Adapting a commercial Quantum Cascade Laser Spectrometer for simultaneous airborne observation of several greenhouse gases

Better understanding of anthropogenic influence on climate is of major global interest. Sources, sinks and transport of climatologically relevant gases in the Earth's atmosphere are still poorly understood, leading towards a fundamental need for accurate, spatially and temporally dense observations. Tunable diode laser absorption spectroscopy is a widely used technique for in-situ sensing of atmospheric composition. Mid-infrared spectrometers have become commercially available, as continuous wave quantum cascade (QCL) and interband cascade lasers (ICL) achieve excellent performance, stability and high enough output power at typical ambient conditions. Aircraft deployment poses a challenging environment for these newly developed instruments. Here, we have adapted a commercially available QCL/ICL based spectrometer for airborne in-situ trace gas measurements. The instrument is demonstrated to measure methane, ethane, carbon dioxide, carbon monoxide, nitrous oxide and water vapor simultaneously, with high precision (740ppt, 205ppt, 460ppb, 2.2ppb, 137ppt, 16ppm) at small time constants (τ ∼ 0.5s). A custom retrieval software has been implemented and instrument performance for a first field test during NASA's Atmospheric Carbon and Transport America (ACT-America) campaign in fall 2017 over the eastern and central U.S. is reported. This includes an inter-instrumental comparison with a calibrated cavity ring-down greenhouse gas analyzer (operated by NASA Langley Research Center, Hampton, USA) and periodic flask samples analyzed at the National Oceanic and Atmospheric Administration (NOAA).