and click an the green box in ihe legend labeled ¦'CAIR, not ARP" (to turn or and highlight emissions fram
these sources) and turn o1f otftef categories of emssiors.
Sou rce: EPA, 2016
Notes:
• For CAIR units not in the ARP, the 2009 annual S02 emissions were applied retroactively for each pre-CAIR year
following the year in which the unit began operating.
• There are a small number of sources in CAIR but not in ARP. Emissions from these sources comprise about 1 percent of
total emissions and are not easily visible on the full chart. To more clearly see these emissions, use the interactive
features of the chart and click on the green box in the legend labeled "CAIR, not ARP" (to turn on and highlight
emissions from these sources) and turn off the other categories of emissions.
Figure 1. SO2 Emissions from CAIR and ARP Sources, 1980-2014
Chapter 3: Emission Reductions - Sulfur Dioxide (SO2)
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https://www3.epa.gov/airmarkets/progress/reports/iridex.html	"¦* pro"*4-
2014 Program Progress - Clean Air Interstate Rule, Acid Rain Program,
and Former N0X Budget Trading Program
State-by-State S0T Emissions from CAIR and ARP
Sources, 1990-2014
SO„ Emissions (tons) =
Zoom
600k
400k
200k
Ok
1990 2000 2005 2014
Alabama
CAIR stales controlled for fine particles 1990 S03 emissions (tons)
1990
2000
2005
2014
Source: EPA. 2016
Figure 2. State-by-State SO2 Emissions
from CAIR and ARP Sources, 1990-2014
Chapter 3: Emission Reductions - Sulfur Dioxide (SO2)
19

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https://www3.epa.gov/airmarkets/progress/reports/iridex.html 4« pro"*4-
2014 Program Progress - Clean Air Interstate Rule, Acid Rain Program,
and Former N0X Budget Trading Program
Comparison of S02 Emissions and Heat Input for CAIR and ARP Sources, 2000-2014 =
SO, Emissions
15
10
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2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014
_ 30
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<3
Heat Input
Q. 10
B
nj
X
2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014
¦ Coal I Gas Oil Other
Notes;
• The data shown here reflect totals for those facilities required to comply with each program in each respective year. This means that CAIR SO, program facilities are not inducted in the
SQ, data ore* to 2009.
• Fuel type represents primary fuel type; units might combust more than one fuel.
• Unless otherwise noted, EPA data are current as ol May 2016, ana may differ from past or future reports as a result of resubmissions by sources and ongoing datB quality assurance
actvibes.
Source: EPA. 2016
Notes:
The data shown here reflect totals for those facilities required to comply with each program in each respective year.
This means that CAIR S02 program facilities are not included in the S02data prior to 2009.
Fuel type represents primary fuel type; units might combust more than one fuel.
Unless otherwise noted, EPA data are current as of May 2016, and may differ from past or future reports as a result of
resubmissions by sources and ongoing data quality assurance activities.
Figure 3. Comparison of SO2 Emissions and Heat Input for CAIR and ARP Sources, 2000-
2014
Chapter 3: Emission Reductions - Sulfur Dioxide (SO2)
20

SO, Emissions (thousand tons)
S02 Rate (Ib/rnmBtu)
Heat Input (billion mmBtu)
Primary
Fuel
2000
2005
2010
2014
2000
2005
2010
2014
2000
2005
2010
2014
Coal
10,708
9,835
5,090
3,118
1.04
0.95
0.53
0.38
20,67
20,77
19.30
16,56
Gas
108
91
20
9
0.06
0.03
0.01
0.00
3.88
5.49
7.28
8.27
Oil
385
292
31
10
0.73
0.70
0.19
0.13
1.06
0.84
0.33
0.15
Other
1
4
26
18
0.22
0.27
0.53
0.21
0.01
0,03
0.10
0.17
Total
11,201
10,223
5,168
3.155
0.88
0.75
0.38
0.25
25.61
27.13
27.00
25.15
The data shown here reflect totals for those facilities required to comply with each program in each respective year. This means that CAIR S02 program
facilities are not included in the S02 data prior to 2009.
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.
Each year's total emission rate does not equal the arithmetic mean of the four fuel-specific rates, as each facility influences the annual emission rate in
proportion to its heat input, and heat input is unevenly distributed across the fuel categories.
Unless otherwise noted, EPA data are current as of May 2016, and may differ from past or future reports as a result of resubmissions by sources and
ongoing data quality assurance activities.
Source EPA, 2016
Notes:
• The data shown here reflect totals for those facilities required to comply with each program in each respective
year. This means that CAIR S02 program facilities are not included in the S02data prior to 2009.
• 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.
• Each year's total emission rate does not equal the arithmetic mean of the four fuel-specific rates, as each facility
influences the annual emission rate in proportion to its heat input, and heat input is unevenly distributed across the fuel
categories.
• Unless otherwise noted, EPA data are current as of May 2016, and may differ from past or future reports as a result of
resubmissions by sources and ongoing data quality assurance activities.
Figure 4. CAIR and ARP SO2 Trends
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Chapter 3: Emission Reductions - Sulfur Dioxide (SO2)
21

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2014 Program Progress - Clean Air Interstate Rule, Acid Rain Program,
and Former NOx Budget Trading Program
https://www3.epa.gov/airmarkets/progress/reports/index.html
Nitrogen Oxides (NOx)
Analysis and Background Information
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 contributes to the formation of ground-level ozone and fine
particle pollution, which cause a variety of adverse health effects.
Overall, N0X emissions have declined dramatically under the ARP, former N0X Budget Trading Program
(NBP), and CAIR programs, with the majority of reductions coming from coal-fired units. Other
programs—such as regional and state N0X emission control programs—also contributed significantly to
the annual N0X emission reductions achieved by sources in 2014.
Key Points
Annual NOx Trends
• ARP: Units in the ARP N0X program emitted 1.6 million tons of N0X in 2014, indicating that ARP
sources reduced emissions by 6.5 million tons from the projected level in 2000 without the ARP, and
over three times the Title IV NOx emission reduction objective.
• CAIR and ARP: In 2014, the sixth year of operation of the CAIR NOx annual program, sources in both
the CAIR NOx annual program and the ARP together emitted 1.7 million tons, a reduction of 4.7
million tons (73 percent reduction) from 1990 levels, 3.5 million tons (67 percent reduction) from
2000, and 2.0 million tons (54 percent reduction) from 2005 levels.
• CAIR: Emissions from CAIR NOx annual program sources alone were about 1.2 million tons in 2014.
This is about 1.5 million tons (56 percent) lower than in 2005 and 340,000 tons (23 percent) below
the CAIR NOx annual program's 2014 regional budget of 1,504,871 tons.
Annual NOx State-by-State Emissions
• CAIR and ARP: All states participating in the ARP and CAIR NOx annual programs decreased
their NOx emissions from 1990 to 2014.
• CAIR: Seventeen states (16 states plus Washington, D.C.) had emissions below their CAIR 2014
allowance budgets, collectively by about 380,000 tons. Another six states exceeded their 2014
budgets by a combined total of about 53,000 tons. This indicates that, on an aggregate basis,
sources within those states covered a portion of their emissions with allowances banked from
earlier years, transferred from an out-of-state account, or purchased from the market. Overall, in
2014 the total NOx emissions from participating sources were about 330,000 tons below the CAIR
regional emission budget of 1,504,871 tons.
Annual NOx Emission Rates
• In 2014, the CAIR and ARP average annual NOx emission rate was 0.13 Ib/mmBtu, a 50 percent
reduction from 2005.
Chapter 3: Emission Reductions - Annual Nitrogen Oxides (NOx)
22

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2014 Program Progress - Clean Air Interstate Rule, Acid Rain Program,
and Former NOx Budget Trading Program
https://www3.epa.gov/airmarkets/progress/reports/index.html
^tDSX
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•	Although heat input has remained relatively steady over the past 14 years, emissions have
decreased dramatically since 2000, indicating an improvement in NOx emission rates (see Figure 4,
below). This is due in large part to greater use of control technology on coal-fired units and
increased heat input at natural gas-fired units that emit less NOx than coal-fired units.
More Information
•	Visit EPA's Power Plant Emission Trends site for the most up-to-date emissions and control data for
sources in CAIR and the ARP https://www3.epa.gov/airmarkets/progress/datatrends/index.html
Air Markets Program Data (AMPD) https://ampd.epa.gov/ampd/
•	Acid Rain Program (ARP) https://www.epa.gov/airmarkets/acid-rain-program
•	Clean Air Interstate Rule (CAIR)
https://archive.epa.gov/airmarkets/programs/cair/web/html/index.html
•	Learn more about nitrogen oxides (N0X) https://www3.epa.gov/airquality/nitrogenoxides/
•	Learn more about particulate matter (PM) https://www.epa.gov/pm-pollution
Chapter 3: Emission Reductions - Annual Nitrogen Oxides (NOx)
23

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2014 Program Progress - Clean Air Interstate Rule, Acid Rain Program,
and Former NOx Budget Trading Program
https://www3.epa.gov/airmarkets/progress/reports/iridex.html
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Subtopic: Nitrogen Oxides (NOx)
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Annual NO Emissions from CAIR and ARP Sources, 1990-2014
CAIR NO; annual program budget
1990
2000
2005
2010
2013
2014
ARP ARP and CAIR ARP, not CAIR CAIR, not ARP
Notes:
•	For CAIR units not in the ARP in 1990, 2000, and 2CG5, the 2008 annual NO_ emissions, were applied retroactively for each pre-CAIR year following the year in which the unit began
operating.
•	There are a small number of sources in CAIR but not in ARP. Ermasora 1rom these sources comprise about 2 percent of total emissions and are not easily visible on the full chart To
more clearly see these emissions, use 1he interactive features of the figure and dick on the yellow box in the legend labeled "'CAIR, not ARP' >;to turn on and highlight emissions from
these sources} and turn off 1he other categories of emfssiora.
Source: EPA, 2016
Notes:
•	For CAIR units not in the ARP in 1990, 2000, and 2005, the 2008 annual NOx emissions were applied retroactively for
each pre-CAIR year following the year in which the unit began operating.
•	There are a small number of sources in CAIR but not in ARP. Emissions from these sources comprise about 2 percent of
total emissions and are not easily visible on the full chart. To more clearly see these emissions, use the interactive
features of the figure and click on the yellow box in the legend labeled "CAIR, not ARP" (to turn on and highlight
emissions from these sources) and turn off the other categories of emissions.
Figure 1. Annual NO* Emissions from CAIR and ARP Sources, 1990-2014
Chapter 3: Emission Reductions - Annual Nitrogen Oxides (NOx)
24

