Acid Rain Program 

2004 Progress Report 

10 YEARS OF A CHIEVEMENT 

Acid Rain Program 

2004 Progress Report 

CONTENTS 

Summary ....................................................................................................2 


Origins of the Acid Rain Program ................................................................3 


SO2 Emission Reductions ............................................................................4 


SO2 Allowance Market ................................................................................6 


SO2 Program Compliance ...........................................................................8 


NOx Emission Reductions............................................................................9 


Emissions Monitoring and Reporting .........................................................11 


Status and Trends in Air Quality, Acid Deposition, and Ecological Effects ...13 


Understanding the Monitoring Networks ...................................................14 


Air Quality ................................................................................................15 


Acid Deposition ........................................................................................17 


Recovery of Acidified Lakes and Streams....................................................19 


Quantifying Costs and Benefits of the Acid Rain Program...........................21 


National Actions for Further Emission Reductions—2005 Clean Air Rules....23 


Online Information, Data, and Resources ............................Inside back cover 


EPA 430-R-05-012 

Clean Air Markets Division 

Office of Air and Radiation 

U.S. Environmental Protection Agency 

October 2005 
E PA publishes an annual report to update the public 

on compliance with the Acid Rain Program, the 

status of implementation, and progress toward 

achieving environmental goals. Because this report builds 

upon and updates previous reports, those who are new to 

the program might find it helpful to first read some background material on the EPA Web site at www.epa.gov/ 

airmarkets/arp. 

The Acid Rain Program 2004 Progress Report updates 

data reported in previous years, specifically: 

• 	 Sulfur dioxide (SO2) emissions, allowance market 

information, and program compliance. 

• 	 Nitrogen oxides (NOx) emissions and program 

compliance. 

• 	 Status and trends in acid deposition, air quality, and 

ecological effects. 

• 	 Benefits and costs of the Acid Rain Program. 

This report marks the 10th year of the Acid Rain 

Program by highlighting some of the major developments 

that have occurred over that time, including advances in 

emission controls, improvements in program management, 

and electronic delivery of services, and maturity of the 

program’s allowance trading market. 

For more information on the Acid Rain Program, 

including additional information on SO2 and NOx emissions, acid deposition monitoring, environmental effects of 

acid deposition, and detailed unit-level emissions data, 

please visit EPA’s Clean Air Markets Web site at 

www.epa.gov/airmarkets. 
2 ✧ Acid Rain Program, 2004 Progress Report 

Summary 


Sulfur dioxide (SO2) and nitrogen oxides (NOx) are the key pollutants in the formation of acid rain.These pollutants also contribute 

to the formation of fine particles (sulfates and nitrates) that are associated with significant human health effects and regional haze. 

Additionally, NOx combines with volatile organic compounds 

(VOCs) to form ground-level ozone (smog) and nitrates that are 

transported and deposited at environmentally detrimental levels in 

parts of the country. In the United States, the electric power industry 

accounts for nearly 70 percent of total annual SO2 emissions and 

slightly more than 20 percent of total annual NOx emissions. 

The Acid Rain Program was created to implement Title IV of 

the 1990 Clean Air Act Amendments.The purpose of Title IV is to 

reduce the adverse effects of acid deposition through reductions in 

annual emissions of SO2 and NOx by 10 million tons and by 2 

million tons below projected levels, respectively. 

Since the start of the Acid Rain Program in 1995, the lower SO2 

and NOx emission levels from the power sector have contributed to 

significant air quality and environmental and human health improvements.The 2004 compliance year marked the 10th year of the program. During that period, the Acid Rain Program has: 

• 	Reduced SO2 emissions by over 5 million tons from 1990 levels, 

or about 34 percent of total emissions from the power sector. 

Compared to 1980 levels, SO2 emissions from power plants have 

dropped by 7 million tons, or more than 40 percent. 

• 	Cut NOx emissions by about 3 million tons from 1990 levels, so 

that emissions in 2004 were less than half the level anticipated 

without the program. Other efforts, such as the NOx Budget 

Trading Program in the eastern United States, also contributed 

significantly to this reduction. 

• 	 Led to significant cuts in acid deposition, including reductions in 

sulfate deposition of about 36 percent in some regions of the 

United States and improvements in environmental indicators, 

such as fewer acidic lakes. 

• 	 Provided the most complete and accurate emission data ever 

developed under a federal air pollution control program and 

made that data available and accessible by using comprehensive 

electronic data reporting and Web-based tools for agencies, 

researchers, affected sources, and the public. 

• 	 Served as a leader in delivering e-government, automating 

administrative processes, reducing paper use, and providing online 

systems for doing business with EPA. 

• 	 Resulted in nearly 100 percent compliance through rigorous 

emissions monitoring, allowance tracking, and an automatic, 

Acid Rain Program 

1995–2005: 

From Grand Policy 

Experiment to 

Demonstrated 

Results 

Congress created the 

Acid Rain Program’s SO2 

emissions cap-and-trade 

approach in 1990 amid 

uncertainty that the innovative, market-based 

control program would 

work. Since the program’s implementation, 

air pollution control 

experts from a wide 

range of perspectives 

agree that it is one of the 

most successful environmental programs in U.S. 

history. The program 

serves as a model for a 

new generation of regional and national control 

programs, such as the 

2005 Clean Air Interstate 

Rule (CAIR). A 2005 

study estimates that in 

2010, the Acid Rain 

Program’s annual benefits will be approximately 

$122 billion (2000$), at 

an annual cost of about 

$3 billion—a 40-to-1 

benefit-to-cost ratio. 
Acid Rain Program, 2004 Progress Report ✧ 3 

easily understood penalty system for noncompliance. Flexibility in compliance strategies 

reduced implementation costs. 

Building on the Acid Rain Program model, EPA 

promulgated the Clean Air Interstate Rule (CAIR) 

in March 2005, to address transport of fine particles 

and ozone in the eastern United States, the Clean 

Air Mercury Rule (CAMR) to reduce nationwide 

mercury emissions from power plants, and the Clean 

Air Visibility Rule (CAVR) to improve visibility in 

national parks and wilderness areas. 

Origins of the Acid Rain Program 


Acid deposition, more commonly known as 

acid rain, occurs when emissions of SO2 and NOx 

react with water, oxygen, and oxidants in the 

atmosphere to form various acidic compounds. 

Prevailing winds transport the acidic compounds 

hundreds of miles, often across state and national 

borders, where they impair air quality and damage 

public health, acidify lakes and streams, harm sensitive forest and coastal ecosystems, degrade visibility, 

and accelerate the decay of building materials. 

The Acid Rain Program, established under 

Title IV of the 1990 Clean Air Act Amendments, 

requires major reductions of SO2 and NOx emissions from the electric power industry.The SO2 

program sets a permanent cap on the total amount 

of SO2 that may be emitted by electric power 

plants in the contiguous United 

power plants regulated under the Acid Rain 

Program to select their own methods of compliance. Currently, one allowance provides a limited 

authorization to emit one ton of SO2.The Clean 

Air Act allocated allowances to regulated units 

based on historic fuel consumption and specific 

emission rates prior to the start of the program.The 

total allowances allocated for each year equal the 

SO2 emissions cap.The program encouraged early 

reductions by allowing sources to bank unused 

allowances in one year and use them in a later year. 

The program uses a more traditional approach 

to achieve NOx emission reductions. Rate-based 

limits apply to most of the coal-fired electric utility 

boilers subject to the Acid Rain Program.The program does not establish a cap on NOx emissions; 

States.The program is phased in, Figure 1. Trends in Electricity Generation and Emissions from 

with the 2010 SO2 cap set at Electric Power Sources 

about one-half of the 1980 emis40% 

sions from the power sector. 

As seen in Figure 1, emissions 30% 

of both SO2 and NOx have fallen 20% 

significantly at the same time as 10% 

combustion of fossil fuel (coal, 

oil, or natural gas), measured as 0% 

“heat input,” for electricity gener- -10% 

ation, has increased.The increase 

in electricity generation has not -20% 

Heat Input 

SO Emissions 2 

Electricity Net Generation 

Average Retail Price 

NOx Emissions of Electricity

Percent Change 

only been achieved at lower 

emission levels, it has occurred 

while the real retail price of electricity has fallen. 

Using a market-based 

cap and trade mechanism to 

reduce SO2 emissions allows 

flexibility for individual fossil 

fuel-burning units at electric 

-30% 

-40% 

-50% 

1990 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 

Year 

Sources: EPA (heat input and emissions) and Energy Information Administration (electricity 

generation and price values). 

Note: Heat input and emissions data reflect Acid Rain Program units. Generation reflects all 

fossil fuel-fired electricity-only plants in the United States. Retail price reflects full national 

values for the electricity-generating sector. 
4 ✧ Acid Rain Program, 2004 Progress Report 

SO2 Emission 

Reductions from 

Acid Rain Program 

Sources: A Decade 

of Cost-Effective 

Progress 

In 1995, the first year of 

implementation, SO2 

emissions decreased by 24 

percent—nearly 4 million 

tons—from 1990 levels. 

During the past decade, 

SO2 emissions dropped an 

additional 13 percent from 

1995 levels despite a 20 

percent increase in utilization (based on heat input). 

In 2004, SO2 emissions 

from all Acid Rain Program 

units totaled 10.3 million 

tons, a 34 percent 

decrease from 1990 levels 

(15.7 million tons). 

Until SO2 allowance prices 

began to increase in 2004 

in anticipation of EPA’s 

2005 Clean Air Interstate 

Rule (CAIR), allowance 

prices generally remained 

under $200/ton, well 

below expected control 

costs for the program. 

instead, it is designed to achieve a 2 million ton reduction from projected 2000 NOx emission levels without implementation of Title IV. 

