Fall-out estimation by lagrangian random walk model

Abstract

The purpose of this paper is an estimation of the concentration of pollutants above the terrain surface based on a lagrangian random walk model. Firstly, an estimation of wind fields in a region of interest using the continuity equation, known vertical profile of wind (modelled by an Ekman spiral and ground parametrized modulus profile) and known density is modelled. A diagnostic model based on a proposed merit function which uses the conservation of mass and knowledge of n measurements of the wind field within the region is derived. The model, of reduced order, is then solved by using variational calculus and finite differences. In the second section a Lagrangian model is presented. It is based on stochastic differential equations. It is necessary to relate the parameters of the stochastic differential equation to the diffusion parameters. The Briggs' parametrization with open-country conditions is used. The Carson and Moses equations are used to model the plume rise. Dry deposition and inversion layer are also modelled. This model has been applied at the hypothetical electrical generation plant at Valdecaballeros, in the North East of the province of Badajoz (Spain), where metereological and topographic measurements are available.