Vertical distribution of aerosols during different air pollution periods around Shanghai

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.