Effects of enhancing nitrogen use efficiency in cropland and livestock systems on agricultural ammonia emissions and particulate matter air quality in China

Abstract. Chinese agriculture has long been characterized by low nitrogen use efficiency (NUE) associated with substantial ammonia (NH₃) loss, which contributes significantly to fine particulate matter (PM_2.5) pollution. However, the knowledge gaps in the spatiotemporal patterns of NH₃ emissions and the states of nitrogen management of agricultural systems render it challenging to evaluate the effectiveness of different mitigation strategies and policies. Here, we explored the NH₃ mitigation potential of various agricultural NUE-improving scenarios and their subsequent effects on PM_2.5 pollution in China. We developed and used a combination of bottom-up emission models and a nitrogen mass flow model to evaluate the NUE of different crop and livestock types at a provincial scale in China. We generated gridded NH₃ emission input to drive a chemical transport model to provide an integrated assessment of the air quality impacts of four improved nitrogen management scenarios. The total agricultural NH₃ emission of China was estimated to be 11.2 Tg NH₃ in 2017, of which 46.2 % and 53.8 % are attributable to fertilizer use and livestock animal waste, respectively. Our results show that grain crops have higher NUE than fruits and vegetables, while high livestock NUE can be found in pork and poultry. We also found that by implementing different mitigation scenarios, agricultural NH₃ emissions can be effectively reduced by 11.6 %–39.3 %. Consequently, annual population-weighted PM_2.5 reductions were estimated to be 1.3–4.1 µg m^–3. Our results provide decision support for policymaking concerning agricultural NH₃ emissions and their public health impacts.