Daniel Thorburn, of Tikipunga Primary School, asks :-

How come the ozone hole occurs over the Antarctic and New Zealand, two of the least polluted places on Earth?

Andrew Matthews, an atmospheric physicist at the National Institute of Water and Air at Lauder in Central Otago, responded.

You are quite correct that ozone depletion and the creation of the ozone hole each year in the spring time are caused from pollution. In particular the special pollution of releasing gases that contain chlorine and bromine are the culprits for removing ozone. However, ozone destruction occurs high in the atmosphere some 25-30 km above the earth.

Consequently even those particular gases that are released into the atmosphere in the northern hemisphere, where most of the atmospheric pollution is, mix into the southern hemisphere and react with "our" ozone. This mixing time in the lower atmosphere is about one year and to reach the stratosphere, where the ozone is, often takes these gases 40 or 50 years. So ozone above Antarctica (where the ozone hole appears and not over New Zealand by the way - we sometimes see remnants of the ozone hole that have peeled off over Antarctic) and over New Zealand are effected by gases released by the populations of other countries.

It shows that this is an international problem and one that New Zealand cannot solve by itself. It needs the cooperation of all nations of the world - particularly those that generate the pollution.