Introduction of a Puff-Particle Approach for Near-Source Dispersion into the Calpuff Model

Abstract

CALPUFF is a Lagrangian puff dispersion model for pollutant transport simulations for inhomogeneous and non-stationary conditions using a one-hour time step. Using so-called „absolute dis-ersion“ parameterizations, the model predicts one-hour-averaged concentrations. In order to be able to predict not only „average“ but also „possible“ concentrations, i. e. the higher moments of the concentra-tion 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. For this, the concept of the Puff-Particle Model (PPM) is introduced as a new near-source dispersion model within dispersion models such as CALPUFF. The PPM combines the advantages of both, puff and par-ticle dispersion models by moving the center of mass of each puff along a trajectory which mimics the quickly changing turbulent flow field (artificial meandering). This trajectory is derived from the low-frequency part of trajectories as simulated by a Lagrangian stochastic particle model. It allows for a new puff-plume meandering scheme. The combination of CALPUFF and PPM improves the prediction of the highest possibly occurring near-source concentration, as well as the distance down-wind from the source where it occurs, while retaining the advantages of the CALPUFF model.