| Atmospheric aerosol is an important component of the atmosphere.By acting as cloud condensation nuclei(CCN),aerosols can modify the cloud microphysics,thereby influencing the environment and climate.In this paper,we carried out a series of field studies(at Nanjing Meteorological Bureau in summer 2014,and at Nanjing University of Information Science&Technology in autumn 2014 and winter 2015).Aerosol properties including CCN number concentration,activation ratio,critical diameter and size-resolved activation were studied based on the experimental data.We also studied the influence of CCN aerosol physicochemical properties when Black Carbon(BC)as cloud condensation nuclei.The relationship of aerosol CCN activity and physicochemical properties was investigated,focusing on the relative importance of particle size and chemical composition.Conclusions are as follows:Field study at representative Nanjing urban site(at Nanjing Meteorological Bureau in Jiangxinzhou):(1)The mean number of CCN concentrations in Jiangxinzhou at different supersaturations(set as 0.1%,0.2%,0.3%,0.4%and 0.6%)were 1234,2803,3494,3946,and 4650 cm-3,respectively.The Critical diameter was respectively 141.19 nm,90.42 nm,74.95 nm,65.88 nm and 54.35 nm,with an average hygroscopic coefficient(κ)of 0.41.(2)The percentage of quality BC in 76,111,138 and 181nm particles respectively 5.4%and 10.0%,10.7%and 6.6%,the BC mainly concentrated between 111 and 138nm,The whole content low,but with black carbon nuclei of aerosol particles accounted for 51%,57%,70%and 59%,suggesting that the BC is important atmospheric condensation nuclei,it has an important contribution to the number of atmospheric particulate matter in Nanjing.(3)CCN activity was affected by the particle size distribution as well as the chemical composition of the particulate matter,but the effect of the aging process on the CCN activity was also significant.When the particle size of aerosol particles is smaller,the chemical composition is dominant.Field study at representative Nanjing northern suburban site(at Nanjing University of Information Science&Technology):(1)In autumn,the mean values of CN were 16679/cm3,and the mean concentrations of CCN in the 0.3%,0.2%,0.4%,0.6%and 0.1%,respectively,were 4115,6524,7495,8305 and 9442/cm3,respectively.(2)Compared with autumn,winter pollution was more serious,in addition to the total concentration of CN was lower than in autumn,corresponding to the CCN number concentration saturation were increased.The saturation changed in the process of CCN(0.1%～0.8%),the number of average concentrations were 4575,6974,8569,9412 and 9974 cm-3.(3)On the setted supersaturation(0.1%～0.6%),the autumn’s average critical dry particle size(Dp50)was 11.949,80.25,66.78 and 57.62 and 47.47 nm,respectively,winter critical dry particle size respectively 114.34 and 76.60,55.06,46.60 and 41.59 nm.(4)The critical supersaturation of autumn were 0.54%,0.22%,0.15%and 0.11%,respectively,and the critical supersaturation of winter was 0.49%,0.18%,0.13%and 0.09%,respectively.The chemical composition of particulate matter and the mixed state have the most significant effect on the CCN activation rate in the vicinity of the critical supersaturation. |
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