Research On The Vertical Structure And Regional Origin Of Black Carbon Aerosols In The Boundary Layer Of The Yangtze River Delta Under Stable Weather Conditions

Black carbon aerosol(BC),as one of the important components of PM_2.5,can influence the boundary layer(BL)structure and the redistribution of atmospheric pollutants through radiative effects.However,due to the distribution of pollutant emissions are heterogeneous and the atmospheric dispersion conditions are complex and variable,regional source contributions to BC are subject to large uncertainties.In addition,due to the lack of vertical observations and emphases on model simulations in the previous study,the characteristics and regional sources of BC in vertical have been relatively under studied.In this study,based on BC and related air quality data and multiple meteorological observations,we analyze the pollution process and its meteorological causes in eastern China of Beijing-Hebei-Tianjin(BTH)and Yangtze River Delta(YRD)under stable weather conditions.In addition,focusing on YRD,the Weather Research and Forecasting model with Chemistry(WRF-Chem)model coupled with the source tagging method is applied to quantify the BC distribution and regional sources from the surface up to the upper BL under stable weather conditions.The results are shown as follows:(1)During the stable pollution process,the eastern China was mainly influenced by the high pressure and the uniform pressure.When impacted by the high pressure,the pollutants in BTH accumulated.In YRD,the pollutants accumulated due to the persistent uniform pressure.The inversion phenomenon near the surface corresponds well with the pollutant accumulation,the thicker the inversion layer was,the heavier the pollution would be.In addition,the low surface wind speed and high relative humidity in BTH were also detrimental to the diffusion and dilution of pollutants.The wind speed in YRD area was low,and due to the removal effect of precipitation on pollutants,the pollution concentration in the YRD was weaker than that in the BTH.(2)The simulation results show that,the local BC source contribution of YRD dominates the whole pollution process(88.5%).During the uniform high-pressure conditions,all three sub-regions of YRD were dominated by local source contributions from themselves(70.6%-98.2%).During the uniform low-pressure conditions,the surface BC concentration could reach a maximum value of 9.45?g·m^-3 due to the combination of local source(63.4%),and inter-regional transport(15.8%,mostly from Anhui(AH),the western neighbour of the YRD).During the uniform low-pressure conditions,as a westerly trough crossing,the BC of long-range inter-transport from North China Plain(NCP,22.4%)and South China(SCHN,14.7%)were transported to the upper BL of YRD.Among them,the BC contribution from the other two sub-regions to Shanghai within the BL accounts for 41.5%,which exceeds its local source contribution(25.2%).In addition,we determined that the BC peaks observed in the central BL over Nanjing(NJ)resulted from the transport of BC from northern Zhejiang(ZJN)and AH via dynamic lifting in the upper BL.