Abstract
Abstract. A laser spectrometer for automated monthly measurements of methane (CH4) mixing ratios aboard the CARIBIC passenger aircraft is presented. The instrument is based on a commercial Fast Greenhouse Gas Analyser (FGGA, Los Gatos Res.), which was adapted to meet the requirements imposed by unattended airborne operation. It was characterised in the laboratory with respect to instrument stability, precision, cross sensitivity to H2O, and accuracy. For airborne operation, a calibration strategy is described that utilises CH4 measurements obtained from flask samples taken during the same flights. The precision of airborne measurements is 2 ppb for 10 s averages. The accuracy at aircraft cruising altitude is 3.85 ppb. During aircraft ascent and descent, where no flask samples were obtained, instrumental drifts can be less accurately determined and the uncertainty is estimated to be 12.4 ppb. A linear humidity bias correction was applied to the CH4 measurements, which was most important in the lower troposphere. On average, the correction bias was around 6.5 ppb at an altitude of 2 km, and negligible at cruising flight level. Observations from 103 long-distance flights are presented that span a large part of the northern hemispheric upper troposphere and lowermost stratosphere (UT/LMS), with occasional crossing of the tropics on flights to southern Africa. These accurate data mark the largest UT/LMS in-situ CH4 dataset worldwide. An example of a tracer-tracer correlation study with ozone is given, highlighting the possibility for accurate cross-tropopause transport analyses.
Highlights
Atmospheric methane (CH4) is the second-strongest longlived anthropogenically influenced greenhouse gas (GHG) after carbon dioxide (CO2) (Solomon et al, 2007)
In this paper we present an airborne diode-laser spectrometer, which is based on a commercial Fast Greenhouse Gas Analyser (FGGA, Los Gatos Research)
The present instrument is based on a commercial Fast Greenhouse Gas Analyser (FGGA1, Los Gatos Research), which measures CH4, CO2, and H2O mixing ratios based on offaxis integrated cavity output spectroscopy (OA-ICOS) (Baer et al, 2002)
Summary
Atmospheric methane (CH4) is the second-strongest longlived anthropogenically influenced greenhouse gas (GHG) after carbon dioxide (CO2) (Solomon et al, 2007). Satellite measurements of CH4 have been performed with various satellite-borne instruments in recent years (Schneising et al, 2009; Payan et al, 2009; Xiong et al, 2010; Wecht et al, 2012; Worden et al, 2012) While these data are provided on a global scale, they cannot resolve small-scale variability of CH4 in the UT/LMS. Diode-laser absorption spectroscopy offers the capability for precise and accurate measurements at small instrument size, and several research instruments have been developed in the past They have provided in-situ measurements in the laboratory (Weibring et al, 2010), field (Werle and Kormann, 2001; Nelson et al, 2004), and aboard balloon and aircraft platforms (Scott et al, 1999; Richard et al, 2002; Durry et al, 2002; Gurlit et al, 2005; Berman et al, 2012).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
