A Widely Tunable Infrared Laser Spectrometer for Measurements of Isotopic Ratios of Carbon Cycle Gases
The atmospheric abundances of carbon dioxide and methane have increased dramatically during the industrial era. Measurements of the isotopic composition of these gases can provide a powerful tool for quantifying their sources and sinks. This report describes the development of a portable instrument for isotopic analysis CO{sub 2} and CH{sub 4} using tunable infrared laser absorption spectroscopy. This instrument combines novel optical design and signal processing methods with a widely tunable mid-infrared laser source based on difference frequency generation (DFG) which will can access spectral regions for all the isotopes of CO{sub 2} and CH{sub 4} with a single instrument. The instrument design compensates for the large difference in concentration between major and minor isotopes by measuring them with path lengths which differ by a factor of 100 within the same multipass cell. During Phase I we demonstrated the basic optical design and signal processing by determining {sup 13}CO{sub 2} isotopic ratios with precisions as small as 0.2{per_thousand} using a conventional lead salt diode laser. During Phase II, the DFG laser source was coupled with the optical instrument and was demonstrated to detect {sup 13}CH{sub 4}/{sup 12}CH{sub 4} ratios with a precision of 0.5{per_thousand} and an averaging time of 20 s using concentrated methane in air with a mixing ratio of 2700 ppm. Methods for concentrating ambient air for isotopic analysis using this technique have been evaluated. Extensions of this instrument to other species such as {sup 13}CO{sub 2}, C{sup 18}OO, and CH{sub 3}D are possible by substituting lasers at other wavelengths in the DFG source module. The immediate commercial application of this instrument will be to compete with existing mass spectrometric isotope instruments which are expensive, large and relatively slow. The novel infrared source developed in this project can be applied to the measurement of many other gas species and will have wide application in atmospheric monitoring, industrial process control, and medical research and diagnostic development.
- Research Organization:
- Aerodyne Research Inc., Billerica MA (US); Sandia National Laboratories, Livermore CA (US); University of California, Irvine CA (US)
- Sponsoring Organization:
- USDOE Office of Energy Research (ER) (US)
- DOE Contract Number:
- FG02-00ER82938
- OSTI ID:
- 836581
- Report Number(s):
- DOE/ER/82938-1; ARI-RR-1396; CRDA SC02/01642; TRN: US200510%%96
- Resource Relation:
- Other Information: PBD: 31 Jan 2005
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
03 NATURAL GAS
47 OTHER INSTRUMENTATION
54 ENVIRONMENTAL SCIENCES
ABSORPTION SPECTROSCOPY
ACCURACY
CARBON CYCLE
CARBON DIOXIDE
DESIGN
GASES
LASERS
METHANE
MIXING RATIO
MONITORING
PROCESS CONTROL
PROCESSING
SPECTROMETERS
WAVELENGTHS
STABLE ISOTOPES
GREENHOUSE GASES
INFRARED ABSORPTION
DIFFERENCE FREQUENCY GENERATION
LASER SPECTROSCOPY