Puff-on-cell model for computing pollutant transport and diffusion

Most finite-difference methods of modeling pollutant dispersion have been shown to introduce numerical pseudodiffusion, which can be much larger than the true diffusion in the fluid flow and can even generate negative values in the predicted pollutant concentrations. Two attempts to minimize the effect of pseudodiffusion are discussed with emphasis on the particle-in-cell (PIC) method of Sklarew. This paper describes a method that replaces Sklarew's numerous particles in a grid volume, and parameterizes subgrid-scale concentration with a Gaussian puff, and thus avoids the computation of the moments, as in the model of Egan and Mahoney by parameterizing subgrid-scale concentration with a Guassian puff