A 3D model study of the global sulphur 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 dimethylsulphide (DMS), sulphur dioxide (SO(2)), and non-sea-salt (nss-) sulphates (SO(4)(2-))] 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 the present-day (c. 1985) atmosphere. Here, in order to assess the relative contributions of biogenic and man-made sources, we compare distributions calculated for the preindustrial atmosphere with the present-day results. The calculations show a large increase in the concentrations of sulphur dioxide and nss-sulphates since preindustrial times, amounting to a factor of 2-3 on global average, and reaching more than two orders of magnitude at the surface in some parts of the Northern Hemisphere. 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 deposition is found to have reached a factor of 30.