The Role of Blowing Snow in the Activation of Bromine over First-Year Antarctic Sea Ice

Abstract:

It is well known that during the polar springtime, halide sea salt ions, in particular Br^-, are through a series of heterogeneous reactions photochemically activated into reactive halogen species, such as Br and BrO, that breakdown polar tropospheric ozone. This research investigated the role of blowing snow in transporting salts from the sea ice/snow surface into reactive bromine species in the air. For two different locations over first-year ice in the Ross Sea, Antarctica, collection baskets captured blowing snow at four different heights on October 25, following a blowing snow event the day before. In addition, sea ice cores and surface snow samples were collected throughout the month long campaign. Cl^-/Br^- ratios were constant in sea ice and surface snow, and only in lofted snow did bromide become depleted relative to chloride. This suggests that replenishment of bromide in the snowpack occurs faster than bromine activation in mid-strength wind conditions (approximately 10 m/s). Sulfate concentrations were stable through the bottom half of sea ice cores, but were quite variable in the upper half and in surface snow. Lofted snow was greatly depleted in sulfate, likely as a result of mirabilite precipitation in brine prior to brine uptake in the snow and subsequent lofting. Nitrate was found in greater quantities for upper level baskets and in some surface snow samples, consistent with active cycling through atmospheric chemical reactions.