Measurement report: Nitrogen Isotope (&delta;<sup>15</sup>N) Signatures of Ammonia Emissions from Livestock Farming: Implications for Source Apportionment of Haze Pollution

Wang, Jinhan; Nie, Zhaojun; Zhang, Yupeng; Jie, Xiaolei; Liu, Haiyang; Zhao, Peng; Liu, Hongen

doi:10.5194/egusphere-2025-4460

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https://doi.org/10.5194/egusphere-2025-4460

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18 Nov 2025

| 18 Nov 2025

Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

Measurement report: Nitrogen Isotope (δ¹⁵N) Signatures of Ammonia Emissions from Livestock Farming: Implications for Source Apportionment of Haze Pollution

Jinhan Wang, Zhaojun Nie, Yupeng Zhang, Xiaolei Jie, Haiyang Liu, Peng Zhao, and Hongen Liu

Abstract. Ammonia emissions from agriculture are the primary source of atmospheric reactive nitrogen, significantly impacting air pollution, soil acidification, eutrophication of water bodies, and human health. Accurate quantification of ammonia from different sources is crucial for effective mitigation. In this study, the air extraction method was employed to collect gases from livestock farms, and the δ¹⁵N values of volatilized ammonia (NH₃) from the animal husbandry industry in the southern Huang - Huai - Hai Plain of China were analyzed using stable nitrogen isotopes. The results show that isotopic signatures differ significantly among livestock types: dairy cows (-20.6 ‰ ± 0.8 ‰), laying hens (-27.4 ‰ ± 1.0 ‰), and pigs (-38.4 ‰ ± 1.7 ‰). These livestock-derived signatures are distinct from those associated with combustion sources (-7.0 ‰ ± 2.1 ‰) and traffic emissions (6.6 ‰ ± 2.1 ‰), and they exhibit considerably lower variability than fertilizer-derived signatures. Overall, this work provides high-precision isotopic source signatures for livestock operations, offering essential parameters for regional atmospheric ammonia source apportionment and highlighting the need for locally tailored mitigation strategies.

Received: 11 Sep 2025 – Discussion started: 18 Nov 2025

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Jinhan Wang, Zhaojun Nie, Yupeng Zhang, Xiaolei Jie, Haiyang Liu, Peng Zhao, and Hongen Liu

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RC1:
'Comment on egusphere-2025-4460', Anonymous Referee #1, 08 Dec 2025 reply
Ammonia (NH₃) emissions from livestock are recognized as a significant source of atmospheric NH₃ and contribute to secondary aerosol and haze formation. This study reports NH₃ concentrations and associated δ¹⁵N-NH₄⁺ values from several livestock farms. Overall, it represents an interesting investigation and adds to the database of atmospheric δ¹⁵N-NH₄⁺. However, the manuscript contains several shortcomings that currently prevent its publication, including spelling and grammatical errors, unclear description of the Materials and Methods, and inadequate presentation in the Results and Discussion. More importantly, the work lacks novelty and in‑depth data analysis, such as source apportionment.
Detailed comments are provided below:
L51: Delete “for.”

L84: Clarify the name, principle, and technical details of the MixSAIR model.

L108: Specify the principle, detection limit, and potential interferences of the method.

L109: Flow rate may affect calculated NH₃ concentrations. Please explain how results obtained with different flow rates were compared.

L116: Remove “T.”

Figure 1 is cluttered and confusing. Please distinguish which data are from your experiments and which are from the literature. Were sampling periods during haze and clean conditions conducted at the same locations? Are the cattle, layer, and fattening pig farms all located in the same city? If so, please include a detailed map showing the sampling points.

L117–118: Specify the absorption solution used.

L122: Which building was selected? Please justify its representativeness for intensive laying‑hen farms.

L144: Should this be “mg L⁻¹”?

L149: Specify what analytical method is being referred to.

The statistical methods should be clearly described.

L185: Should this be “1.7 to 2.5”?

L205: Add a space after “(a)” and “(b).”

L188: Replace the comma before “For” with a period.

Discuss the relationship between temperature and NH₃ emissions, and cite relevant references to support the explanation.

L190: Add a space before “δ¹⁵N.”

L192: Delete “From May to June”; change to “δ¹⁵N-NH₄⁺.”

L194–195: The variations appear too large to support significant differences.

L230: Change to “Martine et al.”

L234: Should this be “David et al. (Felix et al., 2014)”?

L241–243: Add citations to support the argument.

L251–254: Include references and source apportionment calculations to substantiate the conclusions.

L257: Add a space after “(a)” and “(b).”

Figure 4: Clarify the meaning of the boxes or violin plots.

Figure 5: Provide P‑values. The R² values are below 0.1 in both sub‑figures, indicating very weak correlation between GDP/year and δ¹⁵N-NH₄⁺.

