title: Reduction in fine particulate air pollution and mortality: Extended follow-up of the Harvard Six Cities study.
abstract: BACKGROUND
  A large body of epidemiologic literature has found an association of increased fine particulate air pollution (PM2.5) with acute and chronic mortality. The effect of improvements in particle exposure is less clear.
  
  
  OBJECTIVE
  Earlier analysis of the Harvard Six Cities adult cohort study showed an association between long-term ambient PM2.5 and mortality between enrollment in the mid-1970s and follow-up until 1990. We extended mortality follow-up for 8 yr in a period of reduced air pollution concentrations.
  
  
  METHODS
  Annual city-specific PM2.5 concentrations were measured between 1979 and 1988, and estimated for later years from publicly available data. Exposure was defined as (1) city-specific mean PM2.5 during the two follow-up periods, (2) mean PM2.5 in the first period and change between these periods, (3) overall mean PM2.5 across the entire follow-up, and (4) year-specific mean PM2.5. Mortality rate ratios were estimated with Cox proportional hazards regression controlling for individual risk factors.
  
  
  RESULTS
  We found an increase in overall mortality associated with each 10 microg/m3 increase in PM2.5 modeled either as the overall mean (rate ratio [RR], 1.16; 95% confidence interval [CI], 1.07-1.26) or as exposure in the year of death (RR, 1.14; 95% CI, 1.06-1.22). PM2.5 exposure was associated with lung cancer (RR, 1.27; 95% CI, 0.96-1.69) and cardiovascular deaths (RR, 1.28; 95% CI, 1.13-1.44). Improved overall mortality was associated with decreased mean PM2.5 (10 microg/m3) between periods (RR, 0.73; 95% CI, 0.57-0.95).
  
  
  CONCLUSIONS
  Total, cardiovascular, and lung cancer mortality were each positively associated with ambient PM2.5 concentrations. Reduced PM2.5 concentrations were associated with reduced mortality risk.
authors.affiliation: Exposure, Epidemiology, and Risk Program, Department of Environmental Health, Harvard School of Public Health, Boston, MA, USA. Francine.laden@channing.harvard.edu
authors.forename: Francine
authors.initials: F
authors.lastname: Laden
authors.forename: Joel
authors.initials: J
authors.lastname: Schwartz
authors.forename: Frank E
authors.initials: FE
authors.lastname: Speizer
authors.forename: Douglas W
authors.initials: DW
authors.lastname: Dockery
mesh_terms: D000328:Adult; D000368:Aged; D000393:Air Pollutants / Q000009:adverse effects* / Q000032:analysis; D002318:Cardiovascular Diseases / Q000401:mortality*; D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000401:mortality*; D008297:Male; D008875:Middle Aged; D016016:Proportional Hazards Models; D012189:Retrospective Studies; D012307:Risk Factors; D015996:Survival Rate / Q000639:trends; D014481:United States / Q000453:epidemiology; D014505:Urban Population
chemical_list: D000393:Air Pollutants