The overwhelming impression is one of growth (em in volume and in the number of participants.

The early 1990s was an anxious period for advocates of emissions trading. Concerns about whether the sulfur dioxide allowance market would ever develop tempered the heady success of the first national emissions trading program implemented by the Environmental Protection Agency under the Clean Air Act Amendments of 1990, Title IV. These concerns were heightened when in May 1992, Wisconsin Power & Light traded 10,000 allowances to the Tennessee Valley Authority. The response from the media and environmental groups was not good:

• A representative from an environmental group asked a reporter: "What's next, the L.A. Police Department trying to buy civil rights credits from Wisconsin?" %n1%n

• A Tennessee newspaper ran a cartoon of a man trying to arrange his release from hell by making a trade for "a few brownie points." %n2%n

• An op-ed piece in USA Today intoned ominously that because of allowance trading "people will die." %n3%n

The negative public reaction to emissions trading was not the only concern for supporters of market-based environmental programs. Some observers wondered whether long lead times for case-by-case review by government agencies or expensive information requirements that had plagued previous emissions trading programs would also afflict Title IV. %n4%n There were several variations on the "will the government mess it up?" theme. Some questioned whether EPA's stringent requirements for continuous emissions monitors would destroy the market; %n5%n others were convinced that Congress and EPA had destroyed the market by not guaranteeing property rights for emissions allowances. %n6%n The greatest worry, however, was that electric utility industry regulators would interfere with trading through the lack of clear policies on who receives the benefits of trades or through biases against trading within existing cost-recovery rules. %n7%n The

possibility that tax policies surrounding allowances would diminish the incentive to trade also presented concerns. %n8%n

An uncomfortable question hung in the air: Would allowance trading go the way of other well-intended policy initiatives, i.e., good in theory but a failure in practice? Contrary to early fears, the allowance market is alive and well. Using a new framework to categorize transactions in EPA's Allowance Tracking System, a healthy and growing allowance market has developed, particularly in the last two years.

Investigating Allowance Transactions

EPA has developed a new framework to investigate the SO2 allowance market created under the Acid Rain Program. A representative group of utilities, brokers and academics have deemed this classification system credible. %n9%n This system provides substantial insight into the level and type of allowance trading activity under the Acid Rain Program.

ATS began recording transfers in March 1994, and since then has served as a central registry of allowances used for compliance with the Acid Rain Program. Though EPA designed it as an information system for tracking compliance rather than for analyzing market activity, ATS contains details of all private allowance transfers reported. These details allow EPA to distinguish between an allowance transfer that is a "real trade" or one that is simply for administrative or accounting purposes.

One aspect of ATS is worth noting; EPA does not require a company to report allowance transfers unless it will use them for compliance. While some transactions have yet to be reported, ATS represents a significant portion of overall SO2 allowance market activity. %n10%n

EPA's method places the private transfers reported to ATS into one of eight categories presented in Table 1. %n11%n These categories are then divided into three groups:

• Arm's Length Transfers. Transfers between distinct economic entities offer the most classic example of an emissions trade. These types of transactions are assessed together to suggest overall market activity. Alternatively, the subset of these transactions that represents transfers to electric utilities (i.e, inter-utility, broker to utility, fuel company to utility) can provide an estimate of how many allowances utilities have acquired, presumably for future compliance. %n12%n

• Intra-utility transfers. Includes both transfers within the same operating company and transfers between operating companies within the same parent company. Although these are not trades in the classic sense, they may represent a significant cost savings for some companies. %n13%n

• Reallocations. Includes any movement of allowances for administrative or accounting purposes. These transfers facilitate efficient management of allowances by a company, but are not considered economically significant.

Results of Analysis

More than 2,400 transfers moving approximately 38 million allowances were reported to EPA between early 1994 and the end of the first quarter of 1997. Figures 1 and 2 detail the breakdown of this activity by volume of allowances transferred among the categories. Reallocations and intra-utility transfers have accounted for most of this activity since early 1994, representing approximately 50 percent of all transfers and 75 percent of all allowances transferred. Intra-utility transfers have increased substantially from year to year, though growth has tapered off in 1997. Reallocations, on the other hand, almost doubled from 1994 to 1995 and then dramatically decreased in volume in 1996, only to show a slight resurgence in early 1997.

