Resuspension of Particulate Matter from Grass and Soil

摘要

Measurements of resuspension of particulate matter from grassland and bare soil in Britain at controlled wind speeds are described in this report. The measurements were performed in an outdoor wind tunnel. Resuspension factors for a sub-micron powder deposited from the air on to 10m exp 2 of grass and soil and for a suspension of silt, sprayed on to a similar grass area, were similar. The resuspension factor declined as the reciprocal of time of wind exposure and increased as the square or cube of wind speed. An appreciable fraction of the resuspended tracer was in the respirable size range. A large fraction of the total material suspended from a small contaminated area deposited again within three metres. The strong dependence of deposition rates on particle size and the rapid deposition close to the source questions the extrapolation of small scale resuspension measurements to practical situations, suggesting that analysis of the concentrations of widely distributed tracers may usefully supplement resuspension measurements. Atmospheric concentrations of trace elements and the distribution of weapons fallout were used to deduce an upper limit for the resuspension factor for a fifteen year old deposit of 7 x 10 exp -11 m exp -1 . The fraction of deposited fallout resuspended during such a period cannot much exceed 10 per cent. (Atomindex citation 11:499486)