Vertical Evolution of Ozone Formation Sensitivity Based on Synchronous Vertical Observations of Ozone and Proxies for Its Precursors: Implications for Ozone Pollution Prevention Strategies
Qihou Hu, Xiangguang Ji, Qianqian Hong, Jinhui Li, Qihua Li, Jinping Ou, Haoran Liu, Chengzhi Xing, Wei Tan, Jian Chen, Bowen Chang, Cheng Liu
Abstract
High Resolution Image Download MS PowerPoint Slide Photochemical ozone (O 3 ) formation in the atmospheric boundary layer occurs at both the surface and elevated altitudes. Therefore, the O 3 formation sensitivity is needed to be evaluated at different altitudes before formulating an effective O 3 pollution prevention and control strategy. Herein, we explore the vertical evolution of O 3 formation sensitivity via synchronous observations of the vertical profiles of O 3 and proxies for its precursors, formaldehyde (HCHO) and nitrogen dioxide (NO 2 ), using multi-axis differential optical absorption spectroscopy (MAX–DOAS) in urban areas of the Beijing–Tianjin–Hebei (BTH), Yangtze River Delta (YRD), and Pearl River Delta (PRD) regions in China. The sensitivity thresholds indicated by the HCHO/NO 2 ratio (FNR) varied with altitude. The VOC-limited regime dominated at the ground level, whereas the contribution of the NO x -limited regime increased with altitude, particularly on heavily polluted days. The NO x -limited and transition regimes played more important roles throughout the entire boundary layer than at the surface. The feasibility of extreme NO x reduction to mitigate the extent of the O 3 pollution was evaluated using the FNR–O 3 curve. Based on the surface sensitivity, the critical NO x reduction percentage for the transition from a VOC-limited to a NO x -limited regime is 45–72%, which will decrease to 27–61% when vertical evolution is considered. With the combined effects of clean air action and carbon neutrality, O 3 pollution in the YRD and PRD regions will transition to the NO x -limited regime before 2030 and be mitigated with further NO x reduction.