Is there still a hole in the ozone layer?

Atmospheric physicist Ella Gilbert is here to explain...

Ella - It is still there, but it is shrinking. It's one of the few good stories in environmental science and I think in September 2019, it was the lowest, well the smallest on record since the ozone hole was discovered. So that's good.

Chris - What caused it?

Ella - So it's a process that involves light and involves the emission of chlorine and bromine that breaks down or degrades ozone, which is the thing that protects us from horrible UV rays coming from the Sun and stops us all getting very sunburnt. But this chlorine and bromine comes from the emission of ozone depleting substances. Things like CFCs are the most commonly spoken about. They used to be included in refrigerants and coolants. So you'd spray them in your aerosol cans, and you'd find them in fridges.

Chris - Asthma inhalers had them, didn't they?

Ella - Yeah, all over the place. They were totally ubiquitous. And it was actually one scientist at the British Antarctic survey, along with a few others who discovered this ozone hole in the first place, which is quite a funny story actually.

Chris - Jonathan Shanklin I think was one of them. wasn't he, who found it?

Ella - Yes, exactly. Yes. I really like the story because they had a huge amount of data on ozone and the Americans, I think it was who had all of this information coming from their satellites were using an algorithm to detect whether this data was useful, and it was throwing out all of this information because it considered, "Oh no, that's far too low. Those values can't be true. So we'll just get rid of that data."

Chris - Oh, So they discovered the ozone hole, but they chucked it away because they didn't think it could be there.

Ella - Yeah.

Chris - So how did they realise their mistake?

Ella - I think, well I don't actually know the details, but I'm fairly certain that the people who discovered it actually went through the data and went hang on, this could actually be real, and there could be a physical mechanism behind it. And then one thing led to another and they actually underlined the real cause.

Chris - So having found that there is this ozone hole, they then got the mechanism, which is that these refrigerants and things are getting into the atmosphere, concentrating over Antarctica where they deplete ozone. So we understood the mechanism that then led to the Montreal protocol in the late eighties didn't it? Where we banned the use of the worst culprit chemicals. And you're saying that now because we're not using these things anymore, the ozone is recovering.

Ella - Yes.

Chris - But it's still pretty big. That hole though, isn't it? I mean it was Australia sized even as recently as a few years ago.

Ella - Yeah. I mean it varies in size with the season because the destruction of ozone requires light. So in Antarctica you get periods of complete darkness. So when the sun returns in spring, then you start getting this photolytic, or like, controlled destruction of ozone starting again. And that's when the ozone hole starts getting bigger.