Regional characteristics of atmospheric sulfate formation in East Antarctica imprinted on 17O-excess signature

¹⁷O-excess (Δ¹⁷O = δ¹⁷O − 0.52 × δ¹⁸O) of sulfate trapped in Antarctic ice cores has been proposed as a potential tool for assessing past oxidant chemistry, while insufficient understanding of atmospheric sulfate formation around Antarctica hampers its interpretation. To probe influences of regional specific chemistry, we compared year-round observations of Δ¹⁷O of non-sea-salt sulfate in aerosols (Δ¹⁷O(SO₄²⁻)_nss) at Dome C and Dumont d’Urville, inland and coastal sites in East Antarctica, throughout the year 2011. Although Δ¹⁷O(SO₄^2–)_nss at both sites showed consistent seasonality with summer minima (~1.0 ‰) and winter maxima (~2.5 ‰) owing to sunlight-driven changes in the relative importance of O₃-oxidation to OH- and H₂O₂-oxidation, significant inter-site differences were observed in austral spring–summer and autumn. The co-occurrence of higher Δ¹⁷O(SO₄^2–)_nss at inland (2.0 ± 0.1 ‰) than the coastal site (1.2 ± 0.1 ‰) and chemical destruction of methanesulfonate (MS^–) in aerosols at inland during spring–summer (October to December), combined with the first estimated Δ¹⁷O(MS^–) of ~16 ‰, implies that MS^– destruction produces sulfate with high Δ¹⁷O(SO₄^2–)_nss of ~12 ‰. If contributing to the known post-depositional decrease of MS^– in snow, this process should also cause a significant post-depositional increase in Δ¹⁷O(SO₄^2–)_nss over 1 ‰, that can reconcile the discrepancy between Δ¹⁷O(SO₄^2–)_nss in the atmosphere and ice.