Vertical and horizontal distributions of traffic-related pollutants beside an urban arterial road based on unmanned aerial vehicle observations

The increased knowledge in distribution patterns of traffic-related pollutants can help address the problems of air pollution. Utilities of instrumented unmanned aerial vehicles (UAVs) who have high mobility are an effective approach to investigate the pollutant distributions. However, UAV-based observations are mostly conducted in open suburban areas and have been rare in urban areas where present severe pollution problems. In this study, an instrumented six-rotor UAV was carried out to investigate the spatiotemporal distributions of air pollutants beside an urban arterial road in Shanghai, China. Both vertical and horizontal distributions of particulate matters (PM), carbon monoxide (CO) within the height of 120 m were investigated. Results show that the vertical fall-off of roadside CO was mainly in a height range of 0–60 m and was 0–40 m for PM. PM and CO concentrations both presented exponential decay in the vertical direction and showed more significant decay in traffic rush hours compared with that in non-rush hours. Meanwhile, the concentration of fine particles (PM₁) was mostly affected by the background concentration while the concentrations of coarse particles and CO were more related to traffic activities. Additionally, at the height of 40 m, the horizontal dispersion of CO could reach over 60 m away from the road, and the increase in pollutant concentrations was mainly in the downwind direction of the road. This study revealed the general trends of vertical and horizontal distributions of air pollutants beside an urban arterial road, which could provide implications in mitigating traffic-related air pollution.