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

C.3 CAMX SENSITIVITY TESTS
Following the general design of the study for the ETEX tracer database, CAMx sensitivity tests
described in Section 6.4.3, thirty‐two CAMx sensitivity tests were conducted to investigate the
effects of vertical diffusion, horizontal advection solvers and use of the sub‐grid scale Plume‐in‐
Grid (PiG) module on the model performance for the CAPTEX tracer experiment releases 3 and
5. In addition to the sixteen sensitivities conducted for ETEX, a similar set of sensitivity analyses
were conducted using the newer ACM2 vertical diffusion scheme (Pleim, 2007; ENVIRON, 2010)
introduced into CAMx as of Version 5.20 as an alternative to the more traditional fully K‐theory
vertical diffusion schemes that were the only options available in previous versions of CAMx.
C.3.1 SPATIAL PERFORMANCE FOR CTEX3 NOPIG EXPERIMENTS
Figure C‐7 displays the CAMx spatial model performance statistics for the sensitivity tests that
were run without using the PiG subgrid‐scale puff module. For the FMS statistic, the ACM2,
TKE, and CMAQ Kz exhibit very similar performance (40.9%, 40.9%, and 39.4% respectively).
OB70 exhibits the poorest performance with 33.5% for FMS.
For the FAR statistic, ACM2/Bott has the best score (55.6%) followed by TKE/PPM and
ACM2/PPM (tied at 58.5%). Overall ACM2 is the best performing vertical diffusion formulation
and PPM performs better than BOTT for horizontal advection using the FAR statistic.
For the POD and TS spatial statistics, the CMAQ, TKE, and ACM2 vertical diffusion algorithms
perform similarly, and all are substantially better than the OB70 approach (15% lower than
other vertical diffusion schemes). ACM2/BOTT has the best TS score with 28.6% followed by
ACM2/PPM and TKE/PPM (tied at 28.33%). CMAQ/PPM exhibits the best POD score with 52.8%
followed by CMAQ/BOTT, ACM2/PPM, and TKE/PPM (tied at 47.2%). Consistent with the ETEX
spatial results, there are much smaller differences in the model performance using the two
advection solvers for the POD and TS statistics compared to differences between Kz options.
In summary, based on the spatial statistics, the ACM2, CMAQ, and TKE Kz algorithms appear to
be performing similarly, with the older OB70 option exhibiting much poorer overall
performance. The differences in vertical diffusion algorithms have a greater effect on CAMx
model performance than the differences in horizontal advection solvers.
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