Investigation of weather conditions and BrO during ozone depletion events between 2010 and 2021 in Ny-Ålesund

Abstract

Ozone Depletion Events (ODEs) have been observed since the late 1990s in the polar regions during spring, often in combination with Bromine Explosion Events (BEEs). In a heterogeneous, autocatalytic, chemical chain reaction cycle, inorganic bromine is released from the cryosphere into the troposphere and depletes ozone, sometimes to below detection limit. Besides low temperatures favoring the bromine explosion reactions, two different meteorological conditions are mainly observed during these events: on the one hand, low wind speeds and a stable boundary layer, where bromine can accumulate and deplete ozone, and on the other hand, high wind speeds above approximately 10 m/s with blowing snow and a higher, unstable boundary layer. The second condition often occurs in combination with polar cyclones, where bromine can be recycled aloft on snow and aerosol surfaces.In this study, two long term ozone data sets, one from ozone sondes launched in Ny-Ålesund and the other from in-situ measurements on Zeppelin mountain – located close to Ny-Ålesund – have been evaluated from March until May between 2010 and 2021 to detect ODEs. To analyze the prevailing weather conditions during these events, ERA5 reanalysis data has been used and separated between weather conditions during ODEs and no-ODEs based on the respective ozone data set. The evaluation of the two data sets led to very consistent results: during ODEs, lower pressure is observed east of Svalbard and higher pressure over Greenland, leading to a transport of cold polar air from the north to Ny-Ålesund. Also higher wind speed and a higher boundary layer are noticed, supporting the assumption, that ODEs often occur in combination with polar cyclones.Using the same approach, the long-term tropospheric BrO data set from Bougoudis et al., 2020 in combination with S5P TROPOMI retrievals of tropospheric BrO has been used to analyze BrO patterns. During ODEs in Ny-Ålesund, the satellite data show elevated values all over the Arctic, but especially north of Svalbard. This work was supported by the DFG funded Transregio-project TR 172 “Arctic Amplification (AC)³“ in subproject C03.