A Study of the Effect of Size on Ice Nucleation in the Aerodynamic Range of Particles

Abstract

The effect of size on ice nucleation has been experimentally investigated for aerosol particles in the aerodynamic range. Aerosol particles are separated according to their aerodynamic diameter while airborne and deposited on a membrane filter which is then developed in a static diffusion chamber. The effect of competition among nuclei and the effect of particle size, though acting together, have been studied separately by sampling various filters in such a way as to obtain a wide range of surface concentrations of particles in each interval of aerodynamic diameter. Moreover, when sampling atmospheric aerosols, the effect of competition among ice nuclei and cloud condensation nuclei is eliminated in practice, as the latter are mostly deposited, together with other small particles, at the end of the filter. The effect of size has been investigated for homogeneous laboratory dispersed aerosols of clay (mont-morillonite, kaolinite and halloysite). Urban aerosols and the exhaust fumes from an oil-fired power station have also been studied. The usefulness of the technique in investigating the fate of submicron ice nuclei which have become attached to coarser particles has been demonstrated.