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

Abstract 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 S w = 0.2% and 80 to 700 M −3 at S w = 5%; for continental air masses it was 40 to 300 m −3 at S w =0.2% and 5%. Concentrations of IFN of marine origin increased with increasing S w , at a constant temperature; they were constant over a wide temperature range at a constant S w . IFN concentrations in continental air masses were found to be independent of S w at a constant temperature; they were constant for the S w 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 S w ≥0.25%.