Sources, Composition, and Health Effects of Coarse Particulate Matter

SHERRI W. HUNT (1), Barbara S. Glenn (1)

(1) US Environmental Protection Agency

     Abstract Number: 227
     Last modified: November 9, 2009

Abstract
Background
Published studies investigating the associations of mortality and morbidity with coarse thoracic particulate matter (CPM) (PM10-2.5) are limited in number and restricted to a small number of locations. The findings are inconsistent and they do not address effects of different components or sources of CPM particles. However, the composition and toxicity of CPM likely vary significantly across locations with large differences between urban and rural regions because of a variety of different sources (e.g., pollen, endotoxin, road dust, agriculture, mining).

One of the major difficulties in interpreting the findings of epidemiology studies of CPM and estimating risks is the measurement error in exposure estimates. Since the lifetime of CPM in the atmosphere ranges from hours to days, large variations exist in the spatial distribution of particles in the atmosphere. This means that in contrast to fine PM (PM2.5), ozone, and other regional air pollutants, ambient monitors may not represent the CPM concentrations to which the nearby populations are exposed. Instead, monitors may only be indicative of CPM concentrations within a fairly short distance. Improving understanding of how CPM concentrations relate to ambient monitors will help determine their applicability for estimating exposure in health studies and significantly increase our ability to determine how this pollutant affects health and the environment.

In 2006, EPA considered changing the standard for CPM to focus on the mass of particles with a diameter between 10 and 2.5 micrometers, but concluded that although the published evidence raised a concern about the toxicity of CPM, particularly in urban and industrial areas, the level of uncertainty was too great to allow changing the indicator. Therefore, the 24-hour standard for PM10 was retained. The annual standard was revoked because studies published at that time did not provide sufficient evidence that CPM presents a risk for long-term health effects.

Methods
In 2007, the National Center for Environmental Research awarded five grants for research studies to improve understanding of the composition, sources, and health effects of urban and rural coarse particulate matter (CPM), which includes particles in the size range from 2.5 to 10 micrometer in diameter.

Results
The research conducted by these grants is contributing to exposure estimation in population studies, and associations of short-term and long-term exposure to CPM with sophisticated analyses of cardiovascular disease and mortality in U.S. locations with a variety of PM sources. Specifically, these studies will advance understanding of spatial and temporal variation and health effects of CPM among populations residing in several metropolitan areas with distinct atmospheric composition: urban Denver and nearby rural Greely, Chicago, St. Paul and Winston-Salem. In addition, characterization of particle components and toxicity in laboratory and controlled human exposure studies will be assessed for the Los Angeles metropolitan area and several other locations in the U.S.

Conclusion
This presentation will briefly describe the five funded research studies and highlight the science questions that are the focus of these ongoing investigations. Some data analyses have been conducted and any early conclusions will be discussed where appropriate.