Research And Application Of Atmospheric Optical Parameters Retrieval Algorithm Based On Multi-platform DOAS Technology

In recent years,the overall air pollution prevention measures in China have achieved initial results,but there still remain many serious regional pollution problems.Therefore,timely and accurate acquisition of regional air pollution information is an important prerequisite for analyzing sources of pollution and taking preventive measures.Similarly,atmospheric optical parameters are important input parameters for retrieval of atmospheric pollutants,accurate acquisition of atmospheric optical parameter information is of great significance for accurate retrieval of atmospheric pollutants.In this regard,in response to the goal of comprehensively winning the blue sky defense battle proposed by Ministry of Ecology and Environment of the People's Republic of China has built an integrated three-dimensional monitoring system including spaceborne,ground-based and airborne.In this system,a variety of atmospheric composition detection instruments based on differential optical absorption spectroscopy(DOAS)technology play an important role.Among them,the spaceborne Environmental trace gas Monitoring Instrument(EMI)can be used to monitor and analyze the global atmospheric composition concentration and spatial distribution.Airborne DOAS can realize the dynamic study of the atmospheric composition in a large area and at different altitudes.The ground-based 2D MAX-DOAS can be used for near-surface monitoring to realize the study of the evolution and transportation of pollutants such as NO2 and SO2 in the troposphere and stratosphere.Meanwhile,the ground-based data can be used for the verification of satellite monitoring.In order to improve the accuracy of trace gas retrieval,this paper studies the retrieval algorithm of atmospheric optical parameters such as cloud parameters,surface albedo and effective optical path based on the multi-platform DOAS technology.In this paper,the self-developed spaceborne instrument EMI to detect trace gases in the global atmosphere.Because EMI observes scattering light at the top of the atmosphere,the presence of clouds can affect the photon path and cause large errors in the retrieval of trace gases.This paper studies the cloud parameters retrieval algorithm based on the absorption band of O4 at 477 nm.First,the stripe phenomenon in the O4 SCD was corrected,and the reflectance was also correlated;then using the SCIATRAN radiative transfer model to set different parameters and solar geometric information through to simulate radiance to create look-up tables of O4 SCD and reflectance,and then convert them into a look-up table of effective cloud fraction and cloud pressure.Finally,the O4 SCD,continuous reflectance and related solar geometric information are multi-dimensionally interpolated to obtain the EMI effective cloud fraction and cloud pressure.To verify the accuracy of this algorithm,the EMI effective cloud fraction and cloud pressure are compared with OMI cloud products.Among them,the effective cloud fraction frequency distribution of EMI and OMI shows a trend of decreasing frequency from low cloud fraction to high cloud fraction.At the cloud fraction is 0 and 1,EMI and OMI both appear high frequency,the cloud fraction correlation coefficient(R)is 0.82,and the correlation is good;the overall frequency of cloud pressure is relatively consistent,but there are still some inconsistencies that need to be further studied.Based on airborne DOAS instrument,this paper obtain surface albedo by measuring downward and upward scattered light at aircraft altitude,combining with the simulation of SCIATRAN radiative transfer model,and using an iterative retrieval method.By this method,it is clarified that the different types of underlying surfaces correspond to different surface albedo in the flight area between Shijiazhuang and Baoding.In addition,the relationship between the surface albedo and the wavelength in the range of 350-395nm in the center of the city,the middle of the city,and the edge of the city is studied.The study found that the surface albedo in three regions of 350-395nm band goes up slightly with the increase of wavelength.Comparing the surface albedo of different underlying surfaces with MODIS,the results are very consistent.The comparison of different observation areas shows that the albedo of urban area is larger than that of farmland,which shows that surface albedo can reflect the type of underlying surface accurately.In this paper,the self-developed 2D MAX-DOAS was used to continuously monitor the concentration and spatial distribution of tropospheric NO2 in Hefei from June 2015 to May 2016.Since the slant column density(SCD)is the integrated concentration along the light path,it cannot effectively represent the spatial concentration information of NO2.In this method,the effective light path can be calculated based on retrieved O4 SCD and O4 concentration acquired from altitude.And then the NO2 volume mixing ratio(VMR)is calculated by combining the effective optical path and NO2 SCD.It is then concluded that the high concentration of daily NO2 azimuthal distribution in Hefei is located in the economic development zone,industrial zone and Hefei urban area in the east and southeast of the monitoring point,and the low concentration is located in the farmland and forest area in the northwest and west of the monitoring point.The results are highly consistent with the monitoring situation of the Ministry of Ecology and Environment of the People's Republic of China.During the year of monitoring,the four seasons change significantly,with the highest concentration in winter,followed by spring and fall,and the lowest in summer.The averaged NO2 concentration in heating season is 1.68 times that in non-heating season,which is significantly higher than that in non-heating season.