MRI-R2: Development and Deployment of Automated Continuous Wave Quantum Cascade Laser Instruments For On-Site Monitoring of the Four Isotopomers of Nitrous Oxide

Massachusetts Institute Of Technology, Cambridge MA

Investigators

Abstract

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). Nitrous oxide (N2O) is both a significant greenhouse gas (radiative forcing in 2009 is approximately 0.17 W/m2) and a large contributor to the catalytic destruction of the stratospheric ozone layer. Its mole fractions in the atmosphere continue to rise from a natural preindustrial value of about 270 parts per billion (ppb) to about 322 ppb today. However, there are major uncertainties in the global cycle of this third most abundant long-lived greenhouse gas. To address these uncertainties, the investigators propose the development and deployment of two automated high frequency laser-based instruments for analysis of the isotopologues and isotopomers of N2O. Isotopic ratios will be monitored using tunable infrared laser differential absorption spectroscopy (TILDAS) with continuous wave (CW) quantum cascade (QC) lasers. This technology is well suited for long-term deployment at remote sites as the instruments are fully automated and can also be accessed and controlled via the Internet. The new instruments will monitor four isotopologues/isotopomers of nitrous oxide. Continuous surface measurements of the mole fraction of N2O have provided an important resource in analysis of the global budget through inverse modeling studies, but the utilization of these mole fraction data has reached the limit of information that can be extracted and leaves large uncertainty remaining. The development of high-frequency isotopomer/isotopologue measurement capability will greatly enhance current ability to differentiate between the natural and anthropogenic contributions to its budget at the spatial and temporal resolution needed for scientific understanding and policy verification. The deployment at one of the AGAGE (Advanced Global Atmospheric Gases Experiment) stations (that has been measuring trace gases including N2O on site since 1978) will produce an unprecedented set of data including isotopomers with identical molecular mass. Similarly, the in situ high-frequency measurements at field sites of the isotopic signatures of the dominant nitrous oxide sources could potentially yield new insights into source dynamics and isotopic variability. The project will facilitate the collaboration between Aerodyne Research, Inc. (U.S. small business) and Massachusetts Institute of Technology (MIT) for the development of a new generation of isotope monitoring equipment. Graduate students will actively participate in the development and be trained as future atmospheric chemists with strong instrumental background. The MIT instrument will be used for undergraduate level class projects as well as for undergraduate and graduate thesis research projects, and will also be open to collaborative projects with researchers outside MIT.