Pitt, J.R., Le Breton, M., Allen, G., Percival, C.J., Gallagher, M.W., Bauguitte, S.J.-B., O’Shea, S.J., A. Muller, J.B., Zahniser, M.S., Pyle, J., Palmer, P.I. (2015):
The development and evaluation of airborne in situ N2O and CH4 sampling using a Quantum Cascade Laser Absorption Spectrometer (QCLAS)
Atmos. Meas. Tech. Discuss. 8, 8859–8902. doi:10.5194/amtd-8-8859-2015
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-IR Aerodyne Research Inc. Quantum Cascade Laser Absorption Spectrometer (QCLAS) 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 is presented. Total 1σ uncertainties of 1.81 ppb for CH4 and 0.35 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 Los Gatos Research Fast Greenhouse Gas Analyser (FGGA). 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.
Received: 30 Jun 2015 – Accepted: 28 Jul 2015 – Published: 27 Aug 2015
Final revised paper (15 Jan 2016): Pitt et al. (2016): Airborne in situ N2O and CH4 sampling using a QCLAS - AMT