Variations in Vertical Distributions of O, Its Precursors, and Formation Sensitivity in Beijing, China, Based on Ground-Based Remote Sensing.

Developing effective emission reduction strategies to mitigate ozone (O) pollution requires a comprehensive understanding of its dynamics and formation sensitivity. Herein, the continuous vertical profiles of O and its precursors (formaldehyde and nitrogen dioxide), and O formation sensitivity, as well as their temporal variations, were investigated by ground-based remote sensing observations at urban and rural sites in Beijing, China, from 2018 to 2023. The maximum monthly mean O concentration within the boundary layer was observed at an altitude of 100-300 m. Concentrations of O and its precursors declined from 2018 to 2021, followed by slight increases in 2022 and 2023. The combined temporal percentages of O formation under the NO-limited and transition regimes were accessed at both sites. These percentages for the boundary layer condition have reached 69.2% at the rural site during summer 2023. The trend toward a shift from the VOC-limited to NO-limited regime was observed. This shift occurred at a much faster rate at the rural site than at the urban site. The findings of the study indicate that a predominantly VOC-limited regime is expected to be confined to a narrow near-surface layer within the urban areas of Beijing by 2030 if current trends continue.