石家庄地区气溶胶和CCN垂直廓线的飞机观测分析

Aircraft measurements and analysis of the vertical distribution of aerosol particles and CCN over the Shijiazhuang area

利用2010年春夏之交石家庄地区11架次的气溶胶和云凝结核(CCN)飞机同步观测资料,对比分析该地区云天和晴天气溶胶粒子的垂直廓线、不同高度气溶胶数谱特征,以及CCN的垂直分布、活化特性等。结果表明:云天气溶胶数浓度均值为1553.28cm^-3,有效直径均值为0.52μm,比晴天数浓度(883.82cm^-3)大76%,有效直径(0.37μm)大41%。云天气溶胶数浓度呈指数型递减分布,有效半径在2500m以下随高度变化不明显,2500m以上随高度逐渐增大。晴天气溶胶数浓度在800~1500m内有累积,有效半径随高度没有明显的变化趋势。不同高度上气溶胶谱型基本一致,云天和晴天在气溶胶小尺度端(<0.3μm)谱分布是连续的,在0.3μm处数谱均明显下降。云天和晴天CCN数浓度均随高度增大而减小,且各个高度层上云天CCN数浓度均大于晴天。云天CCN活化比率随高度变化不明显,晴天CCN活化比率随高度增大。气溶胶粒子尺度与CCN活化比率之间呈线性正相关。

Increasing attention has been given to aerosols due to their substantial influence on the atmospheric environment, c louds and precipitation,and the climate.Atmospheric aerosols can serve as condensation nuclei for the formation of both cloud droplets and ice nuclei,and can alter the microphysical properties of clouds,which in turn affects the formation of rain, snow and other forms of precipitation.Many studies have been performed with the goal of furthering our understanding of the physical,chemical and optical properties of aerosol particles,along with their effects on cloud,precipitation and other weather phenomena.However, large uncertainties still remain in the study of the aerosol particles, in particular the vertical distributions of aerosols found in the lower troposphere. Therefore, there is a need to better understand aerosol vertical distributions. In addition, to better understand the impact of aerosols on clouds, it is crucial to determine the relationships between aerosols and cloud condensation nuclei( CCN).Aerosol particles which act as CCN,and their interactions with cloud droplets are the key uncertainties in determining the effects of aerosols on climate. Although researches including observations near the ground and many extensive aircraft measurements have previously focused on the activation properties of aerosols and CCN,more direct and long-term observations are required to simultaneously characterize height-resolved aerosol,CCN and clouds properties,as well as to provide essential validation for modeling and satellite remote sensing.Using the aircraft as the observation platform by which to carry the instruments can effectively solve these problems.In the present study, in-situ aircraft measurements of aerosols and CCN of 11 flights during the spring and summer of 2010 in the Shijiazhuang area were analyzed, including the comparison of the vertical distribution of aerosol particles,particle size distribution at different heights,and the vertical distribution and activation characteristics of CCN under both cloudy and clear conditions.The results show that the mean aerosol number concentration( Na ) under cloudy conditions is 1 553. 28 cm^-3,and the mean effective diameter ( De ) is 0. 52 μm,which is 76% larger than that of clear sky ( Na : 883. 82 cm^-3 ) and 41% for effective diameter ( De : 0. 37 μm).Under cloudy conditions,Na decreases exponentially with height,and the particle effective radius ( Re ) does not change significantly at heights below 2 500 m,however it increases gradually at heights greater than 2 500 m.Under clear sky,Na accumulates in the height range of 800 to 1 500 m,while Re does not change significantly with height.The shapes of the aerosol number size distributions remain almost the same at different heights,and have a successive distribution for smaller particles (<0. 3 μm) under both cloudy and clear skies,with a sharp decrease at 0. 3 μm. Above 2. 5 km,Na is lower under cloudy sky than clear sky,while in the near-surface layer and boundary layer Na is higher under cloudy sky than clear sky. For both skies, the number concentration of CCN ( NCCN ) decreases with altitude at each observation height,and is higher under cloudy sky than clear sky.The activation ratio of CCN ( NCCN /NCN ) does not change significantly with height under cloudy conditions,however it increases with altitude under clear sky.Particle size and NCCN /NCN have a positive linear correlation.