Deposition of Aerosol Particles

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Abstract
In still air aerosol particles tended to settle straight down. Under normal conditions convection currents interfere with the settling. Even when deviation occurred, practically all deposition was on horizontal surfaces, or upon horizontal protrusions from vertical surfaces. These results were detd. from mortality of insects confined on surfaces that were previously exposed to aerosols in vertical and horizontal positions, by chemical analysis of DDT on vertical and horizontal slides, by visual observation of deposits of a dye incorporated in the aerosol soln., and by measuring and counting particles deposited on vertical and horizontal slides. The opt. particle size to use on insects increased with the size of the insect. The opt. diam. for mosquitoes was 15.81[mu] as compared with 22.4[mu] for house flies. The deposition on discs of wire cloth, glass, filter paper and leaves exposed to aerosol clouds moving at 2 to 16 m.p.h. was measured and agreed well with the deposit predicted by a formula developed by Sell. It was found that the smaller particles tended to deposit on the backs of the discs and the larger ones on the front. This division occurred at a particle diam. of about 15[mu] at 8 m.p.h., as detd. by the relative amt. of deposit on each side. At 16 m.p.h. the division point was slightly higher.
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