Global ammonia emissions from synthetic nitrogen fertilizer applications in agricultural systems: empirical and process-based estimates and uncertainty

Authors: XU, RONGTING - Auburn University; TIAN, HANQIN - Auburn University; PAN, SHUFEN - Auburn University; Prior, Stephen - Steve; FENG, YUCHENG - Auburn University; BATCHELOR, WILLIAM - Auburn University; CHEN, JIAN - Auburn University; YANG, JIA - Auburn University

Submitted to: Global Change Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/5/2018
Publication Date: 12/12/2018
Citation: Xu, R., Tian, H., Pan, S., Prior, S.A., Feng, Y., Batchelor, W.D., Chen, J.Z., Yang, J. 2018. Global ammonia emissions from synthetic nitrogen fertilizer applications in agricultural systems: empirical and process-based estimates and uncertainty. Global Change Biology. 25(1):314-326. https://doi.org/10.1111/gcb.14499.
DOI: https://doi.org/10.1111/gcb.14499

Interpretive Summary: This effort characterized NH3 emissions from synthetic N fertilizer applied to global crop lands during 1961-2010 using different computer model configurations. Global NH3 emissions increased during this period with large spatial variations. Southern Asia (covering China and India) was responsible for more than 50% of global emissions since the 1980s, followed by North America and Europe. Rice cultivation was the largest contributor since the 1990s, followed by corn and wheat. This modelling effort highlight the importance of considering multiple environmental factors to avoid underestimating global NH3 emissions. This new information will help policy-makers and farmers choose fertilizer management practices that protect air quality and food security.

Technical Abstract: Excessive ammonia (NH3) emitted from nitrogen fertilizer applications in global croplands plays an important role in atmospheric aerosol production, resulting in visibility reduction and regional haze. However, large uncertainties exist in NH3 emission estimates from global and regional croplands, which utilize different data and methods. In this study, we coupled a process-based Dynamic Land Ecosystem Model (DLEM) with the bi-directional NH3 exchange module in the Community Multiscale Air- Quality (CMAQ) model (DLEM-Bi-NH3) to quantify NH3 emissions at global, continental, and crop-type scales at a spatial resolution of 0.5 x 0.5 degrees during 1961-2010. This study indicated that global NH3 emissions increased from 1.91±0.03 to 16.72±0.47 Tg N per yr between 1961 and 2010. The annual increase of NH3 emissions showed large spatial variations. Southern Asia, including China and India, accounted for more than 50% of total global NH3 emissions since the 1980s, followed by North America and Europe. Rice cultivation was the largest contributor to total global NH3 emissions since the 1990s, followed by maize and wheat. In addition, results showed that not considering environmental factors in the empirical methods (constant emission factor in the IPCC Tier 1 guideline) could underestimate NH3 emissions in the context of global warming, with the highest difference (i.e., 6.85 Tg N per yr) occurring in 2010. Estimates by DLEM-Bi-NH3 module provided a scientific understanding of global and regional NH3 emissions over the past 50 years, which offers a reference for policy-makers and farmers to optimally manage nitrogen fertilizer practices to improve air quality and food security.