Collaborative Research: Development of a Diode Laser Cavity-Ringdown Spectrometer for Shipboard Measurements of the Stable Isotopes on Oceanic Methane

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The PIs propose to develop a Cavity-Ringdown Spectrometer (CRDS) capable of measuring methane concentration and stable isotopes (ä2H-CH4 and ä13C-CH4) on a research vessel with a precision comparable to standard laboratory techniques. A portable prototype has been developed that has achieved a measurement reproducibility of 0.01 % standard error. This translates to a sensitivity of 4 ppb and an isotopic precision similar to what is achieved using Isotope. This ?bare-bones? prototype will be advanced to make it more robust for ship-based research. The principal design modifications include: 1) increased thermal and vibrational isolation with caging and insulation, 2) increased sampling rates by incorporating acousto-optic modulators, semiconductor optical amplifiers, and multiple lasers, 3) the ability to lock onto an absorption peak using FM spectroscopy, and 4) minimized susceptibility to misalignment by purchasing components that can be fiber optically coupled together. A front-end sampler will be developed to automatically extract CH4 from an array of serum vials filled with seawater, sediment, or free gas and inject it into the analysis cavity.Having a field-portable instrument that can make high-precision measurements of ä2H-CH4 and ä13C-CH4 will be useful in many areas of oceanographic research (e.g. life in extreme environments, climate change, petroleum research, carbon cycling A DL-CRDS will allow a nearly limitless number of analyses to be conducted, greatly enhancing the understanding of any CH4 system under investigation and since these measurements are ship-based, can also be used to guide subsequent sampling during the same expedition.Broader Impacts: This proposal is aimed at developing a revolutionary new measurement system for the stable isotopes of methane. If the system can be successfully developed to work on ocean-going vessels, then there will be a potential explosion in the amount of methane data that will be produced and, hopefully, a corresponding increase in the understanding of methane budgets sinks and sources worldwide. The realization of a user-friendly and compact device based on optical spectroscopy (several diode laser sources coupled to a high finesse cavity for a high sensitivity and fast CRDS measurement scheme) for methane isotopic ratios measurement will present a high interest for research laboratories in environmental sciences. This Project will train post-docs, graduated and undergraduate students and it will enhance cross disciplinary partnerships. The results will be disseminated to a wider scientific audience and a better understanding of geographical problems will be achieved.