Observational Studies Of Atmospheric NO₂Column Density By Ground-based Multi-axis Differential Optical Absorption Spectroscopy

MAX-DOAS is an advanced remote sensing instrument for atmospheric compositionmeasurement. This ground-based remote sensing technique is highly sensitive to the absorptionsubstances in the atmosphere a few kilometers above the ground. As a result, it is s uitable forthe atmospheric composition measurement in the boundary layer and troposphere, and haspromising application.Nitrogen dioxide （NO₂） is an important atmospheric trace gas species, and is also one of themajor pollutant gases in the atmosphere. In this thesis, we present two NO₂observationexperiments, carried out in Wuqing in Tianjin （industrialized areas） and Tengchong in YunnanProvince （relatively clean region in the west China）, respectively, by using the portable MiniMAX-DOAS instrument in order to do some research on the feasibility of observation andretrieval of tropospheric NO₂column density under the two circumstances. First, a reasonableobservation program was designed according to the observation principle of the sun scatteredlight MAX-DOAS. Then, several aspects which may have important influence on themeasurement accuracy, such as system noise, wavelength calibration, Ring effect, selection andprocessing of molecular cross-section, were identified in the procedure of spectrum analysisand processing. We also proposed optimized processing method for each aspect based on theusage of WINDOAS analysis software. This thesis also gives an introduction of spectrumprocessing procedure with WINDOAS software and investigates the parameter settings. Finally,the NO₂slant column densities were retrieved with least-square method approximation takinginto account the noise elimination, calibration of the spectrum, processed moleculecross-section, Ring effect. We calculated the atmosphere Differential Slant Column Densities（DSCD） of Wuqing and Tengchong, and compared the diurnal variation of DSCD in these tworegions （industrialized area versus "clean" area）. We also describe a geometric approximationconverting DSCD to VCD （tropospheric vertical column density）. With the comparison ofVCDs in Wuqing and Yunnan Tengchong, we can conclude that the geometric approximationmethod works better under strong near-surface pollutant concentration （such as Wuqing）, whilein clean area, such as Tengchong, other factors should be considered in the tropospheric NO₂retrieval.