Page 256 - Materials Chemistry, Second Edition

240 4 Life Cycle Impact Assessment

4.5.2.3 Stratospheric Ozone Depletion
The second global impact category concerns the human caused depletion of
the stratospheric ozone layer responsible for the shielding of short wavelength
solar radiation below 290–300 nm from the earth’s surface. 180) Ozone molecules
of low concentration in the stratosphere but within a large layer (about 20 km)
are in dynamic equilibrium of formation and decomposition (Chapman cycle;
Equations 4.13 and 4.14). High energy UV radiation plays an important part in this
dynamic process:
Formation of stratospheric ozone:
( c )
O + ℎ → 2O = ν < 240nm (4.13)
2
2O + 2O → 2O 3
2
−−−−−−−−−−−−−−−−−−−
3O → 2O 3 Sum
2
Photolysis of ozone:
( c )
O + ℎ → O + O 2 = ν < 320nm (4.14)
3
O + O → 2O 2
3
−−−−−−−−−−−−−−−−−−−−
2O → 3O 2 Sum
3
Besides these, there are numerous ozone-forming and -degrading reactions in the
stratosphere with trace components of the HO and NO ‘family’. 181)
x x
Already around the year 1970 and in connection with the development of
supersonic air planes there had been fears of increased ozone depletion by
nitrogen oxides emitted from aeroplanes into the lower stratosphere. An extension
of this work 182) to the newly developed chlorine cycle by Rowland and Molina in
1974 and 1975 resulted in postulating causality between refrigerants, persistent
spraying agents, and so on, (freons, CFC) and an additional ozone depletion based
on plausible data and assumptions:
Chlorine cycle of catalytic ozone depletion 183)

Cl + O → ClO + O 2 (4.15a)
3
ClO + O → Cl + O 2 (4.15b)
−−−−−−−−−−−−−−−−−−−
O + O → 2O 2
3
180) WMO (1999), Kl¨ opffer and Meilinger (2001b) and Dameris et al. (2007).
181) Finlayson-Pitts and Pitts (1986).
182) Molina and Rowland (1974) and Rowland and Molina (1975).
183) Deutscher Bundestag (1991) and M¨ oller (2010).