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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 groundbased 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.