Regional Characteristics Of Atmospheric Sulfate Formation In East Antarctica Imprinted On O-17-Excess Signature

O-17-excess (Delta O-17 = delta O-17 - 0.52 x delta O-18) 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 Delta O-17 of non-sea-salt sulfate in aerosols (Delta O-17(SO42-)(nss)) at Dome C and Dumont d'Urville, inland and coastal sites in East Antarctica, throughout the year 2011. Although Delta O-17(SO42-)(nss) at both sites showed consistent seasonality with summer minima (similar to 1.0 parts per thousand) and winter maxima (similar to 2.5 parts per thousand) owing to sunlight-driven changes in the relative importance of O-3 oxidation to OH and H2O2 oxidation, significant intersite differences were observed in austral spring-summer and autumn. The cooccurrence of higher Delta O-17(SO42-)(nss) at inland (2.0 parts per thousand +/- 0.1 parts per thousand) than the coastal site (1.2 parts per thousand +/- 0.1 parts per thousand) and chemical destruction of methanesulfonate (MS-) in aerosols at inland during spring-summer (October-December), combined with the first estimated Delta O-17(MS-) of similar to 16 parts per thousand, implies that MS- destruction produces sulfate with high Delta O-17(SO42-)(nss) of similar to 12 parts per thousand. If contributing to the known postdepositional decrease of MS- in snow, this process should also cause a significant postdepositional increase in Delta O-17(SO42-)(nss) over 1 parts per thousand, that can reconcile the discrepancy between Delta O-17(SO42-)(nss) in the atmosphere and ice. The higher Delta O-17(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.