In case of plumes from a tall stack located on flat terrain 'Lofting' type of plume behaviour is observed when in the atmosphere

Correct option is A

Introduction
· Plume behavior refers to the dispersion pattern of gaseous effluents as they exit a smokestack, which is primarily determined by the vertical temperature gradient of the atmosphere.
· The interaction between the stack height and the surrounding Stability conditions (Inversion or Lapse rate) dictates whether pollutants reach the ground or stay aloft.
· Lofting is considered the most favorable dispersion condition for minimizing ground-level pollution near the industrial source.

Information Booster
· Inversion conditions prevailing below the stack height is the correct answer because this structure prevents the downward movement of the plume.
· In a lofting scenario, there is a super-adiabatic lapse rate (unstable air) above the stack and a strong negative lapse rate (stable inversion layer) below the stack.
· The inversion layer acts as a physical barrier or "lid," preventing the pollutants from mixing vertically toward the ground, thus protecting the local population from high concentrations of toxins.
· The unstable air above the stack allows the plume to disperse rapidly upward into the higher atmosphere, effectively diluting the pollutants.
· This condition often occurs during the early evening or late afternoon when the ground starts to cool rapidly, creating a radiation inversion at the surface while the upper air remains relatively warm.

Additional Knowledge
· Strong lapse rate conditions existing throughout the vertical profile would lead to a "Looping" plume, where high turbulence causes the plume to rapidly touch the ground at high concentrations.
· Inversion conditions existing above the stack height combined with a lapse rate below results in "Fumigation," the most dangerous condition where pollutants are trapped near the ground.
· Weak lapse rate conditions existing generally lead to a "Coning" plume, which is a neutral stability condition where the plume spreads out symmetrically like a cone.
· A "Trapping" plume occurs when inversion layers exist both above and below the stack height, confining the pollutants within a narrow horizontal band.