Numerical modelling of transport, dispersion, and deposition — validation against ETEX-1, ETEX-2 and Chernobyl

A comprehensive, high-resolution, 3-dimensional tracer model, DREAM, has been developed for studying transport, dispersion, and deposition of air pollution caused by a single but very strong source. The model is based on a combination of a Lagrangian short-scale puff model and an Eulerian long-range transport model. The meteorological meso-scale model MM5V1 is used as a driver for the transport model. The tracer model and the numerical implementation of the model is described in this paper. The Eulerian transport model has been splitted into different submodels. The advantages of treating the different physical processes on different scales by using different numerical algorithms will be discussed. The model has been run and validated against measurements from the two ETEX releases (the European Tracer EXperiment) and the Chernobyl accident. 2-D and 3-D visualizations together with some comparisons of model results with measurements will be presented and discussed. The combined model is able to reproduce dosages within a factor of 2–3 in the worst case and arrival times within 2–3 h, compared to measurements from ETEX-1 and Chernobyl. This is within the currently achievable limits of accuracy in long-range dispersion modelling, according to the ETEX-1 experiment.