L268–271: Figure 5 does not present data on contributions from combustion and vehicular sources. Please provide supporting data.

L272: Add a space after “signatures.”

L274: Add a space after “emissions.”

L282–283: Figure 5b does not show the proportion of δ¹⁵N-NH₄⁺ attributed to combustion and vehicular sources. Please address this.

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Citation: https://doi.org/10.5194/egusphere-2025-4460-RC1
RC2:
'Comment on egusphere-2025-4460', Anonymous Referee #2, 10 Dec 2025 reply
This manuscript presents δ¹⁵N signatures of NH₃ emitted from three major livestock systems (fattening pigs, laying hens, and dairy cows) across the southern Huang-Huai-Hai Plain, applying active sampling and chemical conversion-IRMS analysis. The authors additionally compare their measured endmembers with global literature via meta-analysis and explore relationships between δ¹⁵N–NH₄⁺, GDP, and NH₃ sources. The study provides valuable isotopic source fingerprints, particularly given the scarcity of livestock NH₃ isotope datasets in China. However, major revisions are needed to improve methodological clarity, strengthen data interpretation, and address limitations regarding isotopic fractionation, representativeness, and modeling. Some structural and analytical improvements would further enhance scientific. Specific comments are as follows:
Active sampling bubbles NH₃ into solution where NH₃/NH₄⁺ equilibrium fractionation occurs. The manuscript does not explicitly quantify or estimate this fractionation. Please discuss or correct for known equilibrium fractionation between NH₃(g) and NH₄⁺(aq), which can exceed 20‰ under typical livestock-house pH conditions.

The manuscript mentions sampling with a bubbler but does not specify the chemical composition (e.g., sulfuric acid? boric acid? DI water?). Absorption efficiency and isotopic stability depend strongly on solution chemistry.

Uncertainties from IRMS measurement, standardization, sample handling, and conversion chemistry must be reported and propagated into δ¹⁵N ranges for each livestock type.

Only one building per livestock type was sampled. Please discuss how representative these δ¹⁵N signatures are for regional livestock practices, especially given variability in feed, manure management, and ventilation system design.

July–August samples are missing due to absence of animals, but this gap may bias seasonal interpretations. Please clarify whether these farms typically have seasonal shutdowns and what implications this has for annual emissions.

The conclusion that combustion and traffic dominate Zhengzhou’s NH₃ is not fully supported by isotopic evidence alone. Please incorporate mixing model tests (e.g., SIAR, MixSIAR) or acknowledge the need for quantitative modeling.

The regression shows extremely low R² (<0.10). The interpretation on economic development stages and shifting NH₃ sources is therefore weak. Authors should either downplay this section or provide stronger, mechanistic justification.

Please specify: how multiple values from a single study were aggregated, how weighting was applied (e.g., by sample size), how passive vs. active sampling differences were handled. This is essential for reproducibility.

Temperature, humidity, ventilation rates, and manure accumulation strongly influence NH₃ fluxes and δ¹⁵ Without these data, some interpretations (e.g., seasonal changes) are speculative.

Several figures (especially Figures 2–5) contain overlapping labels or insufficient axis descriptions. Please enlarge text, improve legends, and ensure data points and error bars are clearly visible.

Isotopic fractionation during urea hydrolysis, ammonification, and manure storage can significantly affect δ¹⁵N–NH₃. A more thorough discussion is needed to explain differences among species and seasons.

The Zenodo link should clarify whether raw IRMS output, calibration curves, and sampling metadata are included, rather than only processed δ¹⁵N values.

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Citation: https://doi.org/10.5194/egusphere-2025-4460-RC2

Jinhan Wang, Zhaojun Nie, Yupeng Zhang, Xiaolei Jie, Haiyang Liu, Peng Zhao, and Hongen Liu

Supplement

https://doi.org/10.5194/egusphere-2025-4460-supplement

Data sets

Measurement report: Nitrogen Isotope (δ15N) Signatures of Ammonia Emissions from Livestock Farming: Implications for Source Apportionment of Haze Pollution Jinhan Wang, Zhaojun Nie, Yupeng Zhang, Xiaolei Jie, Haiyang Liu, Peng Zhao, and Hongen Liu https://doi.org/10.5281/zenodo.17639507

Jinhan Wang, Zhaojun Nie, Yupeng Zhang, Xiaolei Jie, Haiyang Liu, Peng Zhao, and Hongen Liu

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Short summary

1. This study accurately quantified the unique δ¹⁵N signature of ammonia emissions from livestock and poultry in China. 2. Accurate regional source apportionment and targeted emission reduction strategies have been achieved. 3. The isotopic characteristics of ammonia emissions from livestock farms are significantly different from those of other sources. 4. The δ¹⁵N value is not directly correlated with ammonia concentration, but its variation is related to changes in emission levels.


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