Carbon Dioxide Isotope Monitor

Aerodyne’s QC laser based CO2 isotope gas monitors can provide a measurement precision for both  13CO2/12CO2 and 18CO2/12CO2 of less than 0.1 per mil (1σ) in one second and a measurement precision of less than 0.03 per mil with 60 seconds of averaging at ambient atmospheric carbon dioxide mixing ratios.  This incredible combination of high precision with fast time response (10 Hz) enables isotope specific eddy covariance measurements of this globally important greenhouse gas
The two figures show Allan plots of concentration measurements obtained while sampling room air with ambient CO2 for 90 minutes at one second time resolution.  It demonstrates measurement noise of 0.07 per mil for 13R and 0.06 per mil for 18R, both of which are less than our specified noise performance. 
Additional Information:
- Uses room temperature QC laser and detector – no cryogens
- 17R is also measured in the standard instrument
- Enhanced version of the instrument available that also measures water isotopes
- Enhanced version of the instrument available that also measures “clumped” isotope:  13C18O16O
- Instrument is compact and rack mountable
  • Dimensions: 65 cm x 43 cm x 27 cm (core instrument)

  •  Weight: 25 kg (core instrument)

  •  Electric Power: 400 W, 120/240 V, 50/60 Hz (core instrument)



  • Atmospheric monitoring of isotopic gradients from aircraft and other mobile platforms
  • Eddy covariance iso-flux measurements
  • Isotopic composition measurements

Technical Specifications

     δ13CO2 δC18OO
Laser Frequency 2310 cm-1 2310cm-1
RMS noise in ratio
for 1 second data1
0.1 ‰ 0.1 ‰

Intermediate term
precision 100 s from Allan plot

0.03 ‰ 0.03 ‰
Accuracy relative to calibration
standard 2
0.1 ‰ 0.1 ‰
Sampling frequency3 1 Hz to 20 Hz ...
Flow cell 1/e time response3 0.05 seconds ...

1.  The RMS noise definition is defined by the 1 sigma standard deviation of a data stream with a 1 Hz sampling frequency for the ratio of the minor isotope to the major isotope.  The values given are for simultaneous detection of all three isoptopologues with [CO2] = 380 ppm.

2.  The absolute isotopic ratios are based on the periodic addition of calibration gases using automated solenoid valve (included).

3.  The sampling frequency of 1 to 20 Hz is the electronic processing speed.  The gas exchange time constant (1/e) in the 0.3 liter volume sampling cell is tau=0.05 seconds with a 420 liter-per-minute vacuum  pump (optional). 


New Method for Isotopic Ratio Measurements of Atmospheric Carbon Dioxide Using a 4.3  micron Pulsed Quantum Cascade Laser, D.D. Nelson, J. B. McManus, S. C. Herndon, M. S. Zahniser, B. Tuzson,  L. Emmenegger, Applied Physics B., 90, 301-309, 2008.

Infrared laser spectrometer with balanced absorption for measurements of isotopic ratios of carbon gases, J. B. McManus,  M. S. Zahniser, D. D. Nelson, L. R. Williams, C. E. Kolb,  Spectrochim. Acta A, 58, 2465-2479, 2002.

A high precision pulsed QCL spectrometer for measurements of stable isotopes of carbon dioxide, J.B. McManus, D. D. Nelson, J. H.  Shorter, R. Jiménez, S. Herndon, S. Saleska, M. S. Zahniser, J. Modern Optics, 52, 2309-2321, 2005.

What are the instrumentation requirements for measuring the isotopic composition of net ecosystem exchange of CO2 using eddy covariance methods?, S. R. Saleska, J. Shorter, S. Herndon, R. Jimenéz, B.  McManus, D. Nelson, M. S. Zahniser,  Isotopes  Environ. Health Studies, 42, 115-133, 2006.


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