An observed nocturnal ozone transport event in the Sichuan Basin, Southwestern China.

The ozone (O ₃ ) pollution in China drew lots of attention in recent years, and the Sichuan Basin (SCB) was one of the regions confronting worsening O ₃ pollution problem. Many previous studies have shown that regional transport is an important contributor to O ₃ pollution. However, very few features of the O ₃ profile during transport have been reported, especially in the border regions between different administrative divisions. In this study, we conducted tethered balloon soundings in SCB during the summer of 2020 and captured a nocturnal O ₃ transport event during the campaign. Vertically, the O ₃ transport occurred in the bottom of the residual layer, between 200 and 500 m above ground level. Horizontally, the transport pathway was directed from southeast to northwest based on the analysis of the wind field and air mass trajectories. The effect of transport in the residual layer on the surface O ₃ concentration was related to the spatial distribution of O ₃ . For cities with high O ₃ concentrations in the upwind region, the transport process would bring clean air masses and abate pollution. For downwind lightly polluted cities, the transport process would slow down the decreasing or even increase the surface O ₃ concentration during the night. We provided observational facts on the profile features of a transboundary O ₃ transport event between two provincial administrative divisions, which implicated the importance of joint prevention and control measures. However, the sounding parameters were limited and the quantitative analysis was preliminary, more integrated, and thorough studies of this topic were called for in the future.
Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
(Copyright © 2023. Published by Elsevier B.V.)