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

with APS, implementing the slug option decreases the tracer residence time of the 600 km arc
from 17 to 15 hours. However, using the PG dispersion option with APS, the tracer residence
on the 600 km receptor arc increased from 11 to 20 hours when the slug option is invoked using
the PG dispersion option.
Table 3‐16. Duration of time tracer resides on the GP80 600 km receptor arc (hours) for the
CALPUFF slug and puff splitting sensitivity tests.
Duration on 600 km Arc
Scenario MSLUG MSPLIT Time (Hours) Difference (%)
Observed
CALPUFF/CALMET
12
BASEA_CAL 0 0 7 ‐42%
BASEA_APS_CAL 0 1 7 ‐42%
BASEA_SLUG_CAL 1 0 15 +25%
BASEA_SLUG_APS_CAL 1 1
CALPUFF/MMIF
16 +33%
MMIF12_CAL 0 0 6 ‐50%
MMIF12_DPS_CAL 0 1 8 ‐33%
MMIF12_APS_CAL 0 1 17 +42%
MMIF12_SLUG_APS_CAL 1 1 15 25%
MMIF12_PG 0 0 7 ‐42%
MMIF12_DPS_PG 0 1 11 ‐8%
MMMIF12_APS_PG 0 1 11 ‐8%
MMIF12_SLUG_APS_PG 1 1 20 +67%
Table 3‐17 summarizes the plume fitting model performance statistics for the CALPUFF slug and
puff splitting sensitivity tests. For the CALPUFF/CALMET BASEA_CAL slug and puff splitting
sensitivity tests, the improvements in CALPUFF’s estimated tracer residence time on the 600 km
receptor arc when the slug option is invoked is accompanied by a further degradation in
CALPUFF’s ability to estimate the maximum concentrations (Cmax/Omax) as well as increasing
CALPUFF’s overestimate of the observed plume spread (σy) (~16,500 m) from ~120% (~35,000
m) without the slug option to over 250% (~60,000 m) with the slug option. The use of the slug
option also improves the angular offset of the plume centerline from off by ~18 degrees to off
by ~14 degrees. Finally, without using APS, CALPUFF’s CWIC performance is improved from a ‐
38% underestimation to a ‐12% underestimation, whereas with using APS the improvement in
CWIC performance due to using the slug option is less dramatic (‐31% to ‐25%)
Using the CALPUFF/MMIF modeling platform, the changes in the maximum (Cmax/Omax) and
plume spread model performance statistics due to the use of the slug option are much less than
seen with the BASEA CALPUFF/CALMET modeling platform. Use of the slug option using the
CALPUFF/MMIF platform increases the maximum concentrations slightly, whereas with the
CALPUFF/CALMET platform the slug option resulting in slight deceases in concentrations. The
use of puff splitting had little effect on the CALPUFF/MMIF estimated maximum concentrations
and resulted in slightly wider plume widths. The biggest effect puff splitting had on the
CALPUFF/MMIF model performance was for the plume centerline angular displacement that
improved from 16‐17 to 7‐8 degrees offset from observed due to the use of puff splitting (DPS
or APS). In fact, of all the CALPUFF sensitivity tests examined, CALPUFF/MMIF using puff
splitting is the best performing model configuration for estimating plume centerline location.
Puff splitting resulted in small improvements in CALPUFF’s ability to predict CWIC across the
600 km arc. But the slug option greatly improved CALPUFF/MMIF’s ability to reproduce the
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