Abstract
Abstract. Multiple year-round (2006–2015) 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-sea-salt sulfate (nssSO4) 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-nssSO4 ratio (RMSA) 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 RMSA 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 nssSO4 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 (210Pb, 10Be, and 7Be) 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.
Highlights
The coupling between climate and atmospheric aerosol involves complex processes that are not yet fully elucidated
Preunkert et al (2008) proposed that the weakening of marine advection in December–January compared to March associated with an ongoing oxidation of SO2 into sulfate in the buffer layer, where the heterogeneous chemistry of dimethyl sulfoxide (DMSO) is very limited, would account for the drop of ratio of MSA to non-sea-salt sulfate (RMSA) observed in mid-summer at Concordia
We find that the low value of RMSA in mid-summer at Concordia is due to a drop of MSA concentrations that occurs in the small particles (0.3 μm diameter) of sulfuric acid aerosol
Summary
The coupling between climate and atmospheric aerosol involves complex processes that are not yet fully elucidated. The calculations of the non-sea-salt sulfate present in Antarctica are more difficult than at any other place in the world due to a depletion of sulfate relative to sodium caused by precipitation of mirabilite (Na2SO4·10 H2O) during freezing of seawater in winter (Wagenbach et al, 1998) To explain these phenomena, atmospheric records of both DMS and sulfur aerosol are needed, in the vicinity of sites where Antarctic ice cores are extracted. While detailed long-term records of sulfur-derived aerosol species (sometimes completed by DMS and DMSO measurements) are available for the coastal sites of Neumayer (NM) and Dumont d’Urville (DDU) (Wagenbach, 1996; Minikin et al, 1998; Jourdain and Legrand, 2001), only very scattered atmospheric observations of both MSA and sulfate have been obtained so far at central Antarctic positions. The slight difference between the two data sets is likely due to differences (up to a few days) in the sampling time intervals
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