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FIGURE 1.7 Average total column ozone measured in October at Halley Bay, Antarctica, from 1957 to 1994 (adapted from Jones and Shanklin, 1995).

After the first reports of this phenomenon, major field campaigns were launched, which clearly established a relationship between ozone destruction and chlorine chemistry. For example, Fig. 1.8 shows simultaneous aircraft measurements of ozone and the free radical CIO as the plane flew toward the South Pole. As it entered the polar vortex, a relatively well-contained air mass over Antarctica, 03 dropped dramati-

Latitude °S

FIGURE 1.8 Measured concentrations of the chlorine monoxide free radical (CIO) as well as 03 outside and inside the polar vortex on August 23, 1987 (adapted from Anderson, 1989).

Latitude °S

FIGURE 1.8 Measured concentrations of the chlorine monoxide free radical (CIO) as well as 03 outside and inside the polar vortex on August 23, 1987 (adapted from Anderson, 1989).

cally and CIO rose simultaneously. The key to the dramatic changes in 03 occurring in this region now appears to be "heterogeneous" chemistry occurring on and in polar stratospheric clouds (PSC's), combined with the formation of a relatively well-contained air mass over the continent during the polar winter. This unique combination of chemistry and meteorology is discussed in more detail in Chapter 12.

In short, although the history of anthropogenic perturbations to the stratosphere is much shorter, it is clear that these are also important. Indeed, such perturbations are expected to affect the chemistry of the troposphere as well; for example, increased UV radiation will alter photochemistry at the earth's surface.

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