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| Titel |
Determining the ClOOCl absorption spectrum: Removal of the molecular chlorine spectral impurity using broadband cavity enhanced absorption spectroscopy |
| VerfasserIn |
Isla Young, Craig Murray, Chris Blaum, Tony Cox, Rod Jones, Francis Pope |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250053731
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| Zusammenfassung |
| The UV absorption spectrum of chlorine peroxide (ClOOCl) must be known accurately for
atmospheric models to predict the rate of seasonal polar ozone depletion. Current
measurements of the absorption cross section vary significantly, particularly at wavelengths
greater than 300nm which are the most important photolytically. This is largely due to the
contamination of ClOOCl laboratory samples.
The main contaminant in ClOOCl samples is molecular chlorine (Cl2). Cl2 has a smooth
UV absorption feature, with a peak at 330nm, overlapping the ClOOCl spectrum. This means
it is difficult to quantify and remove the Cl2 absorption contribution to reveal the pure
ClOOCl spectrum.
This work characterises the visible Cl2 absorption spectrum using broadband cavity
enhanced absorption spectroscopy (BBCEAS) in the 510-570nm wavelength range.
Simultaneous measurements in the UV wavelength range (230-370nm) provide a means for
accurately calculating Cl2 concentration, and thus the absolute cross section. The result is the
first temperature dependent study of the vibrational structure within the Cl2 absorption cross
section from 520nm to 570nm.
The Cl2 vibrational structure can now be used to independently determine the
concentration of Cl2 in contaminated ClOOCl samples by use of differential optical
absorption spectroscopy (DOAS) processing methods. Accurate subtraction of the calculated
Cl2 contribution in simultaneously measured UV spectra thus reveals the pure ClOOCl
spectrum.
The temperature dependent visible absorption cross sections of Cl2 between 510 and
570nm will be presented together with examples of the deconvolved ClOOCl absorption
cross section from 230 to 370nm. |
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