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Clouds and the ozone hole
What's the connection with the ozone hole? Now, back to the clouds. Even in the stratosphere, most chlorine-containing molecules are thought to be stable and so will not destroy ozone. During the winter, very cold polar air sinks because it is dense. This forms a bowl of cold, dense air above the pole. A polar jet, forms around the bowl, with strong westerly winds extending throughout the atmosphere (westerly winds blow from west to east). Thus, a core of cold and chemically isolated air develops. Important chemical reactions occur on the surfaces of the polar stratospheric cloud particles. For example, the inactive chlorine molecules are converted into more active forms, such as chlorine gas (Cl2). When the sun returns in September, the ultraviolet radiation breaks up chlorine gas into chlorine radicals, which rapidly destroy ozone and are regenerated by the equations on the previous page. Gradually, as temperatures rise, the westerly jet weakens and finally breaks down in November. Once the polar air can mix with air from lower latitudes, the chlorine is diluted and the ozone layer re-stabilizes. NASA provides an Ozone Hole Watch website where you can see the current levels of ozone above Antarctica.
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What's the connection with the ozone hole? Now, back to the clouds. Even in the stratosphere, most chlorine-containing molecules are thought to be stable and so will not destroy ozone. During the winter, very cold polar air sinks because it is dense. This forms a bowl of cold, dense air above the pole. A polar jet, forms around the bowl, with strong westerly winds extending throughout the atmosphere (westerly winds blow from west to east). Thus, a core of cold and chemically isolated air develops. Important chemical reactions occur on the surfaces of the polar stratospheric cloud particles. For example, the inactive chlorine molecules are converted into more active forms, such as chlorine gas (Cl2). When the sun returns in September, the ultraviolet radiation breaks up chlorine gas into chlorine radicals, which rapidly destroy ozone and are regenerated by the equations on the previous page. Gradually, as temperatures rise, the westerly jet weakens and finally breaks down in November. Once the polar air can mix with air from lower latitudes, the chlorine is diluted and the ozone layer re-stabilizes. NASA provides an Ozone Hole Watch website where you can see the current levels of ozone above Antarctica.
