Research On Retrieval Of NO₂ Profiles By Look-up Table Method Based On MAX-DOAS

NO₂is one of the important trace gases in the troposphere.Obtaining NO₂vertical distribution profile is conducive to the study of atmospheric pollution diffusion process.Therefore,it is very important to study the NO₂vertical profiles.Multi-axis differential optical absorption spectroscopy(MAX-DOAS)is an effective optical remote sensing method for monitoring atmospheric pollutant concentration in urban areas.It has been widely used in the field of environmental monitoring due to its advantages of high temporal resolution,high sensitivity and wide measurement range.Based on passive MAX-DOAS technology,this thesis researches the method of retrieving the trace gases vertical column densities and vertical profiles based on look-up table method,and has carried out field application in Huaibei area.(1)The basic principle and retrieval method of MAX-DOAS technology are studied in this thesis.We also build the one-dimensional ground-based MAX-DOAS instrument and test the key parameters of the instrument.The measurement of multi elevation solar scattering spectra is realized,and the trace gases slant column densties are obtained.The average offsets of the two measured spectra were 896.07 counts and891.61 counts respectively,the average dark current of the spectrometer was 0.11782counts/s,the electronic noise of the spectrometer was 0.50731,the electronic noise of a single scan was 0.01604 and the spectral resolution of the spectrometer was 0.65 nm.The test results suggest that the performance of the built instrument meets the observation requirements.(2)A method for retrieving the tropospheric trace gases vertical column densities and vertical profiles is establishd based on look-up table method.Firstly,the sensitivity of input parameters are studied based on McArtim,which improve the performance of the algorithm;Secondly,the look-up table method for retrieving aerosol profile is established to obtain the aerosol extinction profile with the lowest cost function,and then the aerosol extinction profile and the actual observation conditions are brought into the atmospheric radiative transfer model.Finally,the look-up table mehod for retrieving the trace gases vertical column densities and vertical profiles at different elevation angles is established.The method is realized with the help of VB option platform.In this thesis,NO₂is taken as the research object.Through the cost function minimization process,the return values of NO₂VCD,the weight factor of the NO₂and the height of the boundary layer are obtained.It was found that NO₂was mainly distributed at the height below 2.0 km in general.The accuracy of the look-up table method was verified by comparing with the Copernican Atmospheric Monitoring Service(CAMS)model.(3)The constructed one-dimensional ground-based MAX-DOAS instrument was operated to carry out in Huaibei area for nearly one-year field observations.The NO₂slant column densities are retrieved based on MAX-DOAS method,and the conversion of NO₂slant column densities to vertical column densities are realized by the look-up table method.It was found that the monthly mean value of NO₂VCD in Huaibei area roughly presents an inverted“U”type change in this year.The seasonal mean values of NO₂VCD were the highest in winter,followed by autumn and spring,and the lowest in summer.Combined with HYSPLIT backward wind field trajectory model,the wind speeds and directions of high value months(November and December)in Huaibei area were given,and the sources of pollutants were analyzed.Moreover,the daily mean values of MAX-DOAS observation results were compared with OMI satellite measurement results of different effective cloud fractions(0