Anthropogenic nitrogen impacts on global PM2.5-O3 co-pollution health burden

The growing recognition of the adverse health impacts posed by ambient fine particulate matter (PM 2.5 ) and ozone (O 3 ) has driven global efforts to implement stricter regulations on reactive nitrogen emissions, including nitrogen oxides (NO x ) and ammonia (NH 3 ). Nevertheless, effective mitigation strategies remain constrained by the gap between precursor emissions and health effects, especially in regions facing compounded PM 2.5 -O 3 pollution. This work models the synergistic health burden from PM 2.5 -O 3 co-exposure and its complex responses to anthropogenic nitrogen emission controls. Our modelling reveals a significant positive interaction between PM 2.5 and O 3 , with co-exposure mortality 24.8% higher than non-interactive additive estimates. NO x and NH 3 emissions contribute to 20.3% and 19.4% of these deaths, respectively, with relative importance varying across regions and seasons. To mitigate joint PM 2.5 -O 3 health impacts, NO x reduction is currently more effective than NH 3 control, though sustained benefits require coordinated cuts to both species. Importantly, due to a non-linear emission-health relationship, only aggressive emission reductions can generate proportionally significant health gains, exceeding 20.2% improvements over mild control scenarios. These findings challenge conventional uniform emission control measures and provide a scientific basis for developing dynamic air quality and health management frameworks.