Generic Guidance and Optimum Model Settings for the CALPUFF ...

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Figure 3-10 CALPUFF peak, 1-hr average concentration map using 10-minute
meteorological data and default calm threshold of 0.5 m/s. Real turbulence parameters
were used with a minimum σv of 0.2 m/s, σw was left unchanged at the model’s default
values.
Various calm user options were evaluated for a single volume source and using either the 10minute
or 1-hour Caversham, WA meteorological data sets. The results are presented in Figure 3-
11. Both Figures 3-9 and 3-10 are shown a second time in Figure 3-11 for brevity. There is little
difference detected when lowering the minimum calm threshold < 0.5 m/s which forces the model
to step from distance to time based dispersion. In many instances 0.5 m/s is also the threshold of
the instrument. There is also little difference when using 1-hour meteorology and real turbulence
parameters when compared to the case using 1-hour meteorology and computed σv or, the case
using 10-minute meteorology and computed σv.
These results show that the single biggest difference is not the inclusion of the real time
turbulence data or the sub-hourly data but using a σv threshold of 0.2 m/s. Clearly the combined
effect of σv of 0.2 m/s, real turbulence parameters and sub-hourly meteorological data is the
preferred and most realistic option to treat calm and light wind periods, but in the event of not
having sub-hourly meteorological data, or real turbulence data there is still strong evidence to use
a σv value of 0.2 m/s overland (Barclay 2007).
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