Scientists recently discovered that polar stratospheric clouds,long known to play an important role in Antarctic ozonedestruction, are occurring with increasing frequency in the Arctic.These high altitude clouds that form only at very low temperatureshelp destroy ozone in two ways—they provide a surface whichconverts benign forms of chlorine into reactive, ozone-destroyingforms, and they remove nitrogen compounds that moderate the destructiveimpact of chlorine. In recent years the atmosphere above the Arctichas been colder than usual, and polar stratospheric clouds havelasted into the spring. As a result, ozone levels have been decreasing.
This photograph shows polar stratospheric clouds lit from below nearKiruna, Sweden.
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Photograph by Lamont Poole, NASA Langley Research Center
