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

TLDR

Exposure to outdoor fine particulate matter (PM2.5) is a leading risk factor for mortality. The study develops global annual PM2.5 concentration and trend estimates for 1998–2018 using satellite observations, chemical transport modeling, and ground‑based monitoring. High‑resolution satellite aerosol optical depths are combined with GEOS‑Chem–derived geophysical relationships to convert AOD to surface PM2.5 concentrations, improving spatial coverage and temporal stability. The resulting estimates agree well with ground monitors (R²≈0.81–0.92) and reveal significant regional trends, including declines of 0.28 μg/m³/yr in eastern North America, 0.15 μg/m³/yr in Europe, a 1.13 μg/m³/yr rise in India, and a 0.04 μg/m³/yr global increase, with India’s 2.44 μg/m³/yr rise (2005–2013) and China’s 3.37 μg/m³/yr drop (2011–2018) highlighting health implications for billions.

Abstract

Exposure to outdoor fine particulate matter (PM2.5) is a leading risk factor for mortality. We develop global estimates of annual PM2.5 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 PM2.5 concentrations using geophysical relationships between surface PM2.5 and AOD simulated by the GEOS-Chem chemical transport model with updated algorithms. The resultant annual mean geophysical PM2.5 estimates are highly consistent with globally distributed ground monitors (R2 = 0.81; slope = 0.90). Geographically weighted regression is applied to the geophysical PM2.5 estimates to predict and account for the residual bias with PM2.5 monitors, yielding even higher cross validated agreement (R2 = 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/m3/yr), Europe (-0.15 ± 0.03 μg/m3/yr), India (1.13 ± 0.15 μg/m3/yr), and globally (0.04 ± 0.02 μg/m3/yr). The positive trend (2.44 ± 0.44 μg/m3/yr) for India over 2005-2013 and the negative trend (-3.37 ± 0.38 μg/m3/yr) for China over 2011-2018 are remarkable, with implications for the health of billions of people.