Rapid velocity reduction and drift potential assessment of off-nozzle pesticide droplets

[Display omitted] •Spatial velocities of off-nozzle droplets reduce by 50%–80% when falling 200 mm.•The diameter boundary of the droplet sensitive to the drift loss is about 150 μm.•The mechanism of velocity evolution differences between droplets is clarified.•The droplet diameter distribution is well improved by the modification of liquid.•Addition of adjuvant reduces the spatial drift loss of pesticide droplets by 20%–50%. The droplet velocity and diameter significantly affect both the spatial drift loss and the interfacial deposition behaviors, thus determining the ultimate utilization efficiency during pesticide spraying. Investigating the spatial velocity and diameter evolutions can reveal the mechanism of drift loss and guide to design regulation strategy. Here, we explored the spatial velocity distribution of droplets after leaving the nozzle by particle image velocimetry technology and particle tracking model, considering that the effect of nozzle configuration and the air velocity. It shows that all droplets decelerate rapidly with the velocity attenuation ratio ranging from 50% to 80% within the region of 200 mm below the nozzle. The spatial velocity evolution differences between droplets in crossflow are determined by the competition of vertical drag force and net gravity, and the drag force sharply increases as the droplet diameter decreases, especially for that smaller than 150 μm. Based on the spatial evolution differences of the droplet velocity and diameter, a functional adjuvant was added to the liquid for improving the diameter distribution. And the drift loss was significantly reduced due to the reduction of the proportion of easily drifting droplets.