Retrieval of O<sub>3</sub>, NO<sub>2</sub>, BrO and OClO Columns from Ground-Based Zenith Scattered Light DOAS Measurements in Summer and Autumn over the Northern Tibetan Plateau
Ground-based zenith scattered light differential optical absorption spectroscopy (DOAS) measurements were performed in summer and autumn (27 May–30 November) 2020 at Golmud (94°54′ E, 36°25′ N; 2807.6 m altitude) to investigate the abundances and temporal variations of ozone (O<sub>3</sub&g...
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| Autores principales: | , , , , , , , , , , , |
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| Formato: | article |
| Lenguaje: | EN |
| Publicado: |
MDPI AG
2021
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| Materias: | |
| Acceso en línea: | https://doaj.org/article/cbfa0be353744451812094ce972d37e2 |
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| Sumario: | Ground-based zenith scattered light differential optical absorption spectroscopy (DOAS) measurements were performed in summer and autumn (27 May–30 November) 2020 at Golmud (94°54′ E, 36°25′ N; 2807.6 m altitude) to investigate the abundances and temporal variations of ozone (O<sub>3</sub>) and its depleting substances over the northern Tibetan Plateau (TP). The differential slant column densities (dSCDs) of O<sub>3</sub>, nitrogen dioxide (NO<sub>2</sub>), bromine monoxide (BrO), and chlorine dioxide (OClO) were simultaneously retrieved from scattered solar spectra in the zenith direction during the twilight period. The O<sub>3</sub> vertical column densities (VCDs) were derived by applying the Langley plot method, for which we investigated the sensitivities to the chosen wavelength, the a-priori O<sub>3</sub> profile and the aerosol extinction profile used in O<sub>3</sub> air mass factor (AMF) simulation as well as the selected solar zenith angle (SZA) range. The mean O<sub>3</sub> VCDs from June to November 2020 are 7.21 × 10<sup>18</sup> molec·cm<sup>−2</sup> and 7.18 × 10<sup>18</sup> molec·cm<sup>−2</sup> at sunrise and sunset, respectively. The derived monthly variations of the O<sub>3</sub> VCDs, ranging from a minimum of 6.9 × 10<sup>18</sup> molec·cm<sup>−2</sup> in October to 7.5 × 10<sup>18</sup> molec·cm<sup>−2</sup> in November, well matched the OMI satellite product, with a correlation coefficient R = 0.98. The NO<sub>2</sub> VCDs at SZA = 90°, calculated by a modified Langley plot method, were systematically larger at sunset than at sunrise as expected with a pm/am ratio of ~1.56. The maximum of the monthly NO<sub>2</sub> VCDs, averaged between sunrise and sunset, was 3.40 × 10<sup>15</sup> molec·cm<sup>−2</sup> in July. The overall trends of the NO<sub>2</sub> VCDs were gradually decreasing with the time and similarly observed by the ground-based zenith DOAS and OMI. The average level of the BrO dSCD<sub>90°–80°</sub> (i.e., dSCD between 90° and 80° SZA) was 2.06 × 10<sup>14</sup> molec·cm<sup>−2</sup> during the period of June–November 2020. The monthly BrO dSCD<sub>90°–80°</sub> presented peaks in August and July for sunrise and sunset, respectively, and slowly increased after October. During the whole campaign period, the OClO abundance was lower than the detection limit of the instrument. This was to be expected because during that season the stratospheric temperatures were above the formation temperature of polar stratospheric clouds. Nevertheless, this finding is still of importance, because it indicates that the OClO analysis works well and is ready to be used during periods when enhanced OClO abundances can be expected. As a whole, ground-based zenith DOAS observations can serve as an effective way to measure the columns of O<sub>3</sub> and its depleting substances over the TP. The aforementioned results are helpful in investigating stratospheric O<sub>3</sub> chemistry over the third pole of the world. |
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