A Study of Organo-Halogens During Polar Winter

The release of bromine from snow and sea ice surfaces has mainly been attributed to the reaction of hypobromous acid with bromide at acidic conditions to form Br2. Little attention has been given to the role of volatile halogenated organic compounds (organo-halogens) in the formation of reactive halogen species in the atmosphere during bromine explosion events. The load of organo-halogens was studied during a winter expedition to the Weddell Sea in June to August 2013. These compounds are emitted from the different compartments of the cryosphere to the atmosphere where they are photolysed to BrO and IO, which are involved in the degradation of ozone. We will present results that show the importance of organo-halogens formed during polar winter. In newly formed ice, in contrast to summer sea ice, the concentration of organo-bromine was found at levels as high as nM. These high concentrations were reflected both in frost flowers and in the sea-snow interface. Moreover, air measurements revealed high loads of organo-bromine over the sea ice. The situation was similar for iodinated compounds. Interestingly, the precursers of IO, mainly diiodomethane, could be measured in sea ice and snow, most probably due to the low light levels.