Cloud condensation nuclei as a real source of ice forming nuclei in continental and marine air masses

Cloud condensation nuclei (CCN) constitute a source of ice-forming nuclei (IFN) in continental and marine air masses. The mode of ice nucleation studied was condensation-followed-by-freezing. Concentrations of IFN formed by evaporation of cloud droplets and subsequent condensation of water vapor was found to be for marine aerosol particles 40 to 110 m−3 at Sw = 0.2% and 80 to 700 M−3 at Sw = 5%; for continental air masses it was 40 to 300 m−3 at Sw=0.2% and 5%. Concentrations of IFN of marine origin increased with increasing Sw, at a constant temperature; they were constant over a wide temperature range at a constant Sw. IFN concentrations in continental air masses were found to be independent of Sw at a constant temperature; they were constant for the Sw range of 0.2 to 5% (70% of data) and 0.5 to 5% (30% of data). The IFN produced through the evaporation-condensation cycle of marine aerosol particles have properties that are identical to IFN present in a marine atmosphere—their concentrations are independent of temperatures at Sw≥0.25%.