In the Briggs parameterization of passive plume dispersion, the predicted values of sigma_y and sigma_z are independent of atmospheric stability classes.

In the Briggs parameterization of passive plume dispersion, the predicted values of sigma_y and sigma_z are independent of atmospheric stability classes.

• A. True
• B. False
• C. Not determined
• D. Only under neutral conditions

Answer: (B)

The main idea here is that the spread of a plume in the Briggs parameterization is tied to atmospheric stability. In Gaussian plume modeling, sigma_y and sigma_z describe how wide the plume becomes as it travels downwind. Briggs provides these dispersions as functions of downwind distance with coefficients that depend on stability class (A through F). Those coefficients come from empirical fits to field data and are different for stable, neutral, and unstable conditions. Since stability controls turbulence and mixing strength, it directly affects how quickly the plume broadens in both the lateral and vertical directions. Under unstable conditions, stronger turbulent mixing makes sigma_y and sigma_z larger at a given distance; under stable conditions, weaker mixing keeps them smaller. Neutral conditions fall in between. Therefore, sigma_y and sigma_z are not independent of atmospheric stability; they vary with it. That’s why the statement is false.

The main idea here is that the spread of a plume in the Briggs parameterization is tied to atmospheric stability. In Gaussian plume modeling, sigma_y and sigma_z describe how wide the plume becomes as it travels downwind. Briggs provides these dispersions as functions of downwind distance with coefficients that depend on stability class (A through F). Those coefficients come from empirical fits to field data and are different for stable, neutral, and unstable conditions. Since stability controls turbulence and mixing strength, it directly affects how quickly the plume broadens in both the lateral and vertical directions. Under unstable conditions, stronger turbulent mixing makes sigma_y and sigma_z larger at a given distance; under stable conditions, weaker mixing keeps them smaller. Neutral conditions fall in between. Therefore, sigma_y and sigma_z are not independent of atmospheric stability; they vary with it. That’s why the statement is false.