Dispersion of aerial agricultural sprays; model and validation

Abstract

A model has been developed to calculate the dosages of airborne pesticide particles in the downwind area during aerial crop spraying. The model is valid for crosswind flying, small flying heights (∼2 m) and formulations consisting of an involatile pesticide or a combination of an involatile pesticide and a volatile carrier liquid (e.g. water). The model consists of two submodels: a model which describes the development of a pair of initial clouds, mainly owing to the action of the aircraft-induced vortices, and a model which describes the atmospheric dispersion of this pair of initial clouds. The model was validated by means of the results of field experiments carried out by R.S. Crabbe and M. McMooeye. Two formulations were applied during the field trials performed by these researchers: an oil in water emulsion (six trials) and a wettable powder (three trials). The agreement between the calculated and measured dosages was good in the case of the experiments with the oil in water emulsion, especially with respect to the horizontal dosage profile (height 1.5 m; downwind distances up to 500 m). However, the agreement was moderate with respect to the vertical dosage profile (heights up to 20 m) at a distance of 200 m. The agreement between the calculated and measured dosages for the experiments with the wettable powder formulation was poor. It was shown by means of a sensitivity analysis that the influence of the particle size distribution of the emitted spray on the calculated dosage of the airborne pesticide particles is very large.