Mass fluxes and isofluxes of methane (CH4) at a New Hampshire fen measured by a continuous wave quantum cascade laser spectrometer

Authors

Gregory W. Santoni, Harvard University
Ben H. Lee, Harvard University
Jordan P. Goodrich, University of New Hampshire, Durham
Ruth K. Varner, University of New Hampshire, DurhamFollow
Patrick M. Crill, Stockholm University
J. Barry McManus, Aerodyne Research, Inc.
David D. Nelson, Aerodyne Research, Inc.
Mark S. Zahniser, Aerodyne Research, Inc.
Steven C. Wofsy, Harvard University

Abstract

We have developed a mid‐infrared continuous‐wave quantum cascade laser direct‐absorption spectrometer (QCLS) capable of high frequency (≥1 Hz) measurements of 12CH4 and 13CH4 isotopologues of methane (CH4) with in situ 1‐s RMS image precision of 1.5 ‰ and Allan‐minimum precision of 0.2 ‰. We 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−2 hr−1 over two days of EC sampling in July, 2009 were indistinguishable from mean autochamber CH4 fluxes (6.6 ± 0.8 mgCH4 m−2 hr−1) over the same period. Mean image composition of emitted CH4 calculated using EC isoflux methods was −71 ± 8 ‰ (95% C.I.) while Keeling regressions of 332 chamber closing events over 8 days yielded a corresponding value of −64.5 ± 0.8 ‰. Ebullitive fluxes, representing ∼10% of total CH4 fluxes at this site, were on average 1.2 ‰ enriched in 13C 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.

Department

Earth Systems Research Center

Publication Date

5-19-2012

Journal Title

Journal of Geophysical Research: Atmospheres

Publisher

American Geophysical Union (AGU)

Digital Object Identifier (DOI)

https://dx.doi.org/10.1029/2011JD016960

Document Type

Article

Recommended Citation

Santoni, G.W., °B.H. Lee, °J.P. Goodrich, R.K. Varner, P.M. Crill, J.B. McManus, D.D. Nelson, M.S. Zahniser, and S.C. Wofsy (2012) Methane isofluxes by eddy covariance, Keeling regressions of autochamber sampling, and the resulting isotopic composition of methane from a New Hampshire fen using a novel 13CH4 and 12CH4 continuous wave quantum cascade laser spectrometer, J. Geophys. Res. Biogeosciences,117, D10301, 15 PP., doi:10.1029/2011JD016960.

Rights

©2012. American Geophysical Union. All Rights Reserved.

Comments

This is an article published by AGU in Journal of Geophysical Research: Atmospheres in 2012, available online: https://dx.doi.org/10.1029/2011JD016960