CO2 Isotope Trace Gas Monitor
A Novel Dual Cell gas analysis system for continuous, accurate, simultaneous measurement of concentrations of Carbon Dioxide isotopologues.
A room temperature continuous wave QCL laser from Alpes Lasers, is operated in the 2310 to 2315 cm-1 range to obtain simultaneous detection of 13CO2 and C18OO and 12CO2.
Applications
- Atmospheric monitoring of isotopic gradients from aircraft and other mobile platforms
- Eddy covariance iso-flux measurements
- Isotopic composition measurements
Advantages
- Both 13C and 18O Isotopic Ratios are monitored in real-time
- Single TE cooled continuous wave Quantum Cascade Laser (QCL)
- 2 matched absorption cells, 7 m.
- No pre-concentration is required
- Thermo-electrically cooled IR detectors
- Measurement precision:
- 0.2δ in one second, or 0.05δ in 100 sec.
- Fast time response: (1/e) response time of 0.05 sec in the 0.3 liter sampling cell
- Compact 19 inch rack mountable system
Advantages of Novel Dual Cell Approach (Sample + Reference)
(2) negligible spectral interference between the two isotopic species
- The two multi-pass cells are thermally coupled.
- Cell temperatures measured to a relative precision of 1 mK to minimize compensation for the temperature sensitivity.
- Temperature control of entire optical bench and electronics minimizes drifts in laser line width, frequency, tuning rate and power variation.
Technical Specifications
| | δ13CO2 | δC18OO |
| Laser Frequency | 2310 cm-1 | 2310cm-1 |
| RMS noise in ratio for 1 second data1 | 0.2 ‰ | 0.2 ‰ |
Intermediate term | 0.05 ‰ | 0.05 ‰ |
| 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.
2. The absolute concentrations 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).
References
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.
For more information or support for our quantum cascade lasers:
qcl-info@aerodyne.com
