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Cleaned-Up Coal: Technology Improvements, Low-Sulfur Resources Are Winning the Day against Air Pollution

By Mary Hutzler -- June 12, 2009

Air quality from America’s coal plants have been improving for decades, even before Congress passed the Clean Air Act of 1970. And since 1970, the six so-called criteria pollutants have declined significantly overall and in the generation of electricity, even though coal-fired generation has increased by more than 180 percent.[i] (The “criteria pollutants”—those for which the EPA has set criteria for permissable levels—are carbon monoxide, lead, sulfur dioxide [SO2], nitrogen oxides [NOx], ground-level ozone, and particulate matter [PM]).

Specifically, total SO2 emissions from coal-fired plants were reduced by about 40 percent between 1970 and 2006, and NOx emissions were reduced by almost 50 percent between 1980 and 2006. On an output basis, the percent reduction is even greater, with SO2 emissions (in pounds per megawatt-hour) almost 80 percent lower, and NOx emissions 70 percent lower.

The figure below shows the increases in Gross Domestic Product, vehicle miles traveled, energy consumption, and population since 1980, and compares them to the decline in the aggregate emissions of criteria pollutants. Today, we produce more energy, drive further, and live more comfortably than we did in the past, all the while enjoying a cleaner environment.

EPA’s Comparison of Air Quality, Emissions, and Societal Trend

One factor in improving air quality has been the pollution-control technologies used by coal-fired power plants. Today’s coal-fired electricity generating plants produce more power, with less emission of criteria pollutants, than ever before. According to the National Energy Technology Laboratory (NETL), a new pulverized coal plant (operating at lower, “subcritical” temperatures and pressures) reduces the emission of NOx by 86 percent, SO2 by 98 percent, and particulate matter (PM) by 99.8 percent, as compared with a similar plant having no pollution controls. Undoubtedly, air quality will continue to improve in the future because of improved technology.

Today, coal-fired electricity generation produces nearly half of the electricity generation in America and is job- and “shovel” ready. For example, Prairie State Energy Campus, a 1,600-megawatt coal plant under construction in southern Illinois, provides 1,200 people with jobs in around-the-clock construction. Between its power plant, coal mine, and other assets, the campus will inject some $2.8 billion into the Illinois economy, creating 2,300 to 2,500 temporary construction jobs and 500 permanent positions, while emitting 80 percent less in pollutants than most existing power plants.  When completed, the power plant will deliver electricity to 2.4 million homes in at least nine states.

Cap & Trade and Criteria Pollutant Reduction (1990 CAA)

The Clean Air Act, last modified in 1990, requires the Environmental Protection Agency (EPA) to set National Ambient Air Quality Standards to control pollutants considered harmful to public health or the environment: the so-called criteria pollutants. Two of these pollutants, SO2 and NOx are the principal pollutants that cause acid precipitation (colloquially known as acid rain). SO2 and NOx emissions react with water vapor and other chemicals in the air to form acids that fall back to earth. Criteria pollutants are localized emissions, so controlling for them produces better air quality to the local community; the situation is very different when controlling for global emissions, such as carbon dioxide and other greenhouse gases.

The 1990 changes to the Clean Air Act introduced a permanent cap on the total amount of SO2 emissions that may be emitted by electric power plants nationwide, thereby reducing the level of these emissions in the atmosphere. The approach used was a cap-and-trade program with a steadily declining cap through 2010. In order to comply with the Clean Air Act Amendments of 1990, electric utilities could either switch to low-sulfur coal, add commercially available equipment (e.g., scrubbers) to existing coal-fired power plants to remove SO2 emissions, purchase permits from other utilities that exceeded the reductions needed to comply with the cap, or use any other means of reducing emissions below the cap, such as operating high-sulfur units at a lower capacity utilization.

EPA also issues air pollution control standards, called New Source Performance Standards (NSPS) to which new plants must adhere. EPA’s current NSPS require all power plants for which construction commenced after February 28, 2005 to not exceed 1.0 lb/megawatt hour (0.11 lb/million Btu) of NOx, 1.4 lb/megawatt hour (0.15 lb/million Btu) of SO2, and 0.14 lb/megawatt hour (0.015 lb/million Btu) of particulate matter (PM). However, most new plants are built to even more stringent criteria. A study by the National Energy Technology Laboratory (NETL) compared the emission rates from pulverized coal plants and integrated gasification combined cycle plants based on the environmental regulations that would apply to plants built in 2010 using technology designs from several vendors. The rates range from .0105 to .0848 lbs/million Btu for SO2, .055 to .07 lbs/million Btu for NOx, and .0071 to .013 lbs/million Btu for PM, depending on technology type. They are 43 to 93 percent lower than the current NSPS for SO2, 36 to 50 percent lower than the current NSPS for NOx, and 13 to 53 percent lower than the current NSPS for PM. According to NETL, for a new pulverized coal plant (subcritical) built in 2008, pollution controls reduce NOx emissions 86 percent, SO2 emissions by 98 percent, and PM by 99.8 percent when compared with a similar plant with no pollution controls [ii].

The figure below graphically depicts the criteria pollutants from a new controlled plant vs. those from a new uncontrolled plant. NETL estimates that for a pulverized subcritical coal plant, the equipment to control NOx, SO2, and PM comprises $324/kW of the $1,549/kW plant cost (21 percent).

