A new measure of the dilution of contaminant cloud concentration value
s is introduced. The expected-mass-fraction function is shown to have
both experimental and theoretical advantages. There are virtually no m
easurements of dilution for a contaminant cloud. A cloud in homogeneou
s turbulence is used as an illustrative example. These calculations ca
n be validated with conventional, fixed-point concentration measuremen
ts in a wind tunnel.