Optical Carbon Dioxide Field Isotope Ratiometer

Anthropogenic greenhouse gas emissions are best quantified by determining their carbon dioxide isotope ratios. However, the required precision represents a challenge to optical measurement techniques under field deployment conditions. This project will develop a compact, rugged, mid-infrared spectrometer capable of determining isotopic carbon dioxide ratios at atmospherically relevant levels. In Phase I, a mid-infrared spectrometer for the detection of carbon dioxide at 4.3 microns was constructed, based on a pulsed quantum cascade laser (QCL). The sensitivity, selectivity, and precision of the instrument for isotopic carbon dioxide analysis were determined by using a high-performance optical cell specifically suited for QCLs. An isotopic abundance measurement precision below 0.2 'per mil' was predicted. In Phase II, a fully-integrated QCL sensor prototype, based on photoacoustic spectroscopy, will be constructed for field determination of atmospheric CO2 isotope ratios. Standard operating protocols for the sensors will be established. The prototypes will be refined through field-testing in several applications, which also will be Phase III commercialization opportunities. Commercial Applications and other Benefits as described by the awardee: The instrument should provide a compelling blend of price, performance and physical advantages in a variety of gas detection applications. Examples include atmospheric monitoring, environmental regulatory compliance, process gas analysis, and biomedical breath diagnostics. The targeted application for measuring greenhouse gas emissions is of high intrinsic value for the assessment of global warming.