Reduced perchlorate in West Antarctica snow during stratospheric ozone hole

Snowpit samples collected at the West Antarctic Ice Sheet (WAIS) Divide location in January 2013 were analysed to investigate the levels and variations of perchlorate concentrations in Antarctic snow. During 2008–12, the perchlorate concentration in WAIS Divide snow ranged between 6–180 ng l–1 and followed a seasonal cycle. The highest concentrations appeared in the autumn, and the lowest in winter and spring. No apparent correlation was observed between perchlorate and nitrate or chloride concentrations in snow. Since perchlorate is believed to form in the atmosphere when chlorine species are oxidized in reactions involving ozone, perchlorate concentrations were hypothesized to be high during the spring, based on the assumption that stratospheric ozone depletion enhances tropospheric perchlorate production. The data show that perchlorate concentrations in snow were sharply reduced during stratospheric ozone depletion events; the evidence, therefore, does not support the hypothesis. Instead, the results suggest a stratospheric origin of perchlorate in Antarctic snow.