Development of a miniturized intra-cavity spectrometer to determine 14CH4 in the field

• Applicant: Professor Stefan Palzer, Ph.D.
• Subject Area: Measurement Systems ; Atmospheric Science
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 505112684

The aim of the project is to research a new, miniaturized device for isotope-selective detection of methane with a detection limit of 10 ppq or better. It will provide evidence that the proposed device is able to determine the origin and age of greenhouse gases in the field. MUIR thus enables a new class of studies in basic climate research, since for the first time the isotope-resolved study of greenhouse gas concentrations distinguishing between 12CH4, 13CH4, 12CH3D, and 14CH4 is made possible. Since the device can be built more robust, significantly smaller and simpler than current solutions, it is particularly suitable for large-area monitoring of greenhouse gas sources and sinks. In combination with so-called hood measurements, new knowledge about the origin and age of greenhouse gases can be gathered over large areas. Due to the insitu capability of the MUIR device, the isotope-resolved analysis will be enable monitoring large spatial and temporal scales, which is notpossible with currently available technologies. In order to achieve the low detection limits, an intracavity absorption spectroscopy (ICAS) setup is used, in which exactly two modes can oscillate in the active resonator. This makes it possible to significantly simplify the signal evaluation as compared to currently used setups and to make it suitable for the field. A He-Ne mixture is used as the active medium in MUIR. The Ne-laser transition at 3.39 μm almost overlaps with the ν3(P7) transition of methane. With the help of the Zeeman effect, the laser transition is adapted to the resonance frequencies of therespective methane isotopes. Gas samples are filtered and pre-concentrated prior to analysis. The isotope-resolved measurement is made possible by reducing collision broadening, for which a microfluidic system reduces the pressure in the measuring chamber.

• DFG Programme: New Instrumentation for Research
• Major Instrumentation: MID-IR Wavemeter
• Instrumentation Group: 5790 Sonstige Laser und Zubehör (außer 570-578)