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

Abstract

[1] Aerosol sampling was conducted at Syowa Station, Antarctica (coastal station) in 2004 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 À9C, hydrohalite at ca. À23 C and other salts such as ikaite at ca. À5C and gypsum at ca. À22 C during winterspring. 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.

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

“…This lack of correlation holds true when April and May are included in the wintertime ice core Cl À /Na + average, rather than limiting the time frame to the JJAS time period. These observations of positive correlation between Cl so it is also a sea-salt tracer that should be relatively free of influence from secondary dust sources [Hara et al, 2012]. Thus, an increase in the bulk Mg 2+ /Na + ratio should also occur when there is Na + depletion due to mirabilite precipitation as has been observed in aerosol particle studies [Hara et al, 2012].…”

“…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. Abram et al, 2013;Hara et al, 2012;Jourdain et al, 2008;Spolaor et al, 2013;Wolff et al, 2003], and whether the potential sea ice source is dominated by windblown frost flowers or blowing snow is also uncertain [Abram et al, 2013;Yang et al, 2008].…”

“…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].…”

On measurements of aerosol-gas composition of the atmosphere during two expeditions in 2013 along the Northern Sea Route

“…The literature, available to us, provides no unambiguous data on the sources of K-and Ca-enriched substances in this region of the Arctic Ocean, located hundreds to thousands of kilometers away from the continent. Fractionation of sea salts from snow and ice is known to be one of the mechanisms by which aerosol particles are enriched, especially by sulfates and sodium (Domine et al, 2004;Hara et al, 2012). Ship emissions usually influence the arrival of pollutants to the Arctic atmosphere (Zhan et al, 2014); however, ships usually cruise southward of the regions considered here.…”