Study of turbulent atmospheric dispersion of pollutants at low wind velocities

Low wind velocities coupled with strong atmospheric stability constitute complex diffusion situations, surface layer modelling of which proves to be difficult at present because of lack of theoretical bases and experimental data. Under these conditions, diffusion of a pollutant on the vertical plane is governed by thermal phenomena. On the horizontal plance, according to site orography, fluctuations in the wind direction may determine the mixing process. These fluctuations depend on flow velocity as well as on undulatory phenomena generated by the relief of the area and by exchanges with the synoptic layer. 5 refs