The expected mass fraction

A new measure is introduced to characterize the reduction of concentration values found in a contaminant cloud. The “expected mass fraction” presents the mass of contaminant (or exposure time) at the various contaminant concentration values observed when a contaminant cloud passes over a fixed sampling location. This measure is shown to be easy to compile and to provide a reasonable ensemble average approximation with as few cloud releases as would be required for the more conventional dosage measurement. The new measure is shown to have a good prospect of theoretical predictability due to its definition in terms of the one-point probability density function of contaminant concentration and recent advances in predicting the moments of that probability density function. Experiments from the Warren Spring Laboratory are used to illustrate the application of the “expected mass fraction”.