title: Chemical Composition of Fine Particulate Matter and Life Expectancy: In 95 US Counties Between 2002 and 2007.
abstract: 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.
authors.affiliation: 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.
authors.forename: Francesca
authors.initials: F
authors.lastname: Dominici
authors.forename: Yun
authors.initials: Y
authors.lastname: Wang
authors.forename: Andrew W
authors.initials: AW
authors.lastname: Correia
authors.forename: Majid
authors.initials: M
authors.lastname: Ezzati
authors.forename: C Arden
authors.initials: CA
authors.lastname: Pope
authors.forename: Douglas W
authors.initials: DW
authors.lastname: Dockery
mesh_terms: D000393:Air Pollutants / Q000737:chemistry*; D064751:Ammonium Compounds / Q000032:analysis; D002244:Carbon / Q000032:analysis; D004781:Environmental Exposure / Q000706:statistics & numerical data*; D006801:Humans; D008017:Life Expectancy / Q000639:trends*; D016014:Linear Models; D009566:Nitrates / Q000032:analysis; D052638:Particulate Matter / Q000737:chemistry*; D012825:Silicon / Q000032:analysis; D012964:Sodium / Q000032:analysis; D013431:Sulfates / Q000032:analysis; D014481:United States
chemical_list: D000393:Air Pollutants; D064751:Ammonium Compounds; D009566:Nitrates; D052638:Particulate Matter; D013431:Sulfates; D002244:Carbon; D012964:Sodium; D012825:Silicon