A new mixed segment-puff approach for dispersion modeling

This paper presents a new mixed methodology for realistic and cost-effective simulation of shortterm air quality dispersion phenomena using the Gaussian formula. The method can be applied to shortrange, intermediate and, especially, long-range transport simulations. Pollutant dynamics are described by the temporal evolution of plume elements, treated as segments or puffs according to their size. While the segments provide a numerically fast simulation during transport conditions, the puffs allow a proper simulation of calm or low-wind situations.The methodology is incorporated into a computer package (AVACTA II, Release 3) that gives the user large flexibility in defining the computational domain, the three-dimensional meteorological and emission input, the receptor locations, and in selecting plume rise and sigma formulas. AVACTA II provides both pollutant concentration fields and dry/wet deposition patterns. The model uses linear chemistry and is applicable to any two-species reaction chain (e.g., SO₂ and SO²⁻₄) where this approximation is reasonable and an appropriate reaction rate is available.