RESUSPENSION OF MONODISPERSE PARTICLES FROM SHORT GRASS SWARDS - A WIND-TUNNEL STUDY

Measurements of resuspension of 1, 5 and 10 mum diameter particles from grass swards exposed to three wind speeds (3, 5 and 7.8 m s-1) within a wind tunnel are reported. Particles used were monodisperse porous silica spheres of about unit density, and were labelled with a stable tracer so that deposited and resuspended quantities could be established by neutron activation analysis using the imperial College Reactor. Resuspension rates (LAMBDA) may be derived in terms of the fraction of the initial deposit that has occurred per unit time. A useful quantity for analysis where resuspended aerosol is determined on air filters is the cumulative fraction of resuspended material (F). F gives a clear indication of the likely practical significance of resuspension. Two mathematical expressions were fitted to F and their differentiated forms compared with the measured LAMBDA variation with time. The first model is based upon a power law for LAMBDA vs time; the second upon a hyperbolic relation having a limit to F which is determined by long-term particle loss from plants due to biological processes.