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

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 predominant in the boundary layer and lower free troposphere in summer, whereas sea-salt particles were predominant during winter through 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 predominant during winter through 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 SO₄^2− CH₃SO₃^− and their precursors during summer, and were modified slightly through heterogeneous reactions with NO₃^− and its precursors. During winter through 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 the months of April through November. In contrast, Mg-free sea-salt particles and slightly Mg-rich sea-salt particles coexisted in the lower troposphere during summer. Thereby, Mg separation can proceed by sea-salt fractionation during summer in Antarctic regions

Seasonally resolved ice core records from West Antarctica indicate a sea ice source of sea‐salt aerosol and a biomass burning source of ammonium

“…The summertime ExCl À chloride may be derived from volatile chloride that is displaced from sea-salt aerosols in the atmosphere during summer. This process has been observed to be more extensive during summer than winter due to the presence of acids and higher temperatures [Hara et al, 2013;Jourdain and Legrand, 2002], so volatile chloride is not expected to contribute significantly to ExCl À during winter. It is not expected that significant amounts of chloride would mix between summer and winter layers via diffusion or wind pumping in the snowpack given the high snow accumulation rates.…”

“…The sea ice source for aerosol with depleted Na + only occurs in winter, because the salt water brine above the sea ice must reach temperatures below À8°C for mirabilite precipitation to occur [Marion et al, 1999]. Fractionated sea-salt aerosol particles depleted in SO 4 2À [Abram et al, 2013 and references therein;Wagenbach et al, 1998a] and Na + [Hara et al, 2012[Hara et al, , 2013 have been observed to be abundant during Antarctic winter and attributed to mirabilite precipitation and a sea ice source. The prevalence of the sea ice source of sea-salt aerosol versus the open ocean source remains the subject of ongoing research, however [e.g.…”

“…Ammonium (NH 4 + ) previously has been observed to co-occur with biogenic sulfur in the summertime [Legrand et al, 1998;Savoie et al, 1992], and nitrate (NO 3 À ) has shown a late-polar stratospheric clouds (PSCs) and snowpack remission during late winter/ spring and summer, respectively [Jones et al, 2011;Savarino et al, 2007;Wagenbach et al, 1998b;Weller et al, 2002]; however, debate still exists regarding the origin of the summertime peak in high-accumulation coastal locations and the relative magnitude of tropospheric versus stratospheric sources [Frey et al, 2009;Lee et al, 2014]. The chloride to sodium ratio (Cl À /Na + ) of aerosols at coastal Antarctic sites has shown a minimum in summer attributed to displacement of volatile chlorine (primarily hydrochloric acid, HCl) from sea-salt aerosols and a maximum in winter that is interpreted as fractionation from mirabilite (Na 2 SO 4 ·10H 2 O) mineral precipitation in sea ice brine prior to aerosol formation [Hara et al, 2004[Hara et al, , 2012[Hara et al, , 2013Jourdain and Legrand, 2002]. Studies of sea-salt aerosols at high-elevation inland sites also have found evidence of fractionation attributed to mirabilite precipitation that peaks in late winter [Hara et al, 2004;Jourdain et al, 2008].…”

Horizontal distributions of aerosol constituents and their mixing states in Antarctica during the JASE traverse

“…For sample analysis, single particle analysis takes longer than bulk analysis. Therefore, few previous investigations have used single particle analysis (Parungo et al, 1979;Yamato et al, 1987a, b;Artaxo et al, 1992;Mouri et al, 1999;Hara et al, 1995Hara et al, , 2005Hara et al, , 2013.…”

Spatial distributions of soluble salts in surface snow of East Antarctica

“…soot and organics) (Kerminen et al, 2000;Legrand et al, 2001;Jourdain et al, 2008;Preunkert et al, 2008;Udisti et al, 2012). To better understand the origins of these constituents and the chemical reactions that occur on aerosol particles, single-particle analyses of Antarctic aerosols have been done (Parungo et al, 1979;Artaxo et al, 1992;Hara et al, 1995Hara et al, , 2005Hara et al, , 2013Mouri et al, 1999). More recently, Hara et al (2014) showed that most sea-salt particles in the continental region near the coast were modified with acidic sulphur species such as H 2 SO 4 and CH 3 SO 3 H. In contrast, other, non-sulphurous acidic species (likely HNO 3 ) contributed markedly to sea-salt modification in inland areas during the traverse.…”