不同污染条件下南京春季CCN活化特征分析

在2018年3~4月对南京北郊地区的气溶胶开展了云凝结核（CCN）特征的外场观测，并结合气象数据、PM_2.5浓度和化学组分信息以及光学特性等数据，对观测期间的污染天和清洁天进行了对比，分析了典型污染过程和新粒子生成天的CCN特征.结果表明，本次观测中气溶胶CCN活性总体较高，各过饱和度（SS）下的平均吸湿性参数（κ）为0.30，在最低过饱和度下（SS=0.17%）κ最低，且最大活化率（B）仅为0.72，表明气溶胶中有较多不易活化的物质.污染天κ高于清洁天，但活化率更低且外混程度更高，主要是受交通和工业排放的吸湿性较差的粒子影响，而颗粒物在夜间可迅速老化，使其吸湿性提升，CCN数浓度增加.新粒子生成天的κ受到粒子成核的影响有明显日变化，对总气溶胶数浓度（N_CN）和CCN数浓度（N_CCN）也有显著贡献.

Investigation of cloud condensation nuclei activity under different pollution conditions in spring of Nanjing

Filed observation of cloud condensation nuclei (CCN) activation properties of aerosols were carried out from March 2018 to April 2018 in the northern suburbs of Nanjing. Meteorological data, PM_2.5 number concentration, chemical composition and optical properties of particles are also collected for analysis. The CCN activities of aerosols in polluted days and clean days during the observation period were compared, and the characteristics of typical pollution processes and new particle formation days were analyzed. Results showed that the CCN activity of aerosols are generally high during this observation, with an average hygroscopicity parameter (κ) of 0.30under each supersaturation(SS) condition. The lowest κ was observed under the lowest supersaturation (SS=0.17%), and the maximum activation ratio (B) was 0.72, indicating that aerosols contains many substances that are difficult for activation. κ was seen higher in polluted days than in clean days. When compared to that in clean days, the activation ratio in polluted days was relatively lower and the level of external mixing was higher, which was mainly due to the large amount of less hygroscopic particles emitted by traffic and industry. Aging process of particulate matters are observed fast at night, making particles more hygroscopic and leading to higher CCN number concentration. In new particle formation days, κ showed diurnal variation due to particle nucleation, and new particle formation process also made significant contribution to total aerosol number concentration(N_CN) and CCN number concentration(N_CCN).