Pollutant dispersal downstream of a hill in different wind conditions

Pollutant dispersion has been investigated experimentally in a wind tunnel over a flat terrain interrupted by a two-dimensional hill of height equal to two times the elevation of the source. Three conditions were simulated for the incoming wind. All the measurements have been made using light scattering from the smoke-traced plume illuminated by a thin laser-light sheet. The global instantaneous and mean concentration fields, both in the longitudinal and in the transversal cross-sections, have been measured using a CCD TV camera connected to a tape recorder and then using digital image analysis. The local fluctuations in concentration, at predefined position in the plume have been measured using a focused photodiode with high-frequency response. With these techniques mean and instantaneous concentration profiles as function of the different flow conditions, as well as the probability density distribution and the frequency spectra of the concentration fluctuations were obtained.