Environmental Geochemistry, GLY 4241/5243, © David Warburton, 2011
7 - OZONE LAYER: NATURAL
DEPLETION AND CURRENT STATUS
Note: Slide numbers refer to the PowerPoint presentation which accompanies
Natural ozone depletion, slide 1 here
Natural processes contribute to ozone depletion in the stratosphere.
Volcanic eruptions can emit large quantities of sulfur gases, principally SO
Stratovolcanoes are particularly violent and may eject material
through the troposphere into the stratosphere.
Natural ozone depletion, slide 2 here 1997 Montserrat Eruption
In 1982 the volcano El Chichón, in Mexico (17.3°N, 92.3°W), erupted 7 to 20
megatons of SO
(Brasseur and Granier, 1992) into the stratosphere.
temperature of the lower stratosphere warmed (Labitzke
1983; Parker and
Branscombe, 1983; and Pollack and Ackerman, 1983), a reduction in
stratospheric ozone took place (Hofmann and Solomon, 1989), and a slight
depression of surface temperatures probably occurred (Hansen
The surface temperature depression was complicated by a contemporaneous El
Niño event, which made resolution of the volcanic cloud effect from natural
variability difficult to resolve.
The magnitude of the ozone loss in the mid-
latitudes was as great as 15%, compared with an ongoing decline of 5% per
decade in recent times (Kerr, 1990).
Although this decline was temporary, it
points out the potential effects that volcanoes can have on stratospheric ozone
More recently Mount Pinatubo, in the Philippines (15.1°N, 120.4°E),
injected between 10 and 30 million tons of SO
into the stratosphere in June
1991(Brasseur and Granier, 1992; Kerr, 1990).
Since the latitude of the two
volcanoes is similar, the atmospheric distribution should be similar.
Natural ozone depletion, slide 3 here