基于CALIPSO的华北地区气溶胶垂直分布特征

Characteristics of aerosol vertical distribution based on CALIPSO over North China

利用2007—2014年CALIPSO Level 2气溶胶廓线产品,统计分析了华北地区气溶胶垂直分布规律,并以2013年12月发生的一次大范围霾过程为例,探讨了霾天气中气溶胶垂直变化特征。结果表明,华北地区气溶胶消光系数(σ)随高度指数衰减,年平均标高为2.48 km;1 km以下存在σ高值层,冬季较大、春季较小,年平均为0.333km^(-1)。年平均颗粒退偏振比(Particulate Deploarization Ratio,PDR)随高度递增,变化范围为0.18~0.25;PDR春季较大,夏季较小。年平均色比(Color Ratio,CR)随高度弱增加,变化范围为0.7~0.8;春季CR随高度递减,其他季节随高度递增。华北地区近地面以污染沙尘气溶胶为主;春季以沙尘为主,夏秋季以污染沙尘为主,冬季中高层以沙尘为主,低层以污染沙尘为主。霾事件中,霾日1 km以下存在消光高值层,消光系数约为清洁日三倍。霾日PDR和CR都低于清洁日,2 km以下PDR大多小于0.2,CR以0.3~0.5为主。本地烟尘与远距离输送的沙尘相混合形成的污染沙尘是本次霾过程的主要气溶胶类型。

Based on Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations(CALIPSO)Lidar level 2 aerosol data derived from the period of 2007-2014,in this study,the vertical distribution characteristics of aerosols observed in a haze event over North China and during December 2013 are analyzed.The results revealed that the aerosol extinction coefficients(σ)exponentially declinedwith altitudes.The annual mean of aerosol scale height is 2.48 km.Under 1 km,there isa layer of highσvalue with the annual mean of 0.333 km-1,representing maximum annual mean value in Winter and minimum one in Spring.The annual mean Particle Depolarization Ratio(PDR)shows an increase with the altitude,varying from 0.18 to 0.25.It is noteworthy that PDR ration is large in Spring,while it is small in Winter.The annual mean Color Ratio(CR)ranges from 0.7 to 0.8,gradually increasing with the altitude.In addition,CR shows declining the vertical distribution in Spring,while the trend inclines in other seasons.The polluted dust is the major aerosol type in the lower atmosphere.In Spring,the major aerosol type is dust,while the polluted dust is dominant in Summer and Autumn.In winter season,the major aerosol type is dust in middle and upper atmosphere,while the polluted dust is in lower layer.During a haze period,a homogeneous mixing layer with highσexists below1 km.It shows that its value is three times ofσin a haze day in comparison with a clean day.Accordingly,the values of PDR and CR for the haze day are lower than those values in the clean day.Under 2 km,most of PDRs are below 0.2,and CRs are between 0.3 and 0.5.The polluted dust,which is the mixture of the remote transported dust and the local smoke particle,is the major aerosol type during a haze event.