In 1997, the U.S. Environmental Protection Agency (EPA) established regulatory standards to address health risks posed by inhaling tiny particles from smoke, vehicle exhaust, and other sources. At the same time, Congress and the EPA began a multimillion dollar research effort to better understand the sources of these airborne particles, the levels of exposure to people, and the ways that these particles cause disease. To provide independent guidance to the EPA, Congress asked the National Research Council to study the relevant issues. The result was a series of four reports on the particulate-matter research program. The first two books offered a conceptual framework for a national research program, identified the 10 most critical research needs, and described the recommended timing and estimated costs of such research. The third volume began the task of assessing initial progress made in implementing the research program. This, the fourth and final volume, gauged research progress made over a 5-year period on each of the 10 research topics. The National Research Council concludes that particulate matter research has led to a better understanding of the health effects caused by tiny airborne particles. However, the EPA, in concert with other agencies, should continue research to reduce further uncertainties and inform long-term decisions.

Regulatory standards are already on the books at the the U.S. Environmental Protection Agency (EPA) to address health risks posed by inhaling tiny particles from smoke, vehicle exhaust, and other sources. At the same time, Congress and EPA have initiated a multimillion dollar research effort to better understand the sources of these airborne particles, the levels of exposure to people, and the ways that these particles cause damage. To provide independent guidance to the EPA, Congress asked the National Research Council to study the relevant issues. The result is a series of four reports on the particulate-matter research program. The first two books offered a conceptual framework for a national research program, identified the 10 most critical research needs, and described the recommended timing and estimated costs of such research. This, the third volume, begins the task of assessing the progress made in implementing the research program. The National Research Council ultimately concludes that the ongoing program is appropriately addressing many of the key uncertainties. However, it also identifies a number of critical specific subjects that should be given greater attention. Research Priorities for Airborne Particulate Matter focuses on the most current and planned research projects with an eye toward the fourth and final report, which will contain an updated assessment.

In 1997, the U.S. Environmental Protection Agency (EPA) established regulatory standards to address health risks posed by inhaling tiny particles from smoke, vehicle exhaust, and other sources. At the same time, Congress and the EPA began a multimillion dollar research effort to better understand the sources of these airborne particles, the levels of exposure to people, and the ways that these particles cause disease. To provide independent guidance to the EPA, Congress asked the National Research Council to study the relevant issues. The result was a series of four reports on the particulate-matter research program. The first two books offered a conceptual framework for a national research program, identified the 10 most critical research needs, and described the recommended timing and estimated costs of such research. The third volume began the task of assessing initial progress made in implementing the research program. This, the fourth and final volume, gauged research progress made over a 5-year period on each of the 10 research topics. The National Research Council concludes that particulate matter research has led to a better understanding of the health effects caused by tiny airborne particles. However, the EPA, in concert with other agencies, should continue research to reduce further uncertainties and inform long-term decisions.

In 1997, the U.S. Environmental Protection Agency (EPA) established regulatory standards to address health risks posed by inhaling tiny particles from smoke, vehicle exhaust, and other sources. At the same time, Congress and the EPA began a multimillion dollar research effort to better understand the sources of these airborne particles, the levels of exposure to people, and the ways that these particles cause disease. To provide independent guidance to the EPA, Congress asked the National Research Council to study the relevant issues. The result was a series of four reports on the particulate-matter research program. The first two books offered a conceptual framework for a national research program, identified the 10 most critical research needs, and described the recommended timing and estimated costs of such research. The third volume began the task of assessing initial progress made in implementing the research program. This, the fourth and final volume, gauged research progress made over a 5-year period on each of the 10 research topics. The National Research Council concludes that particulate matter research has led to a better understanding of the health effects caused by tiny airborne particles. However, the EPA, in concert with other agencies, should continue research to reduce further uncertainties and inform long-term decisions.

New National Ambient Air Quality Standards for airborne particles smaller than 2.5 micrometers, called PM2.5, were issued by the U.S. Environmental Protection Agency (EPA) amidst scientific uncertainty and controversy. In response to a request from Congress, Research Priorities for Airborne Particulate Matter, the first of four books in a series, 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 timing and estimated costs of such research. The committee concludes that EPA should devote more resources to investigating the relationships between fixed-site outdoor monitoring data and actual human breathing-zone exposures to ambient particulate matter and to identifying the most biologically important constituents and characteristics of particulate matter through toxicological studies. The recommended research activities are critical to determining actual exposures of human subpopulations most susceptible to harm from the most hazardous constituents of particulate matter. Future research will be an investment in public health and a means to ensure that resources spent on control technology and regulatory compliance will have a reasonable probability of success.

In the effort to reduce the scientific and technical uncertainties over regulation of airborne particulate matter in the United States, Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio, the second book in a four-part series requested by Congress, describes the plans of the committee to monitor the progress of the research on particulate matter conducted by the U.S. Environmental Protection Agency (EPA), other federal and state government agencies, and nongovernmental organizations. The book also reviews and updates the committee's portfolio of recommended research in its first volume, Research Priorities for Airborne Particulate Matter: I. Immediate Priorities and a Long-Range Research Portfolio (NRC, 1998). The committee substantially revised two of the ten high-priority research areas recommended in Part I. Part II notes that Congress, EPA, and the scientific community have given strong support to the committee's recommendations and have implemented substantial changes in research efforts in response to Part I of the series. One important research area-studies of the effects of long-term exposure to particulate matter and other major air pollutants-however, does not appear to be underway or planned.