Assessment of aerosol deposition and movement in open field conditions

Abstract

Overall objective of this study was to evaluate the dispersion of aerosol plumes generated by a truck-mounted ultra low-volume (ULV) applicator and a hand-held thermal fogger under open field conditions.  Experiments were also planned to determine the relative capture efficiencies of various sampling techniques in such applications.  The ULV applicator was used at three travel speeds (8.5, 16.8, 24.8 km/h) and the thermal fogger at two release heights (0.6 and 1.1 m above ground) to investigate the effect of speed or release height on deposition at 6, 12, 24, and 48 m downwind.  High volume air sampler (HVS), low volume air samplers (LVS), spinning cotton ribbon (CR) samplers, polypropylene green plastic cards (GC), acetate cards (AC), and water-sensitive papers (WSP) were used to collect deposits.  The ULV applicator was tested with water and oil sprays while the thermal fogger was tested with the latter tracer only.  Using water- and oil-based tracers, all deposition targets were analyzed by fluorometry.  Results showed decreased tracer deposition with increase in sampling distance.  Overall, travel speed affected deposition at the near sample locations only, but in most sample locations, normalized deposits were comparable at all speeds.  Spray release height did not affect deposition of active samplers but had significant effect on deposition of passive samplers at 6 m location only.  Overall, the higher release height resulted in more deposition in most downwind locations.  There were good correlations between depositions on active and passive samplers. The HVS, CR, GC, and AC samplers were effective in sampling aerosol plume dispersion under open field conditions.  The paper includes relationships among capture efficiencies of various samplers.

Keywords: ULV applicator, thermal fogger, deposition samplers, Yellow 131SC dye, Pyranine 10G, fluorometry