The Acid Rain Program is composed of two phases for SO2 and 

NOx. Phase I applied primarily to the largest coal-fired electric generation sources from 1995 through 1999 for SO2 and from 1996 

through 1999 for NOx. Phase II for both pollutants began in 2000. 

In 2004, the SO2 Phase II requirements applied to 3,391 operating 

units; the Phase II NOx requirements applied to 989 operating units 

that burned coal from 1990 to 1995. 

SO2 Emission Reductions 

Electric power generation is by far the largest single source of 

SO2 emissions in the United States, accounting for nearly 70 percent 

of total SO2 emissions nationwide.

1 

In 2004, 3,391 operating units were subject to the SO2 provisions 

of the Acid Rain Program.As shown in Figure 2,Acid Rain Program 

sources have reduced annual SO2 emissions by 40 percent compared to 

1980 levels and 34 percent compared to 1990 levels. Reductions in 

SO2 emissions from other sources not affected by the Acid Rain 

Program, including industrial and commercial boilers and the metals 

and refining industries, and use of cleaner fuels in residential and commercial burners, have also contributed to an even greater decline (45 

percent) in annual SO2 emissions from all sources since 1980 (see 

www.epa.gov/airtrends). 

For 2004, EPA allocated a total of 9.5 million SO2 allowances under 

the Acid Rain Program.Adding these allowances to the 7.6 million 

unused allowances carried over (or banked) from prior years, there were 

17.1 million allowances available for use in 2004. Sources emitted 10.3 

million tons of SO2 in 2004, somewhat more than the allowances allocated for the year but far less than the total allowable level (see Figure 3).2 

The number of banked allowances dropped from 7.58 million 

available for 2004 compliance, to 6.86 million available for compliance in 2005 and future years.This reduction amounts to 9.5 percent 

of the total bank. Over time, the bank is expected to continue to be 

depleted as sources use banked allowances to comply with the stringent Phase II requirements. In 2010, the annual total number of 

allowances allocated drops to 8.95 million (about half of the emissions from the power industry in 1980) and remains statutorily fixed 

at that annual level permanently. Figure 4 explains in more detail the 

origin of the allowances that were available for use in 2004, and 

Figure 9 (on page 8) shows how those allowances were used. 

1 National Emission Inventory 2002: www.epa.gov/ttn/chief/trends/index.html. 

2 	Detailed emissions data for Acid Rain Program sources are available on the Data and Maps 

portion of EPA's Clean Air Markets Web site at www.epa.gov/airmarkets. 
Acid Rain Program, 2004 Progress Report ✧ 5 

Emissions (million tons) Emissions (million tons) 

Figure 2: SO2 Emissions under the Acid Rain 

Program 

20 

18 

16 

14 

12 

10 

8 

6 

4 

2 

0 

9.4 9.3 8.7 

5.3 5.4 5.5 5.3 4.9 

16.1 

17.3 

15.7 

11.9 12.5 13.0 13.1 12.5 

11.2 10.6 10.2 10.6 10.3 

Phase I Sources 

Phase II Sources 

All Sources 

Allowances allocated 

for that year 

1980 1985 1990 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 

Source: EPA Year 

Figure 3: SO2 Emissions and the Allowance 

Bank, 1995–2004 

25 

20 

15 

10 

5 

0 

1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 

8.7 

11.7 

13.5 

15.0 

16.6 

21.6 

19.9 

18.8 18.2 17.1 

Allowances Allocated that Year 

Unused Allowances from Previous 

Year (bank) 

Actual Emissions from affected sources 

Source: EPA Year 

The states with the highest-emitting 

sources in 1990 have seen the greatest SO2 

reductions during the Acid Rain Program. 

Most of these states are upwind of the areas 

the Acid Rain Program was designed to protect, and reductions have resulted in important 

environmental and health benefits over a large 

regional scale (see Figure 5 on page 6). In 

addition, the states that reduced emission from 

1990 to 2004 had total annual reductions of 

approximately 5.9 million tons, while the states 

that had increased emissions—largely attributable to growth and not increases in emission 

Figure 4: Origin of 2004 Allowable SO2 

Emission Levels 

Type of 

Allowance 

Allocation 

Number 

of SO2 

Allowances 

Explanation 

of Allowance 

Allocation Type 

Initial 

Allocation 

9,191,897 Initial allocation is the 

number of allowances 

granted to units* 

based on the product 

of their historic utilization and emission 

rates specified in the 

Clean Air Act. 

Allowance 

Auction 

250,000 The allowance 

Auction provides 

allowances to the 

market that were set 

aside in a Special 

Allowance Reserve 

when the initial 

allowance allocation 

was made. 

Opt-in 

Allowances 

99,188 Opt-in allowances are 

provided to units 

entering the program 

voluntarily. There 

were 11 opt-in units 

in 2004. 

Total 2004 

Allocation 

9,541,085 

Total 

Banked 

Allowances 

7,574,959 Banked allowances 

are those allowances 

accrued in a unit’s 

account from previous years, which can 

be used for compliance in 2004 or any 

future year. 

Total 2004 

Allowable 

Emissions 

17,116,044 

Source: EPA 

*Note: In this report, the term “unit” means a fossil fuel-fired combustor 

that serves a generator that provides electricity for sale. The vast majority 

of SO2 emissions affected by the program come from coal-fired generation units, but oil and natural gas units are also included in the program. 
6 ✧ Acid Rain Program, 2004 Progress Report 

rates—had much smaller annual 

increases (a total increase of 

approximately 430,000 tons). 

For 32 states and the District 

of Columbia, annual SO2 emissions in 2004 were lower than 

emissions in 1990.Among these 

states, 13 decreased their annual 

emissions by more than 100,000 

tons between 1990 and 2004: 

Alabama, Florida, Georgia, 

Illinois, Indiana, Kentucky, 

Massachusetts, Missouri, New 

York, Ohio, Pennsylvania, 

Tennessee, and West Virginia.The 

states with the greatest reductions 

were in the Midwest and include 

Ohio (1.1 million tons reduced), 

Illinois, Indiana, and Missouri, 

each of which reduced over 

500,000 tons. 

Figure 5: State-by-State SO2 Emissions Levels, 1990–2004 

Emissions in 1990 

Phase I Average 1995–1999 

Emissions in 2004 

Source: EPA 

Scale: Largest bar equals 2.2 million tons of emissions in Ohio, 1990 

SO2 Allowance Market 

The allowance trading mechanism enables Acid 

Rain Program sources to pursue a variety of compliance options, while the cap on SO2 emissions 

ensures that reductions are made and maintained 

over time. Some sources have opted to reduce 

their SO2 emissions below the level of their 

allowance allocation in order to bank their 

allowances for use in future years or to sell them. 

Other sources have been able to postpone or 

reduce expenditures for control by purchasing 

Figure 6: SO2 Allowance Prices 

$800 

$700 

$600 

$500 

$400 

$300 

$200 

$100 

$0 

1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 

Year Source: Cantor Fitzgerald 

allowances from sources that controlled below 

their allowance allocation level.The allowance 

prices end up reflecting these flexible compliance 

decisions. Economists refer to this as the marginal 

cost of compliance—the cost of reducing the next 

ton of SO2 emitted from the power sector. 

The price of an allowance increased sharply 

during 2004, ending the year at about $700 after 

beginning the year at about $215 (see Figure 6). 

The increase primarily occurred because of EPA’s 

Clean Air Interstate Rule (CAIR). CAIR requires 

further SO2 reductions from sources in many eastern U.S. states beginning in 2010, and the market 

has already begun to factor the marginal cost of 

future compliance with CAIR and the future 

value of banked allowances today. 

In 2004, nearly 20,000 private allowance transfers affecting roughly 15.3 million allowances (of 

past, current, and future vintages) were recorded in 

the EPA Allowance Tracking System (ATS). Of the 

allowances transferred, 7.5 million (49 percent) 

were transferred in economically significant 

Nominal Price 
Acid Rain Program, 2004 Progress Report ✧ 7 

transactions (i.e., between economically unrelated 

parties).The majority of the allowances transferred 

in economically significant transactions were 

acquired by power companies. Figure 7 (on page 8) 

shows the annual volume of SO2 allowances transferred under the Acid Rain Program (excluding 

allocations, retirements, and other transfers by EPA) 

since official recording of transfers began in 1994. 

Figure 8 (on page 8) shows the cumulative volume of SO2 allowances transferred under the Acid 

Rain Program.The figure differentiates between 

allowances transferred in private transactions and 

those annually allocated and transferred to sources’ 

accounts by EPA. Nearly 270 million allowances 

have been transferred since 1994, with about 68 

percent of those transfers submitted by authorized 

account representatives. In December 2001, parties 

began to use a system developed by EPA to allow 

transfers to occur online. In 2004, account holders 

registered about 93 percent of all private allowance 

transfers through EPA’s online transfer system.3 

3 All official allowance transactions are posted and updated daily on www.epa.gov/airmarkets. 

Then and Now—The Evolving Market for Acid Rain Program SO2 Allowances 

Since the inception of the Acid Rain Program, traders in utilities and brokerages have seen considerable developments in the SO2 allowance market. Changes in fuel supply, trading processes, 

electronic data transfer, market participants, economic and business conditions, weather, EPA 

regulations and settlements, and tax laws have all influenced the market’s first decade. Informal 

discussions with market participants provided anecdotal evidence of several changes, including: 

✧ 	 Early trades required considerable legal advice, cost as much as $5 per ton in brokerage 

fees, and took months to complete. With standardized transaction agreements and contract forms, one broker noted that transaction fees have dropped to $0.50 per ton and 

trades typically take one or two weeks. 

