Determination of the vertical profile of particle number concentration adjacent to a motorway using an unmanned aerial vehicle

•Use of an unmanned aerial system for traffic-related pollutant monitoring.•Determined vertical profile of particle number concentration near a motorway.•Spatial resolution with a high level of precision (±0.5 m).•Over 80 vertical flights, up to a maximum altitude of 100 m above ground.•Particle number concentration increases up to 10 m, then decreases sharply.

A quantitative assessment of the vertical profile of traffic pollution, specifically particle number concentration (PNC), in an open space adjacent to a motorway was possible for the first time, to the knowledge of the authors, using an Unmanned Aerial Vehicle (UAV) system. Until now, traffic pollution has only been measured at ground level while the vertical distribution, is limited to studies conducted from buildings or fixed towers and balloons. This new UAV system demonstrated that the PNC sampled during the period form 10 a.m. to 4 p.m., outside the rush hours with a constant traffic flow, increased from a concentration of 2 × 104 p/cm3 near the ground up to 10 m, and then sharply decreased attaining a steady value of 4 × 103 p/cm3 beyond a height of about 40 m. While more comprehensive investigations would be warranted under different conditions, such as topography and vehicle and fuel type, this finding is of great significance, given that it demonstrates the impact of traffic emissions on human exposure, but less so to pollution within the upper part of the boundary layer.

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