Sigma_y and sigma_z values characterize the plume's dispersion in which directions?

Sigma_y and sigma_z values characterize the plume's dispersion in which directions?

• A. Horizontal along wind direction
• B. Lateral (crosswind) and vertical directions
• C. Upward only
• D. Downwind distance only

Answer: (B)

Sigma_y and sigma_z come from the Gaussian plume framework as the standard deviations of the concentration distribution in directions perpendicular to the wind. Sigma_y represents the lateral spread across the wind, while sigma_z represents the vertical spread due to turbulence and buoyancy. They describe how wide the plume grows sideways and upward as it travels downwind. Dispersion along the wind direction is described by a different term, and downwind distance refers to how far the plume has moved, not how it has spread. So these two together characterize the plume’s dispersion in the lateral (crosswind) and vertical directions.

Sigma_y and sigma_z come from the Gaussian plume framework as the standard deviations of the concentration distribution in directions perpendicular to the wind. Sigma_y represents the lateral spread across the wind, while sigma_z represents the vertical spread due to turbulence and buoyancy. They describe how wide the plume grows sideways and upward as it travels downwind. Dispersion along the wind direction is described by a different term, and downwind distance refers to how far the plume has moved, not how it has spread. So these two together characterize the plume’s dispersion in the lateral (crosswind) and vertical directions.