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Cheryl Klipp

1. Introduction The complexity of urban environments makes interpretation of urban boundary layer data difficult at best, yet it is in urban and suburban areas where the largest population impacts of pollution and accidental releases of hazardous substances occur. The surface heterogeneity produces a complex vertical layering of multiple internal boundary layers and a horizontal patchwork of local microclimates ( Oke 1995 ). The atmosphere immediately above these heterogeneities is not a

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Donald A. Burrows, Eric A. Hendricks, Steve R. Diehl, and Robert Keith

initialization Currently, RUSTIC has three options for initialization. The simplest option uses only wind direction and wind speed at a reference height together with a specified surface roughness and displacement height. A one-dimensional boundary layer model is then used to calculate the vertical profiles of wind speed, turbulent kinetic energy, and specific dissipation, taking into account the vertical heat flux in the upwind environment, which may be specified in the input file as simply stable, unstable

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Steve R. Diehl, Donald A. Burrows, Eric A. Hendricks, and Robert Keith

the size of the smallest building of interest. To initialize the grid and to supply the wind profile and turbulence energy and dissipation at the inflow boundary, a 1D numerical algorithm that contains the k – ω turbulence equations is included. The algorithm computes the flow as a function of altitude over a rough surface based on the sensible heat flux and surface roughness. RUSTIC can be run with an upwind heat flux that differs from the heat flux value around the larger buildings. 3. MESO

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Eric A. Hendricks, Steve R. Diehl, Donald A. Burrows, and Robert Keith

accurate but generally more computationally expensive. Currently, there are limited field data in urban environments that can be used to evaluate the performance of these dispersion models. Thus, their utility for hazard prediction is relatively unknown. The Joint Urban 2003 Atmospheric Dispersion Study (JU2003) was completed to address this data void. It was sponsored by the United States Defense Threat Reduction Agency and the Department of Homeland Security and conducted in July 2003 in Oklahoma

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Stevens T. Chan and Martin J. Leach

) . In addition to model evaluation studies, our model has also been used to investigate the effects of inflow turbulence on dispersion scenarios involving nighttime releases under light and highly variable winds, such as the case of intensive operation period (IOP) 7 of the Urban 2000 experiment ( Allwine et al. 2002 ). Through a series of controlled numerical experiments with variations in time-dependent forcing and turbulence intensity from the inflow boundary, Chan and Leach (2004) demonstrated

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Julia E. Flaherty, Brian Lamb, K. Jerry Allwine, and Eugene Allwine

, large-scale dispersion studies have been performed for more complex settings. These include the Dispersion of Air Pollution and its Penetration into the Local Environment (DAPPLE) field experiment in London ( Arnold et al. 2004 ), which studied a street canyon intersection as a potential hot spot for personal exposure; the Basel Urban Boundary Layer Experiment (BUBBLE), conducted in Basel, Switzerland ( Rotach et al. 2004 ), which investigated dispersion over a fairly regular array of buildings

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