Opportunities to Mitigate PM2.5 and Nitrogen Deposition through Agricultural NH3 Control Strategies in China’s Beijing-Tianjin-Hebei Region

High ammonia (NH3) emissions mostly from agricultural sources have contributed to PM2.5 air pollution and excess nitrogen deposition harmful to human and ecosystem health in China. Here we develop an assessment framework combining an agricultural management technology database and evaluate technology combinations for their potentials in NH3 emission reductions and consequent air quality and ecosystem benefits for the Beijing-Tianjin-Hebei (BTH) region. Results show that BTH agricultural NH3 emissions can be reduced by up to 57% (274 Gg of N per year) in 2019. With maximum feasible NH3 reduction (57%), annual PM2.5 concentrations and nitrogen deposition in BTH can be reduced by up to 7% and 13%, respectively, which are more significant than the effects of halving local anthropogenic NOx emissions. When combining NH3 and NOx emission reductions, the effects of NH3 controls on PM2.5 mitigation will be suppressed while facilitating more efficient local nitrogen deposition mitigation. Our findings implicate that technically feasible NH3 emission reductions are still useful for current PM2.5 management and nitrogen deposition mitigation. In the near future, with continuous NOx controls, additional NH3 controls are required to further mitigate nitrogen deposition in BTH, while associated air quality benefits would depend nonlinearly upon the levels of NH3 and NOx emission reductions.