© 2012 W. H. Freeman & Co.
Jan 20, 2016
© 2012 W. H. Freeman & Co.
Skin cancer
© 2012 W. H. Freeman & Co.
Ozone production
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O2
O2O2
O3
O O
Ozone destruction
Ozone production
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O2
O2O2
O3
O O
Ozone destruction
14a–7
Ozone production
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O2
O2O2
O3
O O
Ozone destruction
Ozone production
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O2
O2O2
O3
O O
h
hOzone destruction
O2 + h O + O 498 kJ/mol
O3 + h O + O2 383 kJ/mol)
O2 + h O + O 498 kJ/mol <242.4 nm
O3 + h O + O2 383 kJ/mol <280 nm
Chapman Mechanism(~1930, Sidney Chapman)
O2 + h O + O 498 kJ/mol <242.4 nm slow
O + O2 + M O3 + M (-106 kJ/mol fast)
O3 + h O + O2 383 kJ/mol <280 nm (fast)
O + O3 2O2
291 kJ/mol slow
O + O + M O2 + M
Ozone production
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O2
O2O2
O3
O O
λ ≤ 240 nm
λ ≤ 280 nm
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hOzone destruction
© 2012 W. H. Freeman & Co.
• Intensity
Transmittance
Absorbance
Transmittance
Absorbance
Beer’s Law
dP(x)/dx = -κ P(x)
P(x) = exp(-κ x)
λ ≥ 280 nm
© 2012 W. H. Freeman & Co.
© 2012 W. H. Freeman & Co.
Mean vertical distribution of the ozone concentration according toobservations at different latitudes. Note the variations in total columnabundance.
1 Dobson unit (DU) is:0.01 mm of pure O3 at 1 atm. and 0 oC
NB: what does 300 DU expand to at 10-6 atm?
Ozone production
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O2
O2O2
O3
O O
λ ≤ 240 nm
λ ≤ 280 nm
h
hWRONG EQUILIBRIUM:
Predicts TOO MUCH OZONE
X = HOx (H, OH, HOO) NOx (NO, NO2) ClOx (Cl, ClO)
Catalytic destruction of ozone
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Chlorine reservoirs
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Chlorine reservoirs
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Atomic Cl and Br as X:
Cl can destroy tens of thousands of O3 molecules each, butis mainly in inactive forms (HCl, ClONO2) in stratosphere.
RESERVOIRS:
ClO + NO2 ClONO2
Cl + CH4 HCl + CH3
CH3 does not operate as an X catalyst, since it combineswith O2 to give CO2.
Recipe for ozone loss:
1. POLAR WINTER Polar vortex Isolates air
2. LOW TEMPERATURE PSC
(=Polar Stratospheric Clouds)(=Nitric acid – HNO3)
3. SURFACE CHEMISTRY Cl2
(+denoxification)4. LIGHT RETUNS
Cl* Catalytic destruction of O3
CHAPTER 02: Figure 2.1
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CHAPTER 02: Figure 2.2
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NASA projections of stratospheric ozone concentrations if chlorofluorocarbons had not been banned.
Mount manitoba, June 1991
CHAPTER 02: Figure 2.10
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Prefix Meaning Atoms in the Molecule
CFC chlorofluorocarbon Cl, F, C
HCFC hydrochlorofluorocarbon H, Cl, F, C
HBFC hydrobromofluorocarbon H, Br, F, C
HFC hydrofluorocarbon H, F, C
HC hydrocarbon H, C
PFC perfluorocarbon F, C
Halon N/ABr, Cl (in some but not all), F, H (in some but not all), C
© 2012 W. H. Freeman & Co.
© 2012 W. H. Freeman & Co.
© 2012 W. H. Freeman & Co.