✧ 	 In 1995, utilities tended to engage in simple trades to cover their needs. By 2000, energy 

marketers had joined in speculative trading and introduced instruments like options and 

vintage year swaps. In 2002, some traders observe that reaction to the dissolution of 

Enron temporarily reversed the trend toward a larger, more complex market. Recently, 

banks and hedge funds have brought back speculative trading, and two trading systems 

(the New York Mercantile Exchange [NYMEX] and the Chicago Climate Exchange [CCX]) 

have created futures markets for allowances. 

✧ 	 Traders note that improved access to allowance and emission data, such as through 

EPA’s Data and Maps Web site, has provided increasingly accessible, up-to-date information, providing a firm foundation for well-informed allowance transactions. 

✧ 	 Initially, utilities banked allowances and prices fell based on the relatively low-cost compliance 

option of using low-sulfur coal from Wyoming’s Powder River Basin. The additional reductions required under CAIR have already begun to influence market prices for SO2 allowances. 
8 ✧ Acid Rain Program, 2004 Progress Report 

Figure 7: SO2 Allowances Transferred under the Figure 8: Cumulative SO2 Allowances 

Acid Rain Program Transferred (through 2004) 

15 

20 

25 

30 

Millions of Allowances

10 

250 

200 

150 

100 

50 

5 

1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 

0 

Between Economically Unrelated Organizations 

Between Economically Related Organizations 

9.2 

16.7 

8.2 

15.2 

13.5 

18.7 

25.0 

22.5 21.4 

16.5 15.3 

Millions of Allowances 

300 

0 

EPA Transfers to Account 

Private Transactions 

1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 Year 

Source: EPA Year Source: EPA 

SO2 Program Compliance 

A total of nearly 10.3 million allowances were does not hold enough allowances in its unit 

deducted from sources’ accounts in 2004 to cover account to cover its annual SO2 emissions has 

emissions. Figure 9 displays these allowance deduc- “excess emissions” and must pay an automatic 

tions, as well as the remaining banked allowances penalty.Title IV set a penalty of $2,000 per ton in 

from 1995 through 2004. 1990, which has been adjusted annually for inflaAs in previous years, compliance with the Acid tion; the 2004 penalty was $2,963 per ton.The 

Rain Program continues to be extraordinarily owners of the four units out of compliance in 

high—nearly 100 percent. In 2004, four units out 2004 were assessed a penalty of approximately $1.4 

of 3,391 were out of compliance.A source that million for emitting 465 tons of SO2 in excess of 

the allowances held in their accounts. 

Figure 9: SO2 Allowance Reconciliation Summary, 2004 

Total Allowances Held (1995-2004 vintages)4 17,116,044 

Unit Accounts 13,610,501 

General Accounts5 3,505,543 

Allowances Deducted for Emissions6 

Penalty Allowance Deductions (2005 Vintage) 

10,259,771 

465 

Banked Allowances 6,856,273 

Unit Accounts 3,350,730 

General Accounts5 3,505,543 

Source: EPA 

4 As of March 1, 2004, the Allowance Transfer Deadline, the point in time at which unit accounts are frozen and after which no transfers of 

1995 through 2004 allowances will be recorded.The freeze on these accounts is removed when annual reconciliation is complete.The total 

held in the ATS accounts equals the number of 2004 allowances allocated (see Figure 4 on page 5) plus the number of banked allowances. 

5 General accounts can be established in the ATS by any utility, individual, or other organization. 

6 Includes 212 allowances deducted from opt-in sources for reduced utilization. 
Acid Rain Program, 2004 Progress Report ✧ 9 

NOx Emission Reductions 


Title IV of the 1990 Clean Air Act 

Amendments requires NOx emission reductions 

for certain coal-fired units. Unlike the SO2 program, Congress applied rate-based emission limits 

based on a unit’s boiler type to achieve NOx 

reductions (see Figure 10).The NOx emission rate 

is expressed as pounds per unit of heat input 

(lbs/mmBtu) to the boiler. Owners can meet the 

NOx limits for each individual unit or meet the 

average of groups of units. 

The NOx program seeks to attain a 2 million 

ton annual reduction from all Acid Rain Program 

sources relative to the NOx emission levels that 

were projected to occur in 2000 (8.1 million tons) 

absent the Acid Rain Program.This goal was first 

realized in 2000, and has been met every year 

thereafter, including 2004. Figure 11 (on page 10) 

shows that NOx emissions from all Acid Rain 

Program sources were 3.8 million tons in 2004. 

This level is more than 4 million tons less than the 

projected level in 2000 without the Acid Rain 

Program, or more than double the Title IV NOx 

emissions reduction objective.These reductions 

have been achieved while the amount of fuel 

burned to produce electricity, as measured by heat 

input, has increased 34 percent since 1990.While 

the Acid Rain Program was responsible for a large 

portion of these annual NOx reductions, other programs, such as the Ozone Transport Commission 

(OTC) NOx Budget Trading Program and the 

EPA’s NOx State Implementation Plan (SIP) Call, 

both of which are seasonal, regional NOx programs, also contributed significantly to the NOx 

reductions achieved by emitting sources in 2004. 

As with SO2, the states with the highest NOx 

emitting sources in 1990 tended to see the greatest 

power plant NOx emission reductions (see Figure 

12 on page 10).The sum of reductions in the 38 

states and the District of Columbia. that had lower 

annual NOx emissions in 2004 than in 1990 was 

approximately 2.7 million tons, while the sum of 

increases in the 10 states that had higher annual 

NOx emissions in 2004 than in 1990 was much 

smaller, less than 63,000 tons. Eight of the 11 states 

with NOx emission decreases of more than 

100,000 tons were in the Ohio River Basin. 

Figure 10: Number of NOx-Affected Title IV Units by Boiler Type 

Coal-Fired Boiler Type Title IV Standard 

Emission Limit 

(lb/mmBtu) 

Number of Units 

Phase I Group 1 Tangentially-fired 0.45 132 

Phase I Group 1 Dry Bottom, Wall-fired 0.50 116 

Phase II Group 1 Tangentially-fired 0.40 301 

Phase II Group 1 Dry Bottom, Wall-fired 0.46 298 

Cell Burners 0.68 37 

Cyclones >155 MW 0.86 54 

Wet Bottom >65 MW 0.84 24 

Vertically-fired 0.80 27 

Total 989 
10 ✧ Acid Rain Program, 2004 Progress Report 

NOx emissions (millions) 

Figure 11: NOx Emission Trends for Acid Rain 


Program Units 1990 to 2004 


7 
 6.7 

6.1 5.9 6.0 6.0 6 


5.5 5.4 5.4 5.5 5.3 

5.5 

NOx Program affected sources 

Title IV sources not affected by 

NOx Program 

4.8 

5.1 

5 


4.5 

4.7 

4.1 

4.5 

4.0 

4.2

4 


3.8 

3.8 

3 


2 


1 


0 


1990 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 


3.4 

Year 

Source: EPA 

Note: The sharp decline in emissions observed since 1999 reflects not 

only the Phase II Acid Rain Program NOx requirements, but also seasonal reductions from May to September that began in nine northeastern U.S. states and D.C. in 1999 and 11 additional states under the 

NOx SIP Call beginning in 2004 (see the shaded states in Figure 12). 

New Hampshire participated in the northeastern U.S. program through 

2002, but does not participate in the NOx SIP Call program. 

Figure 12: State-by-State NOx Emission Levels 


for All Acid Rain Program Sources 1990 to 2004 


Scale: Largest bar equals 500,000 tons of emissions in Ohio, 1990 

Emissions in 1990 

Phase I Average 1996–1999 

Emissions in 2004 

2004 NOx SIP Call States 

Source: EPA 

Sources Achieved 100 Percent NOx Compliance in 2004, Using a 

Variety of NOx Compliance Plan Options 

Standard Limitation. A unit with a standard limit meets the applicable individual NOx limit prescribed for its boiler type under 40 CFR 76.5, 76.6, or 76.7 (116 units used this option in 2004). 

Early Election. Phase II Group 1 NOx affected units could meet a less stringent Phase I NOx 

limit beginning in 1997, three years before 2000, when they would normally become subject to 

an Acid Rain NOx limit. In return for accepting a NOx limit three years earlier than would normally be required, an early election unit does not become subject to the more stringent Phase II 

NOx limit until 2008 (273 units used this option in 2004). 

Emissions Averaging. Many companies have their units meet their NOx emission reduction 

requirements by choosing to become subject to a group NOx limit, rather than by meeting individual NOx limits for each unit. The group limit is established at the end of each calendar year, and 

the group rate for the units must be less than or equal to the Btu-weighted group rate units would 

have had if each had emitted at their standard limit rate (620 units used this option in 2004). 

Alternative Emission Limitation (AEL). A utility can petition for a less stringent AEL if it properly installs and operates the NOx emissions reduction technology prescribed for that boiler, but 

is unable to meet its standard limit. EPA determines whether an AEL is warranted based on 

analyses of emission data and information about the NOx control equipment (21 units used 

this option in 2004). 

Note: Unit counts exclude units with a Retired Unit Exemption. Also, some units used multiple compliance options. Ten units under an emissions averaging plan also were covered by an AEL, and 31 units were under both an emissions averaging and early election plan. 
Acid Rain Program, 2004 Progress Report ✧ 11 

Then and Now: Advances in NOx Control 

Since Congress enacted the Acid Rain Program in 1990, the electric power industry has made 

significant innovations and advances in reducing NOx emissions. The Acid Rain Program 

served as the impetus for some of these changes, but other programs, such as EPA’s 1998 

NOx SIP Call, have led to many of the advances. Some highlights include: 

✧ 	 Boiler optimization. Boiler optimization modeling systems manipulate multiple control 

parameters simultaneously in order to meet a unit’s specific operational needs and emission reduction goals. Sources have shown that optimization is capable of reducing NOx 

emissions by between 13 and 24 percent, while maintaining or increasing boiler efficiency 

and significantly reducing fuel costs. In addition, optimization and NOx reductions in 

units with selective catalytic reduction systems (SCRs) can lower ammonia usage and 

extend catalyst life, resulting in lower operational costs. 

