Chapter 1: What is the ozone layer and why is it important for life on Earth?
You're listening to Shortwave from NPR. Hey, Shortwavers, Emily Kwong here with a love letter to the layer of the Earth's atmosphere that acts like a sunscreen. I'm talking, of course, about ozone. Without ozone, that would be impossible to live on Earth. This is atmospheric scientist Irina Petropadlovskikh.
The ozone is a layer of the stratosphere with a high concentration of ozone molecules, each one made out of three oxygen atoms.
And it's very good for us. It protects us from the harmful muv radiation. And that's why we want more of this, not less of that.
To form, ozone needs sunlight, which bursts oxygen apart. You know, the O2 version we breathe. And then each single atom of oxygen can then connect with another O2 to form our girl O3, a.k.a. ozone. But sunlight can also destroy ozone, and the balance generally depends on the season. But starting in the 1970s, something weird happened.
Chapter 2: How did scientists first discover the ozone hole over Antarctica?
Scientists noticed that ozone is changing slowly but surely. But they didn't know how much it's changing until maybe the beginning of the 80s, when the scientists actually measured ozone. significant change that was happening in the springtime in Antarctica. And so they noticed that there was less ozone.
A giant hole is forming in the Earth's protective ozone layer. Scientists discovered a hole.
Remarkable loss of ozone that occurs over the Antarctic in October. A lot of people call it the ozone hole, but it was really more of a thinning. Scientists launched weather balloons to study its size, and they found something shocking.
High levels of two chemicals, chlorine and bromine, were breaking down ozone faster than it was being made, letting in the kind of radiation that causes cancer, crop failure. And it was happening because of ozone-depleting substances made by us on Earth. So the race was on to save the world. Today on the show, how researchers mobilized on a global scale to close the ozone hole.
Plus, why the ozone layer is still recovering and what climate scientists can learn from this success. You're listening to Shortwave, the science podcast from NPR.
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Chapter 3: What were the major chemicals responsible for ozone depletion?
So, Irina, I want to focus on how the ozone is operating over Antarctica because that's where the hole is. And I know that the ozone layer over Antarctica naturally thins because things are a little different there, right?
Yeah. In Antarctica, the maximum of the ozone is happening during months of December, January. And it's happening naturally. You know, there is an increase in the ozone layer. throughout the year, and then when the polar night comes in, there is no sun, and so there is not much of the ozone production happening during the wintertime.
And that's because sunlight triggers ozone formation, but also sunlight destroys ozone. So the amount of ozone is always kind of fluctuating when the sun is present. And during the Antarctic polar night in June, July, and August, when there's no sun, the ozone amounts are basically steady. They don't really fluctuate.
And then in the spring, the sunlight comes back and these chemical reactions start happening again. But isn't the Earth's atmosphere always moving and mixing? So wouldn't the air from other parts of the world that have access to sunlight mix with Antarctica's air?
Antarctica has a very specific process.
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Chapter 4: What actions were taken globally to address the ozone crisis?
Because it's a continent, the atmosphere can create these strong winds that circulate around Antarctica. And so they separate the air that's over Antarctica from the rest of the other latitudes outside of Antarctic vortex. So there is no really way to mix it with other airflow.
Oh, okay. So the atmosphere of Antarctica is isolated because of this polar vortex, which results in this seasonal cycle that has its rhythms. Now, let's go back in time when scientists really started noticing the ozone layer was changing over Antarctica beyond what was typical for the seasonal rhythm. And these researchers went on an expedition to Antarctica to figure out why.
What did they do? So scientists flew into Antarctica on the aircraft, and they also set up the camp on Antarctica continent. But the most interesting observation they made is that when they're flying inside of Antarctica, They continuously measured both ozone and chlorine, the chemicals that they thought that might be destroying ozone.
And they noticed that flying into Antarctica, the ozone started to go down and chlorine started to go up. And so that made very good sense to them so that those chemicals are destroying ozone.
It's like their Achilles heel.
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Chapter 5: How does the Antarctic atmosphere affect ozone levels?
