Aircraft Applications of Insecticides in East Africa. V.—The Deposition in open Country of a coarse Aerosol released from an Aircraft

Abstract

An investigation has been made of the deposition in open country of a coarse aerosol released from an aircraft flying at approximately 30 feet. A constant drop spectrum was used, with a mass median diameter of approximately 80 microns.It is shown that the rate at which the aerosol deposits is greatly affected by the degree of atmospheric turbulence, a practical measure of which is described. The rate of deposition is approximately inversely proportional to the time interval elapsing between production of the aerosol and deposition, except for deposits laid down near the line of emission.Droplets less than 10 microns in diameter are not deposited appreciably within any useful time interval, and it would be most uneconomical to attempt to produce deposits upon the ground by using drop spectra consisting mainly of such small droplets.The solution used was a 10 per cent. w/v solution of technical DDT in a solvent consisting of 1 part of Shell Power Kerosene to 1 part of Shell Diesoline. Evaporation of the volatile constituents takes place very rapidly during the first few seconds after production of the droplets, and deposits formed immediately beneath the aircraft track have lost 50 per cent of their initial volume. Solvent losses increase significantly with time, but so slowly that for most practical purposes the solution strength of the ground deposit is very nearly constant for all important sampling points.