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

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Figure 6‐16d. Comparison <strong>of</strong> spatial distribution <strong>of</strong> <strong>the</strong> ETEX tracer concentrations 60 hours<br />

after release for <strong>the</strong> observed (top left), <strong>CALPUFF</strong> (top right), SCIPUFF (middle left), FLEXPART<br />

(middle right), HYSPLIT (bottom left) <strong>and</strong> CAMx (bottom right).<br />

6.4.3 CAMx Sensitivity Tests<br />

Sixteen CAMx sensitivity tests were conducted to investigate <strong>the</strong> effects <strong>of</strong> vertical diffusion,<br />

horizontal advection solvers <strong>and</strong> use <strong>of</strong> <strong>the</strong> sub‐grid scale Plume‐in‐Grid (PiG) module on <strong>the</strong><br />

model performance for <strong>the</strong> ETEX tracer experiment.<br />

Plume‐in‐Grid (PiG) Module: The PiG module treats <strong>the</strong> near‐source plume dispersion (<strong>and</strong><br />

chemistry if applicable) <strong>of</strong> a point source plume using a subgrid‐scale Lagrangian puff module.<br />

The mass from <strong>the</strong> PiG puff module is transferred to <strong>the</strong> grid model when <strong>the</strong> plume size is<br />

commensurate with <strong>the</strong> grid cell size used in <strong>the</strong> CAMx simulation. Two types <strong>of</strong> PiG sensitivity<br />

tests were conducted in this study to investigate <strong>the</strong> effects <strong>of</strong> <strong>the</strong> PiG module on model<br />

performance:<br />

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