Documentation of the Evaluation of CALPUFF and Other Long ...

3.0 1980 GREAT PLAINS FIELD STUDY
3.1 DESCRIPTION OF 1980 GREAT PLAINS FIELD STUDY
LRT tracer test experiments were conducted in 1980 with the release of a perfluorocarbon and
sulfur hexafluoride tracers from the National Oceanic and Atmospheric Administration (NOAA)
National Severe Storms Laboratory (NSSL) in Norman, Oklahoma (Ferber et al., 1981). Two arcs
of monitoring sites were used to sample the tracer plumes; an arc of 30 samplers with a 4‐5 km
spacing located approximately 100 km from the release point that sampled at 45 minute
intervals and an arc of 38 samplers through Nebraska and Missouri located approximately 600
km from the release site that sampled at an hourly interval. Figure 3‐1 displays the locations of
the tracer release site and the monitoring sites on the arcs that are 100 km and 600 km
downwind of the source. Two experiments were conducted, one on July 8, 1980 that included
both the 100 km and 600 km sampling arcs and one on July 11, 1980 that only included the 100
km sampling arc. The July 8, 1980 tracer field experiment and subsequent Perfluoro‐Dimethyl‐
cyclohexane (PDCH) observed concentrations were used in this model evaluation study. The
PDCH tracer was released over a three‐hour period from 1900‐2200 GMT (1400‐1700 CDT) on
July 8, 1980 from an open field near the NOAA/NSSL.
3.2 MODEL CONFIGURATION AND APPLICATION
The CALPUFF modeling system uses a grid system consisting of an array of horizontal grid cells
and multiple vertical layers. Two grids must be defined in the CALPUFF model, a meteorological
grid and a computational grid. The meteorological grid defines the extent over which landuse,
winds, and other meteorological variables are defined in the CALMET simulation. The
computational grid defines the extent of the concentration calculations in the CALPUFF
simulation, and is required to be identical to or a subset of the meteorological grid. For the
GP80 simulations, the computational grid is defined to be identical to the meteorological grid.
A third grid, the sampling grid, is optional, and is used by CALPUFF to define a rectangular array
of receptor locations. The sampling grid must be identical to or a subset of the computational
grid. It may also be nested inside the computational grid (i.e., several sampling grid cells per
computational grid cell). For the GP80 applications, a sampling grid identical to the
computational grid was used with a nesting factor of one (sampling grid cell size equal to the
cell size of the computational grid).
To properly characterize the meteorology for the CALPUFF modeling system, a grid that spans,
at a minimum, the distance between source and receptor is required. However, to allow for
possible recirculation of puffs that may be transported beyond the receptors and to allow for
upstream influences on the wind field, the meteorological and computational domains should
be larger than this minimum.
The GP80 site is shown in Figure 3‐1. Two arcs of monitors were deployed during the field
experiment at 100 and 600 kilometers from the source. For this analysis, two separate
modeling domains were defined for simulating tracer concentrations on the 100 km and 600
km receptor arcs. For the 100‐kilometer arc, a grid extending approximately from 35º N to
36.5º N latitude and from 96º W to 98.5º W longitude was defined.
CALPUFF was operated for the July 8, 1980 GP80 tracer experiment using meteorological inputs
based on CALMET and MMIF. For the CALPUFF simulations using CALMET, a UTM coordinate
system was used to be consistent with past CALPUFF evaluations (Policastro et al., 1986; EPA,
1998a).
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