Underappreciated roles of soil nitrogen oxide emissions on global acute health burden

The recognized importance of ambient fine particulate matter (PM_2.5), ozone (O₃), and nitrogen dioxide (NO₂) on human health has prompted the world to enact increasingly strict regulations on anthropogenic nitrogen oxides (NO_x) emissions. However, the health concerns from soil NO_x, potentially driven by fertilizer input but conventionally categorized as natural sources, remain less studied. Here, we emphasize the underappreciated roles of soil NO_x emissions on health burden attributable to short-term PM_2.5, O₃, and NO₂ exposure. Globally, we quantify acute health effects using machine-learning-based daily exposure estimates and identify influences of soil NO_x emissions based on chemical transport model simulations. We find that 72.3% of the globe is affected by soil NO_x emissions, whose contributions to short-term PM_2.5, O₃, and NO₂ pollution lead to 13.9 (95% Confidence Interval [CI]: 9.1-18.8), 26.0 (18.2-34.2), and 13.9 (10.3-17.5) thousand premature mortality, respectively, in 2019. With distinct variations in regions, seasons, and pollutants, soil NO_x-originated air pollution poses a global health concern, particularly for developing regions and intensively agricultural areas. In response to the intensive fertilizer use, South Asia, Southern Sub-Saharan Africa, and Central Europe witness the largest soil NO_x-related health burden of up to 1.6 (95% CI: 1.1-2.1) mortality per 100k population. The overall health risk peaks in May, with O₃ pollution typically dominating the soil NO_x-attributable health burden during warm seasons and NO₂ or PM_2.5 during cold months. Our study highlights the necessity of dynamically adapted agricultural strategies for health-oriented multi-pollutant control, among which the improved use of synthetic fertilizers deserves priority under the ever-changing climate.