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APPLICATION OF CFD SIMULATIONS FOR SHORT-RANGE ATMOSPHERIC DISPERSION OVER OPEN FIELDS AND WITHIN ARRAYS OF BUILDINGS
Citation:
TANG, W., A. H. HUBER, B. BELL, AND W. SCHWARZ. APPLICATION OF CFD SIMULATIONS FOR SHORT-RANGE ATMOSPHERIC DISPERSION OVER OPEN FIELDS AND WITHIN ARRAYS OF BUILDINGS. Presented at 14th Joint Conference on the Applications of Air Pollution Meteorology, A&WMA, Atlanta, GA, January 30 - February 02, 2006.
Impact/Purpose:
The objective of this task is to improve EPA's ability to accurately predict the concentrations and deposition of air pollutants in the atmosphere that are known or suspected to cause cancer or other serious health effects to humans, or adverse environmental effects. It is an essential component of EPA's National Air Toxics Assessment (NATA), which seeks to identify and quantify the concentrations and sources of those hazardous air pollutants which are of greatest potential concern, in terms of contribution to population risk. It is a major contributor to NERL's Air Toxics Research Program.
"Air toxics" or "hazardous air pollutants" (HAPs) is a category that covers a large variety of chemicals, which range from relatively non reactive to extremely reactive; can exist in the gas, aqueous, and/or particle phases; display a large range of volatilities; experience varying deposition velocities, including in some cases revolatilization; and are emitted from a wide variety of sources at a large variety of different scales. In addition, concentrations of air toxics are needed by regulators for both short (days) as well as long (up to a year) time scales. These requirements challenge our current capabilities in air quality models far beyond the needs for other pollutants, such as ozone. The specific work being done under this task involves 1.) developing and testing chemical mechanisms which are appropriate for describing the chemistry of air toxics; 2.) incorporating these chemical and physical mechanisms into EPA's CMAQ modeling system and applying the model at a variety of scales; and 3.) developing the methods for using models to predict HAPs concentrations at subgrid or neighborhood scales; and 4.) using these tools to assess the magnitude and variability of concentrations to which urban populations are exposed.
Description:
Computational Fluid Dynamics (CFD) techniques are increasingly being applied to air quality modeling of short-range dispersion, especially the flow and dispersion around buildings and other geometrically complex structures. The proper application and accuracy of such CFD techniques needs to be assessed. Part of the ongoing work has focused on the development of computer models and the evaluation of the performance of the FLUENT code in simulating: (1) the atmospheric boundary layer, (2) plume dispersion over an open field, and (3) dispersion within arrays of buildings. Case studies based on the Project Prairie Grass field program were used to develop and evaluate CFD simulations of plume dispersion over an open field under thermally neutral and unstable conditions. CFD predictions of arc concentrations were compared with measurements and results of the AERMOD dispersion model. Analyses for the near thermally neutral cases have been completed and are summarized herein. Analyses for the thermally unstable cases are ongoing therefore only a case study is presented. Simulations of dispersion around buildings are being evaluated with data from the Mock Urban Setting Test (MUST) field experiment. Methods for applying CFD simulations for these complex flow situations are being developed.