In the present thesis, a new chamber (the CoLlision Ice Nucleation CHamber, CLINCH) was developed to study two important processes that take place within a cloud. The first process studied was the collection efficiency (E) between submicron aerosol particles (0.05 and 0.33 ?m) and cloud droplets (12.8 and 20.0 ?m). The collection efficiency was determined by either maintaining a fixed droplet size and varying the particle size or vice-versa. The second process studied with CLINCH was the freezing of cloud droplets due to contact freezing. Kaolinite was chosen to test ice nucleation of cloud droplets of 25.7 ?m in diameter. The ice nucleation ability was addressed by varying the kaolinite particle size, the aerosol concentration and temperature. It has been found that both aerosol concentration and particle size are important for contact freezing. At aerosol concentrations >100 cm-3 no significant freezing events were observed within the measurement uncertainties. However, at aerosol concentrations <100 cm-3 ice formation as a function of temperature was detected. When the particle size was changed from 400 to 800 nm the onset freezing temperature was found to be 7øC higher.