Active molecular iodine photochemistry in the Arctic

Significance We report here the first measurements of molecular iodine (I 2 ) in the Arctic atmosphere and iodide (I − ) in the Arctic snowpack. Although iodine chemistry is expected to have significant impacts on Arctic atmospheric ozone destruction and new particle production, sparse measurements of atmospheric iodine have limited our ability to examine sources and impacts. We show, through sunlit and artificially irradiated snowpack experiments, that the coastal Arctic snowpack is capable of photochemical production and release of I 2 to the boundary layer. This is supported by enrichment of the snowpack in I − compared with that expected from sea spray influence alone. Through photochemical modeling, we demonstrate that, at observed I 2 levels, snowpack production can have a significant impact on Arctic atmospheric chemistry.