Transport and boundary layer interaction contribution to extremely high surface ozone levels in eastern China

• Published in: Environmental pollution (1987) 2021-01, Vol.268 (Pt A), p.115804, Article 115804
• Main Authors: Li, Xiao-Bing, Fan, Guangqiang, Lou, Shengrong, Yuan, Bin, Wang, Xuemei, Shao, Min
• Format: Article
• Language: English
• Subjects: Air Pollutants - analysis; China; Downward transport; Environmental Monitoring; Ozone - analysis; Ozone lidar; Ozone pollution; Seasons; Vertical observation; Yangtze river delta
• ISSN: 0269-7491; 1873-6424
• DOI: 10.1016/j.envpol.2020.115804

Vertical measurements of ozone (O3) within the 3000-m lower troposphere were obtained using an O3 lidar to investigate the contribution of the interactions between the transport and boundary layer processes to the surface O3 levels in urban Shanghai, China during July 23–28, 2017. An extremely severe pollution episode with a maximum hourly O3 mixing ratio of 160.4 ppb was observed. In addition to enhanced local photochemical production, both downward and advection transport in the lower troposphere may have played important roles in forming the pollution episode. The O3-rich air masses in the lower free troposphere primarily originated from central China and the northern Yangtze River Delta (YRD) region. The downward transport of O3 from the lower free troposphere may have an average contribution of up to 49.1% to the daytime (09:00–16:00 local time) surface O3 in urban Shanghai during the pollution episode (July 23–26, 2017). As for the advection transport, large amounts of O3 were transported outward from Shanghai in the planetary boundary layer under the influence of southeasterly winds during the field study. In this condition, the boundary-layer O3 that was transported downward from the free troposphere in Shanghai could be transported back to the northern YRD region and accumulated therein, leading to the occurrence of severe O3 pollution events over the whole YRD region. Our results indicate that effective regional emission control measures are urgently required to mitigate O3 pollution in the YRD region. [Display omitted] •The surface O3 episode in Shanghai was closely associated with downward transport.•Contributions of downward transport to surface O3 varied between 12.6% and 78.3%.•O3 was transported to Shanghai from the northern YRD in the lower free troposphere.•O3 was transported to the northern YRD from Shanghai in the boundary layer.