CN, CCN and particle size in Southern Ocean air at Cape Grim

Seasonal changes in atmospheric particle size distribution are derived by combining light-scatter particle size spectrometry with particle sizes derived from cloud condensation nucleus (CCN) concentration and sub-micrometre aerosol composition measurements. The distributions obtained are similar to others obtained in the clean marine boundary layer, using different techniques. They show a division of the aerosol “accumulation” mode into two branches, one largely associated with the CCN population and the other with the condensation nucleus (CN) population. A third, and larger, mode which is attributed to seasalt is also observed. Time series of CN and CCN concentrations at Cape Grim are presented and shown to have opposite trends over the past decade. The trend for CN is an increase of around 1.2% per year whilst CCN have decreased at about 3% per year. These trends are shown to be not seasonally uniform, with different dependences for CN and CCN. Finally, existing and possible future global CN and CCN measuring networks are discussed.