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

Abstract

SignificanceAgricultural 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.

Keywords: agriculture; ammonia emissions; nitrogen deposition; nitrogen overuse.

Fig. 1.

Agricultural NH₃ emissions in 2010. (A) Spatial distribution of cropland NH₃ emissions. (B) Contribution of different crops to cropland NH₃ emissions. (C) Spatial distribution of NH₃ emissions from livestock. (D) Contribution of different animals to livestock NH₃ emissions. (E) NH₃ emissions from agriculture (fertilizer plus livestock). (F) Nonagricultural NH₃ emissions. The agricultural NH₃ emissions were developed in this study at a high resolution (0.083°), while the nonagricultural NH₃ emissions were based on the Community Emissions Data System (CEDS) NH₃ emissions (0.5°).

Fig. 2.

Changes of (A) cropland and (B) livestock NH₃ emissions between 1980 and 2018.

Fig. 3.

Atmospheric N_r deposition simulated by the GEOS-Chem model in 2010. (A–C) Total NH_x, NO_y, and N_r deposition. (D) Gridded ratio of NH_x to NO_y. (E) Gridded ratio of NH_x to total N_r deposition. (F) Ratio of N_r deposition to N_r emissions. Global agricultural NH₃ emissions between 1980 and 2018 were adopted from our developed high-resolution datasets (at 0.083°), while the nonagricultural NH₃ emissions and NO_x emissions were obtained from the Community Emissions Data System (CEDS).

Fig. 4.

Changes of N_r deposition. Spatial changes of (A) NH_x and (B) NO_y deposition between 1980 and 2018. (C) Time series of N_r deposition on land globally in China, the United States, and Western Europe.

Fig. 5.

Contribution of N fertilizer overuse to N_r deposition. (A) Schematic illustration of agricultural NH₃ emissions and N_r deposition. (B) A flowchart of calculating agricultural NH₃ emissions and N_r deposition. (C) Avoidable N application without affecting current yields. N fertilizer overuse by each crop can be found in SI Appendix, Fig. S13. (D) Average percentage of the attainable yield achieved by wheat, maize, and rice. Spatial maps of the percent attainable yield for each crop can be found in SI Appendix, Fig. S12. (E) Contribution of N fertilizer overuse to NH₃ emissions. (F) Contribution of N fertilizer overuse to N_r deposition by country.