1
Introduction

The U.S. electric-utility industry has made considerable strides in reducing emissions of sulfur dioxide, oxides of nitrogen (NOx), and particulate matter (PM) since passage of the 1970 Clean Air Act and its subsequent amendments. Because of new more stringent standards and regulations, however, emissions from coal-fired power plants continue to be targeted for reduction, especially emissions that contribute to ambient fine particulates, tropospheric ozone, regional haze, acidification, and air toxics.1

LEGISLATIVE BACKGROUND

The Clean Air Act directs the Environmental Protection Agency (EPA) to set national ambient air quality standards (NAAQSs), establishing limits for designated air pollutants in ambient air. PM, ozone, nitrogen dioxide, sulfur dioxide, carbon monoxide, and lead (Pb) are the six air pollutants for which NAAQSs have been set. Of these, only PM is not a specific chemical or element.

The NAAQSs are intended to prevent ambient concentrations of the designated air pollutants from rising to levels that may have adverse effects on public health or welfare, with an added margin of safety. For each of the six designated pollutants, EPA periodically prepares a "criteria document," which contains the best scientific information on the pollutant and the relationship between levels of the ambient concentration and adverse effects. Criteria documents are reviewed by the Clean Air Scientific Advisory Committee (CASAC), an independent panel of scientists (mostly from academic or research institutions) appointed by the EPA administrator. Because our understanding of relationships between pollutant levels and health is constantly evolving, the Clean Air Act requires that NAAQSs be reviewed every five years. This review entails writing a new criteria document that incorporates new research findings, followed by a judgment by the EPA administrator as to whether the existing NAAQS is appropriate or should be adjusted.

In principle, the relationship between pollutant levels and adverse health effects is the only criteria for setting the level of a primary NAAQS. The assumption, indicated by the "margin of safety" provision, is that there is a threshold concentration for ambient air pollutants below which adverse health effects will not occur. On the basis of this assumption, setting an NAAQS is an objective, scientific determination of that threshold. The Clean Air Act prohibits considerations of cost, technical feasibility, and other nonhealth criteria in determining an NAAQS. The recent criteria documents for ozone and PM, however, did not find evidence for a threshold.

The first NAAQS for PM, which was set in 1971, targeted the total suspended particulates (TSP) mass per unit volume of air, without regard to chemical composition of the particles. In 1987, EPA revised the standard, changing the indicator from TSP to particles of 10 micrometers (μm) aerodynamic diameter or less (PM10), without regard to chemical composition. This revision was based on the finding that particles with diameters greater than 10 μm are less likely to be inhaled into the lung than smaller particles.

1  

Air toxics is a common technical term for toxic air pollutants, poisonous substances in the air that come from natural or manmade sources that can harm the environment or affect human health.



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Review of the U.S. Department of Energy Office of Fossil Energy's Research Plan for Fine Particulates 1 Introduction The U.S. electric-utility industry has made considerable strides in reducing emissions of sulfur dioxide, oxides of nitrogen (NOx), and particulate matter (PM) since passage of the 1970 Clean Air Act and its subsequent amendments. Because of new more stringent standards and regulations, however, emissions from coal-fired power plants continue to be targeted for reduction, especially emissions that contribute to ambient fine particulates, tropospheric ozone, regional haze, acidification, and air toxics.1 LEGISLATIVE BACKGROUND The Clean Air Act directs the Environmental Protection Agency (EPA) to set national ambient air quality standards (NAAQSs), establishing limits for designated air pollutants in ambient air. PM, ozone, nitrogen dioxide, sulfur dioxide, carbon monoxide, and lead (Pb) are the six air pollutants for which NAAQSs have been set. Of these, only PM is not a specific chemical or element. The NAAQSs are intended to prevent ambient concentrations of the designated air pollutants from rising to levels that may have adverse effects on public health or welfare, with an added margin of safety. For each of the six designated pollutants, EPA periodically prepares a "criteria document," which contains the best scientific information on the pollutant and the relationship between levels of the ambient concentration and adverse effects. Criteria documents are reviewed by the Clean Air Scientific Advisory Committee (CASAC), an independent panel of scientists (mostly from academic or research institutions) appointed by the EPA administrator. Because our understanding of relationships between pollutant levels and health is constantly evolving, the Clean Air Act requires that NAAQSs be reviewed every five years. This review entails writing a new criteria document that incorporates new research findings, followed by a judgment by the EPA administrator as to whether the existing NAAQS is appropriate or should be adjusted. In principle, the relationship between pollutant levels and adverse health effects is the only criteria for setting the level of a primary NAAQS. The assumption, indicated by the "margin of safety" provision, is that there is a threshold concentration for ambient air pollutants below which adverse health effects will not occur. On the basis of this assumption, setting an NAAQS is an objective, scientific determination of that threshold. The Clean Air Act prohibits considerations of cost, technical feasibility, and other nonhealth criteria in determining an NAAQS. The recent criteria documents for ozone and PM, however, did not find evidence for a threshold. The first NAAQS for PM, which was set in 1971, targeted the total suspended particulates (TSP) mass per unit volume of air, without regard to chemical composition of the particles. In 1987, EPA revised the standard, changing the indicator from TSP to particles of 10 micrometers (μm) aerodynamic diameter or less (PM10), without regard to chemical composition. This revision was based on the finding that particles with diameters greater than 10 μm are less likely to be inhaled into the lung than smaller particles. 1   Air toxics is a common technical term for toxic air pollutants, poisonous substances in the air that come from natural or manmade sources that can harm the environment or affect human health.

