Freezing nucleation in aqueous electrolytes

Experiments were performed to determine the extent to which the nucleating abilities of artificial and natural freezing nuclei are influenced by the presence of salts dissolved in water. Four different nucleants (at fixed concentrations) were tested in combinations with 10–20 soluble salts using the drop freezing technique. Changes in freezing temperatures were determined for each nucleant–salt combination at salt concentrations of 0, 0.01, 0.1 and 1 molal. Major differences were noted in the responses of the different nucleants and it was concluded that the influence of dissolved salts on heterogeneous freezing nucleation is not due to changes in the bulk water structure, but results from modifications at the nucleant–embryo interface. The measurements indicate that the salt contents of cloud droplets can be expected to alter the ice nucleating activities of suspended particles by as much as ±4°C.