Why is the gap in the ozon layer the worst above Antartica, given that the highest emission of CFK's happens in the Northern Hemisphere?

Asked by: Micha Duchateau

Answer

Well now this is a really great question. I often wondered about this same fact. Before I explain this I would like to first explain tides to you. If I asked you what makes the tides, I might expect you to tell me the moon, but could you explain why there are 2 high tides and 2 low tides a day even though the moon only circles once a day?

If we look at the situation where we have a lunar eclipse, there is a high tide on the side of the earth that the sun and moon are, and there is another high tide on the opposite side of the earth than the sun and the moon. The gravitational pull of the sun and moon cause the high tide on the side of the earth that they are on but what causes that other high tide? The second high tide is caused by the centrifugal force cause by the earth orbiting the sun. These 2 high tides stay right where they are, and as the earth spins, we see the tides 'go around the earth'. The fact that extra water is pulled to these 2 places makes low tides everywhere else (including the north and south pole).

So why did I tell you about the tides? You see the atmosphere does the same thing that the water does. This means at the north and south pole, the atmosphere is thinner than anywhere else on earth, because the air is pulled away from there. Ozone is in the same percentage all around the earth (because gasses diffuse % evenly) so it is natural that there is less at the poles. This is why the 'gap' in the ozone is thinner at Antarctica than in the populated region of the northern hemisphere.
Answered by: Paul Flaherty Jr, B.S., Mechanical Engineer, Bosch, Charleston SC.

Ozone is an unstable molecular form of oxygen. Each molecule of ozone consists of three, rather than two, atoms of oxygen.

Ozone can be created in any number of ways, but the relatively abundant ozone found in the upper atmosphere is formed when normal oxygen there is bombarded by ultra-violet radiation from the Sun which breaks the molecules apart, and, some people suspect, aid in their combining into the three-atom ozone molecule. Because there is much more ultra-violet radiation high in our atmosphere than there is down near the Earth's surface, there is much more ozone up there than there is down here. In essence the ozone molecules are the 'wounded veterans' of a never-ending war between UV rays and oxygen. This stratospheric 'warfare' between ultra-violet rays and oxygen deflects and renders harmless much of the ultra-violet radiation coming in at us from the Sun. That is why we worry about the so-called 'ozone layer.' It isn't an actual layer of gas, but the constant interaction of UV rays and oxygen way up there protects us from excess UV rays down here.

During the southern hemisphere's winter months the Sun does not shine in Antarctica for many weeks at a time. During that time the Sun does not deliver ultra-violet radiation to the upper atmosphere over the South Pole. So ozone production there ceases during this period of time. Also during the South Polar winter a characteristic whirlpool of winds forms there which prevents the air down there from doing much mixing with the rest of the Earth's atmosphere. The same type of vortex sometimes forms at the North Pole during its winter months, but it is much weaker. Most people knowledgeable on the subject think the difference is due to the fact that Antarctica is a continent with elevated features while the North Polar region is largely flat, frozen ocean. For whatever reasons, the northern vortex is much less isolational than the southern vortex. There is much more exchange movement of air across the North Pole in winter than there is over the South Pole.

So in the southern winter months ozone production over the Antarctic region dwindles and the ozone over the region becomes depleted. This so-called 'ozone hole' -- which is actually nothing more than an area of the atmosphere lower in ozone than the rest of the atmosphere -- then drifts away from the south polar region as the southern winter vortex breaks up and air exchange resumes for the spring, summer and fall.
Answered by: Daniel Rogers, Retired instructor in Environmental Regulation