ESTIMATES OF MAXIMUM GROUND-LEVEL CONCENTRATION IN THE CONVECTIVE BOUNDARY-LAYER - THE ERROR IN USING THE GAUSSIAN DISTRIBUTION

This paper derives expressions for the maximum cross-wind integrated a nd centerline concentrations at ground level for an elevated source in the convective boundary layer. These expressions account for the obse rvation that the probability density function (pdf) of vertical veloci ties in the convective boundary is positively skewed with a negative m ode. The estimates obtained with these formulae compare favorably with observations reported by Briggs (1993; Boundary-layer Met. 62, 311-32 8). The paper also examines the error associated with using a symmetri c Gaussian pdf instead of the skewed pdf to estimate the ground-level concentration. We show that the error is equivalent to an underestimat ion of a factor of almost 1.5 for the cross-wind integrated concentrat ion, and a factor of 1.3 for the ground-level centerline concentration .