Abstract. Triple oxygen isotopic compositions (Δ¹⁷O = δ¹⁷O−0.52 × δ¹⁸O) of atmospheric sulfate (SO₄²⁻) and nitrate (NO₃⁻) in the atmosphere reflect the relative contribution of oxidation pathways involved in their formation processes, which potentially provides information to reveal missing reactions in atmospheric chemistry models. However, there remain many theoretical assumptions for the controlling factors of Δ¹⁷O(SO₄²⁻) and Δ¹⁷O(NO₃⁻) values in those model estimations. To test one of those assumption that Δ¹⁷O values of ozone (O₃) have a flat value and do not influence the seasonality of Δ¹⁷O(SO₄²⁻) and Δ¹⁷O(NO₃⁻) values, we performed the first simultaneous measurement of Δ¹⁷O values of atmospheric sulfate, nitrate, and ozone collected at Dumont d'Urville (DDU) Station (66°40′S, 140°01′E) throughout 2011. Δ¹⁷O values of sulfate and nitrate exhibited seasonal variation characterized by minima in the austral summer and maxima in winter, within the ranges of 0.9–3.4 and 23.0–41.9‰, respectively. In contrast, Δ¹⁷O values of ozone showed no significant seasonal variation, with values of 26±1‰ throughout the year. These contrasting seasonal trends suggest that seasonality in Δ¹⁷O(SO₄²⁻) and Δ¹⁷O(NO₃⁻) values is not the result of changes in Δ¹⁷O(O₃), but of the changes in oxidation chemistry. The trends with summer minima and winter maxima for Δ¹⁷O(SO₄²⁻) and Δ¹⁷O(NO₃⁻) values are caused by sunlight-driven changes in the relative contribution of O₃ oxidation to the oxidation by HO_x, RO_x, and H₂O₂. In addition to that general trend, by comparing Δ¹⁷O(SO₄²⁻) and Δ¹⁷O(NO₃⁻) values to ozone mixing ratios, we found that Δ¹⁷O(SO₄²⁻) values observed in spring (September to November) were lower than in fall (March to May), while there was no significant spring and fall difference in Δ¹⁷O(NO₃⁻) values. The relatively lower sensitivity of Δ¹⁷O(SO₄²⁻) values to the ozone mixing ratio in spring compared to fall is possibly explained by (i) the increased contribution of SO₂ oxidations by OH and H₂O₂ caused by NO_x emission from snowpack and/or (ii) SO₂ oxidation by hypohalous acids (HOX = HOCl+HOBr) in the aqueous phase.

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 ∼ 20ngm⁻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.