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

We describe the development and evaluation of a new reactive plume model that combines a state-of-the-science puff model with an optimized chemistry model that accurately represents the chemistry of a power plant plume at various stages of its evolution. The puff model uses a second-order closure scheme, allowing for an accurate treatment of dispersion and the influence of turbulent concentration fluctuations on chemical rates. The model was tested using helicopter plume measurements from the 1995 Southern Oxidants Study (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 physical and chemical plume characteristics, such as plume width and reactive species concentrations, was evaluated using the helicopter measurements. The best model results are for July 7, 1995, a case corresponding to a high NOx isolated power plant plume traveling over rural regions-model estimates of NOx, NOy, and O-3 are highly correlated with measured values, and most of the measured plume centerline concentrations are reproduced to within 30%. For scenarios involving the interaction of the tracked plume with urban plumes or with other power plant plumes, model estimates of ozone concentrations are poorly correlated with observations, emphasizing the difficulty of characterizing such plumes from both measurement and modeling perspectives.