Low cost, High speed Multi-probe Monitoring System for Subsurface Gases

Determination of soil gas concentrations and isotopologue ratios are a critical tool in plant, microbial and ecosystem ecology, hydrology, biogeochemistry studies, and interrogation of environmental remediation. In addition, 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 respond to redox conditions and have naturally occurring stable isotope forms that can be used as natural tracers for the study and analysis of plant and microbial activities and cycling of carbon and nitrogen between soil, plants, and the atmosphere. In particular, real-time high sensitivity measurements of gases such as methane, nitrous oxide and carbon dioxide concentrations in air and in soil at ppm concentrations at a number of points within a spatial-region of 100 meters would be extremely valuable for a variety of applications and models. Isotopic labeling of these gases would improve the systems usefulness. In this SBIR program Amethyst will team with Appalachian Laboratory at the University of Maryland to construct and deploy an inexpensive subsurface gas measurement system that can measure CH4, N2O and the carbon isotopologues of CO2 in the agricultural soils in eastern Maryland. Analysis of these gases at multiple points within the soil and the air above (including within snow packs) would allow a significantly better understanding of the net effects of roots and soil microorganisms on the oxidation and reduction of soil carbon and nitrogen substrates in a variety of terrestrial environments. The low power automated system will be equipped with multiple senor heads that can be placed above or underground. These sensors will be connected to the main controller box that can record the gas concentrations and CO2 isotopologue ratio at various sites in real time and have unattended operation so these gases can be monitored 24/7. Amethyst’s sensor system will be based on a previously developed resonant cavity detector technology that uses a broadband light source and narrow band multichip detector to measure individual gas concentrations down to the sub-ppm level. During Phase I Amethyst will build and test a resonant cavity detector-based gas sensor capable of detecting N2O at below ppm levels. Amethyst will also design a multi-gas sensor head and investigate an overall system design to optimize detection speed and sensitivity for a number of gases (CH4, 12CO2, 13CO2, and N2O). The Phase II program will construct the multi-point, multi gas sensor system and test and validate it in a field environment. This detection system will be invaluable for real time field measurements of soil methane for a variety of research applications. Once the system in built and proven it could also be used to detect methane leaks in buried pipe lines and less expensive, non-isotopic, systems could be built to detect leaks in above ground applications. By changing the laser source wavelength this system can be used to measure other gases.