Development of Aircraft Borne 13CH4 Analyzer Using a Continuous Wave Quantum Cascade Infrared Laser Spectrometer

Methane (CH4) is the second most important atmospheric greenhouse gas after CO2, yet its global sources and sinks are still inadequately characterized. Monitoring the isotopic composition of atmospheric methane is one of the most promising approaches to closing the methane budget. Recent claims that plants may account for a substantial fraction of atmospheric methane have lead to an increased emphasis on studies of ecosystem CH4 fluxes, with particular interest in using isotopic composition to identify specific production pathways. Currently, field deployable instruments for direct measurements of methane isotopes having sufficient precision do not exist. Recent advances in quantum cascade laser technology have made available continuous wave operation near room temperature without cryogenic cooling. With such devices, it is now feasible to develop a compact portable instrument with sufficient sensitivity for direct measurements. The Phase I project modified an existing optical system and demonstrated the ability to directly detect the ratio of methane isotopes with a precision of 0.2 parts per thousand (0.2 ¿) in an averaging time of 100 seconds in ambient air without pre-concentration, exceeding the Phase I goals. Extended measurements of the isotopic ratio of ambient methane outside the research facility and measurements of the isotopic content of human breath and natural gas were performed. Preliminary designs for the aircraft-borne instrument were developed, and measurement opportunities for Phase II instrument deployment were identified. The Phase II project will complete the design and construction of a prototype instrument, which will be compact, rugged and field-deployable. Commercial Applications and other Benefits as described by the awardee: This instrument will provide scientifically meaningful isotopic ratio measurements in real time, without pre-concentration and without cryogenic cooling of either laser or detector. Other applications of this technology include air pollution monitoring, human breath analysis, geochemical prospecting, and industrial process monitoring.