What is the effect of a stable atmosphere on dispersion?

• A. It has no effect on dispersion.
• B. It reduces mixing and yields higher ground-level concentrations.
• C. It increases plume buoyancy.
• D. It always clears the plume quickly.

Answer: (B)

Atmospheric stability governs how easily air parcels rise or sink, which controls turbulent mixing. In a stable atmosphere, vertical motions are damped by stratification or a temperature inversion, so turbulence is reduced and little vertical mixing occurs. Because dispersion relies on mixing air from different layers to dilute the plume, this suppression means pollutants stay more concentrated near the source and near ground level. The plume can still travel downwind, but it doesn’t dilute as efficiently, so ground-level concentrations tend to be higher.

That’s why higher ground-level peaks occur in stable conditions: mixing is limited, giving less dilution. In contrast, neutral or unstable conditions boost turbulence and vertical mixing, spreading the plume more and lowering peak concentrations near the source.

The other statements don’t fit because stability does matter for dispersion, and stability generally hampers vertical rise rather than increasing it or guaranteeing rapid clearance.