Characteristics Of Spatial-temporal Distribution Of Black Carbon In East China During 2000-2016

China is one of the main source regions for black carbon（BC）emission,especially in the East China（110°E～123°E,23°N～42°N）.Firstly,the observations of BC concentrations from China Aerosol Watching Net（CAWNET）during 2006～2016 and from aircraft measurements in 2015 were used to analyze the variation characteristics of BC in typical sites in East China.Then,the MERRA-2（Modern-era Retrospective Analysis for Research and Applications,Vision2）BC product was validated with ground observation data.Lastly,the temporal-spatial variation of BC and its impact factors were analyzed based on MERRA-2BC data in the period of 2000～2016.The results showed that:（1）From 2000 to 2016,the average BC concentrations in Zhengzhou,Lin’an and Guilin sites were 7.53μg·m^-3、3.84μg·m^-3and 3.40μg·m^-3,respectively.The monthly BC concentrations showed a variation of"U"shape,with the lower concentrations in July and August.The seasonal BC concentrations appeared high in winter and low in summer.Although the annual change of the concentration fluctuated during 2006～2016,the BC concentrations of these three cities decreased during 2012～2016 with the mean reductions of 2.01μg·m^-3,1.32μg·m^-3and 1.00μg·m^-3 in Zhengzhou,Lin’an and Guilin,respectively,compared with the mean values in 2006～2011.（2）The aircraft observations over Beijing,Jinan and Wuhan indicated that the BC mainly accumulated below 1000m.From the near ground（about 70m）,the mass concentration and number density of BC showed a profile of first increasing,then rapidly decreasing and gradually decreasing.The BC gradually aged with the height,and the values of Dp/Dc showed a trend of first increasing then decreasing.（3）The verification results indicated that MERRA-2 slightly overestimated the BC surface concentration in the north part of the study area and slightly underestimated that in the south part.However,a strong correlation（R=0.83）and a small mean deviation(0.21μg·m^-3)were found between the monthly mean BC surface concentrations of the ground observation and the MERRA-2 product,which indicating a good applicability of the MERRA-2 monthly BC data over the study area.（4）The overall annual means of BC surface concentration,column density and the concentration ratio of surface BC and PM_2.5(BC/PM_2.5)over East China were 3.41μg·m^-3,3.78mg·m^-2 and 8.71%,respectively.The highest annual mean(～6.00μg·m^-3)and the fastest growth rate(～0.06μg·m^-3·a^-1)of surface concentration were both presented in the region of Beijing-Tianjin-Hebei（BTH）and Henan area.The annual column density showed an increasing trend in the north part while a decreasing in the south.The seasonal concentration of BC showed a feature of high in winter and low in summer.Although the BTH area was always the high surface concentration center,the location of the column density center appeared a seasonal variation in south-north direction from summer to winter then to next summer.BC concentration began to increase rapidly in 2000 and declined after peaking in2007,especially in the areas to the south of 34°N.In the vertical direction,BC concentration decreased with height.The mass concentration profiles of BC showed the largest in winter and the smallest in summer below 2.00 km.Above the 2.00 km,the BC concentration profiles of autumn and winter decreased rapidly with the height,while the highest concentration profile appeared in spring.