Nucleation Activity of Organic Cloud-Seeding Agents.

The report represents the third of a series of studies concerning the heterogeneous nucleation of supercooled water. The ultimate goal is to obtain fog and cloud seeding agents with a variety of operational characteristics. An equal effort is concerned with obtaining a better understanding of the principles of heterogeneous nucleation and the individual steps involved in freezing processes. The results of this study show that it is not possible to assign a meaningful threshold temperature to organic nucleants. This is particularly true for materials that are water soluble. For those compounds that are stable in the presence of water and are relatively insoluble, at least a two parameter exponential relationship is needed since different compounds show a different increase in the number of active nucleation sites as the temperature decreases.