“Why is there a hole in the ozone layer, and is it shrinking?”
My first actual submitted question, via social media!
First, it might be helpful to explain what the ozone layer is. Normally, oxygen atoms pair up: that’s why the oxygen in the air we breathe is often called O2. But oxygen atoms can also be happy in a crowd, joining in threes: O3, or ozone. Ozone tends to form when ultraviolet light from the sun splits O2, leaving two oxygen atoms which badly want to react. If they meet an intact molecule of O2, they join it to form ozone. The ozone layer is a part of the Earth’s atmosphere, about 6.2 miles (10 km) from the surface, where this is constantly happening, leaving plenty of ozone spread throughout the atmosphere at that altitude.
You probably already know that scientists are concerned about the ozone layer and think it’s very important. That’s because it has a protective effect. The ozone layer absorbs ultraviolet light from the sun, preventing it reaching the Earth’s surface. That’s important because it’s the ultraviolet part of the sun’s light which causes sunburns. While a sunburn doesn’t seem that serious, and on its own it probably isn’t, it’s actually a sign that ultraviolet radiation has damaged your skin. It’s not just like a physical burn, but can actually cause damage at the level of your DNA, changing the sequence. That can be harmless, but sometimes it leads to cancer. That’s why we need to avoid ultraviolet light as much as possible, and why the ozone layer is part of our protection.
The hole in the ozone layer was observed in 1985. It actually forms seasonally over the Antarctic, due to the climate conditions there. Particular types of clouds form over the Antarctic, and the conditions inside them convert gases called CFCs (chlorofluorocarbons) into reactive versions. Once they’re reactive, they quickly react with ozone and deplete it.
There are natural ways that CFCs enter the atmosphere — for example, from volcanic eruptions. However, human activity has also been a contributor. We used CFCs in aerosols and cooling systems, and those CFCs have escaped into the environment. This is why aerosols have had to become CFC free, helped by consumer pressure.
The hole in the ozone layer may be shrinking, but there isn’t enough data yet to be sure. The hole in the ozone layer observed in 2002 was small, but in 2003 there was one of the largest ozone holes on record. We need to keep monitoring it to be sure what’s going to happen in the future. The amount of CFCs in the atmosphere is definitely dropping, though, which may help the ozone layer recover in the long term.