Dry deposition of large, airborne particles onto a surrogate surface

Simultaneous measurements of particle dry deposition flux and airborne numb er concentration in the open atmosphere were made using three different typ es of artificially generated particles in the size range 10-100 mu m - perl ite, diatomaceous earth and glass beads. A combination of gravimetric analy sis,automated microscopy and sonic anemometry provided size-resolved estima tes of both the inertial and gravitational components of the quasi-laminar layer particle deposition velocity, (V-d)(b), as a function of size. Eddy i nertial deposition efficiency (eta(dI)) was determined as a function of dim ensionless eddy Stokes number (Stk(e)). In the range 3 < Stk(e) < 100, the observed eta(dI) agree with the model of Slinn and Slinn (1980, Atmospheric Environment 14, 1013-1016). In addition, the observed (Y-d)(b) values agre e well with the predictions of Pleim et al. (1984, ADOM/TADAP Model Develop ment Program. Volume 4. The Dry Deposition Module. Ontario Ministry of Envi ronment, 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 Labor atories, Richland, WA), used in several regulatory models, significantly un der-predicted (up to seven times) (V-d)(b) for large particles (d(a) > 10 m u m). (C) 2000 Elsevier Science Ltd. All rights reserved.