Reactive bromine in the low troposphere of Antarctica. Estimations at two research sites

Abstract. For decades, reactive halogen species (RHS) have been subject of detailed scientific research due to their influence on the oxidizing capacity of the atmosphere and on the climate. From the RHS, those containing bromine are of particular interest in the polar troposphere as a result of their link to ozone depletion events (ODEs) and to the perturbation of the cycle of e.g. the toxic mercury. Given its remoteness and related limited accessibility compared to the Arctic region, the RHS in the Antarctic troposphere are still poorly characterized. This work presents ground-based observations of tropospheric BrO from two different Antarctic locations: Marambio (64º13′ S, 56º37′ W) and Belgrano II (77º52′ S, 34º37′ W) during the sunlit period of 2015. By means of MAX-DOAS (Multi-axis Differential Optical Absorption Spectroscopy) measurements of BrO performed from the two research sites, the seasonal variation of this reactive trace gas is described along with its vertical and geographical distribution in the Antarctic environment. Results show an overall vertical profile of BrO mixing ratio decreasing with altitude, with a median value of 1.6 pmol mol−1 in the lowest layers of the troposphere and undetectable values above 2 km at both sites. Additionally, observations show that the polar sunrise triggers a heterogeneous increase of bromine content in the Antarctic troposphere yielding a maximum BrO at Marambio (26 pmol mol−1), amounting threefold the values observed at Belgrano at dawn. Data presented herein are combined with previous studies and ancillary data to update and expand our knowledge of the geographical and vertical distribution of BrO in the Antarctic troposphere, revealing Marambio as one of the locations with highest BrO reported so far in Antarctica. Furthermore, the observations gathered during 2015 serve as a proxy to investigate the budget of reactive bromine (BrOx = Br + BrO) and the bromine-mediated ozone loss rate in the Antarctic troposphere.