✧ 	Advanced combustion controls. The design of low-NOx burner (LNB) emission control 

technologies has improved significantly since 1995, leading to lower NOx emission rates. 

The average NOx emission rate from boilers utilizing LNB technology in 2003 was 

between 35 and 60 percent lower than the average emission rate from LNB units in 1995. 

✧ 	Application of SCR to coal-fired boilers. In 1995, there were significant doubts in the 

electric power industry about the application of SCR technology to U.S. coal-fired boilers, 

particularly because of high-sulfur fuel interfering with catalyst performance. With the 

reductions required under the 1998 NOx SIP Call, the industry has moved to resolve those 

issues, and by the end of 2004, over 130 coal-fired boilers in the United States had 

installed SCRs (primarily for NOx SIP Call compliance) and were able to achieve sustained 

emission rates as low as 0.03 lbs/mmBtu. 

Emissions Monitoring and Reporting 

The Acid Rain Program requires program completeness, high quality, and integrity of the 

participants to measure, record, and report emis- emission data. CEMS and approved alternatives are 

sions using continuous emission monitoring sys- a cornerstone of the Acid Rain Program’s accounttems (CEMS) or an approved alternative measure- ability and transparency. 

ment method. Since the program’s inception in The emission monitoring requirements are 

1995, emissions have been continuously monitored found in 40 CFR Part 75. In addition to the Acid 

and reported by sources, verified and recorded by Rain Program, these provisions are also required for 

EPA, and provided to the public through EPA’s 

participation in the NOx Budget Trading Program, Web site.All affected sources report hourly emis- a NOx trading program used by many eastern states 

sion data in electronic reports (submitted quarter- in response to EPA’s 1998 NOx SIP Call, and will 

ly), and EPA conducts automated software audits be used in the future to implement two new rules 

that perform rigorous checks to ensure the 

promulgated in 2005, CAIR and CAMR. 
12 	✧ Acid Rain Program, 2004 Progress Report 

Advances in Emissions and Allowance Transfer Reporting 

✧ 	At the start of the Acid Rain Program, sources used a combination of paper forms 

and floppy disks. The program required submission of emission data on floppy disks, 

and other source information management activities, such as monitoring plan information, allowance transfer, and certificates of representation, were all originally 

addressed through paper forms. 

✧ 	 This approach required manual review and entry for paper submissions and individual file uploads for emission data. EPA feedback on submission issues involved individual letters to sources. 

✧ 	Over time, EPA moved to electronic transfer of information: 

- Monitoring plans moved primarily to electronic submission as part of the quarterly reporting process. EPA released Monitoring Data Checking (MDC) software 

that allowed sources to enter, analyze, print, and export electronic monitoring 

plans. EPA uses MDC to conduct electronic audits of submittals and provide 

automated feedback to sources. 

- Through the Emissions Tracking System file transfer protocol (ETS-FTP), EPA 

moved to direct, secure electronic transfer of quarterly reports from a source’s 

computer to EPA’s mainframe system. EPA then was able to provide instant automated feedback to sources concerning issues with submitted emission data. 

-	 In 2001, an Online Allowance Tracking System enabled direct Internet recording 

for allowance trades. 

✧ 	 Now the Online Allowance Tracking System is integrated with an enhanced Clean Air 

Markets Division Business System (CBS) and offers online allowance trading as well 

as online options for other account and source information management activities. 

✧ 	 Public access to information has advanced dramatically. Early access was through 

paper compliance reports, and then individual unit data files that were difficult to use. Now, detailed unit, facility, state, and national emissions 

and other data for ARP sources is available from EPA’s Data 

and Maps Web site (http://cfpub.epa.gov/gdm/). 

This site provides a combination of easy to access 

“quick” reports and highly flexible, custom 

“query” reports. 

✧ 	 EPA is in the process of designing a comprehensive Emissions Collection and 

Monitoring Plan System (ECMPS) to cover 

all aspects of secure reporting of emissions, monitoring plans, and quality assurance data. 
Acid Rain Program, 2004 Progress Report ✧ 13 

Status and Trends in Air Quality, Acid Deposition, 

and Ecological Effects 

The emission reductions achieved under the fication of fresh water lakes and streams, improveAcid Rain Program have led to important envi- ments in visibility, and reduced risk to forests, 

ronmental and public health benefits.These materials, and structures. Figure 13 shows the 

include improvements in air quality with signifi- regional changes in many of these key variables 

cant benefits to human health, reductions in acid linked to the Acid Rain Program’s SO2 and NOx 

deposition, the beginnings of recovery from acidi- emission reductions. 

Figure 13: Regional Changes in Air Quality and Deposition of Sulfur and Nitrogen 

(1989 to 1991 versus 2002 to 2004) 

Measurement Unit Region Average* Percent 

Change** 1989–1991 2002–2004 

Wet sulfate deposition kg/ha Mid-Atlantic 

Midwest 

Northeast 

Southeast 

27 

23 

23 

18 

20 

16 

14 

15 

-24 

-32 

-36 

-19 

Wet sulfate concentration mg/L Mid-Atlantic 

Midwest 

Northeast 

Southeast 

2.4 

2.3 

1.9 

1.3 

1.6 

1.5 

1.2 

1.0 

-33 

-32 

-35 

-23 

Ambient sulfur dioxide 

concentration 

μg/m3 Mid-Atlantic 

Midwest 

Northeast 

Southeast 

13 

10 

6.8 

5.2 

7.9 

5.7 

3.1 

3.2 

-37 

-46 

-54 

-39 

Ambient sulfate concentration μg/m3 Mid-Atlantic 

Midwest 

Northeast 

Southeast 

6.4 

5.6 

3.9 

5.4 

4.6 

3.8 

2.6 

4.0 

-27 

-33 

-33 

-26 

Wet inorganic nitrogen 

deposition 

kg/ha Mid-Atlantic 

Midwest 

Northeast 

Southeast 

5.9 

6.0 

5.3 

4.3 

5.5 

5.7 

4.5 

4.3 

-8 

-4 

-16 

0 

Wet nitrate concentration mg/L Mid-Atlantic 

Midwest 

Northeast 

Southeast 

1.5 

1.4 

1.3 

0.8 

1.1 

1.3 

1.0 

0.7 

-28 

-12 

-22 

-9 

Ambient nitrate concentration μg/m3 Mid-Atlantic 

Midwest 

Northeast 

Southeast 

0.9 

2.1 

0.4 

0.6 

0.9 

1.8 

0.5 

0.7 

-3 

-11 

27 

14 

Total ambient 

nitrate concentration 

(nitrate + nitric acid) 

μg/m3 Mid-Atlantic 

Midwest 

Northeast 

Southeast 

3.5 

4.0 

2.0 

2.2 

2.9 

3.5 

1.8 

2.0 

-15 

-13 

-7 

-6 

Source: CASTNET and NADP/NTN 


*Measurement data are reported as two significant digits and reflect an updated rounding convention from last year’s report. 


**Percent change is estimated from raw measurement data, not rounded; some of the measurement data used to calculate percentages may be at or 


below detection limits. 

14 ✧ Acid Rain Program, 2004 Progress Report 

Understanding the Monitoring Networks 


To evaluate the impact of emission reductions 

on the environment, scientists and policymakers 

use data collected from long-term national monitoring networks such as the Clean Air Status and 

Trends Network (CASTNET) and the National 

Atmospheric Deposition Program/National Trends 

Network (NADP/NTN).These complementary, 

long-term monitoring networks provide information on a variety of indicators necessary for tracking temporal and spatial trends in regional air quality and acid deposition (see Figure 14). 

CASTNET provides atmospheric data on the 

dry deposition component of total acid deposition, 

ground-level ozone, and other forms of atmospheric pollution. Established in 1987, CASTNET now 

consists of more than 80 sites across the United 

States. EPA’s Office of Air and Radiation operates 

most of the monitoring stations; the National Park 

Service (NPS) funds and operates approximately 30 

stations in cooperation with EPA. Many CASTNET sites are approaching a continuous 20-year 

data record, reflecting EPA’s commitment to longterm environmental monitoring. Public access to 

CASTNET data are available through the Clean 

Air Markets Web site at www.epa.gov/airmarkets. 

NADP/NTN is a nationwide, long-term network 

tracking the chemistry of precipitation. NADP/NTN 

offers data on hydrogen (acidity as pH), sulfate, nitrate, 

ammonium, chloride, and base cations.The network is 

a cooperative effort involving many groups, including 

the State Agricultural Experiment Stations, U.S. 

Geological Survey, U.S. Department of Agriculture, 

EPA, NPS, the National Oceanic and Atmospheric 

Administration (NOAA), and other governmental and 

private entities. NADP/NTN has grown from 22 stations at the end of 1978 to more than 250 sites spanning the continental United States,Alaska, Puerto 

Rico,and the Virgin Islands. 

While CASTNET provides some ambient air 

quality data, EPA also uses data from other ambient monitoring networks, including the State and 

Local Air Monitoring Stations and National Air 

Monitoring Stations (SLAMS/NAMS).These networks are used to document National Ambient Air 

Quality Standards (NAAQS) attainment and show 

trends in ambient air quality over time. 

Figure 14: Air Quality and Acid Deposition Measurements 


Chemicals Why are these measured by the networks? 

