Ice-forming nuclei over the East China Sea

Abstract Ice-forming nucleus (IFN) population was determined for aerosol particles collected on filters over the East China Sea. The mode of ice nucleation studied was condensation-followed-by-freezing; experiments were performed in a dynamic chamber at a constant temperature and with continuous cooling at S w =0.3%. Ratios of IFN concentrations determined at a constant temperature to those determined during continuous cooling simulating an updraft were close to one (35%) and larger than one (65%). Ratios close to one indicate the absence of any deactivation of IFN during the growth of droplets; for ratios larger than one the dilution takes place during the entire cooling process, thus producing more dilute solutions of water-soluble salts in droplets and apparently deactivating some ice nucleating sites. IFN concentration maxima were found at 0600 and 1800 local time. Concentrations of IFN were found to be inversely proportional to the amount of air pollutants, but at a very high SO 4 2− ion concentration IFN concentrations increased.