True or False: The concept of stability class is relevant for both sigma_y and sigma_z predictions.

True or False: The concept of stability class is relevant for both sigma_y and sigma_z predictions.

• A. True
• B. False
• C. Not relevant
• D. Only for sigma_y

Answer: (A)

The key idea is that atmospheric stability class describes how turbulent the air is, which controls how a plume dilutes in all directions. In Gaussian dispersion models, both sigma_y (lateral spread) and sigma_z (vertical spread) are determined from empirical relationships that depend on downwind distance and the stability class. Since the same turbulence that widens the plume horizontally also drives vertical mixing, the stability classification affects both sigmas. So the statement is true: stability class is relevant for both sigma_y and sigma_z.

The key idea is that atmospheric stability class describes how turbulent the air is, which controls how a plume dilutes in all directions. In Gaussian dispersion models, both sigma_y (lateral spread) and sigma_z (vertical spread) are determined from empirical relationships that depend on downwind distance and the stability class. Since the same turbulence that widens the plume horizontally also drives vertical mixing, the stability classification affects both sigmas. So the statement is true: stability class is relevant for both sigma_y and sigma_z.