Chlorine emitted during volcanic eruptions is not responsible for damage to
the ozone layer, say two researchers in the US. This finding reinforces the
idea that it is human activities that are mainly responsible for depleting
ozone in the stratosphere.
Chlorine compounds in the stratosphere are known to be responsible for
destruction of ozone, both in the notorious ‘hole’ over the continent of
Antarctica and, to a lesser extent, elsewhere in the world. The consensus
is that these compounds come from the breakdown of manufactured, or
anthropogenic, chlorine-containing chemicals known as chloroflourocarbons or
CFCs. But a minority view holds that some of the depletion may be ‘natural’,
and due to volcanic chlorine.
This suggestion does not stand up in the light of a new study by A.
Tabazadah and Richard Turco of the University of California in Los Angeles.
They have shown that although large amounts of hydrogen chloride are
released during some volcanic eruptions, the compound is efficiently washed
out in the rain that always accompanies such eruptions. The rain is
‘seeded’ by the volcanic particles (Science, vol 260, p 1082).
However, volcanic eruptions such as that of Mount Pinatubo in the
Philippines do encourage the destruction of stratospheric ozone, by
providing a profusion of aerosol particles. The reactions that destroy ozone
take place on the surface of these particles, which act as catalysts. Those
reactions would not, however, take place if there were no anthropogenic
chlorine in the stratosphere already.