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

Abstract

<p><strong>Abstract.</strong> 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<span class="thinspace"></span>±<span class="thinspace"></span>28<span class="thinspace"></span>ng<span class="thinspace"></span>m⁻³ versus 4.4<span class="thinspace"></span>±<span class="thinspace"></span>2.3<span class="thinspace"></span>ng<span class="thinspace"></span>m⁻³ in July) is consistent with observations made at the coast (280<span class="thinspace"></span>±<span class="thinspace"></span>78<span class="thinspace"></span>ng<span class="thinspace"></span>m⁻³ in January versus 16<span class="thinspace"></span>±<span class="thinspace"></span>9<span class="thinspace"></span>ng<span class="thinspace"></span>m⁻³ in July at Dumont d'Urville, for instance). In contrast, the well-marked maximum of MSA at the coast in January (60<span class="thinspace"></span>±<span class="thinspace"></span>23<span class="thinspace"></span>ng<span class="thinspace"></span>m⁻³ at Dumont d'Urville) is not observed at Concordia (5.2<span class="thinspace"></span>±<span class="thinspace"></span>2.0<span class="thinspace"></span>ng<span class="thinspace"></span>m⁻³ in January). Instead, the MSA level at Concordia peaks in October (5.6<span class="thinspace"></span>±<span class="thinspace"></span>1.9<span class="thinspace"></span>ng<span class="thinspace"></span>m⁻³) and March (14.9<span class="thinspace"></span>±<span class="thinspace"></span>5.7<span class="thinspace"></span>ng<span class="thinspace"></span>m⁻³). As a result, a surprisingly low MSA-to-nssSO₄ ratio (R_MSA) is observed at Concordia in mid-summer (0.05<span class="thinspace"></span>±<span class="thinspace"></span>0.02 in January versus 0.25<span class="thinspace"></span>±<span class="thinspace"></span>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<span class="thinspace"></span>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<span class="thinspace"></span>ng<span class="thinspace"></span>m⁻³ in fall and winter and remains close to 5<span class="thinspace"></span>ng<span class="thinspace"></span>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.</p>