Deposition velocity and the collision model of atmospheric dispersion—I. Framework and application to cases with constant turbulent velocity scale

Abstract

This work shows how to apply the concept of deposition velocity to the collision model of turbulent dispersion, the latter being an alternative to the Langevin-equation approach for retaining a finite memory of turbulent velocity. In terms of the Monte Carlo (MC) solution to the model, this development obviates tracking particles into regions of complex behaviour near the true lower boundary in two- or three-dimensional dispersion-deposition problems. The approach is illustrated for pollutant dispersing in a homogeneous layer with a totally-absorbing lower boundary. In addition, it is shown how the deposition velocity itself can be calculated within the Lagrangian-particle model by solving a one-dimensional equation. Illustrative MC solutions are given for a homogeneous layer and for the neutral surface layer of the atmosphere, for pollutant which is totally absorbed at a lower boundary; these are found to be closely similar to K-theory predictions, as expected for these cases.