176 Ecology and Applied Environmental Science
Extensive research has shown that there is a significant decrease of the
stratospheric ozone layer in many areas of the planet. The quantity of
ozone, for example in the middle latitudes of the northern hemisphere,
showed a decrease of about 8% between 1980 and 1990.
Since the 1970s, the presence of chlorofluorocarbons (CFCs) in the
stratosphere has been considered a principal factor of ozone depletion.
Chlorofluorocarbons are not toxic; they are widely used as propellant gases
(sprays), as refrigerants (in refrigerators and air conditioners) and as solvents. They are stable compounds in low altitudes but they break down in
the stratosphere, releasing Cl atoms that form oxides and other compounds.
The chlorine they contain acts as a catalyst and hinders (through Cl oxides)
the conversion of oxygen to ozone affecting the reaction towards the left:
3
2
2
3
O
O
It is estimated that a Cl atom that comes from a CFC molecule can
break up 100,000 O 3 molecules through successive reactions. Research
has shown that chlorine concentration in the atmosphere increased from
2.5 ppbv (parts in a billion by volume) in 1980 to 3.5 ppbv in 1990. Today,
specialists suspect that various particulates found in the stratosphere play
a non-negligible role in the phenomenon. Such examples are the ice particles of the polar stratospheric clouds and the particles of H 2 SO 4 solution
observed in the stratosphere. The latter come from industrial emissions,
biological processes and volcanic eruptions. These particles do not destroy
ozone directly but they reinforce the action of chloride compounds produced
by the breakup of CFCs.
Recent scientific papers, without questioning the primary role of chlorine,
suggest additional mechanisms of ozone destruction through, for example,
bromine compounds or organic compounds. Also, the role of nitrogen
oxides in the stratosphere has not been fully clarified. The intricate chemistry of the stratosphere is not yet sufficiently known and there are probably
other important mechanisms that have not been identified. The atmosphere
exhibits a high vulnerability to changes of its composition, partially because
it is not able to assimilate pollution through ecological processes. Nevertheless, the CFCs, in addition to their role in ozone destruction, they are
considered significant greenhouse gases (Section 9.4).
The most drastic CFCs are CFC-11, CFC-12 and CFC-113. The damage
caused by the emissions of CFCs dictate their substitution by other chemical compounds that do not destroy ozone. The dramatic character of the
ozone hole and the fear that the depletion of the stratospheric ozone layer
could be faster than what was predicted by the mathematical models drove
the international community to respond immediately to the scientists’
concerns. The international agreements signed for the protection of stratospheric ozone (Vienna Convention in 1985, Montreal Protocol in 1987 and
Extensive research has shown that there is a significant decrease of the
stratospheric ozone layer in many areas of the planet. The quantity of
ozone, for example in the middle latitudes of the northern hemisphere,
showed a decrease of about 8% between 1980 and 1990.
Since the 1970s, the presence of chlorofluorocarbons (CFCs) in the
stratosphere has been considered a principal factor of ozone depletion.
Chlorofluorocarbons are not toxic; they are widely used as propellant gases
(sprays), as refrigerants (in refrigerators and air conditioners) and as solvents. They are stable compounds in low altitudes but they break down in
the stratosphere, releasing Cl atoms that form oxides and other compounds.
The chlorine they contain acts as a catalyst and hinders (through Cl oxides)
the conversion of oxygen to ozone affecting the reaction towards the left:
3
2
2
3
O
O
It is estimated that a Cl atom that comes from a CFC molecule can
break up 100,000 O 3 molecules through successive reactions. Research
has shown that chlorine concentration in the atmosphere increased from
2.5 ppbv (parts in a billion by volume) in 1980 to 3.5 ppbv in 1990. Today,
specialists suspect that various particulates found in the stratosphere play
a non-negligible role in the phenomenon. Such examples are the ice particles of the polar stratospheric clouds and the particles of H 2 SO 4 solution
observed in the stratosphere. The latter come from industrial emissions,
biological processes and volcanic eruptions. These particles do not destroy
ozone directly but they reinforce the action of chloride compounds produced
by the breakup of CFCs.
Recent scientific papers, without questioning the primary role of chlorine,
suggest additional mechanisms of ozone destruction through, for example,
bromine compounds or organic compounds. Also, the role of nitrogen
oxides in the stratosphere has not been fully clarified. The intricate chemistry of the stratosphere is not yet sufficiently known and there are probably
other important mechanisms that have not been identified. The atmosphere
exhibits a high vulnerability to changes of its composition, partially because
it is not able to assimilate pollution through ecological processes. Nevertheless, the CFCs, in addition to their role in ozone destruction, they are
considered significant greenhouse gases (Section 9.4).
The most drastic CFCs are CFC-11, CFC-12 and CFC-113. The damage
caused by the emissions of CFCs dictate their substitution by other chemical compounds that do not destroy ozone. The dramatic character of the
ozone hole and the fear that the depletion of the stratospheric ozone layer
could be faster than what was predicted by the mathematical models drove
the international community to respond immediately to the scientists’
concerns. The international agreements signed for the protection of stratospheric ozone (Vienna Convention in 1985, Montreal Protocol in 1987 and