SCIPUFF capabilities and application in hazard assessment

The turbulence closure methodology forming the basis of the diffusion model in SCIPUFF (Second-order Closure Integrated PUFF) will be discussed, along with the extension of the model to describe phenomena such as buoyant rise, dense gas effects, and liquid droplet evaporation. SCIPUFF uses the closure methodology to provide a probabilistic prediction of the concentration field based on the variance of the statistical fluctuations due to the random nature of turbulent diffusion. The representation of turbulent diffusivity in terms of measurable parameters such as velocity variance and correlation timescales provides a general approach that can be applied at a wide range of scales, from laboratory wind tunnel and short range surface layer to continental scales. Examples of model predictions and comparison with tracer experiment observations will be discussed. In addition to the publicly available version, which is listed as an Alternative Model under EPA Appendix W, SCIPUFF is also the transport and dispersion model in two DoD hazard assessment systems, DTRA's HPAC (Hazard Prediction and Assessment Capability) and the JPM Program of Record, JEM (Joint Effects Model). The use of SCIPUFF in these more comprehensive modeling systems will be described.