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Measurement of tropospheric OH by laser long-path absorption spectroscopyOH-radicals are measured by laser long-path absorption spectroscopy. A tunable Nd:YAG/dye laser system provides broadbanded light at 308 nm. The beam is expanded to 0.3 m and pointed to an array of retroreflectors placed at a distance of 2800 m. The returning beam is separated from the outgoing beam and focused into a spectrometer of 0.3 pm resolution. A 1024 element diode array is used as a detector. The signal is digitized by a 14 bit analog to digital converter. The ultimate aim is a detection limit of 10(exp 5) molecules cm(exp -3) of OH. However the measurements in 1991 allowed only the recognition of OH absorptions corresponding to 3 x 10(exp 6) OH cm(exp -3) with a signal to noise ratio of two. Improvements of the instrument are under way. The advantages of the DOAS method are: the accuracy of detection is guaranteed because loss of OH radicals within the device is avoided, the rate of OH production by the device is negligible, and absorptions of other trace gases could be corrected for; and the calibration procedure for the device is fast and easy. The disadvantages of the system are: time resolution is about minutes because about ten spectra had to be added to keep the noise level down, the OH concentration is averaged along the whole light path, weight (500 kg) and size (4x4 m) of the device; and approximately 10 l/min of coolant and supply of 8 kW electrical power are necessary.
Document ID
19940024093
Acquisition Source
Legacy CDMS
Document Type
Conference Paper
Authors
Kraft, Michael
(Max-Planck-Inst. fuer Chemie Mainz, Germany)
Perner, D.
(Max-Planck-Inst. fuer Chemie Mainz, Germany)
Date Acquired
September 6, 2013
Publication Date
February 1, 1994
Publication Information
Publication: SRI International Corp., Local Measurement of Tropospheric HO(x)
Subject Category
Environment Pollution
Accession Number
94N28596
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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