Why is a ground reflection term important for predicting near-ground concentrations?

Why is a ground reflection term important for predicting near-ground concentrations?

• A. Eliminates the reflection to simplify model.
• B. Increases plume rise.
• C. Introduces a ground-level reflection to keep near-ground concentrations nonzero.
• D. Adds random noise.

Answer: (C)

Ground-boundary effects: the ground acts as a boundary that alters how the plume distributes near the surface. The ground-reflection term adds a mirror image of the source across the ground, representing the portion of the plume that reflects off the surface. This keeps predicted concentrations near the ground nonzero and more realistic for receptors at or near the surface. Without this term, near-ground levels would be underestimated because the model would miss the reflected contribution. The term is not about random noise or increasing plume rise; those aspects are governed by other parts of the model.

Ground-boundary effects: the ground acts as a boundary that alters how the plume distributes near the surface. The ground-reflection term adds a mirror image of the source across the ground, representing the portion of the plume that reflects off the surface. This keeps predicted concentrations near the ground nonzero and more realistic for receptors at or near the surface. Without this term, near-ground levels would be underestimated because the model would miss the reflected contribution. The term is not about random noise or increasing plume rise; those aspects are governed by other parts of the model.