As of the end of March 1997, 8.9 million allowances had traded in more than 1,100 transactions between economically distinct entities. %n14%n In 460 transactions, utilities have acquired approximately 3.5 million of these allowances (Figure 3).

When looking at the number of allowances traded in transactions between economically distinct entities, the overwhelming impression is one of growth (see Figures 4 and 5). The number of allowance transfers between unrelated parties has increased steadily since the start of the program, growing approximately fivefold from 1994 to 1995 and an additional 80 percent from 1995 to 1996. The volume of allowances transferred in these transactions doubled from 1994 to 1995 and more than doubled again between 1995 and 1996. Transfers between brokers or traders and utilities make up the substantial majority of this category, followed by transfers between unrelated utilities, "other" transfers and lastly, those transfers between fuel companies and utilities. %n15%n

Activity through the first quarter of 1997 maintains this upward trend. In fact, the volume of allowances transferred through March nearly equals the annual total for 1995.

More than 25 percent of all utilities and 50 percent of utilities affected in Phase I of the Acid Rain Program have engaged in a trade with an economically distinct utility, broker or fuel company. This group of utilities covers an even larger percentage of the allowances issued, because it includes most of the largest electric utilities in the country. Utilities in 33 different states participate in these types of transactions.

The participation of SO2 allowance brokers and traders is also on the rise. Though the number of brokers and traders with accounts in the ATS has remained relatively static since 1995 (seven companies identify themselves as brokers or traders in the ATS), their level of involvement has increased significantly. From 1995 to 1996, the flow of allowances from brokers or traders to utilities increased sixfold; the stream from utilities to brokers increased threefold. Early 1997 activity suggests continued rising numbers.

Finally, a small but growing number of environmental, nonprofit and student organizations have entered the allowance market to purchase allowances for retirement. Retiring an allowance ensures the emission of one less ton of pollution into the air in a given year, since the total number of allowances is fixed under the cap. Almost 20 different groups have purchased and retired approximately 1,400 allowances. %n16%n In addition, utilities have retired at least 35,000 allowances through charitable donations. %n17%n Though this participation is largely symbolic, it marks an important stride in the democratization of pollution abatement since individuals and nongovernmental organizations are taking direct action to reduce pollution.

EPA's overall assessment of the market, which is consistent with a similar analysis conducted by researchers at the Massachusetts Institute of Technology, %n18%n shows significant allowance trading activity in a variety of states. The possibility exists, however, that even greater levels of allowance trading would occur if there were changes in state commission policies to facilitate trading. Nevertheless, the growing level of allowance trading shows that a properly designed emissions trading market can develop.

Making It Work

Some of the same features that make an emissions trading program environmentally successful also make for an effective allowance market. Strong environmental goals are critical for an effective emissions trading system. By capping emissions and allocating allowances equal to the total emissions cap, the environmental integrity of Title IV's SO2 emission reductions is ensured. Even if total electricity generation grows at a much faster rate than expected, emissions will not exceed the cap and the total number of allowances in the system remains unchanged.

The cap on SO2 emissions, the environmental cornerstone of Title IV, also facilitates trading. Because allowances are allocated at a level that already reflects an overall emission reduction, there is no need to certify emission reductions case by case. Moreover, the larger the overall reduction reflected in the cap, the less concern there is about the environmental impacts of any individual trade or group of trades.

This point is particularly relevant in addressing concerns about "hotspots" that may arise due to trading (em i.e., that sources upwind of a sensitive area may buy allowances and exacerbate acid deposition or cause violations of ambient air quality standards. For example, economic and atmospheric modeling done with a recent EPA study showed that in the eastern U.S., the difference in acid deposition with and without trading was less than 5 percent. Differences in deposition of less than 10 percent are not expected to change the acidification of lakes and streams measurably. %n19%n

This is not to say, however, that setting an emissions cap at an appropriate level can eliminate all local environmental problems. For some problems, local controls on specific sources also may prove necessary. For example, under Title IV, sources also must comply with source-specific emission reductions set by states to ensure attainment of ambient standards. Sources are not authorized to use allowances to exceed these state limits. Automatic trading ratios or ratios on the allowed use of banked allowances can also help address concerns about environmental hotspots. %n20%n

Emissions monitoring. Measurement and reporting of pollution are critical to ensuring that reductions are achieved under an emissions trading system. While traditional programs required facilities to meet specific rates, a trading program requires an accounting of each ton of emissions from each source of pollution. Compliance is then determined through a direct comparison of total tons of pollution measured and total allowances held by the operator of a source. Essentially, measured emission data is the "gold standard" to back up a traded allowance.

