The EPA Fluid Modeling Facility’s contributions to the understanding of atmospheric dispersion

Over the past thirty years, scientists at the Environmental Protection Agency's (EPA) Fluid Modeling Facility (FMF) have conducted laboratory studies of fluid flow and pollutant dispersion within three distinct experimental chambers: a meteorological wind tunnel, a water-channel towing tank, and a convection tank. The laboratory is staffed by both National Oceanic and Atmospheric Administration (NOAA) and EPA scientists and technicians with the collaborative mission of advancing our understanding of atmospheric dispersion. Experimental studies within the FMF laboratory have produced more than 250 publications and reports contributing directly to the development and improvement of many of EPA's and NOAA's numerical models of pollutant transport and diffusion. Studies include simulations of flow around stacks, buildings and building arrays, within complex topography, within and around surface coal mines and within model urban areas. Pollutant tracers are emitted from continuous point and area sources and from instantaneous-type releases for buoyant, neutral, and dense gases. With use of the three chambers, scaled atmospheric stability is varied from stable to neutral to convective. In addition to studies of more general scientific design, the laboratory engages in source-specific and site-specific experiments to support particular environmental concerns of the Agency. These have included an examination of dispersion of pollutants from a municipal incinerator within a deep river valley, the downwash and re-entrainment of routine releases from EPA's new research facility in North Carolina, and the dispersion of gases and particles from the collapsed World Trade Center.

Following the evolving needs of NOAA and EPA, in the mid-1990s the laboratory began to shift away from studies of flow and dispersion around individual buildings and terrain features to that within complex building arrays as they relate to urban and suburban areas. Since 2001, the laboratory focus has been extended to include concerns of homeland security. Urban experiments have included examination of regular arrays of cubical buildings to site specific studies of Lower Manhattan and the area around the Pentagon building near Washington D.C. It is expected that the focus of the FMF work will remain on urban flows and homeland security issues over the next few years.

In summary, this paper will include a discussion of the FMF mission, a description of the facility and its capabilities, and a brief overview of the FMF history and the variety of flow and dispersion studies that have been undertaken. Some of the more significant scientific findings and how they have influenced applied dispersion models will be described. Recent studies as well as planned experiments concerning urban dispersion issues will also be described.