Site-selective nitrogen isotopic ratio measurement of nitrous oxide using a TE-cooled CW-RT-QCL based spectrometer

• Isotopic analysis is an attractive method for tracing the budgets of atmospheric trace gases.
• QCLs are promising spectroscopic sources for developing analytical instrumentation.
• Wavelength modulation spectroscopy is a powerful technique for gas sensing.
• Site-selective 15N/14N ratio measurement with a precision of 3‰.

The feasibility of laser spectroscopic isotopic composition measurements of atmospheric N2O was demonstrated, although making them useful will require further improvements. The system relies on a thermoelectrically (TE) cooled continuous-wave (CW) room temperature (RT) quantum cascade laser source emitting wavelength of around 4.6 μm, where strong fundamental absorption bands occur for the considered specie and its isotopomers. The analysis technique is based on wavelength modulation spectroscopy with second-harmonic detection and the combination of long-path absorption cell. Primary laboratory tests have been performed to estimate the achievable detection limits and the signal reproducibility levels in view of possible measurements of 15N/14N and 18O/16O isotope ratios. The experiment results showed that the site-selective 15N/14N ratio can be measured with a precision of 3‰ with 90 s averaging time using natural-abundance N2O sample of 12.7 ppm.

Figure optionsDownload as PowerPoint slide