Impact of anthropogenic emissions on the global tropospheric ozone under the carbon neutrality scenario

Based on the Community Earth System Model (CESM2), future emission scenarios, and the stratospheric ozone tracer O3S, this study reveals the changes of tropospheric O3 and its precursors, and the impact of stratospheric intrusion on tropospheric O3 under a carbon neutral scenario. The results show that, surface anthropogenic and aircraft emissions of NOx were significantly reduced under a carbon neutral scenario, especially during the winter and spring seasons, which lead to a significant decrease in surface NOx concentrations. Along with the reduction of O3 precursors, global surface O3 concentration was also decreasing, except in Eastern China, where the titration of O3 by NO was weakened. In the vertical, the most substantial decrease of O3 concentration was concentrated around the tropopause, with a reduction of more than 26×10-9, especially in summer. The decrease of stratospheric O3 concentration caused by reduced aircraft emissions also contributed to the reduction in tropospheric O3. Under a carbon neutral scenario, the decrease of stratospheric invasion to surface O3 was the highest in winter with reduced values of 1.7×10-9, and the lowest in summer with reduced values of 0.9×10-9. In the northern hemisphere, the most substantial decrease was located at high latitudes with values of more than 4×10-9. In the vertical, the decrease of stratospheric contributions to tropospheric O3 increased with altitude, with high values of more than 24×10-9 in the free troposphere during winter. Therefore, the decreases in surface anthropogenic and aircraft emissions under the carbon neutral scenario will benefit the improvement of global ozone pollution, and the decrease of stratospheric contribution also had an important contribution to the future change of ozone concentration. © 2024 Chinese Society for Environmental Sciences. All rights reserved.