Spectroscopic Measurement of Carbon Isotope Ratios in Methane

Concentrations of methane in the atmosphere have increased 150% in the past three centuries, and accurate measurements are need to characterize the sources of this greenhouse gas. Isotope measurements are a candidate technology, but existing measurement approaches are cumbersome, and require that samples be collected and returned to a lab for analysis. This project will use a near-room-temperature, infrared diode laser to probe strong transitions of methane, including 12C and 13C isotopes. The laser will be combined with compact optics and digital signal processing to achieve high precision measurments of isotope ratios. Phase I will characterize the laser source (including its wavelength, spectral bandwidth, power, and tuning) as a function of current and temperature, integrate it into a spectrometer based on a proprietary optical cell, and use it to measure the carbon isotope ratio of methane in air. The target sensitivity is the measurement of isotope ratios with a precision between 0.1 and 1 parts per thousand. Commercial Applications And Other Benefits as described by the Applicant: An instrument for measuring methane isotope ratios should have application for the atmospheric sciences, providing lower cost, greater portability, and longer time between servicing. Other applications would include the detection of leaks in the natural gas distribution network and the monitoring of on-site production at natural gas wells.