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

Abstract

Aerosol sampling was conducted at Syowa Station, Antarctica (coastal station) in 2004–2006. SO 4 2− depletion by mirabilite precipitation was identified from April through November. The fractionated sea‐salt particles were distributed in ultrafine– coarse modes. Molar ratios of Mg 2+ /Na + and K + /Na + were higher than in bulk seawater ratio during winter–spring. The Mg 2+ /Na + ratio in aerosols greatly exceeded the upper limit in the case only with mirabilite precipitation. The temperature dependence of Mg 2+ /Na + ratio strongly suggested that higher ratios of Mg 2+ /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.