Mitigating ammonia emission from agriculture reduces PM_2.5 pollution in the Hai River Basin in China

The Hai River Basin (HRB), one of the most populated areas in China, is experiencing high NH₃ emissions, mostly from agricultural sources, and suffering from strongly enhanced PM_2.5 concentrations in all urban areas. Further population growth and urbanization projected until 2030 may exacerbate this situation. Here, the NUFER (NUtrient flows in Food chains, Environment and Resources use) and GAINS (Greenhouse gas - Air pollution Interactions and Synergies) models have been coupled for the first time to understand possible changes of agricultural NH₃ emission between 2012 and 2030 and their impacts on ambient PM_2.5 concentrations, and to explore options to improve this situation. Results show that agricultural ammonia emissions in the HRB were 1179kt NH₃ in 2012, 45% of which was from the hotspots at or near conurbation areas, including Beijing-Tianjin, Tangshan-Qinhuangdao, Shijiazhuang-Baoding, Dezhou, Handan-Liaocheng, and Xinxiang. Without intervention, agricultural ammonia emissions will further increase by 33% by 2030. The impacts of several scenarios were tested with respect to air pollution. Compared to the business-as-usual scenario, a scenario of improved technology and management combined with human diet optimization could greatly reduce emission (by 60%), and lead to 22-43% and 9-24% decrease of the secondary inorganic aerosols and PM_2.5 concentrations, respectively, in the hotspots of NH₃ emissions. Our results further confirmed that ammonia control is needed for air pollution abatement strategies (SO₂, NO_x and primary PM reduction) to be effective in terms of PM_2.5.