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https://doi.org/10.5194/egusphere-2025-1432
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/egusphere-2025-1432
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
19 Dec 2025
| 19 Dec 2025
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).
Technical note: Quantifying the Nitrogen Isotope Difference between Ammonium in the Atmosphere and Ammonia Emitted from Sources
Abstract. The difference (δ15N4a-3s) in nitrogen isotopes (δ15N) between NH4+ and source - emitted NH3 is a crucial factor influencing the source apportionment of atmospheric NH4+. This δ15N4a-3s is mainly due to isotopic fractionation during NH3 - NH4+ gas - particle conversion and atmospheric deposition. The impact of isotope fractionation on δ15N4a-3s had been well quantified by simplified method, but that of atmospheric deposition had often been overlooked. This study developed a model to assess δ15N4a-3s variations by considering both the atmospheric deposition and isotope fractionation. The results of six model scenarios showed the difference between δ15N4a-3s values under both influences and under isotope fractionation alone increased with the rise of ξA (the molar fraction of NH4+ to NHx in the atmosphere). At 20 °C, when ξA = 0.9, the maximum gap could reach 10.7%. δ15N4a-3s was insensitive to NH3 and NH4+ deposition rates, NH4+ generation rate, and temperature, but it was sensitive to ξA. A prediction function for δ15N4a-3s was constructed and applied for atmospheric NH4+ source apportionment in the Yellow River Delta. Compared with the simplified method, the fitted equation could more reasonably reflect the contribution of agricultural sources (e.g., fertilizer application). The constructed equation could be used for tracing atmospheric NH4+origin, thus improving the accuracy of atmospheric NH4+ source apportionment.
How to cite. Tian, C., Yin, X., Yang, X., Yu, X., Zong, Z., Tian, X., Li, Y., Kallenborn, R., and Li, Y.-F.: Technical note: Quantifying the Nitrogen Isotope Difference between Ammonium in the Atmosphere and Ammonia Emitted from Sources, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2025-1432, 2025.
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Status: open (until 30 Jan 2026)
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RC1: 'Comment on egusphere-2025-1432', Anonymous Referee #1, 08 Jan 2026
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- The parameter t is introduced too briefly in the methodology. Is t computed from 0 until NH3 and NH4+ reach equilibrium? The influence of the evolution of t on the model output is not made clear.
- It is unclear how the [NH3d]t and [NH4+d]t terms in Eq. (6) are used to calculate d15N4a-3s.
- Eq. (10) assumes that the d15N of deposition equals that of the atmosphere. How is this assumption carried into the calculation of d15N4a-3s in Eq. (4)? Also, should NH4 in the equation read NH4+?
- How is the d15N-NHx value obtained from Eq. (8) passed to Eq. (4) to compute d15N-NH4+ or d15N-NH3s, which is later set to 0.
- In Eq. (6) the [NH3a]t is [NH3a]t-1 times 1-G4-D3. Here, Are G4 and D3 rates or ratios?
- Line 146 states that G4/D3 ≈ 3 %. The subsequent sensitivity tests set G4 to 0.5–2 × D3, which spans one to two orders of magnitude above this ratio.
- In Fig. 2, which input parameters are used for the sensitivity tests? Are they the D3, D4, G4, T, and ξ values shown in the figure? Ξ and the molar fraction of NH4+/NHx appear to be identical, so how should these parameters be assigned?
- Section 3.4 uses several datasets without citation, e.g. the d14N of NH3 emission sources and the NH4+ fraction of NHx for 2013 and 2021.
ReplyCitation: https://doi.org/10.5194/egusphere-2025-1432-RC1
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Chongguo Tian
CORRESPONDING AUTHOR
Key Laboratory of Land and Sea Ecological Governance and Systematic Regulation, Shandong Academy for Environmental Planning, Jinan, 250101, P.R. China
Shandong Key Laboratory of Coastal Environmental Processes, CAS Key Laboratory of Coastal Environmental Processes and Ecological Remediation, Yantai Institute of Coastal Zone Research, Chinese Academy of Sciences, Yantai 264003, P.R. China
Xuehua Yin
Shandong Key Laboratory of Coastal Environmental Processes, CAS Key Laboratory of Coastal Environmental Processes and Ecological Remediation, Yantai Institute of Coastal Zone Research, Chinese Academy of Sciences, Yantai 264003, P.R. China
University of Chinese Academy of Sciences, Beijing, 100049, P.R. China
Xuena Yang
Key Laboratory of Land and Sea Ecological Governance and Systematic Regulation, Shandong Academy for Environmental Planning, Jinan, 250101, P.R. China
Xiaoxia Yu
Key Laboratory of Land and Sea Ecological Governance and Systematic Regulation, Shandong Academy for Environmental Planning, Jinan, 250101, P.R. China
Zheng Zong
Environment Research Institute, Shandong University, Qingdao 266237, P.R. China
Xinpeng Tian
Shandong Key Laboratory of Coastal Environmental Processes, CAS Key Laboratory of Coastal Environmental Processes and Ecological Remediation, Yantai Institute of Coastal Zone Research, Chinese Academy of Sciences, Yantai 264003, P.R. China
Yuchen Li
Shandong Key Laboratory of Coastal Environmental Processes, CAS Key Laboratory of Coastal Environmental Processes and Ecological Remediation, Yantai Institute of Coastal Zone Research, Chinese Academy of Sciences, Yantai 264003, P.R. China
University of Chinese Academy of Sciences, Beijing, 100049, P.R. China
Roland Kallenborn
Norwegian University of Life Sciences, Faculty of Chemistry, Biotechnology and Food Sciences, Christian Magnus Falsens vei 18, 1433, As, Norway
Yi-Fan Li
International Joint Research Center for Persistent Toxic Substances (IJRC-PTS), State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin 150090, P.R. China
Short summary
This study explores the neglected role of atmospheric deposition in δ15N4a-3s (δ15N difference between NH4+ and source NH3), a key parameter in atmospheric NH4+ source tracing. We develop an integrated model coupling these two processes and find that the difference in δδ15N4a-3s between the combined effect and the pure fractionation scenario increases with ξA (NH4+/NHx molar ratio). This work provides a new idea for precise NH4+ source partitioning.
This study explores the neglected role of atmospheric deposition in δ15N4a-3s (δ15N difference...