Using unmanned aerial vehicle to investigate the vertical distribution of fine particulate matter

The vertical distribution of fine particulate matter (PM_2.5) is a vital link in understanding the transport and evolution of haze. However, existing ground stations cannot provide sufficient vertical observations of PM_2.5, especially at fine scales regarding space and time. This study deployed a six-rotor unmanned aerial vehicle (UAV) equipped with portable monitors to observe the vertical distributions of PM_2.5 and meteorological parameters within 1000 m lower troposphere. By comparing with ground-based monitoring station and tethered balloon platform for PM_2.5 measurements, the UAV was improved and then used to perform a field observation experiment in the Qingpu district of Shanghai, China. The UAV-based observations showed a decreasing vertical profile of PM_2.5 in the experimental day, with a decrease of more than 50% at 0–1000 m height. PM_2.5 had a vertical pattern that declined rapidly after 700 m in the afternoon, but the morning PM_2.5 had a rapid decline from 200 to 500 m compared with other height intervals in this period. A temperature inversion at a lower height in the morning blocked newly formed PM_2.5 at ground to disperse upward, and PM_2.5 above the temperature inversion was composed of residuals in last night. The temperature inversion gradually climbed up in the afternoon, which was beneficial to the dispersion of near-ground PM_2.5. The difference of relative humidity above and below 700 m height implies different geographical origins that were well identified and explained by a cluster analysis. This study generally highlights the significance of using a lightweight UAV to understand air pollution and governance environments in the urban area.