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Particulate Matter

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Particulate Matter: Background Goals & Objectives

Particulate matter (PM) has been linked to a range of serious respiratory and cardiovascular health problems. The key effects associated with exposure to ambient particulate matter include: premature mortality, aggravation of respiratory and cardiovascular disease (as indicated by increased hospital admissions and emergency room visits, school absences, work loss days, and restricted activity days), aggravated asthma, acute respiratory symptoms, chronic bronchitis, decreased lung function, and increased risk of myocardial infarction. Recent epidemiologic studies estimate that exposures to PM may result in tens of thousands of excess deaths per year, and many more cases of illness among the US population.

NCER's extramural PM research is designed to assist in solving many uncertainties about the impacts of PM exposure on mortality and illness. NCER has been conducting PM research indirectly through our Air Quality and Air Pollution Chemistry and Physics solicitations since 1995 and directly with solicitations dedicated to PM topics since 1998. In 1999 NCER funded 5 PM Centers through a competitive solicitation. These efforts were designed to support the priorities identified by the National Research Council and assist the Office of Air in the review and revision of the PM National Ambient Air Quality Standard. In 2005, the EPA funded 5 new PM Centers to further improve our understanding of how particulate matter or PM affects human health and the types and sources of PM most responsible for these effects. The new centers were established at Johns Hopkins University, Harvard University, the University of Rochester, the University of California at Davis, and the University of California at Los Angeles to study high-priority issues related to the effects of airborne particles on human health. These centers are focussing on human susceptibility, mechanisms of health effects, exposure-response relationships, and the cross-cutting issue of linking health effects with particulate matter sources and components.

ORD laboratories and EPA's Office of Air and Radiation are also conducting PM research that addresses the NRC PM research priorities and supports the establishment of air quality standards and the implementation of strategies to reduce PM-related health risks. The extramural and intramural PM research programs are guided by the Research Priorities for Airborne Particulate Matter exit EPA. The ORD laboratories' research program includes: health effects and exposure assessment research, risk assessment activities to periodically review and update the PM Air Quality Criteria Document; and, risk management research support the implementation of air quality standards by state and local governments.

NCER's goals are to support a peer reviewed research program that provides high quality scientific information across the range of PM health research priority topics identified by the National Research Council, and supports the review and revision of the PM National Ambient Air Quality Standards (NAAQS). NCER's research also addresses the NAAQS implementation needs identified in ORD's PM research strategy.

NCER's PM Research is being performed under:

  • GPRA Goal 1- Clean Air
  • Objective 1- Attain NAAQS for Tropospheric Ozone and Particulate Matter
  • Sub-objective 005: Particulate matter health risk model
  • Provide new information on the atmospheric concentrations, human exposure, health effects and mechanisms of toxicity of particulate matter, and facilitate PM NAAQS review through Air Quality Criteria Document development and consultation. Provide data on health effects and exposure to PM and provide methods for assessing the exposure and toxicity of PM in healthy and potentially susceptible populations to strengthen the scientific basis for reassessment of the NAAQS for PM. (NRC Topics 5, 8 and 9)

What is PM?

PM represents a broad class of chemically and physically diverse substances. Particles can be described by size, formation mechanism, origin, chemical composition, atmospheric behavior and method of measurement. The concentration of particles in the air varies across space and time, and is related to the source of the particles and the transformations that occur in the atmosphere.

PM can be principally characterized as discrete particles spanning several orders of magnitude in size, with inhalable particles falling into the following general size fractions:

  • PM10 (generally defined as all particles equal to and less than 10 microns in aerodynamic diameter; particles larger than this are not generally deposited in the lung);
  • PM2.5, also known as fine fraction particles (generally defined as those particles with an aerodynamic diameter of 2.5 microns or less)
  • PM10-2.5, also known as coarse fraction particles (generally defined as those particles with an aerodynamic diameter greater than 2.5 microns, but equal to or less than a nominal 10 microns); and
  • Ultrafine particles generally defined as those less than 0.1 microns.

