EXECUTIVE SUMMARY

On July 18, 1997, the administrator of the U.S. Environmental Protection Agency (EPA) issued new National Ambient Air Quality Standards (NAAQS) for airborne particles smaller than 2.5 µm in diameter, called PM2.5. Under the Clean Air Act, the administrator is required to set and to review at least every 5 years the health-based (primary) standards for several major air pollutants (so-called "criteria" pollutants), including particulate matter (PM). The standards are required to ensure the protection of public health, including potentially susceptible subpopulations, with "an adequate margin of safety." The process for setting the standards requires EPA to make both scientific assessments and policy decisions.

Airborne particulate matter is a generic term for a broad class of materials of varying chemical composition and sizes that are transported in the air as discrete solid particles or liquid droplets. Ambient (outdoor) particles originate from diverse natural processes and human activities, such as forest fires, wind erosion, agricultural practices, fossil fuel combustion, industrial manufacturing, and construction of buildings and roads. The particles can be emitted directly from such sources or formed in the atmosphere from gaseous precursors such as sulfur dioxide or nitrogen oxides. The particles can contain heavy metals, acids, biological or biogenic material, and a great variety of other organic and inorganic materials.

The new PM2.5 standards were developed by EPA largely on the basis of evidence from epidemiological studies that found relatively consistent



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Research Priorities for Airborne Particulate Matter: I Immediate Priorities and a Long-Range Research Portfolio EXECUTIVE SUMMARY On July 18, 1997, the administrator of the U.S. Environmental Protection Agency (EPA) issued new National Ambient Air Quality Standards (NAAQS) for airborne particles smaller than 2.5 µm in diameter, called PM2.5. Under the Clean Air Act, the administrator is required to set and to review at least every 5 years the health-based (primary) standards for several major air pollutants (so-called "criteria" pollutants), including particulate matter (PM). The standards are required to ensure the protection of public health, including potentially susceptible subpopulations, with "an adequate margin of safety." The process for setting the standards requires EPA to make both scientific assessments and policy decisions. Airborne particulate matter is a generic term for a broad class of materials of varying chemical composition and sizes that are transported in the air as discrete solid particles or liquid droplets. Ambient (outdoor) particles originate from diverse natural processes and human activities, such as forest fires, wind erosion, agricultural practices, fossil fuel combustion, industrial manufacturing, and construction of buildings and roads. The particles can be emitted directly from such sources or formed in the atmosphere from gaseous precursors such as sulfur dioxide or nitrogen oxides. The particles can contain heavy metals, acids, biological or biogenic material, and a great variety of other organic and inorganic materials. The new PM2.5 standards were developed by EPA largely on the basis of evidence from epidemiological studies that found relatively consistent

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Research Priorities for Airborne Particulate Matter: I Immediate Priorities and a Long-Range Research Portfolio associations between outdoor particulate-matter concentrations and various adverse health effects, including premature mortality, exacerbation of asthma and other respiratory-tract diseases, and decreased lung function. The biological basis of most of the associations is essentially unknown (at the ambient particulate levels at which the associations were observed). There is a great deal of uncertainty about the implications of the findings for risk management, due to the limited scientific information about the specific types of particles that might cause adverse health effects, the contributions of particles of outdoor origin to actual human exposures, the toxicological mechanisms by which the particles might cause adverse health effects, and other important questions. These questions are not presented here as a rationale for abandoning efforts to control public exposures to fine particulate matter and other pollutants, but they do indicate the critical need for better scientific knowledge to guide such efforts. EPA has estimated that implementation of the new PM2.5 standards will prevent approximately 15,000 premature deaths per year in the United States. By law, EPA cannot consider compliance costs when setting these standards. EPA has announced, along with its timetable for implementing the new PM2.5 standards, that it contemplates no actual regulatory emission-control requirements to be implemented until well after the next scheduled review of the particulate-matter standards in the year 2002. In the meantime, Congress has mandated and has begun to fund a major program of research to reduce the key scientific uncertainties. In EPA's Fiscal 1998 appropriations, Congress provided $49.6 million for particulate-matter research—nearly twice the amount requested by EPA. Congress also directed the EPA administrator to arrange for this independent study by the National Research Council (NRC) to identify the most important research priorities relevant to setting NAAQS for particulate matter, to develop a conceptual plan for particulate-matter research, and, over the next 5 years, to monitor and evaluate research progress toward improved understanding of the relationship between particulate matter and its effects on public health. In response to the request from Congress, the Committee on Research Priorities for Airborne Particulate Matter was established in

