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 D-v0.5 of 18.5 (+/- 0.4) mu m at air speeds ranging from 0.4-4.0 m/s. 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 on 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.
