Cross Appalachian Tracer Experiment - CAPTEX

The need to develop economical methods to test atmospheric transport and dispersion models at distances of 100's to 1000's of kilometers led to the development of a unique methodology using perfluorocarbon tracers (PFTs). Most of the tracer development was coordinated by NOAA and sponsored by the U.S. Department of Energy and its Brookhaven National Laboratory and Environmental Measurements Laboratory. The PFTs permit the controlled release of small amounts of tracer for each experiment, generally in the range of 10's of kg/hr, which due to its low and stable ambient background concentration, results in detectable air concentrations at great distances from the source.

The first in the series of experiments (sometimes called Pre-CAPTEX), consisted of two releases from Norman, Oklahoma, on July 8th and July 11th, 1980. Sampling arcs were placed at 100 and 600 km from the source. Because this was the first experiment, two different PFTs as well as SF6 and Methane 20 and 21 were released simultaneously to test the accuracy and precision of the entire tracer system. The sampling results showed that perhaps one of the most interesting features was the strong nocturnal jet that formed during the night transporting the tracer to the 600 km sampling arc sooner than expected, i.e. prior to the time the samplers were preprogrammed to start.

Research Summary

The next complete series of experiments was conducted between September 18th and October 29 of 1983. The Cross-Appalachian Tracer Experiment (CAPTEX) consisted of 5 releases from Dayton, Ohio and 2 releases from Sudbury, Ontario. Each release was independent of the others and was conducted when the forecast was for the tracer to pass through the center of the sampling network. Samplers were placed at a variety of locations in the northeast US to distances of about 1000 km from Dayton. Although synoptic meteorological conditions were similar between releases at each location, there were large differences in the spatial concentration patterns - from narrow to wide. There was even a case of the tracer plume passing over the samplers without mixing to the surface.

     Release   Date      Hour-UTC  Amount-kg

     1-Dayton  18 Sep    1700      208
     2-Dayton  25 Sep    1700      200
     3-Dayton  02 Oct    1900      200
     4-Dayton  14 Oct    1600      200
     5-Sudbury 26 Oct    0400      180
     6-Dayton  28 Oct    1600       32
     7-Sudbury 29 Oct    0600      184

The Hysplit_4 model simulation of release #1 is shown in the illustrations below as 6-h averages (g/m3) for the first 24 hours after the release. The model calculation used the rawinsonde observations collected during the experiment.


Click HERE for a gif movie (58K) of this simulation.

Future Activities

The experimental data will be integrated into a master data base of all ARL sponsored long-range tracer experiments available over the Web and on CD ROM. In conjunction with a standard set of meteorological fields, the concentrations will be used to test various dispersion modeling parameterizations. Click here to download data and reports.

References

Draxler, R.R., and B.J.B. Stunder, 1988: Modeling the CAPTEX vertical tracer concentration profiles. J. Appl. Meteorol., 27:617-625.

Ferber G.J., J.L. Heffter, R.R. Draxler, R.J. Lagomarsino, F.L. Thomas, R.N. Dietz, and C.M. Benkovitz, 1986: Cross-Appalachian tracer experiment (CAPTEX-83), Final Report. NOAA Tech. Memo ERL ARL-142, Air Resources Laboratory, Silver Spring, MD, 60 p.

Ferber G.J., K. Telegadas, J.L. Heffter, C.R. Dickson, R.N. Dietz, P.W. Krey, 1981: Demonstration of a long-range atmospheric tracer system using perfluorocarbons - final report, EPA-600/7-81-006, U.S EPA Office of Research and Development, Washington, D.C., January, 55 p.