Concentration fluctuations and peak-to-mean concentration ratios in plumes from a ground-level continuous point source

Abstract

Diffusion data collected by 63 incremental samplers during four short duration, continuous releases of 85Kr are used to examine concentration fluctuations and peak-to-mean concentration ratios in the atmosphere. Cumulative frequency distributions and the intensity of short-term concentrations are shown to be a function of the relative crosswind position within the mean plume. Peak-to-mean concentration ratios are shown as a function of relative crosswind position within the plume and the ratio of the durations of the mean and the peak (time ratio). The relationship between the intensity of concentration fluctuations and the relative crosswind position is similar to that reported for laboratory data. The relationship between peak-to-mean ratios and the time-ratio was found to differ from the simple power law relationship suggested by several workers. Previous estimates of the peak-to-mean/time ratio relationship for positions near the mean plume axis are shown to be too low.