EGU21-15424
https://doi.org/10.5194/egusphere-egu21-15424
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Laboratory evaluation of water vapour concentration dependence of commercial water vapour isotope cavity ring-down spectrometers for continuous onsite atmospheric measurements in the Amazon rainforest

Shujiro Komiya1, Fumiyoshi Kondo2, Heiko Moossen1, Thomas Seifert1, Uwe Schultz1, Heike Geilmann1, David Walter1,3, and Jost Lavric1
Shujiro Komiya et al.
  • 1Max Planck Institute for Biogeochemistry, Biogeochemical Systems, Jena, Germany (skomiya@bgc-jena.mpg.de)
  • 2Japan Coast Guard Academy, Kure, Japan
  • 3Max Planck Institute for Chemistry, Mainz, Germany

Commercially available laser-based spectrometers permit continuous field measurements of water vapour (H2O) stable isotope compositions, yet continuous observations in the Amazon, a region that significantly influences atmospheric hydrological cycles on regional to global scales, are largely missing. In order to achieve accurate on-site observations in such conditions, these instruments will require regular on-site calibration, including for H2O concentration dependence ([H2O]-dependence) of isotopic accuracy.

With the aim of conducting accurate continuous δ18O and δ2H on-site observation in the Amazon rainforest, we conducted a laboratory experiment to investigate the performance and determine the optimal [H2O]-dependence calibration strategy for two commercial cavity-ring down (CRDS) analysers (L1102i and L2130i models, Picarro, Inc., USA), coupled to our custom-built automated calibration unit. We particularly focused on the rarely investigated performance of the instruments at atmospheric H2O contents above 35,000 ppm, a value regularly reached at our site.

The later analyser model (L2130i) had better precision and accuracy of δ18O and δ2H measurements with a less pronounced [H2O]-dependence compared to the older L1102i. The [H2O]-dependence calibration uncertainties did not significantly change with calibration intervals from 28 h up to 196 h, suggesting that one [H2O]-dependence calibration per week for the L2130i and L1102i analysers is enough. This study shows that with both CRDS analysers, correctly calibrated, we should be able to discriminate natural diel, seasonal and interannual signals of stable water vapour isotopes in a tropical rainforest environment.

 

How to cite: Komiya, S., Kondo, F., Moossen, H., Seifert, T., Schultz, U., Geilmann, H., Walter, D., and Lavric, J.: Laboratory evaluation of water vapour concentration dependence of commercial water vapour isotope cavity ring-down spectrometers for continuous onsite atmospheric measurements in the Amazon rainforest, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15424, https://doi.org/10.5194/egusphere-egu21-15424, 2021.

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