Real-time Autonomous Gas Analyzer for Soils

Terrestrial ecosystems as an important source and sink for critical atmospheric gases, nutrients, and water play a vital role in the larger ecosystem. Gaining insights into these systems requires computational studies involving coupled reactions between complex subsurface systems. However, the predictive value of these studies is currently limited by the availability and accuracy of relevant data. Thus, a need exists for instrumentation capable of field measurements of high accuracy over extended periods. Of particular interest is the measurement of changes in concentration and identification of gases present as the result of hydrobiogeochemical processes in subsurface soil, such as nitrous oxide and carbon dioxide which are the result of micro-organism metabolic activities. Traditional measurement methods that require on-site sample preparation, followed by chemical analysis in a laboratory setting, are laborious and time consuming. A field-deployable instrument capable of high-quality analytical monitoring of subsurface gases over extended periods of time is thus an essential tool for measuring the subsurface gases with high resolution autonomously. To address the need for monitoring subsurface gases in real time, a novel soil gas chemical analysis system is proposed. The system is based on a custom-developed subsurface soil gas sampling system for variable-depth acquisition and tunable energy electron impact ionization source within a compact mass spectrometry system, as well as multidimensional analysis of gas mixtures. Currently available systems utilize an array of different sensing approaches specific to gases of interest at varying accuracy levels, which increase complexity and cost for soil gas monitoring. Thus, the proposed system builds on a proven sensing approach based on mass spectrometry, which is currently unavailable to the terrestrial ecosystem soil gas analysis research community. A benchtop prototype for analyzing soil gas chemical composition will be constructed and tested on samples of different chemical compositions with molecular components of nearly identical atomic masses, such as nitrous oxide and carbon dioxide which are relevant to understanding hydrobiogeochemical processes. The proposed technology will enable real-time monitoring of soil gas compositions at different depths in a robust fieldable device. Mixtures containing different amounts of relevant gases with various concentration levels will be used in the feasibility demonstration. The design for a Phase II prototype will also be proposed by the end of Phase I. A robust instrument providing real-time analysis of various gas mixtures will have a broad impact in many industries requiring advanced monitoring and control of industrial processes. Other than its immediate application in the soil gas analysis community, the proposed instrument for gas analysis can be used in environmental monitoring and protection, forensic science, chemical research and development, as well as in clinical studies.