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(SO₄²⁻)_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 intersite differences were observed in austral spring–summer and autumn. The cooccurrence of higher Δ¹⁷O(SO₄²⁻)_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–December), combined with the first estimated Δ¹⁷O(MS^–) of ∼16‰, implies that MS^– destruction produces sulfate with high Δ¹⁷O(SO₄²⁻)_nss of ∼12‰. If contributing to the known postdepositional decrease of MS^– in snow, this process should also cause a significant postdepositional increase in Δ¹⁷O(SO₄²⁻)_nss over 1‰, that can reconcile the discrepancy between Δ¹⁷O(SO₄²⁻)_nss in the atmosphere and ice. The higher Δ¹⁷O(SO₄²⁻)_nss at the coastal site than inland during autumn (March–May) may be associated with oxidation process involving reactive bromine and/or sea-salt particles around the coastal region.