Abstract: Ammonia is an alkaline reactive nitrogen gas in the atmosphere. A large amount of ammonia is emitted due to increasing anthropogenic activities such as intensive farming and livestock production in agriculture, causing a series of eco-environmental problems. Ammonia can react with acidic precursors (such as SO₂ and NO_x) to form secondary inorganic aerosols, which are the main components of PM_2.5, leading to severe haze episodes that reduce air quality and affect public health. In response to the research objectives of the Premier's Fund 'Agricultural Emission Status and Enhanced Governance Plan' implemented in 2017, and the ammonia emission reduction action plan proposed in the 'Three-year Action Plan for Winning the Blue Sky Defense War' in 2018, research on the reduction of agricultural ammonia emission in China, especially in the Beijing-Tianjin-Hebei and surrounding areas, was carried out to improve the efficient utilization of regional agricultural resources and air pollution control. In 2018, China's total ammonia emissions were 9.90×10⁶ t, with the largest emissions in the Beijing-Tianjin-Hebei and surrounding regions ('2+26' cities) (1.41×10⁶ t), which was consistent with the measured ammonia concentration distribution across China. For example, high ammonia concentrations occurred in the North China Plain, where the '2+26' cities are located. Agricultural emissions were the main ammonia sources, and 50% and 30% of total ammonia emissions came from livestock and crop production systems, respectively. However, non-agricultural sources (such as industry and traffic) made a larger contribution in urban areas, based on nitrogen isotope source apportionment. We simulated an ammonia mitigation scenario (40% reduction) in the North China Plain, which reduced NO₃^- concentration by 50% and the peak concentration of PM_2.5 by 15%-20%. Effective ammonia mitigation actions should be taken urgently to improve air quality. For ammonia emission reduction in crop production, there is an urgent need to control synthetic fertilizer application rates. However, using deep placement of fertilizers or replacing traditional fertilizers (such as urea) with organic manures, nitrate-based fertilizers and enhanced efficiency fertilizers could achieve a higher reduction. For livestock production systems, we identified a series of ammonia reduction options for pigs, broilers and beef production, using a low protein diet as the base measure, followed by improved housing and manure/waste management with optimized field application of manure, urine and slurry. Based on the ammonia emission status and the reduction potential, we propose an ammonia reduction goal for China. This must be accompanied by improved atmospheric ammonia monitoring and isotope source apportionment to identify sources to prove effectiveness of the technologies in key areas (ammonia pollution hot spots) and improve their uptake. This research will provide theoretical and technological support for better control of air pollution and a return to the 'blue skies'.