Global Estimates and Long-Term Trends of Fine Particulate Matter Concentrations (1998-2018).

Exposure to outdoor fine particulate matter (PM) is a leading risk factor for mortality. We develop global estimates of annual PM concentrations and trends for 1998-2018 using advances in satellite observations, chemical transport modeling, and ground-based monitoring. Aerosol optical depths (AODs) from advanced satellite products including finer resolution, increased global coverage, and improved long-term stability are combined and related to surface PM concentrations using geophysical relationships between surface PM and AOD simulated by the GEOS-Chem chemical transport model with updated algorithms. The resultant annual mean geophysical PM estimates are highly consistent with globally distributed ground monitors ( = 0.81; slope = 0.90). Geographically weighted regression is applied to the geophysical PM estimates to predict and account for the residual bias with PM monitors, yielding even higher cross validated agreement ( = 0.90-0.92; slope = 0.90-0.97) with ground monitors and improved agreement compared to all earlier global estimates. The consistent long-term satellite AOD and simulation enable trend assessment over a 21 year period, identifying significant trends for eastern North America (-0.28 ± 0.03 μg/m/yr), Europe (-0.15 ± 0.03 μg/m/yr), India (1.13 ± 0.15 μg/m/yr), and globally (0.04 ± 0.02 μg/m/yr). The positive trend (2.44 ± 0.44 μg/m/yr) for India over 2005-2013 and the negative trend (-3.37 ± 0.38 μg/m/yr) for China over 2011-2018 are remarkable, with implications for the health of billions of people.