Air motions in and around cities are very complicated and the increasing threat of toxic agents being released into urban atmospheres makes advancing the state-of-science of understanding and modeling atmospheric flows in and around cities essential. Quality-assured meteorological and tracer data sets are vital for establishing confidence that indoor and outdoor dispersion models used to simulate dispersal of potential toxic agents in urban atmospheres are giving trustworthy results. To provide this critically needed high-resolution dispersion data, the U.S. Department of Defense – Defense Threat Reduction Agency (DTRA) and the U.S. Department of Homeland Security (DHS) joined in an effort to conduct the Joint Urban 2003 atmospheric dispersion study in Oklahoma City, Oklahoma during July 2003. Numerous investigators from government laboratories, universities and private companies conducted the multi-million dollar Oklahoma City study. Additionally, several other U.S. federal agencies and foreign government agencies contributed to the study by providing support for additional investigators to participate.

This major urban study was conducted beginning June 28 and ending July 31, 2003. It included several integrated scientific components necessary to describe and understand the physical processes governing dispersion within and surrounding an urban area and into and within building environments. The components included characterizing: 1) the urban boundary layer and the development of the urban boundary layer within the atmospheric boundary layer, 2) the flows within and downwind of the tall-building core, 3) the flows within a street canyon including the effects of traffic on turbulence, 4) the surface energy balance within an urban area , 5) the dispersion of tracer into, out of and within buildings, and 6) the dispersion of tracer throughout the tall-building core and out to four km downwind from the release. The scientific elements of the study were accomplished using state-of-the-art meteorological and tracer instruments including lidars, sodars, radars, sonic anemometers, airplane-based meteorological sensors, fast-response tracer analyzers and helicopter-based remote tracer detectors. Winds and other meteorological quantities were measured continuously at nearly 200 locations in and around downtown Oklahoma City.

Ten intensive operation periods (IOPs) of 8-hours each were completed during the 34-day study period where detailed meteorological, turbulence and tracer measurements were made. Sulfur hexafluoride tracer was released in downtown Oklahoma City and sampled in and around downtown and as far as four km downwind. During four of the ten IOPs the infiltration of tracer into four downtown buildings was studied with detailed measurements of tracer and flows within and surrounding some buildings. Tracer was sampled using over 200 integrated samplers and 25 fast response analyzers. Vertical measurements of tracer were made by placing samplers on the tops of nearly 20 buildings and using a 90 m crane with tracer sampled at 7 levels.

An overview of the Joint Urban 2003 field study is presented identifying scientific objectives and the deployment of instruments to accomplish the scientific objectives. Examples of some tracer and meteorological measurements are given.