Which factors primarily determine the transport of residual smoke?

• A. Temperature and humidity
• B. Wind direction only
• C. Transport wind and mixing height
• D. Sunlight exposure

Answer: (C)

Residual smoke transport is governed by how air carries it horizontally and how high it can mix vertically. The wind acts as the conveyor belt, moving smoke downwind and shaping how far it travels and in which direction. The mixing height sets the vertical extent of dilution; a taller mixing height allows smoke to spread upward and dilute more, reducing surface concentrations, while a shallow mixing height confines smoke closer to the ground and can increase ground-level impact. Temperature, humidity, and sunlight can influence plume buoyancy and chemistry, but they don’t determine the primary transport path as directly as the combination of transport wind and mixing height. A wind direction alone misses the speed and vertical mixing, so the key to where residual smoke ends up lies in the transport wind together with the mixing height.