Inversion Of NO₂ Vertical Distribution Based On Sciatran Atmospheric Radiative Transfer Model

With human activities emitting a large number of harmful chemical substances,it is inevitable that the atmospheric environment has been harmed,and atmospheric environmental problems such as photochemical smog and acid rain have emerged frequently.Atmospheric pollution has become a hot issue for research nowadays.Easy,fast and accurate access to atmospheric pollution information is a prerequisite for research and pollution prevention and control,and the monitoring of atmospheric pollutant concentration and vertical distribution has important scientific significance and application value for atmospheric environmental monitoring and prevention.The multi-axis differential absorption spectrometry（MAX-DOAS）,as a mainstream passive detection method,can be used to monitor and study atmospheric pollutant gases.In this paper,a ground-based MAX-DOAS measurement system from the Lidar Remote Sensing Research Centre of Xi’an University of Technology is used as the experimental system,and the SCIATRAN atmospheric radiative transfer model is used as the main tool for inversion,to carry out inversion research on NO₂ concentration and vertical distribution profiles with the pollutant nitrogen dioxide（NO₂）as the main research object.Firstly,a QDOAS-based differential slant column concentration inversion based on the MAX-DOAD measurement principle is carried out.The QDOAS software is configured with the required wavelength bands,gas absorption cross sections and reference spectra,and the differential slant column concentrations of NO₂ and oxygen dimer（O₄）are obtained by inversion with the measured solar spectrum.Simulations of the O₄AMF were carried out using the SCIATRAN atmospheric radiative transfer model,and the analysis showed the important influence of parameters such as observational geometry factors and aerosol optical thickness on the simulation results.Further,in order to achieve the inversion from NO₂ differential slant column concentrations to vertical profiles,the thesis carries out a vertical profile inversion and study of atmospheric aerosol extinction coefficients based on the look-up table method.In view of the distribution pattern of aerosols in the vertical direction,the aerosol extinction coefficient profiles were parameterised by using parameters such as the proportional fraction F,the boundary layer height H and the aerosol optical thickness τ.3696 atmospheric aerosol extinction coefficient profiles were finally obtained,representing different aerosol loading conditions.The O₄AMF was obtained by combining the SCIATRAN radiative transfer model model calculation,and the lookup table corresponding to the O₄DAMF（AMF（α）-AMF（90°））and aerosol parameters was established.Finally,the O₄DAMF measurements are calculated from the experimental solar spectral curve,and the vertical profile of the atmospheric aerosol extinction coefficient and the aerosol optical thickness can be inferred using the look-up table method.By comparing with the horizontal visibility meter data,the trend shows that the aerosol extinction coefficient profile based on the look-up table method can be used for the inversion of the vertical distribution profile of tropospheric NO₂.Finally,the optimal estimation method（OEM）proposed by Rodgers was used to invert and analyse the NO₂ vertical distribution profiles.The contours of atmospheric aerosol extinction coefficients that have been obtained from the inversion are fed into the SCIATRAN model to calculate the weighting matrix required for the OEM.The distribution information and a priori contours contained in the NO₂ differential slant column concentration are used to input the algorithm with the weighting matrix obtained from the SCIATRAN model to finally obtain the NO₂ vertical distribution.The results show that NO₂ gas is mainly concentrated within 1.5 km,with a maximum NO₂ concentration of 141.8 μg/m³ and a minimum of 8.4 μg/m³.By comparison with the point instruments of the monitoring station,the correlation coefficient Rsquare of the two reaches 0.86,which is in good agreement.The obtained NO₂ profiles were also discussed in layers,and the trend of each layer was more consistent.The reliability of the inversion results was proved,and the optimal estimation method was verified to be applicable to the inversion of the vertical distribution of NO₂ in the Xi’an area.