Fifteen-year global time series of satellite-derived fine particulate matter.

Ambient fine particulate matter (PM2.5) is a leading environmental risk factor for premature mortality. We use aerosol optical depth (AOD) retrieved from two satellite instruments, MISR and SeaWiFS, to produce a unified 15-year global time series (1998–2012) of ground-level PM2.5 concentration at a resolution of 1° x 1°. The GEOS-Chem chemical transport model (CTM) is used to relate each individual AOD retrieval to ground-level PM2.5. Four broad areas showing significant, spatially coherent, annual trends are examined in detail: the Eastern U.S. (−0.39 ± 0.10 μg m–3 yr–1), the Arabian Peninsula (0.81 ± 0.21 μg m–3 yr–1), South Asia (0.93 ± 0.22 μg m–3 yr–1) and East Asia (0.79 ± 0.27 μg m–3 yr–1). Over the period of dense in situ observation (1999–2012), the linear tendency for the Eastern U.S. (−0.37 ± 0.13 μg m–3 yr–1) agrees well with that from in situ measurements (−0.38 ± 0.06 μg m–3 yr–1). A GEOS-Chem simulation reveals that secondary inorganic aerosols largely explain the observed PM2.5 trend over ...