Elucidating Contributions of Anthropogenic and Soil NO x Emissions Changes to O 3 Trends Over China

Abstract Surface ozone (O 3 ) pollution is a critical environmental challenge, but existing research predominantly focuses on its summer peaks. Our analysis shows that high‐O 3 episodes now expand into spring and autumn in China, with warm‐season (April–September) maximum daily average 8‐hr (MDA8) O 3 concentrations rising at 5.2 μg m −3 yr −1 during 2014–2023. Current O 3 mitigation focuses on anthropogenic NO x emissions (ANO x ) while neglecting the contribution of soil NO x emissions (SNO x ) to tropospheric O 3 formation. Here, we developed an innovative framework combining the machine learning model (XGBoost) with the Unified Inputs for WRF‐Chem (UI‐WRF‐Chem) to quantify the impacts of ANO x and SNO x on O 3 increases during 2015–2019. Results show that although warm‐season SNO x constitute only 23%–27% of total NO x emissions in China (2015–2022), they generally drive O 3 increases, exhibiting distinct regional and seasonal heterogeneities. Compared to urban areas, the O 3 formation regimes in rural areas of the Yangtze River Delta region predominantly shift to NO x ‐limited, making O 3 highly sensitive to SNO x . SNO x changes lead to warm‐season MDA8 O 3 increases of 1.0–1.3 μg m −3 during 2016–2019 relative to 2015. Although similar regime shifts have occurred, rural areas in the Beijing‐Tianjin‐Hebei and Fenwei Plain regions still retain strong VOCs‐limited characteristics; thus, SNO x perturbation impacts on O 3 are smaller. Although summer SNO x are higher, their contribution to O 3 increases in transitional seasons (April, May, and September) shows an upward trend, suggesting more attention should be paid to fertilization‐driven SNO x . Our study highlights that future O 3 control strategies should account for SNO x and their regional and seasonal differences.