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Chemical Composition of Fine Particulate Matter and Life Expectancy: In 95 US Counties Between 2002 and 2007

Dominici, Francescaa; Wang, Yuna; Correia, Andrew W.b; Ezzati, Majidc; Pope, C. Arden IIId; Dockery, Douglas W.e,f

doi: 10.1097/EDE.0000000000000297
Air Pollution

Background: In a previous study, we provided evidence that a decline in fine particulate matter (PM2.5) air pollution during the period between 2000 and 2007 was associated with increased life expectancy in 545 counties in the United States. In this article, we investigated which chemical constituents of PM2.5 were the main drivers of the observed association.

Methods: We estimated associations between temporal changes in seven major components of PM2.5 (ammonium, sulfate, nitrate, elemental carbon matter, organic carbon matter, sodium, and silicon) and temporal changes in life expectancy in 95 counties between 2002 and 2007. We included US counties that had adequate chemical components of PM2.5 mass data across all seasons. We fitted single pollutant and multiple pollutant linear models, controlling for available socioeconomic, demographic, and smoking variables and stratifying by urban and nonurban counties.

Results: In multiple pollutant models, we found that: (1) a reduction in sulfate was associated with an increase in life expectancy; and (2) reductions in ammonium and sodium ion were associated with increases in life expectancy in nonurban counties only.

Conclusions: Our findings suggest that recent reductions in long-term exposure to sulfate, ammonium, and sodium ion between 2002 and 2007 are associated with improved public health.

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From the aDepartment of Biostatistics, Harvard T.H. Chan School of Public Health, Boston, MA; bNMR Group, Inc., Somerville, MA; cMRC-PHE Centre for Environment and Health and Department of Epidemiology and Biostatistics, Imperial College London, London, United Kingdom; dDepartment of Economics, Brigham Young University, Provo, UT; and eDepartment of Environmental Health, fDepartment of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, MA.

Submitted 17 December 2013; accepted 26 March 2015.

This study was partially supported by the US National Institutes of Health (P30-ES000002, R01-ES019560, R01-ES019955, R21-ES020152, R21-ES021427), US Environmental Protection Agency (RD-83490001, RD-83479801, R834894), and the Health Effects Institute (4909).

The authors report no conflicts of interest.

Supplemental digital content is available through direct URL citations in the HTML and PDF versions of this article ( This content is not peer-reviewed or copy-edited; it is the sole responsibility of the authors.

Correspondence: Francesca Dominici, Department of Biostatistics, Harvard T.H. Chan School of Public Health, 655 Huntington Avenue, HSPH Building 2, 4th Floor, Boston, MA 02115. E-mail:

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