Measure the air temperature 1 foot above the soil surface or a closed crop canopy, and at 10 feet above. If the temperature is coolest at the surface, a temperature inversion exists. The greater the temperature difference, the more intense the inversion.
Devices for measuring temperature with cellphones to determine if an inversion exists:
Avoid spraying during an inversion because smaller droplets (200 microns in diameter and smaller) fall as little as a few inches per second and could ﬂoat for long distances. Volatized chemical particles can float until they evaporate.
The Droplet Size Classification System is a helpful aid in selecting spray nozzles. The classification ranges from extremely fine to ultra-coarse. (Figure 3)
Some pesticides are more volatile than others. Check labels for information on volatility.
Figure 3. Nozzle Droplet Size Classification (ASABE Standard). These colors can be found in nozzle manufacturer catalogs. Note that actual nozzle colors are different than nozzles on the chart.