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2014 Program Progress - Clean Air Interstate Rule, Acid Rain Program,
and Former NOx Budget Trading Program
https://www3.epa.gov/airmarkets/progress/reports/iridex.html
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Figure 2. State-by-State Annual N0X Emissions from CAIR and ARP Sources, 1990-2014
State-by-State Annual NO_ Emissions from CAIR and =
ARP Sources, 1990-2014
Zoom
CAIR states controlled for fine particles 1990 NOt emissions (tons)
NO Emissions (tons) =
1990
2000
2005
2014
250k
200k
150k
100k
50k
0k
1990 2000 2005 2014
[ Alabama
Swirte: EPA, 2016
Chapter 3: Emission Reductions - Annual Nitrogen Oxides (NOx)
25

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https://www3.epa.gov/airmarkets/progress/reports/iridex.html 4« pro"*4-
2014 Program Progress - Clean Air Interstate Rule, Acid Rain Program,
and Former N0X Budget Trading Program
Comparison of Annual NOi Emissions and Heat Input for CAIR and ARP Sources, =
2000-2014
NO< Emissions
Heat Input
30
=3
m
E
E
20
Q- 10
a
8
T.
2000
2001
2002 2003 2004 2005 2006 2007
2000
2009 2010
2011
2012 2013
2014
¦ Coal ¦ Gas ¦ Oil Other
Notes:
• The data shown here for the annual programs reflect totals tor those facilities required to comply with each program in eacft respective year. This means lhat CAIR NQe annual program
lac&lies are no1 included m fine annual NOt data for 2000 and 2005.
• Fuel type represents primary fuel type; units might combust more than one fuel.
• Unless otherwise noted, EPA data are current as of May 2016, and may differ Irom past or future reports as a result of resubmissions by sources and ongoing data quality assurance
activities.
Source: EPA. 2016
Notes:
The data shown here for the annual programs reflect totals for those facilities required to comply with each program in
each respective year. This means that CAIR NOx annual program facilities are not included in the annual NOxdata for
2000 and 2005.
Fuel type represents primary fuel type; units might combust more than one fuel.
Unless otherwise noted, EPA data are current as of May 2016, and may differ from past or future reports as a result of
resubmissions by sources and ongoing data quality assurance activities.
Figure 3. Comparison of Annual NOx Emissions and Heat Input for CAIR and ARP
Sources, 2000-2014
Chapter 3: Emission Reductions - Annual Nitrogen Oxides (NOx)
26

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2014 Program Progress - Clean Air Interstate Rule, Acid Rain Program,
and Former N0X Budget Trading Program
https://www3.epa.gov/airmarkets/progress/reports/iridex.html
CAIR and ARP Annua! N0X Trends

NOx Emissions (thousand tons)
NOx Rate (Ib/mtnBtu)
Heat Input (billion mmBtu)
Primary
Fuel
2000
2005
2010
2014
2000
2005
2010
2014
2000
2005
2010
2014
Coal
4,587
3,356
1,923
1,517
0.44
0.32
0.20
0.18
20.67
20.77
19,30
16,61
Gas
354
167
150
124
0.18
0.06
0.04
0.03
3,88
5.49
7.28
8.27
Oil
162
104
24
11
0.31
0.25
0.15
0.15
1.06
0.84
0.33
0.15
Other
2
6
7
10
0.25
0.42
0.13
0.11
0.01
0,03
0.10
0.17
Total
5,104
3,633
2,103
1,663
0.40
0.27
0.16
0.13
25.61
27.13
27.00
25.16
The data shown here for the annual programs reflect totals for those facilities required to comply with each program in each respective year. This
means that CAIR NO* annual program facilities are not included in the annual NO, data for 2000 and 2005.
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.
Each year's total emission rate does not equal the arithmetic mean of the four fuel-specific rates, as each facility influences the annual emission rate in
proportion to its heat input., and heat input is unevenly distributed across the fuel categories.
Unless otherwise noted, EPA data are current as of May 2016, and may differ from past or future reports as a result of resubmissions by sources and
ongoing data quality assurance activities.
Source EPA, 2016
Notes:
• The data shown here includes emissions and heat input data for 2000 and 2005 that were reported under other
programs. For facilities that were not covered by another program and did not report 2005 emissions, their reported
emissions for the 2008 training year were substituted.
• 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.
• Each year's total emission rate does not equal the arithmetic mean of the four fuel-specific rates, as each facility
influences the annual emission rate in proportion to its heat input, and heat input is unevenly distributed across the fuel
categories.
• Unless otherwise noted, EPA data are current as of May 2016, and may differ from past or future reports as a result of
resubmissions by sources and ongoing data quality assurance activities.
Figure 4. CAIR and ARP Annual NOx Trends
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Chapter 3: Emission Reductions - Annual Nitrogen Oxides (NOx)
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and Former NOx Budget Trading Program
https://www3.epa.gov/airmarkets/progress/reports/index.html
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Ozone Season Nitrogen Oxides (NOx)
Analysis and Background Information
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 contributes to the formation of ground-level ozone and fine
particle pollution, which cause a variety of adverse human health effects.
The CAIR N0X ozone season program was established to reduce interstate transport during the ozone
season (May 1 - September 30), the warm summer months when ozone formation is highest, and to
help eastern U.S. counties attain the 1997 ozone standard.
In general, the states with the highest emitting sources of ozone season N0X in 2000 have seen the
greatest reductions under the CAIR NOx ozone season program. Most of these states are in the Ohio
River Valley and are upwind of the areas CAIR was designed to protect. Reductions by sources in these
states have resulted in important environmental and human health benefits over a large region.
In addition to the CAIR and ARP NOx programs and the former NBP, current regional and state NOx
emission control programs have also contributed significantly to the ozone season NOx emission
reductions achieved by sources.
Key Points
Ozone Season NOx Trends
• CAIR: Units in the CAIR NOx ozone season program emitted 450,000 tons in 2014, a reduction of 1.6
million tons (78 percent) from 1990, 1.0 million tons lower (69 percent reduction) than in 2000
(before implementation of the NBP), 350,000 tons lower (44 percent reduction) than in 2005 (before
implementation of CAIR), and about 25,000 tons lower (5 percent reduction) than in 2013. In 2014,
CAIR NOx ozone season program emissions were 21 percent below the regional emission budget of
567,744 tons.
• CAIR and NBP: In 2014, sources from both CAIR and the former NBP, together with a small number
of sources that were previously in the NBP but did not enter CAIR, reduced their overall NOx
emissions from 820,000 tons in 2005 (before implementation of CAIR) to 450,000 tons in 2014 (45
percent reduction).
Ozone Season NOx State-by-State Emissions
• CAIR and NBP: Between 2005 and 2014, ozone season NOx emissions from CAIR and former NBP
sources fell in every state participating in the CAIR NOx ozone season program except Arkansas,
Rhode Island, and West Virginia, where emissions increased by a combined total of 3,000 tons.
• CAIR: In 2014, every state and Washington, D.C. had emissions below their CAIR allowance budgets,
collectively by about 250,000 tons.
Chapter 3: Emission Reductions - Ozone Season Nitrogen Oxides (NOx)
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and Former NOx Budget Trading Program
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Ozone Season NOx Emission Rates
• In 2014, the average N0X ozone season emission rate fell to 0.13 Ib/mmBtu. This indicates a 68
percent reduction from 2000 emission rates, with the majority of reductions coming from coal-fired
•	Although heat input has remained relatively constant over the past 14 years, emissions have
decreased dramatically since 2000, indicating an improvement in NOx emission rate. This is due in
large part to greater use of control technology on coal-fired units and increased heat input at
natural gas-fired units, which emit less NOx than coal-fired units.
More Information
•	Visit EPA's Power Plant Emission Trends site for the most up-to-date emissions and control data for
sources in CAIR and the ARP https://www3.epa.gov/airmarkets/progress/datatrends/index.html
•	Air Markets Program Data (AMPD) https://ampd.epa.gov/ampd/
•	NOx Budget Trading Program (NBP) / NOx SIP Call https://www.epa.gov/airmarkets/nox-budget-
trading-program
•	Clean Air Interstate Rule (CAIR)
https://archive.epa.gov/airmarkets/programs/cair/web/html/index.html
•	Learn more about nitrogen oxides (NOx) https://www3.epa.gov/airquality/nitrogenoxides/
•	Learn more about ozone https://www.epa.gov/ozone-pollution
units.
Chapter 3: Emission Reductions - Ozone Season Nitrogen Oxides (NOx)
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2014 Program Progress - Clean Air Interstate Rule, Acid Rain Program,
and Former NOx Budget Trading Program
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Figures
Subtopic: Ozone Season Nitrogen Oxides (NOx)
«- 2 5
§
i
= 2
1.5
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m
Ozone Season NO Emissions from CAIR and NBP Sources, 1990-2014
CAIR NO^ ozone season budget
1990
2000
2005
2010
2013
2014
I NBP, including future CAIR Non-NBP, future CAIR NBP, future CAIR NBP, not CAIR
¦ CAIR, including former NBP
Notes:
•	For CAIR units not in the NBP, 1he 2008 HOt emissions were applied retroactively to 19&D and 2000 if One unit operated in the previous year's ozone season.
•	There are a small number of sources IhaE were in N9P but not in CAIR. Emissions from these sources compfise about 2 percent of total emissions and are ro1 easily visible on the ful
chart. To more clearly see &*ese emissions, use the interactive features of the chart and clfck on the yellow box in the legend labeled 'NBP, not CAIR' (to turn on and htghight emissions
Irom tr»sse sources) and turn off the other categories of emissions.
Source: EPA, 2016
Notes:
•	For CAIR units not in the NBP, the 2008 NOx emissions were applied retroactively to 1990 and 2000 if the unit operated
in the previous year's ozone season.
•	There are a small number of sources that were in NBP but not in CAIR. Emissions from these sources comprise about 2
percent of total emissions and are not easily visible on the full chart. To more clearly see these emissions, use the
interactive features of the chart and click on the yellow box in the legend labeled "NBP, not CAIR" (to turn on and
highlight emissions from these sources) and turn off the other categories of emissions.
Figure 1. Ozone Season NOx Emissions from CAIR and NBP Sources, 1990-2014
Chapter 3: Emission Reductions - Ozone Season Nitrogen Oxides (NOx)
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2014 Program Progress - Clean Air Interstate Rule, Acid Rain Program,
and Former N0X Budget Trading Program
State-by-State Ozone Season NOa Emissions from
CAIR Sources, 2000-2014
NO Emissions (tons) =
Zoom
100k
75k
50k
25k
Ok
2000	2005	2014
Alabama
CAIR states controlled for ozone 2000 N0_ emissions (tons)
Notes:
' The 2000 and 2005 ozone season values reflect data that were reported under other programs. Foe Facilities ihat were
rx>l covered by another program and <§d not report 2000 or 2005 emissions, their reported emissions for the earliest
subsequent year (usually the 2008 training year) were substituted.
2000
2005
2014
Source: EPA, 2016
Notes:
The 2000 and 2005 ozone season values reflect data that were reported under other programs. For facilities that were
not covered by another program and did not report 2000 or 2005 emissions, their reported emissions for the earliest
subsequent year (usually the 2008 training year) were substituted.
Figure 2. State-by-State Ozone Season NOx Emissions
from CAIR Sources, 2000-2014
Chapter 3: Emission Reductions - Ozone Season Nitrogen Oxides (NOx)
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and Former N0X Budget Trading Program
Comparison of Ozone Season NO^ Emissions and Heat Input for CAIR NO^ Ozone
Season Sources, 2000-2014
a 2
NO Emissions
E
UJ
Q*
z
2000
2005
2008
2009
2010
2011
2012
2013
2014
7.5
Heat Input
3
CO
E
E
B- 2.5
1
1
x
2000
2005
2008
2009
2010
2011
2012
2013
2014
Coal
Gas
Oil
Other
Notes:
• The data shown here include emissons and heal input data for 2000 and 2005 that were reported undw other programs. For facilities that were not covered by another program and
dd not report 2005 emissions, their reported emissions for the 2008 training year were substituted.
• Fuel type represents primary fuel type; units might combust more than one fuel.
• Unless otherwise noted, EPA data are current as o1 May 2016, and may differ 1rom past or fulure reports as a result of resubmissions by sojrces and ongoing data quality assurance
activities.
Source: EPA, 2016
Notes:
The data shown here include emissions and heat input data for 2000 and 2005 that were reported under other
programs. For facilities that were not covered by another program and did not report 2005 emissions, their reported
emissions for the 2008 training year were substituted.
Fuel type represents primary fuel type; units might combust more than one fuel.
Unless otherwise noted, EPA data are current as of May 2016, and may differ from past or future reports as a result of
resubmissions by sources and ongoing data quality assurance activities.
Figure 3. Comparison of Ozone Season NOx Emissions and Heat Input for CAIR Sources,
2000-2014
Chapter 3: Emission Reductions - Ozone Season Nitrogen Oxides (NOx)
32

