Active And Passive Remote Sensing Detection Method For Aerosols In The Free Troposphere

The free tropospheric anthropogenic aerosols refer to particulate matter such as black carbon,dumpling carbon,sulfate,nitrate,ammonium salt,etc.emitted by biomass burning,factories and urban traffic.Studying the temporal and spatial distribution characteristics of anthropogenic aerosols in the free troposphere is of great significance for pollutant transmission,climate forcing effect assessment,and satellite remote sensing estimation of ground particulate matter concentration.Although ground and spaceborne lidars are commonly used active remote sensing methods to detect the vertical distribution of aerosols,they can only represent small-scale observations of"points"and"lines".Passive remote sensing satellites can quantitatively obtain information on the temporal and spatial distribution of trace gases in a wide range.Therefore,this article aims to propose a method for identifying anthropogenic aerosols in the free troposphere combined with active and passive remote sensing observation data.First,based on ground-based lidar data,the characteristics of the interannual and seasonal aerosol vertical distribution in Zhejiang from 2017 to 2018 were studied,and two aerosol transboundary transport events that occurred in April and July 2018 were selected,with the help of CALIPSO and MODIS Satellite data and backward trajectory,PSCF and CWT modes explore the source and transmission mechanism of pollutants during transmission.Furthermore,the lidar active remote sensing technology is combined with the passive remote sensing observations of OMI and MOPPIT satellites,and different pollution sources are distinguished based on the significant difference in the survival life of carbon monoxide(CO)and nitrogen dioxide(NO₂).The correlation analysis between the NO₂/CO ratio and the results of active remote sensing detection of high-altitude aerosol transport is established through the probability distribution function,so as to realize the long-term(2010?2019)free tropospheric anthropogenic aerosol spatiotemporal distribution mapping.Research indicates:(1)The aerosol extinction coefficient of most Lidar sites in Zhejiang Province in2018 is less than that in 2017;the extinction coefficient below 0.9 km is spatially high in the middle and low in the east,the higher extinction coefficient near the ground is mainly due to the large amount of anthropogenic aerosol emissions.The seasonal variation of extinction coefficient is the highest in winter,followed by autumn,and lower in spring and summer.Aerosols are concentrated 1 to 2 km above the ground in spring and summer,and are mainly distributed below 1 km in winter.Due to the influence of high aerosols in autumn,the six stations present different vertical distribution patterns.Using the ratio of PM_2.5/PM₁₀ to distinguish between natural and man-made pollution,the results show that Zhejiang Province has serious fine particle pollution and is greatly affected by man-made sources.Two transboundary pollution transmission incidents show that,in addition to local pollutants,the transboundary transportation of aerosols will increase the degree of pollution in Zhejiang Province,especially when the airflow passes through the high AOD area,it will carry a large amount of pollutants and be transported to the study area,which caused heavy pollution.(2)The tropospheric NO₂ and CO total column concentration in Zhejiang Province is low in the western region and high in the eastern region.The NO₂ heavily polluted areas are represented by the North China Plain,the Yangtze River Delta and South China,while the CO heavily polluted areas are concentrated in Beijing.Tianjin,Hebei and Shandong regions.Western China is located in the low-value area of both NO₂ and CO,with the Qinghai-Tibet Plateau as the low-value center.(3)The K-means algorithm was used to cluster analysis of the aerosol extinction coefficient profile of each region of CALIPSO L2 532 nm and matched with the NO₂/CO grid data.The results show that the frequency distribution of NO₂/CO ratio is significantly different between case 1 and case 2.When the high aerosol is relatively clean(case 1),the NO₂/CO value corresponding to the high-frequency interval is significantly greater than the ratio corresponding to the high-frequency interval when there is high aerosol pollution(case 2).This may be due to the different life cycles of NO₂ and CO in the atmosphere.The long life of CO is easily accompanied by the transport of pollutants in the atmosphere.When there is high aerosol transport in the study area,the CO content increases,which leads to a decrease in the ratio;while the short life of NO₂ makes it difficult to diffuse and transport over long distances,resulting in more NO2 Exist in local emission sources.When the pollution is dominated by local emissions,the NO₂ content increases and the ratio increases accordingly.(4)According to the difference in frequency distribution of case 1 and case 2,the corresponding threshold is statistically obtained as a reference condition for judging whether aerosols exist at high altitude.The high aerosol judgment results based on the NO₂/CO threshold were compared and analyzed with the attenuated backscatter coefficient,extinction coefficient and VFM data of the CALIPSO satellite passing through the study area,and the results showed that the spatial distribution of the free tropospheric aerosols was relatively consistent.From the perspective of the average annual free tropospheric aerosol spatial distribution,energy-intensive areas,Japan,South Korea,and India are areas with a high incidence of free tropospheric aerosols.The paper has 28 pictures,6 tables,and 86 references.