Evaluation of the airborne quantum cascade laser spectrometer (QCLS) measurements of the carbon and greenhouse gas suite – CO 2, CH 4, N 2O, and CO – during the CalNex and HIPPO campaigns

Santoni, G. W.; Daube, B. C.; Kort, E. A.; Jiménez, R.; Park, S.; Pittman, J. V.; Gottlieb, E.; Xiang, B.; Zahniser, M. S.; Nelson, D. D.; McManus, J. B.; Peischl, J.; Ryerson, T. B.; Holloway, J. S.; Andrews, A. E.; Sweeney, C.; Hall, B.; Hintsa, E. J.; Moore, F. L.; Elkins, J. W.; Hurst, D. F.; Stephens, B. B.; Bent, J.; Wofsy, S. C.

We present an evaluation of aircraft observations of the carbon and greenhouse gases CO 2, CH 4, N 2O, and CO using a direct-absorption pulsed quantum cascade laser spectrometer (QCLS) operated during the HIPPO and CalNex airborne experiments. The QCLS made continuous 1 Hz measurements with 1σ Allan precisions of 20, 0.5, 0.09, and 0.15 ppb for CO 2, CH 4, N 2O, 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 CO 2 and CH 4 (CalNex), two broadband non-dispersive infrared (NDIR) spectrometers measuring CO 2 (HIPPO), two onboard gas chromatographs measuring a variety of chemical species including CH 4, N 2O, 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 CO 2, CH 4, N 2O, 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.

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Santoni, G. W. / Daube, B. C. / Kort, E. A. / et al: 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. 2014. Copernicus Publications.

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