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Skin cancer

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Ozone production

hn

hn

O2

O2O2

O3

O O

Ozone destruction

Ozone production

hn

hn

O2

O2O2

O3

O O

Ozone destruction

14a–7

Ozone production

hn

hn

O2

O2O2

O3

O O

Ozone destruction

Ozone production

hn

hn

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

hn

hn

O2

O2O2

O3

O O

λ ≤ 240 nm

λ ≤ 280 nm

h

hOzone destruction

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• 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

hn

hn

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

© 2012 W. H. Freeman & Co.

Chlorine reservoirs

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Chlorine reservoirs

© 2012 W. H. Freeman & Co.

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.