Development of Novel Instrumentation to Measure All Nitrous Oxide Mono-Substituted Rare Isotopic Species

Abstract:

Analysis of isotopic ratios is of great importance to study the sources and sinks of nitrous oxide (N₂O) in atmosphere. N₂O has four mono-substituted rare isotopic species – ¹⁴N¹⁵N¹⁶O, ¹⁵N¹⁴N¹⁶O, ¹⁴N₂¹⁸O, and ¹⁴N₂¹⁷O. Here we report on the development of novel instrumentation which is capable of measuring all four N₂O isotopic species and therefore enables a complete characterization of abundance variations of these species. This instrument, which employs cavity enhanced absorption technology and a mid-infrared laser, has been developed for simultaneous measurements of all four isotopic species in either a continuous flow mode or a batch mode. A precision of better than 1 per mil for ¹⁴N₂¹⁷O has been achieved with samples of 10 ppm N2O in 300 seconds of measurement time. In addition, a precision of better than 1 per mil for ¹⁴N¹⁵N¹⁶O and ¹⁵N¹⁴N¹⁶O and 2 per mil for ¹⁴N₂¹⁸O has been achieved with samples of 300 ppb N2O or higher in 300 seconds of measurement time.