Now that you have understood the scientific background, you can understand that this ozone hole is not actually a hole. It is a metaphorical way of saying that the ozone layer has thinned a lot. Over that area. The phenomenon which we call the ‘ozone hole’, is that part of the ozone layer whose thickness has decreased by one-third. In 1977, its readings measured 250 DU. In reading from 1984, it was measured to be 160 DU.
It was obvious that immediate action was needed. But the scientists were still stumped by a question. Why is the ozone hole forming only over Antarctica? Many reasons were speculated. First, the air that rises converges towards the North and South Poles. So, the depletion of the ozone layer was not only seen over Antarctica but was also seen over the Arctic. But in Antarctica, it was more prominent.
The reason behind this was said to be the polar stratospheric clouds. These are a type of clouds that are seen over Antarctica. The droplets of these clouds contain a mixture of nitric and sulfuric acids. And chemicals like chlorine and bromine react on the surface of these droplets to break down the ozone. These clouds form only at a temperature of -78° Celsius. Because of this, this reaction progresses. But such cold conditions are not so common in the Arctic. They are mostly found over Antarctica. That’s why this ozone layer thinning was most visible here.
