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Variation of haze events occurred in the Yangtze River Delta (YRD) of China,the characteristics of meteorological elements and the vertical distribution of aerosols during haze episodes were analyzed by utilizing data of ground observation,radiosonde and CALIPSO.The results illustrate that the frequency of haze events between 1981 and 2010 peaked in winter but bottomed out in summer and decreased from north to south in the YRD region,reaching at the lowest point in low frequency center-Shanghai.When haze happened,the most seriously affected area was 2-4 km above the ground and the concentrated range of total backscattering coefficient (TBC) that decreased with altitude was 0.8 x 10-3-2.5 × 10-3 km-1·sr-1.Particulate depolarization ratio (PDR) was less than 40％ in a large part and 93％ aerosols over the YRD area were regular particles,while the irregular ones concentrated on 2 km above the surface and the irregularity rose up but the diversity diminished when altitude increased.Color ratio (CR) was lower than 1.2 mostly at all altitudes and distributed asymmetrically above the ground.Nearly 80％ aerosols under 10 km were fine particles (CR ＜ 1.0) and 22.54％ coarse particles (CR ＞ 1.0) clustered at 2-4 km.Large particles (CR ＞ 1.2) aggregated in lower troposphere massively yet relatively smaller ones gathered in middle and upper troposphere.In the YRD region,aerosols with more powerful capabilities were wider and less regular than the ones of Northwest China.