Deposition and suspension of large, airborne particles

The focus of this paper is the experimental determination of size-resolved estimates of both deposition and suspension velocities for large, airborne particles (greater than 10 mu m diameter). Measurements of particle dry flux onto the top and bottom surface of a smooth, horizontal, surrogate surface were divided by measurements of the concentration of airborne particles to provide estimates of deposition and suspension velocities in 14 size intervals between 5 and 100 mu m diameter. Eddy inertial deposition efficiencies (eta(di)) were determined as a function of eddy Stokes numbers (Stke) larger than 1 and the results agree with the model of Slinn and Slinn (1980). The model was used to provide estimates of both the inertial and gravitational components for total upward and downward particle velocities. Experimental results for individual particle size intervals produced highly variable results. Much of this variation can be attributed to experimental errors associated with the nature of the atmospheric experiments and not to problems with the model. Upward large particle suspension velocities are similar in magnitude to downward deposition velocities at higher wind speeds and represent a counteracting process to deposition processes that cannot be ignored for accurate representation of the long-range transport for particles between 5 and 50 mu m diameter.