Evaluation of the Airborne Quantum Cascade Laser Spectrometer (QCLS) measurements of the carbon and greenhouse gas suite - CO2, CH4, N2O, and CO - during the CalNex and HIPPO campaigns.

We present an evaluation of aircraft observations of the carbon and greenhouse gases (CO₂, CH₄, N₂O, and CO) using a direct-absorption pulsed quantum cascade laser spectrometer (QCLS) operated during the HIPPO and CalNex airborne experiments. The QCLS made continuous 1Hz measurements with 1-sigma Allan precisions of ₂0, 0.5, 0.09, and 0.15 ppb for CO₂, CH₄, N₂O, and CO, respectively, over >500 flight hours on 79 research flights. The QCLS measurements are compared to two vacuum ultraviolet (VUV) CO instruments (CalNex and HIPPO), a cavity ring-down spectrometer (CRDS) measuring CO₂ and CH4 (CalNex), two broadband non-dispersive infrared spectrometers (NDIR) measuring CO₂ (HIPPO), two onboard gas chromatographs measuring a variety of chemical species including CH₄, N₂O, and CO (HIPPO), and various flask-based measurements of all four species. QCLS measurements are tied to NOAA and WMO standards using an in-flight calibration system and mean differences when compared to NOAA CCG flask data over the 59 HIPPO research flights were 100, 1, 1, and ₂ ppb for CO₂, CH₄, N₂O, and CO, respectively. The details of the end-to-end calibration procedures and the data quality-assurance and quality-control (QA/QC) are presented. Specifically, we discuss our practices for the traceability of standards given uncertainties in calibration cylinders, isotopic and surface effects for the long-lived greenhouse gas tracers, interpolation techniques for in-flight calibrations, and the effects of instrument linearity on retrieved mole fractions. [ABSTRACT FROM AUTHOR]