Lidar Detection Of Vertical Distribution And Typical Processes Of Aerosols In Southern Suburbs Of Beijing

Aerosols can affect the radiation balance between the earth and the atmosphere through direct and indirect effects.Haze and dust are related to aerosol pollution.Lidar has the capability of long-range detection,high spatial and temporal resolution and the 24/7 continuous work.The aerosol profile obtained by lidar can make up for the lack of high spatial-temporal resolution data,improve the scientific understanding of the aerosol's impact on climate.The real-time observation capabilities make it can be applied in the field of pollution monitoring.Related to the project(Early Warning and Prevention of Major Natural Disasters-Research and Test of Vertical Integrated Meteorological Observation Technology in Megacities),many studies have been done by our self-made AWRL-II lidar in southern suburbs of Beijing.The first part is an introduction.The significance of aerosol research is introduced.The basic properties including sources,types,distribution and its role in the atmosphere of aerosol are outlined.The interaction mechanism of laser and aerosol is expounded.The technical classification and inversion formula of atmospheric detection lidar are introduced.The next part is the examination work about lidar calibration and data verification.The novel CCD lateral scattering iterative method is used to correct the lidar geometric overlap factor.The gain ratio of the two polarization channels of the lidar is calibrated.The four-quadrant detection and molecular Rayleigh signal test ensure the reliability of the AWRL-? lidar system and data.By comparing with the results of the sunphotometer results and the EARLINET standard algorithm,the accuracy of the lidar data and the results of the inversion method is verified since the goodness of fit with the results of the sunphotometer is as high as 0.93.A method of dynamic threshold of the range correction signal are proposed to eliminate the unveracious large depolarization ratio of the position successively above a thick cloud or a thick aerosol layer.This method is also effective for the removal of abnormal depolarization ratio caused by noise at far range.And then the typical pollution process cases in Beijing are studied.Combining with the meteorological parameters,ground particulate matter,satellite instrument and atmospheric models,the aerosol spatial distribution,generation and dissipation processes,pollution sources and transmission paths are analyzed.The impact of pollution on air quality,the types of pollutants and optical properties are also studied.During the haze period,the minimum value of the boundary layer at 0.6 km is found.The primary pollutant is PM2.5.And the main component of PM2.5 in this haze period is the spherical urban aerosol with the depolarization ratio less than 0.1 that comes from the industrial cities in the southwest of Beijing.In the dust pollution,the primary pollutant is PM 10 consisting of non-spherical dust with the depolarization ratio in the range of 0.2 to 0.3.Even if the concentration of the primary pollutants in dust far exceeds the concentration of the primary pollutants in haze period,the impact of dust on reduced visibility is less than that of haze.A study on a persistent pollution event of mid-snow shows that the aerosol concentration increases after snowfall.It is maybe that the high-humidity environment accelerates the generation of secondary pollutants.Finally,a database of 532nm extinction coefficient is established by using the lidar data from 2017 to 2019.The database can provide data support for climate radiation models and numerical prediction models.Monthly and seasonal statistics are conducted on the vertical profile of the extinction coefficient.The result shows that the aerosol is basically distributed below 2km,and in the near-ground layer extinction coefficient of the heavily polluted days is generally greater than 1km-1.But there is no obvious seasonal and monthly distribution characteristics of vertical structure.