Puff Models

Instead of describing smoke concentrations as a steadily growing plume, puff models characterize the source as individual puffs being released over time. Each puff expands in space in response to the turbulent atmosphere, which usually is approximated as a Gaussian dispersion pattern. Puffs move through the atmosphere according to the trajectory of their center position. Because puffs grow and move independently of each other, tortuous plume patterns in response to changing winds, varying topography, or alternating source strengths can be simulated with some accuracy.

Some models allow puffs to expand, split, compact, and coalesce (Hysplit: Draxler and Hess 1998; Calpuff: Scire and others 2000a) while others retain coherent puffs with constantly expanding volumes (NFSpuff: Harrison 1995). In either case, the variability of puff generation, movement, and dispersion does not restrict the time or distance with which a plume can be modeled. Most puff models are computed in Lagrangian coordinates that allow accurate location of specific concentrations at any time.