Improving our understanding of atmospheric mercury and bromine over the Southern Ocean and Antarctic sea-ice region

Of the reactive halogens, those containing reactive bromine are of particular scientific interest as they play a key role in the chemistry and oxidising capacity of the polar troposphere (Simpson et al., 2015). In early spring, bromine molecules (as Br2) are rapidly released from the sea ice via heterogenous reactions on sea salt surfaces, both in the sea ice itself and on blowing snow (Simpson et al., 2015; Huang et al., 2018; Peterson et al., 2019). This rapid bromine release can initiate a chemical reaction, known as a bromine explosion, which oxidises gaseous elemental mercury, resulting in the subsequent deposition of toxic water-soluble mercury into the polar environment (Prados-Roman et al., 2018). However, reactive bromine and mercury measurements in coastal Antarctica are mostly limited to a handful of short-term campaigns, limiting current understanding of the sources and drivers controlling variability. To further investigate these processes, observations of bromine monoxide (BrO) were acquired via Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) during six resupply voyages of the Aurora Australis to the coast of east Antarctica during the CAMMPCAN 2017-19 campaign, along with in situ measurements of gaseous elemental mercury (Hg0) and reactive mercury (RM). These were analysed along with meteorological measurements from the Aurora Australis, satellite observations of sea ice cover and modelled air mass back trajectories.