NO:< Emissions (thousand tons)
NO, Rate (Ib/mmBtu)
Heat Input (billion mmBtu)
Primary
Fuel
2000
2005
2010
2014
2000
2005
2010
2014
2000
2005
2010
2014
Coal
1,395
692
527
404
0.45
0.22
0.18
0.17
6.17
6.30
5,85
4,68
Gas
78
58
49
37
0.17
0.08
0.05
0.03
0.92
1.54
2,02
2,18
Oil
66
57
16
4
0.27
0.25
0.15
0.12
0.48
0.45
0,22
0.07
Other
1
2
2
3
0.15
0.17
0.12
0.10
0.02
0.02
0.04
0.07
Total
1,541
809
594
449
0.41
0.20
0.15
0.13
7.59
8.31
8.13
7.00
The data shown here includes emissions and heat input data for 2000 and 2005 that were reported under other programs. For facilities that were not
covered by another program and did not report 2005 emissions, their reported emissions for the 2008 training year were substituted.
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.
Each year's total emission rate does not equal the arithmetic mean of the four fuel-specific rates, as each facility influences the annual emission rate in
proportion to its heat input, and heat input is unevenly distributed across the fuel categories.
Unless otherwise no-ted, EPA data are current as of May 2016, and may differ from past or future reports as a result of resubmissions by sources and
ongoing data quality assurance activities.
Source EPA, 2016
Notes:
• The data shown here include emissions and heat input data for 2000 and 2005 that were reported under other
programs. For facilities that were not covered by another program and did not report 2005 emissions, their reported
emissions for the 2008 training year were substituted.
• 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.
• Each year's total emission rate does not equal the arithmetic mean of the four fuel-specific rates, as each facility
influences the annual emission rate in proportion to its heat input, and heat input is unevenly distributed across the fuel
categories.
• Unless otherwise noted, EPA data are current as of May 2016, and may differ from past or future reports as a result of
resubmissions by sources and ongoing data quality assurance activities.
Figure 4. CAIR Ozone Season NOx Trends
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and Former NOx Budget Trading Program
https://www3.epa.gov/airmarkets/progress/reports/index.html
Chapter 4: Emission Controls and Monitoring
Allowance trading allows sources in cap and trade programs to adopt the most cost-effective strategy to
reduce emissions. To meet the Acid Rain Program (ARP) and Clean Air Interstate Rule (CAIR) emission
reduction targets, some sources opted to install control technologies. A wide set of controls is available
to help reduce emissions. The tracking and reporting of accurate and consistent emissions monitoring
data is important to ensure program compliance and is achieved through the use of continuous emission
monitoring systems (CEMS). The following is an analysis of controls on ARP and CAIR units.
Analysis and Background Information
Continuous Emission Monitoring Systems (CEMS)
Accurate and consistent emissions monitoring is the foundation of a successful cap and trade program.
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, accuracy, reliability, and
consistency. Sources are required to use CEMS or other approved methods to record and report
pollutant emissions data. Sources conduct stringent quality assurance tests of their monitoring systems
to ensure the accuracy of emissions data and to provide assurance to market participants that a ton of
emissions measured at one facility is equivalent to a ton measured at a different facility. EPA conducts
comprehensive electronic and field data audits to validate the reported data.
SO2 Controls
Sources in the ARP and CAIR S02 program have a number of S02 control options available. These include
switching to low sulfur coal, employing various types of flue gas desulfurization technologies (FGDs), or
utilizing fluidized bed limestone units. FGDs on coal-fired generators are the principal means of
controlling S02 and tend to be present on the highest generating coal-fired units. While some units with
low levels of emissions are allowed to use other approved methods, the vast majority of S02 emissions-
over 99 percent-were measured by CEMS.
NOx Controls
Sources in the ARP and CAIR N0X annual and ozone season programs have a variety of options by which
to reduce N0X emissions, including advanced controls such as selective catalytic reduction (SCR) or
selective non-catalytic reduction (SNCR), combustion controls, and others. While some units with low
levels of emissions are allowed to use other approved methods, the vast majority of N0X emissions-
over 99 percent—were measured by CEMS.
Key Points
ARP and CAIR S02 Program Controls
• Of all coal-fired generation (measured in megawatt hours, or MWh) from sources participating in
the ARP and CAIR S02 program, 73 percent was produced in 2014 by units with pollution controls.
• FGD-controlled units accounted for 51 percent of coal-fired units and 72 percent of coal-fired
generation in 2014.
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and Former NOx Budget Trading Program
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•	In 2014, 77 percent of units, accounting for 38 percent of energy generation, primarily use natural
gas, oil, or other fuel sources, and make up 1 percent of S02 emissions.
•	In 2014, CEMS monitored over 99 percent of S02 emissions from CAIR sources, including 100
percent from coal-fired units.
CAIR NOx Annual Program Controls
•	In 2014, the 371 coal-fired units with add-on controls (either SCRs or SNCRs) generated 70 percent
of coal-fired generation. At oil- and natural gas-fired units, SCR- and SNCR- controlled units
produced 71 percent of generation.
•	Although 52 coal-fired units remain uncontrolled, they represent one percent of coal-fired
generation under the CAIR NOx annual program in 2014.
•	In 2014, CEMS monitored over 99 percent of S02 emissions from CAIR sources, including 100
percent from coal-fired units.
CAIR NOx Ozone Season Program Controls
•	In 2014, SCR or SNCR accounted for 72 percent of coal-fired generation. At oil- and natural gas-fired
units, SCR- and SNCR- controlled units produced 74 percent of generation.
•	Although 63 coal-fired units remain uncontrolled in 2014, they represent 2 percent of coal-fired
generation under the CAIR NOx ozone season program.
More Information
•	Visit EPA's Power Plant Emission Trends site for the most up-to-date emissions and control data for
sources in CAIR and the ARP https://www3.epa.gov/airmarkets/progress/datatrends/index.html
•	Air Markets Program Data (AMPD) https://ampd.epa.gov/ampd/
•	Learn more about emissions monitoring https://www.epa.gov/airmarkets/emissions-monitoring
•	Continuous emission monitoring systems (CEMS) https://www3.epa.gov/ttnemc01/cem.html
•	Plain English guide to 40 CRF Part 75 https://www.epa.gov/airmarkets/plain-english-guide-part-75-
rule
Chapter 4: Emission Controls and Monitoring
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and Former N0X Budget Trading Program
Figures
SO, Controls in the ARP and CAIR
S02 Program in 2014
Generation Load (MWh) by Control Type
FGD x
Emissions (tons SO.)
by Primary Fuel Type
Unknown
Unknown
Uncontrolled
Other
FGD
Uncontrolled
Olher
Uncontrolled
FGD
Coal
Other
Gas
Oil
Other *
Number of Units
by Primary Fuel Type
Uncontrolled
Other
Notes.
¦ Due t-D rounding, percentages shown may nc! add up to 100%.
• 'FGD' refers to Flue-gas desufturization: 'Other'' 1uel refers to units that bum waste, woo-d, petroleum oo&e,
tire-derived Kiel, etc.; "Unknown* is counted as uncontrolled.
• Emissions data collected and reported using CEM3.
¦ EPA data in this figtffe are current as of May 2016, sro may s£1fer from past or future reports as a resuttot
resubmissions by sources and ongoing data quaLty assurance activities.
Source: EPA, 2016
Notes:
Due to rounding, percentages shown may not add up to 100%.
"FGD" refers to Flue-gas desulfurization; "Other" fuel refers to units that burn waste, wood, petroleum coke, tire-
derived fuel, etc.; "Unknown" is counted as uncontrolled.
Emissions data collected and reported using CEMS.
EPA data in this figure are current as of May 2016, and may differ from past or future reports as a result of
resubmissions by sources and ongoing data quality assurance activities.
Figure 1. SO2 Controls in the ARP and CAIR SO2 Program in 2014
Chapter 4: Emission Controls and Monitoring
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2014 Program Progress - Clean Air Interstate Rule, Acid Rain Program,
and Former N0X Budget Trading Program
NO Controls in the CAIR NO
X X
Annual Program in 2014
Generation Load (MWh) by Control Type
SCR
SNCR
Olhef Control - " " ~ I / Combustion
Combustion
Non-Controlled
SCR
SCR
Combustion
Olhef Control
Non-Controlled —^
Non-Controlled —
Olhef Coriljol
SNCR
SCR
Emissions (tons NQt)
by Primary Fuel Type
Coal
Other
Gas
Oil
Number of Units
by Primary Fuel Type
Notes:
• Due to rounding, percentages shown may not add up to 100%.
' "SCR" refers 10 selective catalytic reduction; 'SNCR* tuel refers to selective non-catafytic reduction; 'Combustion'
relers to low NOa burners, combustion modification/fuel reburning, or overfire air. and "Other* fuel refers to units that
burn waste, wood, petroleum coke, tire-derived fuel, elc.
' Emissions data collected and reported using CEMS.
• EPA data in this figure are current as of May 2016, and may cttfer from past or luture reports as a result ot
resubmissions by sources and ongoing data quality assurance activities.
Source: EPA, 2016
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" refers
to low NOx burners, combustion modification/fuel reburning, or overfire air; and "Other" fuel refers to units that burn
waste, wood, petroleum coke, tire-derived fuel, etc.
Emissions data collected and reported using CEMS.
EPA data in this figure are current as of May 2016, and may differ from past or future reports as a result of
resubmissions by sources and ongoing data quality assurance activities.
Figure 2. NOx Controls in the CAIR NOx Annual Program in 2014
Chapter 4: Emission Controls and Monitoring
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NO Controls in the CAIR NO Ozone
x	*
Season Program in 2014
Generation Load 
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2014 Program Progress - Clean Air Interstate Rule, Acid Rain Program,
and Former NOx Budget Trading Program
https://www3.epa.gov/airmarkets/progress/reports/index.html
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Chapter 5: Program Compliance
This analysis shows how the Acid Rain Program (ARP) and Clean Air Interstate Rule (CAIR) allowances are
used for compliance under the trading programs in 2014. Because sulfur dioxide (S02) allowances from
the ARP are used by sources to comply with the CAIR S02 program, compliance results for both programs
are displayed together.
Analysis and Background Information
The year 2014 was the fifth and final year for compliance with the CAIR S02 program. Under this
program, allowances are used to cover emissions based on the vintage year of the allowances, with pre-
2010 vintage allowances used at one allowance for 1 ton of S02 emissions, and 2010-2014 vintage
allowances used at two allowances for 1 ton of S02 emissions. For facilities covered by both CAIR and
the ARP, reconciliation is a two-step process. First, ARP deductions are made; then, any additional
deductions to comply with the CAIR S02 program are made. The additional deductions under CAIR could
be used to cover the two-for-one use of 2010-2014 allowances or to cover emissions for units that are
subject to CAIR, but not the ARP.
Because of variation in rounding conventions, changes due to resubmissions by sources, and allowance
compliance issues at certain units, the compliance summary emissions number cited in "Key Points" may
be lower than the sums of emissions used for reconciliation purposes shown in the "Allowance
Reconciliation Summary" figures. Therefore, the allowance totals deducted for actual emissions in those
figures differ from the number of emissions shown elsewhere in this report.
Key Points
ARP and CAIR SO2 Programs
•	The reported 2014 S02 emissions by CAIR and ARP sources totaled 3,155,031 tons.
•	Over 33 million S02 allowances were available for compliance under both programs (9 million
vintage 2014 and over 24 million banked from prior years).
•	Just over 3.1 million allowances were deducted for ARP compliance and an additional 2.3 million
allowances were deducted to complete reconciliation for CAIR. After reconciliation for both
programs, over 27.7 million ARP S02 allowances were banked and carried forward to the 2015 ARP
compliance year.
•	All ARP and CAIR S02 facilities were in compliance for both programs in 2014 and held enough
allowances to cover their S02 emissions.
CAIR NOx Annual Program
•	The reported 2014 annual NOx emissions by CAIR sources totaled 1,164,280 tons.
•	All covered facilities were in compliance with the CAIR NOx annual program in 2014 and held enough
allowances to cover their NOx emissions.
Chapter 5: Program Compliance
39
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2014 Program Progress - Clean Air Interstate Rule, Acid Rain Program,
and Former NOx Budget Trading Program
https://www3.epa.gov/airmarkets/progress/reports/index.html
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CAIR NOx Ozone Season Program
•	The reported 2014 ozone season N0X emissions by CAIR sources totaled 448,991 tons.
•	All covered facilities were in compliance with the CAIR N0X ozone season program in 2014 and held
enough allowances to cover their NOx emissions.
More Information
•	Learn more about allowance markets https://www.epa.gov/airmarkets/allowance-markets
•	Air Markets Business Center https://www.epa.gov/airmarkets/business-center
•	Air Markets Program Data (AMPD) https://ampd.epa.gov/ampd/
•	Learn more about emissions trading https://www.epa.gov/emissions-trading-resources
Chapter 5: Program Compliance	40
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2014 Program Progress - Clean Air Interstate Rule, Acid Rain Program,	|	g
and Former NOx Budget Trading Program	\ V\l/ / *
https://www3.epa.gov/airmarkets/progress/reports/iridex.html	pro"*4-
Figures
ARP and CAIR SO, Allowance Reconciliation Summary, 2014
Total Allowances Held (1995-2014 Vintage) 33,203,985
Meld by Affected Facility Accounts
22,486,133
Held by Other Accounts (General
and Non Affected Facility Accounts)
10,717,852
Allowances Deducted for Acid Rain Compliance* 3,132,176


