Cloud Physics and Nucleation Theory: Revisions Indicated by New Measurements of the Electrical Conductivity of Evaporation-Humidified Air

摘要

A new theory of cloud physics is presented, based on new measurements of the electrical conductivity of moist air humidified by evaporation, combined with other measurements of related phenomena by mass spectrometry, infrared spectroscopy, and adiabatic expansion experiments in cloud chambers. It is shown that enormous populations of large, neutral molecular clusters of water molecules can exist in the vapor produced by evaporating liquid water, and at the vapor/liquid boundary layer that virtually all vapor initially can be clustered. The neutral clusters dissociate into ions or serve as charge carriers to a small extent (given by the equilibrium dissociation constant or 'ion product' of water) as measured by electrical conductivity using cells of a new design to monitor the temperature and humidity dependencies of the neutral cluster populations. The hydrogen bonds in the neutral clusters are strong absorbers of infrared radiation. Therefore, the activity of the neutral clusters in water vapor or moist air also can be monitored by infrared absorption and emission. The theory is supported by cluster modeling, as well as thermodynamic studies. It is shown that water droplet nucleation can be a temperature phenomenon and that supersaturations of more than perhaps one percent need not exist. The possible existence of a temperature-dependent energy barrier to nucleation in subsaturated conditions is demonstrated. (Author)