What does the term exp(-y^2/(2 σ_y^2)) represent in the Gaussian plume model?

What does the term exp(-y^2/(2 σ_y^2)) represent in the Gaussian plume model?

• A. Vertical dispersion.
• B. Temporal decay.
• C. Chemical decay due to reactions.
• D. Lateral (crosswind) dispersion of the plume.

Answer: (D)

In the Gaussian plume model, the pollutant concentration is described by Gaussian spreads in both the crosswind (lateral) and vertical directions. The term exp(-y^2/(2 σ_y^2)) specifically comes from the crosswind, or lateral, Gaussian distribution. Here, y is the distance from the plume’s centerline in the crosswind direction, and σ_y is the standard deviation of the plume's spread in that direction (which grows with downwind distance due to turbulence). This factor shows how the concentration decays as you move away from the plume centerline laterally, independent of how far downwind you are. It is not a vertical dispersion term (that would involve z) nor a temporal or chemical decay term, but the crosswind spread component of the Gaussian plume.

In the Gaussian plume model, the pollutant concentration is described by Gaussian spreads in both the crosswind (lateral) and vertical directions. The term exp(-y^2/(2 σ_y^2)) specifically comes from the crosswind, or lateral, Gaussian distribution. Here, y is the distance from the plume’s centerline in the crosswind direction, and σ_y is the standard deviation of the plume's spread in that direction (which grows with downwind distance due to turbulence). This factor shows how the concentration decays as you move away from the plume centerline laterally, independent of how far downwind you are. It is not a vertical dispersion term (that would involve z) nor a temporal or chemical decay term, but the crosswind spread component of the Gaussian plume.