Measurements of atmospheric constituents by tunable diode laser absorption spectrometry
Evaluation of acid deposition models require accurate measurements of the concentrations of a number of important trace constituents. Tunable diode laser absorption spectrometry (TDLAS) operating in the 5 to 10 micron region affords a number of advantages for measuring these species. It is a universal method applicable, in principal, to any gas of atmospheric interest. Because of its high resolution, it provides a positive identification with no interferences from other gases. By utilizing the long path length of a White cell it can detect most molecules at concentrations less than 1 ppbv. It is a passive technique which can provide real time, in situ measurements, with a time resolution better than 1 min. The high specificity of the method results from the spectral resolution of the tunable laser diodes being much less than the Doppler width of the rotational-vibrational linewidth of the absorbing molecule. Interferences from other molecules are unlikely with this resolution but can, in any case, be readily identified by changes in lineshape. In addition, an unequivocal test for the absence of interferences is afforded by comparison of the mixing ratios calculated from two separate absorption lines. There is a vanishingly small probability that any interfering gas could have exactly the same line shapes and intensities as the target gas at both wavelengths. The application of this method to the measurement of trace atmospheric constituents has three requirements: 1) the selection of an appropriate absorption line - this usually involves a compromise between the line strength of the absorber and the operating characteristics of the diode, 2) the development of a calibration procedure for the target gas and 3) the development of procedures to ensure sampling integrity and tests to assure linearity between absorption signal and concentration of the target gas in the sampled air.
- Research Organization:
- Unisearch Associates, 222 Snidercroft, Concord, Ontario L4K 1B5
- OSTI ID:
- 5431878
- Journal Information:
- Am. Chem. Soc., Div. Pet. Chem., Prepr.; (United States), Vol. 31:2
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ACID RAIN
LASER SPECTROSCOPY
FORMALDEHYDE
AIR POLLUTION MONITORING
HYDROGEN PEROXIDE
NITRIC ACID
NITROGEN OXIDES
SULFUR DIOXIDE
AMMONIA
CALIBRATION
ECOLOGICAL CONCENTRATION
ELEMENTS
POLLUTANTS
QUANTITATIVE CHEMICAL ANALYSIS
SAMPLING
SPECTROPHOTOMETRY
TRACE AMOUNTS
ALDEHYDES
ATMOSPHERIC PRECIPITATIONS
CHALCOGENIDES
CHEMICAL ANALYSIS
HYDRIDES
HYDROGEN COMPOUNDS
INORGANIC ACIDS
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PEROXIDES
RAIN
SPECTROSCOPY
SULFUR COMPOUNDS
SULFUR OXIDES
500200* - Environment
Atmospheric- Chemicals Monitoring & Transport- (-1989)
400104 - Spectral Procedures- (-1987)