Passive dispersion coefficients are typically not provided for distances:

Passive dispersion coefficients are typically not provided for distances:

• A. Less than 10 meters
• B. 10 meters or more
• C. Exactly 10 meters
• D. All distances

Answer: (B)

Passive dispersion coefficients describe how quickly the air near the release spreads under a simple, near-field diffusion assumption. That view works only for a short distance from the source, where turbulence is relatively uniform and advection hasn’t yet shaped the plume. As you move to distances of about ten meters or more, the plume’s spread is increasingly controlled by wind transport, changing atmospheric stability, and obstacles, so a single fixed passive coefficient no longer represents the spreading reliably. Because of that, these coefficients are not provided for longer distances; you instead use distance-dependent dispersion parameters or standard sigma_y and sigma_z formulations that account for how dispersion changes with downwind distance. So the statement that they’re not provided for distances 10 meters or more reflects the shift from a simple near-field coefficient to more complex, distance-aware dispersion descriptions.

Passive dispersion coefficients describe how quickly the air near the release spreads under a simple, near-field diffusion assumption. That view works only for a short distance from the source, where turbulence is relatively uniform and advection hasn’t yet shaped the plume. As you move to distances of about ten meters or more, the plume’s spread is increasingly controlled by wind transport, changing atmospheric stability, and obstacles, so a single fixed passive coefficient no longer represents the spreading reliably. Because of that, these coefficients are not provided for longer distances; you instead use distance-dependent dispersion parameters or standard sigma_y and sigma_z formulations that account for how dispersion changes with downwind distance. So the statement that they’re not provided for distances 10 meters or more reflects the shift from a simple near-field coefficient to more complex, distance-aware dispersion descriptions.