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

Figure 4‐2. Comparison of predicted fitted plume with observations for the SRL75 tracer
experiments (Source: EPA, 1998a). Note that results from this study are not shown.
With the exception of the plume centerline statistic, the Irwin plume fitting evaluation
approach was not a very useful evaluation tool for comparing the model predictions and
observations using the SRL75 field experiment data. However, it is a useful tool for comparing
the CALPUFF simulations using the different versions of CALPUFF/CALMET. The BASE
CALPUFF/CALMET sensitivity test in this study was designed to be setup in the same fashion as
the 1998 EPA tracer modeling study. Although there are some similarities, there are also some
differences. For example, using the PG dispersion results in much higher CWIC in both the 1998
EPA (129,000 ppt/m 2 ) and BASE (127,400 ppt/m 2 ) sensitivity tests versus using the CAL
turbulence/similarity dispersions options (77,000 ppt/m 2 for 1998 EPA and ~58,000 ppt/m 2 for
BASE). The maximum estimated concentration at any of the 200 receptors along the 100 km
arc using the PG dispersion are very similar for the 1998 EPA (6.9 ppt) and BASE sensitivity (6.7
ppt) scenario and lower concentrations are estimated using the CAL turbulence dispersion in
the 1998 EPA (5.0 ppt) and the BASE (3.2 ppt) sensitivity test.
4.5 CONCLUSIONS OF THE SRL75 MODEL PERFORMANCE EVALUATION
Because the fit of the Gaussian plume to the observed tracer concentrations along the SRL75
100 km receptor arc did not match the observed values well, the fitted plume evaluation
approach did not work well using the SRL75 database. Thus, there are few conclusions that can
be drawn about the CALPUFF model performance using the SRL75 tracer field experiment data.
The plume centerline evaluation is still valid and the use of CALPUFF without using
meteorological observations with CALMET either through MMIF or with CALMET using no
observations (NOOBS = 2) produces better plume centerline performance than when
meteorological observations are used with CALMET. These results are consistent with EPA’s
thoughts in the 2009 IWAQM Reassessment Report (EPA, 2009a) and August 2009 Clarification
Memorandum (EPA, 2009b); it is better to pass through the wind fields and other
meteorological field from MM5/WRF to CALPUFF, rather than running them through CALMET,
which can introduce artifacts and upset the dynamic balance of the meteorological fields.
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