| Most volcanoes do not penetrate the stratosphere. In fact, only
a small number of eruptions have produced a significant amount of aerosols in
this century. (Note that volcanic aerosols are totally unrelated to
consumer aerosol products, like hair spray, that have not used
ozone-depleting substances since the 1970s.) One example is Mt.
Pinatubo, which injected 30 million tons of aerosols into the
stratosphere during its 1991 eruption in the Philippines. That
amount is represented by the peak in the graph below. The topmost
graph shows measurements from Barrow, Alaska; the lower graph
represents measurements taken at Mauna Loa, Hawaii .
These tiny particles can provide a surface where the ozone
destruction reactions take place very rapidly. Aerosols only have an
effect because of the currently high levels of stratospheric
chlorine released from ODS. They improve
a chlorine atom's effectiveness at destroying ozone molecules,
producing a short-lived spurt in ozone depletion.
![[Graph showing stratospheric aerosols falling rapidly after 1992]](U_S_ EPA Ozone Depletion_files/aerosol2.gif)
Source: NOAA
CMDL 
However, as the graph also shows, these particles were fairly
quickly removed from the stratosphere. A standard way to quantify
the longevity of a substance in the atmosphere is its "lifetime" --
the time that it takes for an initial amount to be cut by about
two-thirds. More precisely, for an initial amount of 1000 tons
injected into the stratosphere, about 368 tons would be left after
one lifetime. Each subequent lifetime would reduce the remaining
amount by about 63%. As the graph shows, the amount of aerosols in
the stratosphere dropped at about the same rate as would a substance
with a lifetime of about 11 months. Three years after the eruption,
nearly all of the Mt. Pinatubo aerosols were gone.
One disturbing point to note from the above graph is that it
appears to take much longer for aerosols to be removed from polar
regions than from tropical regions. The polar regions, particularly
Antarctica, are particularly susceptible to major drops in
stratospheric ozone.
In comparison, CFC-12 has a lifetime of 100 years and CFC-11 has
a lifetime of 45 years (as reported in the Scientific Assessment
of Ozone Depletion: 2002). Hence, the impact of aerosols is
much shorter in duration than that of the CFCs. The fact that CFCs
have long lifetimes is one reason why it will take so long for the
ozone layer to recover after the production
phaseout.
 Volcanoes &
Ozone Depletion
Myths About Ozone Depletion CFCs are
Heavier Than Air, So They Can't Reach the Ozone Layer
Ozone
Depletion Occurs Only In Antarctica
No Link Exists
Between Ozone Depletion and Higher UV Levels
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