Can SO2 photoexcitation explain S-MIF in present-day stratospheric sulfate?

Abstract

Mass-independent sulfur isotopic anomalies have been found in ice core sulfate associated with volcanic events. It has been suggest that this isotope anomaly is a reliable metric for events with a Volcanic Explosivity Index of 3 or above, with obvious utility in reconstructing the history of volcanic events able to impact climate. However a physicochemical model is necessary to extract information from the record and the details of the chemical mechanism have been lacking. Using UV absorption cross sections of 32SO2, 33SO2, 34SO2 and 36SO2 from 250 to 320 nm , calculated isotopic fractionation factors for SO2 photoexcitation at altitudes of 10 to 60 km predict mass-independent distributions that are consistent with those found in stratospheric sulfate preserved in Antarctic snow and ice cores.