I read that one chlorine atom can destroy over 100,000 ozone molecules. Yeah, definitely. What the heck were we doing in the 50s and 60s that created this abundance of chemicals in the atmosphere?
Yeah. chemicals that we can use in refrigeration. Those chemicals were put in the firefighting equipment, for example. They were very effective at that. They were put in the aerosols, sprays. And so they've been used for fumigation of the vegetables and the fruits. So they were working really well.
But what I think people did not realize right away is that those chemicals actually are capable of escaping into the stratosphere.
But I'm, like, curious, like, how did stuff made on Earth produce molecules that got all the way up there? Because the stratosphere is miles above our heads. It's, like, where planes fly. Like, how could chemicals travel upwards that high?
Chapter 6: What were the key findings from the scientists' expedition to Antarctica?
Well, the atmosphere has these mixing properties. You know, there are a lot of exchange between the troposphere and stratosphere and the tropics. Oh. And they can travel also with this flow of the air from the tropics into the middle latitudes in the polar region. There is the so-called Brewer-Dobson circulation in the atmosphere. And they get distributed everywhere.
Oh, so they hang out a long time.
And then they can hang out for a long time, yes. Oh, there's another thing that we need to remember. There is also the specific clouds that are formed in Antarctica, and they're called the polar stratospheric clouds. Polar stratospheric clouds. So they're also quite essential for this depletion to occur.
And the reason for that is that they actually set up this activation of the chlorines that are typically not very active. So they set them up such that there will be only chlorines and bromines released once the sun comes back. And so then those chemicals are released, and then they will start to destroy ozone very, very rapidly.
Chapter 7: Why is the recovery of the ozone layer progressing slowly?
But there are also other chemicals that get frozen into the polar stratospheric clouds that typically neutralize these reactions. And so there is nothing to stop those chemicals to destroy ozone for some period of time until the polycystic clouds disappear.
What an accumulation of forces that led to this problem. Okay, so what did scientists do in response? Because obviously today the ozone is okay. So why? What happened, ultimately, to save the world?
Right, exactly. So they started to present their findings to the public, to the governments. And so eventually they got enough people to listen to their worries that the Vienna Convention happened, where the representatives from many, many countries got together and they discussed these issues. Wow.
And then the Montreal Protocol in 1987, actually signed by every country, I mean, this is really amazing, agreed to stop production and use of those ozone-depleting substances.
Right, and that is how we get to the point now where the ozone layer is doing well. I read it's the fifth smallest since the crisis. Why hasn't the ozone fully thickened over Antarctica?
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Chapter 8: What lessons can we learn from the ozone layer crisis for current environmental issues?
Is it because people are still using chemicals even though they're banned?
Some chemicals actually can leave, once they get into stratosphere, they can live up to 100 years. So once they're released, let's say they've been released in the 50s and even before that, they have quite a long way to go before they get completely removed from the stratosphere.
So the ozone hole is recovering, but very slowly because we still have a lot of these chemicals in the atmosphere still.
And to this day, people are still monitoring the ozone layer, right? Like, we didn't fix the problem and just abandon Antarctica, right?
No, we are very lucky. We still have a lot of observations. So, yes, I mean, we still need to monitor it. And the reason for that is that... There are some other chemicals that have been released in the atmosphere. They're not really destroying ozone. They are a replacement for those CFCs. We need to know how they're impacting the atmosphere. And some of them are so-called greenhouse gases.
So they're heating the atmosphere. And with that, there is also some impact on the way how the Ozone is recovering.
Yeah. Greenhouse gas emissions. We talk about that a lot on shortwave. And it's a useful comparison because that existential issue is also human caused and could be human solved, so to speak. So in comparison to climate change that we're all struggling with now, why do you think the ozone issue was dealt with so swiftly?
I think because that was a problem affecting everybody. It wasn't something that would require people to stop using, for example, you know, that people were advised not to use the aerosols, for example, by scientists. But it wasn't a very big impact on everybody's life.
Giving up CFCs was a lot easier than giving up like oil and gas.
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