CILAS: Fast, Accurate Analysis of Carbon’s Isotopic Fingerprints
Vast quantities of carbon dioxide (CO2) cycle between Earth’s atmosphere, oceans, and soils. By knowing the location of CO2 sources (regions where more carbon is released than taken up) and sinks (where more carbon is absorbed than released), scientists can refine theories about how carbon gets processed and distributed, and how it evolves in a particular location or region. This in turn feeds understanding of regional and global climate change trends.
Funded by an NSF biocomplexity grant, CILAS exploits the latest optical fiber and photonics technologies, providing a laser-based gas sensor system that can take continuous, in situ measurements of 13CO2 /12CO2 ratios.One method of answering the source-sink question is to compare ratios of CO2 isotope--13CO2 and 12CO2. These isotopes provide clues as to where and how carbon was generated--for example, what percentage of the carbon originated from fossil fuel burning, what percentage was generated by plant respiration, and what percentage resulted from ocean uptake or release of CO2. Lest it sound like an obvious or easy solution for understanding carbon dynamics, distinguishing between the processes involving these two isotopes requires extreme measurement precision.
To obtain the full story from carbon isotopes using traditional techniques, samples of air are collected in glass flasks at different heights and locations in the atmosphere. Once collected, the flasks are taken to a laboratory and the constituents are measured using an isotope ratio mass spectrometer (IRMS)--an instrument capable of providing very precise measurements of the sample’s chemical constituents. Despite their accuracy, using mass spectrometers as a research tools poses some problems. Often it takes weeks to months to obtain results, and because these large instruments are difficult to move, making field measurements is not possible. Additionally, transporting flask samples back to the lab limits the number of measurements that can be taken.
Scientists have long seen the need for a field instrument that can provide real-time readings that approach the precision of an IRMS. Collaborating with scientists at the University of Colorado, Rice University, and NOAA, NCAR scientists and research engineers have created just such an instrument--the high-precision carbon isotope laser absorption spectrometer (CILAS).
Funded by an NSF biocomplexity grant, CILAS exploits the latest optical fiber and photonics technologies, providing a laser-based gas sensor system that can take continuous, in situ measurements of 13CO2 /12CO2 ratios. The high quality of the custom-developed laser source combined with advanced spectroscopic techniques and data processing enables precision and accuracy that approaches the performance of laboratory-bound IRMS. A recent performance analysis of CILAS indicated that an accuracy of 0.005% or better can be obtained.
A critical component in CILAS’s creation was the support by NCAR’s Design and Fabrication Services Facility in the Earth Observing Laboratory, which helped to create an infrastructure--metal instrument casing, compact design, external frame--that ensured CILAS would be both portable and rugged enough to withstand harsh field conditions. Researchers will put CILAS through additional calibration verification in the laboratory by simulating a host of field conditions and comparing the instrument’s performance with an IRMS before it enters an intensive field testing period. CILAS, developed from the ground up and vetted through an extensive performance verification protocol, is well on its way to becoming an invaluable state-of-the-art tool for carbon cycle research for NCAR and the university community.
