Inversions are most likely to occur between sunset and two hours after sunrise.

• A. True
• B. False
• C. Not sure
• D. Throughout the day

Answer: (A)

When the ground loses heat after sunset, the air near the surface cools and becomes denser than the air above it. This creates a stable layer where temperatures rise with height, known as a temperature inversion. Inversions suppress vertical mixing, so any airborne particles or droplets tend to stay trapped near the ground rather than dispersing upward. This situation is most common during the night and the early morning, persisting from after sunset through the hours shortly after sunrise. As the sun climbs higher and starts heating the surface, the inversion weakens and mixing increases, typically within a few hours after sunrise. Because of this, inversions are most likely to occur between sunset and a couple of hours after sunrise, which is why spraying during this window can lead to poor deposition and drift.