How does increasing wind speed affect ground-level concentration for fixed Q and dispersion parameters?

How does increasing wind speed affect ground-level concentration for fixed Q and dispersion parameters?

• A. Increases ground-level concentration due to faster advection and dilution.
• B. Only affects high altitude concentrations.
• C. It tends to decrease ground-level concentration due to faster advection and dilution.
• D. It has no effect.

Answer: (C)

Increasing wind speed mainly moves the plume away faster and distributes the emitted material over a larger moving volume. With the emission rate fixed and the dispersion parameters held constant, the ground-level concentration at a given receptor falls roughly in proportion to 1 over the wind speed (C ∝ Q/(u σ_y σ_z)). Faster advection means the pollutant spends less time near the receptor and is diluted more quickly as it travels, so the concentration you measure at ground level decreases. Real conditions can tweak σ_y and σ_z with distance and stability, but the dominant effect under fixed dispersion is a reduction in ground-level concentration as wind speed rises.

Increasing wind speed mainly moves the plume away faster and distributes the emitted material over a larger moving volume. With the emission rate fixed and the dispersion parameters held constant, the ground-level concentration at a given receptor falls roughly in proportion to 1 over the wind speed (C ∝ Q/(u σ_y σ_z)). Faster advection means the pollutant spends less time near the receptor and is diluted more quickly as it travels, so the concentration you measure at ground level decreases. Real conditions can tweak σ_y and σ_z with distance and stability, but the dominant effect under fixed dispersion is a reduction in ground-level concentration as wind speed rises.