EPA - Near Roadway Tracer Study (2008)
The Field Research Division conducted a tracer field experiment sponsored by the
U.S. Environmental Protection Agency (EPA) at the Idaho National Laboratory (INL) during
October 2008. The Near Roadway Tracer Study was designed to quantify the effects of
roadside barriers on the downwind dispersion of atmospheric pollutants emitted by roadway
sources (e.g. vehicular transport). Pollutant transport and dispersion was measured
during the field tests using sulfur hexafluoride (SF6) tracer gas as a pollutant surrogate.
The turbulence field driving the dispersion was also measured. The ultimate goal was to
produce a dataset that could be used to guide development of the application of the
AMS/EPA Regulatory Model AERMOD to roadway emissions.
Aerial view of the Grid 3 study domain.
Generate an atmospheric tracer and turbulence dataset that can be used to model
pollutant dispersion around and downwind of roadway barriers.
Gather dispersion data over a wide range of atmospheric stability conditions. At least
one, and possibly two tracer release experiments will each be conducted in unstable, neutral,
and stable conditions.
Execute a concurrent experiment identical in every way except no barrier will be used.
The purpose is to have a non-barrier control or reference for comparison with the barrier
component of the experiment. The line source, bag sampling, and mobile fast response analyzer
measurements will all be identical. The only differences will be the lack of a barrier and
only one sonic anemometer will be deployed at the non-barrier site to provide data on the
The mock sound barrier was constructed of 300 1-ton straw bales and was 6 m
in height and 90 m in length.
FRD conducted five 3-hour tracer field tests in various conditions of atmospheric stability.
The experiment was conducted in the pristine environment of the INL to enable clearer and
less ambiguous interpretation of the data. Roadway emissions were simulated by release of an
atmospheric tracer (SF6) from two 54 m long line sources. A 90 m long, 6 m high mock
sound barrier constructed of straw bales was installed on one grid while the other grid had no
barrier. Simultaneous tracer concentration measurements were made with 2 real-time and 58 bag
samplers on each of the identical sampling grids downwind from the two line sources. An array
of 6 sonic anemometers were employed to measure the barrier-induced turbulence. Supporting
meteorological measurements came from infrastructure already in place at the test site including
a radar wind profiler with RASS, a mini sodar, an eddy flux station, and nearby NOAA/INL Mesonet
stations. The results will augment those of a wind tunnel study conducted by the U.S. EPA in a
similar manner to this field study.
Key findings of the study are: (1) the areal extent of the concentration footprint
downwind of the barrier was a function of atmospheric stability with the footprint
expanding as stability increased; (2) normalized concentrations were a function of
atmospheric stability, increasing in magnitude as atmospheric stability increased;
(3) there was a concentration deficit in the wake zone of the barrier with respect
to concentrations at the same grid locations on the non-barrier side at all atmospheric
stabilities; (4) lateral dispersion was significantly greater on the barrier grid than
the non-barrier grid; and (5) the barrier tended to trap high concentrations in the
“roadway” (i.e. upwind of the barrier) in low wind speed conditions, especially in
SF6 release site and miscellaneous pictures.
Poster presented at the 2009 AMS Conference.
Clawson, K.L., R. Eckman, R.C. Johnson, R.G. Carter, D. Finn, J.D. Rich, N.F. Hukari, T. Strong, S.A. Beard,
B.R. Reese, 2009: Near Roadway Tracer Study (2008). NOAA Technical Memorandum OAR ARL-260 , Air Resources Laboratory, Idaho Falls,
Idaho. 212 pp.
Clawson, K. L., D. Finn, R. G. Carter, J. D. Rich, R. M. Eckman, S. G. Perry, V. Isakov, D. K. Heist,
and T. Pierce, 2010: NOAA EPA Near-Roadway Sound Barrier Atmospheric Tracer Study 2008. Chapter 1.5, in Air Pollution
Modeling and its Application XX, edited by D. G. Steyn, and S.T. Rao, pp. 27-31, Springer, New York.
Clawson, K.L., R. Eckman, T. Pierce, R. Carter, D. Finn, S. Perry, and
V. Isakov, 2009: 2008 Roadway Sound Barrier Atmospheric Tracer Study.
Eighth Symposium on the Urban Environment, Special Symposium on Measurements in the
Urban Environment and Observations. Phoenix, AZ, Amer. Meteor. Soc., JP1.6.
Clawson, K.L., D. Finn, R.G. Carter, J.D. Rich, R.M. Eckman, S.G. Perry, V. Isakov, D.K.
Heist, and T. Pierce, 2009: NOAA EPA Near-roadway Sound Barrier Atmospheric Tracer Study
2008. International Technical Meeting on Air Pollution Modeling and its Application, 30th
NATO/SPS International Technical Meeting on Air Pollution Modelling and its Application. 18-22 May, 2009, San Francisco.
Finn, D., K.L. Clawson, R.G. Carter, J.D. Rich, R.M. Eckman, S.G. Perry, V. Isakov, and
D.K. Heist, 2010: Tracer studies on the effects of roadside noise barriers on near-road pollutant
dispersion in varying atmospheric stability conditions. Atmospheric Environment (2010), vol. 44, p. 204-214.
(Published online in November, 2009)
Perry, S.G., D.K. Heist, V. Isakov, T. Pierce, K.L. Clawson, and R. Eckman, 2009 Near-roadway
Tracer Study 2008. International Technical Meeting on Air Pollution Modeling and its Application, 30th NATO/SPS International
Technical Meeting on Air Pollution Modelling and its Application. 18-22 May, 2009, San Francisco.
Pierce, T., D. Heist, V. Isakov, S. Perry, K. Clawson, and R. M. Eckman, 2010: Towards an improved
characterization of dispersion near major roadways. Chapter 1.16, in Air Pollution Modeling and its Application XX,
edited by D. G. Steyn, and S.T. Rao, pp. 95-98, Springer, New York.
Vette, A., R. Williams, T. Barzyk, L. Baxter, R. Baldauf, V. Isakov, D. Olson, S. McDow, S. Kimbrough,
R. Shores, D. Whitaker, C. Croghan, G. Norris, J. Hirtz, V. Martinez, K. Black, S. Perry, D. Heist,
T. Pierce, K. Clawson, R. Eckman, G. Hagler, I. Gilmour, L. Neas and D. Costa, 2009:
Near-Road Research at EPA, 2009 Bernstein Symposium - Air Toxics Workshop University of Michigan, Ann Arbor May 6-7.
1750 Foote Dr.
Idaho Falls, ID 83402