If stability class is mis-specified, predicted sigma values may be:

If stability class is mis-specified, predicted sigma values may be:

• A. Inaccurate
• B. More accurate
• C. Unaffected
• D. Random

Answer: (A)

The spread of the plume, described by the dispersion coefficients sigma_y and sigma_z, depends strongly on atmospheric stability. These sigmas come from empirical curves tied to a chosen stability class and downwind distance. If the stability class is mis-specified, the model uses the wrong dispersion curves, so the sigma values it computes don’t match the real turbulent spreading. That leads to errors in predicted concentrations and plume width. In short, mis-specifying stability makes the sigma values inaccurate. They aren’t inherently more accurate, and they aren’t guaranteed to be random or unchanged. The direction of the error depends on whether the mis-specified class is more or less stable than the actual conditions, but the key point is the predictions become inaccurate.

The spread of the plume, described by the dispersion coefficients sigma_y and sigma_z, depends strongly on atmospheric stability. These sigmas come from empirical curves tied to a chosen stability class and downwind distance. If the stability class is mis-specified, the model uses the wrong dispersion curves, so the sigma values it computes don’t match the real turbulent spreading. That leads to errors in predicted concentrations and plume width.

In short, mis-specifying stability makes the sigma values inaccurate. They aren’t inherently more accurate, and they aren’t guaranteed to be random or unchanged. The direction of the error depends on whether the mis-specified class is more or less stable than the actual conditions, but the key point is the predictions become inaccurate.