Abstract

Vector-borne diseases remain a public health concern, and ultra-low-volume (ULV) systems generate adulticide droplets that must remain airborne long enough to contact flying mosquitoes. Accurate droplet and aerosol size characterization is essential for equipment calibration, interpretation of efficacy studies, and evaluation of the airborne fraction relevant to spray transport. This study evaluated complementary nozzle-level and downstream airborne measurements under controlled chamber conditions using a DC-IV droplet counter, TSI APS 3321, and GRIMM MiniWRAS 1.371. Mineral oil and kerosene were atomized at 1.0 to 10.5 bar and 0.20 to 1.00 mL/min. Mass median diameter (MMD), count median diameter (CMD), regression relationships, and size distributions were evaluated. Four MMD calculation methods were also assessed, including Hatch–Choate conversion and a Volume-Based method. For mineral oil, DC-IV reported a mean MMD of 30.78 µm, compared with 4.88 µm for APS and 3.15 µm for MiniWRAS. For kerosene, differences narrowed to 6.21, 6.45, and 4.09 µm, respectively. Hatch–Choate estimates were unstable when lognormal assumptions were violated, whereas the Volume-Based method reproduced reported APS and MiniWRAS MMD values within ±1%. These findings support continued DC-IV use for nozzle calibration and indicate that APS and MiniWRAS can provide complementary real-time characterization of the downstream airborne spray aerosols.

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