Variations in Vertical Distributions of O3, Its Precursors, and Formation Sensitivity in Beijing, China, Based on Ground-Based Remote Sensing.

Developing effective emission reduction strategies to mitigate ozone (O3) pollution requires a comprehensive understanding of its dynamics and formation sensitivity. Herein, the continuous vertical profiles of O3 and its precursors (formaldehyde and nitrogen dioxide), and O3 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 O3 concentration within the boundary layer was observed at an altitude of 100-300 m. Concentrations of O3 and its precursors declined from 2018 to 2021, followed by slight increases in 2022 and 2023. The combined temporal percentages of O3 formation under the NOx-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 NOx-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.