Mid-century Air Quality and Public Health Responses to Future Agricultural Ammonia Emission Pathways

Agricultural ammonia (NH₃) emissions, primarily released from livestock waste and synthetic fertilizer application, are a major precursor of fine particulate matter (PM_2.5), imposing considerable public health burdens worldwide. Although these emissions are strongly linked to socioeconomic factors and agricultural development pathways, a comprehensive mid-century assessment of air quality and health benefits under different agricultural futures has yet to be fully established. In this study, we scaled NH₃ emissions from various crop and livestock species under three scenarios developed by the Food and Agriculture Organization: Business as Usual (BAU), Stratified Societies (SSS), and Toward Sustainability (TSS), using documented and projected agricultural data. PM_2.5-attributable health outcomes were quantified via a hybrid approach integrating the GEOS-Chem High Performance (GCHP) model, machine learning bias correction, and the Global Exposure Mortality Model (GEMM). Results indicate that global NH₃ emissions substantially increase under BAU and SSS (+50–51% relative to the 2012 baseline), but remain nearly stable under TSS, where growth in livestock emissions is offset by fertilizer phase-out. Global population-weighted PM_2.5 concentrations are projected to rise by 1.2 μg m⁻³ under BAU and 1.3 μg m⁻³ under SSS, but decline by 1.0 μg m⁻³ under TSS. Under baseline conditions, PM_2.5 is estimated to cause 4.3 million premature deaths annually. Projections suggest that premature deaths would rise by more than 80000 under BAU and SSS, affecting Europe, India, and East China in particular, where equitable development is essential to mitigate the future mortality. Although TSS – characterized by equal access to basic services, universal food availability, and widespread conservation – could reduce premature deaths by nearly 50000, increases are still expected in Sub-Saharan Africa due to elevated emissions and worsened PM_2.5 air quality driven by population growth and economic development. Our findings underscore the need for further agricultural transformations – towards crops with higher nitrogen use efficiency, livestock with lower emission factors, and less meat-intensive diets – to prevent disproportionate public health burden. This scenario-based analysis highlights the benefits of sustainable agricultural pathways, demonstrating that strategies ensuring nutritious and sustainable food production can simultaneously improve air quality and reduce global mortality.