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| Titel |
ACE-FTS and MIPAS observations of phosgene (COCl2) and comparisons with SLIMCAT chemical transport model calculations |
| VerfasserIn |
Jeremy Harrison, Martyn Chipperfield, David Moore, Christopher Boone, Peter Bernath, Ryan Hossaini |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250149479
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| Publikation (Nr.) |
 EGU/EGU2017-13833.pdf |
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| Zusammenfassung |
| The majority of chlorine in the atmosphere has arisen from anthropogenic emissions of
‘organic’ species such as chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons
(HCFCs). Due to their long lifetimes, many of these species reach the stratosphere where they
break down, liberating chlorine which catalyses the destruction of ozone. The principal
degradation products of Cl-containing organic species are carbonyl chloride (phosgene,
COCl2), carbonyl chloride fluoride (COClF), and hydrogen chloride (HCl). Of these,
phosgene is probably the most notorious, having been used as a chemical weapon in
World War I. In the lower stratosphere, where the phosgene mixing ratios peak,
the principal sources are the photolysis of carbon tetrachloride (CCl4) and, to a
lesser extent, methyl chloroform (CH3CCl3). Smaller contributions arise from very
short-lived substances such as CH2Cl2, CHCl3 and C2Cl4. Due to the success of the
Montreal Protocol in phasing out the use of CCl4 and CH3CCl3, the abundance of
phosgene continues to fall. Observing and understanding phosgene in the stratosphere
helps us better understand the chlorine budget, and particularly the atmospheric
removal of CCl4, which has attracted particular interest recently on account of the
inconsistency between observations of its abundance and estimated sources and
sinks.
This work presents global distributions and trends of COCl2 using data from two satellite
limb instruments: the Atmospheric Chemistry Experiment Fourier transform spectrometer
(ACE-FTS), and the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS).
The ACE-FTS instrument, on board the SCISAT satellite, has been recording solar
occultation spectra through the Earth’s atmosphere since 2004 and continues to take
measurements with only minor loss in performance. ACE-FTS time series are available for a
range of chlorine ‘source’ gases, including CCl3F (CFC-11), CCl2F2 (CFC-12), CHF2Cl
(HCFC-22) and CCl4, and the chlorine ‘product’ gases COCl2, COClF and HCl. The MIPAS
instrument, onboard ENVISAT (ENVIronmental SATellite), recorded atmospheric limb
emissions spectra between 2002 and 2012, with time series available for the key
Cl-containing species except HCl. ACE-FTS and MIPAS phosgene observations are
compared with the output of SLIMCAT, a state-of-the-art offline three-dimensional chemical
transport model (CTM), which contains a detailed treatment of stratospheric chemistry,
including the major species in the Ox, NOy, HOx, Fy, Cly, and Bry chemical families. |
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