A 3D MODEL STUDY OF THE GLOBAL SULFUR CYCLE - CONTRIBUTIONS OF ANTHROPOGENIC AND BIOGENIC SOURCES

The impact of anthropogenic emissions on the global distributions and budgets of the main atmospheric sulphur species [namely dimethylsulphi de (DMS), sulphur dioxide (SO2), and non-sea-salt (nss-) sulphates (SO 42-)] is investigated using the IMAGES three-dimensional tropospheric chemistry-transport model. A previous study showed a broad consistency between modelled and observed concentrations of sulphur species for t he present-day (c. 1985) atmosphere. Here, in order to assess the rela tive contributions of biogenic and man-made sources, we compare distri butions calculated for the preindustrial atmosphere with the present-d ay results. The calculations show a large increase in the concentratio ns of sulphur dioxide and nss-sulphates since preindustrial times, amo unting to a factor of 2-3 on global average, and reaching more than tw o orders of magnitude at the surface in some parts of the Northern Hem isphere. Biogenic species such as DMS are also shown to be influenced by industrialization through changes in the oxidizing capacity of the atmosphere. Over the most polluted areas, the increase in sulphates de position is found to have reached a factor of 30.