Exploring global changes in agricultural ammonia emissions and their contribution to nitrogen deposition since 1980

Global gains in food production over the past decades have been associated with substantial agricultural nitrogen overuse and ammonia emissions, which have caused excessive nitrogen deposition and subsequent damage to the ecosystem health. However, it is unclear which crops or animals have high ammonia emission potential, how these emissions affect the temporal and spatial patterns of nitrogen deposition, and where to target future abatement. Here, we develop a long-term agricultural ammonia emission dataset in nearly recent four decades (1980-2018) and link it with a chemical transport model for an integrated assessment of global nitrogen deposition patterns. We found global agricultural ammonia emissions increased by 78% from 1980 and 2018, in which cropland ammonia emissions increased by 128%, and livestock ammonia emissions increased by 45%. Our analyses demonstrated that three crops (wheat, maize, and rice) and four animals (cattle, chicken, goats, and pigs) accounted for over 70% total ammonia emissions. Global reduced nitrogen deposition increased by 72% between 1980 and 2018 and would account for a larger part of total nitrogen deposition due to the lack of ammonia regulations. Three countries (China, India, and the United States) accounted for 47% of global ammonia emissions, and had substantial nitrogen fertilizer overuse. Nitrogen deposition caused by nitrogen overuse accounted for 10 to 20% of total nitrogen deposition in hotspot regions including China, India, and the United States. Future progress toward reducing nitrogen deposition will be increasingly difficult without reducing agricultural ammonia emissions.