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

particle hybrid (same used by the NOAA ARL for their ETEX evaluation) was used for the model
intercomparison (i.e., INITD = 104)
Note that the FLEXPART and HYSPLIT meteorological inputs were based on the 36 km MM5
meteorological model output, so they used the same transport conditions and resolution as the
other LRT models. The FLEXPART (~18 km) and HYSPLIT (~28 km) horizontal grid resolution is
used to convert the particles (mass) to concentrations (mass divided by volume).
CAMx was operated on a 148 x 112 horizontal grid with 36 km grid resolution with 25 vertical
layers up to a 50 mb pressure level (~15 km). CAMx is a photochemical grid model that includes
state‐of‐science gas, aerosol and aqueous phase chemistry modules and dry and wet deposition
algorithms. However, for the ETEX tracer modeling CAMx was operated with no chemistry and
no wet or dry removal mechanisms. The MM5CAMx processor was used to process the MM5
output to the variables and formats required by CAMx. CAMx has several options for vertical
mixing (from MM5CAMx), horizontal advection as well as a subgrid‐scale Plume‐in‐Grid (PiG)
module. Several alternative configurations of CAMx were investigated using sensitivity tests.
When comparing with the other LRT models, we used a CAMx configuration with the following
attributes, which are fairly typical for many CAMx simulations:
• CMAQ‐like vertical diffusion coefficients from MM5CAMx;
• Piecewise Parabolic Method (PPM) horizontal advection solver; and
• No PiG module.
6.3 QUALITY ASSURANCE
Quality assurance (QA) of the LRT dispersion runs was conducted by evaluating the MM5
meteorological model output against surface meteorological observations and by examining of
the LRT model inputs and outputs, as available, to assure that the intended options and
configurations were used.
6.3.1 Quality Assurance of the Meteorological Inputs
A limited statistical evaluation of the MM5 simulation for the ETEX period was conducted as
part of this evaluation. The meteorological observations collected at the 168 sampling stations
during the ETEX exercise were not used as part of the MM5 data assimilation strategy;
therefore, these observations could reliably be used to provide an independent evaluation of
the MM5 simulation.
MM5 model performance evaluation results are presented in Figure 6‐4. The MM5
performance statistics presented in Figure 6‐4 are compared to performance criteria typically
recommended for meteorological model applications for regional air quality studies in the
United States (Emery et al. 2001) that were presented previously in Table 5‐7. In general, MM5
verification scores indicate a persistent negative bias and higher error for both wind speed (‐
1.67 m/s and 4.73 m/s, respectively) and temperature (‐1.1 °K and 2.36 °K, respectively)
averaged across all 168 sites that are outside of target performance benchmark values for each
of these meteorological parameters. Wind direction bias and error were within the
performance benchmarks. Typically, these performance statistics would likely cause the
modeler to consider experimenting with additional physics configurations and/or altering the
data assimilation strategy to enhance meteorological model verification statistics. However,
the MM5 simulation was not optimized for this project for several reasons:
• First, from an operational perspective, the meteorological model errors are likely
consistent with the magnitude of model prediction errors that would have been
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