Monitoring costs are significant. A recent study found that in 1995, a continuous emissions monitors system (CEMS) constituted about 7 percent of overall compliance costs. %n21%n However, an essential feature of an efficient market is a method for certifying the existence of the traded commodity. As one broker noted, CEMS data also gives market participants information that helps them determine allowance prices. %n22%n

Moreover, the rigor of the CEMs gives regulators the confidence that they have the best emissions data available. With CEMS, they can focus on tracking emissions rather than requiring submission of costly, case-specific information with every trade. When CEMS costs are put in context of the overall savings from emissions trading versus a command-and-control approach, they are worth the cost. The General Accounting Office has estimated that full trading in 2010 could save up to $3 billion annually. %n23%n

Automatic compliance penalties. Under the Acid Rain Program, if an electric utility unit emits more than the number of allowances in its account, there is an automatic and immediate financial penalty for every excess ton. The penalty, which Congress established at $2,000 per ton, increases each year by the Consumer Price Index. In 1996, it was $2,454. Beyond the automatic penalties, violating utilities must offset the excess SO2 emissions with allowances in an amount equivalent to the excess. These stringent penalties (plus conscientious implementation by

the electric utility industry) have contributed to 100-percent compliance during the first two years of the Acid Rain Program. After all, why would a company pay a $2,500/ton penalty when it can purchase an allowance for $100/ton before the end of the compliance deadline?

Although the environmental importance of a good enforcement mechanism is clear, good enforcement also is important to the adequate operation of an allowance market. Without adequate enforcement, a market for pollution credits would break down as emitters lose confidence in the underlying value of credits or in the need to buy credits at all.

Banking. The ability to over control emissions in a given year and "bank" the unused portion for future use has led to significant cost savings in Title IV. %n24%n Although banking is often discussed as a cost-saver, environmental benefits result from the early emission reductions spurred by the provision. The 3.4 million allowances banked in 1995 and the additional 2.9 million allowances banked in 1996 represent extra emissions reductions of approximately 40 percent and 35 percent, respectively. EPA has estimated that the bank will increase to 11 to 13 million allowances by the end of Phase I. %n25%n

The Phase I bank of allowances will delay the full effect of the 8.95-million-ton cap on SO2 until 2010, extending the time for achieving the ultimate emissions target. Nevertheless, the early reductions may provide greater benefits in improved health and visibility than would have occurred with no banking.

The Government Doesn't

Always Mess Up

Several recent papers have noted the low transaction costs of the SO2 allowance market. %n26%n Fears about high transaction costs from long administrative reviews have not materialized. According to an analysis of log-in dates in the ATS, 99 percent of 1996 allowance transactions were processed within five days; 83 percent were processed within 24 hours. %n27%n Processing time could move even faster in the future if a pilot program with the Southern Co. to submit allowance trades electronically works out well. EPA also hopes to change existing rules to require only the signature of sellers (and not buyers) to sign off on an allowance trade. This change would further reduce transaction costs and the time necessary to make a trade.

The fundamentally different approach to air pollution control embodied by the SO2 allowance trading program can minimize many administrative costs associated with "command and control" and previous trading programs. For example, the performance-based approach under Title IV eliminates the need to devise source-specific emission limits. It also eliminates the need for review of control technologies and detailed compliance schedules. In addition, eliminating case-by-case review and approval of each trade (including determining "useful life" of equipment, the intent of the sources regarding future emissions and activity levels, and "real" emission reductions achieved), greatly reduces the costs associated with trading programs. %n28%n While regulators focus on verifying and tracking emissions and allowances, companies are given complete freedom to choose the methods by which they reduce emissions.

Besides reducing transaction costs, this approach to regulation also has low administrative costs. The program's administrative costs of roughly $12 million per year translate into about $1.50/ton of pollution reduced. Most of these costs go toward operating the emissions monitoring and reporting components of the program. To put these expenditures into context, during the first five years of the program, government spending to set up and operate the SO2 allowance program totaled less than $60 million out of the $3.5 billion estimated for air pollution control. %n29%n Thus, the program is achieving 40 percent of the emissions reductions under the Clean Air Act with only about 2 percent of the staff and other resources. %n30%n

Success and Acceptance

Several observers have noted that the key to selling Title IV's emissions trading to the public and environmental groups is to make the point that flexibility of emissions trading is tied to a significant environmental benefit. %n31%n The argument is that the cost savings from the allowance trading program were used to "buy" additional environmental benefits,

easing concern over this nontraditional form of regulation. During the 1980s, nearly 70 bills were introduced before Congress to address acid rain. Competing constituencies fought over the cost and environmental stringency of prospective legislation.

