Particulate matter is composed of small solid and liquid particles suspended in the ambient air, and research studies have associated exposure to elevated levels of these particles in the air with damaging health effects.

The information on these pages describes the research being done by EPA to better understand how particles are emitted into the air or how they form in the air from gaseous pollutants, how they are transported, how people are exposed to them, and the health effects people may experience after they breathe in these particles.

PM Research Hot Topics

• Particulate Matter Research Program: Five Years of Progress - this report highlights early results of EPA's substantial investment in particulate matter research by EPA scientists and grantees from universities and other research institutions across the country. The report also includes an in-depth examination of the health effects, exposure and prevention or mitigation of PM2.5.
• EPA Awards $30 Million Dollar Grant for Particulate Matter Research.  Michael O. Leavitt, the Administrator of the United States Environmental Protection Agency, today awarded the University of Washington with a $30 million grant to study the connection between air pollution and cardiovascular disease.
• The National Academy of Sciences has released their fourth and final report on PM research priorities. The report, "Research Priorities for Airborne Particulate Matter: IV. Continuing Research Progress," can be accessed at the Academy's website.
• PM Research Centers Annual Meeting - The annual progress meeting of the five EPA-funded PM Research Centers provided a rare opportunity for some of the world’s most prominent scientific experts on air pollution to communicate directly with the nation’s stakeholders and policymakers about the latest in PM research. The meeting offered a clear and concise summary of the important research findings and accomplishments related to PM that have been developed by the EPA-funded PM research centers, EPA scientists, and EPA’s research partners. Leading researchers discussed and synthesized scientific advances in three key topical areas: the uncertainties in PM epidemiologic studies; the biological explanations for how PM is causing premature mortality and who is most susceptible to PM effects; and how sources, ambient particles, and their toxic components impact health.
• List of Publications from the PM Research Program (PDF, 66 pp., 1 MB) - The EPA PM Research Program has been a major contributor to the scientific literature since its initiation. EPA researchers and researchers funded by EPA have authored approximately 2,400 articles for publication in peer-review scientific journals. These articles cover the full range of topics associated with PM, from emissions and control technologies to atmospheric chemistry and transport, from ambient measurements to personal exposure, from dosimetry to toxicology, human clinical studies, and epidemiology. A comprehensive bibliography of these articles is now available.
• Air Quality Criteria for Particulate Matter (October 2004) - This fourth external review draft document is an updated revision of the Air Quality Criteria for Particulate Matter, published by the United States Environmental Protection Agency (EPA) in 2001, and it will serve as the basis for reevaluating the current National Ambient Air Quality Standards (NAAQS) for particulate matter (PM) set in 1997. The present external review draft critically assesses the latest scientific information relative to determining the health and welfare effects associated with exposure to various concentrations of PM in ambient air.
• Detroit Exposure and Aerosol Research Study - The Detroit Exposure and Aerosol Research Study (DEARS) will help develop data that improves our understanding of human exposure to various air pollutants in our environment. The primary objective of DEARS is to compare air pollutant concentrations and their sources measured at central or community air-monitoring stations with those measured in various neighborhoods in the Detroit, Michigan area.
• A new EPA study has found associations between particles in the air inside automobiles and cardiovascular health. The Car-related Occupational PM and Air Toxics Exposure of Patrolmen (COPP) Study measured several pulmonary, cardiac, and vascular effects of highway patrol troopers during their patrol shifts and simultaneously monitored air quality in their patrol cars. Details can be found at http://www.epa.gov/nheerl/copp/

What is Particulate Matter, and Why and How Do We Study It?

Particulate matter (PM) in the ambient air comes from a variety of sources and has an equally broad range of size, composition, and other characteristics. Numerous scientific studies have provided evidence that PM in the ambient air is associated with increases in daily mortality, even at levels below the National Ambient Air Quality Standards (NAAQS, usually pronounced as "nacks") for PM that were in place before 1997. In that year, EPA set new NAAQS for PM that included standards for PM2.5, particles smaller than 2.5 µm in aerodynamic diameter. PM2.5 is composed of particles that are directly emitted and particles that are products of chemical reactions of gases in the atmosphere. Examples of directly emitted particles (both PM2.5 and larger, or "coarse," particles) include those from combustion sources such as residential wood combustion, agricultural open burning, coal and oil fired power plants and industries, as well as dust particles from roads and fields. Particles formed in the atmosphere are referred to as "secondary" particles, and the majority of these particles in many areas of the country are from gases from fuel combustion in automobiles, trucks, and power plants such as sulfur dioxide (SO2) and nitrogen oxides (NOx) released by anthropogenic and natural sources.

Many questions remain about particles and why they are associated with adverse health effects, including premature mortality and higher instances of respiratory illness. EPA is conducting research to better understand which attributes of particles may be causing these health effects and who may be most susceptible to their effects, how people are exposed to PM air pollution, how particles form in the atmosphere, and what the contributions are from various sources in the different regions of the country. Three research laboratories and two research centers in EPA's Office of Research and Development are participating in these studies, through work by EPA scientists and researchers at universities and research institutes across the nation. Health research is being conducted by EPA's National Health and Environmental Effects Research Laboratory, and by five PM Research Centers supported by the National Center for Environmental Research. Studies of how people are exposed to ambient particles are being conducted by the National Exposure Research Laboratory, whose scientists are also working to find better means of predicting how particles and gases transform and move in the ambient air, developing air quality models for use by decision makers, improved approaches to accurately measure the levels of PM in the air, and methods to more accurately link particles collected in ambient air to their originating sources. The National Risk Management Research Laboratory is conducting tests to measure the size and composition of particles emitted from different types of sources, including industrial boilers, the burning of biomass in fields and forests, and diesel engines, as well as measuring emissions of gases such as ammonia that can react with other gases in the air to form particles. The research conducted by EPA scientists in each of these areas is expanded by drawing on the expertise of researchers across the country through grants developed and awarded by the National Center for Environmental Research. These efforts, and research results from around the world, are collected and evaluated by the National Center for Environmental Assessment, which develops EPA's official review of the scientific evidence of health and environmental damage from exposure to ambient PM, called the Air Quality Criteria Document for Particulate Matter.

Details on EPA's research and assessment efforts are found by accessing the links below, which describe the ongoing work at each Laboratory and Center.

• National Center for Environmental Assessment
• National Center for Environmental Research
• National Exposure Research Laboratory
• National Health and Environmental Effects Research Laboratory
• National Risk Management Research Laboratory

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