Penalty Allowance Deductions 0



Held by Affected Facility Accounts
19,353,957
Banked Allowances (after ARP Compliance) 30,071,809


Held by Other Accounts (General
and Non Affected Facility Accounts)
10,717,852
Acid Rain Program Allowances Deducted for CAIR 2,289,419
Banked Allowances (after ARP and CAIR) 27,782,390
Held by Affected Facility Accounts
17,064,538
Held by Other Accounts (General
and Non Affected Facility Accounts)
10,717,852
ARP and CAIR S02 Program Compliance Results


Reported emissions (tons)

3,155,031
Compliance issues, rounding, and report resubmission adjustments (tons)

-31,644
emissions not covered by allowances (tons)

0
Additional vintage 2010 2014 allowances deducted for CAIR

2,289,419
Total allowances deducted for emissions (includes some 2 for 1 CAIR
deductions)

5,412,806
Notes:


¦ * include 8,739 allowances deducted from opt-ins for reduced utilization.


• Compliance emissions data may vary from other report sections as a result of variation in rounding conventions, changes due to resubmissions
by sources, or allowance compliance issues at certain units-
• Reconciliation and compliance data are current as of May 2016 and subsequent adjustments or penalties are not reflected.
	Source EPA, 2016
Notes:
•	"Include 8,789 allowances deducted from opt-ins for reduced utilization.
•	Compliance emissions data may vary from other report sections as a result of variation in rounding conventions,
changes due to resubmissions by sources, or allowance compliance issues at certain units.
•	Reconciliation and compliance data are current as of May 2016, and subsequent adjustments of penalties are not
reflected.
Figure 1. ARP and CAIR SO2 Allowance Reconciliation Summary, 2014
Chapters: Program Compliance
41
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2014 Program Progress - Clean Air Interstate Rule, Acid Rain Program,
and Former NOx Budget Trading Program
https://www3.epa.gov/airmarkets/progress/reports/iridex.html
CAIR NO,, Annual Allowance Reconciliation Summary, 2014



Held by Affected Facility Accounts
2,268,483

Total Allowances Held (2009-2014 Vintage) 2.596,619
Held by Other Accounts (General,
State Holding, and Non Affected
Facility Accounts)
328,136
Allowances Deducted for CAIR NQX Annual Trading 1,1 £>4,345
Program


Penalty Allowance Deductions 0




Held by Affected Facility Accounts
1,104,138

Banked Allowances 1,432,274
Held by Other Accounts (General,
State Holding, and Non Affected
Facility Accounts)
328,136
CAIR NOK Annual Program Compliance Results


Reported emissions (tons)

1,164,280
Compliance issues, rounding, and report resubmission adjustments (tons)

65
Emissions not covered by allowances (tons)

0
Total allowances deducted for emissions

1,164,345
Notes:


• Compliance emissions data may vary from other report sections as a result of variation in rounding conventions, changes due to resubmissions by
sources, or allowance compliance issues at certain units.
• Reconciliation and compliance data are current as of May 2016 and subsequent adjustments or penalties are not reflected.



Source EPA, 2016
Notes:
•	Compliance emissions data may vary from other report sections as a result of variation in rounding conventions,
changes due to resubmissions by sources, or allowance compliance issues at certain units.
•	Reconciliation and compliance data are current as of May 2016 and subsequent adjustments of penalties are not
reflected.
Figure 2. CAIR N0X Annual Allowance Reconciliation Summary, 2014
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https://www3.epa.gov/airmarkets/progress/reports/iridex.html
CAIR N0X Ozone Season Allowance Reconciliation Summary, 2014


Held by Affected Facility Accounts 1,051,553

Total Allowances Held (2009-2014 Vintage) 1,269,146
Held by Other Accounts (General, 217,593
State Holding, and Mon Affected
Facility Accounts)
Allowances Deducted for CAIR NO„ Ozone Season 449,28?
Trading Program

Penalty Allowance Deductions 0



Held by Affected Facility Accounts 602,266

Banked Allowances 819,859
Held by Other Accounts (General, 217,593
State Holding, and Non Affected
Facility Accounts)
CAIR NOk Ozone Season Program Compliance Results

Reported emissions (tons)
448,991
Compliance issues, rounding, and report resubmission adjustments (tons)
296
Emissions not covered by allowances (tons)
0
Total allowances deducted for emissions
449,287
Nates:

* Compliance emissions data may vary from other report sections as a result of variation in rounding conventions changes due to resubmissions by
sources, or allowance compliance issues at certain units.
• Reconciliation and compliance data are current as of May 2016 and subsequent adjustments or penalties are not reflected.

