Articles | Volume 7, issue 6
Atmos. Meas. Tech., 7, 1509–1526, 2014
Atmos. Meas. Tech., 7, 1509–1526, 2014

Research article 02 Jun 2014

Research article | 02 Jun 2014

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

G. W. Santoni1, B. C. Daube1, E. A. Kort2, R. Jiménez3, S. Park4, J. V. Pittman1, E. Gottlieb1, B. Xiang1, M. S. Zahniser5, D. D. Nelson5, J. B. McManus5, J. Peischl6, T. B. Ryerson7, J. S. Holloway7, A. E. Andrews7, C. Sweeney6, B. Hall7, E. J. Hintsa6,7, F. L. Moore6,7, J. W. Elkins7, D. F. Hurst6,7, B. B. Stephens8, J. Bent9, and S. C. Wofsy1 G. W. Santoni et al.
  • 1Harvard University, School of Engineering and Applied Sciences and Department of Earth and Planetary Sciences, Cambridge, Massachusetts, USA
  • 2University of Michigan, College of Engineering, Department of Atmospheric, Oceanic and Space Sciences, Ann Arbor, Michigan, USA
  • 3Universidad Nacional de Colombia – Bogota, Department of Chemical and Environmental Engineering, Bogota, Colombia
  • 4Department of Oceanography, College of Ecology and Environmental Science, Kyungpook National University, Sangju, Korea
  • 5Aerodyne Research, Inc., Center for Atmospheric and Environmental Chemistry, Billerica, Massachusetts, USA
  • 6Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA
  • 7Earth System Research Laboratory, National Ocean and Atmospheric Administration, Boulder, Colorado, USA
  • 8National Center for Atmospheric Research, Earth Observing Laboratory, Boulder, Colorado, USA
  • 9Scripps Institution of Oceanography, La Jolla, California, USA

Abstract. 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 1 Hz measurements with 1σ 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 (NDIR) spectrometers 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.