A LABORATORY INVESTIGATION OF DROPLET FREEZING

Laboratory experimentation was undertaken to investigate the effects of various soluble and insoluble nuclei on the freezing temperature of water droplets. The freezing temperature and size of over 15,000 droplets were obtained. Pure water was produced, and subsequently frozen in droplet form. The freezing temperatures of various sizes of pure water droplets were used as a reference standard for the other phases of the experiment. The experiment showed that soluble salts, commonly found in the atmosphere, caused the freezing temperatures of the droplets to become colder than would be anticipated by bulk freezing point lowering calculations in all cases. Insoluble nuclei increased the freezing temperatures of the droplets. The addition of soluble salts to water droplets containing insoluble nuclei caused a marked depression of the freezing point below that originally observed. The magnitude of the depression was found to be a function of the solute concentration. Certain aspects of the role of droplet freezing in the atmosphere are discussed by extending the experimental results to atmospheric processes.