Application of quantum cascade laser-infrared absorption spectroscopy for methane clumped isotope thermometry using doubly isotope substituted methane (13CH3D)

点击翻译按钮获取中文摘要

Technical description. In this project, we apply quantum cascade laser infrared absorption spectroscopy (QCLAS) to precisely measure abundance of doubly isotope-substituted methane (13CH3D) as a new and robust proxy for the source of methane in geologic environments. On the first order, 13CH3D abundance would indicate the temperature at which the methane was produced or internally equilibrated for its 13C-D bond abundance. On the second order, kinetic process may produce different clumped isotope effect that may be used to fingerprint unique processes, as has been seen for the 13C16O18O system. The QCLAS instrument has already been installed in the PI's laboratory and the precision of 0.1 to 0.5 permil have been achieved for four major isotopologues of methane (12CH4, 13CH4, 12CH3D, and 13CH3D). The goal of the project is to further optimize the QCLAS and sample inlet system, and calibrate the 13CH3D clumped isotope thermometry scale by using thermally scrambled methane (200 °C) as well as microbially produced methane (100°C). Some geologic methane will be analyzed as a pilot study.Tunable laser spectroscopy is an emerging new technology only recently applied in the field of stable isotope geochemistry. This research explores its application to precise measurements of isotopologue species that are technically challenging by conventional magnetic sector-isotope ratio mass spectrometry instruments. Applications of this new technology are not limited to 13CH3D, and it could be applied to other clumped isotopologue systems (e.g., CO2, N2O and SO2). The proposed project will facilitate the close collaboration between Aerodyne Inc. (US small business) and MIT, as well as other US and international collaborators, for the development of new generation isotope monitoring equipment. One graduate student will actively participate in development and be trained as a future isotope geochemist with a strong instrumental background in this emerging new optical technology. This project will be included in undergraduate class materials. This project also helps to add to scientific infrastructure via development of an instrument that will be available to researchers at MIT and beyond.Non-technical description.Methane is both an alternative energy source as well as being a potent greenhouse gas. It is likely to play a significant role in future diversification of our energy resources through new harvesting technologies such as fracking. Further harvesting of methane has the potential for increase release of methane to the atmosphere, which may impact climate. The project outlined in this proposal is for the development of a new, lower-cost method to measure carbon and hydrogen isotope abundances in methane from natural sources (e.g. wetlands, permafrost) and anthropogenic sources (e.g. agriculture). These measurements can provide us with a far better understanding of methane cycling, which may have implications for environmental management of methane.