Direct and indirect drift assessment means, Part 1: PDPA laser based droplet characterisation

The spray quality generated by agricultural nozzles is important considering the efficiency of the pesticide application process because it affects spray deposits, biological efficacy and driftability. That is why a measuring set-up for the characterisation of spray nozzles was developed. This set-up is composed of a controlled climate room, a spray unit, a three-dimensional automated positioning system and an Aerometrics PDPA laser system which measures droplet size and velocity characteristics based on light scattering principles. Using this set-up and a well defined measuring protocol, droplet size and velocity characteristics of 15 different nozzle-pressure combinations were measured. It was found that at a nozzle distance of 0.50 m, droplet sizes vary from a few up to some hundreds of micrometres and droplet velocities from about 0 m.s^-1 up to 16 m.s^-1. From the results, the importance of the nozzle type and size on the droplet size and velocity spectra is clear. Standard flat fan nozzles produced the finest droplet size spectrum followed by low-drift and the air injection nozzles which results in significant differences in the proportion of small droplets. The larger the ISO nozzle size, the coarser is the droplet size spectrum and the lower is the proportion of small droplets. This effect is most pronounced for the standard flat fan followed by the low-drift nozzles and is less important for the air inclusion nozzles. Comparing the PDPA measuring results with other studies confirmed the need for reference nozzles to classify sprays because of the considerable variation of absolute results depending on variations in reference sprays, measuring protocol, measuring equipment and settings. As described in part 4, these results will be linked with the drift potential of different nozzle-pressure combinations.