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 the Eastern U.S., South Asia, and East Asia, while mineral dust largely explains the observed trend over the Arabian Peninsula.

Abstract. Using OMI (Ozone Monitoring Instrument) tropospheric NO 2 columns and a nested-grid 3-D global chemical transport model (GEOS-Chem), we investigated the growth in NO x emissions from coal-fired power plants and their contributions to the growth in NO 2 columns in 2005-2007 in China. We first developed a unit-based power plant NO x emission inventory for [2005][2006][2007] to support this investigation. The total capacities of coal-fired power generation have increased by 48.8 % in 2005-2007, with 92.2 % of the total capacity additions coming from generator units with size ≥300 MW. The annual NO x emissions from coal-fired power plants were estimated to be 8.11 Tg NO 2 for 2005 and 9.58 Tg NO 2 for 2007, respectively. The modeled summer average tropospheric NO 2 columns were highly correlated (R 2 = 0.79-0.82) with OMI measurements over grids dominated by power plant emissions, with only 7-14 % low bias, lending support to the high accuracy of the unitbased power plant NO x emission inventory. The ratios of OMI-derived annual and summer average tropospheric NO 2 columns between 2007 and 2005 indicated that most of the grids with significant NO 2 increases were related to power plant construction activities. OMI had the capability to trace the changes of NO x emissions from individual large power plants in cases where there is less interference from other NO x sources. Scenario runs from GEOS-Chem model suggested that the new power plants contributed 18.5 % and 10 % to the annual average NO 2 columns in 2007 in Inner Mongolia and North China, respectively. The massive new power plant NO x emissions significantly changed the local NO 2 profiles, especially in less polluted areas. A sensitivity study found that changes of NO 2 shape factors due to including new power plant emissions increased the summer average OMI tropospheric NO 2 columns by 3.8-17.2 % for six selected locations, indicating that the updated emission information could help to improve the satellite retrievals.