In Chapters 1-5 we discussed the processes that produce, destroy, and transport Or Together, these processes determine the distribution of O, in the stratosphere. In this chapter we study the effect of a perturbation to the stratosphere—in this case, a large increase in SO, abundance following a major volcanic eruption.
The focal point of this discussion is the eruption of Mount Pinatubo in the Phillipines (15°N, 12()°E) on June 15, 1991. This eruption injected ~20xl0,J g (20 Mt) of S02 into the tropical stratosphere (22,23). Figure 1.9 shows that in the years after the eruption, global average column O, declined significantly (see also [24—26]). There is now a general consensus that this decrease in O, was causally linked to the injection of SO, into the stratosphere by Mount Pinatubo. In this chapter, we will discuss the theories about how this injection of S02 led to the reduction of stratospheric Or This exercise will demonstrate the subtlety and complexity that makes ozone such an interesting constituent.
It should be noted that volcanic perturbations to the stratosphere are not rare events but occur on average every few years . Between 1984 and 1996, for example, there were at least three eruptions besides Mount Pinatubo that perturbed the stratosphere [194|. And just prior to that time frame, in March and April 1982, there was a major eruption of El Chichon (17.3°N), which is also believed to have reduced stratospheric O, .
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