Collection efficiency of various airborne spray flux samplers used in aerial application research

Authors: Fritz, Bradley - Brad; Hoffmann, Wesley

Submitted to: American Society for Testing and Materials
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/3/2007
Publication Date: 1/19/2008
Citation: Fritz, B.K., Hoffmann, W.C. 2008. Collection efficiency of various airborne spray flux samplers used in aerial application research. Journal of ASTM International. 5(1):Paper ID JAI01493.

Interpretive Summary: Airborne movement of aerially applied agricultural sprays is generally quantified using a passive droplet collector. The efficiency with which this collector samples spray droplets, which is critical to interpreting the results, is a function of the spray droplet size and the wind speed in which the spray is entrained. A low air speed, spray dispersion tunnel was constructed and evaluated for use in passive spray collector efficiency studies. Using previously established evaluation protocols, the collection efficiency of a nylon screen cylinder, used in previous drift studies, was measured and expressed as a function of wind speed and drop size. These results allow for greater understanding of previously collected data detailing spray movement downwind of the application aircraft. Additionally, the testing protocols used provide a method for determining collection efficiencies for a number of spray flux collectors used by researchers, thus allowing for more detailed and comparative analysis of field collected data.

Technical Abstract: A low air speed, spray dispersion tunnel was constructed and used to evaluate the collection efficiency of passive spray flux collectors. The dispersion tunnel utilizes an air-assisted nozzle to generate a spray cloud with a DV0.5 of 18.5 (±0.4) µm at air speeds ranging from 0.45-4.0 m/sec. A sampling protocol was developed to minimize spray flux and air speed variation effects while providing a check on theoretical collection efficiency calculations. A soda straw and monofilament line was placed either side of a nylon screen cylinder collector, and all three were positioned in the center of the tunnel’s cross-sectional area. Twelve replicated trials were conducted at air speeds of 0.4, 1.3, 2, and 3.8 m/s. Droplet size was measured every replication using a Sympatec HELOS laser diffraction system. Using theoretical collection efficiencies for cylinders and the measured fractional droplet size, the actual flux was estimated from the volume of spray collected on the soda straw and monofilament samplers and used to determine the collection efficiency of the nylon screen cylinder. Collection efficiency increased with air speed for all collectors and results ranged from 5 to 40% for the soda straws, 46 to 83% for the monofilament line, and 9 to 98% for the nylon screen cylinders. Collection efficiency data are crucial to the evaluation of field collected data from aerial application research studies with respect to mass accountability and comparisons to other studies and drift model results.