Seasonal relationship between cloud condensation nuclei and aerosol methanesulphonate in marine air

Abstract

CHARLSON,et al.1 have suggested that cloud-droplet concentrations in remote marine regions might be indirectly controlled by dimethylsulphide (DMS) emissions from marine phytoplankton. Attempts to test the hypothesis that variations in DMS emissions lead to corresponding variations in marine aerosol composition and hence concentrations of cloud condensation nuclei (CCN) have so far proved inconclusive, primarily because of the inherent variability of the atmospheric species involved over the timescales typical of individual field measurements2. Here we present nine years of data from Cape Grim (41°S) which show that there is a significant seasonal relationship between cloud condensation nuclei and methanesulphonate, an easily sampled oxidation product of DMS, but the relationship is nonlinear. These results confirm that DMS emissions strongly influence CCN concentrations, but we note that at low concentrations of methanesulphonate, there are indications that there may be another source of CCN, apart from DMS. © 1991 Nature Publishing Group.