SO2 Sulfur Dioxide Indicator of ambient air quality; measured in dry monitoring networks; major 

precursor to acid deposition 

SO4 

2­ Ionic Sulfates, 

Particulate Sulfates 

Indicators of ambient air quality and sulfur deposition; regional transport; 

correlated with sulfur dioxide emissions; measured in wet and dry monitoring 

networks 

NO3­ Ionic Nitrates, 

Particulate Nitrates 

Indicators of ambient air quality and nitrogen deposition; correlated with 

NOx emissions; measured in wet and dry monitoring networks 

HNO3 Nitric Acid Strong acidic compound; main component of dry nitrogen deposition; measured in dry monitoring networks 

NH4 

+ Ionic Ammonium, 

Particulate Ammonium 

Indicators of ambient air quality and nitrogen deposition; associated with 

production of fine particles; aerosol ammonium is associated with sulfate 

ion; can play a role neutralizing atmospheric acidic species; measured in wet 

and dry monitoring networks 

H+ Ionic Hydrogen Indicator of acidity in precipitation; measured in wet deposition monitoring 

networks 

Ca2 

+ 

Mg2 

+ 

K+ 

Na+ 

Calcium 

Magnesium 

Potassium 

Sodium 

These base cations are indicators of the ability to neutralize acids in precipitation; also play an important role in plant nutrition and soil productivity 
Acid Rain Program, 2004 Progress Report ✧ 15 

Air Quality 

Data collected from monitoring networks 

show that the decline in SO2 emissions from the 

power industry has improved air quality.

7 Based on 

EPA’s latest air emissions trends data located at 

www.epa.gov/airtrends/index.html, the national 

composite average of SO2 annual mean ambient concentrations decreased 49 percent between 1990 and 

2004 as shown in Figure 15.The largest single-year 

reduction (21 percent) occurred in the first year of 

the Acid Rain Program, between 1994 and 1995. 

These trends are consistent with the ambient 

trends observed in the CASTNET network. 

During the late 1990s, following implementation of 

Phase I of the Acid Rain Program, dramatic 

regional improvements in SO2 and ambient sulfate 

concentrations were observed at CASTNET sites 

throughout the eastern United States, due to the 

large reductions in SO2 emissions from Acid Rain 

Program sources.Analyses of regional monitoring 

data from CASTNET show the geographic pattern 

of SO2 and airborne sulfate in the eastern United 

States.Three-year mean annual concentrations of 

SO2 and sulfate from CASTNET long-term monitoring sites are compared from 1989 through 1991 

and 2002 through 2004 in both tabular form and 

graphically in maps (see Figure 13 on page 13 and 

Figures 16a through 17b on page 16). 

The map in Figure 16a shows that from 1989 

through 1991, prior to implementation of Phase I 

of the Acid Rain Program, the highest ambient 

concentrations of SO2 in the East were observed 

in western Pennsylvania and along the Ohio River 

Valley. Figure 16b indicates a significant decline in 

those concentrations in nearly all affected areas. 

Before the Acid Rain Program, in 1989 

through 1991, the highest ambient sulfate concentrations, greater than 7 μg/m3

, were observed in 

western Pennsylvania, along the Ohio River Valley, 

and in northern Alabama. Most of the eastern 

United States experienced annual ambient sulfate 

concentrations greater than 5 μg/m3

. Like SO2 

Concentration, ppm 

Figure 15: SO2 Air Quality, 1990–2004 


(Based on Annual Arithmetic Average) 


0.04

19901991 19921993 19941995199619971998199920002001200220032004 

National Standard 

90% of sites have concentrations below this line 

10% of sites have concentrations below this line 

Average 

334 Sites 

0.03 

0.02 

0.01 

0.00 

Source: EPA air emission trends, www.epa.gov/airtrends/2005/ 

econ-emissions.html 

concentrations, ambient sulfate concentrations have 

decreased since the program was implemented, 

with average concentrations decreasing approximately 30 percent in all regions of the East. Both 

the size of the affected region and magnitude of 

the highest concentrations have dramatically 

declined, with the largest decreases observed along 

the Ohio River Valley (see Figures 17a and 17b). 

Although the Acid Rain Program has met its 

NOx reduction targets, emissions from other sources 

(such as motor vehicles and agriculture) have led to 

increased ambient nitrate concentration in some areas 

of the country (see Figure 13 on page 13). NOx levels in some areas can also be affected by emissions 

transported via air currents over wide regions.8 In 

2004, reduced NOx emissions from power plants 

under the NOx Budget Trading Program led to more 

significant region-specific improvements in some 

indicators than have been seen in previous years. For 

instance, total annual mean ambient nitrate concentrations (nitric acid plus particulate nitrate) for 2002 

through 2004 have decreased in the Mid-Atlantic 

and Midwest by about 15 percent from the annual 

mean concentration in 1989 through 1991 (see 

Figures 18a and 18b on page 17).While these 

improvements may be partly attributed to added 

NOx controls installed for compliance with the NOx 

SIP Call, the findings at this time are not conclusive. 

7 It should be noted that there has not been a violation of the SO2 standard at any of the monitoring sites since 2000. 

8 See the EPA Office of Transportation and Air Quality Web site at www.epa.gov/otaq for information on recent rules to reduce NOx emissions from mobile sources.Additional NOx reductions are occurring as a result of the NOx Budget Trading Program. See EPA's August 

2005 report, Evaluating Ozone Control Programs in the Eastern United States: Focus on the NOx Budget Trading Program, 2004, at 

www.epa.gov/airtrends/2005/ozonenbp.pdf, which discusses these NOx reduction efforts. 
16 ✧ Acid Rain Program, 2004 Progress Report 

Figure 16a: Annual Mean Ambient Sulfur Figure 16b: Annual Mean Ambient Sulfur 

Dioxide Concentration, 1989 through 1991 Dioxide Concentration, 2002 through 2004 

SO2 

(�g/m3) 

– 0 

– 2 

– 4 

– 6 

– 8 

– 10 

– 12 

– 14 

– 16 

– 18 

–> 20 Source: CASTNET 

Figure 17a: Annual Mean Ambient Sulfate 

Concentration, 1989 through 1991 

SO2 

(�g/m3) 

– 0 

– 2 

– 4 

– 6 

– 8 

– 10 

– 12 

– 14 

– 16 

– 18 

–> 20 

Source: CASTNET 

Figure 17b: Annual Mean Ambient Sulfate 

Concentration, 2002 through 2004 

SO4

2­

(�g/m3) 

– 1 

– 2 

– 3 

– 4 

– 5 

– 6 

– 7 

– >8 

Source: CASTNET 

SO4

2­

( g/m3 � )

– 1 

– 2 

– 3 

– 4 

– 5 

– 6 

– 7 

– >8 

Source: CASTNET 
Acid Rain Program, 2004 Progress Report ✧ 17 

Figure 18a: Annual Mean Total Ambient Nitrate Figure 18b: Annual Mean Total Ambient Nitrate 

Concentration, 1989 through 1991 Concentration, 2002 through 2004 

Total NO3 

(�g/m3) 

– 0.0 

– 1.0 

– 2.0 

– 3.0 

– 4.0 

– 5.0 

– >6.0 

Source: CASTNET 

Total NO3 

(�g/m3) 

– 0.0 

– 1.0 

– 2.0 

– 3.0 

– 4.0 

– 5.0 

– >6.0 

Source: CASTNET 

The CASTNET maps in this report represent ambient concentrations for the eastern United States only. During the 

early years of CASTNET (1989 to 1991), monitoring coverage was limited to the East with only a handful of sites in 

the West, which were located primarily in National Park Service-Class I areas. Today, EPA, together with its partners 

such as NPS, has added many sites to the network, which now consists of more than 80 sites across the country. 

Acid Deposition 

NADP/NTN monitoring data show significant 

improvements in some deposition indicators. For 

example, wet sulfate deposition—sulfate that falls 

to the earth through rain, snow, and fog—has 

decreased since the Acid Rain Program was implemented with some of the greatest reductions 

occurring in the Mid-Appalachian region, including Maryland, New York,West Virginia,Virginia, 

and most of Pennsylvania.Wet sulfate deposition 

decreased throughout the early 1990s in much of 

the Ohio River Valley and northeastern United 

States. Other less dramatic reductions have been 

observed across much of New England, portions of 

the southern Appalachian Mountains and in some 

areas of the Midwest.Average decreases in wet 

deposition of sulfate range from 36 percent in the 

Northeast to 19 percent in the Southeast (see 

Figure 13 on page 13, and Figures 19a, and 19b on 

page 18). 

Since 1991, wet sulfate concentrations have 

decreased significantly as well, with average levels 

decreasing 35 percent in the Northeast, 33 percent 

in the Mid-Atlantic, and 32 percent in the 

Midwest.A strong correlation between large scale 

SO2 emission reductions and large reductions in 

sulfate concentrations in precipitation has been 

noted in the Northeast, one of the areas most 

affected by acid deposition. 

A principal reason for reduced concentrations 

of sulfate in precipitation in the Northeast is a 

reduction in the long-range transport of sulfate 
f

f

f

r

r

f

r

18 ✧ Acid Rain Program, 2004 Progress Report 

from emission sources located in the Ohio River 

Valley.The reductions in sulfate documented in the 

Northeast, particularly across New England and 

portions of NewYork, were also affected by SO2 

emission reductions in eastern Canada. NADP data 

indicate that similar reductions in precipitation 

acidity, expressed as hydrogen ion (H+) concentrations, occurred concurrently with sulfate reductions, but have not decreased as dramatically due to 

a simultaneous decline in acid-neutralizing base 

cations, which act to buffer acidity. 

Reductions in nitrogen deposition recorded 

since the early 1990s have been less dramatic than 

Figure 19a: Annual Mean Wet Sulfate 

Deposition 1989 through 1991 

those for sulfur.As noted earlier, emission trends 

from source categories other than Acid Rain 

Program sources significantly affect air concentrations and deposition of nitrogen. Inorganic nitrogen deposition decreased modestly in the MidAtlantic and Northeast (averaging 8 to 16 percent) 

but remained virtually unchanged in other regions 

(see Figures 20a and 20b).Wet nitrate concentrations have dropped significantly in the MidAtlantic and Northeast regions, but are not tied to 

precipitation (see Figure 13 on page 13). Modest 

reductions of about 10 percent have occurred in 

the Midwest and Southeast. 

