In the Gaussian plume model, what do h and Δh represent in H = h + Δh?

In the Gaussian plume model, what do h and Δh represent in H = h + Δh?

• A. h is the physical stack height; Δh is the plume rise due to buoyancy and momentum.
• B. h is roughness length; Δh is temperature gradient.
• C. h is wind speed; Δh is humidity.
• D. h is boundary layer height; Δh is mixing height.

Answer: (A)

The key idea is that the height used in the Gaussian plume model for where the plume starts mixing with the atmosphere is not just the actual stack height. It also includes how much the plume rises after leaving the stack. This effective height, H, is the physical stack height plus the plume rise, Δh. The physical stack height is simply how tall the stack is, while Δh comes from the plume rising due to buoyancy (hot, lighter exhaust pushing the plume upward) and momentum (exit velocity that carries the plume upward as it entrains surrounding air). This upward rise changes where the plume begins to dilute and disperse, influencing ground-level concentrations downwind. The other options mix in parameters (like roughness length, temperature gradient, wind speed, humidity, or large-scale boundary/mixing heights) that describe atmospheric conditions, but they do not define the emission height used in the model.

The key idea is that the height used in the Gaussian plume model for where the plume starts mixing with the atmosphere is not just the actual stack height. It also includes how much the plume rises after leaving the stack. This effective height, H, is the physical stack height plus the plume rise, Δh. The physical stack height is simply how tall the stack is, while Δh comes from the plume rising due to buoyancy (hot, lighter exhaust pushing the plume upward) and momentum (exit velocity that carries the plume upward as it entrains surrounding air). This upward rise changes where the plume begins to dilute and disperse, influencing ground-level concentrations downwind. The other options mix in parameters (like roughness length, temperature gradient, wind speed, humidity, or large-scale boundary/mixing heights) that describe atmospheric conditions, but they do not define the emission height used in the model.