Newswise \u2014 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.<\/p>\n
NH\u2083 is the most important alkaline gas in the atmosphere and a major contributor to air pollution. It reacts with sulfur dioxide (SO\u2082) and nitrogen oxides (NO\u2093) to form ammonium sulfate and ammonium nitrate, key components of fine particulate matter (PM\u2082.\u2085) that threaten human health, ecosystems, and climate balance. Because agricultural activities dominate NH\u2083 emissions, accurate source identification is essential for effective air-quality management. \u03b4\u00b9\u2075N 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.<\/p>\n
A\u00a0study\u00a0(DOI: 10.48130\/nc-0025-0017)<\/a>\u00a0published in\u00a0Nitrogen Cycling<\/a>\u00a0on\u00a016 January 2026 by Chaopu Ti\u2019s 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.<\/p>\n To evaluate the suitability of different acidic absorbents for NH\u2083 recovery and \u03b4\u00b9\u2075N analysis, researchers conducted controlled laboratory experiments using (NH\u2084)\u2082SO\u2084 and certified N isotope reference materials (USGS-25, USGS-26, and IAEA-N1) as volatilization substrates, each with an initial NH\u2084\u207a\u2013N mass of 2.00 mg. NH\u2083 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 NH\u2084\u207a concentrations of 20\u2013100 \u03bcmol L\u207b\u00b9. Results showed that sulfuric acid achieved consistently high NH\u2083 recovery rates (95.98\u201396.88%, mean 96.43%, CV 0.47%) for (NH\u2084)\u2082SO\u2084 and similarly high recoveries for isotope standards (96.03\u201399.09%), indicating excellent precision and minimal isotopic bias. In contrast, boric acid produced significantly lower recovery rates (80.47\u201386.48%, mean 83.90%) and greater variability, suggesting potential isotope fractionation, especially at low concentrations. Conversion curves between \u03b4\u00b9\u2075N\u2013NH\u2084\u207a and \u03b4\u00b9\u2075N\u2013N\u2082O 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 \u03bcmol L\u207b\u00b9, where slopes deviated markedly from theoretical expectations, though higher concentrations improved accuracy after correction. Accuracy tests confirmed that both methods reproduced certified \u03b4\u00b9\u2075N values within \u00b10.5\u2030, but sulfuric acid exhibited superior stability and lower impurity interference. Field application of the optimized sulfuric acid method further revealed distinct \u03b4\u00b9\u2075N signatures among agricultural NH\u2083 sources: cropland (\u221232.87\u2030), livestock (\u221236.64\u2030), orchards (\u221219.63\u2030), and vegetables (\u221224.95\u2030), with cropland and livestock significantly more depleted in \u00b9\u2075N. Overall, the results demonstrate that 0.1 mol L\u207b\u00b9 sulfuric acid provides higher recovery, stronger reproducibility, and more reliable \u03b4\u00b9\u2075N determination across variable concentration ranges, making it the preferred absorbent for atmospheric NH\u2083 source apportionment.<\/p>\n This study identifies sulfuric acid as the optimal absorbent for accurate \u03b4\u00b9\u2075N analysis across varying NH\u2083 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 PM\u2082.\u2085 formation and mitigating regional air pollution.<\/p>\n ###<\/p>\n References<\/p>\n DOI<\/p>\n 10.48130\/nc-0025-0017<\/a><\/p>\n Original Souce URL<\/p>\n https:\/\/doi.org\/10.48130\/nc-0025-0017<\/a><\/p>\n Funding information<\/p>\n 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).<\/p>\n About\u00a0Nitrogen Cycling<\/a><\/p>\n