After almost 10 years of debate, Congress passed an acid rain bill that struck a balance between cost and environmental concerns. For environmentalists and representatives of states with acid rain impacts, the bill required a

10-million-ton annual reduction

in sulfur dioxide from 1980 levels (one of the largest emission reduction among the proposals) and a permanent cap on emissions (which none of the earliest proposals contained). For the electric utility industry and advocates of market-based environmental policies, the bill minimized the cost of compliance through an emissions trading system. %n32%n

Environmental results. The excellent environmental results achieved during the first years of the program have helped to reinforce the idea that the design of Title IV provides both economic and environmental benefits. In 1995, the first year of the program, the largest, one-year drop in SO2 in the history of the U.S. took place. Electric utilities in the program reduced emissions 40 percent below the levels required by law. %n33%n A 10- to 25-percent reduction in wet sulfur deposition (acid rain) accompanied these emissions reductions over large areas of the eastern U.S. in 1995. %n34%n These decreases are considered substantial in magnitude and spatial extent compared with the previous 12-year analyzed record from 1983 through 1994. Dry sulfur deposition has decreased by 30 percent in the eastern U.S. between 1989 and 1995. %n35%n Ambient concentrations of SO2 also declined by 17 percent between 1994 and 1995. %n36%n

Moreover, significant emission reductions were experienced in some of the highest emitting areas of the country. For example, electric utilities in Ohio and Indiana reduced 1995 SO2 emissions by 46 percent and 37 percent,

respectively, from 1990 levels. %n37%n This outcome is important because emissions reductions in these high-emitting states support a fundamental premise of Title IV's market-based approach (em that the highest emitting plants have an incentive to make substantial reductions in emissions because they face lower costs per ton to reduce SO2. Concerns that the biggest emitters of SO2 would simply buy allowances and continue to emit at their historical levels have proven unwarranted.

Based on several recent studies, substantial health, visibility and other benefits will accrue from the full 10-million-ton reduction in SO2 emissions. These benefits include annual health benefits of $12 billion to $40 billion %n38%n and annual improved visibility benefits of $3.5 billion. %n39%n

The response. Favorable editorials and op-ed pieces on the actual or projected results of Title IV have appeared in many newspapers. %n40%n Interestingly, a broader range of environmental groups, and not just longtime supporters of emissions trading such as the Environmental Defense Fund, are either embracing emissions trading or acknowledging that there are environmentally preferable ways to do trading. For example:

• The Natural Resources Defense Council is advocating a cap-and-trade system for electric utility SO2, NOx, CO2, and mercury emissions as a component of restructuring legislation. %n41%n

• The Adirondacks Council, a grassroots group active on the acid rain issue in New York, is supporting legislation introduced by Sen. Alfonse D'Amato (R-N.Y.) that would further reduce SO2 and NOx emissions in the Midwest through a cap and trade approach. %n42%n

• A representative of the Ohio Sierra Club has been writing op-ed pieces that use the health benefits and low cost of the Acid Rain program to counter arguments against the revised National Ambient Air Quality Standards. %n43%n Although the Sierra Club does not generally advocate emissions trading, a September 1994 Guide for Activists on emissions trading noted that trading may be acceptable if programs are designed to ensure that environmental goals are met. The guide concludes, "If trading schemes at the local, state, and national levels are properly designed, implemented, and monitored, environmentalists, business and regulators will gain experience and new approaches to environmental protection that could serve everyone better down the road." %n44%n

Five years after the harsh reactions to the first publicly announced allowance trade, emissions trading has become routine. It is too early, however, to determine whether and how much additional trading would occur if certain market barriers did not exist. It is safe to say, though, that fears about high transaction costs and public rejection of allowance trading have not come true. A large part of the program's success is attributable to the design of Title IV. Features included for environmental reasons, such as the

emissions cap and stringent monitoring, also helped facilitate an emissions trading market and lower administrative and transaction costs. These same features lead to greater acceptance by environmental groups and the public because, because when designed and implemented correctly, they provide environmental results.

