Abstract: Observation data from the polarized-LiDARs of Zhenhai district and Fenghua,as well as conventional surface meteorological data,wind profile radar data and atmospheric composition data were used to analyze the vertical distribution characteristics of aerosol over Ningbo during two haze events,occurring on February 12-14 and 16-18,2015,respectively.Their formation mechanisms were further evaluated by means of vertical-temporal variations of extinction and depolarized coefficients at 532 nm and 355 nm.The results show that the first event was caused by local pollutants accumulation,whereas the second event was caused by the transboundary transport,deposition and near-surface mixing of pollutants.Particulate matters appeared below 1 km and between 1-2 km during the two events,respectively.High-level wind fields from wind profile radars were in good agreement with particulate matter characteristics observed by polarized-LiDARs,which can further interpret the different formation mechanisms of the two events.Using LiDAR-network technology to observe high-level particulate matters altered the limitation of near surface observations and single site soundings,providing reasonable technological methods for the quantitative analysis of pollutant transport intensities and spatial-temporal variations.Through LiDAR network,monitoring and early warning of haze events will be further promoted.

Key words: Haze, Aerosol, AQI, Extinction coefficients, Depolarization coefficients, Wind profile