Development of a field-deployable method for simultaneous, real-time measurements of the four most abundant N₂O isotopocules^*

* Originally presented at the Joint European Stable Isotopes User Group Meeting JESIUM 2016, Ghent University, Belgium, 4–9 September 2016.

ABSTRACT

Understanding and quantifying the biogeochemical cycle of N₂O is essential to develop effective N₂O emission mitigation strategies. This study presents a novel, fully automated measurement technique that allows simultaneous, high-precision quantification of the four main N₂O isotopocules (¹⁴N¹⁴N¹⁶O, ¹⁴N¹⁵N¹⁶O, ¹⁵N¹⁴N¹⁶O and ¹⁴N¹⁴N¹⁸O) in ambient air. The instrumentation consists of a trace gas extractor (TREX) coupled to a quantum cascade laser absorption spectrometer, designed for autonomous operation at remote measurement sites. The main advantages this system has over its predecessors are a compact spectrometer design with improved temperature control and a more compact and powerful TREX device. The adopted TREX device enhances the flexibility of the preconcentration technique for higher adsorption volumes to target rare isotope species and lower adsorption temperatures for highly volatile substances. All system components have been integrated into a standardized instrument rack to improve portability and accessibility for maintenance. With an average sampling frequency of approximately 1 h^–1, this instrumentation achieves a repeatability of 0.09, 0.13, 0.17 and 0.12 ‰ for δ¹⁵N^α, δ¹⁵N^β, δ¹⁸O and site preference of N₂O, respectively, for pressurized ambient air. The repeatability for N₂O mole fraction measurements is better than 1 ppb (parts per billion, 10^–9 moles per mole of dry air).

KEYWORDS:

• Quantum cascade laser spectrometer
• trace gas analysis
• isotope measurement techniques
• nitrogen-14
• nitrogen-15
• nitrous oxides
• oxygen-16
• oxygen-18
• quantum cascade laser absorption spectrometry (QCLAS)

Acknowledgements

Sakae Toyoda, Naohiro Yoshida and Yuma Watanabe are kindly acknowledged for conducting IRMS measurements within the inter-laboratory comparison conducted in early 2016. Furthermore, we would like to thank Marco Weber for his technical support during the construction of the TREX device and Juanfernando Angel-Ramelli for his support with LabVIEW adaptations.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Erkan Ibraim http://orcid.org/0000-0002-1246-4369

Eliza Harris http://orcid.org/0000-0002-7102-8305

Béla Tuzson http://orcid.org/0000-0001-7442-5405

Lukas Emmenegger http://orcid.org/0000-0002-9812-3986

Johan Six http://orcid.org/0000-0001-9336-4185

Joachim Mohn http://orcid.org/0000-0002-9799-1001

Notes

* Originally presented at the Joint European Stable Isotopes User Group Meeting JESIUM 2016, Ghent University, Belgium, 4–9 September 2016.

Additional information

Funding

This work was financially supported by the Swiss National Science Foundation (Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung) [grant number 200021L_150237].