IntroductionUrban and suburban neighborhoods present challenges for the prediction of pollutant dispersion due to the heterogeneity of building configurations which sets up irregular, complex wind patterns. There is a need to identify and quantify the relative importance of the dominant factors that affect the dispersion. There have been many studies on regular arrays of buildings to develop an understanding of the phenomena involved in urban dispersion, focusing on such factors as street canyon width, building aspect ratio, traffic, and orientation of street canyons to prevailing winds.1–5These studies have produced a better understanding of the importance of near-field effects on the initial dispersion of a plume arising from an urban source (e.g., traffic) within the street canyon. Several recent studies6–10have highlighted the effect variations in building height can have on the airflow patterns in urban areas. These variations enhance the transfer of momentum from the winds aloft into the building canopy and provide for the rapid vertical mixing of the pollutant from the street canyons. In this paper, we examine the effect of a single building that towers above a neighborhood of buildings of uniform height.A wind tunnel study was undertaken to supplement a field study performed in Brooklyn, NY, USA, designed to study the dispersion of pollutants from a line source in an urban neighborhood. Preliminary computational fluid dynamics (CFD) simulations were also performed to visualize the flow with greater resolution. This paper is the first of two papers describing flow and pollutant dispersion for an idealized scale model of the site (see also Brixeyet al.11). The field study, the Brooklyn Traffic Real-Time Ambient Pollutant Penetration and Environmental Dispersion (B-TRAPPED) study, was performed in May 2005 with the goal of improving the understanding of airflow patterns through a complex area to be able to predict the dispersion patterns of pollution from traffic and hazardous releases along the roadway.12–16The section of the city chosen for the study has fairly regular city block shapes comprising row houses with uniform heights and common backyards that form a courtyard. Adjacent to the major thoroughfare passing through the study area was one tall building that dominated the area. Standing 12 stories tall, it was significantly higher than the neighborhood row houses which were typically three stories tall. Upwind of the city block containing the tall building was an industrial dock area and Upper New York Harbor.The wind tunnel study was designed to provide insight into the flow patterns throughout the study area, supplementing the information gathered from a limited number of field instruments deployed in typical field studies. Numerical simulations were also performed to visualize the flow and concentration fields since the resulting velocity and concentration fields are computed throughout the whole domain. The goal of this study was to identify important flow phenomena in urban and suburban areas shown by both techniques.