Sulfuric acid method improves accuracy of nitrogen isotope tracking for atmospheric ammonia
By comparing sulfuric and boric acid absorption systems, they found sulfuric acid delivers higher recovery rates and reduces isotope fractionation, even at low concentrations. Field applications successfully distinguished emissions from cropland, livestock, orchards, and vegetables, improving the accuracy of ammonia source identification.
NH₃ is the most important alkaline gas in the atmosphere and a major contributor to air pollution. It reacts with sulfur dioxide (SO₂) and nitrogen oxides (NOₓ) to form ammonium sulfate and ammonium nitrate, key components of fine particulate matter (PM₂.₅) that threaten human health, ecosystems, and climate balance. Because agricultural activities dominate NH₃ emissions, accurate source identification is essential for effective air-quality management. δ¹⁵N provides a powerful tool for distinguishing among fertilizers, livestock waste, and other sources. However, reliable isotope tracing depends on precise sampling. Common acidic absorbents used in passive collection may introduce isotope fractionation, particularly at low concentrations, highlighting the need for systematic methodological evaluation.
A study (DOI: 10.48130/nc-0025-0017) published in Nitrogen Cycling on 16 January 2026 by Chaopu Ti’s team, Chinese Academy of Sciences, establishes a more accurate and reliable method for nitrogen isotope analysis of atmospheric ammonia, improving source identification and supporting effective air pollution control strategies.
To evaluate the suitability of different acidic absorbents for NH₃ recovery and δ¹⁵N analysis, researchers conducted controlled laboratory experiments using (NH₄)₂SO₄ and certified N isotope reference materials (USGS-25, USGS-26, and IAEA-N1) as volatilization substrates, each with an initial NH₄⁺–N mass of 2.00 mg. NH₃ released during reaction was passively captured using sponge samplers containing either sulfuric acid or boric acid solutions, and recovery efficiency, reproducibility (CV), and isotope conversion performance were systematically assessed across NH₄⁺ concentrations of 20–100 μmol L⁻¹. Results showed that sulfuric acid achieved consistently high NH₃ recovery rates (95.98–96.88%, mean 96.43%, CV 0.47%) for (NH₄)₂SO₄ and similarly high recoveries for isotope standards (96.03–99.09%), indicating excellent precision and minimal isotopic bias. In contrast, boric acid produced significantly lower recovery rates (80.47–86.48%, mean 83.90%) and greater variability, suggesting potential isotope fractionation, especially at low concentrations. Conversion curves between δ¹⁵N–NH₄⁺ and δ¹⁵N–N₂O demonstrated that sulfuric acid maintained slopes close to the theoretical 0.5 across all concentrations, even before correction, reflecting stable isotope conversion and minimal blank effects. Boric acid showed weaker performance at 20 μmol L⁻¹, where slopes deviated markedly from theoretical expectations, though higher concentrations improved accuracy after correction. Accuracy tests confirmed that both methods reproduced certified δ¹⁵N values within ±0.5‰, but sulfuric acid exhibited superior stability and lower impurity interference. Field application of the optimized sulfuric acid method further revealed distinct δ¹⁵N signatures among agricultural NH₃ sources: cropland (−32.87‰), livestock (−36.64‰), orchards (−19.63‰), and vegetables (−24.95‰), with cropland and livestock significantly more depleted in ¹⁵N. Overall, the results demonstrate that 0.1 mol L⁻¹ sulfuric acid provides higher recovery, stronger reproducibility, and more reliable δ¹⁵N determination across variable concentration ranges, making it the preferred absorbent for atmospheric NH₃ source apportionment.
This study identifies sulfuric acid as the optimal absorbent for accurate δ¹⁵N analysis across varying NH₃ concentrations, providing a more reliable framework for ammonia source tracing. Enhanced isotope precision improves quantification of emissions from fertilizers, livestock, and other agricultural sources. The method strengthens nitrogen source apportionment, supports targeted fertilizer management, and offers robust scientific evidence for reducing PM₂.₅ formation and mitigating regional air pollution.
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References
DOI
10.48130/nc-0025-0017
Original Souce URL
https://doi.org/10.48130/nc-0025-0017
Funding information
This work was supported by the National Natural Science Foundation of China (Grant No. 42177313), and the National Key Research and Development Program of China (Grant No. 2023YFC3707402).
