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Chinese Journal of Applied Ecology ›› 2019, Vol. 30 ›› Issue (6): 1847-1853.doi: 10.13287/j.1001-9332.201906.011

• Special Features of Stable Isotope Ecology • Previous Articles     Next Articles

Hypobromite oxidation combined with hydroxylamine hydrochloride reduction method for analyzing ammonium nitrogen isotope in atmospheric samples.

XIANG Yan-kun1,2, CAO Fang1,2,*, YANG Xiao-ying1,2, ZHAI Xiao-yao1,2, ZHANG Yan-lin1,2   

  1. 1Yale-NUIST Center on Atmospheric Environment, International Joint Laboratory on Climate and Environment Change (ILCEC), Nanjing University of Information Science & Technology, Nanjing 210044, China;
    2Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters (CIC-FEMD), Nanjing University of Information Science & Technology/Key Laboratory of Meteorological Disaster, Ministry of Education (KLME), Nanjing 210044, China
  • Received:2018-11-19 Online:2019-06-15 Published:2019-06-15
  • Supported by:
    This work was supported by the National Key Research and Development Program of China (2017YFC0212302), the National Natural Science Foundation of China (91644103), and the Natural Science Foundation of Jiangsu Province (BK20180040)

Abstract: Ammonium salts, including ammonium nitrate, ammonium sulfate and ammonium hydrogen sulfate, are the main components of secondary inorganic aerosols and play an important role in the formation of haze events. The sources and transformation processes of atmospheric ammonium have received more and more attention. In this study, we modified the previous stable isotope analysis technique by improving the injection volume and adding a pH adjustment step, which gave a rapid and accurate measurement of ammonium nitrogen isotope ratio in atmospheric aerosol samples. Firstly, we added alkaline hypobromite to the extracted solution of the atmospheric aerosol filter samples (0.25 μg·mL-1 ammonium nitrogen in 4 mL) to oxidize ammonium (NH4+) to nitrite (NO2-). Then, after adjusting the pH, nitrite (NO2-) was reduced to nitrous oxide (N2O) by hydroxylamine hydrochloride under pH <0.3. Finally, nitrous oxide (N2O) was analyzed by Precon-GasBench-IRMS system to measure ammonium nitrogen isotope ratio. Our approach required low amount of NH4+ and avoided the use of highly toxic and explosive reagents. Meanwhile, the precision of our method could reach as high as 0.2‰ (n=10). This method could increase the NH4+ reduction efficiency to 100% at a condition of pH <0.3 and satisfy the demands of precision and accuracy for determination of ammonium nitrogen isotope in atmospheric aerosol samples. This method would help us better understand the sources, evolutions, chemical and deposition processes of atmospheric ammonium.