Note that the success of this program was principally due to the availability of cost-effective technology that could be added to existing as well as new power plants and to the America’s vast resources of low sulfur coal, principally in the Powder River Basin, that could be cost-effectively transported by unit trains to power plants across the nation.

Cap & Trade and Global GHG Emissions

The results of using a cap-and-trade system to fight “acid rain” have led some to argue that it is a model for efforts to reduce carbon dioxide emissions. However, stark differences exist between the “acid rain” emission-reduction program and the challenge of reducing carbon dioxide, a natural byproduct of combustion, emitted by natural and man-made sources.

Carbon dioxide is emitted by hundreds of millions of sources, including personal automobiles, the appliances used to cook our food and heat our homes, and the businesses upon which we depend for our livelihoods, to name just a few. The “acid rain” emission reduction program was initially limited to 110 site-specific utility plants, and then later expanded to 445 plants. In addition, carbon dioxide is a world-wide byproduct of combustion, whereas all criteria pollutants are local or regional. In other words, what the United States did for SO2 and NOx directly affected air quality here, while national action to limit carbon dioxide emissions will have little bearing on aggregate global greenhouse gas emissions.

Furthermore, at the time of the SO2 and NOx reduction program, alternative low-sulfur coal sources existed and utilities had available, affordable, and proven technologies to reduce their criteria emissions. When Congress passed the Clean Air Act Amendments of 1990, therefore, coal-fired utilities could responsibly reduce emissions from their plants using various options that limited cost impacts to the consumer.

In addition, attempts to extrapolate the “acid rain” success story to the challenge of reducing carbon dioxide emissions fail to recognize the history of similar programs in other parts of the world. For example, the “Emissions Trading Scheme” of the European Union has been ineffective at reducing carbon dioxide emissions and at the same time it has increased prices and harmed businesses and consumers. Further, the EU program has enriched some companies and industries at the expense of consumers.

A recent study by Laurie Williams and Allen Zabel, career employees of the Environmental Protection Agency, makes these points about what the authors call the “Acid Rain Myth.”  As the authors explain, those who champion the use of cap-and-trade to address global warming ignore the crucial distinctions between the issues the U.S. faced in 1990 with acid rain and the issues faced today with global warming.

The following highlights Williams and Zabel’s study demonstrate that the experience of the acid rain program cannot and should not be compared to cap and trade for greenhouse gas emissions:

  • “Most importantly, the success of the Acid Rain program did not depend on replacing the vast majority of our existing energy infrastructure with new infrastructure in a relatively short time. Nor did it depend on spurring major innovation. Rather, the Acid Rain program was successful as a mechanism to guide existing facilities to undertake a fuel switch to a readily available substitute, the low sulfur coal in Wyoming’s Powder River Basin.”
  • “The goal of the Acid Rain program was to reduce sulfur dioxide emissions, while keeping the cost of energy from coal low. To be effective, climate change legislation must do the opposite; it must gradually increase the relative price of energy from coal and other fossil fuels to create the appropriate incentives for both conservation and the scale-up of clean energy.”
  • “Further, the Acid Rain program did not allow any outside offsets and so provides no basis for the widespread assumption that an offset program will help with climate change. In addition, the success of the program was aided by the low, competitive price of low-sulfur coal.”
  • “According to Professor Don Munton, author of ‘Dispelling the Myths of the Acid Rain Story’ the impact of the program has been overstated: The potential for a massive switch to low sulfur coal was no secret. Such coal was cheap and available, and it became cheaper and more available throughout the 1980s. Indeed, low-sulfur coal became very competitive with high-sulfur supplied well before the Clean Air Act became law.”

In short, the mechanisms available to reduce pollutants allowed for more generation of energy with less pollution. But this success cannot be extrapolated to the regulation and reduction of carbon dioxide, a much more challenging undertaking. None of the conditions existing at the time of the apparent success of the SO2 and NOx reduction program apply to carbon dioxide. Unilateral action by the United States will have little impact upon global carbon dioxide concentrations. The challenges presented by the control and regulation of carbon dioxide have no parallels in the history of emission regulation.

[i] Air quality was improving before 1970, even before Congress created the Environmental Protection Agency in 1970 and passed the Clean Air Act Amendments of 1970.

[ii] Email from J. Kukielka ,NETL to M. Hutzler, IER, January 9, 2009.


  1. Ed Reid  

    The logical approach to dealing with the issue of increasing atmospheric carbon concentrations from anthropogenic sources begins with stabilizing current emissions rates by halting the construction and commissioning of new, incremental anthropogenic emissions sources. (When you find that you are digging yourself into a hole, the first priority is to STOP DIGGING.)

    The logical second step is to begin reducing emissions from current anthropogenic sources, either through replacement with non-emitting alternatives upon retirement or through the application of CCS technology when available and economically viable.

    The logical third step, if deemed necessary, is the application of technologies to remove carbon from the atmosphere to return the atmospheric carbon concentration to the desired level.

    The above suggests that , if limiting anthropogenic carbon concentrations in the atmosphere is desirable, W-M could be a national component of the second logical global step. However, it also suggests that halting the construction and commissioning of new fossil-fueled facilities, especially in the developing countries, is the FIRST logical step.

    Any attempt, even on a sub-global scale, to reduce anthropogenic carbon emissions from existing sources while new sources of anthropogenic carbon emissions with 40-60 year economic lives are being constructed and commissioned at a rapid pace, is a fools errand.

    However, there appears to be an adequate supply of individuals fully qualified to be sent on the errand.


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