@article { doi:10.1073/pnas.2121998119,
	title = {Exploring global changes in agricultural ammonia emissions and their contribution to nitrogen deposition since 1980},
	journal = {Proceedings of the National Academy of Sciences},
	volume = {119},
	number = {14},
	year = {2022},
	pages = {e2121998119},
	abstract = {Agricultural systems are already major forces of ammonia pollution and environmental degradation. How agricultural ammonia emissions affect the spatio-temporal patterns of nitrogen deposition and where to target future mitigation efforts, remains poorly understood. We develop a substantially complete and coherent agricultural ammonia emissions dataset in nearly recent four decades, and evaluate the relative role of reduced nitrogen in total nitrogen deposition in a spatially explicit way. Global reduced nitrogen deposition has grown rapidly, and will occupy a greater dominant position in total nitrogen deposition without future ammonia regulations. Recognition of agricultural ammonia emissions on nitrogen deposition is critical to formulate effective policies to address ammonia related environmental challenges and protect ecosystems from excessive nitrogen inputs. 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{\textendash}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.},
	doi = {10.1073/pnas.2121998119},
	url = {https://www.pnas.org/doi/abs/10.1073/pnas.2121998119},
	author = {Lei Liu and Wen Xu and Xiankai Lu and Buqing Zhong and Guo, Yixin and Xiao Lu and Yuanhong Zhao and Wei He and Songhan Wang and Xiuying Zhang and Liu, Xuejun and Peter Vitousek}
}
