Isotopic Carbon Dioxide Analyzer for Flux Measurements

Los Gatos Research, Inc. (LGR) proposes to develop a rugged, field-deployable, Off-Axis Integrated Cavity Output Spectroscopy (Off-Axis ICOS) instrument for atmospheric carbon dioxide isotopic flux measurements. The instrument will provide highly accurate and precise measurements of 12C16O18O, 13C16O16O, and 12C16O17O, for the determination of CO2, 13C and 18O and 17O in CO2 in ambient air at high measurement rate (10 Hz) for direct determination of fluxes. In addition to continuous measurements of CO2 in air, the instrument will be capable of discrete measurements of batch samples via syringe injection. The detailed understanding of atmospheric chemistry, greenhouse gas emissions and sequestration, and pollution transport in the troposphere, on large and small spatial scales, is limited by the availability of reliable, sensitive, and accurate instrumentation that is easy to use, economical and yields rapid, real-time results. This project will develop a novel, rugged instrument that sensitively and accurately measures the flux of CO2, 13C and 18O (and possibly 17O) in CO2 in ambient air. The instrument, based on LGRs patented cavity-enhanced absorption spectroscopy technology called Off-Axis Integrated Cavity Output Spectroscopy (ICOS) and on state-of-the-art room-temperature continuous-wave quantum-cascade lasers, will be simple to use and will provide fast, real-time measurements in the field from diffuse sources (continuous flow mode) and from discrete point sources (batch sample mode). The Phase I prototype instrument will be tested under realistic conditions on calibrated gas mixtures to determine the accuracy, precision, sensitivity and time response. The Phase I prototype instrument will also be deployed for eddy covariance flux measurements (peatland ecosystems, at AmeriFlux site) to establish the ruggedness, reliability and time response of the instrument in the field. Finally, a Phase II instrument will be designed for autonomous long-term measurements, and the costs of building and selling instruments in small and large quantities will be quantified. In Phase I, LGR will demonstrate technical feasibility by fabricating an Off-Axis ICOS instrument employing a novel, room-temperature continuous-wave, commercially available quantum cascade laser operating near 4.3 microns (CO2 fundamental vibration band), capable of measuring 12CO2, 13C and 18O (and 17O) in ambient air continuously and in batch samples (via syringe injection). Several significant improvements to LGRs standard technique will be implemented (including improved data analysis methods, higher power and lower noise mid-IR laser, lower photodetector noise, improved optical configuration and noise filtering, faster data acquisition rate and temperature stabilization) to enhance the system performance to achieve 0.3 precision at a 10-Hz measurement rate (0.1 seconds per measurement point). This performance will be confirmed by measuring a series of calibrated CO2 standards (obtained from NOAA CMDL Carbon Cycle Group) whose concentrations and isotope ratios are known to better than 0.1 ppmv and 0.02. Finally, the isotope flux measurement system will be configured with a batch injection system for measurements of discrete gas samples where sample size is limited. This comprehensive carbon dioxide isotope instrument will have low power requirements (less than 300 watts) to facilitate field use, low sample volume requirements (2.6 mL) to minimize consumption of sample and calibration gas, report data quickly (10 Hz) and enable detailed characterization of isotopic carbon dioxide distributions over large and small spatial scales.