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Review of the U.S. Department of Energy Office of Fossil Energy's Research Plan for Fine Particulates In July 1997, the EPA revised the PM NAAQS to include ambient air concentrations of PM with an aerodynamic diameter of 2.5 μm or less (PM2.5, or fine particulate matter), again without regard to chemical composition. PM2.5 was selected because particles of this size or smaller penetrate more deeply into the lung. The new PM2.5 standard establishes a 24-hour average ambient concentration limit of 65 micrograms per cubic meter (μg/m3) and an annual mean concentration limit of 15 μg/m3 to protect human health from both acute and chronic effects associated with the respiration of fine particulate matter. To meet the new ambient concentration levels, many different sources of emissions would have to reduce their current emissions that contribute to primary and secondary PM concentrations, especially in urban areas of the eastern United States where many coal-fired power plants are located. The EPA also promulgated regional haze regulations in April 1999 that focused on the impact of PM2.5 on visibility in Class I ("pristine") areas of the United States. On May 14, 1999, the U.S. Court of Appeals for the District of Columbia remanded the new ambient PM2.5 standards on the grounds that the EPA had interpreted provisions of the Clean Air Act in a way that was unconstitutional. The court did not vacate EPA's PM2.5 NAAQS but invited EPA to provide additional justification for the level of the standard and retained jurisdiction over future hearings on the matter. EPA has indicated that it plans to appeal this ruling. The major components of PM2.5 are nitrates, sulfates, carbonaceous materials, and varying amounts of crustal dust. PM is defined by the federal reference method (FRM) of measurement. A national PM2.5 monitoring network, consisting of 1,500 air monitors, is being deployed to collect data. The network will also include 70 National Park Service sites in remote locations to study background concentrations and to monitor for regional haze. Air quality data will be collected for three years, beginning in 1999, to determine attainment (i.e., areas that meet the NAAQS) and non-attainment areas. In non-attainment areas, states must draft plans (state implementation plans [SIPs]) to limit emissions of specific pollutants to make the necessary improvements in air quality. The combustion of coal to generate electricity produces both primary PM2.5 (e.g., fly ash, carbon soot, acid mist) and the gaseous precursors (e.g., sulfur dioxide and NOx) that lead to the formation of secondary fine particles (principally sulfates and nitrates). The gaseous precursors contribute substantially more to the total ambient PM2.5 mass than primary PM2.5. However, because of recent modifications in emission-control technologies for coal-fired power plants, the relationship between coal-fired boiler emissions and the concentration and composition of ambient fine particulate matter is still uncertain. In fiscal year 1998, congressional appropriations called for the U.S. Department of Energy's Office of Fossil Energy (DOE-FE) to initiate a research program to address the key technical and scientific issues on the effects of the new standard for coal-based power systems. In response to this directive, the DOE-FE staff at DOE headquarters in Washington, D.C., and at the Federal Energy Technology Center (FETC) in Pittsburgh, Pennsylvania, developed a fine particulate research plan and program (FETC, 1999a). SOURCES OF FINE PARTICULATE MATTER Atmospheric aerosols are particles ranging in size from a few nanometers to tens of micrometers. Particles less than 2.5 μm in diameter are generally referred to as "fine" and particles between 2.5 and 10 μm in diameter as the "coarse" fraction of PM10. Fine particles with diameters of less than 0.1 μm are referred to as ''ultrafine." Atmospheric PM is either directly emitted to the atmosphere (primary PM) or formed in-situ by gas-to-particle conversion processes (secondary PM). Sources of primary particles can be natural or anthropogenic. Significant natural sources of particulates include soil and windblown dust, sea spray, and volcanic action. Natural particles are formed from mechanical processes and are mostly coarse. However, some of these particles are small enough to belong to the fine particulate category. Terrestrial dust is also emitted as the result of human activities (e.g., from construction, resuspension of dust during driving, or agricultural activities). Smoke from forest, agricultural, and other fires also contributes to ambient fine particles. Fuel combustion, industrial processes, transportation, and fugitive dust (e.g., from paved and unpaved roads or from construction) are the most important sources of primary anthropogenic particles. Combustion of coal, oil, or biomass results in the emission of mostly fine particles (diameters around 0.1-0.5 μm) of various compositions, depending on the fuel and combustion conditions. These particles consist mainly of carbonaceous matter, sulfates, and trace metals. Most of the ambient fine particulate mass is

