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A simulation model was developed to predict on-target spray deposition in citrus tree canopies when using an air-carrier sprayer. It was developed as a compartment model in which the space between the sprayer and tree and within the canopy was divided into small elements to achieve the needed simplification for simulation purposes. This article presents the initial part of the model, which considers no tree canopy (i.e., spray dispersion between the sprayer and tree boundary or where there is a missing tree situation), and its validation with a field experiment. The experiment involved the use of a conventional airblast sprayer and absorbent paper targets to sample airborne spray at five distances and four heights. Spray treatments consisting of combinations of two nozzles (Albuz ATR Lilac and Blue) and two forward speeds (2.4 and 4.8 km h-1) were applied in four replications. Spray liquid was a solution of Pyranine 10G fluorescent dye; samples were analyzed by fluorometry. The results showed good agreements between the model output and the experimental data, with the best predictions yielding modeling efficiencies and correlation coefficients of 78% and 0.90 for airborne spray and 50% and 0.62 for ground deposit, respectively. The second part of this article focuses on deposition on the tree canopy.