Production of Monodisperse Sub-micron Aerosols of which Each Particle carries a Specified Number of Electronic Charges

Abstract

EXPERIMENTAL studies of aerosols can be simplified by producing them with particles which are, within narrow limits, of the same size. The most convenient particles are often Dow polystyrene spheres (Serva Entwicklungslabor 6900 Heidelberg 1, Postfach 1505) available as suspensions in liquid with particle diameters ranging from 0.1 to 1.0 µm, and aerosols are produced by diluting, spraying and drying¹. Such an aerosol contains a proportion of particles which carry very high electrical charges, and the consequence may be that the results of experiments such as the measurement of the diffusion coefficient of polystyrene spheres are vitiated, possibly because of image effects. Exposure of the aerosol to a concentration of small ions, for example from a radioactive source¹ (often loosely termed “neutralizing the aerosol”²), can overcome these effects. The particles acquire a steady charge distribution, their electrical energy following, to a good approximation, a Boltzmann distribution^3,4. Such an aerosol will contain uncharged particles and progressively smaller numbers carrying one, two, three and more electronic charges, depending on the particle diameter.