Evaporation Decay Organic Nucleus of ice Particle

Abstract

Evaporation rates have been determined for two organic ice nucleus particles: 1,5-Dihydroxynaphthalene and metaldehyde aerosols, produced by powder vaporization-condensation method and by vapor activation method, respectively. The aerosols are injected into a large smoke chamber inside a walkin environmental room and allowed to evaporate under dry conditions at different temperatures. The decay rates of aerosols are determined in a mixing chamber at -15 C with intermittent sampling at predetermined time intervals. The aerosol concentration losses are compared with cumulative size distributions, and assuming that the decay proceeds from smaller sizes, lifetimes of particles for different temperatures are determined as a function of minimum size. Metaldehyde particles less than 0.6 um in diameter de- cay within 20 minutes at temperature as cold as -20 C, and 1,5-dihydroxynaphthalene particles within several hours, if particle diameters are smaller than 0.2 um at the same temperature. These data are expected to provide the basis for estimating, as well as minimizing, the extent of possible downwind and environmental contamination through use of these organic ice nucleants.