Atmospheric stability and the dispersion of pesticides

Applicators have long recognized that temperature inversions dramatically influence the behavior of pesticide material released into the atmosphere during pesticide application. This behavior can be explained in terms of the relationship between vertical atmospheric temperature gradients (stability) and atmospheric mixing (turbulence). This relationship is not intuitively obvious, but once it is understood, it provides the applicator with a tool to use for anticipating pesticide drift potential. The term inversion is synonymous with a stable thermal layer in the atmosphere. In stable thermal layers, mixing is suppressed and both dispersion and translation (or mean movement) of material is slow. This is typical of clear nights. Conversely, under clear, sunny conditions mixing is strong and dispersion is rapid. This situation indicates an unstable thermal layer.