A Supersonic Expansion Method of Ice Nuclei Generation for Weather Modification

Abstract

Aerosols of organic ice nucleating agents were formed by rapid adiabatic expansion, by passing superheated steam laden with the organic vapors through a supersonic nozzle. The effect of the Mach number of the flow through the nozzle on the aerosol particle size and number concentration was investigated. It was found that the number of particles formed increased by a factor of 103 as the Mach number increased from 1 to 2, but further increases in Mach number had little effect. The ice nuclei activity spectra of the organic aerosols thus generated showed plateaus at colder temperatures, with approximately 1014 nuclei per gram below ?9°C for 1,5-dihydroxynaphthalene and 1012 g?1 below ?7°C for metaldehyde. Coagulation rates of both organic smokes were determined. Coagulation of 1,5-dihydroxynaphthalene aerosols followed the Smoluchowski equation. Coagulation of metaldehyde aerosols was not only extremely rapid, but in addition the coagulation constant increased with time. The latter effect was attributed to the strong electrical dipole of metaldehyde particles.