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

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

Tong Sha, Siyu Yang, Qingcai Chen, Jing Wei, Mingchen Ma, Yang Gao, Yufan Zhu, Yan Hu, K. Folkert Boersma and Jun Wang
Journal of geophysical research. Atmospheres, Vol.130(21), e2025JD044623
11/16/2025
DOI: 10.1029/2025JD044623
url
https://research.wur.nl/en/publications/elucidating-contributions-of-anthropogenic-and-soil-nosubxsub-emiView
Open Access

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. Surface ozone (O 3 ) pollution in China is no longer confined to summer. Our study reveals that high‐O 3 episodes have extended into spring and autumn, with concentrations increasing significantly each year. While strategies to reduce anthropogenic NO x emissions (ANO x ) remain crucial for O 3 mitigation, our study highlights the underappreciated role of soil NO x emissions (SNO x ), which constitute 23%–27% of total NO x during warm seasons (April–September) in China. In this study, we employed an innovative approach combining machine learning and a numerical model to assess the impacts of ANO x and SNO x on warm‐season O 3 increases from 2015 to 2019. Our simulations suggest that SNO x can exacerbate O 3 pollution across China, and its impact varies by region and season. Notably, fertilization‐driven SNO x contribute to rising O 3 levels, even though soil emission levels are lower than in summer. As China successfully reduces industrial and vehicle emissions, O 3 formation is likely to become more sensitive to SNO x . Our findings highlight the importance for policymakers to develop tailored, season‐specific strategies for controlling soil emissions to effectively mitigate O 3 pollution. Warm‐season soil NO x emissions (SNO x ) account for 23%–27% of total NO x emissions in China during 2015–2022 As anthropogenic emissions decline, SNO x changes can promote the increase in warm‐season O 3 concentrations O 3 pollution control must consider both soil and anthropogenic NO x emissions and take into account regional and seasonal differences
 nitrogen dioxide soil emissions O3 pollution machine learning model simulation

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