Research On The Method Of Obtaining Tropospheric Vertical Column Density Of NO₂ By One-dimensional MAX-DOAS

NO₂ is one of the most important polluted gases in the atmosphere,which can lead to acid rain,photochemical smog and haze and so on.One dimensional multi-axis differential absorption spectroscopy（MAX-DOAS）can be used for real-time,non-contact and on-line measurement of atmospheric trace gases（NO₂,etc.）,The method of obtaining the concentration of tropospheric NO₂ column based on one-dimensional MAX-DOAS is studied in this paper.（1）For the observation elevation angle of existing commercial one-dimensional MAX-DOAS cannot be changed according to the requirement of measurement,which has limitations in the further application.In this thesis,the STC12C5A60S2 chip was used as the control unit to control the rotation of the stepping motor and the telescope.The observation angle was set up and the range of elevation scanning is expanded to Increased commercial one-dimensional MAX-DOAS flexibility.And perform performance tests,including dark current,electronic bias,electronic noise and resolution.The linearity of dark current is 0.99587,the electronic noise value is1.5615,and the system performance is good.（2）One dimensional MAX-DOAS instrument was used to monitor the air quality of Huaibei area,and the observation scheme was designed according to the factors such as the sun’s scattered light,observation location and observation time.The noise was eliminated and the wavelength was calibrated according to the WINDOAS software.The Ring effect and the cross section of gas molecules were selected,and the NO₂ oblique column concentration was obtained by using the cross section of polymer cross section combining with the least squares fitting.The concentration of NO₂ inclined column was converted to vertical column concentration by geometric method and the level of regional pollutants was characterized by vertical column concentration.Based on the optimal estimation algorithm and two step inversion method,the aerosol profile is first obtained and then the vertical distribution profile of NO₂ is retrieved（3）The time series of NO₂ vertical column concentration obtained by MAX-DOAS were compared with that of OMI satellite and the results show that both of them have good consistency（R²=0.8046）in clear weather.The results of satellite measurements under two weather conditions in clear and cloudy days are lower than the results of MAX-DOAS,which is mainly due to the difference in the observation methods and resolution between the two instruments.Finally,data from monitoring stations in huaibei area were compared with the concentration of NO₂ column measured by improving one-dimensional max-doas.The variation trend of the two measurement data is consistent,indicating that the possible source of NO₂ pollution source is mainly local.