Using a cloud condensation nuclei counter to study CCN properties and concentrations

A Cloud Condensation Nuclei Counter (CCNC) has been constructed, calibrated and used in field conditions. The CCNC was used in a rural/boreal forest site (Hyytiälä), in marine/coastal sites (Tenerife and Mace Head), and in an urban site (Helsinki). Expressions for determining the soluble volume fraction of particles were derived. The soluble fraction of Aitken mode particles was determined and the CCNC number concentrations were observed. In the marine air masses the soluble fraction was seen to be around 0.8. In the rural site the soluble fraction was around 0.3 and some diurnal variation was seen. In Helsinki the soluble fraction was somewhat higher than in the boreal forest site.