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Review of the U.S. Department of Energy Office of Fossil Energy's Research Plan for Fine Particulates composed of secondary particles, which are usually the product of gas-to-particle conversion. Compounds emitted to the atmosphere as vapors (oxides of sulfur and nitrogen, ammonia, and volatile organic compounds) undergo chemical transformations resulting in the formation of low volatility products and their transfer to the condensed phase. Sulfur dioxide is oxidized both in the gas phase (by the hydroxyl radical) and inside cloud droplets (e.g., by hydrogen peroxide, ozone, or oxygen) eventually forming sulfate compounds. Oxides of nitrogen react to form nitric acid vapor, which can then react with the available ammonia to form ammonium nitrate, with sodium chloride from sea spray to form sodium nitrate, or with carbonates from dust to form calcium, potassium, or magnesium nitrate. Several organic compounds (usually aromatics, but also high molecular weight alkanes, alkenes, and oxygenates) form low volatility products during photooxidation that condense on available particles to form secondary organic aerosols. Although most secondary PM is the result of anthropogenic activities, naturally emitted precursors are often significant contributors to ambient fine aerosols. Biogenic hydrocarbons (e.g., terpenes, sesquiterpenes, and oxygenates) produce a variety of secondary organic aerosol compounds during photooxidation. Dimethylsulfide emitted by the oceans produces sulfur dioxide and sulfate during atmospheric reactions with the hydroxyl radical. All of these gas-to-particle conversion processes form significant amounts of particulate mass but generally do not form new particles. The products of these chemical transformations are simply transferred to the available particles. New ultrafine particle formation in the atmosphere can occur during the rapid formation of one or more compounds with an exceptionally low vapor pressure. The nucleation of particles with diameters of a few nanometers during the reaction of sulfuric acid and water is believed to be the most important in-situ source of aerosols. These nucleations can create thousands of new particles per cubic centimeter in a few hours. Because of the small size of these fresh nuclei, the contribution of nucleation to atmospheric particulate mass is negligible. Because most of the fine particle mass is formed by gas-to-particle conversion, establishing the specific sources of PM2.5 has been difficult. One advantageous feature of atmospheric primary particles is that their chemical composition can often be used to identify their source types because each source type has a chemical "fingerprint." In fact, one of the most reliable methods of establishing primary sources of ambient PM is through chemical mass balance (CMB)-based source apportionment. The same method cannot be used, however, to identify sources of precursor gases that form secondary particulates. In 1996-1997, coal-fired power plants emitted approximately 60 percent of the total sulfur dioxide and 25 percent of the NOx emissions, which are precursors of secondary particulate matter, in the United States (EPA, 1998a). The amount of primary particulate emissions from coal-fired power plants is currently estimated to be less than 1 percent of the total primary PM10 emissions in the United States (EPA, 1996). Data are not yet available on the percentage of primary PM2.5 emissions attributable to coal-fired power plants, but this number is also expected to be small. RESEARCH ON PARTICULATE MATTER The National Research Council (NRC) Committee on Research Priorities for Airborne Particulate Matter was established to identify the most important research priorities relevant to setting and reviewing NAAQSs for PM, to develop a conceptual plan for PM research, and to monitor and report on progress toward characterizing the relationship between PM and its effect on public health. That committee was asked to produce four reports over a five-year period (1998-2002). The first report, Research Priorities for Airborne Particulate Matter. I. Immediate Priorities and a Long-Range Portfolio (NRC, 1998), recommended a long-range research strategy for PM over the next 13 years. One purpose of that strategy was to disseminate the results relevant to policy-related scientific questions as quickly as possible. The 10 PM research needs identified in the first report are considered to be the most critical scientific questions to be answered for characterizing the complex relationships between particle sources (including the formation of secondary particles from gaseous interactions) and ambient PM concentrations, actual human exposures, doses delivered to the lung, and, ultimately, adverse health effects from the most biologically active constituents or characteristics of PM. These same questions are obviously relevant to the DOE-FE fine particulate research program. The first report also included an early inventory (especially Appendix B of that report) of ongoing research on exposure to ambient PM and the health effects of PM. In the second report, Research Priorities for

