THEORETICAL CONSIDERATIONS FOR THE PARTICLE SIZE SPECTRUM OF STRATOSPHERIC AEROSOL

Abstract

An equation is derived for the time rate of change of the size spectrum function of the stratospheric aerosol. Based on the assumption of local equilibrium between the effects of coagulation and sedimentation, a form is deduced for the shape of the upper end of the size spectrum function, that is the range of radii larger than about 0.1 microns. Dimensional considerations indicate that the equilibrium range may include two subranges in which the spectrum function varies with the particle radius as r⁻² and r⁻⁴. The theoretical predictions are consistent with available experimental data. The theory should permit the estimation of complete particle size spectra from a minimum amount of experimental data. A similarity transformation is given for the lower end of the size spectrum. Based on the transformation, a law of decay with time, t, is derived for the total particulate concentration, N. The decay law is of the form 1/N² ∼ N t.