ALBERT

Description: Multiple year-round records of bulk and size-segregated composition of aerosol were obtained at the inland site of Concordia located at Dome C in East Antarctica. In parallel, sampling of acidic gases on denuder tubes was carried out to quantify the concentrations of HCl and HNO3 present in the gas phase. These time-series are used to examine aerosol present over central Antarctica in terms of chloride depletion relative to sodium with respect to freshly emitted sea-salt aerosol as well as depletion of sulfate relative to sodium with respect to the composition of seawater. A depletion of chloride relative to sodium is observed over most of the year, reaching a maximum of ~20 ng m-3 in spring when there are still large sea-salt amounts and acidic components start to recover. The role of acidic sulfur aerosol and nitric acid in replacing chloride from sea-salt particles is here discussed. HCl is found to be around twice more abundant than the amount of chloride lost by seasalt aerosol, suggesting that either HCl is more efficiently transported to Concordia than sea-salt aerosol or reemission from the snow pack over the Antarctic plateau represents an additional significant HCl source. The size-segregated composition of aerosol collected in winter (from 2006 to 2011) indicates a mean sulfate to sodium ratio of sea-salt aerosol present over central Antarctica of 0.16 ± 0.05, suggesting that, on average, the sea-ice and open ocean emissions equally contribute to sea-salt aerosol load of the inland Antarctic atmosphere. The temporal variability of the sulfate depletion relative to sodium was examined at the light of air mass backward trajectories, showing an overall decreasing trend of the ratio (i.e. a stronger sulfate depletion relative to sodium) when air masses arriving at Dome C had travelled a longer time over sea-ice than over open-ocean. The findings are shown to be useful to discuss sea-salt ice records extracted at deep drilling sites located inland Antarctica.

Description: We measured aerosol size distributions and conducted bulk as well as size segregated aerosol sampling during two summer campaigns in January 2015 and January 2016 at the continental Antarctic station Kohnen (Dronning Maud Land). Physical and chemical aerosol properties differ conspicuously during the episodic impact of an outstanding low pressure system in 2015 (LPS15) compared to the prevailing clear sky conditions (CSC): The about three days persisting LPS15, located in the eastern Weddell Sea, was associated with marine boundary layer (MBL) air mass intrusion, enhanced condensation particle concentrations (1400±700 cm-3 compared to 250±120 cm-3 during CSC; mean ± SD), occurrence of a new particle formation (NPF) event exhibiting a continuous growth of particle diameters (Dp) from 12 nm to 43 nm over 44 hours (growth rate 0.6 nm h-1), peaking methane sulfonate (MS-), non-sea salt sulfate (nss-SO42-) and Na+ concentrations (190 ng m-3 MS-, 137 ng m-3 nss-SO42-, and 53 ng m-3 Na+ compared to 24±15 ng m-3, 107±20 ng m-3 and 4.1±2.2 ng m-3, respectively, during CSC), and finally an increased MS-/nss-SO42- mass ratio ßMS of 0.4 up to 2.3 (0.21±0.1 during CSC) comparable to typical values found at coastal Antarctic sites. Throughout the observation period a larger part of MS- could be found in super micron aerosol compared to nss-SO42-, i.e. (10±2) % by mass compared to (3.2±2) %, respectively. On the whole, during CSC aged aerosol characterized by an usually mono-modal size distribution around Dp = 60 nm was observed. Although our observations indicate that sporadic impacts of coastal cyclones were associated with enhanced marine aerosol entry, at large aerosol deposition on-site during austral summer should be dominated by the typical steady CSC.

Description: Multiple year-round (2006-2015) records of the bulk and size-segregated composition of aerosol were obtained at 15 the inland site of Concordia located in East Antarctica. The well-marked maximum of non-sea-salt sulfate (nssSO4) in January (84 ± 25 ng m-3 against 4.4 ± 2.3 ng m-3 in July) is consistent with observations made at the coast (280 ± 78 ng m-3 in January against 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 (4.6 ± 2.4 ng m-3 in January). Instead, the MSA level at Concordia peaks in October (5.6 ± 1.9 ng m-3) and March (13.2 ± 6.1 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 against 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 below 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 DMS emissions from the southern ocean.