{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,12,18]],"date-time":"2025-12-18T09:34:08Z","timestamp":1766050448025,"version":"build-2065373602"},"reference-count":47,"publisher":"MDPI AG","issue":"19","license":[{"start":{"date-parts":[[2023,9,25]],"date-time":"2023-09-25T00:00:00Z","timestamp":1695600000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Nature Foundation of Tibet Autonomous Region","award":["XZ202301ZR0011G","SKLAO2021001A02"],"award-info":[{"award-number":["XZ202301ZR0011G","SKLAO2021001A02"]}]},{"name":"Fund of the State Key Laboratory of Applied Optics","award":["XZ202301ZR0011G","SKLAO2021001A02"],"award-info":[{"award-number":["XZ202301ZR0011G","SKLAO2021001A02"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Remote Sensing"],"abstract":"<jats:p>In order to investigate the abundance of and temporal variation in nitrogen dioxide (NO2) in the troposphere and validate the corresponding satellite products during a normal year and the lockdown period of coronavirus disease 2019 (COVID-19) in Lhasa, a city on the Tibetan Plateau (TP), ground-based remote-sensing measurements captured by applying multi-axis differential optical absorption spectroscopy (MAX-DOAS) were recorded from August 2021 to March 2023 at the Lhasa site (91.14\u00b0E, 29.66\u00b0N; 3552.5 m altitude). The NO2 differential slant column densities (dSCDs) were retrieved from the spectra of scattered solar light at different elevation angles. Then, the tropospheric NO2 vertical column densities (VCDs) were calculated with the geometric approximation method. Based on the retrieved tropospheric NO2 VCDs, we found that the pattern of monthly variation in tropospheric NO2 VCDs in Lhasa presented two peaks, one in winter and one around May. According to the monthly means of tropospheric NO2 VCDs during the COVID-19 lockdown, the NO2 background level in Lhasa was estimated to be 0.53 \u00d7 1015 molecules\u00b7cm\u22122. For diurnal variations in tropospheric NO2 VCDs, the morning and evening peaks disappeared during the COVID-19 lockdown period. The east\u2013west direction (i.e., along the river valley) was the main path of NO2 transport and dispersion in Lhasa, but the tropospheric NO2 VCDs were little dependent on the wind direction or wind speed during the COVID-19 lockdown. The correlation coefficient of tropospheric NO2 VCDs was R = 0.33 (R = 0.43), with the averaged relative deviation of \u221228% (99%) for the TROPOMI (GEMS) relative to ground-based MAX-DOAS. The monthly deviations of tropospheric NO2 VCDs between ground-based MAX-DOAS and the satellite showed a dependence on NO2 abundance, with the maxima of the monthly positive deviations during the COVID-19 lockdown period. The GEMS could not capture the strong and systematic diurnal variation in tropospheric NO2 VCDs in the \u201cnormal\u201d year well. During the COVID-19 lockdown, the GEMS (&gt;2 \u00d7 1015 molecules\u00b7cm\u22122) overestimated the hourly levels measured by ground-based MAX-DOAS (&lt;1.6 \u00d7 1015 molecules\u00b7cm\u22122). As a whole, these results are beneficial to understanding the influences of anthropogenic activities on NO2 background levels in Lhasa and to learning the accuracy of satellite products over the TP, with its high altitude and complex terrain.<\/jats:p>","DOI":"10.3390\/rs15194689","type":"journal-article","created":{"date-parts":[[2023,9,26]],"date-time":"2023-09-26T02:31:29Z","timestamp":1695695489000},"page":"4689","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":8,"title":["Retrieval of Tropospheric NO2 Vertical Column Densities from Ground-Based MAX-DOAS Measurements in Lhasa, a City on the Tibetan Plateau"],"prefix":"10.3390","volume":"15","author":[{"given":"Siyang","family":"Cheng","sequence":"first","affiliation":[{"name":"State Key Laboratory of Severe Weather & Institute of Tibetan Plateau Meteorology, Chinese Academy of Meteorological Sciences, Beijing 100081, China"},{"name":"State Key Laboratory of Applied Optics, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033, China"},{"name":"Shigatse National Climate Observatory, Shigatse 857000, China"}]},{"given":"Guijuan","family":"Pu","sequence":"additional","affiliation":[{"name":"Tibet Institute of Plateau Atmospheric and Environmental Sciences, Lhasa 850000, China"}]},{"given":"Jianzhong","family":"Ma","sequence":"additional","affiliation":[{"name":"State Key Laboratory of Severe Weather & Institute of Tibetan Plateau Meteorology, Chinese Academy of Meteorological Sciences, Beijing 100081, China"}]},{"given":"Hyunkee","family":"Hong","sequence":"additional","affiliation":[{"name":"National Institute of Environmental Research, Incheon 22689, Republic of Korea"}]},{"given":"Jun","family":"Du","sequence":"additional","affiliation":[{"name":"Shigatse National Climate Observatory, Shigatse 857000, China"},{"name":"Tibet Institute of Plateau Atmospheric and Environmental Sciences, Lhasa 850000, China"}]},{"given":"Tseten","family":"Yudron","sequence":"additional","affiliation":[{"name":"Tibet Institute of Plateau Atmospheric and Environmental Sciences, Lhasa 850000, China"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0468-0966","authenticated-orcid":false,"given":"Thomas","family":"Wagner","sequence":"additional","affiliation":[{"name":"Max Planck Institute for Chemistry, 55020 Mainz, Germany"}]}],"member":"1968","published-online":{"date-parts":[[2023,9,25]]},"reference":[{"key":"ref_1","unstructured":"Seinfeld, J.H., and Pandis, S.N. 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