Modifications of Highway Air Pollution Models for Complex Site Geometries, Volume I: Data Analysis & Model Development
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2002-09-01
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Abstract:This study is an evaluation of flow patterns and dispersion of air contaminants for complex site geometries, such as semi-confined, cut-section highways and urban street canyons. Highway vehicle exhaust entrainment, air contaminant dispersion, and impacts from contaminants for such locations are in contrast to those noted from field, wind tunnel, and related models for flat, open sites and can be significantly important in environmental assessments. This research study was initiated by the Federal Highway Administration (FHW A) to explore the limits of flat, open site dispersion measurements and models, and to develop modified or new dispersion models for complex sites based upon flow, turbulence, and concentration data from full-scale and wind tunnel-scale studies for numerous complex geometries and other variables. After the investigation was underway, the Federal Aviation Administration (FAA) joined in sponsorship of this study because the FAA and the U.S. Air Force have concerns about the windperturbing characteristics of buildings at airports and air bases and about air quality and related impacts. Air contaminant problems at complex sites can also result from accidental or deliberate releases of toxic air contaminants. This investigation should also interest others concerned with airflows and dispersion of gases and contaminants. The report includes: • A review of what is known from flat terrain highway modeling and experimental studies. Consideration of the status of street canyon modeling, field studies, and wind tunnel studies. • Analyses of the experimental flow, turbulence, and concentration data obtained from this program to expand the useful validity range of the original Canyon Plume Box (CPB-I) developed by Dr. Yamartino and European experts for sites in Germany and The Netherlands. • Creation of a more comprehensive model, CPB-3, that can simulate cut-sections and street canyons having width-to-height ratios (W IH) ranging from Y.. to 6, geometries having unequal height sides, semi-open walls, and roadway curvature, and includes wind direction variability. (A disk with this program, CPB-3-6a [sixth release], is available.) • Evaluation of the applicability limits of this new model, CPB-3, relative to existing roadway models for open, flat terrain, which are usually satisfactory for most of the areas of cutsections and downwind of cut-sections with a W IH greater than 6.
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