In Gaussian plume modeling, what does the term exp(-(z - H)^2/(2 σ_z^2)) represent?

In Gaussian plume modeling, what does the term exp(-(z - H)^2/(2 σ_z^2)) represent?

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

Answer: (C)

This term is the vertical Gaussian distribution that describes how the concentration from an emission located at height H is spread and diminishes with height difference. It forms the vertical shape factor of the plume, showing how concentration at height z falls off as the distance from the source height (z − H) increases, scaled by the vertical dispersion parameter σ_z. The larger σ_z is, the more the plume spread in the vertical, and the slower the concentration drops with height. If ground reflection is included, you’d also add a second similar term with (z + H) to represent particles that reflect off the ground and arrive at height z from an image source below the ground. That makes the total vertical profile the sum of the direct contribution and the reflected one. This exponential is not a wind speed correction, which would enter differently in the solution, nor a standalone vertical diffusive adjustment. It specifically encodes the direct vertical distribution of the plume from the source height.

This term is the vertical Gaussian distribution that describes how the concentration from an emission located at height H is spread and diminishes with height difference. It forms the vertical shape factor of the plume, showing how concentration at height z falls off as the distance from the source height (z − H) increases, scaled by the vertical dispersion parameter σ_z. The larger σ_z is, the more the plume spread in the vertical, and the slower the concentration drops with height.

If ground reflection is included, you’d also add a second similar term with (z + H) to represent particles that reflect off the ground and arrive at height z from an image source below the ground. That makes the total vertical profile the sum of the direct contribution and the reflected one.

This exponential is not a wind speed correction, which would enter differently in the solution, nor a standalone vertical diffusive adjustment. It specifically encodes the direct vertical distribution of the plume from the source height.