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| Titel |
Real-time measurement of δ¹³C and δ¹⁸O in CO2 by QCLAS - from the soil to the free troposphere |
| VerfasserIn |
Lukas Emmenegger, Béla Tuzson, Joachim Mohn, Mark Zahniser, Adrian Kammer, Matthias Zeeman |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250039869
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| Zusammenfassung |
| Isotope ratios of CO2 are highly valuable to investigate CO2 sources, sinks and transport at
local and global scales. However, relevant studies often require extensive and long term
measurements under field conditions, which may not be feasible with standard isotope ratio
mass spectrometers (IRMS). We have developed and validated an entirely cryogen-free
quantum cascade laser absorption spectrometer (QCLAS) using a room temperature 4.3 μm
QC laser. The QCLAS is based on the differential absorption technique and suited for
long-term, unattended field applications, delivering both δ13C and δ18O in CO2 with a
precision of 0.05 permil. The spectrometer was validated against IRMS in laboratory and
field studies, and has been employed in a range of studies, including forest soil
respiration, grassland sub canopy respiration and long-term measurements at a remote
location.
In a beech forest of the Swiss Jura, we applied the QCLAS to investigate 13C and 18O
dynamics of CO2 in a closed chamber system placed on soils with a 13C labelled litter layer.
A recirculation sampling scheme permitted the real-time monitoring of the CO2
isotope ratios in the chamber headspace on a timescale of seconds. We performed 90
measurement cycles, resulting each in Keeling plots of 1200 data points. The high
time-resolution data revealed very distinct and at first sight surprising patterns for δ13C and
δ18O.
High frequency (ca. 5 Hz) measurements were performed during summer at an intensively
managed grassland site in central Switzerland with the aim to quantify atmosphere-biosphere
carbon exchange for this type of ecosystem. The effects of a grass cut during the
measurement period could be detected and resulted in a sub-canopy source conditional flux
classification, for which the isotope composition of the CO2 could be confirmed to be of a
respiration source.
Currently, the instrument is operating at the high alpine research station Jungfraujoch (3580
m a.s.l.), and delivers for the first time continuous measurements of CO2 isotopologues of the
free troposphere. Several pollution events during January and February 2009 were identified
by the strong patterns for δ13C and δ18O which may also be analyzed using the Keeling
intercept method. In combination with Lagrangian backward trajectory models and other
trace compounds, these data can be employed for the characterization of CO2 source
regions.
In this presentation we will highlight the characteristics, strength and limitations of
our current QC laser spectrometer based on laboratory data and the above case
studies. |
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