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Abstract Existing motor vehicle pollutant measurement techniques, including those that employ ground-based and multirotor small uncrewed aircraft system (sUAS) methods, can accurately measure traffic-related air pollution (TRAP) concentrations at a single location. However, these techniques often lack the mobility to assess pollutant trends across a large horizontal area. Fixed-wing sUAS represents an alternative instrument platform compared to ground-based systems and multirotor sUAS, as fixed-wing sUASs are able to carry air pollutant monitor payloads, have extended endurance, and offer expansive three-dimensional ranges across a field site. To demonstrate the utility of fixed-wing sUAS for urban TRAP assessment, we conducted two flights using a Super Robust Autonomous Aerial Vehicle–Endurant Nimble (RAAVEN) sUAS [University of Colorado (CU) Boulder] at a large field site adjacent to a major highway in Erie, Colorado. Concentrations of solid particulate matter (PM₁₀) and gas-phase (carbon monoxide) pollutants displayed decay as a function of altitude. During the morning flight, PM₁₀concentrations decreased from 19.0μg m⁻³at ground level to a minimum concentration of 14.3μg m⁻³at 90 m above ground level. During the afternoon flight, concentrations of PM₁₀displayed minimal vertical stratification, ranging from 8.9 at ground level to 10.0μg m⁻³at 45 m above ground level. Similarly, pollutants displayed decreasing concentrations as the horizontal distance from the roadway increased. Concentrations of TRAP may be significantly elevated in the area both above and beyond roadways, which contribute to additional pollutant exposure from on-road pollution sources. This study demonstrated that the general behavior of TRAP in near-road environments and that the use of fixed-wing sUAS are viable option for urban air quality measurements. Significance StatementThis study represents one of the first uses of a fixed-wing small uncrewed aircraft system (sUAS) to assess near-roadside concentrations of traffic-related air pollution (TRAP) in urbanized areas. We found that local meteorology, including local wind and solar radiation, had a substantial influence on the concentrations of common air pollutants, including particulate matter, black carbon, carbon monoxide, and carbon dioxide. Furthermore, we found large-scale spatiotemporal variation in pollutant concentrations as a function of the vertical and horizontal distance from the highway, indicating that diminished spatial variation employed in multirotor sUAS studies may not be sufficient to fully assess TRAP in roadside environments. 

A method for calibrating a multi-hole probe (MHP) used for inertial wind vector measurements from a small Uncrewed Aircraft System (sUAS) is presented. The first phase of the calibration process is broken into three parts: Obtaining reference airspeed, angle of attacks and side slip angles; calibrating MHPs with experimental data; mitigating bias errors to improve calibrations.The method follows the established wind tunnel calibration procedures and includes two additional steps to increase calibration accuracy. The calibration process begins with a computational fluid dynamics (CFD) study on blockage effects in the wind tunnel. CFD results indicate nontrivial deviations of the mean flow due to blockage in wind tunnel test section. Analysis shows a linear relationship between experimental setup position and the resulting deviation from unidirectional flow. The relationship is incorporated into the routine to develop a calibration model. This augments previously demonstrated techniques by processing experimental data from the probe using CFD results. Then the model is refined by removing experimental bias angles. The next phase is to account for upwash effects caused by the sUAS lifting surfaces. Initial CFD analysis has been conducted to determine the relationship between the perceived airframe orientation measured from the relative wind, and the angle of attack measured by the MHP. Preliminary results show that there is a measurable linear relationship between the perceived and actual angles of attack. The objective these additional steps is to increase the accuracy of MHP calibration and characterize the error in inertial wind vector measured during field experiments.