Projecting future climate change impacts on ozone pollution with machine learning

Ozone (O₃) is a secondary pollutant in the atmosphere formed by photochemical reactions that endangers human health and ecosystems. Since the mid-1990s, Asian regions have experienced the fastest O₃ increase rate of 2–8 ppb per decade at remote surface sites and in the lower free troposphere across the world. Therefore, a deeper understanding of the long-term changes and causes of tropospheric O₃ concentrations is of significance in both the environment and climate policy making.

In this study, to quantify the impacts of future climate change on O₃ pollution, near-surface O₃ concentrations over Asia in 2020–2100 are projected using a machine learning (ML) method along with multi-source data. The ML model is trained with assimilated O₃ data from a global atmospheric chemical transport model and real-time observations. The ML model is then used to predict future O₃ with meteorological fields from CMIP6 multi-model simulations under various climate scenarios. The climate penalty on future O₃ is robust over most regions of Asia. The near-surface O₃ levels are projected to increase by 5 %–20 % over South China, Southeast Asia, and South India under the high-forcing scenarios in the last decade of 21st century, compared to the first decade of 2020–2100. We also find that the summertime O₃ pollution over eastern China will expand from North China to South China and extend into the cold season in a warmer future.

Unlike the traditional “black box” ML models, we predict near‐surface O₃ concentrations in China in 2030 and 2060 based on a process‐based interpretable ML method, integrated with physical and chemical processes of O₃, natural emissions of O₃ precursors, and other multi‐source data. The direct (via changing physical and chemical processes of O₃) and indirect (via changing natural emissions of O₃ precursors) impacts of future climate change on O₃ concentrations are quantitatively analyzed. The results suggest that the climate‐driven O₃ levels are projected to decrease by more than 0.4 ppb in 2060 over eastern China under a carbon neutral scenario relative to a high emission scenario. The physical and chemical processes under climate change play a more important role in regulating O₃ concentrations than natural emissions in the future under the carbon neutral scenario.