CCN Activation Characteristics And Prediction Based On Long-term Measurement In A Background Station Of Yangtze River Delta

Cloud condensation nuclei(CCN)is a key element in the relationship of cloud and aerosols,and carries the largest uncertainty in the climate change research.The high concentration of CCN also can cause serve air-pollution,and be recognized as an important reason for haze-fog weather.The measurement of CCN can help understanding the relationship of aerosol chemical composition and activation ability,provide substantial information for model studies,and also can be used for model verify.Currently,CCN measurements have been taking place worldwide,however,there mainly assembled in Europe and North American,the measurement in Asia is very rare,not mention the long-term measurement.Based on this fact,a long-term aerosol measurement campaign had been carried out in Lin An,a regional GAW(Global Atmospheric Watch)station in the Yangtze River Delta of China.The measurement including observation of aerosol chemical composition and number size distribution,CCN activation characteristics.Results show the CCN activation spectrum have distinctive difference under different kinds of pollution episodes.The major variation of CCN spectrum during different environments was the degree of tilt of the activation curve.By using 3-parameters Guass Cumulative Function fitting,this variation can be represented by a parameter,which further indicates the mixing status of aerosol at the critical diameter.In order to investigate the CCN characteristics in different environments,the weather-pollution were future divided into nine types according to relative humidity and visibility.Results indicated the CCN under pollution episodes were more aged with homogeneous chemical composition,especially at larger diameters.The CCN in the clean environment were more homogeneous at Aitkin mode with higher hygroscopicity.For different weather types with same level visibility but different RH,the CCN mixing status and hygroscopicity show variations.Compare with CCN measurement under different locations,the campaign averaged maximum activation fraction in Lin An were higher than those in clean environments.The CCN concentration of 0.1% supersaturation count for ~20% of CN,with mode diameter around 200 nm.While at higher SS,the CCN concentration increased from 5000 to 7000 cm-3.The high activation ability and high hygroscopicity in Lin An show the influence of anthropogenic inorganic aerosol on CCN activation.The CCN concentration and activation parameters in Lin An have a seasonal variation,indicating the influence of aerosol mass source and concentration,also indicate the advantage of long-term measurement for averaged CCN characteristics estimation.According to the analyze of aerosol hygroscopicity,the aerosol can be regarded as two components,inorganics and organics.The hygroscopic parameter for each component was different in different weather-pollution types,which may due to the variation of chemical composition and mixing status.In order to improve the CCN prediction parameterisation in mesoscale weather-air pollution model,the CCN prediction was performed based on different assumptions,including particles mixing status and chemical composition size dependency.The results show under different weather types and supersaturations,the prediction should use different assumption for a more accurate result,which can be accounted for the aerosol mixing status and chemical variation.In general,the CCN prediction with external assumption were better in mist weathers,while the prediction with internal assumption were rubust in haze weather.As for different supersaturations,the prediction with size resolved assumption were better in higher supersaturations,and the bulk chemical compositon was enough for prediction in lower supersaturations.This results indicating the aerosol number size distribution,sizeresolved chemical composition and mixing status shoud be taking into consideration for CCN prediction.At the end of the dissertation,a new method was introduced for CCN number size distribution calculation,the value range and empirical formula for newly added parameters were summarized by review of published literature.