Quantum Cascade Laser System for Simultaneous Measurements of 13CO and C18O Carbon Monoxide Isotopologues

Carbon monoxide (CO) is a key sink for atmospheric OH and thus changes in carbon monoxide concentrations have an impact on the abundance and chemistry of many other atmospheric gases. Monitoring the isotopic composition of atmospheric carbon monoxide (13CO, C18O and CO) is one of the most promising approaches to determining global sources and sinks of CO and closing the CO budget. There are no existing field deployable instruments for the sensitive, real time measurement of the isotopologues of carbon monoxide. This proposal directly addresses the solicitations call for a field deployable CO isotope monitor under topic 29b, item (4). The proposed CO isotope monitor will couple room temperature continuous wave quantum cascade lasers with advanced infrared detectors and new optical designs for longer absorption path length in a compact instrument. The resulting instrument will simultaneously measure the isotopic ratios of 13CO and C18O with excellent precision in real time (one minute resolution). We project isotopic ratio precisions of 0.25 per mil and 1.5 per mil for 13CO and C18O, respectively, for a typical ambient CO mixing ratio of 200 ppb. The resulting instrument will be compact, portable, autonomous and field ready. The successful Phase I results demonstrated sensitive measurement of the CO isotopologues, 13CO, C18O, and CO in a 204 m absorption cell. Isotopic ratio precisions for 13CO and C18O to 12C16O of 0.4 per mil and 3.6 per mil, respectively, were obtained with a real time cw quantum cascade laser instrument. The laser was operating at a less than ideal wavelength due to the time constraints in Phase I. A preliminary design for the Phase II instrument was developed which includes obtaining lasers that operate at the ideal wavelengths. In the first year of the project, design improvements in optical and electronics will lead to production of a sensitive portable instrument for simultaneously monitoring multiple CO isotopologues. The resulting instrument will be applied in the second year to both laboratory and field measurements to evaluate CO isotopic signatures of atmospheric sources. Additional commercial applications of the monitor will be studied including the development of a pre-concentration method to allow the study of rare isotopic species like C17O and 13C18O. Commercial Applications and Other Benefits: This instrument will provide atmospheric scientists with scientifically meaningful isotopic ratio measurements in real time, without pre-concentration and without cryogenic cooling of either laser or detector. Other applications of this technology include air pollution monitoring, human breath analysis, and industrial process monitoring. This technology will provide a significant societal benefit through improved understanding and mitigation of global warming and global climate change.