![]() The release of Br 2 from the surface snowpack ( Pratt et al., 2013) following polar sunrise leads to boundary layer ozone depletion events (ODEs) ( Barrie et al., 1988 Simpson et al., 2007b), as well as mercury deposition events ( Schroeder et al., 1998 Steffen et al., 2008). Snowpack-driven halogen chemistry has a profound impact on atmospheric composition in the polar regions ( Simpson et al., 2007b Abbatt et al., 2012). The ability of MYI regions to participate in springtime atmospheric halogen chemistry should be considered in regional modeling of halogen activation and interpretation of satellite-based tropospheric bromine monoxide column measurements. ![]() Calculated enrichment factors for bromide and chloride, relative to sodium, in the MYI snow samples suggests that MYI regions, in addition to FYI regions, have the potential to play an active role in Arctic boundary layer bromine and chlorine chemistry. Measurements at various snow depths indicate that the deposition of sea salt aerosols and halogen-containing trace gases to the snowpack surface played a larger role in determining surface snow halide concentrations compared to upward brine migration from sea ice. In contrast, surface snow in MYI regions was more often depleted in bromide, indicating it served as a source of bromine-containing trace gases to the atmosphere prior to sampling. Surface snow in FYI regions was typically enriched in bromide and chloride compared to seawater, indicating snowpack deposition of bromine and chlorine-containing trace gases and an ability of the snowpack to participate further in bromine and chlorine activation processes. Regardless of sea ice region, these surface snow samples generally featured lower salinities, compared to coastal snow. To address this gap, we measured concentrations of chloride, bromide, and sodium in snow samples collected during polar spring above remote multi-year sea ice (MYI) and first-year sea ice (FYI) north of Greenland and Alaska, as well as in the central Arctic, and compared these measurements to a larger dataset collected in the Alaskan coastal Arctic by Krnavek et al. However, measurements of snowpack halide concentrations remain sparse, particularly in the high Arctic, limiting our understanding of and ability to parameterize snowpack participation in tropospheric halogen chemistry. As sources of reactive halogens, snowpacks in sea ice regions control the oxidative capacity of the Arctic atmosphere.
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