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 (PM2.5) 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 explore the NH3 mitigation potential of various agricultural NUE-improving scenarios and their subsequent effects on PM2.5 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 the 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 PM2.5 reductions were estimated to be 1.3-4.1 μgm-3. Our results provide decision support for policymaking concerning agricultural NH3 emissions and their public health impacts.