Denser-than-air COTAs can fail to travel in the wind direction.

Denser-than-air COTAs can fail to travel in the wind direction.

• A. True
• B. False
• C. Sometimes
• D. Always

Answer: (A)

Dense-than-air releases don’t simply ride the wind. Gravity pulls the heavier gas (or particles) downward, so the plume’s trajectory contains a downward component and can settle to the ground before it moves far in the wind direction. The result is that, especially near the source or under stable, low-turbulence conditions, a dense cloud may not follow the wind path and can deposit or spread in directions not aligned with the horizontal wind. Over time and with strong mixing, it may start to drift more with the wind, but it’s entirely reasonable for the dense cloud to fail to travel in the wind direction initially.

Dense-than-air releases don’t simply ride the wind. Gravity pulls the heavier gas (or particles) downward, so the plume’s trajectory contains a downward component and can settle to the ground before it moves far in the wind direction. The result is that, especially near the source or under stable, low-turbulence conditions, a dense cloud may not follow the wind path and can deposit or spread in directions not aligned with the horizontal wind. Over time and with strong mixing, it may start to drift more with the wind, but it’s entirely reasonable for the dense cloud to fail to travel in the wind direction initially.