Differential optical absorption spectrometer

Applications The differential optical absorption spectrometer has been used to monitor concentrations of gases or intermediate compounds such as SO, NO, O5, HCHO, HNO, CS, NO, and OH in the atmosphere.In atmospheric measurements with open paths of 100 to 1000 m, a detection limit of about 1 ppb can be achieved. In the emission measurements, the path length across the duct or the plume can range in meters. 

In the late 1970 s, a group of German researchers developed a novel instrument, the long-path length (e.g., 1-17 km) ultraviolet-visible differential optical absorption spectrometer, DOAS (Platt et al., 1979). Application of this instrument in field studies in remote... 

Gas phase component concentrations A number of standard gas analysers are routinely available for determination of gaseous mixing ratio of CH4, CO, O3, NO, NO2 and SO2 at moderate atmospheric concentrations. GC determination of a limited number of NMHC species is also available for appropriate experiments. An Aerodyne Quantum Cascade Tunable Diode Laser Absorption Spectrometer (QC-TDLAS) is periodically available for NH3 measurements using tiie line at 967 cm and for NO2 measurement at 1606 cm . There are several potential experiments which may benefit from measurement of other trace species. The Differential Optical Absorption Spectrometer (DOAS) described below may be used for determination of lO, OIO, BrO, NO3, HCHO, SO2 and other trace species. 

GOME is a nadir sounding spectrometer which observes the up-welling radiance from the top of the atmosphere and the extra-terrestrial solar irradiance between 240 and 790 nm. The resolution of the measurements is chosen to be suitable for the application of the differential optical absorption spectroscopy (DOAS) technique, which was developed for long-path measurements and zenith sky observations (e.g. Platt and Pemer, 1980 Mounter a/., 1987 Eisinger etal., 1997). 

The observed mixing ratios of active halogen species in the troposphere is in general 1-100 ppt, and the direct measurements of these species are usually made by using the methods, Long-Path Differential Absorption Spectroscopy (LP-DOAS), Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS), Chemical Ionization Mass Spectrometer (CIMS) and Laser Induced Fluorescence (LIF). As for BrO and lO, satellite observation gives spatial distribution of its tropospheric column. 

A Nicolet Magna 550 Fourier Transform Infrared Spectrometer (FTIR) and a Bruker MW 250 MHz proton NMR were used to verify the chemical structure of all monomers and polymers. Optical activity of the compounds was measured at 25 on a Perkin-Elmer Polarimeter in chloroform. A Waters Gel Permeation Chromatograph with 440 UV absorption detector and R401 differential refructometer was used to determine the molecular weights of the polymers tetrahydrofuran was used as the mobile phase at 1.0 mL/min, and the Waters polystyrene gel columns were calibrated with monodisperse polystyrene standards. Polarizing optical microscopy was used to identify liquid crystalline phases using a Leitz optical microscope with a CCD camera attachment... 

Optical activity also manifests itself as a differential absorption of left and right CPL, AA = Al - Ar or Ae = i, - Cr, the wavelength dependence of which is called circular dichroism (CO), and is measured on a CD spectrometer. The area under the CD absorption band of a given transition, /, is the rotatory strength, [R], ... 

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