Terrestrial sources and distribution of atmospheric sulphur

Abstract

The general circulation model ECHAM has been coupled to a chemistry and sulphur cycle model to study the impact of terrestrial, i.e. mostly anthropogenic sulphur dioxide (SO 2 ), sources on global distributions of sulphur species in the atmosphere. We briefly address currently available source inventories. It appears that global estimates of natural emissions are associated with uncertainties up to a factor of 2, while anthropogenic emissions have uncertainty ranges of about +/− 30 per cent. Further, some recent improvements in the model descriptions of multiphase chemistry and deposition processes are presented. Dry deposition is modelled consistently with meteorological processes and surface properties. The results indicate that surface removal of SO 2 is less efficient than previously assumed, and that the SO 2 lifetime is thus longer. Coupling of the photochemistry and sulphur chemistry schemes in the model improves the treatment of multiphase processes such as oxidant (hydrogen peroxide) supply in aqueous phase SO 2 oxidation. The results suggest that SO 2 oxidation by ozone (O 3 ) in the aqueous phase is more important than indicated in earlier work. However, it appears that we still overestimate atmospheric SO 2 concentrations near the surface in the relatively polluted Northern Hemisphere. On the other hand, we somewhat underestimate sulphate levels in these regions, which suggests that additional heterogeneous reaction mechanisms, e.g. on aerosols, enhance SO 2 oxidation.