1School of Earth, Atmospheric and Environmental Sciences,
University of Manchester, Oxford Road, Manchester, M13 9PL,
2Facility for Airborne Atmospheric Measurements (FAAM),
Building 125, Cranfield University, Cranfield, Bedford, MK43 0AL,
3Aerodyne Research, Inc., Center for Atmospheric and
Environmental Chemistry, Billerica, Massachusetts, USA
4Centre for Atmospheric Science, University of Cambridge,
Cambridge, CB2 1EW, UK
5School of GeoSciences, University of Edinburgh,
Edinburgh, EH9 3JN, UK
anow at: Deutscher Wetterdienst, Meteorologisches
Observatorium Hohenpeißenberg, Hohenpeißenberg, Germany
Received: 30 Jun 2015 – Discussion started: 27 Aug 2015
Abstract. Spectroscopic measurements of atmospheric N2O and CH4 mole fractions were made on board the FAAM (Facility for Airborne Atmospheric Measurements) large atmospheric research aircraft. We present details of the mid-infrared quantum cascade laser absorption spectrometer (QCLAS, Aerodyne Research Inc., USA) employed, including its configuration for airborne sampling, and evaluate its performance over 17 flights conducted during summer 2014. Two different methods of correcting for the influence of water vapour on the spectroscopic retrievals are compared and evaluated. A new in-flight calibration procedure to account for the observed sensitivity of the instrument to ambient pressure changes is described, and its impact on instrument performance is assessed. Test flight data linking this sensitivity to changes in cabin pressure are presented. Total 1σ uncertainties of 2.47 ppb for CH4 and 0.54 ppb for N2O are derived. We report a mean difference in 1 Hz CH4 mole fraction of 2.05 ppb (1σ = 5.85 ppb) between in-flight measurements made using the QCLAS and simultaneous measurements using a previously characterised Fast Greenhouse Gas Analyser (FGGA, Los Gatos Research, USA). Finally, a potential case study for the estimation of a regional N2O flux using a mass balance technique is identified, and the method for calculating such an estimate is outlined.
Revised: 30 Nov 2015 – Accepted: 03 Dec 2015 – Published: 15 Jan 2016
Pitt, J. R., Le Breton, M., Allen, G., Percival, C. J., Gallagher, M. W., Bauguitte, S. J.-B., O'Shea, S. J., Muller, J. B. A., Zahniser, M. S., Pyle, J., and Palmer, P. I.: The development and evaluation of airborne in situ N2O and CH4 sampling using a quantum cascade laser absorption spectrometer (QCLAS), Atmos. Meas. Tech., 9, 63-77, doi:10.5194/amt-9-63-2016, 2016.