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

appreciably closer.

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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