Temperature inversions, which can increase drift, occur when ground level air is _________ the air above it.

• A. Warmer than
• B. The same temperature as
• C. Cooler than
• D. Much cooler than

Answer: (C)

Inversions create a stable lower atmosphere when the air at ground level is cooler than the air above it. That cool surface air under warmer air aloft resists vertical mixing, so droplets from spraying stay in a shallow layer near the ground rather than dispersing upward. Because horizontal winds can move this near-surface layer, pesticides can travel farther than expected, increasing drift. If the ground were warmer than the air above, the atmosphere would be unstable with more vertical mixing and less near-surface drift; neutral conditions (same temperature) mix moderately; a much cooler surface just strengthens the same effect of stability.