The fundamental "deal" struck in Title IV (em large reductions of emissions with a cap, stringent monitoring and automatic enforcement provisions in return for flexibility and trading (em was one of the best environmental bargains ever cut by Congress, industry, environmental groups and other stakeholders. We hope that the lessons from this deal will illuminate policy discussions as we tackle future environmental challenges. t

Joseph Kruger is chief of the Energy, Evaluation and International Branch of EPA's Acid Rain Division, which studies the effects of the SO2 emissions trading program and implements incentives that encourage use of energy-efficient and renewable technologies. His group also manages the U.S./Canada Air Quality Agreement, which addresses transboundary air pollution. Prior to joining EPA, he was an energy and environmental analyst at the Investor Responsibility Research Center in Washington, D.C. In 1985, he was an Argonne National Laboratory research resident at the U.S. Department of Energy. Melanie Dean is an environmental policy analyst with EPA's Acid Rain Program. Her work focuses on analysis of the SO2 allowance market and development of other market-based trading programs. The authors thank Brian McLean, Claire Schary, Janice Wagner, Dallas Burtraw, and Denny Ellerman for helpful comments. The views expressed here are solely the authors' and do not necessarily reflect the policies of the EPA.

Table 1. EPA's Classification Scheme

Transfers Between Economically Distinct Parties

Inter-Utility. Any transfer of allowances from one utility operating company's account to a different utility operating company's account, provided the operating companies are not controlled by the same parent company.

Broker/Trader to Utility. Any transfer from an allowance broker or trader to a utility.

Utility to Broker/Trader. Any transfer from a utility to an allowance broker or trader.

Fuel Company to Utility. Any transfer from a fuel supplier (e.g., coal, gas) to a utility.

Utility to Fuel Company. Any transfer from a utility to a fuel supplier.

Other. Any transfer between two unrelated parties that does not fit into any of the above categories. This class includes transfers involving environmental groups, nonutility accounts or individuals, Also included are broker to broker transfers, fuel supplier to broker transfers, etc.

Intra-Utility Transfers

Class I. Any transfer from one unit account to another unit account within the same operating unit.

Class II. Any transfer from one operating company's unit account to another's unit account within the same parent company.

Reallocations

Any transfer from a unit or general account of one operating company to a general account of the same operating company or a parent company (some may become intra-utility in the future), any pooling activity (e.g., Phase I extension redistributions), or any transfer in which the transferor is a partial owner of the transferee account, or vice versa.

Endnotes

1"Ecologists Criticize TVA Pollution Pact," Kentucky New Era, May 13, 1992.

2Knoxville News-Sentinel, May 17, 1992, p. A-2.

3Michael Gartner, "Polluters Ought to Pay, Not Deal," USA Today, May 27, 1992.

4See for example, Robert H. Hahn and Gordon L. Hester, "Marketable Permits: Lessons for Theory and Practice," Ecology Law Quarterly, Vol. 16, No. 2, 1989.

5For a discussion of early experience with emissions trading programs, see the comments of Dave Wojick in Kennedy P. Maize, "Uncertainties, Wide Price Swings Could Sabotage Emissions Trading," Electricity Journal, Volume 5, No. 3, April 1992, p. 7.

6See for example, Jim Johnston, "We Told You So," Regulation, No. 3, 1995.

7See Douglas R. Bohi and Dallas Burtraw, "Utility Investment Behavior and the Emission Trading Market," Resources and Energy, vol. 14, 129-153, 1992. Kenneth Rose, Public Utility Commission Implementation of the Clean Air Act's Allowance Trading Program, The National Regulatory Research Institute, Ohio State University, May 1992.

8See comments filed on behalf of the Chicago Board of Trade by George B. Javaras and Donald E. Rocap in response to IRS request for comments on tax issues of SO2 trading program.

9R.D. Lile, D.R. Bohi, and D. Burtraw, An Assessment of the EPA's SO2 Emission Allowance Tracking System, Resources for the Future, November 1996.

10See Lile et. al., above.

11For a more detailed explanation, see Melanie Dean and Joseph Kruger, Using EPA's Allowance Tracking System to Assess the Allowance Market, presented at Air and Waste Management Association Acid Rain II Specialty Conference, Scottsdale, Ariz., January 1997 and Lile, et. al., above.

