Low-Level Atmospheric Temperature Inversions and Atmospheric Stability: Characteristics and Impacts on Agricultural Applications

Drift from aerial application of crop protection and production materials is influenced by many factors. The applicator is responsible for considering these factors and adjusting application techniques, where applicable, to reduce the potential for drift as much as possible. In an effort to study the uncontrollable factors and provide guidance for agricultural applicators, this study monitored and documented atmospheric conditions at two locations. The measured meteorological data was used to assess how atmospheric stability varied as a function of time of day, location, and other meteorological conditions. Additionally, inversion periods were examined for strength, time of occurrence, and duration. Stable and very stable atmospheric conditions, which would tend to produce the most drift, primarily occurred between the hours of 6 p.m. and 6 a.m., with a few occurrences between 6 a.m. and 6 p.m. Between the hours of 6 a.m. and 6 p.m., unstable atmospheric conditions tended to dominate. Of the days monitored, however, almost half experienced inversion periods between the hours of 6 a.m. and 6 p.m., with more than half of these inversion periods being after 4 p.m. and having durations an order of magnitude greater than periods of inversions seen between 6 a.m. and 4 p.m. Generally, these late afternoon periods are of most concern as the probability of experiencing increasingly stable conditions or long inversion periods increases. Based on these results, agricultural applicators should take caution when spraying in the morning or, most particularly, evenings, especially when wind speeds are below 2 m/s