Abstract:

Aerosol activity of forming cloud droplets affects cloud micro-physics and indicates aerosol hygroscopicity. Application of the cloud condensation nuclei (CCN) counter (CCNC) is an important method for studying CCN-active particles. Factors impacting measurements using CCNC are analyzed by laboratory study. In CCNC, variations of supre-saturations (SS) are found to be proportional to variations of the pressure and the flow-rate. Temperature conditions, under which CCNC is working, exhibit nonlinear influnces on SSs in CCNC. Varying aerosol losses with particle size due to the pressure adjustment is found when differential pressure is higher than 300 hPa. Underestimation of CCN number concentration is found when particle number concentration is higher than 10000/cm³ and SS in CCNC is lower than 0.2%. This is because only part of CCN-active particles can activate due to the vapor depletion in CCNC. The results and suggestions provide instructions for CCN measurment and would help improving quality control and analysis of CCN data.

Key words: cloud condensation nulcei, CCN Counter (CCNC), super-saturation, atmospheric aerosol

摘要：

气溶胶的云滴活化能力影响云的微物理特性, 还表征气溶胶吸湿性的强弱。活化气溶胶(即云凝结核, Cloud Condensation Nuclei, CCN)的观测研究中的重要方法是CCN计数器(CCN Counter, CCNC)的应用。针对CCNC观测的影响因子进行了实验室研究。实验结果表明, CCNC所处的气压和设置的流量会对过饱和比产生等比例的影响, 而进气温度可能导致非线性的影响。实验中发现当气压差超过300 hPa时, CCNC气压调节装置会导致气溶胶的损失, 且损失的比例随着压差的增大而增大。在气溶胶浓度超过10000个/cm³、过饱和比低于0.2%时, 会出现对CCN数浓度的低估, 可能是由于水汽消耗导致CCN无法全部活化而不能被CCNC观测。研究结果及给出的建议对CCN的观测有指导意义, 同时有利于CCN数据的质量控制和分析工作。

关键词: 云凝结核, 云凝结核计数器(CCNC), 过饱和比, 大气气溶胶