Source EPA,. 2016
Notes:
•	Compliance emissions data may vary from other report sections as a result of variation in rounding conventions,
changes due to resubmissions by sources, or allowance compliance issues at certain units.
•	Reconciliation and compliance data are current as of May 2016 and subsequent adjustments of penalties are not
reflected.
Figure 3. CAIR N0X Ozone Season Allowance Reconciliation Summary, 2014
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and Former NOx Budget Trading Program
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Chapter 6: Market Activity
Allowance trading allows sources in cap and trade programs to adopt the most cost-effective strategy to
reduce emissions. Sources that reduce their emissions below the number of allowances they hold may
trade allowances with other sources in their system, sell them to other sources on the open market or
through EPA auctions, or bank them for use in future years.
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 by finding the cheapest emission reductions
across the marketplace.
Analysis and Background Information
Transaction Types and Volumes
Allowance transfer activity includes two types of transfers: EPA transfers to accounts and private
transactions. EPA transfers to accounts include the initial allocation of allowances by states or EPA, as
well as transfers into accounts related to set-asides. This category does not include transfers due to
allowance retirements. Private transactions include all transfers initiated by authorized account
representatives for any compliance or general account purposes.
To help 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
Allowance Markets
The 2014 emissions were below emission budgets for the Acid Rain Program (ARP) and for all three
Clean Air Interstate Rule (CAIR) programs. As a result, CAIR allowance prices were well below the
marginal cost for reductions projected at the time of the final rule, and are subject, in part, to downward
pressure from the available banks of allowances.
Overall, allowance prices in 2014 remained relatively stable until October 23, 2014 when the D.C. Circuit
granted EPA's motion to lift the stay on the Cross-State Air Pollution Rule (CSAPR) and allow it to replace
CAIR starting in 2015. The increased certainty regarding CSAPR implementation and the resulting phase-
out of CAIR, including the future use of CAIR allowances, significantly decreased the value of CAIR
facility).
allowances.
Chapter 6: Market Activity
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and Former NOx Budget Trading Program
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Key Points
Transaction Types and Volumes
•	In 2014, the majority of ARP and CAIR sulfur dioxide (S02) program allowances were traded between
related organizations. In contrast, about one-third of CAIR nitrogen oxides (N0X) ozone season and
CAIR NOx annual program allowance transactions were between unrelated parties (distinct
organizations), often with a broker facilitating the trade.
2014 Allowance Prices
•	ARP* S02 allowance prices averaged less than $1 per ton.
•	CAIR NOx annual program allowances averaged** $50 per ton.
•	CAIR NOx ozone season program allowances averaged** $24 per ton.
* ARP allowances are used for CAIR compliance at a two-to-one ratio, with two ARP allowances
available to cover 1 ton of emissions under CAIR.
** Average spot price was calculated between January and October. All CAIR NOx allowance prices
dropped to $10 per ton after the October 2014 D.C. Circuit decision to lift the stay on the CSAPR.
More Information
•	Learn more about allowance markets https://www.epa.gov/airmarkets/allowance-markets
•	Air Markets Business Center https://www.epa.gov/airmarkets/business-center
•	Air Markets Program Data (AMPD) https://ampd.epa.gov/ampd/
•	Learn more about emissions trading https://www.epa.gov/emissions-trading-resources
Chapter 6: Market Activity
45
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2014 Program Progress - Clean Air Interstate Rule, Acid Rain Program,
and Former NOx Budget Trading Program
https://www3.epa.gov/airmarkets/progress/reports/iridex.html
Figures
2014 Allowance Transfers under CAIR and ARP

Transactions Conducted
in 2014
Allowances Transferred
In 2014
Share of Program's
Allowances Transferred in 2014
ARP and CAIR S02
1,196 transactions
8,111,813 allowances
Distinct Organizations
18%
Programs
Related Organizations
82%
CAIR NO,. Annual
1,064 transactions
700,747 allowances
Distinct Organizations
28%
Program
Related Organizations
72%
CAIR NOx Ozone
863 transactions
251,436 allowances
Distinct Organizations
35%
Season Program
Related Organizations
65%
Notes:
•	Most, but not all, of the transactions are shown above. The actual percentage shares may vary by less than 1% of the total allowances
transferred for each program.
•	Percentages may not add up to 100% due to rounding.
•	ARP allowances are used for CAIR compliance at a two-to-one ratio, with two ARP allowances available to cover 1 ton of emissions under CAIR-
Source EPA, 2016
Notes:
•	Most, but not all, of the transactions are shown above. The actual percentage shares may vary by less than 1% of the
total allowances transferred for each program.
•	Percentages may not add up to 100% due to rounding.
•	ARP allowances are used for CAIR compliance at a two-to-one ratio, with two ARP allowances available to cover 1 ton of
emissions under CAIR.
Figure 1. 2014 Allowance Transfers under CAIR and ARP
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Allowance Spot Price (Prompt Vintage), January-December 2014
70 -
60 -
50 -
| 40-
0}
a
W 30 -
20 -
10 ¦
OCT
MAY
JAN
FEB
MAR
APR
JUN
JUL
AUG
SEP
NOV
DEC
JAN
	ARP SO, 		 CAIR NO* ozone season 	CAIR NO* annual
Notes:
•	Prompt vintage is 1he vintage for the "current" compiiance year.
•	ARP allowances are used few CAIR compliance at a two-to-one ratio, with two ARP allowances available to cover 1 ton of emissions under CAIR.
Source: SNL Financial, 2010
Notes:
Prompt vintage is the vintage for the "current" compliance year.
ARP allowances are used for CAIR compliance at a two-to-one ratio, with two ARP allowances available to cover 1 ton of
emissions under CAIR.
Figure 2. Allowance Spot Price (Prompt Vintage), January-December 2014
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Chapter 7: Ambient Air Quality
The Acid Rain Program (ARP), N0X Budget Trading Program (NBP), and Clean Air Interstate Rule (CAIR)
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 (smog) and particulate matter (soot),
which cause a range of serious health effects and visibility degradation in 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 trends in regional air quality over time
and in different areas.
Analysis and Background Information
Sulfur Dioxide
S02 is one of a group of highly reactive gases known as "oxides of sulfur." 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 ships, and non-road equipment. S02 contributes to the formation of fine particle
pollution (PM2.5) and is linked with a number of adverse health effects on the respiratory system.1 In
addition, particulate sulfates degrade visibility and, because they are typically acidic, can harm
ecosystems when deposited.
Nitrogen Oxides
N0X is 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 is linked with a number of
adverse health 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 NH4NO3, reported as total nitrate, can
also lead to adverse health effects and, when deposited, cause damage to sensitive ecosystems.
Although the ARP, NBP, and CAIR N0X 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.
Key Points
National SO2 Air Quality
• Based on EPA's air trends data, the national average of S02 annual mean ambient concentrations
decreased from 12.1 parts per billion (ppb) to 1.5 ppb (87 percent) between 1980 and 2014.
Sulfur Dioxide and Nitrogen Oxides Trends
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•	The two largest single-year reductions (over 20 percent) occurred in the first year of the ARP,
between 1994 and 1995, and more recently between 2008 and 2009, just prior to the start of the
CAIR S02 program.
Regional Changes in Air Quality
•	Average ambient S02 concentrations declined in the eastern United States following
implementation of the ARP and other emission reduction programs. Regional average
concentrations declined 84 percent from the 1989-1991 to 2012-2014 observation periods.
•	Ambient particulate sulfate concentrations have decreased since the ARP was implemented, with
average concentrations decreasing by 64 to 68 percent in observed regions from 1989-1991 to
2012-2014.
•	Average annual ambient total nitrate concentrations declined 48 percent from 1989-1991 to 2012-
2014 in the eastern United States, with the largest reductions in the Mid-Atlantic and Northeast.
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
•	Learn more about sulfur dioxide (S02) https://www.epa.gov/so2-pollution
•	Learn more about nitrogen oxides (NOx) https://www3.epa.gov/airquality/nitrogenoxides/
•	Learn more about EPA's Clean Air Market Programs https://www.epa.gov/airmarkets/programs
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). 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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Subtopic: Sulfur Dioxide and Nitrogen Oxides Trends
National SO Air Quality Trend, 1980—2014
35
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| 25
20
15
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5 5
8"
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1980	1965	1990	1 995	2000	2005	2010
Average Concentration 90% of sites have concentrations below this line
10% of sites have concentrations below this line
Notes:
• Data baseo on state, beat, and EPA monitoring &les wtoch are located pnmarily in urban areas.
Source: EPA, 2016
Notes:
Data based on state, local, and EPA monitoring sites which are located primarily in urban areas.
Figure 1, National S02 Air Quality Trend, 1980-2014
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Regional Changes in Air Quality
Measurement
Region
Annual
Average,
1989-1991
Annual
Average,
2012-2014
Percent
Change
Number of
Sites
Statistical
Significance
Ambient particulate
sulfate concentration
Mid Atlantic
6.3
2.1
-67
12
***
Midwest
5.8
2.1
-64
9

iMg/m3)
Northeast
3.4
1.1
-68
4


Southeast
5.5
1.9
-65
8
»**
Ambient sulfur
Mid Atlantic
13.0
2.0
-85
12
-frUrtt
dioxide concentration
Midwest
11.0
2.1
-81
9
***
(Hg/m3)
Northeast
5.2
0.7
-86
4


Southeast
5.1
0.7
-86
8
Mnk
Ambient total nitrate
concentration (jjg/m3)
Mid Atlantic
3.3
1.6
-52
12
***
Midwest
4.6
2.6
-43
9
«Hr
Northeast
1.7
0.8
-53
4


