Abstract
The fall-out meter is an instrument used in the evaluation of deposits from aerosol and spray clouds. It consists of a motor-driven rotating or transversely moving platform which carries slides beneath a slit in a cover plate. The fall-out meter relates, in time, deposition of particles on a slide with particle spectrum and particle concentration in the aerosol or spray cloud above the slit. Simultaneously, it produces a space dilution of the deposited particles. Examples are given of uses to measure horizontal downwind velocity and lateral and vertical expansion rates of aerosol and spray clouds in the field and their particle-size distributions.