Measurements related to the fundamental processes of aerosol electrification

Abstract

With the object of illuminating the fundamental processes responsible for the electrification of aerosols, a number of measurements have been made to compare the initial distribution of charges carried by various aerosols with their final equilibrium state. Measurements have been made on freshly condensed water droplets and sulfur particles, on both freshly dispersed and aged silica dust particles, and on sprayed water droplets; all lying within the 1- to 2-μ radius range. The measurements show that when numerous ions are formed within the aerosol space the particle charges are not completely discharged but rather the ions greatly hasten the attainment of an equilibrium distribution. Moreover, it is found that irrespective of the initial measured distribution of charges, the final equilibrium distribution approaches a Gaussian curve whose width is dependent upon the mean particle radius and is usually symmetrical about the axis of zero charge. Because the infrequent collision of water droplets can hardly produce appreciable electrification by friction, and because the equilibrium charge on water droplets and that on silica particles of the same size are indistinguishable, it is concluded that the maintained charges on aerosols are a direct consequence of the diffusion of the ambient atmospheric ions onto the particles. The equilibrium distributions approach the theoretical form recently worked out by Ross Gunn.