Second-order Closure Integrated Puff (SCIPUFF) model with gas and aqueous phase chemistry and aerosols

Reactive plume models are often used to estimate the local or short- to medium-range (i.e., up to a few hundred km) impacts of power plants or smelters on air quality. Issues of interest typically include ozone and particulate matter concentrations above the National Ambient Air Quality Standards (NAAQS), visibility degradation and acid deposition. These models use detailed gas-phase mechanisms to describe the chemical transformations. Significant chemical conversion can also occur in cloud or fog droplets, for example, the conversion of SO2 to sulfate. In addition, the atmospheric removal of a species in the particulate phase can differ significantly from that of the gas phase. Therefore, it is important to treat both aqueous and aerosol chemistry in reactive plume models. Although other existing plume models do treat these phenomena, they lack in their treatment of plume dispersion and their ability to treat the chemistry of interacting plumes. The Second-order Closure Integrated Puff model (SCIPUFF) is a state-of-the-science Lagrangian atmospheric transport and diffusion model that uses a collection of three-dimensional Gaussian puffs to represent an arbitrary time-dependent concentration field. Second-order turbulence closure is used to parameterize turbulent diffusion in the model, providing a direct connection between measurable velocity statistics and the predicted dispersion rates. This allows an accurate treatment of dispersion and the influence of turbulence on chemical rates. SCIPUFF has recently been enhanced to incorporate detailed gas-phase chemistry mechanisms. The combined puff and gas-phase chemistry model, referred to as SCICHEM, was recently evaluated using data from the 1995 Southern Oxidants Study (SOS) Nashville/Middle Tennessee Ozone Study. SCICHEM has now been expanded to include the treatment of aqueous-phase chemistry and gas-particle partitioning. Existing modules for aqueous-phase chemistry and aerosol thermodynamics were implemented within the SCICHEM framework. The enhanced model was then tested for a range of conditions to ensure that model results were physically and chemically consistent. The model will be evaluated against existing data in future work.