Deposition velocity and the collision model of atmospheric dispersion—II. Extension to cases with variable turbulent velocity scale

Abstract

The collision model of turbulent dispersion has been extended to deal with situations where the turbulent velocity scale is dependent on position, which requires that the particles of the Monte Carlo simulation accelerate between collisions. The theory has been applied to an idealized vegetative canopy in order to illustrate the differences from the predictions of eddy-diffusivity (K)-theory arising from the finite decorrelation length scale associated with vertical turbulent velocity. For cases of high deposition to canopy elements, the collision-model results do deviate from K-theory results, although the differences are not practically significant. An extension to the model enables gravitational settling to be handled in a more realistic manner than in K-theory. By this means, it is found that the simple expedient of adding the settling velocity to the deposition velocity due to other processes is more closely valid than appears from K-theory results.