Diffusion near buildings as determined from atmospheric tracer experiments. Technical memo

Data from the innermost arcs and roof top samplers of the Rancho Seco and EOCR field studies were used to examine diffusion close to a building. The minimum length plume paths were determined from each release location to each sampler position at these two test sites. The curves from the two sites were similar in shape and implied three zones of diffusion. It is speculated that the three zones represent the rapid diffusion in the building wake; a transition zone where the plume leaves the wake where larger scale atmospheric turbulence again causes more rapid diffusion. By scaling the plume path length by the minimum cross sectional area of the structure, the curves for Rancho Seco and EOCR showed no significant difference in magnitude for about one scaled distance. Since these studies were conducted at two dissimilar sites, the consistency in measured concentrations suggests that the technique may be useful in predicting maximum expected concentrations near a building. Comparisons were also made with current NRC methods for predicting maximum expected concentrations close to a building. The NRC model overestimated concentrations in all but one case. A bibliography is presented in an appendix