Tethered balloon-borne aerosol measurements: seasonal and vertical variations of aerosol constituents over Syowa Station, Antarctica

Abstract

Abstract. Tethered balloon-borne aerosol measurements were conducted at Syowa Station, Antarctica during the 46th Japanese Antarctic expedition (2005–2006). Direct aerosol sampling was operated from near the surface to the lower free troposphere (approximately 2500 m) using a balloon-borne aerosol impactor. Individual aerosol particles were analyzed using a scanning electron microscope equipped with an energy dispersive X-ray spectrometer. Seasonal and vertical features of aerosol constituents and their mixing states were investigated. Results show that sulfate particles were dominant in the boundary layer and lower free troposphere in the summer, whereas sea-salt particles were dominant during winter–spring. Minerals, MgSO4, and sulfate containing K were identified as minor aerosol constituents in both boundary layer and free troposphere over Syowa Station. Although sea-salt particles were dominant during winter–spring, the relative abundance of sulfate particles increased in the boundary layer when air masses fell from the free troposphere over the Antarctic coast and continent. Sea-salt particles were modified considerably through heterogeneous reactions with SO42−, CH3SO3−, and their precursors during the summer, and were modified slightly through heterogeneous reactions with NO3− and its precursors. During winter–spring, sea-salt modification was insignificant, particularly in the cases of high relative abundance of sea-salt particles and higher number concentrations. In August, NO3− and its precursors contributed greatly to sea-salt modification over Syowa Station. Because of the occurrence of sea-salt fractionation on sea-ice, Mg-rich sea-salt particles were identified during April–November. In contrast, Mg-free sea-salt particles and slightly Mg-rich sea-salt particles co-existed in the lower troposphere during summer. Thereby, Mg separation can proceed by sea-salt fractionation during summer in Antarctic regions.