Unlocking nitrogen management potential via large-scale farming for air quality and substantial co-benefits.

China's sustained air quality improvement is hindered by unregulated ammonia (NH₃) emissions from inefficient nitrogen management in smallholder farming. Although the Chinese government is promoting a policy shift to large-scale farming, the benefits of this, when integrated with nitrogen management, remain unclear. Here we fill this gap using an integrated assessment, by combining geostatistical analysis, high-resolution emission inventories, farm surveys and air quality modeling. Smallholder-dominated farming allows only 13%–31% NH₃ reduction, leading to limited PM_2.5 decreases nationally due to non-linear PM_2.5 chemistry. Conversely, large-scale farming would double nitrogen management adoption rates, increasing NH₃ reduction potential to 48%–58% and decreasing PM_2.5 by 9.4–14.0 μg·m⁻³ in polluted regions. The estimated PM_2.5 reduction is conservative due to localized NH₃-rich conditions under large-scale livestock farming. This strategy could prevent over 300 000 premature deaths and achieve a net benefit of US $68.4–86.8 billion annually, unlocking immense benefits for air quality and agricultural sustainability. [ABSTRACT FROM AUTHOR]