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Review of the U.S. Department of Energy Office of Fossil Energy's Research Plan for Fine Particulates Airborne Particulate Matter. II. Evaluating Research Progress and Updating the Portfolio (NRC, 1999), plans for monitoring progress in research were described, the research recommendations from the first report were reviewed and updated, and two of the recommended research areas were substantially revised. The third and fourth reports in 2000 and 2002 will describe and evaluate the results of the research. In the first report, the Committee on Research Priorities for Airborne Particulate Matter concluded that research on PM is still largely uncoordinated and fragmented. Better coordination of federal and nonfederal PM research would increase the likelihood of yielding information that will be useful for public-policy decisions and will ultimately improve public health. In the second report, the committee concluded that meeting the overall objectives of the PM research portfolio recommended in the first report would require that PM research be considered a national effort involving Congress and many agencies of the executive branch of government, as well as states and the private and nonprofit sectors. DOE's research on fine particulates is a small part of the international and national research being conducted or planned in the public and private sectors. In addition to DOE, research on PM is funded by several federal agencies, including EPA, the U.S. Department of the Interior, the National Institute of Environmental Health Sciences, the National Oceanic and Atmospheric Administration, and others. The scope of funded research on PM is expanding rapidly. The growing diversity of sponsors and the many different kinds of scientific investigations uncle way add to the complexity of the task of monitoring progress and increase the need for federal interagency coordination and management. Integrated management is essential to the implementation of the nation's PM research portfolio. In September 1998, an inventory of federal research programs on atmospheric PM was prepared by the interagency Committee on the Environment and Natural Resources Air Quality Research Subcommittee chaired by a DOE official (Martha Krebs, director, Office of Science) (OSTP, 1998). FETC staff attend monthly meetings of this subcommittee and provide information on the DOE-FE air quality monitoring. The subcommittee's report summarizes research by 14 federal agencies. Total federal funding for the projects included in the report was approximately $26 million in fiscal year 1998. Of the total, DOE's share was 26 percent, or about $6.75 million. The only research from the DOE's FETC mentioned in the report is the Upper Ohio River Valley Project (UORVP) (see Chapter 3), although some Tennessee Valley Authority (TVA) research that might be related to TVA projects partially supported by DOE are mentioned. The subcommittee recommended that federal research be continued "if we are to better characterize PM exposures and understand the processes that control the formation and distribution of PM" (OSTP, 1998). The recommended areas of emphasis were: measurement technology; atmospheric chemistry; modeling; and emission characterization and source apportionment. SCOPE OF THIS STUDY AND ORGANIZATION OF THE REPORT In 1998, the DOE's Deputy Assistant Secretary for Coal and Power Systems, Office of Fossil Energy, requested that the NRC review the DOE-FE's research plan for fine particulates. In response to that request, the NRC appointed the Committee to Review the Office of Fossil Energy's Fine Particulate Research Plan. The committee is composed of individuals with expertise in the operation of coal-fired power plants, emissions from coal-fired power plants, air quality monitoring and modeling, atmospheric chemistry, health effects of PM, and emission-control technologies (see Appendix A for biographical sketches of the committee members). The committee's statement of task includes the following statement: Examine and review the DOE Office of Fossil Energy's research plan for fine particulate matter including reviewing the goals and objectives of the plan, planned efforts on PM2.5 monitoring, particulate matter emissions characterization from coal-fired power plants, and R&D on approaches to control emissions (e.g., feedstock composition, combustion modifications, control technologies) that contribute to ambient PM2.5, and make recommendations for improving the plan, as appropriate. This report documents the committee's review of the research plan and program and its conclusions and recommendations. Prior to its first meeting, the committee reviewed DOE-FE's research plan and program on fine particulates (see Appendix B for a list of projects in the program) (FETC, 1999a). At the first meeting, the committee was given a series of presentations by DOE representatives on the plan and program and related

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Review of the U.S. Department of Energy Office of Fossil Energy's Research Plan for Fine Particulates activities (see Appendix C). These presentations were followed by presentations by outside speakers. The committee then formulated questions to elicit additional information and data from DOE, which was used to supplement the brief project descriptions in the DOE written program plan. At the second committee meeting, the committee discussed and agreed on the substance of the report and the major conclusions and recommendations. This report is organized into three chapters. Chapter 1 provides a brief background and introduction to the issue. Chapter 2 provides a general background and summary of the current state of knowledge on PM2.5 issues and the specific issues relevant to the DOE-FE. Chapter 3 reviews the substance of the DOE-FE research program on fine particulates and provides recommendations for improving the program. These recommendations address the salient questions regarding fossil-fueled power plants and fine particulates. (The reader familiar with PM2.5 issues can focus on Chapter 3, which contains the committee's review of the DOE-FE fine particulate research program.)