Cutting Pesticide Exposure by Nozzle and Drift Physics: Droplet Spectra, Settling and Evaporation Trajectories, and a Costed Low-Drift Configuration

First-principles computation of pesticide spray drift and exposure by nozzle choice. SIMULATED, NOT MEASURED; nothing was built or field-tested. A standard flat-fan nozzle at 3 bar places 15.25% of spray volume below 100 micrometres and deposits 31.48% of applied active ingredient off target in a field-edge pass at 3 m/s wind; a designed low-exposure configuration (air-induction nozzle at 2 bar, 0.35 m release height, wind shield) places 0.01% below 100 micrometres, deposits 2.83% off target (11.12-fold reduction), reduces the operator airborne cloud 91.21-fold, and reduces bystander deposition at 5 m to the model resolution floor (floor-capped factor 626.8). The efficacy cost is stated in full: droplet density on target falls from 451.3 to 44.5 droplets per cm2 and modelled area coverage from 31.9% to 19.5%. The change costs US$436 fitted to a 12 m boom (US$352 incremental) or US$22.50 for a knapsack sprayer (US$19.00 incremental). Limits are printed at full size: the ballistic model contains no sprayer wake, gusts, or wind meander, and drift physics cannot address vapour drift, temperature inversions, in-field exposure during application, or near-field ground fallout, which increases under the designed configuration.