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Research Priorities for Airborne Particulate Matter: I Immediate Priorities and a Long-Range Research Portfolio January 1998 by the National Research Council, the principal operating agency of the National Academy of Sciences and the National Academy of Engineering. The committee (see Appendix A for biographical information) consists of 20 experts, chosen by the NRC, in epidemiology, medicine, pulmonary physiology, toxicology, public health, exposure assessment, atmospheric chemistry and transport, air quality modeling, air monitoring techniques, biostatistics, risk assessment, research management, and regulatory policy. Its members come from universities and other organizations and perform this public service without financial compensation through the NRC. In forming the committee, the NRC deliberately sought a balance of candidates with differing views on relevant major issues. Committee members were asked to serve as individual experts, not as representatives of any organization. The committee is charged to produce 4 reports between 1998 and 2002. To date, the committee has held two working meetings at the National Academy of Sciences in Washington, D.C., on January 20-21 and February 18-19, 1998. Those meetings included public sessions at which the committee heard presentations from representatives of the U.S. Environmental Protection Agency (EPA), EPA's Clean Air Scientific Advisory Committee (CASAC), the National Institute of Environmental Health Sciences (NIEHS), National Institute for Occupational Safety and Health (NIOSH), North American Research Strategy for Tropospheric Ozone (NARSTO), Health Effects Institute (HEI), Lovelace Respiratory Research Institute (LRRI), American Petroleum Institute (API), Chemical Industry Institute of Toxicology (CIIT), Electric Power Research Institute (EPRI), American Industrial Health Council (AIHC), and Natural Resources Defense Council (NRDC). This report, the first of the 4 planned reports from this NRC committee, offers a conceptual framework for an integrated national program of particulate-matter research, identifies the 10 most critical research needs linked to key policy-related scientific uncertainties, and describes the recommended short-term and long-term timing and estimated costs of such research in an integrated research strategy, or "research investment portfolio." The committee has made no attempt to evaluate the adequacy of the current scientific basis for EPA's new PM2.5 standards, and no evaluation should be inferred, because the process of setting

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Research Priorities for Airborne Particulate Matter: I Immediate Priorities and a Long-Range Research Portfolio such standards also involves legal requirements and policy choices that the present committee was neither charged nor constituted to address. The committee organized its evaluation of particulate-matter scientific uncertainties and research needs according to a simple, coherent, science-based conceptual framework (see Chapter 3), whose components are generally familiar to EPA and the environmental research community. The framework has 5 main components: Sources—Outdoor sources of particulate matter (or gaseous precursors) that can adversely affect public health. Sources include motor vehicles; fossil-fueled electric power plants; industrial facilities; agricultural practices, consumer products; other human sources; and natural processes, such as forest fires or wind erosion. This element of the framework includes factors determining the release characteristics, dispersal, and transport of emissions that lead to atmospheric contamination. Ambient Indicators—The mass concentration or other measures of indicators such as PM10 (airborne particles smaller than 10 µm diameter) or PM2.5 in ambient air. Data for the indicators are collected at fixed outdoor monitoring sites to determine regulatory attainment of the NAAQS, or in some health studies, to represent particulate-matter exposure in a given area. Exposure—The concentration of particulate-matter indicator actually coming into contact with an individual over a specified period. Actual exposure to humans is determined by ambient air concentrations, contributions from indoor sources, and human time-activity patterns. The relevant point of contact is the breathing zone of the individual. For EPA, the aspect of exposure most relevant to regulatory policy is the portion of total exposure that is attributable to outdoor air.

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Research Priorities for Airborne Particulate Matter: I Immediate Priorities and a Long-Range Research Portfolio Dose—The amount and specific types of toxicants deposited in various parts of the respiratory tract and other sites within the body over a specified period. The dose of specific toxicants received by an individual is affected by factors such as retention and clearance of PM (or specific constituents of PM) from target tissues in the lung and respiratory tract. The dose delivered to specific tissues might result in injury and altered performance of repair mechanisms. Response—Changes in specific human health parameters attributable to tissue doses resulting from inhaled particulate matter. These biological responses can be expressed in terms of molecular or cellular changes in the lung or other tissues, overall tissue damage, or ultimately, clinical signs of toxicity, such as illness or premature death. In evaluating the key scientific uncertainties and assigning priorities to research needs on particulate matter, the committee used both strategic and practical criteria (see Chapter 3) organized in three categories: scientific value, the value of information for decisionmaking, and feasibility and timing considerations. The committee judged the following 10 research topics (see Chapter 4) to warrant the highest priority. The order in which these research topics are presented does not represent relative ranking or sequence of the research topics recommended by the committee. All 10 topics met the committee's ranking criteria, and they are highly interdependent and interactive within the committee's research portfolio. Investigate quantitative relationships between particulate-matter concentrations measured at stationary outdoor monitoring sites and the actual breathing-zone exposures of individuals to particulate matter and gaseous copollutants, taking ambient outdoor and indoor pollutant sources and human time-activity patterns into account, especially for potentially susceptible subpopulations.

