5.1 Protocol for Level I Long Range Transport Analysis

The IWAQM is suggesting that a steady-state, Gaussian

plume model may be acceptable as a first level long range

transport analysis technique under many conditions. It is

anticipated that this first level technique will, under most

conditions, yield a conservative estimate of ambient air

quality concentrations. However, under conditions of extended

stagnation or where recirculation patterns or convergence zones

are known to occur, this Level I technique should not be used.

If a Level I analysis indicates that there are exceedances of

the appropriate parameters, the more refined analyses, using

the Level II long range transport models, should be run for all

meteorological conditions, not just those identified through

the Level I technique. Level I analyses will consist of

running the appropriate steady-state, Gaussian plume models

with five years of meteorological data. Steady-state Gaussian

plume models used for Level I long range transport analyses

should utilize bivariate plume dispersion factors. It is

generally anticipated that plume impaction models, utilizing

uniform horizontal plume dispersion, would not be appropriate

for a long range transport analysis.

While the IWAQM is suggesting a relatively simple, Level

I, technique, it should not be construed as an endorsement of

that approach. With limited testing, the suggested Level I

technique appears to yield higher ambient pollutant estimates

than the Level II procedures. However, if there is any

question about the technical veracity of using the Level I

technique in a given situation, then it is completely

appropriate to proceed directly to a Level II analysis.

In general, the steady-state Gaussian plume models will

yield a high estimate of concentrations at distances beyond 50

kilometers, due to the spatially varying paths of puffs in the

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