When a stable layer exists below the stack height and an unstable layer above, which of the following types of plume behaviour is expected to be observed?

Correct option is D

Explanation:
In atmospheric science, the behavior of a plume emitted from a stack is significantly influenced by the surrounding atmospheric stability. When there is a stable layer below the stack height, it means that vertical mixing of air is restricted in that layer. Conversely, an unstable layer above allows for vertical motion and mixing.
1. Lofting Plume: In the case of a stable layer beneath the stack and an unstable layer above, the plume is likely to rise into the unstable air. The upward motion is facilitated by the instability present above the stable layer. The buoyancy of the warm gases from the stack enables the plume to "loft" above the stable layer, resulting in dispersion at higher altitudes, thereby minimizing the ground-level concentration of pollutants.
2. Looping: This type of plume behavior occurs under unstable atmospheric conditions throughout the vertical layer, where the plume rises and falls due to thermal updrafts and downdrafts, which is not the case when a stable layer is present below.
3. Coning: In stable conditions, coning may occur where the plume expands horizontally, but this does not indicate a direct upward movement into an unstable layer above.
4. Fumigating: This occurs when a plume is pushed downwards into the stable layer, increasing ground-level concentrations, which is not applicable when the plume can rise into an unstable layer.
Information Booster:
· Stable Layer: Restricts vertical motion and is typically characterized by a temperature inversion.
· Unstable Layer: Promotes vertical mixing, allowing plumes to disperse higher into the atmosphere.
· Lofting: Reduces ground-level pollution by dispersing the plume into the upper atmosphere.
· Importance of Understanding Plume Behavior: Knowing how atmospheric layers affect plume behavior is crucial for air quality management and pollution control strategies.
· Impact on Air Quality: Lofting can result in lower concentrations of pollutants at the surface, thereby mitigating potential health risks associated with high pollutant levels.
Additional Information:
· Option (a) Looping: Not applicable in this case as looping occurs in uniformly unstable conditions.
· Option (b) Coning: Although it may happen in stable conditions, it does not imply upward motion.
· Option (c) Fumigating: Involves downward movement of pollutants into stable layers, not applicable here.
· Option (d) Lofting: Correct answer, as it accurately describes the expected upward movement of the plume into the unstable layer.