THE EXPECTED MASS FRACTION

A new measure is introduced to characterize the reduction of concentra tion values found in a contaminant cloud. The ''expected mass fraction '' presents the mass of contaminant (or exposure time) al the various contaminant concentration values observed when a contaminant cloud pas ses over a fixed sampling location. This measure is shown to be easy t o compile and to provide a reasonable ensemble average approximation w ith as few cloud releases as would be required for the more convention al dosage measurement. The new measure is shown to have a good prospec t of theoretical predictability due to its definition in terms of the one-point probability density function of contaminant concentration an d recent advances in predicting the moments of that probability densit y function. Experiments from the Warren Spring Laboratory are used to illustrate the application of the ''expected mass fraction''.