Southeast
2.2
1.1
-50
8
#**
Notes:
• Averages are the arithmetic mean of all sites in a region that were present and met the completeness criteria in both averaging periods. Thus, average
concentrations for 1989 to 1991 may differ from past reports.
¦ Statistical significance was determined at the 95 percent confidence level (p <0.05) using Student's t-test. Changes that are not statistically significant may
be unduly influenced by measurements at only a few locations or large variability in measurements.
Source EPA, 2016
Notes:
•	Averages are the arithmetic mean of all sites in a region that were present and met the completeness criteria in both
averaging periods. Thus, average concentrations for 1989 to 1991 may differ from past reports.
•	Statistical significance was determined at the 95 percent confidence level (p <0.05) using Student's t-test. Changes that
are not statistically significant may be unduly influenced by measurements at only a few locations or large variability in
measurements.
Figure 2. Regional Changes in Air Quality
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Ozone
Analysis and Background Infoimation
Ozone pollution forms when N0X and volatile organic compounds (VOCs) react in the presence of
sunlight. Major sources of N0X and VOC emissions include electric power plants, motor vehicles,
solvents, and industrial facilities. Meteorology plays a significant role in ozone (smog) formation and
hot, sunny days are most favorable for ozone production. For ozone, EPA and states typically regulate
N0X emissions during the ozone season (May 1-September 30) when sunlight intensity and
temperatures are highest.
Ozone Standards
In 1979, EPA established the National Ambient Air Quality Standard (NAAQS) for 1-hour ozone at 0.12
parts per million (ppm) (124 ppb), and in 1997, a more stringent daily maximum 8-hour ozone standard
of 84 ppb was finalized, revising the 1979 standard. CAIR was designed to help downwind states in the
eastern United States achieve the 1997 ozone NAAQS; therefore, analyses in this report focus on that
standard. Based on extensive scientific evidence about ozone's effects on public health and welfare, EPA
strengthened the daily maximum 8-hour ozone standard to 75 ppb in March 2008 and further
strengthened the 8-hour NAAQS for ground-level ozone to 70 ppb in October 2015. EPA revoked the 1-
hour ozone standard in 2005 and also recently revoked the 1997 8-hour standard in April 2015.
Regional Trends in Ozone
EPA investigated trends in daily maximum 8-hour ozone concentrations as measured at rural Clean Air
Status and Trends Network (CASTNET) monitoring sites within the CAIR NOx ozone season program
region and in adjacent states. Rural ozone measurements are useful in assessing the impacts on air
quality resulting from regional NOx emission reductions because they are typically less affected by local
sources of NOx (e.g., industrial and mobile) than urban measurements. Reductions in rural ozone
concentrations are largely attributed to reductions in regional NOx emissions and transported ozone.
An Autoregressive Integrated Moving Average (ARIMA) model is an advanced statistical analysis tool
used to determine the trend in regional ozone concentrations since implementation of various programs
geared toward reducing ozone season NOx emissions. The average of the 99th percentile of the daily
maximum 8-hour ozone concentrations measured at CASTNET sites (as described above) was modeled
to show the shift in the highest daily ozone levels. The decrease in the modeled trend is likely due to
actions taken for CAIR compliance however, other factors may include meteorology and changes in
electricity demand.
Meteorologically-Adjusted Daily Maximum 8-Hour Ozone Concentrations
Meteorologically-adjusted ozone trends provide additional insight on the influence of CAIR NOx ozone
season program emission reductions on regional air quality. Daily maximum 8-hour ozone concentration
data from EPA and daily meteorology data from the National Weather Service were retrieved for 81
urban areas and 39 rural CASTNET monitoring sites located in the CAIR NOx ozone season program
region. EPA uses these data in a statistical model to account for the influence of weather on seasonal
average ozone concentrations at each monitoring site.1,2
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Changes in Ozone Nonattainment Areas
The majority of ozone season N0X emission reductions in the power sector that occurred after 2003 are
attributable to the NBP and CAIR. As power sector emissions are an important component of the NOx
emission inventory, it is reasonable to conclude that ozone season NOx emission reduction programs
have significantly contributed to these improvements in ozone air quality. However, because areas
continue to be out of attainment for both the 1997 and 2008 ozone NAAQS, additional NOx ozone
season emission reductions are needed to attain EPA's health-based air quality standards.
As part of an effort to help address the Agency's Clean Air Act (CAA) role to backstop states' obligations
to address the problem of air pollution that is transported across state lines, the EPA issued the Cross-
State Air Pollution Rule (CSAPR) in July 2011. The CSAPR addresses interstate transport of ozone
pollution with respect to the 1997 ozone NAAQS. Additionally, on September 7, 2017, EPA finalized an
update to the CSAPR ozone season program by issuing the CSAPR Update to address interstate transport
of air pollution for the newer 2008 ozone NAAQS.
Key Points
Changes in 1-Hour Ozone during Ozone Season
•	An overall regional reduction in ozone levels was observed between 2000-2002 and 2012-2014,
with a 19 percent reduction in the highest (99th percentile) ozone concentrations in CAIR states.
•	Results demonstrate how NOx emission reduction policies have affected ozone concentrations in the
eastern United States-the region the policies were designed to target.
Trends in Rural Ozone
•	The ARIMA model of rural ozone concentrations shows ozone reductions of 20 ppb (23 percent)
from 1990 to 2014.
•	A significant decrease of modeled ozone concentrations occurred in 2003, following implementation
of the NBP (12 ppb reduction from the previous year). That event was followed by an additional
14 percent (11 ppb) reduction just prior to the start of the CAIR NOx ozone season program in 2009.
Changes in 8-Hour Ozone Concentrations
•	The average reduction in ozone concentrations not adjusted for weather in the CAIR NOx ozone
season program region from 2000-2002 to 2012-2014 was about 8 ppb (15 percent).
•	The average reduction in the meteorologically-adjusted ozone concentrations in the CAIR NOx ozone
season program region from 2000-2002 to 2012-2014 was about 10 ppb (17 percent).
Changes in Ozone Nonattainment Areas
•	Ninety-one of the 113 areas originally designated as nonattainment for the 1997 8-hour ozone
NAAQS (0.08 ppm) are in the eastern United States and are home to about 122 million people.3
These nonattainment areas were designated in 2004 using air quality data from 2001 to 2003.4
Chapter 7: Ambient Air Quality - Ozone
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•	Based on data from 2012 to 2014, 99 percent (90 areas) of the eastern ozone nonattainment areas
now show concentrations below the level of the 1997 standard, while one area continues to show
concentrations above the 1997 standard.
•	Compared with the 2001-2003 period, all 91 areas showed improvement in the 2012-2014 period
toward meeting the 1997 standard.
•	Given that the majority of ozone season NOx emission reductions in the power sector that occurred
after 2003 are attributable to the NBP and CAIR, it is reasonable to conclude that ozone season NOx
emission reduction programs have significantly contributed to these improvements in ozone air
quality.
More Information
•	Clean Air Status and Trends Network (CASTNET) https://www.epa.gov/castnet
•	Air Quality System (AQS) https://www.epa.gov/aqs
•	National Ambient Air Quality Standards (NAAQS) https://www.epa.gov/criteria-air-pollutants
•	Learn more about ozone https://www.epa.gov/ozone-pollution
•	Learn more about nitrogen oxides (NOx) https://www3.epa.gov/airquality/nitrogenoxides/
•	Learn more about Nonattainment Areas https://www3.epa.gov/airquality/greenbook/
•	Learn more about EPA's Clean Air Market Programs https://www.epa.gov/airmarkets/programs
References
1.	Cox, W.M. & Chu, S.H. (1996). Assessment of interannual ozone variation in urban areas from a
climatological perspective. Atmospheric Environment, 30 (16): 2615-2625.
2.	Camalier, L., Cox, W.M., & Dolwick, P. 2007. The effects of meteorology on ozone in urban areas
and their use in assessing ozone trends. Atmospheric Environment, 41(33): 7127-7137.
3.	U.S. Census. (2010).
4.	40 CFR Part 81. Designation of Areas for Air Quality Planning Purposes.
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Figures
Subtopic: Ozone
Percent Change in the Highest Values (99,h percentile) of 1-Hour Ozone
Concentrations during the Ozone Season, 2000-2002 versus 2012-2014



i j . m. I
• •' ¦ ' ft -
©* *
. & "If
- •T* *
'



