Some features of instantaneous point source diffusion within a turbulent boundary layer

Diffusion of helium gas from an instantaneous point source within a neutral boundary layer has been studied. Concentrations from a simulated point source, located at a fixed height of 8 inches above a smooth surface, were measured for several downstream cross-sections of the diffusing cloud. Separation of the total dispersion into two components, spreading and meandering, is obtained on the basis of Gifford's fluctuating model. The results of this analysis are used to determine the Hay-Pasquill scale parameter which relates the Lagrangian and Eulerian scales of turbulence. Meandering is shown to have a significant effect on the scale parameter.