Mobile MAX-DOAS observations of tropospheric NO.sub.2 and HCHO during summer over the Three Rivers' Source region in China

The tropospheric concentrations of nitrogen dioxide (NO.sub.2) and formaldehyde (HCHO) have high spatio-temporal variability, and in situ observations of these trace gases are still scarce, especially in remote background areas. We made four similar circling journeys of mobile multi-axis differentia...

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Published in:Atmospheric chemistry and physics 2023-03, Vol.23 (6), p.3655
Main Authors: Cheng, Siyang, Cheng, Xinghong, Ma, Jianzhong, Xu, Xiangde, Zhang, Wenqian, Lv, Jinguang, Bai, Gang, Chen, Bing, Ma, Siying, Ziegler, Steffen, Donner, Sebastian, Wagner, Thomas
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Language:English
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Nitrogen dioxide
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Summary:The tropospheric concentrations of nitrogen dioxide (NO.sub.2) and formaldehyde (HCHO) have high spatio-temporal variability, and in situ observations of these trace gases are still scarce, especially in remote background areas. We made four similar circling journeys of mobile multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements in the Three Rivers' Source region over the Tibetan Plateau in summer (18-30 July) 2021 for the first time. The differential slant column densities (DSCDs) of NO.sub.2 and HCHO were retrieved from the measured spectra, with very weak absorptions along the driving routes. The tropospheric NO.sub.2 and HCHO vertical column densities (VCDs) were calculated from their DSCDs by the geometric approximation method, and they were further filtered to form reliable data sets by eliminating the influences of sunlight shelters and the vehicle's vibration and bumpiness. The observational data show that the tropospheric NO.sub.2 and HCHO VCDs decreased with the increasing altitude of the driving route, whose background levels ± standard deviations were 0.40 ± 1.13x10.sup.15 molec. cm.sup.-2 for NO.sub.2 and 2.27±1.66x1015 molec. cm.sup.-2 for HCHO in July 2021 over the Three Rivers' Source region. The NO.sub.2 VCDs show similar geographical distribution patterns between the different circling journeys, but the levels of the HCHO VCDs are different between the different circling journeys. The elevated NO.sub.2 VCDs along the driving routes usually corresponded to enhanced transport emissions from the towns crossed. However, the spatial distributions of the HCHO VCDs depended significantly on natural and meteorological conditions, such as surface temperature. By comparing TROPOMI satellite products and mobile MAX-DOAS results, we found that TROPOMI NO.sub.2 and HCHO VCDs have large positive offsets in the background atmosphere over the main area of the Three Rivers' Source. Our study provides valuable data sets and information of NO.sub.2 and HCHO over the Tibetan Plateau, benefitting the scientific community in investigating the spatio-temporal evolution of atmospheric composition in the background atmosphere at high altitudes, validating and improving the satellite products over mountain terrains, and evaluating the model's ability to simulate atmospheric chemistry over the Tibetan Plateau.
ISSN:1680-7316
1680-7324