12One complication in establishing how many allowances were acquired is that many are held by brokers for acquiring electric utilities. For example, as of May 1997, one large broker, Cantor Fitzgerald Environmental Brokerage Services, held almost half a million allowances and reported that the vast majority were held for utility clients.

13U.S. General Accounting Office, Allowance Trading Offers an Opportunity to Reduce Emissions at Less Cost, GAO/RECD-95-30, December 1994.

14Note that some double counting occurs due to brokers holding allowances for utilities. When brokers ultimately transfer allowances to the buying utility, it is the completion of the original transaction, rather than the initiation of a new one.

15Brokerage and trading firm involvement may be larger than indicated in Figure 2. Even when transfers are recorded as occurring between two market parties, a broker or trader often is involved.

16One group, Clean Air Conservancy, which represents several school groups and individuals, has retired 1,000 allowances.

17Niagara Mohawk Power Corp. donated 25,000 allowances to EDF, the Adirondack Council, and others. Northeast Utilities has donated 10,000 allowances to the American Lung Association.

18Paul L. Joskow, Richard L. Schmalensee, and Elizabeth Bailey, "Auction Design and the Market for Sulfur Dioxide Allowances," 1996 MIT CEEPR.

19U.S. EPA, Acid Deposition Standard Feasibility Study Report to Congress, U.S. EPA 430-R-95-001a, October 1995.

20For a description of this partial restriction on banked allowances, see Claire Schary, "The Role of EPA's Acid Rain Division in the Ozone Transport Commission's NOx Budget Program," proceedings of the AWMA Acid Rain II Specialty Conference, Scottsdale, Ariz., January 1997.

21A. Denny Ellerman, Richard L. Schmalensee, Paul Joskow, Juan Pablo Montero, and Elizabeth Bailey, SO2 Emissions Trading Under Title IV of the 1990 Clean Air Act Amendments: Evaluation of Compliance Costs and Allowance Market Performance, Center for Energy and Environmental Policy Research, MIT, forthcoming.

22Carlton Bartels, "Recent Trends in SO2 Allowance Marketplace," proceedings of Acid Rain & Electric Utilities II, AWMA, Scottsdale, Ariz., Jan. 21, 1997.

23U.S. General Accounting Office, above.

24Ellerman, et. al. above.

25U.S. EPA, Economic Analysis of The Title IV Requirements of the 1990 Clean Air Act Amendments, prepared by ICF Inc., February 1994.

26See for example Ellerman, et. al., Bartels, Conrad, Klaus and Robert E. Kohn, "The U.S. Market for SO2 Permits," Energy Policy, Vol. 24, No. 12, pp. 1051-1059, 1996.

27U.S. EPA, 1996 Compliance Report: Acid Rain Program, EPA 430-R-97-025.

28Brian J. McLean, U.S. EPA Sulfur Dioxide (SO2) Allowance Trading Program: The First Five Years, Jan. 19, 1996.

29McLean, above.

30McLean, above.

31See for example, Alan Loeb, "Addressing the Public's Goals for Environmental Regulation When Communicating Acid Rain Allowance Trades," Electricity Journal, May 1995, and Robert H. Hahn, and Carol May, "The Behavior of the Allowance Market: Theory and Evidence," Electricity Journal, March 1994.

32For a discussion of politics behind Title IV, see Nancy Kete, The Politics of Markets: The Acid Rain Control Policy in the 1990 Clean Air Act Amendments, unpublished dissertation, Johns Hopkins University, 1992 and Paul L. Joskow and Richard Schmalensee, The Political Economy of Market-Based Environmental Policy: The U.S. Acid Rain Program, Journal of Law and Economics (forthcoming).

33U.S. EPA, 1995 Compliance Results: Acid Rain Program, 430-R-96-012, July 1996.

34U.S. Geological Survey, Trends in Precipitation Chemistry in the U.S., 1983-94 (em An Analysis of the Effects in 1995 of Phase I of the CAAA of 1990, Title IV, USGS 96-0346, June 1996.

35U.S. EPA, Office of Research and Development, 1997 [Preliminary] Examination of CASTNet: Data, Results, Costs, and Implications, National Exposure Research Laboratory, Research Triangle Park, N.C.

36U.S. EPA, National Air Quality and Emissions Trends Report, 1995, EPA 454-96-008, December 1996.

37U.S. EPA, Acid Rain Program Emissions Scorecard 1995, EPA

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