Abstract
Abstract. 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 sea-salt aerosol, suggesting that either HCl is more efficiently transported to Concordia than sea-salt aerosol or re-emission 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 traveled 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.
Highlights
The understanding of the atmospheric budget of sea-salt aerosol at high latitudes is important for several reasons
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 when air masses arriving at Dome C had traveled a longer time over sea ice than over open ocean
Note that the cases for which such an examination of the sulfate depletion vs. the size can be conclusive with respect to error uncertainties in the estimated R values are very rare; only sampling corresponding to a high sea-salt load permits that. If confirmed, such a depletion of sulfate relative to sodium being larger on the smaller particles than on the larger particles reaching Concordia in winter suggests that the process related to sea ice involved in the production of sea-salt aerosol in winter produces more small particles than the more common open-ocean bubble bursting process
Summary
The understanding of the atmospheric budget of sea-salt aerosol at high latitudes is important for several reasons. In addition to the sea-salt fractionation discussed above, related to the presence of sea ice in winter, the more commonly observed release of chloride from sea-salt particles (Graedel and Keene, 1995) is taking place in summer in coastal Antarctica This is suggested by values of the chloride to sodium mass ratios (r) in bulk aerosol filters that are lower than the seawater reference value of 1.8 (Wagenbach et al, 1998; Jourdain and Legrand, 2002; Legrand et al, 2016). With a sampling interval of 6 days and a flow rate of 0.6 m3 h−1 (i.e., a total air sampled volume of ∼ 80 m3) and extraction of tubes with 5 mL of ultra pure Milli-Q water, the blank www.atmos-chem-phys.net/17/14039/2017/. Meteorological data from Global Data Assimilation Process (available at ftp://arlftp.arlhq.noaa.gov/pub/archives/gdas1) were used as input, and the model was run every 6 h in backward mode for three different altitudes (0, 250 and 500 m above ground level, a.g.l.)
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