A NUMERICAL-MODEL OF THE TRANSPORT AND DIFFUSION OF PERONOSPORA-TABACINA SPORES IN THE EVOLVING ATMOSPHERIC BOUNDARY-LAYER

Numerical solutions of the diffusion equation of Peronospora tabacina spores from a finite-area source over flat terrain in the evolving con vective boundary layer are presented. Temporal variations in the relea se of spores, atmospheric stability, wind speed, and eddy diffusivity are considered. The model also includes the vertical variations of win d and eddy diffusivity. The model results indicate that ground level c oncentrations decrease with time as wind speed and eddy diffusivity in crease in the evolving convective boundary layer. The loss of P. tabac ina spores due to deposition at the surface also decrease with increas ing instability and wind speed. Deposition is found to be particularly important close to the source area. (C) 1997 Published by Elsevier Sc ience Ltd.