The exponent term exp(-(z - H)^2/(2 σ_z^2)) represents what aspect of the plume distribution?

The exponent term exp(-(z - H)^2/(2 σ_z^2)) represents what aspect of the plume distribution?

• A. Ground reflection term
• B. A wind speed correction
• C. The vertical diffusion term
• D. The direct plume concentration contribution at height z from an emission at height H

Answer: (D)

This term is the vertical shape of the plume in a Gaussian dispersion model. It encodes how concentrated the plume is at a height z given that the emission originates at height H. Because it’s a Gaussian centered at H, the concentration is highest when z equals H and then falls off as you move away from that height; the rate of spread is controlled by σ_z—the larger σ_z, the more the plume spreads vertically. This component specifically represents the direct contribution to concentration at height z from an emission at height H, not a ground reflection or a wind correction. Ground reflections would introduce additional terms to satisfy boundary conditions at the ground, and wind speed affects the overall dilution and transport, not this vertical shape term.

This term is the vertical shape of the plume in a Gaussian dispersion model. It encodes how concentrated the plume is at a height z given that the emission originates at height H. Because it’s a Gaussian centered at H, the concentration is highest when z equals H and then falls off as you move away from that height; the rate of spread is controlled by σ_z—the larger σ_z, the more the plume spreads vertically. This component specifically represents the direct contribution to concentration at height z from an emission at height H, not a ground reflection or a wind correction. Ground reflections would introduce additional terms to satisfy boundary conditions at the ground, and wind speed affects the overall dilution and transport, not this vertical shape term.