FIELD ASSESSMENT PROBLEMS. THE DIFFUSION OF POLYDISPERSE PARTICULATE CLOUDS
NEW YORK UNIV BRONX SCHOOL OF ENGINEERING AND SCIENCE
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Separation of particles released in the atmosphere is due to small scale turbulence and varying terminal velocity of the particles. The distribution of particles downwind, which satisfies the differential equation of turbulent diffusion, is obtained by numerical integration when the distribution of terminal velocity is lognormal. The non-dimensional ground deposition depends only on the logarithm of the ratio of the median terminal velocity to the friction velocity, and on the coefficient of variation of the terminal velocity distribution. An analytic approximation is obtained, which is quite good for a wide range of basic parameters. Another approximation is used which neglects the variation of terminal elocity. This procedure is reasonable for a much smaller range of basic parameters. Application to a diabatic atmosphere is also given.