Stratospheric Ozone Depletion - The Changing Arctic Environment: The Arctic Messenger - page 100

and decomposition of ozone”. It is now known that the chemistry of ozone depletion is
quite complex in the details, but it still conforms to the general explanation collectively
worked out by Molina, Rowland and Crutzen.
Further studies suggested that within about 60 years, the ozone layer would be de-
pleted by about 7% (soon shown to be a major underestimate). These developments pre-
cipitated a fierce reaction from segments of the chemical industry and associated lobby
groups, largely in the United States. One of the main arguments they posited was that vol-
canic eruptions were the main source of chlorine in the stratosphere. Rowland essentially
debunked this idea by pointing out that most volcanoes emit huge amounts of water va-
pour, along with other substances, such as chlorine. Consequently, most such substances
are washed out in the troposphere. He showed that when El Chichón erupted in 1982, hy-
drogen chloride increased in the stratosphere by only 10%. The much larger eruption of
Mount Piatubo in 1991 led to an even smaller increase. Meanwhile, chlorine levels had
continuedtosteadilyrisebetweenthetwoeruptions.Clearly,volcanoeswerenotthesource
of rising levels of stratospheric chlorine. Undeterred, the lobbyists fought on. Topics by
Dotto and Schiff and by Oreskes and Conway listed in the bibliography provide narratives
of how all this unfolded. Just for the record, in 1994, the WMO estimated that less than
18% of the stratospheric chlorine then being measured in the atmosphere came from nat-
ural sources. These are mainly forest fires and an unusual gas released by some marine
plankton.
Bytheway,thesulphate aerosols injected intothestratosphere bythese twovolcanoes
enhanced ozone destruction, an effect that increased depletion for several years. The
strength of this response depends on the concentrations of chlorine and bromine in the stra-
tosphere.Therefore, oncetheselevels godown,theperturbations causedbysuchvolcanoes
weaken.
Oreskes and Conway also record how the public quickly began to make up its own
mind about the use of CFCs and began to abandon products that used CFC propellants in
spray cans. By 1979, the first regulations controlling CFC use as a propellant gas in spray
cans came into effect in the United States. They were quickly followed by similar actions