Time-dependent estimates of concentration mean and variance for replicated instantaneous heavy gas releases

Abstract

This report presents sets of time-dependent estimates of concentration mean, standard deviation and variance for a series of replicated instantaneous releases of heavy gas carried out in a wind tunnel at Warren Spring Laboratory. The replicated nature of these experiments - there are 50 or 100 repetitions of each experimental situation - provides a rare and welcome opportunity to derive these estimates. More usually it is necessary to calculate time averages within a single release; this, however, is appropriate only for a statistically stationary continuous release, it cannot be used for an instantaneous release. Considerable interest has lately attached to the time-dependent behaviour of mean and variance and to how these quantities depend on atmospheric conditions, source conditions and position; this interest has been expressed in terms of separate consideration of the quantities, in terms of the intensity (standard deviation divided by mean), and in terms of possible fundamental relationships between them as suggested by Chatwin and Sullivan (1990). The sets of estimates are presented here, without comment or discussion, in the hope of aiding this work.