title: Use of satellite observations for long-term exposure assessment of global concentrations of fine particulate matter.
abstract: BACKGROUND
  More than a decade of satellite observations offers global information about the trend and magnitude of human exposure to fine particulate matter (PM2.5).
  
  
  OBJECTIVE
  In this study, we developed improved global exposure estimates of ambient PM2.5 mass and trend using PM2.5 concentrations inferred from multiple satellite instruments.
  
  
  METHODS
  We combined three satellite-derived PM2.5 sources to produce global PM2.5 estimates at about 10 km × 10 km from 1998 through 2012. For each source, we related total column retrievals of aerosol optical depth to near-ground PM2.5 using the GEOS-Chem chemical transport model to represent local aerosol optical properties and vertical profiles. We collected 210 global ground-based PM2.5 observations from the literature to evaluate our satellite-based estimates with values measured in areas other than North America and Europe.
  
  
  RESULTS
  We estimated that global population-weighted ambient PM2.5 concentrations increased 0.55 μg/m3/year (95% CI: 0.43, 0.67) (2.1%/year; 95% CI: 1.6, 2.6) from 1998 through 2012. Increasing PM2.5 in some developing regions drove this global change, despite decreasing PM2.5 in some developed regions. The estimated proportion of the population of East Asia living above the World Health Organization (WHO) Interim Target-1 of 35 μg/m3 increased from 51% in 1998-2000 to 70% in 2010-2012. In contrast, the North American proportion above the WHO Air Quality Guideline of 10 μg/m3 fell from 62% in 1998-2000 to 19% in 2010-2012. We found significant agreement between satellite-derived estimates and ground-based measurements outside North America and Europe (r = 0.81; n = 210; slope = 0.68). The low bias in satellite-derived estimates suggests that true global concentrations could be even greater.
  
  
  CONCLUSIONS
  Satellite observations provide insight into global long-term changes in ambient PM2.5 concentrations. Satellite-derived estimates and ground-based PM2.5 observations from this study are available for public use.
authors.affiliation: Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia, Canada.
authors.forename: Aaron
authors.initials: A
authors.lastname: van Donkelaar
authors.forename: Randall V
authors.initials: RV
authors.lastname: Martin
authors.forename: Michael
authors.initials: M
authors.lastname: Brauer
authors.forename: Brian L
authors.initials: BL
authors.lastname: Boys
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D000397:Air Pollution / Q000706:statistics & numerical data; D004781:Environmental Exposure / Q000032:analysis / Q000706:statistics & numerical data*; D004784:Environmental Monitoring; D006801:Humans; D010316:Particle Size; D052638:Particulate Matter / Q000032:analysis*; D063809:Satellite Imagery
chemical_list: D000393:Air Pollutants; D052638:Particulate Matter