Dispersion Characteristics of Project Sagebrush Phase 1

Most of the open-terrain tracer studies that researchers use for evaluating dispersion models at short ranges were conducted in the 1950s and 1960s. In fact, the Atomic Energy Commission's book Meteorology and Atomic Energy 1968 still provides a fairly complete review of the available studies as of 2012. Tracer experiments have of course continued since then, but they usually have been more narrowly focused on a specific issue or they were conducted in complicated environments such as cities or complex terrain. Overall, the quantity of open-terrain tracer data is limited, and the results do not always show consistency from one study to another. Nearly all of the studies predate the use of newer technology such as electron capture detection (ECD) for tracer measurements and sonic anemometers for turbulence measurements.

The Field Research Division (FRD) of the NOAA Air Resources Laboratory has undertaken a new series of tracer experiments to revisit short-range dispersion in open terrain. These studies, called Project Sagebrush, use modern meteorological instrumentation and tracer technology not available during the classical experiments. Project Sagebrush is taking place at the NOAA Tracer Test Facility located at the U.S. Department of Energy's Idaho National Laboratory (INL).

The field deployment portion of Phase 1 of Project Sagebrush was conducted in October 2013. Five tests of two-hour duration were conducted in neutral to moderately unstable atmospheric conditions. Approximately 130 bag samplers were deployed on 5 sampling arcs ranging from 200 to 3200 m from the point source. The samplers contained 12 bags that sampled the tracer plume for 10 minutes each. Five real-time tracer analyzers were also collocated with the bag samplers at key locations on the sampling arcs. Tracer dispersion characteristics, such as Sigma y have been calculated from the resulting database. These tracer dispersion characteristics have been compared with classical dispersion curves such as Pasquill-Gifford. These results will be presented and discussed in detail.