La chimie de la stratosph

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La chimie de la stratosphère de la Terre

• Richard Wayne
• Department of Chemistry
• University of Oxford

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Too many papers on ozone(in 1865!)
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Chapman Layers
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SCIAMACHY Total Ozone 20042007 (DU)
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CTM Simulated Total Ozone 20042007
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Comparison
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Stratospheric NOx Production
(11.9)
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Stratospheric HOx Production
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Removal of NOx and HOx Reservoirs
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Removal of Clx Reservoirs
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Fractional losses in different cycles
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Chlorofluorocarbons Are Derived From Methane
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Chlorine Compounds
Mixing ratio Chemical
(pptv) Lifetime
(yr) Chlorofluorocarbons CFCl3 (CFC-11)
(1932) 270 45 CF2Cl2 (CFC-12) (1928)
550 100 CFCl2CF2Cl (CFC-113) (1934)
70 85 Hydrochlorofluorocarbons (HCFCs) CF2ClH
(HCFC-22) (1943) 130 11.8 Other chlorinated
compounds CCl4 (Carbon tetrachloride) 100 35 CH3
CCl3 (Methyl chloroform) 90 4.8 CH3Cl (Methyl
chloride) 610 1.3 HCl (Hydrochloric
acid) 10-1000 lt1
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Bromine and Fluorine Compounds
Mixing ratio
Chemical Chemical
(pptv) Lifetime (yr) Bromocarbons-Halons CF3
Br (H-1301) 2 65 CF2ClBr (H-1211) 2 11 Oth
er bromocarbons CH3Br (Methyl bromide) 12 0.7
Fluorine compounds CH2FCF3 (HFC-134a) 4 13.6 C
2F6 (Perfluoroethane) 4 10,000 SF6 (Sulfur
hexafluoride) 3.7 3200
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Reported Sales of CFC-11 and 12 in 1976 and 1998
CFC sales (1000 metric tonnes/year)
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Variations With Altitude of CFCs and Other
Chlorinated Compounds
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Chlorine Emission to Stratosphere
Chemical Percent emission to
stratosphere Anthropogenic sources CFC-12
(CF2Cl2) 28 CFC-11 (CFCl3) 23 Carbon
tetrachloride (CCl4) 12 Methyl
chloroform(CH3CCl3) 10 CFC-113
(CFCl2CF2Cl) 6 HCFC-22 (CF2ClH) 3 Natural
sources Methyl chloride (CH3Cl) 15 Hydrochloric
acid (HCl) 3 Total 100
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Chlorofluorocarbons use and trends
CFC11 CFCl3

• Chemical properties of CFCs
• tightly bound, nonreactive molecules
• not soluble in water
• dont absorb visible or near-ultraviolet
  radiation
• Non-toxic, easily compressible
• ? long atmospheric residence times (50-300 years)

Montreal Protocol
Spray-can ban
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Decline in mean October ozone levels over Halley
Bay
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Total O3 from GOME/SCIAMACHY October, SH,
19952006
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Total O3 from GOME/SCIAMACHY October, NH,
19962007
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Mixing ratios of O3 and ClO in late August and
early September 1987
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Concentration changes on entering perturbed region
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PSCs
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PSC formation and composition
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Heterogeneous Reactions
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Dimer Mechanism
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Conversion of Chlorine Reservoirs to Active
Chlorine
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Conversions in ClOx chemistry in presence of PSCs
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Satellite observations of ClO, O3, HNO3 and ClONO2
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Measurements of ClO, HCl and ClONO2 made in
20052006
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Timeline of ozone depletion
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Photochemistry and dynamics in the polar
stratosphere