Volume 1 - The Atmospheric Studies Group at TRC

that are simulated during the one-hour sampling period. The peak simulated
concentration on each sampling arc is retained for comparison with the corresponding
peak observed concentration. Because the sampling period spans two simulation
hours on May 16 th (1330-1430) and May 18 th (1220-1320), the appropriate simulation
hour is ambiguous. For these two experiments, the peak one-hour concentration from
the two-hour simulation period that contains the sampling hour is selected for each
arc.
Tracer emissions are characterized as non-reacting passive Gaussian puffs with no
plume rise. Turbulence-based dispersion is selected, with the default transition to
Heffter curves for σ y at σ y = 550m. The Draxler F y function is selected for lateral
cloud growth with the standard CALPUFF turbulence profiling assumptions. Default
plume-path-coefficient terrain adjustments are used. The subgrid TIBL option is
used here to better resolve its onshore development because the grid resolution is 1
km.
For each of the 4 CALMET configurations, two CALPUFF configurations are run to
identify the performance impact of using a minimum σ v = 0.5 m/s (CALPUFF
default) versus σ v = 0.37 m/s (OCD default).
Evaluation Statistics
The evaluation focuses on the peak observed concentrations each hour, paired in time
but not in space. As in the OCD applications, the wind direction used in the
CALMET input files for the OCD4 datasets (Carpinteria, Cameron, Pismo Beach and
Ventura) is that which is directed from the source to the sampler with the peak
concentration. Unlike OCD, this may not align the center of the CALPUFF footprint
with a sampler location due to changes in the transport direction (CALPUFF
trajectories are not straight lines). Therefore, additional receptors are placed along
the sampling arcs in the OCD4 datasets to better resolve peak modeled
concentrations within the sampling zone. Spacing for additional receptors along
sampling lines is typically 100 m or less. For the Oresund simulations, wind
directions are used as measured (adjusted for grid North), and no additional receptors
are used.
Model predictions are quantitatively compared against measured concentrations and
the resulting performance measures are compared with those for OCD5 (Carpinteria,
Cameron, Pismo Beach and Ventura). The original OCD4 input files are recast for
OCD5, and the revised OCD model is rerun on these data. Using the peak observed
(Co) and peak modeled (Cp) concentrations each hour, the evaluation measures are
computed from ln(Co/Cp). This gives equal weight to overpredictions and
underpredictions (e.g., ln(Co/Cp) for Co/Cp = ½ and two are equal in magnitude but
of opposite sign). The performance measures are the geometric mean (MG),
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