Growth of salt and acid aerosol particles in humid air

Aerosols of industrial significance like ammonium chloride, hydrochloric acid and sulphuric acid aerosols have been generated with particle number concentrations between 106 and 108 cm−3 and particle sizes between 0.1 and 0.5μmn (NH4Cl), 0.8–1.5 μm (HCI) and 0.2–0.5 μm (H2SO4 ). The influence of the generating conditions on the size and the concentration of the aerosol particles have been investigated. After the generation, the particles were exposed to atmospheres of different relative humidity. If a certain level of relative humidity is exceeded, the solid salt particles dissolute and become droplets. The particle diameter of the salt and acid droplets increases if the relative humidity is raised. The particle diameters and concentrations were measured to show the dependence on the generating conditions and the relative humidity by a laseroptical extinction technique. The results of the measurements were compared with growth models. There was a very good agreement between the experimental data and the growth models for salt and acid aerosols. It is therefore possible to evaluate the limit of the growth by pure water vapour saturation, which is especially useful for the design of particle separators.