Extended Abstract (576K)6.2
Initial application of a coupled LES-photochemical model to examine near-source ozone production from industrial emissions
Jerold A. Herwehe, NOAA/ARL/ATDD, Oak Ridge, TN; and R. T. McNider, A. P. Blazar, and R. K. Decker
Turbulent mixing via large eddies in the daytime convective boundary layer (CBL) can either enhance or retard individual photochemical reaction rates, depending on the chemical lifetime and segregation of the trace gas reactants. The LESchem model was built by integrating the SMVGEAR II (Sparse-Matrix Vectorized Gear) chemistry solver into the RAMS (Regional Atmospheric Modeling System) mesoscale model for the purpose of conducting large-eddy simulations (LES) with reactive photochemistry in the turbulent CBL. LESchem is a directly coupled (on-line) model that computes the LES dynamics and chemical transformations together each time step. An updated Carbon Bond Mechanism - Version IV (CB4) chemistry mechanism (with 81 kinetic reactions and 12 photolysis reactions for 39 chemical species) was used in LESchem to examine the photochemistry near an industrial source. The numerical studies reported here are idealized coupled simulations of the midday CBL with a specified mean wind on a 10 km by 20 km by 4 km domain using a grid spacing of order 100 m. The Mahrer-Pielke radiation scheme, a multi-layered soil model and a vegetation parameterization were used to determine the surface energy balance and drive the convection. Photolysis rates (J values) were computed at a specified time interval using the Tropospheric Ultraviolet and Visible (TUV) radiation model from the National Center for Atmospheric Research (NCAR). Initial meteorological soundings and initial trace gas mixing ratio profiles were based on observational data plus gridded results from a pertinent CAMx model regional air quality simulation. Representative background biogenic and anthropogenic emissions were specified uniformly over the bottom domain surface. One or more point sources of heat and pollutants (such as ethylene or propylene, NO, and NO2) representing industrial flare stacks were added to the background simulation scenario. These coupled LESchem model results were analyzed in the context of near-source ozone production and will be presented. Many industrial complexes have process emissions of volatile organic compounds released separately from combustion-based NOx emissions. A crucial question in air quality modeling is whether emissions released into different parts of the large eddy structure affect ozone production rates and near and far downwind ozone levels. Using the coupled LESchem model the impact of separation of sources is examined.
Session 6, Chemical Processes and Dispersion
Tuesday, 16 July 2002, 10:30 AM-12:30 PM
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