Description of vertical dispersion influenced by roughness elements.

A tentative method to include the dispersion effect of roughness elements is suggested. The method is based on data for the intensity and scale of turbulence. The intensity may be calculated in well defined wind conditions. In weak or variable wind conditions the turbulence intensity should be measured. The scale of turbulence is assumed to be proportional to the height of the roughness elements close to the ground and approaches a constant value with increasing height. The asymtotic value is determined by the surface layer structure.