What is the South Pole “ozone hole”?
Scientists believed that ozone levels were quite stable until the late 1970s. Since then, a general decline in ozone levels has been seen. This ozone loss is believed to be related, in part, to increases in chlorine and bromine in the stratosphere from human-produced chemicals. However, every year during September and October (the Southern Hemisphere spring), ozone loss is much greater over Antarctica, where an ozone hole forms. The hole forms because the stratosphere above Antarctica becomes very cold in winter and is cut off from the rest of the world by a natural circulation of wind called the Polar Vortex. This prevents mixing in the atmosphere and so any ozone depletion is concentrated here. In addition, the very cold temperatures in the air cause clouds in the stratosphere which speed up ozone depletion by chlorine and bromine. In summer (December and January), the ozone hole repairs itself when new ozone comes from lower latitudes, but forms again the following spring.