20
Notes:
¦ Data are from State and LocaJ Air Monitoring Stations (SLAMS) AGS 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.
Source: EPA. 2010
Notes:
Data are from State and Local Air Monitoring Stations (SLAMS) AOS and CASi NEI 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.
Figure 1. Percent Change in the Highest Values (99th percentile) of 1-hour Ozone
Concentrations during the Ozone Season, 2000-2002 versus 2012-2014
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o
®
100
90
SO
70
60
Shift in 8-hour Seasonal Rural Ozone Concentrations
in the CAIR MOx Ozone Season Region, 1990-2014
1990 1992
1994 1996
o Actual
1998
2000 2002 2004 2006 2008
- Predicted ~ 95% Confidence Limits
2010 2012 2014
Notes:
• Ozone concentration data are an average of the 99" percentile of the 8-hour daiity maximum ozone concentrations measured at rural CASTNET sites that meet
completeness criteria and are located in and adjacent Id the CAIR NO* ozone season program region.
Source: EPA, 2010
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 and adjacent to the CAIR NOx ozone
season program region.
Figure 2. Shift in 8-hour Seasonal Rural Ozone Concentrations
in the CAIR NOx Ozone Season Region, 1990-2014
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Seasonal Average of 8-Hour Ozone Concentrations in CAIR States, Unadjusted and =
Adjusted for Weather
80
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ii
ID
I O
1°
l»
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			I						L	
2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010
2011
2012 2013 2014
Unadjusted concentrations
Adjusted concentrations
Notes:
• 8-Hour daily maximum ozone concentration data from EPA's AQ5 and daily meteorology data from the National Weather Service were retrieved for 81 urban areas and 39 rural
CASTNET monitoring sites iocated in the CAIR NO_ 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 «the May 1o September period, few each of the years tram 2000
to 2014. In urban areas wslh mora 1han one monitoring site, the highest observed ozone concentration in Ihe area was used for each day.
Source: EPA, 2016
Notes:
8-Hour daily maximum ozone concentration data from EPA's AQS and daily meteorology data from the National
Weather Service were retrieved for 81 urban areas and 39 rural CASTNET monitoring sites located in the CAIR 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 2014. In urban areas with more than one
monitoring site, the highest observed ozone concentration in the area was used for each day.
Figure 3. Seasonal Average of 8-Hour Ozone Concentrations
in CAIR States, Unadjusted and Adjusted for Weather
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Changes in 1997 Ozone NAAQS Nonattainment Areas in the CAIR Region,
2001-2003 (Original Designations) versus 2012-2014
I | Meets 1997 8-hr ozone NAAQS
(90 areas)
I | Does not meet NAAQS,
improved since original
designation (1 area)
I I CAIR states (controlled for
PM and/or ozone)
Source: EPA, 2010
Figure 4. Changes in 1997 Ozone NAAQS Nonattainment Areas in the CAIR Region,
2001-2003 (Original Designations) versus 2012-2014
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Particulate Matter
Analysis and Background Information
Particulate matter—also known as soot, particle pollution, or PM—is a complex mixture of extremely
small particles and liquid droplets. Particle pollution is made up of a number of components, including
acid-forming nitrate and sulfate compounds, organic compounds, metals, and soil or dust particles. Fine
particles (defined as particulate matter with aerodynamic diameter < 2.5 (j,m, and abbreviated as PM2.5)
can be directly emitted or can form when gases emitted from power plants, industrial sources,
automobiles, and other sources react in the air.
Particle pollution—especially fine particles—contains microscopic solids or liquid droplets so small that
they can get deep into the lungs and cause serious health problems. Numerous scientific studies have
linked particle pollution exposure to a variety of problems, including the following: increased respiratory
symptoms, such as irritation of the airways, coughing, or difficulty breathing; decreased lung function;
aggravated asthma; development of chronic bronchitis; irregular heartbeat; nonfatal heart attacks; and
premature death in people with heart or lung disease.1,2,3
Particulate Matter Standards
The CAA requires EPA to set NAAQS for particle pollution. In 1997, EPA set the first PM standard for fine
particles at 65 micrograms per cubic meter (ng/m3) measured as the three-year average of the 98th
percentile for 24-hour exposure, and at 15 ng/m3 for annual exposure measured as the three-year
annual mean. EPA revised the air quality standards for particle pollution in 2006, tightening the 24-hour
fine particle standard to 35 ng/m3 and retaining the annual fine particle standard at 15 ng/m3. In
December 2012, EPA strengthened the annual fine particle standard to 12 ng/m3.
CAIR was promulgated to help downwind states in the eastern United States achieve the 1997 annual
average PM2.5 NAAQS; therefore, analyses in this report focus on that standard.
Changes in PMzsNonattainment Areas
The majority of S02 and annual NOx emission reductions in the power sector that occurred after 2003
are attributable to the ARP, NBP, and CAIR. 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. However, because
areas continue to be out of attainment for the 1997 PM2.5 NAAQS, additional S02 and annual NOx
emission reductions are needed to attain EPA's health-based air quality standards.
As part of an effort to help support states' obligations to address the problem of air pollution that is
transported across state lines and help address the Agency's Clean Air Act role in backstopping these
obligations, the EPA issued the Cross-State Air Pollution Rule (CSAPR) in July 2011. The CSAPR, which
began in January 2015, addresses interstate transport of fine particle pollution with respect to the 1997
PM2.5 NAAQS.
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Key Points
PM Seasonal Trends
•	Average PM2.5 concentration data were assessed from 195 urban Air Quality System (AQS) areas
located in the CAIR S02 and N0X annual 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 annual average PM2.5 concentration has decreased by about 37 percent in both the warm and
cool season months between 2000 and 2014.
Changes in PM2.5 Nonattainment
•	Thirty-six of the 39 designated nonattainment areas for the 1997 annual average PM2.5 standard are
in the eastern United States and are home to about 75 million people.4,5 The nonattainment areas
were set in January 2005 using 2001 to 2003 data.
•	Based on data gathered from 2012 to 2014, 32 of these original eastern areas show concentrations
below the level of the 1997 PM2.5 standard (15.0 ng/m3), indicating improvements in PM2.5 air
quality. Four areas have incomplete data.
•	Given that the majority of power sector S02 and annual NOx emission reductions occurring after
2003 are attributable to the ARP, NBP, and CAIR, it is reasonable to conclude that these emission
reduction programs have significantly contributed to these improvements in PM2.5 air quality.
More Information
•	Clean Air Status and Trends Network (CASTNET) https://www.epa.gov/castnet
•	Air Quality System (AQS) https://www.epa.gov/aqs
•	National Ambient Air Quality Standards https://www.epa.gov/criteria-air-pollutants
•	Learn more about particulate matter (PM) https://www.epa.gov/pm-pollution
•	Learn more about sulfur dioxide (S02) https://www.epa.gov/so2-pollution
•	Learn more about nitrogen oxides (NOx) https://www3.epa.gov/airquality/nitrogenoxides/
•	Learn more about Nonattainment Areas https://www3.epa.gov/airquality/greenbook/
•	Learn more about EPA's Clean Air Market Programs https://www.epa.gov/airmarkets/programs
References
1.	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.
2.	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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3.	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.
4.	40 CFR Part 81. Designation of Areas for Air Quality Planning Purposes.
5.	U.S. Census. (2010).
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Figures
Subtopic: Particulate Matter
PM25 Seasonal Trends, 2000—2014
2000
2001
2002 2003 2004 2005 2006 2007
2008
2009 2010
2011
2012 2013
2014
— Cool season — Warm season
Notes:
•	For a PMis mentoring site to be included in the trends analy&s. 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) afl four quarterly mean values had lo be va&d for a given year (i.e., meet criterion #1), and 3) af 15 years of ste-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 quartedy mean values. Annual "warm* season mean values tor each site-
year were computed as the average of 1he second and third quarterly mean values. For a given year, all of the seasonal mean values tor the monitoring sites located m the CAIR region
were then averaged together to obt&.n a single year (composite) seasonal mean value.
Source: EPA, 2016
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 15 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
CAIR region were then averaged together to obtain a single year (composite) seasonal mean value.
Figure 1. PM2.5 Seasonal Trends, 2000-2014
Chapter 7: Ambient Air Quality - Particulate Matter
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I I Meet 1997 annual PMIC
NAAQS (32 areas)
| | Incomplete data for
2012-2014 (4 areas)
t~~| CAIR states (controlled for
PM and/or ozone)
Source: EPA, 2010
Changes in PMZ5 Nonattainment Areas in the CAIR Region,
2001-2003 (Original Designations) versus 2012-2014
Figure 2. Changes in PM2.5 Nonattainment Areas in the CAIR Region,
2001-2003 (Original Designations) versus 2012-2014
Chapter 7: Ambient Air Quality - Particulate Matter
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Chapter 8: Acid Deposition
Acid deposition, commonly known as "acid rain," is a broad term referring to the mixture of wet and dry
deposition from the atmosphere containing higher than normal amounts of sulfuric acids and nitric
acids. 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.
Analysis and Background Information
Acid Deposition
As S02 and N0X gases react in the atmosphere with water, oxygen, and other chemicals, they form acidic
compounds that get deposited to the ground in the form of wet and dry acid deposition.
Monitoring network data show significant improvements in the primary acid deposition indicators. For
example, wet sulfate deposition (sulfate that falls to the earth through rain, snow, and other
precipitation) has decreased since the implementation of the Acid Rain Program (ARP) in much of the
Ohio River Valley and Northeastern United States. 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+)
concentration, have 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 CAIR sources
contribute to changes in air concentrations and deposition of nitrogen.
Monitoring Networks
The Clean Air Status and Trends Network (CASTNET) provides long-term monitoring of regional air
quality to determine trends in atmospheric concentrations and deposition of nitrogen, sulfur, and ozone
in order to evaluate the effectiveness of national and regional air pollution control programs. CASTNET
now operates more than 90 regional sites throughout the contiguous United States, Alaska, and Canada.
Sites are located in areas where urban influences are minimal.
The National Atmospheric Deposition Program/National Trends Network (NADP/NTN) is a nationwide,
long-term network tracking the chemistry of precipitation. The NADP/NTN provides concentration and
wet deposition data on hydrogen ion (acidity as pH), sulfate, nitrate, ammonium, chloride, and base
cations. The NADP/NTN has grown to more than 250 sites spanning the United States, Canada, Puerto
Rico, and the Virgin Islands.
Together, these complementary networks provide long-term data needed to estimate spatial patterns
and temporal trends in total deposition.
Chapter 8: Acid Deposition
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Key Points
Wet Sulfate Deposition
•	The Northeast and Mid-Atlantic have shown the greatest improvement with an overall 64 percent
reduction in wet sulfate deposition in the eastern United States from 1989-1991 to 2012-2014.
•	A decrease in both S02 emissions from sources in the Ohio River Valley and 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 33 percent in the Mid-Atlantic and
Northeast but decreased only 12 percent in the Midwest from 1989-1991 to 2012-2014.
•	Reductions in nitrogen deposition recorded since the early 1990s have been less pronounced than
those for sulfur. Emission changes from other source categories (e.g., mobile sources and
manufacturing) contribute to changes in air concentrations and deposition of nitrogen.
Regional Trends in Deposition
•	Between 1989-1991 and 2012-2014, the Northeast and Mid-Atlantic experienced the largest
reductions in wet sulfate deposition, 68 percent and 70 percent, respectively.
•	The reduction in total sulfur deposition (wet plus dry) has been of similar magnitude to that of wet
deposition with an overall average reduction of 72 percent from 1989-1991 to 2012-2014.
•	Decreases in dry and total inorganic nitrogen deposition have generally been greater than that of
wet deposition, with average reductions of 56 percent and 34 percent, respectively. In contrast, wet
deposition from inorganic nitrate reduced by an average of 21 percent from 1989-1991 to 2012-
More Information
•	Learn more about acid rain https://www.epa.gov/acidrain
•	Clean Air Status and Trends Network (CASTNET) https://epa.gov/castnet
•	National Atmospheric Deposition Program (NADP) http://nadp.isws.illinois.edu/
References
1. Government of Canada, Environment Canada. (2015). Canada-United States Air Quality
Agreement Progress Report 2014. ISSN: 1910-5223: Cat. No.: En85-1/2014E-PDF.
2014.
Chapter 8: Acid Deposition
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Figures
Three-Year Wet Sulfate Deposition
1989-1991	2012-2014
Wet S04
(kg/ha)
Source: EPA, 2016
Figure 1. Three-Year Wet Sulfate Deposition
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Figure 2. Three-Year Wet Inorganic Nitrogen Deposition
Three-Year Wet Inorganic Nitrogen Deposition
Source: EPA. 2016
1989-1991
Inorganic
Nitrogen
(kg/ha)
I 0.0
1.0
2.0
- 3.0
4.0
5.0
6.0
7.0
8.0
9.0
>10,0
2012-2014
Chapters: Acid Deposition
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Regional Trends in Deposition


Annual
Annual



Measurement
Region
Average.
1989-1991
Average,
2012-2014
Percent
Change
Number of
Sites
Statistical
Significance
Dry inorganic nitrogen
deposition (kg-N/ha)
Mid Atlantic
2.5
1.0
-60
12

Midwest
2.4
1.3
-46
9
*r**
Northeast
1.3
0.4
-69
4


Southeast
1.7
0.8
-53
8

Dry sulfur deposition
(kg-S/ha)
Mid Atlantic
7.0
1.1
-84
12
***
Midwest
6.5
1.4
-78
9


Northeast
2.6
0.4
-85
4


Southeast
3.1
0.6
-81
8
•M
Total inorganic
nitrogen deposition
(kg-N/ha)
Mid Atlantic
8.8
5.2
-41
12

Midwest
3.6
6.4
-26
9
M*
Northeast
6.6
4.2
-36
4

Southeast
6.4
4.4
-31
8

Total sulfur deposition
(kg-S/ha)
Mid Atlantic
16.0
4.0
-75
12

Midwest
15.0
4.0
-73
9

Northeast
9.5
2.6
-73
4


Southeast
10.4
3.2
-69
8

Wet nitrogen
deposition from
Mid Atlantic
6.2
4.1
-34
11
#*•#
Midwest
5.8
5.1
-12
27

inorganic nitrogen
Northeast
5.7
3.9
-32
16

(kg-N/ha)
Southeast
4.3
3.5
-19
22
Mr*
Wet sulfur deposition
from sulfate (kg-S/ha)
Mid Atlantic
9.2
2.8
-70
11