Figure 19b: Annual Mean Wet Sulfate 

Deposition 2002 through 2004 

W

Source: National Atmospheric Deposition Program 

Figure 20a: Annual Mean Wet Inorganic 

Nitrogen Deposition 1989 through 1991 

Source: National Atmospheric Deposition Program 

Figure 20b: Annual Mean Wet Inorganic 

Nitrogen Deposition 2002 through 2004 

Source: National Atmospheric Deposition Program Source: National Atmospheric Deposition Program 

Note: Dots on maps represent monitoring sites 
Acid Rain Program, 2004 Progress Report ✧ 19 

Recovery of 

Acidified Lakes 

and Streams 

Over the past 25 years, the 

effect of acid deposition on lakes 

and streams has been the focus 

of much research, particularly in 

areas of the eastern United States 

that are both sensitive to acid 

deposition and receiving significant levels over time.These areas 

encompass New England, the 

Adirondack Mountains, the 

northern Appalachian Plateau 

(including the Catskill and 

Pocono Mountains), and the 

Blue Ridge region (including 

streams in western Virginia) (see 

Figure 21).As shown in the deposition maps, above, implementation of Title IV has resulted in 

decreased sulfate deposition 

across the East, while changes in 

nitrate deposition have been 

small. Recent studies provide 

data regarding the response of 

lakes and streams to changes in 

emissions. 

A 2005 study9 examined 

alterations in lake water chemistry as a result of deposition 

changes at 130 monitoring sites 

between 1984 and 2001.The 

sites were chosen to allow generalizations regarding the effects 

of decreases in acidic deposition 

in 3,666 lakes throughout the 

entire northeastern United 

9 Warby, R.A.F., Johnson, C.E., and Driscoll, 

C.T. Chemical recovery of surface waters across 

the northeastern United States from reduced 

inputs of acidic deposition: 1984-2001. 

Syracuse, New York: Syracuse University. 

Improvements in Surface Water 

EPA’s Temporally Figure 21: Regional Trends in Lake and 

Integrated Monitoring of Stream Acidification, 1990-2000 

Ecosystems (TIME) and 

Long-Term Monitoring sulfate 

(LTM) programs 

(described in a text box nitrate 

on page 20) provide 

information on the chem- ANC 

istry of lakes and streams, 

which allows researchers base 

to understand how water cations 

bodies are responding to 

changes in emissions. The Slope of Trend 

data presented here show 

-3 -2 -1 0 1 2 

* 

* 

* 

* * 

* * 

* * 

Maine lakes (n=11) 

Vermont lakes (n=11) regional trends in acidifi- Adirondack lakes (n=50 

Catskill streams (n=4) cation from 1990 to 2000 Pennsylvania streams (n=5) 

Virginia streams (n=74) in areas of the eastern * = not significant 

United States. For each 


lake or stream in the net- Source: Stoddard, J.L., Kahl, J.S., Deviney, F.A., 


DeWalle, D.R., Driscoll, C.T., Herlihy,A.T., work, measurements of Kellogg, J.H., Murdoch, P.S.,Webb, J.R., and 

various indicators of recov- Webster, K.E. (2003) Response of surface water 

ery from acidification were chemistry to the Clean Air Act Amendments of 1990. 

EPA620-R-03-001. Washington, DC: U.S. taken. These measurements Environmental Protection Agency. 

were plotted against time, 

and trends for the given lake or stream during the 10-year period 

were then calculated as the change in each of the measurements 

per year (e.g., change in concentration of sulfate per year). Using 

the trends calculated for each water body, median regional 

changes were determined for each of the measures of recovery. A 

negative value of the “slope of the trend” means that the measure 

has been declining in the region, while a positive value means it 

has been increasing. The greater the value of the trend, the 

greater the yearly change in the measurement. Movement 

toward recovery is indicated by positive trends in acid 

neutralizing capacity (ANC) and negative trends 

in sulfate, nitrate, hydrogen ion, and aluminum. Negative trends in base 

cations can balance out the 

decreasing trends in sulfate and 

nitrate and hinder improvements in ANC. 
20 	✧ Acid Rain Program, 2004 Progress Report 

Long-Term Environmental 

Monitoring at EPA 

EPA’s Temporally Integrated Monitoring 

of Ecosystems (TIME) and Long-Term 

Monitoring (LTM) programs are 

designed to detect trends in the chemistry of regional populations of lakes or 

streams and to determine whether emission reductions have had the intended 

effect of reducing acidification. 

These programs monitor a total of 145 

lakes and 147 streams, representing all 

of the major acid-sensitive regions of the 

northern and eastern United States, 

including the upper Midwest, New 

England, Adirondack Mountains, northern Appalachian Plateau (including the 

Catskill Mountains), and the Blue Ridge 

Mountain region of Virginia. TIME/LTM 

measure a variety of important chemical 

characteristics, including acid neutralizing capacity (ANC), pH, sulfate, nitrate, 

major cations (e.g., calcium and magnesium), and aluminum. While the representativeness of the TIME/LTM network 

is somewhat limited, the TIME program 

provides a coherent individual regional 

dataset for this kind of analysis. In addition, the U.S. Geological Survey (USGS) 

has been measuring surface water quality at several research watersheds 

throughout the United States, where 

sample collection during hydrologic 

events and ancillary data on other watershed characteristics have been used to 

assess the watershed processes controlling acidification of surface waters. 

States.The overall decrease in acidic deposition has 

resulted in some chemical recovery of surface 

waters, with increases in pH and ANC and 

decreases in strong acidic anions and inorganic 

monomeric aluminum.The 2005 study reports a 

systematic increase in ANC in lakes across the 

Northeast: 

• 	 Approximately 4.5 percent of lakes in the 

Northeast are chronically acidic (ANC<0), 

down from 6 percent in 1984. 

• 	 Eleven percent of lakes have low ANC levels 

(ANC 0-25), down from 13 percent in 1984. 

• 	 Approximately 84.5 percent of lakes have 

moderate ANC levels (ANC>25), up from 81 

percent in 1984. 

• 	 Despite region-wide increases in ANC in 

recent years, waters with ANC<50 remain sensitive to acidic deposition and could experience 

adverse biological response associated with 

episodic acidification. It is also important to 

note that estimates of the numbers of acidic 

and low-ANC lakes would increase if smaller 

lakes (<4 hectares) were considered. 

Another recent study10 focused specifically on a 

subset of northeastern lakes in the Adirondack 

Mountain region from 1992 to 2004.This study 

found trends similar to those for the northeastern 

region for 48 lakes included in the Adirondack 

Long-Term Monitoring Program: 

• 	 Forty-seven of 48 sites showed significant 

decreases in combined concentrations of sulfate 

and nitrate. 

• 	 The declines in sulfate concentrations have not 

been uniform over the 1992 to 2004 period, 

with greater declines in the 1990s and a leveling of sulfate concentrations over the last five 

years as emissions of SO2 and wet sulfate deposition have leveled off. 

• 	 Twenty-seven of the 48 lakes showed significant decreases in nitrate concentrations, with 

only three exhibiting increases. It is unclear 

why nitrate concentrations have declined at 

10 	Driscoll, C.T., Driscoll, K.M., Roy, K.M., and Dukett, J. Changes 

in the chemistry of lakes in the Adirondack region of New York 

following declines in acidic deposition. Environmental 

Geochemistry and Health. (in review) 
Acid Rain Program, 2004 Progress Report ✧ 21 

certain locations while there has not been any 

appreciable change in emissions of NOx or 

atmospheric nitrate deposition. 

• 	 Thirty-seven of the 48 lakes showed significant 

trends of increasing ANC, attributed to 

decreasing concentrations of both SO4

2- and 

NO3-. Rates of ANC increase are relatively 

slow, however, and, at current rates, it will be 

several decades before full chemical recovery is 

approached. 

Recent studies11 used data on Shenandoah 

National Park watershed ecosystems to determine 

regional trends for streams in western Virginia: 

• 	 An analysis using data from 1988 to 2003 

showed that sulfate concentrations were generally not decreasing and, in many cases, were 

increasing. Decreases in nitrate concentrations 

were generally greater than those for sulfate 

and could account for much of the observed 

increase in ANC concentrations. Changes in 

nitrate concentrations were attributed to the 

gypsy moth defoliation of watersheds during 

the late 1980s and early 1990s; the same conclusion was reached in a 1998 to 2001 analysis. 

Thus, the 1988 to 2003 trend analysis provides 

less evidence for recovery from acidification 

due to atmospheric deposition. 

Implementation of the Acid Rain Program has 

substantially reduced emissions of SO2 and NOx 

from power generation sources. However, the 

National Acid Precipitation Assessment Program 

(NAPAP) 2005 Report to Congress,12 recent modeling, and many published articles indicate that SO2 

and NOx emission reductions achieved under Title 

IV are insufficient to achieve full recovery or to prevent further acidification in some regions.The studies 

described above support that conclusion, showing 

that environmental improvements have been slow in 

many sensitive areas, and signs of recovery still are not 

evident in some areas.The NAPAP Report to 

Congress concluded that additional SO2 and NOx 

emission reductions from power plants and other 

sources are necessary to decrease deposition and further reduce the number of acidic lakes and streams in 

many regions of the United States.Additional emission reductions will be achieved through implementation of existing or future regulations to address 

transport of ozone and fine particles and mercury 

deposition, including the NOx SIP Call in the 

Eastern United States;Tier II and diesel rules affecting mobile sources; state implementation plans to 

achieve the ozone and fine particle National Ambient 

Air Quality Standards (NAAQS); and the recent rules 

to reduce interstate transport of fine particles and 

ozone, mercury, and regional haze from power plants. 

