Concentration and Size Distribution Measurements of Atmospheric Aerosols and a Test of the Theory of Self-Preserving Size Distributions

Abstract

The concentration and size distribution of particles from 0.001 to 3 μ in radius dispersed in the urban atmosphere was measured with a continuous-sampling sizing system composed of a nuclei counter, an electrical particle-counter, and an optical counter. Atmospheric aerosol size distribution measurements made by previous investigators are reviewed and compared with the new information. The diurnal variation of size distribution was measured for four 24-hr periods, and concentration variations are shown to be related to local particulate source and meteorological conditions. The self-preserving size distribution theory of Friedlander is reviewed and tested with 58 size distributions measured under a variety of conditions. The experimental data are consistent with the theory for particles of radii greater than about 0.05 μ, and the size distribution function, dN/dr, is found to he equal to 0.05ϕr⁻⁴ for the size range 0.05–3 μ where N is the number of particles cm⁻³, r the particle radius, and ϕ the particle volume per unit volume of aerosol. A good approximation to the size distribution of atmospheric aerosol for particles greater than 0.05 μ is shown to result from determining ϕ from the weight of high-volume filter samples and the particle density.