The five principal emissions from coal power plants are carbon dioxide, SO, particulate matter, and mercury. For the purposes of this report, we are focusing on power plants’ emissions of SO, NO, and particulate matter since they, along with ozone, are the focus of a rule currently proposed by EPA—the Transport Rule—which seeks to limit the interstate transport of emissions of SO in order to abate violations of particulate matter and ozone NAAQS in downwind states. According to an EPA analysis, as of 2008, power plants emitted over 65 percent of SO emissions and almost 20 percent of NO emissions, nationwide. These emissions impact local air quality, but they can also travel hundreds of miles to impact the air quality of downwind states. In developing the Transport Rule, EPA has found that emissions of SO from 31 eastern states and the District of Columbia prevent downwind states from meeting NAAQS for ozone and particulate matter. SO and NO emissions contribute to the formation of fine particulate matter, and NO emissions contribute to the formation of ozone, which can cause or aggravate respiratory illnesses. the atmosphere, known as volatile organic compounds; and sunlight. Cars and power plants that burn fossil fuels are contributors of NO pollution. stack. In 1970, there were only 2 stacks higher than 500 feet in the United States, but this number had increased to more than 180 by 1985. While constructing a tall stack is a dispersion technique that helps to reduce pollution concentrations in the local area, using tall stacks does not reduce total emissions that can potentially be transported to downwind states. The 1977 amendments to the Clean Air Act discouraged the use of dispersion techniques to help attain NAAQS. Specifically, section 123 prohibits states from counting the dispersion effects of stack heights in excess of a stack’s GEP height when determining a source’s emissions limitation. The Clean Air Act defines GEP as “the height necessary to insure that emissions from the stack do not result in excessive concentrations of any air pollutant in the immediate vicinity of the source as a result of atmospheric downwash, eddies, or wakes which may be created by the source itself, nearby structures, or nearby terrain obstacles.” According to federal regulations, a stack’s GEP height is the higher of 65 meters, measured from the ground-level elevation at the base of the stack; a formula based on the height and width of nearby structure(s) (height plus 1.5 times the width or height, whichever is lesser); or the height demonstrated by a fluid model or field study that ensures the emissions from a stack do not result in excessive concentrations of any air pollutant as a result of atmospheric downwash created by the source itself, nearby structures, or nearby terrain features. Downwash occurs when large buildings or local terrain distort or impact wind patterns, and an area of more turbulent air forms, known as a wake. Emissions from a stack at a power plant can be drawn into this wake and brought down to the ground near the stack more quickly (see fig. 1). States issue air permits to major stationary sources of air pollution, such as power plants, and determine GEP for stacks when they set emissions limitations for these sources. Emissions limitations may be reset when plants undergo New Source Review. New Source Review is a preconstruction permitting program which requires a company that constructs a new facility or makes a major modification to an existing facility to meet new, more stringent emissions limitation based on the current state of pollution control technology. A stack’s GEP height is used in air dispersion modeling that takes place when emissions limitations are developed for a source as part of the permitting process. Many sources contribute to levels of pollution that affect the ability of downwind states to attain and maintain compliance with NAAQS, and some of these pollutants may originate hundreds or thousands of miles from the areas where violations are detected. The Clean Air Act’s “good neighbor provisions” under section 110 of the Act require states to prohibit emissions that significantly contribute to nonattainment or interfere with maintenance of NAAQS in downwind states or which will interfere with downwind states’ ability to prevent significant deterioration of air quality. Section 126 of the Clean Air Act also allows a downwind state to petition EPA to determine that specific sources of air pollution in upwind states interfere with the downwind state’s ability to protect air quality and for EPA to impose emissions limitations directly on these sources. As detailed in the timeline below, Congress granted EPA increased authority to address interstate transport of air pollution under the Clean Air Act, and EPA acted on this authority. 1977 amendments to the Clean Air Act. These amendments contained two provisions that focused on interstate transport of air pollution, the predecessor to the current good neighbor provision of section 110 of the Act and section 126. These amendments also established the New Source Review program. 