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Research Priorities for Airborne Particulate Matter: I Immediate Priorities and a Long-Range Research Portfolio Investigate exposures to the most biologically important constituents and characteristics of particulate matter that might adversely affect health, especially for potentially susceptible subpopulations. Develop advanced mathematical, modeling, and monitoring tools to represent the relationships between specific sources of particulate matter and human exposures. Apply modeling and other analytical tools to link sources of toxicologically important constituents and characteristics of particulate matter to exposed individuals and populations. Assess through toxicological and epidemiological studies the most biologically important physical and chemical characteristics and constituents of particulate matter that produce adverse health effects. Investigate the deposition patterns and fate of particles in the respiratory tract of individuals potentially susceptible to particulate matter. Investigate through toxicological and epidemiological studies the interactions between particulate matter and gaseous copollutants in producing harmful short-term and long-term exposures and resulting adverse health effects. Identify the human subpopulations that are potentially most susceptible to adverse health effects from particulate-matter exposures (e.g., children, the elderly, and people with chronic respiratory diseases, cardiopulmonary diseases, or compromised immune systems). Investigate the toxicological mechanisms by which particulate matter produces mortality and acute or chronic morbidity, using laboratory-animal models, human clinical studies, and in vitro test systems.

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Research Priorities for Airborne Particulate Matter: I Immediate Priorities and a Long-Range Research Portfolio Develop and apply advanced methods for statistical analysis of epidemiological studies and for dealing with measurement and misclassification errors in estimating adverse health effects of particulate matter. For each of these research priorities, the committee presents in Chapter 4 of this report a description of the recommended research, comments on the potential scientific value of the research, comments on the potential value for decisionmaking, guidance as to feasibility and timing, and rough but informed collective-judgment cost estimates for the recommended research. In Chapter 5, the committee summarizes the above research recommendations in an integrated strategic plan (or research investment portfolio), designed for optimal sequencing of a goal-oriented, multidisciplinary research program on particulate matter. The portfolio is designed to maximize the growth of critical scientific knowledge about particulate matter expeditiously and cost-effectively through interactive components and iterative stages, providing a continuing stream of scientific evidence on continuously advancing topics. It spans 13 years, from 1998 to 2010—the estimated closure date for scientific input to EPA's anticipated 2012 review of particulate-matter standards. It is designed for the difficult goal of reconciling research and regulatory timetables to emphasize both early and longer-term research results to address key uncertainties about particulate matter and its health effects. This portfolio, if aggressively and properly implemented by EPA, should result in substantial new information for the next scheduled EPA review of the particulate-matter standards in the year 2002. By that time, critical information would be expected regarding the most biologically important components and characteristics of particulate matter, the toxicological mechanisms through which they act, and how well the data from ambient air monitors represent the actual exposure of people to particulate matter, especially for the most potentially susceptible individuals. Later in the plan, the portfolio emphasizes epidemiological studies that will use the results of the earlier research activities to identify potentially susceptible human subpopulations, assess the effects of particulate-matter exposures on such subpopulations, and provide surveillance of the public-health consequences of implementing

