How do stability class values numerically affect σy and σz?

How do stability class values numerically affect σy and σz?

• A. They assign smaller σy and σz values to unstable classes
• B. They assign larger σy values to unstable classes only
• C. They assign larger σy and σz values to unstable classes (A, B) and smaller values to stable classes
• D. They have no effect on σy or σz

Answer: (C)

Stability class describes how turbulent the atmosphere is, and that turbulence controls how a plume spreads. The horizontal spread (σy) and the vertical spread (σz) are determined by this turbulence: more turbulent conditions mix the plume more and cause greater spreading, while stable conditions suppress mixing and keep the plume tighter. In the usual parameterizations, the numerical values assigned to σy and σz grow with instability and shrink with stability. So unstable classes have larger σy and σz at a given distance, and stable classes have smaller σy and σz. This is why the correct statement says that unstable classes (A, B) yield larger dispersion parameters, while stable classes yield smaller ones. The neutral class falls in between.

Stability class describes how turbulent the atmosphere is, and that turbulence controls how a plume spreads. The horizontal spread (σy) and the vertical spread (σz) are determined by this turbulence: more turbulent conditions mix the plume more and cause greater spreading, while stable conditions suppress mixing and keep the plume tighter. In the usual parameterizations, the numerical values assigned to σy and σz grow with instability and shrink with stability. So unstable classes have larger σy and σz at a given distance, and stable classes have smaller σy and σz. This is why the correct statement says that unstable classes (A, B) yield larger dispersion parameters, while stable classes yield smaller ones. The neutral class falls in between.