Quantifying Costs and Benefits of the Acid Rain Program 


A new 2005 analysis13 of the annual benefits and 

costs of the Acid Rain Program updates those of the 

NAPAP 1990 Integrated Assessment and a 1995 EPA 

report,14 and integrates scientific knowledge that has 

emerged since the 1990s.An expanded list of impacts 

increases the program’s estimated benefits, while 

newer implementation strategies—unforeseen in 

1990—lower estimated costs.The estimated value of 

the program’s annual benefits in the year 2010 now 

totals $122 billion (2000$).These benefits result 

mostly from the prevention of health-related impacts 

(such as premature deaths, illnesses, and work days 

missed due to illness), but also include improved visibility in parks, and other recreational and ecosystem 

improvements.The paper indicates that these 

benefits stem from the substantial difference that the 

Acid Rain Program is expected to make in many 

areas meeting NAAQS by 2010 for fine particles less 

than 2.5 micrometers in diameter (PM2.5) and ozone 

standards (see Figure 22 on page 22). Notably, some 

11 Webb, J.R., Deviney, F.A., Jr., and Maben, S. Shenandoah Watershed Study (SWAS) Annual Report for 2003. University of Virginia. 

Webb, J.R., Cosby, B.J., Deviney, F.A., Jr., Galloway, J.N., Maben, S.W., and Bulger,A.J. (2004) Are brook trout streams in western Virginia 

and Shenandoah National park recovering from acidification? Environmental Science and Technology, 38. 

12 2005 National Acid Precipitation Assessment Program Report to Congress, www.al.noaa.gov/AQRS/reports/napapreport05.pdf. 

13 Chestnut, L.G. and Mills, D. A fresh look at the benefits and cost of the U.S.Acid Rain Program. Journal of Environmental Management. 

(article in press) 

14 Human Health Benefits from Sulfate Reduction under Title IV of the 1990 Clean Air Act Amendments. EPA-430-R-95-010. 
22 ✧ Acid Rain Program, 2004 Progress Report 

significant benefits are not quantified, such as the 20 percent reduction in mercury emissions from 

power plants; improvements to 

urban visibility, forest health, and 

surface water quality; and increased 

longevity and reduced soiling of 

painted and stone surfaces. 

The 2005 study finds that 

the estimated annual cost of the 

Acid Rain Program in 2010 is 

$3 billion, with the SO2 program 

accounting for about $2 billion per 

year in 2010.These findings are 

generally consistent with other 

recent independent findings, and 

are far less than the original 

NAPAP estimates.15 EPA expects 

NOx costs to be no more than $1 

billion annually, and likely less, from 

the limited analysis that has been 

completed in this area.This leads to 

a more than 40-to-1 benefit-cost 

ratio.Among the most important 

factors in reducing SO2 program 

costs was improved transportation 

and production of coal, which 

enabled sources to increase the use 

of low-sulfur coal.The flexibility 

offered by the SO2 program also 

may have enabled technological 

innovations that lowered compliance costs. For instance, boiler 

adaptations and lower than expected installation and operation costs 

for flue gas desulfurization systems 

(scrubbers) reduced costs below 

original estimates.16 

Figure 22: Human Health Benefits from Acid Rain Program 

PM2.5 and Ozone Reduction 

Avoided Health Effects Related to Title 

IV’s PM2.5 and Ozone Reductions 

Number 

of Cases 

Avoided* 

Monetary 

Value—Millions 

(U.S. 2000$) 

PM2.5 Reduction 

Mortality (adults) 18,000 $106,171 

Infant mortality (children less than 1) 100 $779 

Chronic bronchitis (adults) 11,000 $4,274 

Nonfatal heart attacks (adults) 24,000 $2,018 

Respiratory hospital admissions (all ages) 8,700 $130 

Cardiovascular hospital admissions (adults) 11,400 $246 

Emergency room visits for asthma (children) 14,700 $4 

Acute bronchitis (children) 27,700 $10 

Asthma exacerbations (children with asthma) 29,400 $1 

Upper respiratory symptoms (children with asthma) 353,400 $9 

Lower respiratory symptoms (children) 299,500 $5 

Minor restricted activity days (adults) 12,766,400 $677 

Work loss days (adults) 

Total related to PM2.5 reduction 

2,200,000 $240 

$114,564 

Ozone Reduction 

Mortality 700 $4,101 

Respiratory hospital admissions (age ≥ 65) 1,500 $27 

Respiratory hospital admissions (age ≤ 2) 1,800 $14 

Emergency room visits for respiratory illness 400 $0.1 

School loss days 785,500 $59 

Acute respiratory symptoms, minor restricted activity 1,612,100 $161 

Worker productivity loss 

Total related to ozone reduction 

n.a. $22 

$4,384 

Total related to PM2.5 and ozone reductions $118,949 

Source: Chestnut, L.G. and Mills, D. A fresh look at the benefits and cost of the U.S. Acid Rain 

Program. Journal of Environmental Management. (article in press) 

* Rounded to the nearest hundred 

15 See, for example: 

Ellerman, D. (2003) Lessons from Phase 2 compliance with the U.S.Acid Rain Program. Cambridge, Massachusetts: MIT Center for Energy and 

Environmental Policy Research 

Carlson, C.P., Burtraw, D., Cropper, M., and Palmer, K. SO2 control by electric utilities:What are the gains from trade? Journal of Political 

Economy,Vol. 108, No. 6: 1292-1326. 

Informing Regulatory Decisions: 2003 Report to Congress on the Costs and Benefits of Federal Regulations and Unfunded Mandates on State, 


Local, and Tribal Entities (2003) Office of Management and Budget, Office of Information and Regulatory Affairs: 


www.whitehouse.gov/omb/inforeg/2003_cost-ben_final_rpt.pdf 


16 	EPA estimates recognize that some switching to lower-sulfur coal (and accompanying emission reductions) would have occurred in the 

absence of Title IV as railroad deregulation lowered the cost of transporting coal from Wyoming's Powder River Basin electric power 

plants in the Midwest and as plant operators adapted boilers to different types of coal. 
Acid Rain Program, 2004 Progress Report ✧ 23 

Interstate Rule (CAIR) 

Ozone and particles 

Particles only 

Ozone only 

Source: EPA 

Note: EPA proposed in March 2005 to add Delaware and New Jersey to 

the states in CAIR covered for fine particles. 

National Actions for Further Emission Reductions— 

2005 Clean Air Rules Figure 23: States Covered by the Clean Air 

In the spring of 2005, in the absence of new 

legislation, EPA promulgated a suite of air quality 

rules designed to address additional reductions of 

SO2, NOx, and mercury (Hg) from power plants. 

These rules include the Clean Air Interstate Rule 

(CAIR), the Clean Air Mercury Rule (CAMR), 

and the Clean Air Visibility Rule (CAVR).17 

CAIR will permanently lower and cap emissions 

of SO2 and NOx in 28 eastern states and the District 

of Columbia (see Figures 23 and 24), starting in 

2009 for NOx and 2010 for SO2.The rule addresses 

the transport of ozone and fine particles resulting 

from these emissions. States have the option to adopt 

a model cap and trade program administered by EPA 

to achieve the cap.The CAIR SO2 trading program 

is designed to work with the existing Acid Rain Figure 24: CAIR/CAMR Emission Caps 

Air Emission 

Cap 

CAIR (for 28 Eastern 

States and DC) 

CAMR 

SO2—Phase 1 3.6 million tons in 2010 

SO2—Phase 2 2.5 million tons in 2015 

NO —Phase 1 x 1.5 million tons in 2009 

(annual) 

0.6 million tons 2009 

(ozone season) 

NO —Phase 2 x 1.3 million tons in 2015 

(annual) 

0.5 million tons 2015 

(ozone season) 

Hg—Phase 1 38 tons in 2010 

Hg—Phase 2 15 tons in 2018 

Program. Sources turn in Acid Rain allowances at a 

ratio of greater than 1-to-1 to achieve reductions 

beyond Title IV of the Clean Air Act.When fully 

implemented, CAIR will reduce SO2 emissions by 

over 70 percent and NOx emissions by over 60 percent from 2003 levels, leading to decreased particulate matter, ozone concentrations, and acid deposition.According to EPA models, CAIR will provide 

health and environmental benefits valued at more 

than 25 times the expected costs of compliance.

17 

CAMR is the first-ever rule to permanently cap 

and reduce mercury emissions from coal-fired power 

plants in all 50 states and the District of Columbia. 

CAMR establishes standards of performance limiting Technology (BART), scrubbers for SO2, and 

mercury emissions from new and existing coal-fired advanced low-NOx burners, on many coal-fired 

power plants and creates a cap and trade program to units outside of the CAIR region in 2013/2014.17 

reduce nationwide utility emissions in two distinct Based on these three regulations, EPA estimates 

phases. By 2018,a 15-ton cap will be in place.Along that power plants will install pollution control techwith the CAIR rule, this will result in a mercury nology, such as scrubbers for SO2 control and SCRs 

reduction from coal-fired power plants of nearly 70 for NOx control. By 2010, nearly half (46 percent) of 

percent from current levels.17 

the units in the nationwide coal-fired fleet totaling 

CAVR applies to non-CAIR states, primarily in roughly 146.3 GW of capacity will have installed 

the West, and affects power plants and other major scrubbers, while about 39 percent, or 126.5 GW of 

sources with the potential to impact visibility, fine power plant capacity, will have installed SCRs. By 

particles, acid deposition, and ozone in certain areas 2020, nearly two-thirds (72 percent) of units will 

of the country. CAVR places Best Available Retrofit have scrubbers (230.5 GW of capacity) and over 56 

17 CAIR (See www.epa.gov/cair/index.html), CAMR (See www.epa.gov/air/mercuryrule), CAVR (See www.epa.gov/oar/visibility/index.html) 
24 ✧ Acid Rain Program, 2004 Progress Report 

percent will have installed SCR (180.9 GW), according to 

EPA’s projections.17 

EPA projects that these rules will result in significant 

monetized health benefits (1999$).These estimates range 

from $62 billion to $73 billion annually in 2010, and from 

$120 billion to $140 billion annually in 2020.The vast 

majority of these benefits result from the reduced levels of 

fine particles in the ambient air that will occur from 

reductions in SO2 and NOx emissions. Reductions in SO2 

emissions from 1993 levels (by 4.3 million tons in 2010 

and by 6.1 million tons in 2020) account for the largest 

portion of improvements in ambient fine particle conditions.The remaining benefits result from ozone improvements associated with NOx emission reductions. Notably, 

these rules also provide multiple unquantified benefits, 

including the value of increased agricultural crop and 

commercial forest yields, visibility improvements, reductions in nitrogen and acid deposition and the resulting 

changes in ecosystem functions, and health and welfare 

benefits associated with reduced mercury emissions.17,18 

EPA expects that the air quality impacts of these regulations, coupled with recent rules to reduce fine particles and NOx from motor vehicles, will be extensive. 

