What is the primary characteristic of a temperature inversion in relation to pesticide application?

The primary characteristic of a temperature inversion is that the ground air is cooler than the air above it, typically ranging from two to five degrees cooler. This phenomenon occurs when a layer of warmer air traps cooler air closer to the ground. During temperature inversions, pesticides may become trapped in the cooler air layer, preventing them from dispersing and leading to issues such as drift and accumulation. This makes it particularly important for applicators to be aware of temperature inversions, as they can directly impact the effectiveness of the pesticide being applied as well as environmental safety.

The other options do not accurately describe the situation during a temperature inversion. For instance, ground air being warmer than surrounding air would not lead to the same trapping effect seen in inversions. Similarly, significant decreases in humidity or drastic increases in wind speeds are not defining characteristics of temperature inversions. In fact, inversions often lead to stable air conditions with limited air movement, which can exacerbate pesticide drift. Understanding these conditions is essential for proper pesticide application and minimizing environmental impact.