Under stable atmospheric conditions, how does dispersion near the ground typically change?

Under stable atmospheric conditions, how does dispersion near the ground typically change?

• A. Dispersion is unchanged with stability.
• B. Turbulence is reduced, leading to smaller dispersion parameters and higher ground-level concentrations.
• C. Dispersion increases due to enhanced mixing.
• D. Plume height increases near the ground.

Answer: (B)

Stability controls how vigorously air mixes. In stable conditions, the atmosphere resists vertical motions, so turbulent mixing is suppressed. That means the plume doesn’t spread as much in both the horizontal and vertical directions, so dispersion parameters (the spreads in crosswind and vertical directions) become smaller. With less dilution, the pollutant concentration remains higher near the ground, especially close to the source. The plume also tends to stay closer to the ground rather than rising into higher layers, which further reduces dilution near the surface.

Stability controls how vigorously air mixes. In stable conditions, the atmosphere resists vertical motions, so turbulent mixing is suppressed. That means the plume doesn’t spread as much in both the horizontal and vertical directions, so dispersion parameters (the spreads in crosswind and vertical directions) become smaller. With less dilution, the pollutant concentration remains higher near the ground, especially close to the source. The plume also tends to stay closer to the ground rather than rising into higher layers, which further reduces dilution near the surface.