Investigating secondary organic aerosol formation pathways in China during 2014

The concentrations of organic aerosol (OA) in central and eastern China are much higher than those in Europe and North America. Compared with observations, recent numerical modeling studies have largely underestimated the concentrations of OA, especially the secondary components. Based on the volatility basis set framework, a secondary OA (SOA) module is developed and coupled into the nested air quality prediction modeling system (NAQPMS). This model is applied to investigate the concentration and formation pathways of SOA in central and eastern China during 2014, and the simulation performance is validated through observation. The oxidation of intermediate volatile organic compounds (IVOCs) is significant to SOA formation and could reduce the great discrepancy between simulations and observations. In winter, the contribution of IVOCs accounted for 60%-80% of SOA formation. In spring and autumn, IVOCs and volatile organic compounds (VOCs) have a considerable effect on SOA formation. In summer, the contributions of VOCs reach 40%-60% due to an increase in the emissions of biogenic VOCs. The mass yields and other parameters of IVOCs remain largely uncertain. By using the latest mass yields obtained from chamber experiments, the simulated SOA concentrations in winter increase by 10-20 mu g m(-3) compared with the base scenario. To more thoroughly understand SOA formation in China, further research on the emission sources and mass yields of IVOCs is warranted.