Development of a field-deployable method for simultaneous, real-time measurements of the four most abundant NO isotopocules.

Understanding and quantifying the biogeochemical cycle of NO is essential to develop effective NO emission mitigation strategies. This study presents a novel, fully automated measurement technique that allows simultaneous, high-precision quantification of the four main NO isotopocules (NNO, NNO, NNO and NNO) 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.

Reassessment of the NH NO thermal decomposition technique for calibration of the N O isotopic composition.

Rationale: In the last few years, the study of N O site-specific nitrogen isotope composition has been established as a powerful technique to disentangle N O emission pathways. This trend has been accelerated by significant analytical progress in the field of isotope ratio mass spectrometry (IRMS) and more recently quantum cascade laser absorption spectroscopy (QCLAS).

Methods: The ammonium nitrate (NH NO ) decomposition technique provides a strategy to scale the N site-specific (SP ≡ δ N - δ N ) and bulk (δ N  = (δ N  + δ N )/2) isotopic composition of N O against the international standard for the N/ N isotope ratio (AIR-N ).