Question

Describe the conditions which are favorable for ozone destruction in polar regions. Include what occurs in polar spring which causes the rather abrupt commencing of ozone destruction.

What happens in polar summer that reverses some of the effects of ozone destruction that occur in polar spring?

Answer 1

Man-made emissions of CFCs occur mainly in the northern hemisphere, with about 90% released in Europe, Russia, Japan, and North America. Gases such as CFCs that are insoluble in water and relatively unreactive are mixed throughout the lower atmosphere and rise from the lower atmosphere into the stratosphere; winds then move this air poleward.

Normally, chlorine and bromine is inactive, locked up in stable compounds, and does not destroy the ozone. However, during the Antarctic winter months (June to August) when the region receives no sunlight, the stratosphere becomes cold enough (-80°C) for high level [ice] clouds to form, called Polar Stratospheric Clouds (PSCs). These PSCs provide an ideal catalytic surface on which the chlorine can react with the ozone, thus destroying the ozone layer. This reaction requires sunlight, and therefore only begins when the Sun returns to Antarctica in spring (September to October), before the PSCs have had a chance to melt. The ozone hole disappears again when the Antarctic air warms up enough during late spring and summer.