北京地区一次霾污染过程的星-地激光雷达联合观测与分析

Observation and Analysis of a Haze Pollution Event in Beijing by Spaceborne and Ground-based Lidars

以北京市2015年1月11-17日发生的连续灰霾污染过程为例,采用地基和星载激光雷达联合观测,反演得到气溶胶的垂直分布特征。由MODIS卫星遥感数据和HYSPLIT后向轨迹模式分析得出污染来源和传输路径,结合地面空气质量和气象观测数据揭示了本次污染的成因。结果发现,根据激光雷达数据反演的近地面气溶胶消光系数与地面PM2.5浓度变化总体较为一致,而气溶胶边界层高度与PM2.5浓度呈相反变化趋势,且最低边界层高度为500 m。污染期间为小风高湿天气,地面平均风速和相对湿度分别为1.35 m/s和66%,连续多日逆温层的出现抑制了污染物在垂向空间的扩散传输,逆温强度高达5℃,这两方面因素导致污染物的持续积累,最终,在16日凌晨,PM2.5浓度达到448μg/m^(3)。污染最后在16日偏南风的作用下得以解除,PM2.5浓度的下降速度达到82μg/(m^(3)·h)。观测期间,PM2.5与NO_(2)、CO的相关系数分别为0.766和0.901,呈显著正相关,可见NO_(2)等气态前体污染物转化而来的二次气溶胶是霾的重要来源。综合分析表明,本次污染以灰霾为主,由区域传输和局地排放的气溶胶叠加、累积而成,河北南部及河南、山西等地的污染物随高空气团传输到北京地区,与本地排放的污染气溶胶混合在一起,导致污染加重。

Taking the continuous haze pollution process that occurred on January 11-17,2015 in Beijing as an example,the vertical distribution characteristics of aerosols were obtained by inversion using joint observations of ground-based and space-borne lidar.The pollution sources and transport paths were derived from MODIS satellite remote sensing data and HYSPLIT backward trajectory model analysis,after which the causes of this pollution were revealed by combining ground-based air quality and meteorological observation data.The results show that the near-surface aerosol extinction coefficients inferred from lidar data are generally consistent with the variation of PM2.5 concentrations on the ground,while the planetary boundary layer height shows an opposite trend to PM2.5 concentrations,and the lowest boundary layer height is 500 m.During the pollution period,it is light wind and high humidity,and the average wind speed and relative humidity are 1.35 m/s and 66%,respectively.The presence of the inversion layer for several days inhibited the diffusion and transport of pollutants in the vertical space,and the intensity of the inversion was as high as 5°C.These two factors led to the continuous accumulation of pollutants,and finally,the PM2.5 concentration reached 448μg/m^(3)in the early morning of the January16th,and the pollution was finally disappeared because of the southerly wind on the January 16th,and the PM2.5 concentration decreased at a rate of 82μg/(m^(3)·h).During the observation period,the correlation coefficients of PM2.5 with NO_(2) and CO were 0.766 and 0.901,respectively,showing a significant positive correlation,which shows that secondary aerosols from the transformation of gaseous precursor pollutants such as NO_(2)are an important source of haze.Comprehensive analysis shows that this pollution is dominated by haze,which is caused by the superposition and accumulation of aerosols from regional transmission and local emissions.Pollutants from southern Hebei,Henan and Shanxi are transmitted to Beijing with highaltitude air masses and mixed with locally emitted pollution aerosols,leading to increased pollution.