Dry deposition of large, airborne particles onto a surrogate surface

Abstract

Simultaneous measurements of particle dry deposition flux and airborne number concentration in the open atmosphere were made using three different types of artificially generated particles in the size range 10–100 μm – perlite, diatomaceous earth and glass beads. A combination of gravimetric analysis, automated microscopy and sonic anemometry provided size-resolved estimates of both the inertial and gravitational components of the quasi-laminar layer particle deposition velocity, ( V d) b, as a function of size. Eddy inertial deposition efficiency ( η dI) was determined as a function of dimensionless eddy Stokes number (Stk e). In the range 3<Stk e<100, the observed η dI agree with the model of Slinn and Slinn (1980, Atmospheric Environment 14, 1013–1016). In addition, the observed ( V d) b values agree well with the predictions of Pleim et al. (1984, ADOM/TADAP Model Development Program. Volume 4. The Dry Deposition Module. Ontario Ministry of Environment, Rexdale, Ontario). However the dry deposition model of Sehmel and Hodgson (1978, a model for predicting dry deposition of particles and gases to environmental surfaces. DOE Report PNL-SA-6721, Pacific Northwest Laboratories, Richland, WA), used in several regulatory models, significantly under-predicted (up to seven times) ( V d) b for large particles ( d a>10 μm).