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In this work, we presented the characteristics of PM_2. 5 chemical composition over China for the period of 2005–2012 by synthesis of in situ measurement data collected from literatures and satellite-based estimates using aerosol optical depth (AOD) data and the GEOS-Chem chemical transport model. We revealed the spatiotemporal variations in PM_2. 5 composition during 2005–2012 and investigated the driving forces behind the variations by examining the changes in precursor emissions using a bottom-up emission inventory. Both in situ observations and satellite-based estimates identified that secondary inorganic aerosols (i.e., sulfate, nitrate, and ammonium; SNA) ranked as the highest fraction of dust-free PM_2. 5 concentrations, followed by organic matter (OM) and black carbon (BC). For instance, satellite-based estimates found that SNA, OM, and BC contributed to 59, 33, and 8 %, respectively, of national population-weighted mean dust-free PM_2. 5 concentrations during 2005–2012. National population-weighted mean PM_2. 5 concentration increased from 63.9 µg m⁻³ in 2005 to 75.2 µg m⁻³ in 2007 and subsequently decreased to 66.9 µg m⁻³ from 2007 to 2012. Variations in PM_2. 5 concentrations are mainly driven by the decrease in sulfate and the increase in nitrate. Population-weighted mean sulfate concentration decreased by 2.4 % yr⁻¹ during 2005–2012 (from 14.4 to 12.9 µg m⁻³), while population-weighted mean nitrate concentration increased by 3.4 % yr⁻¹ during 2005–2012 (from 9.8 to 12.2 µg m⁻³), largely offsetting the decrease in sulfate concentrations. By examining the emission data from the …