Midwest
7.1
2.8
-59
27
Urtrt
Northeast
7.5
2.4
-68
16


Southeast
5.9
2.3
-61
22

Notes:
•	Averages are the arithmetic mean of all sites in a region that were present and met the completeness criteria in both averaging periods. Thus, average
concentrations for 1989 to 1991 may differ from past reports.
•	Total deposition is estimated from raw measurement data, not rounded, and may not equal the sum of dry and wet deposition.
•	Statistical significance was determined at the 95 percent confidence level (p <0.05) using Student's t-test- Changes that are not statistically significant may
be unduly influenced by measurements at only a few locations or large variability in measurements.	„ 		
Source EPA, 2016
Notes:
Averages are the arithmetic mean of ail sites in a region that were present and met the completeness
criteria in both averaging periods. Thus, average concentrations for 1989 to 1991 may differ from past
reports.
Total deposition is estimated from raw measurement data, not rounded, and may not equal the sum of
dry and wet deposition.
Statistical significance was determined at the 95 percent confidence level (p <0.05) using Student's t-
test. Changes that are not statistically significant may be unduly influenced by measurements at only a
few locations or large variability in measurements.
Figure 3. Regional Trends in Deposition
Chapters: Acid Deposition
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Chapter 9: Ecosystem Response
Acidic deposition resulting from sulfur dioxide (S02) and nitrogen oxides (N0X) emissions may negatively
affect the biological health of lakes, streams, 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 acidic deposition levels of sulfur and nitrogen resulting from
S02 and N0X emission reductions may protect aquatic resources.
Analysis and Background Information
Acidified Surface Water Trends
Acidified surface water mobilizes toxic forms of aluminum from soils, particularly in clay rich soils,
harming fish, other aquatic life, and wildlife. 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. Aquatic ecosystem recovery is indicated by increasing trends in ANC and
base cations and decreasing trends in sulfate and nitrate concentrations in surface waters. 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 and leach base cations and toxic forms of aluminum from soils.
•	Nitrate has the same potential as sulfate 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, with the weathering
of base cations from the underlying rocks, soil age, and vegetation community.
Highly weathered soils of the central Appalachians are able to store deposited sulfate, such that the
decrease in acidic deposition has not yet resulted in lower sulfate concentrations in many of the
monitored streams. However, as long-term sulfate deposition exhausts the soil's ability to store
additional sulfate, a decreasing proportion of the deposited sulfate will be retained in the soil and an
increasing proportion is exported to surface waters. Thus, sulfate concentrations in some streams in this
region are not changing or are still increasing despite reduced sulfate deposition.1
Chapter 9: Ecosystem Response - Ecosystem Health	69
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Monitoring Networks
In collaboration with other federal and state agencies and universities, EPA administers two monitoring
programs that provide information on the impacts of acidic deposition on otherwise pristine lakes and
streams: the Temporally Integrated Monitoring of Ecosystems (TIME) and the Long-term Monitoring
(LTM) programs. These programs are designed to track changes in surface water chemistry in the four
regions sensitive to acid rain in the eastern United States: New England, the Adirondack Mountains, the
Northern Appalachian Plateau, and the central Appalachians (the Valley, Ridge, and Blue Ridge
Provinces).
Key Points
Regional Trends in Water Quality
•	Between 1990 and 2014, significant improving trends in sulfate concentrations are found at all LTM
lake and stream monitoring sites in New England, the Adirondacks, and the Catskill mountains.
•	On the other hand, between 2013 and 2014, streams in the central Appalachian region have
experienced mixed results. Only 26 percent of monitored streams show lower sulfate
concentrations (and statistically significant trends), while 14 percent show increased sulfate
concentrations.
•	Nitrate concentrations and trends are highly variable and many sites do not show improving trends
between 1990 and 2014, despite reductions in NOx emissions and inorganic nitrogen deposition.
•	In 2014, levels of ANC, a key indicator of ecosystem recovery, have increased significantly from 1990
in lake and stream sites in the Adirondack Mountains, New England, and the Catskill mountains.
More Information
•	Learn more about surface water monitoring at EPA http://www.epa.gov/airmarkets/monitoring-
surface-water-chemistry
•	Learn more about acid rain http://www.epa.gov/acidrain/
References
1. Burns, D.A., Lynch, J. A., Cosby, B.J., Fenn, M.E., & Baron, J.S. (2011). National Acid Precipitation
Assessment Program Report to Congress 2011: An Integrated Assessment U.S. EPA, National
Science and Technology Council, Washington, D.C.: 114 p.
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Figures
Subtopic: Ecosystem Health
Zoom
Long-term Monitoring Program Sites and Trends, 1990-2014
(hover over a site for more information)
• TIME lakes • TIME streams • LTM lakes • LTM streams
Notes:
- Trends are significant at the 95 percent confidence imrterva) (p < 0-05).
» Base cations are calculated as the sum of calcium, magnesium, potassium, and sodium ions.
' Trends are determined by multivariate Ntam-Kendafl tests.
Source: EPA, 2016
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.
Figure 1. Long-term Monitoring Program Sites and Trends, 1990-2014
Chapter 9: Ecosystem Response - Ecosystem Health
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Regional Trends in Sulfate, Nitrate, ANC, and Base Cations
at Long-term Monitoring Sites, 1990-2014
Region
Water Bodies 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
38 lakes
in NY*
100%
42%
87%
92%
New England
26 lakes
in ME and VT
100%
21%
58%
67%
Catskills*
4 streams
in NY
100%
0%
50%
100%
Central
Appalachians
66 streams
in VA
26%
52%
14%
23%
Notes:
•	Trends are statistically significant at the 95 percent confidence interval (p < 0.05).
•	Base cations are calculated as the sum of calcium |Ca), magnesium (Mg)r potassium (K), and sodium (Na) ions.
•	Trends are determined by multivariate Mann-Kendall tests.
•	'Trends are based on a different subset of 38 lakes in New York than the results presented in previous reports.
	Source £FAr 2016
Notes:
•	Trends are statistically significant at the 95 percent confidence interval (p < 0.05).
•	Base cations are calculated as the sum of calcium (Ca), magnesium (Mg), potassium (K), and sodium (Na) ions.
•	Trends are determined by multivariate Mann-Kendall tests.
•	Trends are based on a different subset of 38 lakes in New York than the results presented in previous reports.
Figure 2. Regional Trends in Sulfate, Nitrate, ANC, and Base Cations
at Long-term Monitoring Sites, 1990-2014
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Chapter 9: Ecosystem Response - Ecosystem Health
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Critical Loads Analysis
Analysis and Background Information
A critical loads analysis is an assessment tool used to provide a quantitative estimate of whether acid
deposition levels resulting from S02 and N0X emission reductions are sufficient to protect aquatic
biological resources. If acidic deposition is less than the calculated critical load, harmful ecological
effects (e.g., reduced reproductive success, stunted growth, loss of biological diversity) are not expected
to occur, and ecosystems damaged by past exposure are expected to eventually recover.1
Lake and stream waters having an ANC value greater than 50 neq/L are classified as having a moderately
healthy aquatic biological community; therefore, this ANC concentration is often used as a goal for
ecological protection of surface waters affected by acidic deposition. In this analysis, the critical load
represents the amount of sulfur and nitrogen that could be deposited annually to a lake or stream and
its watershed and still support a moderately healthy ecosystem (i.e., having an ANC greater than 50
pieq/L). Surface water samples from 6,001 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
Key Points
Critical Loads and Exceedances
•	For the period from 2012 to 2014, 16 percent of all studied lakes and streams were shown to still
receive levels of combined total sulfur and nitrogen deposition exceeding their calculated critical
load. This is a 52 percent improvement over the period from 2000 to 2002 when 34 percent of all
studied lakes and streams exceeded their calculated critical load.
•	Emission reductions achieved between 2000 and 2014 are anticipated to contribute to broad
surface water improvements and increased aquatic ecosystem protection across the five regions
along the Appalachian Mountains.
•	Based on this modeled approach, in 2014, current sulfur and nitrogen deposition loadings still
exceed levels required for recovery of many lakes and streams, indicating that additional emission
reductions would be necessary for some acid-sensitive aquatic ecosystems along the Appalachian
Mountains to recover and be protected from acid deposition.
More Information
•	Learn more about surface water monitoring at EPA http://www.epa.gov/airmarkets/monitoring-
surface-water-chemistry
•	National Acid Precipitation Assessment Program (NAPAP) Report to Congress
http://ny.water.usgs.gov/projects/NAPAP/
Chapter 9: Ecosystem Response - Critical Load 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.
Chapter 9: Ecosystem Response - Critical Load Analysis	74
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Figures
Subtopic: Critical Loads Analysis
Lake and Stream Exceedances of Estimated Critical Loads for Total Nitrogen and =
Sulfur Deposition, 2000-2002 versus 2012-2014
Zoom
Sites that never exceeded the critical load • Sites that exceed the critical load
• Sites that now do not exceed critical load compared to 2000-2002
Note:
*	Surface water samples from the represented lakes and streams were compiled from surface monitoring programs, such as National Surface Water Survey |NSWS), Er/vironmervtal
Monitoring and Assessment Program (EMAP), Wadeable Stream Assessment , National Lake Assessment (NLA). Temporally Integrated Monitoring of Ecosystems (TIME). Long-
term Moriloring |LTM>, and other water quality monitc*irg programs.
•	Steady state exceedances calculated in units of meqi'rrftyr.
Source: EPA, 2016
Notes:
Surface water samples from the represented lakes and streams were compiled 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 9: Ecosystem Response - Critical Load Analysis
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Figure 1. Lake and Stream Exceedances of Estimated Critical Loads for Total
Nitrogen and Sulfur Deposition, 2000-2002 versus 2012-2014
Critical Load Exceedances by Region
Region
Number
of Water
Bodies
Modeled
Water Bodies in Exceedance of Critical Load
Percent
Reduction
2000-2002
2012-2014
Number
of Sites
Percent
of Sites
Number
of Sites
Percent
of Sites
New England
(ME, NH.VT, Rl, CT)
2,027
461
23%
214
11%
54%
Adirondack
Mountains (NY)
315
144
46%
67
21%
53%
Northern
Mid-Atlantic
(PA, NY, NJ)
1,166
279
24%
116
10%
58%
Southern
Mid-Atlantic
(VA. WV, MD)
1,597
856
54%
447
28%
48%
Southern
Appalachian
Mountains
(NC, TN, SC, GA.AL)
S96
286
32%
133
15%
53%
Total Units
6,001
2,026
34%
977
16%
52%
Notes:
•	Surface water samples from the represented lakes and streams were compiled 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/m'/yr.
Source EPAf 2016
Notes:
•	Surface water samples from the represented lakes arid streams were compiled 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.
Figure 2. Critical Load Exceedances by Region
Chapter 9: Ecosystem Response - Critical Load Analysis
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