Year-round record of bulk and size-segregated aerosol composition in central Antarctica (Concordia site) – Part 2: Biogenic sulfur (sulfate and methanesulfonate) aerosol

Abstract

Abstract. Multiple year-round (2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015) records of the bulk and size-segregated composition of aerosol were obtained at the inland site of Concordia located in East Antarctica. The well-marked maximum of non-seasalt sulfate (nssSO 4 ) in January (100 ± 28 ng m −3 versus 4.4 ± 2.3 ng m −3 in July) is consistent with observations made at the coast (280 ± 78 ng m −3 in January versus 16 ± 9 ng m −3 in July at Dumont d'Urville, for instance). In contrast, the well-marked maximum of MSA at the coast in January (60 ± 23 ng m −3 at Dumont d'Urville) is not observed at Concordia (5.2 ± 2.0 ng m −3 in January). Instead, the MSA level at Concordia peaks in October (5.6 ± 1.9 ng m −3 ) and March (14.9 ± 5.7 ng m −3 ). As a result, a surprisingly low MSA-to-nssSO 4 ratio (R MSA ) is observed at Concordia in mid-summer (0.05 ± 0.02 in January versus 0.25 ± 0.09 in March). We find that the low value of R MSA in mid-summer at Concordia is mainly driven by a drop of MSA levels that takes place in submicron aerosol (0.3 µm diameter). The drop of MSA coincides with periods of high photochemical activity as indicated by high ozone levels, strongly suggesting the occurrence of an efficient chemical destruction of MSA over the Antarctic plateau in mid-summer. The relationship between MSA and nssSO 4 levels is examined separately for each season and indicates that concentration of non-biogenic sulfate over the Antarctic plateau does not exceed 1 ng m −3 in fall and winter and remains close to 5 ng m −3 in spring. This weak non-biogenic sulfate level is discussed in the light of radionuclides ( 210 Pb, 10 Be, and 7 Be) also measured on bulk aerosol samples collected at Concordia. The findings highlight the complexity in using MSA in deep ice cores extracted from inland Antarctica as a proxy of past dimethyl sulfide emissions from the Southern Ocean.

Year-round records of bulk and size-segregated aerosol composition in central Antarctica (Concordia site) – Part 1: Fractionation of sea-salt particles

“…9e) falling on a straight line through zero). This then supports the assumption that in winter the size distributions of biogenic sulfate and MSA are the same and that the nssSO 4 / MSA ratio is constant over the entire size distribution (see also Legrand et al, 2017). The similarity of the nssSO 4 / MSA ratio over the entire size distribution was already pointed out by Jourdain et al (2007).…”

“…However, at Concordia the separation of the non-sea-salt and sea-salt sulfate modes is less straightforward than at coastal sites. Confirming several previous Antarctic studies, Legrand et al (2017) concluded that non-sea-salt sulfate present in winter there mainly originates from marine biogenic emissions. As seen in Fig.…”

“…8) in late winter (September-October). The corresponding increase of the MSA to non-sea-salt ratio (from 6 to 13 %), already seen at the coast by Legrand and Pasteur (1998), is discussed in Legrand et al (2017) for Concordia in terms of source regions of biogenic sulfur aerosol over the course of the year. For the five lowest stages (smallest particle sizes) of the impactor, we find that the ratio of nssSO 4 / MSA is reasonably constant (red dots in Fig.…”

“…Initiated in 2006, the impactor samplings were done continuously over 3 years (2009)(2010)(2011). Impactor data are used in this paper for accurately quantifying the contribution of sea-ice-related emissions to the sea-salt budget over inland Antarctica and are also essential for discussing biogenic sulfur aerosol as done in the accompanying paper from Legrand et al (2017). Gaseous acidic species were also sampled year-round since 2009 at Concordia using coated denuder tubes.…”

High summertime aerosol organic functional group concentrations from marine and seabird sources at Ross Island, Antarctica, during AWARE

“…This low winter and high summer seasonal difference has also been observed at coastal Antarctic sites, but the average concentrations were typically higher, with summertime concentrations ranging from 300 to 2000 cm −3 and wintertime concentrations from 10 to 200 cm −3 (Kim et al, 2017;Gras, 1993). Consistent with this seasonal difference in particle number concentrations, most summertime non-sea salt sulfate mass concentrations were at least 5 times higher than winter concentrations (Jourdain and Legrand, 2002;Weller and Wagenbach, 2007;Udisti et al, 2012;Legrand et al, 2017a;Asmi et al, 2018), likely because of the contributions from biogenic DMS emissions from the surrounding Southern Ocean. However, most sea salt aerosols had wintertime maximum concentrations with more than 2 times more Na + mass concentrations in winter than summer (Parungo et al, 1981;Wagenbach et al, 1998;Jourdain and Legrand, 2002;Weller and Wagenbach, 2007;Jourdain et al, 2008;Udisti et al, 2012;Legrand et al, 2017a, b;Asmi et al, 2018).…”