Including of Surface Source in a Surface Layer Parameterization

Abstract

A PC-oriented Eulerian multi-layer model EMAP [5,6] was developed. The vertical diffusion block of the model uses a 2nd order implicit scheme realised on a non-homogeneous staggered grid which includes the dry deposition flux as a bottom boundary condition. Experiments with EMAP show that, if the concentration at the first computational level is used for calculation of the dry deposition flux, the deposited quantity changes when the height of the level is changed. Roughness level is necessary to calculate properly the dry deposition. It is impossible to have such a model level, since roughness changes from one grid point to another. On the other hand, because of the steep gradients in the surface layer (SL), many levels must be introduced near the ground for adequate description of pollution profiles. This would enormously increase memory and time requirements without any practical need. The first computational level is usually placed high enough above the surface and parameterization of all transport processes in the layer bellow is applied. The problem becomes much more complex if sources at the surface have to be treated. Such are the processes of evaporation and re-emission of the tracer under consideration. An effective parameterization of SL diffusion processes, based on similarity theory, was developed and tested in [8,9]. It allows to have the first computational level at the top of this layer. Here, an upgrade of this parameterization is presented, taking into account the presence of a continuous surface source. This parameterization is built in in EMAP and applied to different pollution problems. In addition, a simple re-emiss emission can cause severe redistribution of the pollutant. The scheme can be used for long term integration of persistent organic pollutants as well as some heavy metals on regional and continental scale.ion scheme is built in to make use of this SL parameterization.