| Summary: | The research conducted and presented herein concentrates primarily on the life cycle of a cloud condensation nucleus CCN. The primary motivation of the work is the importance of CCN in the global aerosol-cloud-climate system, and focus is placed on the production of CCN, their behaviour in the atmosphere and their properties with respect to CCN activation, as well as the removal pathways. The work presented in this thesis covers measurements performed at 16 locations around the world. The results further corroborated the notion that atmospheric new particle formation NPF is an important and widespread source of CCN in the atmosphere. The number of newly formed CCN from NPF depends on many factors, including, but not limited to, biogenic and anthropogenic emissions, frequency of NPF events, nucleation and growth rates and pre-existing CCN concentrations; method of calculation also affects the estimate of NPF contribution to CCN budgets. Highest relative increase in CCN as a result of NPF was observed at a clean remote location in Northern Finland, where in the summer the number concentration of particles above 50 nm in diameter N50 can increase by as much as 800%. Highest absolute increases in NCCN as a result of NPF (up to 3500 particles cm 3 for N50) were found at a dry savannah location of Botsalano in South Africa. In Hyytiälä Type I nucleation events were found to always, at the very least, double NCCN concentrations. It was found that in many environments around the world a rather similar fraction of aerosols activated into cloud droplets at any given level of supersaturation S, and a simple linear parameterisation is provided for an easy calculation of annual mean CCN concentration NCCN based only on total number concentration NCN and the desired S. At the majority of studied locations hygroscopicity was found to increase with size, with accumulation mode hygroscopicity parameter κ values being significantly larger than Aitken mode κ at some locations. Depending on the focus and desired accuracy, the use ...
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