Figure 1 - Modeling domain used in comparison analysis.
Surface meteorological stations are indicated by place name.
Rawinsonde stations are indicated by station number.
Elevations contours are in meters.
The concentrations of pollution calculated by the ARM3
were approximately an order of magnitude higher than those
calculated using MESOPUFF-II. Since this result was not
expected, the IWAQM undertook a series of model runs to
determine whether some of the fundamental differences in the
air quality model formulations were responsible for the
dramatic concentration differences or whether differences in
the generation of the meteorological fields were responsible.
First, both models were run in an inert mode; that is, the
options for calculation of chemical transformation and
deposition were turned off. The dissimilarities in results,
were again, essentially the same. It was considered that
differences in the results stemmed from the treatment of
complex terrain in the ARM3, either in the wind fields or the
plume dispersion and transport algorithms. Complex terrain
potentially has two effects when considering concentration
calculations from the ARM3 air quality model. First, under the
options selected for this series of tests of ARM3, the
dispersion of pollutants is enhanced by the effects of the
complex terrain. The second effect was the influence terrain
has on bringing the receptor closer to the plume elevation.
The first effect would have a tendency to lower the
concentration estimates, while the latter could potentially
increase the concentration estimates. Therefore, it was
decided to run the ARM3 without the plume height to receptor
correction included on the original runs. The removal of this
option had little effect on the concentrations calculated by
the model; this was not the expected result. Furthermore,
selecting the option within the ARM3 to use the MESOPUFF-II
dispersion parameters did not bring the modeled concentrations
3.3.2 Meteorological Processor Comparisons
Since different options in the air quality models, which
should force them to be nearly the same, could not account for
the discrepancies in the concentrations calculated in the
initial runs, the meteorological fields generated by the
models' respective processors were examined. Each model treats
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