[AAS03-02] Modeling diurnal variation of surface PM2.5 concentration over East China with WRF-Chem: Impacts from boundary layer mixing and anthropogenic emission
★Invited Papers
Keywords:WRF-Chem, PBL mixing, diurnal cycle
Diurnal variation of surface PM2.5concentration (diurnal PM2.5) could dramatically affect aerosol radiative and healthy impact, and can also well reflect the physical and chemical mechanisms of air pollution formation and evolution. So far, diurnal PM2.5and its modeling capability over East China has not been investigated, and therefore, is examined in this study. Based on the observations, the normalized diurnal amplitude of surfacePM2.5concentrations averaged over East China is the weakest (~1.2) in winter, and reaches ~1.5 in other seasons. The diurnal PM2.5shows the peak concentration during the night in spring and fall and during the daytime in summer. The simulated diurnal PM2.5with WRF-Chem and its contributions from multiple physical and chemical processes are examined in the four seasons. The simulated diurnal PM2.5with WRF-Chem is primarily controlled by planetary boundary layer (PBL) mixing and emission variations, andis significantly overestimated against the observation during the night. This modeling bias is likely primarily due to the inefficient PBL mixing of primary PM2.5during the night. The simulated diurnal PM2.5is sensitive to the PBL schemes and vertical layer configurations with WRF-Chem. Besides the PBL height, the PBL mixing coefficient is also found as the critical factor determining the PBL mixing of pollutants in WRF-Chem. With reasonable PBL height, the increase of lower limit of PBL mixing coefficient during the night can significantly reduce the modeling biases in diurnal PM2.5and also the mean concentrations, particularly at the major cities of East China. It can also reduce the modeling sensitivity to the PBL vertical layer configurations. The diurnal variation and injection height of anthropogenic emissions also play roles on simulating diurnal PM2.5, but the impact is relatively smaller than that from the PBL mixing. This study underscores that more efforts are needed to improve the boundary mixing process of pollutants in models with observations of PBL structure and mixing fluxes in addition to PBL height, in order to simulate reasonably the diurnal PM2.5over East China. The diurnal variation and injection height of anthropogenic emissions are also necessary to be included to simulate the diurnal PM2.5 over East China.