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

MODEL PERFORMANCE EVALUATION OF LRT DISPERSION MODELS
The CALPUFF LRT dispersion model was evaluated using four tracer test field study
experiments. Up to five additional LRT models were also evaluated using some of the field
experiments.
1980 Great Plains (GP80) Field Experiment
The CALPUFF LRT dispersion model was evaluated against the GP80 July 8, 1980 GP80 tracer
release from Norman, Oklahoma. The tracer was measured at two receptor arcs located 100
km and 600 km downwind from the tracer release point. The fitted Gaussian plume approach
was used to evaluate the CALPUFF model performance, which was the same approach used in
the EPA 1998 CALPUFF evaluation study (EPA, 1998a). CALPUFF was evaluated separately for
the 100 km and 600 km arc of receptors.
GP80 CALPUFF Sensitivity Tests
Several different configurations of CALMET and CALPUFF models were used in the evaluation
that varied CALMET grid resolution, grid resolution of the MM5 meteorological model used as
input to CALMET, and CALMET and CALPUFF model options, including:
• CALMET grid resolution of 4 and 10 km for 100 km and 4 and 20 km for 600 km receptor
arc.
• MM5 output grid resolution of 12, 36 and 80 km, plus no MM5 data.
• Use of surface and upper‐air meteorological data used as input to CALMET:
‐ A = Use surface and upper‐air observations;
‐ B = Use surface but not upper‐air observations; and
‐ C = Use no meteorological observations.
• Three CALPUFF dispersion algorithms:
‐ CAL = CALPUFF turbulence dispersion;
‐ AER = AERMOD turbulence dispersion; and
‐ PG = Pasquill‐Gifford dispersion.
• MMIF meteorological inputs for CALPUFF using 12 and 36 km MM5 data.
The “BASEA” CALPUFF/CALMET configuration was designed to emulate the configuration used
in the 1998 EPA CALPUFF evaluation study, which used only meteorological observations and
no MM5 data in the CALMET modeling and ran the CALPUFF CAL and PG dispersion options.
However, an investigation of the 1998 EPA evaluation study revealed that the slug near‐field
option was used in CALPUFF (MSLUG = 1). The slug option is designed to better simulate a
continuous plume near the source and is a very non‐standard option for CALPUFF LRT
dispersion modeling. For the initial CALPUFF simulations, the slug option was used for the 100
km receptor arc, but not for the 600 km receptor arc. However, additional CALPUFF sensitivity
tests were performed for the 600 km receptor arc that investigated the use of the slug option,
as well as alternative puff splitting options.
Conclusions of GP80 CALPUFF Model Performance Results
For the 100 km receptor arc, there was a wide variation in CALPUFF model performance across
the sensitivity tests. The results were consistent with the 1998 EPA study with the following
key findings for the GP80 100 km receptor arc evaluation:
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