上海不同污染等级下气溶胶光学特性垂直分布特征

Vertical distribution of aerosols during different air pollution periods around Shanghai

气溶胶光学特性是可吸入颗粒物的重要表征指标之一,而针对不同空气污染等级的气溶胶光学特性的垂直分布特征当前研究较少.本文利用上海地区(30°E,120°N^33°E,123°N)2006年6月至2011年12月的星载云-气溶胶激光雷达(Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations,CALIOPSO)资料分析不同季节气溶胶光学特性垂直分布的基础上,深入探讨了不同空气污染等级下的气溶胶垂直(0~6km)分布特征.结果表明:上海地区气溶胶粒子多聚集在0~2 km的高度上且具有明显的季节特征,冬春季节气溶胶粒子后向散射系数集中于0.005以上,颗粒物散射能力较大,其中冬季偏振比范围为0.15~0.25,色比范围为0.57~0.77,主要为不规则的小颗粒;夏季气溶胶粒子的偏振比(0.03~0.09)较小,气溶胶颗粒物较为规则;秋季各种形态的颗粒混合程度较高,其偏振比的范围为0.12~0.23,色比范围为0.58~0.90;不同污染等级下的气溶胶光学特性在垂直分布上具有明显的差异,在重污染时期散射能力大不规则颗粒物增多,垂直差异不明显,污染高度较高;轻度污染以规则颗粒物为主,颗粒物散射能力较小,表现出低层以粗颗粒为主,高层以细颗粒物为主的特征;轻微污染和无污染的气溶胶垂直分布类似,颗粒物散射能力较小.

Aerosol optical property is an important index to characterize the inhalable particles. However, few studies were focused on its vertical distribution with respect to different air pollution levels. This study first analyzes the seasonal variations of aerosol optical property in the vertical distribution, and further distinguishes their features among different air pollution levels at the altitude of 0~6 km around Shanghai. The aerosol data products are derived from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations （CALIPSO） during June 2006 to December 2011. Results show that aerosol vertical distribution around Shanghai has a clear seasonal variation, with the majority of aerosols concentrating at the altitude of 0 to 2 km. Specifically, the aerosols in spring and winter exhibit higher scattering ability with backscatter coefficients mostly over 0.005, larger volume depolarization ratios （0.15~0.25）, and smaller color ratios （0.57~0.77）, indicating that the particles are generally fine and irregular. The volume depolarization ratios in summer （0.03~0.09） are relatively smaller, implying that the particles are more regular. On the other hand, the volume depolarization ratios and color ratios in autumn are concentrated within the range of 0.12~0.23 and 0.58~0.90 respectively, suggesting the presence of highly-mixed particles. More importantly, the vertical distributions of aerosol optical property vary greatly at different air pollution levels. For instance, during severely polluted period, higher scattering ability and an increasing concentration of irregular particles are observed, but with insignificant vertical contrasts. Aerosols during the light polluted periods, however, generally show lower scattering ability. They are mainly in regular shapes with fine particles dominated at the higher altitude but course particles prevailing at the lower height. In contrast, the aerosol vertical distributions during slightly polluted and clear air periods both have lower scattering abilities with similar characteristics regarding the backscatter coefficient, depolarization ratio and color ratio.