Nozzle Characterisation to Support Aerosol Spray Drift Measurement in a Semi-Controlled Environment

One of the largest and most felt problems of plant protection is the spray drift generated by agricultural sprayers, that is the movement of aerosolised plant protection product (PPP) outside of the target area. Understanding aerosol generation from sprayers is key to understanding their introduction mechanisms in the atmosphere and potentially their diffusion processes at regional scale. In this context, a joint study has been organised by the Agroforestry Innovations Laboratory (AFI-lab) of the Free University of Bozen-Bolzano (unibz) and the Department of Environmental Sciences, Informatics, and Statistics of Ca' Foscari University of Venice (UNIVE). The study aims to characterise the aerosol generated by an orchard airblast sprayer as a function of distance, correlating it with the droplets produced by the employed nozzles. Controlled amounts of a fluorescent tracer solution were sprayed by a commercial sprayer in the wind tunnel at the AFI-lab of unibz. The experiment was repeated with two sets of nozzles of the same ISO size class, conventional hollow cone and air-inclusion flat fan. The aerosol was sampled at several distances from the sprayer using a 12-stage cascade impactor able to collect the different droplet sizes independently. The current work presents the outline of the study and, specifically, the preliminary characterisation of the employed spray nozzles by Particle/Droplet Image Analysis (PDIA). The behaviour of the nozzles is represented by their drop size distributions (DSD). Five randomly selected nozzles of each type were characterised by an Oxford Lasers VisiSize N60 PDIA system on a dedicated nozzle test bench. The nozzles were tested under the same working conditions of the experiment. The DSD of the nozzles show reasonable uniformity, with slight variability due to the manufacturing of the nozzles. The next steps in the study are the characterisation of the same nozzles while mounted on the machine, to understand differences in performance, and the analysis of the correlation with the aerosol distributions in the tunnel.