Measurements report: The unusual spring 2020 Arctic stratospheric ozone depletion above Ny-Ålesund by ground-based ZSL-DOAS

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Of the severe stratospheric ozone depletion events (ODEs) reported over the Arctic, the most severe occurred during the spring of 2020; we analyzed the reasons for this event herein. We retrieved the critical indicator ozone vertical column density (VCD) using zenith scattered light differential optical absorption spectroscopy (ZSL-DOAS) from March 2017 to September 2021 located in Ny-Ålesund, Svalbard, Norway. The average ozone VCD over Ny-Ålesund between March 18 and April 18, 2020, was approximately 274.8 Dobson units (DU), which was about 64.7±0.1% of that in the other years (2017, 2018, 2019, and 2021), and the daily peak difference was 195.7 DU during this period. The retrieved daily averages of ozone VCDs were compared with satellite observations from Global Ozone Monitoring Experiment-2 (GOME-2), a Brewer spectrophotometer, and a Système d’Analyze par Observation Zénithale (SAOZ) spectrometer at Ny-Ålesund; the resulting Pearson correlation coefficients were relatively high at 0.94, 0.86, and 0.91, with relative deviations of 2.3%, 3.1%, and 3.5%, respectively. Polar observations are still inadequate and accurate ZSL-DOAS observations can provide reliable data for polar ozone study. We also considered the chemical components of this process in the Arctic winter of 2019/2020 with the specified dynamics version of the Whole Atmosphere Community Climate Model (SD-WACCM). The SD-WACCM results indicated that both ClO and BrO concentrations peaked in late March, which was a critical factor during the ozone depletion observed in Ny-Ålesund. Chlorine and bromine activation were clearly obvious during the Arctic spring of 2020, whereas the partitioning of bromine compounds was different from that of chlorine. Before activation, chlorine was predominantly present as HCl and ClONO2, whereas bromine was predominantly present as HOBr and BrCl. Particularly, before chlorine activation began, bromine mainly existed as HOBr; however, after chlorine activation, bromine mainly existed in the form of BrCl. By ZSL-DOAS observations, we provided another evidence for unprecedented ozone depletion during the Arctic spring of 2020. The ZSL-DOAS ozone VCD observations can also provide calibration for satellite observations and model simulations, and in the future can provide the support for observations at more Chinese research stations or international local stations in the polar area.

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