Introduction: In the context of hydrogen, N2O will become crucial to monitor and urgently avoid an excess of emissions following the emerging ammonia use as hydrogen-based fuel. This work describes the current situation with respect to measurements of N2O in terms of its metrological traceability. We report on the outlined development of new N2O gas standards and compare them to the needs in emissions monitoring applications and greenhouse gas measurements.
Methodology: We investigated the present situation on available gas standards applicable to calibrate continuous emission measurements (CEMs) of N2O as an emission from hydrogen’s derivative ammonia (NH3) used as fuel. While real-world data on N2O emissions of maritime ammonia engine tests is not available, a maximum emission factor of 0.06 g N2O per kWh (0.158 g N2O per kg NH3 consumed) is targeted by the industry. This performance value would guarantee a negligible effect on green ammonia trade and consumption as a fuel. The Key Comparison Database of the International Bureau of Weights and Measures reveals only eight institutes worldwide who can offer N2O standards, needed for accurate measurements aiming at metrological traceability. Of them, each calibration and measurement capability is related to a reference material-based gas standard, i.e. a certified reference material (CRM).
An alternative concept to CRM-based gas standards is given by optical gas standards (OGS). Yielding gas concentrations that are directly metrological traceable, OGS offer a flexible alternative to CRM-based gas standards, particularly where CRMs are less stable and difficult to be carried to the field, as, e.g., for CEM.
Experimental Evaluation: Experimental collaborations have been started on nitrous oxide spectroscopy in the 1.65 mm near infrared wavelength range for N2O emissions and the mid infrared range around 4.5 µm wavelength for background N2O quantifications. This underlying spectroscopy work is required for the development of new optical N2O standards as sketched in Fig. 1. In cases a thorough spectroscopic line selection is crucial to customize the optical gas standard for a specific application – or to have it available for general purpose N2O certification and calibration for example. Metrological characterization and comparisons to available CRM-based N2O standards are underway.