21 Oct 2022
21 Oct 2022
Status: this preprint is open for discussion.

Source Mechanisms and transport Patterns of tropospheric BrO: Findings from long-term MAX-DOAS Measurements at two Antarctic Stations

Udo Frieß1, Karin Kreher3, Richard Querel2, Holger Schmithüsen4, Dan Smale2, Rolf Weller4, and Ulrich Platt1 Udo Frieß et al.
  • 1Institute of Environmental Physics, Heidelberg University, Germany
  • 2National Institute of Water and Atmospheric Research, Lauder, New Zealand
  • 3BK Scientific GmbH, Mainz, Germany
  • 4Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany

Abstract. The presence of reactive bromine in Polar Regions is a widespread phenomenon that plays an important role in the photochemistry of the Arctic and Antarctic lower troposphere, including the destruction of ozone, the disturbance of radical cycles, and the oxidation of gaseous elemental mercury. The chemical mechanisms leading to the heterogeneous release of gaseous bromine compounds from saline surfaces are in principle well understood. There are, however, substantial uncertainties about the contribution of different potential sources to the release of reactive bromine, such as sea ice, brine, aerosols and the snow surface, as well as about the seasonal and diurnal variation and the vertical distribution of reactive bromine. Here we use continuous long-term measurements of the vertical distribution of bromine monoxide (BrO) and aerosols at the two Antarctic sites Neumayer (NM) and Arrival Heights (AH), covering the periods of 2003–2021 and 2012–2021, respectively, to investigate how chemical and physical parameters affect the abundance of BrO. We find the strongest correlation between BrO and aerosol extinction (R = 0.56 for NM and R = 0.28 for AH during spring), suggesting that the heterogeneous release of Br2 from saline airborne particles (blowing snow and aerosols) is a dominant source for reactive bromine. Positive correlations between BrO and contact time of air masses both, with sea ice and the Antarctic ice sheet suggest that reactive bromine is not only emitted by the sea ice surface, but by the snowpack on the ice shelf and in the coastal regions of Antarctica. In addition, the open ocean appears to represent a source for reactive bromine during late summer and autumn when the sea ice extent is at its minimum. A source-receptor analysis based on back trajectories together with sea ice maps shows that main source regions for BrO at NM is the Weddell Sea and the Filchner-Ronne Ice Shelf, as well as coastal polynias where sea ice is newly formed. A strong morning peak in BrO frequently occuring during summer, and particular during autumn, suggests a night-time built up of Br2 by heterogeneous reaction of ozone on the saline snow pack in the vicinity of the measurement sites. We furthermore show that BrO can be sustained for several days while travelling across the Antarctic continent in the absence of any saline surfaces that could serve as a source for reactive bromine.

Udo Frieß et al.

Status: open (until 02 Dec 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-1074', Anonymous Referee #1, 13 Nov 2022 reply
  • RC2: 'Comment on egusphere-2022-1074', Anonymous Referee #2, 16 Nov 2022 reply

Udo Frieß et al.


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Short summary
Reactive bromine compounds, emitted by the sea ice during polar spring, play an important role in the atmospheric chemistry of the coastal regions of Antarctica. We investigate the sources and impacts of reactive bromine in detail using many years of measurements at two Antarctic sites, located at opposite sides of the Antarctic continent. Using a multitude of meteorological observations, we were able to identify the main triggers and source regions for reactive bromine in Antarctica.