Development and evaluation of a state-of-the-science reactive plume model

We describe the development and evaluation of a new reactive plume model th at combines a state-of-the-science puff model with an optimized chemistry m odel that accurately represents the chemistry of a power plant plume at var ious stages of its evolution. The puff model uses a second-order closure sc heme, allowing for an accurate treatment of dispersion and the influence of turbulent concentration fluctuations on chemical rates. The model was test ed using helicopter plume measurements from the 1995 Southern Oxidants Stud y (SOS) Nashville/Middle Tennessee Ozone Study. The model was applied for 6 days in June and July of 1995, and the model's ability to estimate physica l and chemical plume characteristics, such as plume width and reactive spec ies concentrations, was evaluated using the helicopter measurements. The be st model results are for July 7, 1995, a case corresponding to a high NOx i solated power plant plume traveling over rural regions-model estimates of N Ox, NOy, and O-3 are highly correlated with measured values, and most of th e measured plume centerline concentrations are reproduced to within 30%. Fo r scenarios involving the interaction of the tracked plume with urban plume s or with other power plant plumes, model estimates of ozone concentrations are poorly correlated with observations, emphasizing the difficulty of cha racterizing such plumes from both measurement and modeling perspectives.