Which lapse rate is associated with unstable conditions that promote pollutant dispersion?

Which lapse rate is associated with unstable conditions that promote pollutant dispersion?

• A. Subadiabatic Lapse Rate
• B. Adiabatic Lapse Rate
• C. Superadiabatic Lapse Rate
• D. Inversion

Answer: (C)

Understanding how temperature changes with height helps explain how pollutants disperse. The key is buoyancy: when a parcel of air rises, it cools. If the environment cools more rapidly with height than the rising parcel (the environmental lapse rate is steeper than the dry adiabatic lapse rate), the parcel stays warmer than its surroundings as it ascends. That warmth makes it buoyant, so it keeps rising and mixes more vigorously with the surroundings—creating unstable conditions that promote pollutant dispersion. A superadiabatic lapse rate is exactly this situation, where the environmental lapse rate exceeds the dry adiabatic rate, leading to strong instability. Inversions or subadiabatic lapse rates produce stable conditions that suppress vertical mixing, and the basic adiabatic lapse rate describes how a rising parcel cools, not the ambient temperature change with height.

Understanding how temperature changes with height helps explain how pollutants disperse. The key is buoyancy: when a parcel of air rises, it cools. If the environment cools more rapidly with height than the rising parcel (the environmental lapse rate is steeper than the dry adiabatic lapse rate), the parcel stays warmer than its surroundings as it ascends. That warmth makes it buoyant, so it keeps rising and mixes more vigorously with the surroundings—creating unstable conditions that promote pollutant dispersion. A superadiabatic lapse rate is exactly this situation, where the environmental lapse rate exceeds the dry adiabatic rate, leading to strong instability. Inversions or subadiabatic lapse rates produce stable conditions that suppress vertical mixing, and the basic adiabatic lapse rate describes how a rising parcel cools, not the ambient temperature change with height.