Abstract: Based on airborne observations over the Pearl River Delta from 6 flights during 14-27 September 2017, characteristics of low-level vertical distributions (below 3 km) of aerosol and cloud condensation nuclei (CCN) in northern and southern parts of Shenzhen (22 km) is studied. The vertical distribution of aerosol and CCN number concentration and aerosol number concentration spectrum are calculated and analyzed. The weather situation, meteorological conditions and air mass backward trajectory model are used to investigate the aerosol spatial features. Combined with CCN data under different supersaturations conditions, the activation characteristic of aerosol is obtained. Results show that low-level aerosol in Shenzhen varies from 500 to 9000 cm^-3. About 50% sample points (≤ 1.5 km) of the aerosol average number concentration are lower than 1000 cm^-3. As a coastal city, Shenzhen's aerosol concentration is lower than inland cities under some weather conditions, with a uniform aerosol distribution within the boundary layer. Three aerosol types in Shenzhen are summarized according to the main impacting factors, which is ocean (Ⅰ), land (Ⅲ) and combined ocean-land (Ⅱ). Comparing with type Ⅲ of aerosol, type I has less number concentration and larger size. The aerosol spectrum of pattern I is bimodal distribution, while type Ⅲ is trimodal distribution. The number concentration of type Ⅲ is highest and the particle size type Ⅲ is small. The number concentration of type Ⅱ is between the type Ⅰ and Ⅲ, with a bimodal distribution. Aerosol in northern Shenzhen is higher than that in southern, as northern Shenzhen closed to city cluster of the Pearl River Delta suffering more anthropogenic aerosol impact than that of southern Shenzhen. Activation spectrums of CCN are fitted by 3-flight data including clean and polluted aerosol patterns. Parameters C and k of the empirical function N_CCN(S)=CS^k are 695 and 0.65 under clean conditions (23 September 2017), and their counterparts under polluted conditions are 4108 and 1.11 (27 September 2017). The aerosol activation efficiency which is the ratio of number concentration between CCN and aerosol is calculated under different supersaturations conditions.