Comparison of Droplet Spectra of Fluorescent Tracers Commonly used to Measure Pesticide Deposition and Drift

Five water soluble fluorescent tracers, (Rhodamine WT, Tinopal CBS-X, Eosin OJ, Brilliant Sulphaflavine, and Uvitex EC), and one non-ionic adjuvant, Induce, were studied to determine their effects upon atomization. The solutions were sprayed through an XR8004VS fan nozzle tip at 276 kPa (40 psi). The drop spectra were measured using an Aerometrics PDPA 100-ID with the nozzle positioned 30 cm above the probe volume.

Several differences in important droplet size distribution parameters were found between the tracers at various rates and between tracer/adjuvant combinations. The greatest difference occurred when comparing Tinopal CBS-X (6.5 g liter^-1) to Eosin OJ (3.5 g liter^-1), where there was a 200% and a 107% increase in the % volume of droplets < 100 μm and 150 μm diameter, respectively. There was also an approximately 61% and 35% increase in the % number of droplets < 100 μm and 150 μm, respectively. Similar results, although not as marked, occurred when comparing these two tracers both at 1 g liter^-1. The other tracers showed differences when compared to water and water/adjuvant mixtures. The results are considered in terms of their implications for quantification of drift and deposition studies.