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S. K. Friedlander

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S. K. Friedlander

Abstract

An explanation is offered for the similarities observed experimentally among size distributions of natural aerosols measured at different places and times. This explanation is based on a similarity transformation of the equation describing the kinetics of a coagulating, settling aerosol. On dimensional grounds, an approximate shape is derived for the upper end of the spectrum which compares well with the available experimental data. An estimate is given for the rate at which matter is transferred from the lower to the upper end of the spectrum.

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S. K. Friedlander

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/N 2 ∼ N t.

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S. K. Friedlander
and
Ralph E. Pasceri

Abstract

Previous experimental measurements of particle size spectra of the atmospheric aerosol are reviewed. A four-stage impactor was used to sample the Baltimore aerosol in the size range above 0.4 microns in radius. Particle size was measured with an optical microscope. The size range below 0.1 microns was sampled with a novel rotating disk device and the particle size distribution was measured by electron microscopy. The theory of the disk as applied to the diffusion of aerosol particles is discussed.

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Ralph E. Pasceri
and
S. K. Friedlander

Abstract

Distribution data obtained by sampling the Baltimore aerosol with a cascade impactor are reported for the range between 0.4 and 20 microns radius. Data for the range between 70 Å and 0.1 microns in radius were obtained in two runs with the rotating disk sampler. Greater variations were observed in the lower end of the spectrum than in the upper end. The theory of self-preserving size distributions was used with some success to correlate data obtained in this and other studies. When the theory applies and the r −4 subrange exists, the size distribution is given by n(r)=0.04ϕr −4 where ϕ is the volume fraction of aerosol material.

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