Chemical composition of ambient PM2.5 over China and relationship to precursor emissions during 2005-2012.

We estimated the changes in chemical composition of ambient PM_2.5 over China during 2005-2012 using satellite-based aerosol optical depth (AOD) data and the GEOS-Chem chemical transport model, and investigated the driving forces behind the changes by examining the changes in precursor emissions using a bottom-up emission inventory. We found that the national population-weighted mean PM_2.5 concentration increased from 63.9 μg/m³ in 2005 to 75.2 μg/m³ in 2007 (+18.19 % per year), and subsequently decreased to 66.9 μg/m³ from 2007 to 2012 (-2.67 % per year), composing a flat trend of population-weighted mean PM_2.5 concentration during 2005-2012. Variations in PM_2.5 concentrations are mainly driven by the changes in sulfate and nitrate concentrations. Population-weighted mean sulfate concentration increased by 10.72 % from 2005-2006 (from 14.4 μg/m³ to 15.9 μg/m³) and then decreased by 4.30 % per year from 2006-2012, dominating the variations of total PM_2.5 concentrations. The decrease of sulfate concentration is partly offset by the increase of nitrate concentration: population-weighted mean nitrate concentration increased by 3.39 % per year during 2005-2012 (from 9.8 μg/m³ to 12.2 μg/m³). The changes in sulfate and nitrate concentrations were in line with the changes in SO₂ and NO_x emissions during the same period. By examining the emission data from the MEIC emission inventory, we found that the desulfurization regulation enforced around 2005 in power plants was the primary contributor to the SO₂ emissions reduction since 2006. In contrast, growth of energy consumption and lack of control measures for NO_x resulted in persistent increase in NO_x emissions until the installation of denitrification devices on power plants late in 2011, which began to take effect in 2012. The results of this work indicate that the synchronized abatement of emissions for multi-pollutants are necessary for reducing ambient PM_2.5 concentrations over China. [ABSTRACT FROM AUTHOR]