ATMOSPHERIC SULFUR AND CLOUD CONDENSATION NUCLEI IN MARINE AIR IN THESOUTHERN-HEMISPHERE

Measurements of atmospheric sulphur species made in Southern Ocean air , at the Cape Grim Baseline Air Pollution Station, are reviewed in an attempt to discern the role played by oceanic emissions of dimethyl su lphide (DMS) as a source of cloud condensation nuclei (CCN). Consisten t with conclusions reached by others, our data indicate that the conne ction between DMS concentration and CCN concentration is neither simpl e nor direct, being mediated through a range of chemical pathways and intermediate species that are subject to considerable variability over timescales ranging from minutes to months. Physical and meteorologica l processes are no less important than chemical processes as sources o f complexity in the DMS --> CCN transformation process. Moreover, the considerable uncertainty that currently exists about both the number o f chemical pathways involved in DMS oxidation, and the kinetic coeffic ients associated with the proposed pathways, make quantitative modelli ng studies problematic. Nevertheless, synthesis of a large body of dat a available from Cape Grim and other Southern Ocean sites does permit some refinement of our understanding of the DMS;CCN connection. Here, these data are employed to illustrate the current state of knowledge a bout the connections between DMS, CCN and cloud properties at Cape Gri m, and to highlight the many complexities that underlie these connecti ons.