Developing an enhanced preconcentration system (RAPTOR) for high-precision tropospheric nitrous oxide isotope measurements by laser spectroscopy

The mixing ratio of nitrous oxide (N₂O), an important greenhouse gas and ozone-depleting substance, in the troposphere has increased by 25% (~336 ppb) since the preindustrial period, with increased emissions in the last few years showing that effective mitigation policies are urgently required.  N₂O is emitted from a range of anthropogenic sources, particularly fertilised agricultural soils. N₂O sources and sinks can be constrained using measurements of four isotopocules: ¹⁴N¹⁵N¹⁶O (α), ¹⁵N¹⁴N¹⁶O (β), ¹⁴N¹⁴N¹⁶O, and ¹⁴N¹⁴N¹⁸O, and the site-specific relative isotope ratio differences (δ¹⁵N^α and δ¹⁵N^β); however, N₂O’s long tropospheric lifetime requires high precision (<0.1 ‰) to distinguish source signals from background variability. Existing preconcentration-laser spectrometry (TREX-QCLAS) systems lack the sufficient precision required for detailed tropospheric N₂O budget studies, for example, resolving trends in site preference or the interhemispheric gradient in isotopic composition. In this project, we build upon preconcentration system development with key innovations: (1) a simplified single 6-port VICI valve design; (2) a system-wide reduction of dead volumes to minimise memory effects; (3) a smaller trap enabling faster heating/cooling without linear actuators; and (4) integration with MIRO Analytical's first commercial N₂O isotope spectrometer featuring a temperature/pressure-controlled measurement cell. This system will measure N₂O isotopic composition in flask samples from Jungfraujoch High-Altitude Research Station and other background sites, establishing global isotope scale compatibility through multi-site measurements and inter-laboratory comparisons. These advances will improve constraints on regional and temporal variability in the global N₂O budget to support effective mitigation strategies.