Page 257 - Materials Chemistry, Second Edition

4.5 Impact Categories, Impact Indicators and Characterisation Factors 241

The chlorine atom in Equation 4.15a necessary for the initiation of the cycle, derives
from photolysis of long-lived (persistent) chlorine compounds of anthropogenic
origin which due to their persistence are capable of entering the stratosphere intact,
particularly as a result of an extremely slow reaction with OH-radicals. 184) This is
a very slow process – otherwise even more easily degradable compounds could
enter into the stratosphere – and there is a temporal delay of several years between
releases and the start of effectiveness.
The reaction to the work of Rowland and Molina was a direct and immense one.
The few measurements of 185) on the concentration of freons in the atmosphere,
which the authors had referred to, were confirmed and updated again and again.
A trend of increasing concentrations of the freons or CFC was observed, above all
for the most important 186) ones: trichlorofluoromethane (CFC 11, R11), dichlorod-
ifluoromethane (CFC-12, R12) and 1,1,2-trichloro-1,2,2-trifluoroethane (CFC-113,
R113). Besides, some chlorinated solvents, not considered as freons, were recog-
nised as potential ozone-destroying substances and pursued by an analytical series
of measurements for many years.
4.5.2.3.1 Causing Substances Freons were and still are partly used (in medicine)
for the following:

• Propellant for sprays,
• Propellant for foam materials (e.g. polyurethanes),
• Refrigerant for refrigerators and smaller air conditioning systems (especially for
cars),
• Cleaning agent (e.g. in the electronic industry),
• Smaller applications in medicine (asthma spray), analytic and spectroscopy
(extraction agent, solvent for IR spectroscopy), and so on.
Already within a few years following the forecast of the effect, the use of CFC
propellants was banned in the USA and several alternatives were quickly developed.
A setback within the model calculations (simulating the ozone depletion) at the
beginning of the 1980s indicated smaller ozone degradation rates as in earlier
forecasts whereby the urgency of the measures seemed to have diminished.
4.5.2.3.2 The ‘Ozone Hole’ and Legal Measures After the wrong ‘all-clear’ signal,
a totally unexpected discovery indicated the formation of an antarctic ‘ozone hole’
during the spring of the Southern hemisphere. 187) The formation of the ozone hole
is related, but not identical, to the impact prognosticated by Rowland and Molina,
of chlorine compounds. 188) It turns out that heterogeneous catalytic reactions on

184) Atkinson (1989) and Kl¨ opffer and Wagner (2007a).
185) Lovelock, Maggs and Wade (1973) and Lovelock (1975).
186) Deutscher Bundestag (1991, 1992), Krol, van Leeuwen and Lelieveld (1998) and Bousquet et al.
(2005).
187) Farman, Gardiner and Shanklin (1985).
188) McIntyre (1989).