N2O isotope research: development of reference materials and metrological characterization of OIRS analyzers within the SIRS project

Measurements of the four most abundant stable isotopocules of N2O (14N14N16O, 15N14N16O, 14N15N16O, and 14N14N18O) can provide a valuable constraint on source attribution of atmospheric N2O. N2O isotopocules at natural abundance levels can be analyzed by isotope-ratio mass-spectrometry (IRMS) [1] and more recently optical isotope ratio spectroscopy (OIRS) [2]. OIRS instruments can analyze the N2O isotopic composition in gaseous mixtures in a continuous-flow mode, providing real-time data with minimal or no sample pretreatment, which is highly attractive to better resolve the temporal complexity of N2O production and consumption processes. Most importantly, OIRS laser spectroscopy is selective for position-specific 15N substitution due to the existence of characteristic rotational-vibrational spectra.By allowing both in-situ application and measurements in high temporal resolution, laser spectroscopy has established a new quality of data for research on N2O in particular and N cycling in general. However, applications remain challenging and are still scarce as a metrological characterization of OIRS analyzers, reporting factors limiting their performance is still missing. In addition, only since recently two pure N2O isotopocule reference materials have been made available through the United States Geological Survey (USGS), which however, only offer a small range of δ15N and δ18O values (< 1 ‰) and are therefore not suited for a two-point calibration approach [3].This presentation will highlight the recent progress achieved within the framework of the EMPIR project “Metrology for Stable Isotope Reference Standards (SIRS)”, namely:(1) The development of pure and diluted N2O reference materials (RMs), covering the range of isotope values required by the scientific community. These gaseous standards are available as pure N2O or N2O diluted in whole air. N2O RMs were analyzed by an international group of laboratories for δ15N, δ18O (MPI-BGC, Tokyo Institute of Technology