A Low Cost Multipoint Gas Sensor for Monitoring Subsurface Isotopologues

Statement of the Problem Isotopologues are a critical tool in monitoring plant hydrobiogeochemical and microbial systems and processes. The most abundant elements utilized and exchanged by plants, microbes and ecosystems are carbon (C), hydrogen (H), oxygen (O) and nitrogen (N), all of which have naturally occurring stable isotope forms that can be used as natural tracers for understanding and interrogating these systems. However, current technologies for real time in situ monitoring of isotopologues are expensive, require power sources, and have limited spatial capacity. Statement of How this Problem is Being Addressed In this program Amethyst Research in partnership with the University of Oklahoma Department of Microbiology and Plant Biology and the Climate Change Science Institute, Oak ridge National Laboratory will develop a multi-spectral soil gas sensor that can accuracy and rapidly measure the concentration and isotopic ratio of N2O, CO2, CH4 gases and their isotopologues as well as water vapor. A novel infrared resonant cavity photo-detector, that does not require expensive and/or power hungry laser sources (currently employed in existing isotopologue spectroscopy systems) will be demonstrated in Phase I and an inexpensive, portable system will be field tested and developed in Phase II. The high performance detectors will employ two advanced detector concepts, unipolar barrier device architectures coupled to resonant cavities. Unipolar barrier detectors developed by Amethyst have demonstrated a million fold suppression of dark current, thereby dramatically decreasing detector noise. The combination of both detector advances will be developed for the first time in this program and integrated with proven subsurface monitoring system and plant and environmental researchers to ensure relevancy. What is to be done in Phase I Amethyst Research will develop and optimize a high sensitivity resonant cavity infrared photo-detector that will be used to measure isotopologue distributions. In Phase I, detectors for N2O, CO2 and CH4 will be designed, and a functioning CH4 detector will be fabricated and performance evaluated. The system will be tested at the University of Oklahoma Department of Microbiology and Plant Biology field facilities and will proceed in collaboration with the Climate Change Science Institute, Oak Ridge National Laboratory where additional testing and validation will be performed. Commercial Application and Other Benefits Development of this robust field portable soil gas sensor system will have a significant impact on measuring biological activity in soils and monitoring greenhouse active gases and processes. The system will reliably measure sub-ppm concentrations of gas phase greenhouse gases and their isotopes and will be field portable. End users will find this system attractive due to overall dependability, accuracy, field robustness and low operational cost. Key Words: Isotope monitoring, Resonant Cavity Photo-Detector, Gas Sensors, Subsurface Instrumentation Summary for Members of Congress: Amethyst Research in partnership with the University of Oklahoma Department of Microbiology and Plant Biology, and in collaboration with the Climate Change Science Institute, Oak Ridge National Laboratory is developing a real time, in-situ gas detection system that is able to monitor hydrobiogeochemical processes in subsurface environments for plant and environmental monitoring processes.