About Nitrogen Cycling
Nitrogen Cycling is a multidisciplinary platform for communicating advances in fundamental and applied research on the nitrogen cycle. It is dedicated to serving as an innovative, efficient, and professional platform for researchers in the field of nitrogen cycling worldwide to deliver findings from this rapidly expanding field of science.
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NH₃ is the most important alkaline gas in the atmosphere and a major contributor to air pollution. It reacts with sulfur dioxide (SO₂) and nitrogen oxides (NOₓ) to form ammonium sulfate and ammonium nitrate, key components of fine particulate matter (PM₂.₅) that threaten human health, ecosystems, and climate balance. Because agricultural activities dominate NH₃ emissions, accurate source identification is essential for effective air-quality management. δ¹⁵N provides a powerful tool for distinguishing among fertilizers, livestock waste, and other sources. However, reliable isotope tracing depends on precise sampling. Common acidic absorbents used in passive collection may introduce isotope fractionation, particularly at low concentrations, highlighting the need for systematic methodological evaluation.
A study (DOI: 10.48130/nc-0025-0017) published in Nitrogen Cycling on 16 January 2026 by Chaopu Ti’s team, Chinese Academy of Sciences, establishes a more accurate and reliable method for nitrogen isotope analysis of atmospheric ammonia, improving source identification and supporting effective air pollution control strategies.
To evaluate the suitability of different acidic absorbents for NH₃ recovery and δ¹⁵N analysis, researchers conducted controlled laboratory experiments using (NH₄)₂SO₄ and certified N isotope reference materials (USGS-25, USGS-26, and IAEA-N1) as volatilization substrates, each with an initial NH₄⁺–N mass of 2.00 mg. NH₃ released during reaction was passively captured using sponge samplers containing either sulfuric acid or boric acid solutions, and recovery efficiency, reproducibility (CV), and isotope conversion performance were systematically assessed across NH₄⁺ concentrations of 20–100 μmol L⁻¹. Results showed that sulfuric acid achieved consistently high NH₃ recovery rates (95.98–96.88%, mean 96.43%, CV 0.47%) for (NH₄)₂SO₄ and similarly high recoveries for isotope standards (96.03–99.09%), indicating excellent precision and minimal isotopic bias. In contrast, boric acid produced significantly lower recovery rates (80.47–86.48%, mean 83.90%) and greater variability, suggesting potential isotope fractionation, especially at low concentrations. Conversion curves between δ¹⁵N–NH₄⁺ and δ¹⁵N–N₂O demonstrated that sulfuric acid maintained slopes close to the theoretical 0.5 across all concentrations, even before correction, reflecting stable isotope conversion and minimal blank effects. Boric acid showed weaker performance at 20 μmol L⁻¹, where slopes deviated markedly from theoretical expectations, though higher concentrations improved accuracy after correction. Accuracy tests confirmed that both methods reproduced certified δ¹⁵N values within ±0.5‰, but sulfuric acid exhibited superior stability and lower impurity interference. Field application of the optimized sulfuric acid method further revealed distinct δ¹⁵N signatures among agricultural NH₃ sources: cropland (−32.87‰), livestock (−36.64‰), orchards (−19.63‰), and vegetables (−24.95‰), with cropland and livestock significantly more depleted in ¹⁵N. Overall, the results demonstrate that 0.1 mol L⁻¹ sulfuric acid provides higher recovery, stronger reproducibility, and more reliable δ¹⁵N determination across variable concentration ranges, making it the preferred absorbent for atmospheric NH₃ source apportionment.
This study identifies sulfuric acid as the optimal absorbent for accurate δ¹⁵N analysis across varying NH₃ concentrations, providing a more reliable framework for ammonia source tracing. Enhanced isotope precision improves quantification of emissions from fertilizers, livestock, and other agricultural sources. The method strengthens nitrogen source apportionment, supports targeted fertilizer management, and offers robust scientific evidence for reducing PM₂.₅ formation and mitigating regional air pollution.
###
References
DOI
10.48130/nc-0025-0017
Original Souce URL
https://doi.org/10.48130/nc-0025-0017
Funding information
This work was supported by the National Natural Science Foundation of China (Grant No. 42177313), and the National Key Research and Development Program of China (Grant No. 2023YFC3707402).
About Nitrogen Cycling
Nitrogen Cycling is a multidisciplinary platform for communicating advances in fundamental and applied research on the nitrogen cycle. It is dedicated to serving as an innovative, efficient, and professional platform for researchers in the field of nitrogen cycling worldwide to deliver findings from this rapidly expanding field of science.
END