Regional Characteristics of Atmospheric Sulfate Formation in East Antarctica Imprinted on ¹⁷O‐Excess Signature

Abstract

Abstract 17 O‐excess ( Δ 17 O = δ 17 O − 0.52 × δ 18 O) 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 Δ 17 O of non‐sea‐salt sulfate in aerosols ( Δ 17 O(SO 4 2− ) nss ) at Dome C and Dumont d'Urville, inland and coastal sites in East Antarctica, throughout the year 2011. Although Δ 17 O(SO 4 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 O 3 oxidation to OH and H 2 O 2 oxidation, significant intersite differences were observed in austral spring–summer and autumn. The cooccurrence of higher Δ 17 O(SO 4 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–December), combined with the first estimated Δ 17 O(MS – ) of ∼16‰, implies that MS – destruction produces sulfate with high Δ 17 O(SO 4 2− ) nss of ∼12‰. If contributing to the known postdepositional decrease of MS – in snow, this process should also cause a significant postdepositional increase in Δ 17 O(SO 4 2− ) nss over 1‰, that can reconcile the discrepancy between Δ 17 O(SO 4 2− ) nss in the atmosphere and ice. The higher Δ 17 O(SO 4 2− ) 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.