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Student Research

Ryan Allen
PhD Student, Industrial Hygiene

Advances in Particulate Matter Exposure Assessment
(from SPHCM's Spotlight on Research, Issue 17:Summer 2004 (pdf))

As of 2002, more than 65 million Americans lived in cities with unhealthy levels of particulate matter (PM) air pollution. PM, tiny solid and liquid particles suspended in the air, can be generated by motor vehicles, industry, woodstoves, atmospheric processes, smoking, and
cooking. Exposure to PM results in thousands of premature deaths in the US every year, and epidemiological studies have linked outdoor PM
concentrations to a number of adverse health effects including asthma aggravation, decreased lung function, chronic bronchitis, and elevated mortality rates.

In any epidemiological study, the understanding of the relationship between exposure and effect is enhanced by improved exposure characterization. Although people spend the vast majority of their time indoors, where they are exposed to a complex combination of particles
generated both indoors and outdoors, nearly all of the epidemiological studies of PM health effects have relied exclusively on stationary outdoor PM monitors to estimate exposure. Since PM toxicities and control strategies differ depending on where the particles originate, there is a need to develop more sophisticated exposure assessment
methods to estimate how much outdoor- and indoor generated
PM contributes to personal exposures.

Ryan Allen, a PhD candidate in the Department of Environmental and Occupational Health Sciences, with support from the Environmental Protection Agency (EPA) and the Northwest Research Center for Particulate Air Pollution and Health, has been working with Drs. Sally Liu, Tim Larson, and Lianne Sheppard at the UW and Dr. Lance
Wallace of the EPA to separate personal exposure into outdoor- and indoor-generated components. Allen’s research is focused on people who are particularly sensitive to the health effects of PM, including children with asthma and older adults with coronary heart disease
and chronic obstructive pulmonary disease.

Allen’s results reinforce the EPA’s air pollution control strategy that has focused on reducing outdoor PM emissions. On average, 80% of the PM measured inside subjects’ homes was the result of outdoor-generated
particles that had entered through windows and doors. (Just how much outdoor-generated PM contributed to indoor concentrations depended on the type of house and its ventilation characteristics.) Although these sensitive individuals spent an average of only 6% of their time
outdoors, outdoor particle sources contributed nearly half of the average exposure in this study population.

The exposure assessment methods produced by Allen’s research have improved our understanding of the health effects of PM. His methods for separating exposure into indoor- and outdoor-generated components were used in a recent study that assessed the health effects of these two PM source categories.

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