Sensitivity Analysis of Chemical Mechanisms in the WRF-Chem Model in Reconstructing Aerosol Concentrations and Optical Properties in the Tibetan Plateau

To investigate the effect of gas-phase chemical schemes and aerosol mechanisms on the reconstruction of the concentrations and optical properties of aerosols in the Tibetan Plateau (TP) and adjacent regions, two simulation experiments using the mesoscale Weather Research and Forecasting (WRF) meteorological model with the chemistry module (WRF-Chem) were performed in 2013. The RADM2 gas-phase chemical mechanism and the MADE/SORGAM aerosol scheme were selected in the first configuration, whereas the CBMZ gas and MOSAIC aerosol reaction schemes were included in the second simulation. The comparison demonstrated that chemical mechanisms play a key role in affecting the evolution of gas-phase precursors and aerosol processes. Specifically, compared with RADM2, CBMZ revealed lower O3 and higher NO2 surface concentrations, because of more efficient O3-NO titration, and higher HNO3 concentrations owing to more effective NO2 + OH reaction. SO2 could easily form particulate sulfate through cloud oxidation in RADM2. The MADE/SORGAM module presented higher surface PM2.5 and PM10 concentrations than did the MOSAIC module over the TP and in surrounding regions, because of the difference in aerosol compounds and the distribution of computed aerosol concentrations between modes and bins. The aerosol optical depth at 550 nm indicated a potential correlation with surface secondary inorganic aerosols concentrations. Higher surface sulfate and nitrate concentrations appeared to determine higher AOD values in MADE/SORGAM than in MOSAIC. Finally, the comparison with observations suggested that, the simulation performed using the CBMZ gas-phase chemical mechanism and MOSAIC aerosol module could be suitable for the efficient reconstruction of aerosols and their optical depth over the TP.