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

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 degrees C. These two factors led to the continuous accumulation of pollutants, and finally, the PM2.5 concentration reached 448 mu g/m(3) in the early morning of the January 16th, 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 82 mu g/(m(3) . h). During the observation period, the correlation coefficients of PM2.5 with NO2 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 NO2 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 high-altitude air masses and mixed with locally emitted pollution aerosols, leading to increased pollution.