1990 amendments to the Clean Air Act. These amendments added the Acid Rain Program (Title IV) to the Clean Air Act, which created a cap- and-trade program for SO emissions by 10 million tons from 1980 levels and reducing annual NO emissions by 2 million tons from 1980 levels by the year 2000. 1998 NO SIP Call. After concluding that NO emissions from 22 states and the District of Columbia contributed to the nonattainment of NAAQS for ozone in downwind states, EPA required these states to amend their SIPs to reduce their NO emissions. EPA took this regulatory action based on section 110 of the Clean Air Act. 2005 Clean Air Interstate Rule (CAIR). This regulation required SIP revisions in 28 states and the District of Columbia that were found to contribute significantly to nonattainment of NAAQS for fine particulate matter and ozone in downwind states. CAIR required reductions for SO emissions from 28 eastern states and the District of Columbia and included an option for states to meet these reductions through regional cap-and-trade programs. When the rule was finalized, EPA estimated it would annually reduce SO and NO emissions by 3.8 million and 1.2 million tons, respectively, by 2015. The U.S. Court of Appeals remanded CAIR to EPA in 2008 because it found significant flaws in the approach EPA used to develop CAIR, but allowed the rule to remain in place while EPA develops a replacement rule. 2010 Transport Rule. EPA proposed this rule to replace CAIR, which aims to reduce emissions of SO from power plants. If finalized as written, the rule would require emissions of SO to decrease 71 percent over 2005 levels and emissions of NO to decrease by 52 percent over 2005 levels by 2014. As described above, EPA’s efforts to address the interstate transport of air pollution from power plants have focused on reducing the total emissions of SO from these plants. Unlike tall stacks, pollution controls help to reduce the actual emissions from power plants by either reducing the formation of these emissions or capturing them after they are formed. At coal power plants, these controls are generally installed in either the boiler, where coal is burned, or the duct work that connects a boiler to the stack. A single power plant can use multiple boilers to generate electricity, and the emissions from multiple boilers can sometimes be connected to a single stack. Figure 2 shows some of the pollution controls that may be used at coal power plants: fabric filters or electrostatic precipitators (ESP) to control particulate matter, flue gas desulfurization (FGD) units—known as scrubbers—to control SO emissions, and selective catalytic reduction (SCR) or selective non-catalytic reduction (SNCR) units to control NO emissions. The reduction in emissions from a coal power plant by the use of pollution controls can be substantial, as shown in table 1. The installation of pollution control equipment can also be expensive. According to a Massachusetts Institute of Technology study of coal power plants, it may cost anywhere from $215,000 per megawatt to $330,000 per megawatt to install controls at a coal power plant for particulate matter, SO. For a typical coal power plant with a capacity of 500 megawatts, this means that it could cost from $107 million to install these controls at a newly built facility up to $165 million to retrofit these controls at an existing facility. Additionally, pollution controls can require additional energy to operate, known as an energy penalty. According to our analysis of EIA data, which we updated with our survey results, we found a total of 284 tall smokestacks were operating at 172 coal power plants in 34 states, as of December 31, 2010. While about half of the tall stacks began operating more than 30 years ago, there has been an increase in the number of tall stacks that have begun operating in the last 4 years, which several stakeholders attributed to the need for new stacks when retrofitting existing plants with pollution control equipment. As of December 31, 2010, we found a total of 284 tall stacks were operating at 172 coal power plants in the United States. These tall stacks account for about 35 percent of the 808 stacks operating at coal power plants in the United States, and they are generally located at larger power plants. Specifically, we found these stacks are associated with 64 percent of the coal generating capacity. We found that 207 tall stacks (73 percent) are between 500 and 699 feet tall and that 63 stacks (22 percent) are between 700 and 999 feet tall. The remaining 14 stacks (5 percent) are 1,000 feet tall or higher, with the tallest stack at a coal power plant in the United States having a height of 1,038 feet at the Rockport Power Plant in Indiana. In figure 3, we show how a tall stack compares to the heights of other well-known structures. Thirty-five percent of the 284 tall stacks are concentrated in 5 states along the Ohio River Valley—Kentucky, Ohio, Indiana, Illinois, and Pennsylvania—at 59 coal power plants.