Three models and one experience: a performance study

In the field of transport-diffusion of passive pollutants in the atmosphere lots of different techniques yielding air concentration values are used. In this paper the performances of three different models of passive dispersion in the atmosphere when using the same meteorological data provided by ECMWF for the simulation of the first ETEX release are presented. The first model DIFTRA (DIFfusion around TRAjectories) is a gaussian puff model around 3D large scale trajectories. The second model DIFEUL (abbreviation of the french term 'DIFfusion EULerienne') is an eulerian off-line dispersion model solving an advection diffusion equation for a passive (optionally radioactive) scalar. The last model DIFPAR ('DIFfusion of PARticles') is a lagrangian particle model where the evolution of the cloud of pollutant is simulated by tracking a large number of particles following the eulerian mean flow to which one adds random perturbations simulating the effects of turbulence