Development of a Methane Isotope Quantum Cascade Laser Spectrometer and Measurements at a New Hampshire Fen
Gregory
W.
Santoni, Harvard U, gsantoni@gmail.com
Ben
H.
Lee, Harvard U, hwanlee@fas.harvard.edu
Jordan
P.
Goodrich, Aerodyne, jordan.goodrich@aerodyne.com
Ruth
K.
Varner, U New Hampshire, rkv@gust.sr.unh.edu
David
D.
Nelson, Aerodyne, ddn@aerodyne.com
Mark
S.
Zahniser, Aerodyne, mz@aerodyne.com
Steven
C.
Wofsy, Harvard, swofsy@seas.harvard.edu
(Presenting)
Estimates of methane sources to the atmosphere are poorly constrained, particularly in terms of their seasonal, inter-annual, and spatial variability. Isotopic measurements of methane can help constrain sources and identify processes responsible for methanogenesis. The development of high-power infrared quantum cascade lasers provides a means to perform continuous high-frequency spectroscopic measurements of the 12C and 13C isotopologues of methane, with precisions approaching those of traditional Isotope Ratio Mass-Spectrometry (IRMS) methods using discrete sampling. Presented here is a description of a methane isotope continuous wave quantum cascade laser spectrometer (QCLS) and results from 4 months of measurements on automated NEE chambers at a nutrient poor fen in Barrington, NH. Analysis of ~700 chamber closings highlights the heterogeneity of the fen. Individual Keeling plots of chamber methane buildups produce mean source methane isotopic composition of -64.5 ‰ with standard deviation of 6.91 ‰ for the fen. Comparisons of individual chambers illustrate the importance of local ecosystem demographics on methane fluxes, with Carex-dominated chambers, for example, generating more linear methane buildups. Ebullition events, on average, have more depleted source isotopic composition, potentially explained by methane oxidation during diffusive fluxes which would leave the sampled methane slightly enriched, dependent on timescales. Ebullition events at greater depths would be less affected by methane oxidation. These measurements demonstrate how continuous isotopic data afforded by QCLS can illustrate the various processes affecting methane production.
Presentation Type: Poster
Poster Session: Carbon Cycle Science
NASA TE Funded Awards Represented:
Wofsy, Stev
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