Optical Properties Of Black Carbon In Shanghai And WRF-Chem Simulation Of Its Temporal And Spatial Variation

In this study,Shanghai urban area is taken as the research area.Based on the on-line monitoring data of near-surface black carbon concentration at a fixed site for four consecutive years,the temporal and spatial variation characteristics of black carbon concentration at the site are studied and the source analysis is carried out.At the same time,combined with multiple data such as optical parameters,meteorological conditions and concentrations of other atmospheric pollutants,the impact mechanism on Shanghai black carbon concentration was analyzed.Based on WRF-Chem model and backward trajectory model,the spatial distribution pattern of concentration in different seasons was simulated.The following preliminary conclusions are drawn:The average concentration of black carbon from 2013 to 2016 is(2.86±1.78)μg/m3 and the average annual concentration has a significant downward trend.Winter is the highest,followed by spring and autumn,and summer is the lowest.The diurnal variation of black carbon aerosol has obvious "double peaks and double valleys"characteristics and seasonal Period.The average value of BC/PM2.5 is 5.8%,highest in autumn and lowest in winter.The transport in Beijing,Tianjin,Hebei,East China and Central China has a great influence on the black carbon concentration in spring and winter,and the black carbon concentration corresponding to the proportion of different types of pollution tracks has seasonal differences.The annual average absorption coefficient of black carbon aerosol is(26.19±18.76)Mm-1,and the diurnal variation is bimodal.Precipitation has a great influence on the absorption coefficient of black carbon aerosol.The seasonal mean values of the scattering coefficient and extinction coefficient are winter>spring>autumn>summer,and the diurnal variation curves are similar to a typical "double peak" structure.WRF-Chem model simulates the weather situation when the typical black carbon aerosol pollution occurs and the spatio-temporal variation characteristics of various pollutants,which are in good agreement with the observation data at fixed stations.The model results clearly and intuitively reproduced the mass concentration of black carbon transported from different time periods and different directions,highlighting the adverse local diffusion conditions and the transportation of surrounding areas that jointly caused the occurrence of black carbon aerosol pollution.