Opportunities to Mitigate PM_2.5 and Nitrogen Deposition through Agricultural NH₃ Control Strategies in China's...

High ammonia (NH₃) emissions mostly from agricultural sources have contributed to PM_2.5 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 PM_2.5 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 NO_x emissions. When combining NH₃ and NO_x emission reductions, the effects of NH₃ controls on PM_2.5 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 PM_2.5 management and nitrogen deposition mitigation. In the near future, with continuous NO_x 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 NO_x emission reductions.