Vertical distributions of boundary-layer ozone and fine aerosol particles during the emission control period of the G20 summit in Shanghai, China

Vertical observations of ozone (O₃) and fine aerosol particles (PM_2.5) below 3000 m above ground level were made by an O₃ lidar and two hexacopter unmanned aerial system (UAS) platforms to investigate vertical distributions of the boundary-layer O₃ and PM_2.5 and their effects on surface air quality. Field observations were conducted in Shanghai, China before, during, and after the G20 Summit (Hangzhou) from 23 August to 13 September 2016, when stringent emission control measures were implemented over the Yangtze River Delta region. The results show that surface O₃ and PM_2.5 concentrations increased evidently during the emission control period due to the significant contribution of transport. Different transport types including regional transport, recirculation transport, and long-range transport were captured in the three stages of the emission control period. Regional transport mainly occurred in the middle and upper boundary layer, leading to positive altitude dependence of the boundary-layer O₃ and PM_2.5. Recirculation transport mainly occurred in the lower boundary layer, leading to negative altitude dependence of the boundary-layer O₃ and PM_2.5. Long-range transport of O₃ mainly occurred in the lower free troposphere, leading to positive altitude dependence of the boundary-layer O₃. Under the influence of northeasterly winds, Shanghai exhibited considerable transport potential of pollutants to Hangzhou during the emission control period. The findings in this study could help to understand complex interactions between different transport types and variations in surface air pollutant concentrations, as well as provide important implications in making regional emission control measures in the future.