years (1998-2002) in understanding the relationships among airborne PM, its various sources, and its effects on public health.2 The committee’s formal statement of task is presented in Appendix B.

This final report of the committee addresses progress since its first report, published in 1998 (NRC 1998). That report, Research Priorities for Airborne Particulate Matter: I. Immediate Priorities and a Long-Range Research Portfolio, proposed a conceptual framework for a national program of PM research (Figure 1-1); identified 10 high-priority research topics linked to key policy-related scientific uncertainties (Box 1-1); and presented a 13-year integrated “research investment portfolio” containing recommended short- and long-term phasing of research and estimated costs of such research. This fourth report assesses progress on the research agenda set out in the portfolio and offers an enhancement of the portfolio and recommendations for follow-up monitoring, oversight, and evaluation as research on PM extends beyond the time-frame of this committee.

This report also draws on the committee’s second and third reports, published in 1999 and 2001, respectively. In its second report, Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio, the committee described its initial plans for monitoring the progress of research (NRC 1999). In addition, it reviewed and updated the research recommendations from the committee’s first report and substantially revised two of the recommended research topics related to emissions characterization and air pollution modeling.

The third report, Research Priorities for Airborne Particulate Matter. III. Early Research Progress, provided an overview of progress through approximately mid-2000 on the research agenda (NRC 2001). In preparing that report, the committee attempted to catalog the major studies that had been initiated subsequent to its first report, as well as ongoing but relevant studies that were started before the first report. Its review covered research funded by EPA, the Health Effects Institute, and several other agencies that were supporting research on PM. The committee found substantial progress on several research topics, particularly studies directed at assessment of exposure to PM2.5 (research topic 1) and methodological issues (research topic 10). Progress and planning were particularly lacking for research


In addition to effects on human health, airborne particles have other important effects, such as reduction of atmospheric visibility, and interference with particle borne nutrients that can affect ecosystem and agricultural productivity. However, the work of the committee has been directed solely on research that elucidates the human health effects of PM.

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