Evaluation of different wind tunnel protocols for spray drift risk assessment

46 Wind tunnel measurements were carried out to measure airborne and fallout spray volumes for 10 different spray nozzles. Based on these measurements, drift potential reduction percentages (DPRP), expressing the percentage reduction of the drift potential compared with the reference spraying, were calculated following three different approaches (DPRP_V1, DPRP_V2 & DPRP_H).
The results showed the expected fallout and airborne spray profiles and the effect of nozzle type and size on DPRP values was demonstrated. For the standard flat fan nozzles, DPRP_V1 values were the highest followed by DPRP_V2 and DPRP_H while for the low-drift nozzles opposite results were found. For the air inclusion nozzles, there was a relatively good agreement between DPRP_V1, DPRP_V2 and DPRP_H values. All of this is important in the interpretation of wind tunnel data for different nozzle types and sampling methodologies.
A comparison was made between the results obtained from the wind tunnel measurements and the results from direct field drift measurements. Results showed that in the wind tunnel, driftability experiments can be made with different spraying systems under directly comparable and repeatable conditions and this methodology is well suited to permit relative studies of drift risk. The wind tunnel approach, calculating the surface under the measured fallout deposit curve (DPRP_H), was best suited to represent real near-field sedimenting drift characteristics.