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Spatial and Temporal Variation in PM2.5 Chemical Composition in the United States

Bell, M*; Ebisu, K*; Dominici, F

ISEE/ISEA 2006 Conference Abstracts Supplement: Poster Abstracts: Abstracts

*Yale University, New Haven, CT. Johns Hopkins Bloomberg School of Public Health, Baltimore, MD.


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Numerous studies have linked levels of fine particulate matter (PM2.5) to adverse health incomes. While particles' size affects health through differential deposition in the respiratory system, which chemical components of PM are most harmful is not well understood. There is mounting evidence that chemical composition also plays a role in particles' toxicity, as the effect estimates for the association between PM2.5 and health outcomes varies by season and region.

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We analyzed the spatial and temporal variability of 53 components of PM2.5 chemical composition for the United States using data from 199 counties for the years 2000 to 2003. Components include sulfate, nitrate, metals, organic carbon, and others. We developed a protocol for combining data from individual monitors to generate countywide averages, and we performed factor analysis to identify common factors for component concentrations.

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In development of the dataset, several key issues were identified including: suspect data, monitors with little data, extreme values, and co-location of monitors. We developed a protocol to combine monitor information into daily county-wide averages. Components' concentrations demonstrated different spatial and temporal patterns. For example variation in seasonal patterns was evident with higher levels in northern California in winter and the eastern U.S. in summer. Some components were highly correlated indicating similar sources and chemical links, such as ammonium and sulfur). Preliminary factor analysis identified components relating to crustal materials, traffic, coal combustion, sea salt, oil combustion, and other combustion sources. Because any individual PM2.5 component comes from a variety of sources and because this dataset is based on national data rather than a single community, it is difficult to label each factor as a definitive single source.

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Discussion and Conclusions:

Results indicate important temporal and spatial variation in components of PM2.5, which could explain regional and seasonal differences in effect estimates between PM2.5 and mortality and hospital admissions. Understanding these relationships could lead to a better understanding of the toxicity of PM components and which sources are most damaging, which would allow more effective control of PM air pollution.

© 2006 Lippincott Williams & Wilkins, Inc.