A Model of Plume Advection Velocity for Dispersion in Urban Arrays

In the basic Gaussian plume model (GPM) used for predicting concentrations due to continuous plume releases, the mean concentrations in the plume are inversely proportional to the mean plume advection speed U_p. For elevated releases, U_p is evaluated at the height of the release or some other representative height. For ground level releases in a shear layer, U_p varies with distance from the source, since as the plume grows vertically in the boundary layer, it encounters progressively higher wind speeds. From similarity theory, it is possible to show that the correct wind speed to use in this case is U_p ≈ U(0.5σ_Z), that is to say the wind speed evaluated at approximately one half the plume vertical standard deviation.