AN EXPERIMENTAL-STUDY OF THE DRY DEPOSITION MECHANISM FOR AIRBORNE DUST

A study of dry deposition of the coarse mode of airborne dust an mirro r surfaces has been performed at Sede Boqer, Israel, as a part of a re search program to protect the reflective surfaces of solar concentrati ng collectors. In particular, the angular dependence of the deposition rate was measured in order to separate between its diffusive (isotrop ic) and vertical components. Dust was collected on a flat sampler with changeable slope, mounted on a wind vane. No deviation from a cosine- type angular dependence was found for dust particles larger than 4 mu m. This result is interpreted as domination, in the vicinity of the co llecting surface, of vertically directed particle flux over diffusive components. This conclusion was compared to the results of existing dr y-deposition models. The size distribution of particles, collected on the flat horizontal surface, was converted to a volume-mass concentrat ion using calculated sedimentation velocity as the only component of d eposition velocity. The resulting value was confirmed by our control m easurements of the volume-mass concentration. Our results are also com pared with recent data on deposition velocities, published by Lin er a l. (1994). (C) 1998 Elsevier Science Ltd. All rights reserved.