Abstract: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.