Seasonal variation of fractionated sea-salt particles on the Antarctic coast



[1] Aerosol sampling was conducted at Syowa Station, Antarctica (coastal station) in 2004–2006. SO42−depletion by mirabilite precipitation was identified from April through November. The fractionated sea-salt particles were distributed in ultrafine– coarse modes. Molar ratios of Mg2+/Na+ and K+/Na+ were higher than in bulk seawater ratio during winter–spring. The Mg2+/Na+ ratio in aerosols greatly exceeded the upper limit in the case only with mirabilite precipitation. The temperature dependence of Mg2+/Na+ ratio strongly suggested that higher ratios of Mg2+/Na+ and K+/Na+were associated with sea-salt fractionation by precipitation of mirabilite at −9°C, hydrohalite at ca. −23°C and other salts such as ikaite at ca. −5°C and gypsum at ca. −22°C during winter–spring. Mg-salts with lower deliquescence relative humidity can be enriched gradually in the fractionated sea-salt particles. Results suggests that sea-salt fractionation can alter aerosol hygroscopicity and atmospheric chemistry in polar regions.