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Research Priorities for Airborne Particulate Matter: I Immediate Priorities and a Long-Range Research Portfolio the new PM2.5 standards. The portfolio also places emphasis on research into combined exposures to particulate matter and gaseous copollutants. The development of advanced methods and models needed for research and assessment is also emphasized. In Chapter 6, the committee compares its research recommendations with EPA's published statements of particulate-matter research needs and research-program strategy, and with EPA's current research activities and plans. Although the committee concludes at this early stage of its 5-year study that EPA's current and planned research activities generally appear to be reasonable and potentially useful, the committee disagrees with the early timing and funding of some elements of EPA's research plans, based on the briefings and documentation thus far provided by EPA staff. Most notably, the committee concludes that EPA should immediately devote more intramural as well as extramural resources to investigating the relationships between fixed-site outdoor monitoring data and actual human exposures to ambient particulate matter, and to identifying the most biologically important constituents and characteristics of particulate matter through toxicological studies. EPA's current plans appear to focus only about 4% of its intramural research resources on investigating ambient-versus personal-exposure relationships, and only about 3% of EPA's entire particulate-matter research budget appears to be focused on biologically important components of the particulate-matter mixture. This is crucially inadequate. If the current mix of scientific expertise among the federal career staff of EPA's intramural laboratories is unable to respond expeditiously to this committee's recommendations, then EPA should look into the possibility of conducting this work extramurally. Moreover, because the competitively selected, university-based particulate-matter research centers requested by Congress will require time to develop before producing results, the committee recommends that some centers be initiated in 1998, instead of 1999 as currently planned. The competitively selected centers should be separate and in addition to the research funded through competitive, investigator-initiated research grants and cooperative agreements, because their role as multidisciplinary centers for integrated research should complement the more targeted research projects.

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Research Priorities for Airborne Particulate Matter: I Immediate Priorities and a Long-Range Research Portfolio Independent of the research program, EPA's air regulatory office is initiating an extensive PM2.5 NAAQS-attainment monitoring program to obtain data on PM2.5 levels across the United States. The committee considered EPA's plans for this regulatory program and for the allocation of research resources to the development of new monitoring techniques (including new, more-sophisticated monitoring platforms). The committee recognizes that substantial resources must be applied to ambient monitoring to ascertain attainment of the standards in various geographic areas, but it is concerned that the monitoring program is moving forward rapidly with too narrow a focus on PM2.5. The committee is concerned about the scientific value of the data to be collected in these efforts if such monitoring is fully planned and implemented before some of the immediate research priorities are addressed and data gaps are filled. Moreover, as a secondary but critical goal, such a monitoring program should also be designed to support relevant health-effects, exposure, and atmospheric-modeling research efforts, or else the costs of some important research will increase greatly because of the need for additional monitoring. EPA cannot assume that the implementation of the national PM2.5 monitoring network will provide useful data for improving research or risk assessments for particulate matter. Current plans (e.g., speciation of particulate matter at least every sixth day) are inadequate for this purpose. EPA's monitoring plans will undoubtedly provide substantial amounts of data useful for determining attainment of new PM2.5 standards in various locations. However, these data will only be useful in research if monitoring-system design and site location lead to population-exposure measures of sufficient biological relevance and accuracy. Without this, the State Implementation Plans may miss important targets for control. Based upon theoretical considerations, the Federal Reference Method (FRM) sampler to be used by EPA is expected to lose volatile material (e.g., some nitrates and organics) from particle samples in quantities that are likely to depend upon location and season. Ongoing experiments are attempting to quantify the extent of this loss, and some data showing the bias toward undersampling of organics and nitrates have been presented at several conferences during the past 12 months.

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Research Priorities for Airborne Particulate Matter: I Immediate Priorities and a Long-Range Research Portfolio If those losses turn out to be substantial, then using the FRM would amount to quantifying only a fraction of the outdoor concentration, and that fraction would vary geographically and seasonally. Alternative technologies that overcome some of these biases are available and could instead be adopted. EPA's planned PM2.5 monitoring network appears to place great emphasis on site zones intended to represent the outdoor exposure of large communities. Greater use of continuous (hourly) monitors would help determine the times of day and the exposures of people who are commuting, working, or exercising outdoors. Such monitoring would facilitate time-series epidemiological studies. More chemical characterization of particulate matter would help to enable testing of more specific indicators than PM2.5 mass alone. The committee recommends that EPA re-evaluate its current plans for the PM2.5 monitoring program in light of this report. The committee recommends that EPA consider more fully the possibility that future research results might indicate that the expensive monitoring program is not measuring the most biologically important aspects of particulate matter. The plans for this program (e.g., number and location of monitors and specific objectives and operating conditions) should be thoroughly and independently peer-reviewed at an early date, while the opportunity still exists for such review to influence the monitoring-network design and operation. Changes could then be made to increase the scientific utility of EPA's monitoring data, while still meeting the need for assessing regulatory attainment of particulate-matter standards at selected sites. Included in the EPA monitoring program are plans for several ''super" monitoring sites where more extensive monitoring efforts will take place. At these sites, ambient-concentration data will be collected for gaseous pollutants, as well as for several size and chemical fractions of particulate matter. The costs of these monitoring efforts will be considerable, but their utility for health-effects studies has not been adequately considered to date. EPA has proposed to spend more funds on the PM2.5 monitoring network than on all particulate-matter-research activities combined. Therefore, it is essential to leverage both regulatory monitoring and research efforts together to

