Employing infrared spectroscopy to measure gases and quantify gas mixture components is a common approach. Typically, spectrometers used for such purposes are calibrated by means of reference gases which in turn are traceable to primary gas mixtures. An alternative approach is seen in the development of spectroscopic transfer standards, i.e. spectrometers that directly yield absolute and – preferably – traceable results of a species amount of substance fraction, therefore avoiding the need to be calibrated by gaseous reference materials. This idea has been promoted for ozone for a long time already. Here, we report on developments towards spectroscopic transfer standards for carbon monoxide, water vapor, and ammonia; the first two based on interband-cascade laser and tunable diode laser absorption spectroscopy (ICLAS/TDLAS), the latter on cavity ring-down spectroscopy (CRDS). We present the spectrometric approaches and the results on validation measures, proving the concept feasible for further applications. Our CO-ICL-spectrometer was validated by means of gravimetric standards, showing an excellent agreement for CO amount fractions from 0.1 µmol/mol to 1000 µmol/mol in nitrogen and air. The measurement uncertainty is currently at 1.4 % relative. The water TDLAS instrument is flying on board the HALO aircraft and has been validated against the German national humidity standard in the range of 10 to 20000 µmol/mol. The NH3 spectroscopic transfer standard is based on a commercial CRDS analyzer, operated by means of our own retrieval strategy. With that, the system’s performance was recently tested from 10 to 200 nmol/mol NH3 in (humidified) synthetic air against a traceable, permeation-based NH3 generator. This work was supported by EMRP projects. The EMRP is jointly funded by the EMRP participating countries within EURAMET and the European Union.
Dr. Javis Nwaboh is research scientist at the Physikalisch-Technische Bundesanstalt (PTB) in Germany. The focus of his current research work is laser absorption spectroscopy. He is an experienced scientist in the design, development and validation of laser spectrometers, starting from the laser and molecular spectroscopic background to testing and metrological validation of the spectrometers for applications such as natural gas and atmospheric monitoring.