Electrization of aerosol wetted in bipolarly ionized air

Abstract

We studied the influence of the characteristics of the atmospheric ionization and physical-chemical state of condensation nuclei on the electric state of convective cells. Based on the results of experiments in an adiabatic chamber with a volume of 3200 m3, we found that, with increase in relative air humidity H from 40 to 95% with an equivalent ascent rate of 100–400 cm/s, excessive charges in amounts of about 103 or more elementary charges per cm3 may be accumulated on the nuclei. The sign of the charge depends on the chemical composition of the hygroscopic nuclei. For instance, media with insoluble nuclei (porous silica, etc.) typically have prevailing negative charges; those with soluble nuclei (sodium chloride, etc.) are dominated by positive charges. At H = 60−90%, the electrization of soluble nuclei can be interpreted in the diffusion-kinetic models of the ion charging of aerosols. Considerable negative volume charges, which appear on insoluble hygroscopic nuclei during a rise in humidity from 40 to 70%, are explained by the structuring of surface water films, which exhibit a resemblance to negative lightweight ions. At high values (H > 90%), it is necessary to take into account the resemblance of the wetted surfaces to positive lightweight ions. We showed for the first time that, at ion formation rates of 3 and 1010 ion pairs/(cm3 s), the differences in the volume charge and wetting rate of condensation nuclei are insignificant. It is concluded that, in many meteorological situations, the first stage of electrization of the convection-derived cloud media is the ion charging of the condensation nuclei.