Empa, Laboratory for Air Pollution/Environmental Technology, Dübendorf, 8600, Switzerland.
ETH Zürich, Department of Earth Sciences, Zürich, 8092, Switzerland.
Rapid Commun Mass Spectrom. 2020 Aug 15;34(15):e8836. doi: 10.1002/rcm.8836.
Unravelling the biogeochemical cycle of the potent greenhouse gas nitrous oxide (N O) is an underdetermined problem in environmental sciences due to the multiple source and sink processes involved, which complicate mitigation of its emissions. Measuring the doubly isotopically substituted molecules (isotopocules) of N O can add new opportunities to fingerprint and constrain its cycle.
We present a laser spectroscopic technique to selectively and simultaneously measure the eight most abundant isotopocules of N O, including three doubly substituted species - so called "clumped isotopes". For the absolute quantification of individual isotopocule abundances, we propose a new calibration scheme that combines thermal equilibration of a working standard gas with a direct mole fraction-based approach.
The method is validated for a large range of isotopic composition values by comparison with other established methods (laser spectroscopy using conventional isotopic scale and isotope ratio mass spectrometry). Direct intercomparison with recently developed ultrahigh-resolution mass spectrometry shows clearly the advantages of the new laser technique, especially with respect to site specificity of isotopic substitution in the N O molecule.
Our study represents a new methodological basis for the measurements of both singly substituted and clumped N O isotopes. It has a high potential to stimulate future research in the N O community by establishing a new class of reservoir-insensitive tracers and molecular-scale insights.
由于涉及到多种源和汇过程，氮氧化物（N O）这一强效温室气体的生物地球化学循环是环境科学中一个尚未完全确定的问题，这使得减少其排放的工作变得复杂。测量双同位素取代的 N O 分子（同位素簇）可以为其循环的示踪和约束提供新的机会。
我们提出了一种激光光谱技术，可选择性和同时测量 N O 的八个最丰富的同位素簇，包括三种双取代物种 - 所谓的“聚集同位素”。为了对各个同位素簇丰度进行绝对定量，我们提出了一种新的校准方案，该方案将工作标准气体的热平衡与直接基于摩尔分数的方法相结合。
该方法通过与其他已建立的方法（使用常规同位素标度的激光光谱学和同位素质谱法）进行比较，在很大的同位素组成值范围内得到了验证。与最近开发的超高分辨率质谱法的直接比较清楚地表明了新激光技术的优势，特别是在 N O 分子中同位素取代的位置特异性方面。
我们的研究为单取代和聚集 N O 同位素的测量提供了新的方法学基础。它有可能通过建立一类新的不依赖于储层的示踪剂和分子尺度的新见解，激发 N O 研究领域的未来研究。
