Mass fluxes and isofluxes of methane (CH^sub 4^) at a New Hampshire fen measured by a continuous wave quantum cascade laser spectrometer

• Published in: Journal of geophysical research. Atmospheres Vol. 117; no. 10; p. 1I
• Main Authors: Santoni, Gregory W, Lee, Ben H, Goodrich, Jordan P, Varner, Ruth K, Crill, Patrick M, McManus, J Barry, Nelson, David D, Zahniser, Mark S, Wofsy, Steven C
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 15.05.2012
• Subjects: Geophysics; Methane; Methanogenesis
• ISSN: 2169-897X; 2169-8996

In this paper, the authors have developed a mid-infrared continuous-wave quantum cascade laser direct-absorption spectrometer (QCLS) capable of high frequency measurements of ^sup 12^CH4 and ^sup 13^CH4 isotopologues of methane (CH4) with in situ 1-s RMSδ^sup 13^CCH4 precision of 1.5[per thousand] and Allan-minimum precision of 0.2[per thousand]. The authors deployed this QCLS in a well-studied New Hampshire fen to compare measurements of CH4 isoflux by eddy covariance (EC) to Keeling regressions of data from automated flux chamber sampling. Mean CH4 fluxes of 6.5 ± 0.7 mg CH4 m^sup -2^ hr^sup -1^ over two days of EC sampling in July 2009, were indistinguishable from mean autochamber CH4 fluxes over the same period. Ebullitive fluxes, representing ∼ 10% of total CH4 fluxes at this site, were on average 1.2[per thousand] enriched in ^sup 13^C compared to diffusive fluxes. CH4 isoflux time series have the potential to improve process-based understanding of methanogenesis, fully characterize source isotopic distributions, and serve as additional constraints for both regional and global CH4 modeling analysis.