What is a temperature inversion?

• A. When the air near the soil is warmer than the air above
• B. When the air near the soil is cooler than the air above
• C. When humidity drops to zero
• D. When wind speed exceeds 50 mph

Answer: (B)

A temperature inversion happens when the air near the ground is cooler than the air above it. In this situation, temperature actually increases with height in the lowest part of the atmosphere, creating a stable layer that resists vertical mixing. That stability means spray droplets don’t rise and dilute as much, so they stay closer to the ground and can drift farther with light surface winds. Inversions commonly form on clear, calm nights or early mornings when the ground cools quickly but the air above remains warmer. This helps explain why spraying during such times can lead to more off-target deposition. The other scenarios—air near the soil being warmer than above, humidity dropping to zero, or very high wind speeds—don’t describe this stable near-surface layering.