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Research Priorities for Airborne Particulate Matter: I Immediate Priorities and a Long-Range Research Portfolio make the most effective use of resources to improve the scientific basis for decisionmaking. Chapter 7 presents additional guidance for implementation of the committee's recommended research program. It discusses the need for a comprehensive, continually updated, on-line inventory of federal and nonfederal particulate-matter research activities; periodic reassessments of the focus, effectiveness, and accountability of ongoing research activities; a clear strategy for integrating extramural contributions with EPA's intramural research activities; and sustained funding for particulate-matter research. The committee is encouraged by the leadership shown by Congress when it provided Fiscal 1998 funds for particulate-matter research well above the amounts requested by EPA, and recommends support of the highest-priority particulate-matter research at roughly similar levels for the next decade and beyond. Specifically, as detailed in Chapters 4 and 5, the committee estimates that the highest-priority particulate-matter research recommendations presented in this report will require the following funding over the next 13 years: Fiscal Estimated Cost Year ($ million, rounded) 1998 40 1999 46 2000 51 2001 57 2002 55 2003 46 2004 31 2005 31 2006 19 2007 19 2008 19 2009 15 2010 15 These cost estimates are not intended to represent the recommended total particulate-matter research budget for EPA or the nation.

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Research Priorities for Airborne Particulate Matter: I Immediate Priorities and a Long-Range Research Portfolio Instead, they represent the estimated costs of the committee's recommended 10 highest-priority particulate-matter-research activities. Other particulate-matter-related research beyond that recommended in this report can be useful or even necessary. Examples of such additional research are the completion of worthwhile projects already under way, research that meets various technical information requirements of regulatory program offices, and the administrative and infrastructure costs of creating and operating the particulate-matter research centers mandated by Congress. These were not included in the committee's cost estimates. The committee has not yet had time to evaluate in detail all of EPA's particulate-matter research plans and proposed budget allocations at this early stage of the 5-year study. More detailed assessments will be presented in the committee's second report in December 1998. The committee's cost estimates are probably more accurate for the early years than for later years in the portfolio plan, because results of early research will undoubtedly influence substantially the direction and costs of research in the later years. The highest-priority research activities recommended in this report are critical to determining actual exposures of human subpopulations most susceptible to harm from the most hazardous constituents of particulate matter. Such research will be an investment in public health and a means to ensure that resources spent in the future on control technology and regulatory compliance will have a reasonable probability of success. The committee is convinced that success is achievable and that the research recommended in this report can help achieve better public-health protection and more effective regulatory efforts. The potential cost of ignorance is by no means limited to wasting considerable dollars and effort, but, more important, failing to protect people from preventable harmful exposures. Failure to plan, implement, and sustain an integrated program of the highest-priority research activities could have undesirable consequences. If particular biologically important constitutents or characteristics of particulate matter exist and are not adequately identified, then fixed-site or personal monitors could fail to indicate the most serious particulate-matter risks to public health. Epidemiological and experimental studies

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Research Priorities for Airborne Particulate Matter: I Immediate Priorities and a Long-Range Research Portfolio that rely upon such information could be impeded or misdirected. In addition, sources of the most toxic components of particulate matter could be misidentified, leading to ineffective air-pollution control strategies. The research costs estimated by the committee can be viewed as investments in the scientific foundation upon which all particulate-matter regulatory activities—planning, implementation, monitoring, compliance, and enforcement—of EPA, state and local governments, and the private sector will be built. A solid scientific foundation can help ensure that all of these other investments will yield a sound return. An inadequate scientific foundation will lead to continued uncertainty, contentious debates, and potentially unwise regulatory efforts that fail to minimize the risks of particulate matter to public health. The committee's second report is scheduled for completion in December 1998. It is expected to include more detailed assessments of the ongoing and planned particulate-matter research activities of EPA and other organizations, as well as expanded descriptions of the committee's research recommendations and long-range strategy for improving the scientific basis for particulate-matter decisionmaking. The committee's third and fourth reports, scheduled for completion in December 2000 and December 2002, respectively, will report upon the progress of particulate-matter-research activities of EPA and other agencies and organizations within and outside the United States.

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