Fluctuations in dense gas concentrations measured in a wind-tunnel

Concentration time series from FID (flame ionisation detector) sensors and catharometers downstream of an instantaneous release of dense gas contaminants are analysed by statistical methods. For each experiment there are either 50 or 100 replications, thus allowing estimates of statistical properties to be made even though the dispersion is nonstationary. The time history of the first four central moments is estimated, and they are plotted against each other, in the manner suggested by Mole and Clarke (1995). The collapse of the skewness-kurtosis plot onto a universal quadratic curve, similar to that found by Mole and Clarke for continuous releases, is observed. In this paper, we show how this observation is consistent with the form of the pdf postulated by Chatwin and Sullivan (1989).