For risk assessments and odor impact analyses, the highest possibly occurring
concentration during a time considerably shorter than one hour is more decisive than
one-hour average values. For this, the probability density function of
concentration for a given location and a specific averaging time is required.
In order to be able to predict the higher moments of concentration (the
probability density function), the "absolute dispersion" has to be separated
in its puff-growth part and the additional contribution from the meandering
of the plume during the averaging time. The Puff-Particle Model (PPM) has
been developed as such a puff-meandering model.
Follow this link for more information on the modeling of concentration