Compact, Autonomous, Carbon Isotope Flux Monitor Using Difference Frequency Generation Infrared Absorption

75422B The increase of atmospheric CO2 from fossil fuel combustion is a major contributor to global warming and climate change. Improved measurement technology for directly determining the exchange fluxes of the stable isotopes of CO2 is crucial to understanding the natural carbon cycle, which transforms atmospheric CO2 into biological carbon, and to develop strategies to mitigate the problem. This project will develop a field-portable instrument to directly measure both 13CO2 and C18OO fluxes from terrestrial ecosystems ¿ needed to differentiate the carbon exchange mechanisms of photosynthesis and respiration, and to assess the relative importance of different vegetation types for carbon sequestration. The instrument will have sufficient precision and time response, and will be capable of continuous, unattended operation at remote field sites, without the use of cryogenic lasers or detectors. In Phase I, a direct-frequency-generation (DFG) light source was designed, and the feasibility of obtaining sufficient power in an ultra-compact package was shown. A pulsed quantum cascade laser (QCL) was shown to provide measurement precision of 0.1 parts-per-thousand for the 13CO2/12CO2 ratio with an averaging time of 200 s. Phase II will complete the designs of the DFG source module, the optical module, and the electronics data acquisition modules. A prototype instrument will be designed and constructed. The prototype instrument will be tested in the laboratory using flask samples of known isotopic abundance ratios, and by using roof top sampling of ambient tropospheric air mixed with local combustion CO2 sources. Commercial Applications and Other Benefits as described by the awardee: The instrument would provide a simpler and more compact alternative to presently available isotope ratio mass spectrometer systems. Potentially larger commercial markets exist in medical research, where stable isotope metabolic tracers can be used to monitor the isotopic ratio in exhaled breath, and in the oil and gas exploration industry, where stable isotopes can be indicative of oil-well productivity.