基于航测的珠三角气溶胶垂直分布及活化特性

2017年9月14—27日在珠江三角洲地区开展了6个架次飞机观测试验。利用飞行获取的气溶胶、云凝结核、云滴及常规气象探头观测资料，结合天气形势、气象条件及气团后向轨迹分析，研究了珠江三角洲地区深圳气溶胶数浓度及其谱的垂直分布特征，配合不同过饱和度条件下云凝结核浓度观测，分析了气溶胶活化特性。结果表明：在不同天气条件下，深圳低层气溶胶数浓度变化范围为500~9000 cm-3；边界层内气溶胶分布相对均匀，谱型随高度变化与气象条件相关。将6个架次气溶胶观测资料根据数浓度及谱型分为3种类型：类型Ⅰ为海洋型气溶胶，数浓度小，粒子尺度大，谱型呈双峰分布；类型Ⅲ为大陆型气溶胶，数浓度高，粒子尺度小，谱宽较宽且呈三峰分布；类型Ⅱ为海洋大陆影响型气溶胶，即受海洋和大陆共同影响，数浓度低于类型Ⅲ高于类型Ⅰ，谱型为双峰分布。拟合了包含海洋型及大陆型气溶胶的3个架次近地面云凝结核活化谱，计算了气溶胶在不同过饱和度条件下的活化效率。

Aircraft Measurements of Aerosol Vertical Distributions and Its Activation Efficiency over the Pearl River Delta

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)=CSk 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.