It is well accepted that the climate impact of large explosive volcanic eruptions results from reduction of solar radiation following atmospheric conversion of magmatic SO emissions into HSO aerosols. Thus, understanding the fate of SO in the eruption plume is crucial for better assessing volcanic forcing of climate. Here we focus on the potential of tephra to interact with and remove SO gas from the eruptive plume. Scavenging of SO by tephra is generally assumed to be driven by in-plume, low-temperature reactions between HSO condensates and tephra particles. However, the importance of SO gas-tephra interaction above the dew point temperature of HSO (190-200°C) has never been constrained. Here we report the results of an experimental study where silicate glasses with representative volcanic compositions were exposed to SO in the temperature range 25-800°C. We show that above 600°C, the uptake of SO on glass exhibits optimal efficiency and emplaces surficial CaSO deposits. This reaction is sustained via Ca diffusion from the bulk to the surface of the glass particles. At 800°C, the diffusion coefficient for Ca in the glasses was in the range 10-10cms. We suggest that high temperature SO scavenging by glass-rich tephra proceeds by the same Ca diffusion-driven mechanism. Using a simple mathematical model, we estimated SO scavenging efficiencies at 800°C varying from
Bibliographical noteP.A. was funded by a Natural Environment Research Council Blue Skies Ph.D. studentship grant. P.D. acknowledges support from the University of York (Vice-Chancellor University Anniversary Lectureship) and the Belgian Fonds de la Recherche Scientifique (MIS-Ulysse F.6001.11). We thank two anonymous reviewers and the editor for helpful and constructive comments. We have
greatly benefited from discussions with L. Mastin, B. Scheu and K. Wohletz, and we are grateful to N. Carslaw for careful comments on a previous version of the manuscript. We thank R. Sutton and D. Hay for technical assistance, and M. Ward and A. Walton.
Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.gca.2013.02.018 at the Leeds EPSRC Nanoscience and Nanotechnology Facility (LENNF) for SEM and TEM access.