Figures 25, 26, and 27 show areas projected to exceed 

NAAQS in 2010 and 2020, compared to today. Figure 

25 shows ozone and PM2.5 nonattainment areas primarily occurring in eastern states and California.As the new 

rules are implemented, nonattainment is expected to 

decline progressively, with 92 fewer areas by 2010 (see 

Figure 26), and 106 fewer areas by 2020 (see Figure 27). 

As these maps indicate, implementing these three new 

regulations is an important step toward improving future air 

quality in the United States and helping states and local 

communities meet NAAQS for fine particles and ozone. 

Future progress reports will begin to provide information important to the transition to CAIR, CAMR, 

and CAVR, while continuing to report on compliance 

under the Acid Rain Program. 

17 CAIR (See www.epa.gov/cair/index.html), CAMR (See 

www.epa.gov/air/mercuryrule/), CAVR (See www.epa.gov/ 

oar/visibility/index.html) 

18 Multi-pollutant legislative analysis, October 2005, EPA 

19 	Current rules include Title IV of CAA, NOx SIP Call, and some 

existing state rules. 

20 Areas forecast to remain in nonattainment may need to adopt 

additional local or regional controls to attain the standards by

dates set pursuant to the Clean Air Act.These additional local or 

regional measures are not forecast here, and therefore this figure 

overstates the extent of expected nonattainment. 

Figure 25: Current Nonattainment Areas 


Source: EPA 

Legend Area Count 

Both PM and Ozone Nonattainment 36 

PM Only Nonattainment 3 

Ozone Only Nonattainment 90 

Note: Currently, 129 areas are designated as nonattainment for PM2.5 

and/or 8-hour Ozone (April 1, 2005). 

For further information on designations and related requirements, see 

www.epa.gov/air/oaqps/glo/designations/index.htm and 

www.epa.gov/pmdesignations. 

Figure 26: PM2.5 and Ozone Attainment in 2010 

Source: EPA 

Legend Area Cou nt

Both PM and Ozone Nonattainment 6 

PM Only Nonattainment 15 

Ozone Only Nonattainment 16 

Nonattainment areas projected to attain 92 

Note: 92 areas are projected to meet the PM2.5 and 8-Hour Ozone 

Standards in 2010 with CAIR/CAMR/CAVR and some current rules, 

absent additional local controls.19,20 

Figure 27: PM2.5 and Ozone Attainment in 2020 

Source: EPA 

Legend Area Count 

Both PM and Ozone Nonattainment 3 

PM Only Nonattainment 13 


Ozone Only Nonattainment 7 


Nonattainment areas projected to attain 106 


Note: 106 areas are projected to meet the PM2.5 and 8-Hour Ozone 

Standards in 2020 with CAIR/CAMR/CAVR and some current rules, 

absent additional local controls.19,20 
Online Information, Data, and Resources 


About the Clean Air Markets Division 

The availability and transparency of data— 

from emission measurement to allowance 

trading to deposition monitoring—is a 

cornerstone of effective cap and trade 

programs. The Clean Air Markets Division 

in the Office of Air and Radiation’s Office 

of Atmospheric Programs manages programs 

for collecting these data and assessing the 

effectiveness of cap and trade programs, 

including the Acid Rain Program. 

www.epa.gov/airmarkets 

Regulatory Information 

To learn more about how emissions 

cap and trade programs work, see: 

www.epa.gov/airmarkets/arp 

Acid Rain Program 

www.epa.gov/airmarkets/progsregs/ 

noxview.html 

NOx Trading Programs 

www.epa.gov/airmarkets/capandtrade/ 

index.html 

General Cap-and-Trade Information 

Also see recent related rulemakings, 

including: 

www.epa.gov/cair 

Clean Air Interstate Rule (CAIR) 

www.epa.gov/CAMR/index.htm 

Clean Air Mercury Rule (CAMR) 

www.epa.gov/visibility 

Clean Air Visibility Rule (CAVR) 

Progress and Results 

Several reports have assessed the progress 

and results and projected future impacts of 

the Acid Rain Program. 

www.sciencedirect.com/science/ 

journal/03014797 

A Fresh Look at the Benefits and Costs of the U.S. 

Acid Rain Program 

www.al.noaa.gov/AQRS/reports/ 

napapreport05.pdf 

2005 National Acid Precipitation Assessment 

Program Report to Congress 

www.rff.org/Documents/ 

RFF-RPT-Adirondacks.pdf 

Valuation of Natural Resource Improvements in the 

Adirondacks 

www.adirondacklakessurvey.org 


Jenkins, J., Roy, K., Driscoll, C., Beurkett, C. 


Acid Rain and the Adirondacks: A Research 

Summary. Adirondack Lakes Survey Corporation 

Emission, Allowance, and 

Environmental Data 

For more information on emissions, 

allowance, and environmental data, see: 

cfpub.epa.gov/gdm 

EPA Clean Air Markets Data and Maps 

www.epa.gov/castnet 

Clean Air Status and Trends Network 

(CASTNET) 

www.epa.gov/airmarkets 

2005 Atlas: Atmosphere in Motion 

nadp.sws.uiuc.edu 

National Atmospheric Deposition Program/ 

National Trends Network 
1970 – 1994 

1970 

20 million people 

celebrate the first 

Earth Day. 

1978 

The National Atmospheric Deposition 

Program/National Trends Network 

(NADP/NTN) begins monitoring sulfur 

and nitrogen and deposition to 

ecosystems. 

1990 

Congress strengthens the 

CAA and establishes the Acid 

Rain Program using a marketbased approach to reduce 

SO2 from power plants by 

more than 50 percent. 

1994 

Projected costs of compliance 

re-estimated by the 

Government Accountability 

Office and the Electric Power 

Research Institute at less than 

half of original estimates. 

1977 

Congress strengthens the 

CAA and includes requirements for SO2 pollution control at power plants. 

1970 

Clean Air 

Act (CAA) 

is passed. 

1980 

Lake acidification 

and fish loss in the 

Adirondacks, Green 

Mountains, and 

Sierra Nevada make 

national news. 

1987 

The Clean Air 

Status and Trends 

Network (CASTNET) is established 

to monitor dry 

deposition. 

1993 

EPA publishes acid 

rain regulations, 

and Chicago Board 

of Trade holds first 

auction of SO2 

allowances. 

1986 

The United States and Canada 

begin study of cross-border acid 

rain transport. The United States 

is called upon to reduce emissions of SO2 and NOx, especially 

from coal-burning power plants. 

1980 

The National Acid 

Precipitation Assessment 

Program (NAPAP), mandated 

by Congress, begins study on 

acid rain. 
2000 – 2005 

1998 

Regulatory revisions 

enhance efficiencies 

of compliance and 

administration. Nearly 

10 million economically 

significant allowance 

transfers take place. 

1999 

Allowance 

banking peaks. 

SO2 early 

reductions 

total over 11 

million tons. 

1995 – 1999 

1995 

Phase I of Acid Rain Program implementation begins. SO2 emissions fall 

to 5 million tons below 1980 levels. 

Acidity of rainfall in the eastern United 

States drops 10 to 25 percent. 

1996 

About 150 of the largest 

coal-fired power plants 

begin to implement Acid 

Rain Program NOx 

requirements. 

1997 

More than 80 

percent of affected 

companies have 

engaged in private 

allowance transactions. 

2000 


Phase II of Acid Rain Program 

begins, regulating additional 

smaller/cleaner plants and 

requiring further reductions in 

NOx and SO2. 

2001 

Introduction of the 


On-line Allowance 


Tracking System begins 


an era of paperless 


allowance transfer 


recording. 


2002 

EPA begins electronic 

audit process to 

supplement existing 

rigorous monitoring 

program. 

2003 

Lakes and streams 

in the Adirondacks, 

Upper Midwest 

and Northern 

Appalachian 

Plateau show 

signs of recovery. 

2004 

Acid Rain Program 

sources emit 34 

percent less SO2 and 

43 percent less NOx 

than in 1990, despite 

a 34 percent increase 

in fuel usage. 

2005 

New study estimates 2010 annual Acid Rain 

Program benefits at $122 billion and annual costs 

at $3 billion. According to 2005 NAPAP report, 

further emission reductions are necessary to 

achieve broader environmental recovery. EPA 

promulgates CAIR, CAMR, and CAVR. 
1EPA

United States Environmental Protection Agency Office of Air and Radiation Clean Air Markets Division 1200 Pennsylvania Ave, NW (6204J) Washington, DC 20460 www.epa.gov/airmarkets Official Business Penalty for Private Use $300 EPA 430-R-05-012 October 2005 

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