Effects of UAS Rotor Wash on Air Quality Measurements

Laboratory and field tests examined the potential for unmanned aircraft system (UAS) rotor wash effects on gas and particle measurements from a biomass combustion source. Tests compared simultaneous placement of two sets of CO and CO₂ gas sensors and PM_2.5 instruments on a UAS body and on a vertical or horizontal extension arm beyond the rotors. For 1 Hz temporal concentration comparisons, correlations of body versus arm placement for the PM_2.5 particle sensors yielded R² = 0.85 and for both gas sensor pairs exceeded R² of 0.90. Increasing the timestep to 10 s average concentrations throughout the burns improved the R² value for the PM_2.5 to 0.95 from 0.85. Finally, comparison of whole-test average concentrations further increased the correlations between body- and arm-mounted sensors, exceeding R² of 0.98 for both gases and particle measurements. Evaluation of PM_2.5 emission factors with single factor ANOVA analyses showed no significant differences between the values derived from the arm, either vertical or horizontal, and those from the body. These results suggest that rotor wash effects on body- and arm-mounted sensors are minimal in scenarios where short duration, time-averaged concentrations are used to calculate emission factors and whole-area flux values.