南京夏季气溶胶吸湿增长因子和云凝结核的观测研究

为了更加全面地研究长三角地区气溶胶的理化特性,尤其是吸湿和活化特性,于2013年8月在南京市区对气溶胶的吸湿增长因子(GF)和云凝结核(CCN)展开相关观测研究.使用串联电迁移率颗粒物吸湿粒径分析仪(H-TDMA)观测32~350nm气溶胶在相对湿度为90%条件下的吸湿性参数,使用云凝结核计数器(CCNC)观测过饱和度在0.2%~0.8%的CCN数浓度.结果表明,不同气溶胶粒子的吸湿增长行为均表现出较为明显的双峰分布,即一个强吸湿模态和一个弱吸湿模态,且吸湿性在不同粒径(爱根核模态和积聚模态)上存在较为明显的不同,不溶性物质和二次气溶胶所占比重较大,并且在稳定的天气条件下,气溶胶的混合状态表现为由外混向内混发展的过程.观测期间该区域CCN的平均数浓度为13776(0.6%)cm-3,比沿海区、山区、干旱地区及清洁城市地区要高很多.其日变化表现为中午时刻出现峰值,影响因素主要与光化学反应有关.同时25日出现的轻雾过程对CCN有较为明显的清除作用.通过吸湿性参数计算得到的CCN数浓度和实际观测得到的CCN数浓度进行了闭合实验,结果显示出较好的相关性,表明将未饱和条件下观测得到的吸湿性参数带入到K?hler方程中,即可预测过饱和条件下气溶胶的活化能力.

An observational study of aerosol hygroscopic growth factor and cloud condensation nuclei in Nanjing in summer

In order to study the physical and chemical properties of aerosols in Yangtze River delta (YRD) more comprehensively, especially the hygroscopic growth and activation feature. In this study, aerosol hygroscopic growth factor (GF) and cloud condensation nuclei (CCN) in urban Nanjing were studied in August 2013. A Hygroscopic Tandem Differential Mobility Analyzer (H-TDMA) was utilized to observe the hygroscopic parameters at 90% relative humidity (RH) for particles with dry diameter between 32~350nm. And a Cloud Condensation Nuclei Counter (CCNC) was employed to measure the number concentration of CCN (NCCN) at supersaturation of 0.2%~0.8% simultaneously. The statistical results show that, the hygroscopic growth behavior of aerosol particles is shown as a distinct bimodal distribution, and can be classified into a dominant more-hygroscopic (MH) group and a smaller less-hygroscopic (LH) group. In addition, the hygroscopic growth factor of particles of different diameters, especially the Aitken mode and accumulation mode particles, exhibited clear differences. Meanwhile, insoluble substances and secondary aerosols accounted for a large proportion. It was also found that, in a stable weather condition, aerosol tended to be in an internally mixed state. During the period of observation, the average NCCN was 13776cm-3 (at 0.6% supersaturation), which was higher than other coastal, mountains, arid and clean urban areas. The peak diurnal variation of NCCN appeared at noon, which was mainly related to the photochemical reactions. The observations also show that the light fog process on August 25 had a clear wet scavenging effect on CCN. A comparison of the NCCN calculated from hygroscopic parameter-k with actual measured NCCN, indicating that combination of the hygroscopic parameter-k under sub-saturation from actual measurement and the K?hler equation may well predict the activation ability of aerosols to CCN under supersaturation.