In dispersion modeling, what is meant by upwind vs downwind?

In dispersion modeling, what is meant by upwind vs downwind?

• A. Upwind is the direction from which the wind is coming; downwind is the direction toward which the wind is blowing, where concentrations are typically greater.
• B. Upwind is the direction toward which the wind is blowing.
• C. Upwind and downwind refer to vertical coordinates.
• D. Upwind means the plume centerline direction.

Answer: (A)

Upwind means the direction from which the wind is coming, while downwind is the direction toward which the wind is blowing. In dispersion modeling, the plume is carried with the wind, so it travels along the downwind direction. Receptors located downwind are exposed to the moving contaminant along the plume’s path and tend to show higher concentrations than those upwind, where the air has not yet encountered the source. This directionality is about horizontal transport by the wind, not vertical position or an abstract centerline.

Upwind means the direction from which the wind is coming, while downwind is the direction toward which the wind is blowing. In dispersion modeling, the plume is carried with the wind, so it travels along the downwind direction. Receptors located downwind are exposed to the moving contaminant along the plume’s path and tend to show higher concentrations than those upwind, where the air has not yet encountered the source. This directionality is about horizontal transport by the wind, not vertical position or an abstract centerline.