Modeling of dispersion, deposition and evaporation from ground deposition in a stochastic particle model

Often when hazardous substances are released in the atmosphere there will be one fraction of pure gas and another fraction of aerosols. The gas cloud, i.e. the primary cloud transports a rather long distance with the wind, disperse due to turbulence and deposits on the ground with a specific dry deposition velocity. The aerosols, which also transport with the wind but in a rahter short distance, fall down towards the ground where they are deposited. From this ground deposition layer gas evaporates and creates a gas cloud called the secondary cloud. In this work, evaporation from the ground deposition layer has been implemented in a particle dispersion model based on the Langevin equation and furthermore the parametrization of the dry deposition velocity is documented. A verification of the evaporation rate is also made with the conclusion that the evaporation error is small and acceptable.