title: Long-Term Trends Worldwide in Ambient NO2 Concentrations Inferred from Satellite Observations.
abstract: BACKGROUND
  Air pollution is associated with morbidity and premature mortality. Satellite remote sensing provides globally consistent decadal-scale observations of ambient nitrogen dioxide (NO2) pollution.
  
  
  OBJECTIVE
  We determined global population-weighted annual mean NO2 concentrations from 1996 through 2012.
  
  
  METHODS
  We used observations of NO2 tropospheric column densities from three satellite instruments in combination with chemical transport modeling to produce a global 17-year record of ground-level NO2 at 0.1° × 0.1° resolution. We calculated linear trends in population-weighted annual mean NO2 (PWMNO2) concentrations in different regions around the world.
  
  
  RESULTS
  We found that PWMNO2 in high-income North America (Canada and the United States) decreased more steeply than in any other region, having declined at a rate of -4.7%/year [95% confidence interval (CI): -5.3, -4.1]. PWMNO2 decreased in western Europe at a rate of -2.5%/year (95% CI: -3.0, -2.1). The highest PWMNO2 occurred in high-income Asia Pacific (predominantly Japan and South Korea) in 1996, with a subsequent decrease of -2.1%/year (95% CI: -2.7, -1.5). In contrast, PWMNO2 almost tripled in East Asia (China, North Korea, and Taiwan) at a rate of 6.7%/year (95% CI: 6.0, 7.3). The satellite-derived estimates of trends in ground-level NO2 were consistent with regional trends inferred from data obtained from ground-station monitoring networks in North America (within 0.7%/year) and Europe (within 0.3%/year). Our rankings of regional average NO2 and long-term trends differed from the satellite-derived estimates of fine particulate matter reported elsewhere, demonstrating the utility of both indicators to describe changing pollutant mixtures.
  
  
  CONCLUSIONS
  Long-term trends in satellite-derived ambient NO2 provide new information about changing global exposure to ambient air pollution. Our estimates are publicly available at http://fizz.phys.dal.ca/~atmos/martin/?page_id=232.
authors.affiliation: Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia, Canada.
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Geddes
authors.forename: Randall V
authors.initials: RV
authors.lastname: Martin
authors.forename: Brian L
authors.initials: BL
authors.lastname: Boys
authors.forename: Aaron
authors.initials: A
authors.lastname: van Donkelaar
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D000397:Air Pollution / Q000706:statistics & numerical data; D001272:Atmosphere / Q000737:chemistry; D004781:Environmental Exposure / Q000032:analysis / Q000706:statistics & numerical data*; D004784:Environmental Monitoring; D006801:Humans; D008956:Models, Chemical; D009585:Nitrogen Dioxide / Q000032:analysis*; D063809:Satellite Imagery
chemical_list: D000393:Air Pollutants; D009585:Nitrogen Dioxide