Fine and coarse particles are distinct in terms of the emission sources, formation processes, chemical composition, atmospheric residence times, transport distances and other parameters. Fine particles are directly emitted from combustion sources and are also formed secondarily from gaseous precursors such as sulfur dioxide, nitrogen oxides, or organic compounds. Fine particles are generally composed of sulfate, nitrate, chloride and ammonium compounds, organic and elemental carbon, and metals. Combustion of coal, oil, diesel, gasoline, and wood, as well as high temperature process sources such as smelters and steel mills, produce emissions that contribute to fine particle formation. Fine particles can remain in the atmosphere for days to weeks and travel through the atmosphere hundreds to thousands of kilometers, while most coarse particles typically deposit to the earth within minutes to hours and within tens of kilometers from the emission source. Some scientists have postulated that ultrafine particles, by virtue of their small size and large surface area to mass ratio may be especially toxic. There are studies which suggest that these particles may leave the lung and travel through the blood to other organs, including the heart. Coarse particles are typically mechanically generated by crushing or grinding and are often dominated by resuspended dusts and crustal material from paved or unpaved roads or from construction, farming, and mining activities.

Congressional Directives

In fiscal year 1998 Congress urged EPA to establish as many as five university-based research centers focused on PM research. Congress also asked EPA to arrange for an independent study by the National Academy of Sciences, National Research Council (NRC), to develop priorities for a comprehensive PM research plan, develop a near and long-term PM research program, and to monitor research progress over the next five years. On March 31, 1998, the NRC released its first report entitled Research Priorities for Airborne Particulate Matter: 1. Immediate Priorities and Long-Range Research Portfolio. Based on recommendations from this NRC report and earlier strategic assessments, ORD is developing and implementing an integrated research program for PM which includes in-house studies, interagency research, and RFAs through which scientists may compete for grant awards.

See Research Priorities for Airborne Particulate Matter exit EPA for more details about the NRC’s recommendations.

NRC Priorities

PM Research Priorities identified by the National Research Council:

  1. Outdoor Measures vs. Actual Human Exposures: What are the relationships between concentrations of PM and gaseous copollutants measured at stationary outdoor air monitoring sites and what are the contributions of these concentrations to actual personal exposures?
  2. Exposures of Susceptible Subpopulations to Toxic PM components: What are the exposures to the most biologically important constituents of PM that cause responses in potentially susceptible subpopulations and the general population?
  3. Characterization of Emission Sources: What are the size-distribution, chemical-composition, and mass-emission rates of PM emitted from primary-particle sources in the U.S, and what are the emissions of the reactive gases that lead to secondary particle formation through atmospheric chemical reactions?
  4. Air Quality Modeling and Testing: What are the linkages between emission sources and ambient concentrations of the biologically important components of PM?
  5. Assessment of Hazardous PM Components: What is the role of biological, chemical, and physical characteristics of PM in eliciting adverse health effects?
  6. Dosimetry-Deposition of PM in the Respiratory Tract: What are the deposition patterns and fate of particles in the respiratory tract of individuals belonging to presumed susceptible subpopulations?
  7. Combined Effects of PM and Gaseous Copollutants: How can the effects of PM be disentangled from the effects of other pollutants? How can the effect of long-term exposures to PM and other pollutants be better understood?
  8. Susceptible Subpopulations: What subpopulations are at increased risk of adverse health outcomes from PM?
  9. Mechanism of Injury: What are the underlying mechanisms that can explain the epidemiological findings of mortality and morbidity associated with exposure to PM?
  10. Analysis and Measurement: To what extent does the choice of statistical models in the analysis of data from epidemiologic studies influence estimates of health risks from PM? Can existing methods be improved? What is the effect of measurement error and misclassification on the estimates of the association between air pollution and health?

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