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Toward continuous monitoring of seawater 13 CO 2 / 12 CO 2 isotope ratio and p CO 2 : Performance of cavity ringdown spectroscopy and gas matrix effects
Author(s) -
Friedrichs Gernot,
Bock Julia,
Temps Friedrich,
Fietzek Peer,
Körtzinger Arne,
Wallace Douglas W. R.
Publication year - 2010
Publication title -
limnology and oceanography: methods
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.898
H-Index - 72
ISSN - 1541-5856
DOI - 10.4319/lom.2010.8.539
Subject(s) - laser linewidth , analytical chemistry (journal) , seawater , isotope , chemistry , calibration , oxygen 18 , supersaturation , partial pressure , stable isotope ratio , physics , oxygen , optics , nuclear physics , laser , environmental chemistry , oceanography , organic chemistry , quantum mechanics , geology
The potential of a continuous wave cavity ringdown spectrometer for monitoring the isotope ratio 13 CO 2 / 12 CO 2 and the partial pressure p CO 2 of CO 2 dissolved in water was thoroughly analyzed by quantitative measurements. Running calibration gas standards under typical operation conditions, a relative accuracy of Δ(δ 13 C[CO 2 ]) = ±0.1‰ with 120 min averaging time has been demonstrated. Absolute uncertainties were determined to be Δ(δ 13 C[CO 2 ]) = ±0.2‰ and Δ( x CO 2 ) = ±0.5 ppmv. No principle problems were encountered when using the instrument in combination with a water‐air equilibration setup. By contrast, when performing measurements of CO 2 in gas matrices with a composition different from that of ambient air, pressure broadening linewidth effects induced significant errors in both δ 13 C(CO 2 ) and x CO 2 values. These effects, which compromise the accessible accuracy in environmental studies, can be quantitatively taken into account by using a spectroscopically based correction procedure. Relying on linewidth analysis, the instrument was shown to be capable of continuous and simultaneous measurement of δ 13 C(CO 2 ), p CO 2 , as well as water content and O 2 supersaturation, and thus holds the potential for online monitoring of these quantities aboard research vessels.