Ask The Scientist
Frequently Asked Questions
What is ozone, and why is it important?
Ozone is simply a molecule consisting of 3 oxygen atoms, which reacts strongly with other molecules. Ozone is created in the stratosphere when high energy uv radiation causes on O2 molecule to split. The free oxygen atoms collide and react with other O2 molecules to form O3.
Production is highest where the solar uv is the greatest eg near the tropics, but once created, the ozone is then circulated towards the poles by the atmosphere. The amount of ozone in the stratosphere can vary with location, season and even day to day climatic conditions.
The process of ozone creation is what makes the O3 in the atmosphere very effective at shielding the Earth from harmful uv radiation, which can cause many biological problems, such as skin cancer. However, due to its high reactivity, the uv found in the tropospher at ground level can aslo be dangerous as a toxic pollutant which is harmful to plants and lung tissue, and is a major cause of smog.
When was the ozone hole
Why does the ozone hole form over Antarctica ?
The answer is essentially 'because of the weather in the ozone layer'. In order for rapid ozone destruction to happen, clouds (known as PSCs, Stratospheric Clouds Mother of Pearl or Nacreous Clouds) have to form in the ozone layer. In these clouds surface chemistry takes place. This converts chlorine or bromine (from CFCs and other ozone depleting chemicals) into an active form, so that when there is sunlight, ozone is rapidly destroyed. Without the clouds, there is little or no ozone destruction. Only during the Antarctic winter does the atmosphere get cold enough for these clouds to form widely through the centre of the ozone layer. Elsewhere the atmosphere is just too warm and no clouds form. The northern and southern hemispheres have different 'weather' in the ozone layer, and the net result is that the temperature of the Arctic ozone layer during winter is normally some ten degrees warmer than that of the Antarctic. This means that such clouds are rare, but sometimes the 'weather' is colder than normal and they do form. Under these circumstances significant ozone depletion can take place over the Arctic, but it is usually for a much shorter period of time and covers a smaller area than in the Antarctic.
How long has the Antarctic
ozone layer been studied?
Does the ozone hole affect the
rest of the world?
Limited ozone depletion can occur
above the Arctic, but at present it is confined to parts of the region and only
lasts for a few days at a time. If CFC releases had continued at the high rates
of the mid 1980s, a continental sized ozone hole might have appeared over the
Arctic. Elsewhere in the northern hemisphere, stratospheric ozone amounts over
temperate latitudes have fallen by 5 to 10% during the winter.
How does the ozone hole damage
Does the Greenhouse effect
cause the ozone hole?
A further link is that although the Greenhouse Effect warms the surface, it allows the higher atmosphere, where ozone is present, to cool. This means that more stratospheric clouds may form and so make the ozone hole worse.
Even if the problem of ozone
depletion is solved, global warming will still remain. It will cause a rise in
sea-level and change the regions where crops can be grown. The issue will be
harder to tackle than ozone depletion, but is one which concerns everyone on our
What is the Montreal Protocol?
Independent reviews by panels of
scientist (eg the UK Stratospheric Ozone Review Group reports) present
conclusive evidence that CFCs are still increasing in the atmosphere and that
chlorine from them is also increasing and is responsible for ozone depletion.
Thanks to the provisions of the Montreal Protocol and its subsequent amendments
the level of ozone depleting gases in the atmosphere will start dropping by the
end of the 1990s.
Where were CFCs used?
Some reports in the media suggest that the ozone layer over Antarctica is now recovering. This message is a little confused. Recent measurements at surface monitoring stations show that the loading of ozone destroying chemicals at the surface has been dropping since about 1994 and is now about 6% down on that peak. The stratosphere lags behind the surface by several years and the loading of ozone depleting chemicals in the ozone layer is at or near the peak. Satellite measurements show that the rate of decline in ozone amount in the upper stratosphere is slowing, however the total ozone amount is still declining. The small size of the 2002 ozone hole was nothing to do with any reduction in ozone depleting chemicals and it will be a decade or more before we can unambiguously say that the ozone hole is recovering. This assumes that the decline in ozone depleting chemicals continues and that there are no other perturbations to the ozone layer, such as might be caused by a massive volcanic eruption or Tunguska like event. It will be the middle of this century or beyond before the ozone hole ceases to appear over Antarctica. What we saw in 2002 is just one extreme in the natural range of variation in the polar stratosphere and is the equivalent of an extreme in 'stratospheric weather'. By contrast the 'weather' in 2003 moved to the opposite extreme and we saw one of the largest ozone holes on record.
How can we mend the ozone