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

the amount of time that the tracer was observed on the 600 km receptor arc. The standard
application of CALPUFF for LRT applications is the puff model formulation rather than the slug
model formation, which is designed to better simulate a near‐source continuous plume. The
fact that the slug formulation is needed to produce reasonable CALPUFF model performance
for residence time on the 600 km receptor suggests that the findings of the 1998 EPA CALPUFF
evaluation study should be re‐evaluated.
In general, the CALPUFF/CALMET sensitivity tests that are based on CALMET using MM5 data
with no meteorological observations exhibit better plume fitting model performance statistics
for the 600 km receptors arc than when meteorological observations are used with CALMET.
The use of the slug option with CALMET/CALPUFF, which improved the plume residence time
statistics, degrades the maximum concentrations and plume width statistics, but improves the
plume centerline and CWIC average plume concentration statistics. Puff splitting had little
effect on the CALPUFF/CALMET model predictions on the 600 km receptor arc. However, puff
splitting did improve the CALPUFF/MMIF plume centerline and CWIC average plume
concentration statistics, as well as the tracer residence time statistics. Puff splitting resulted in
a slight degradation of the plume width statistics in CALPUFF/MMIF. Using the slug option with
puff splitting in CALPUFF/MMIF results in the best performing CALPUFF model configuration of
all the sensitivity tests for the plume centerline and CWIC average plume statistics, although
the use of slug and puff splitting does degrade the plume width statistic.
54