Why ozone depletion is a problem

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Subscriber Exclusive Content. Hegglin Lead Author , David W. Montzka, and Eric R. Because all sunlight contains some UVB, even with normal stratospheric ozone levels, it is always important to protect your skin and eyes from the sun. See a more detailed explanation of health effects linked to UVB exposure. EPA uses the Atmospheric and Health Effects Framework model to estimate the health benefits of stronger ozone layer protection under the Montreal Protocol.

UVB radiation affects the physiological and developmental processes of plants. Despite mechanisms to reduce or repair these effects and an ability to adapt to increased levels of UVB, plant growth can be directly affected by UVB radiation. Indirect changes caused by UVB such as changes in plant form, how nutrients are distributed within the plant, timing of developmental phases and secondary metabolism may be equally or sometimes more important than damaging effects of UVB.

These changes can have important implications for plant competitive balance, herbivory, plant diseases, and biogeochemical cycles. Phytoplankton form the foundation of aquatic food webs. Phytoplankton productivity is limited to the euphotic zone, the upper layer of the water column in which there is sufficient sunlight to support net productivity. Exposure to solar UVB radiation has been shown to affect both orientation and motility in phytoplankton, resulting in reduced survival rates for these organisms.

Scientists have demonstrated a direct reduction in phytoplankton production due to ozone depletion-related increases in UVB. UVB radiation has been found to cause damage to early developmental stages of fish, shrimp, crab, amphibians, and other marine animals. They completely revolutionized cooling and refrigeration, making them much safer and much more widely available. Instead of using ammonia as a coolant, we could use CFCs, which were nontoxic.

And as far as anyone could tell at the time, they were inert and completely safe. So we kept manufacturing them and kept pumping them into the atmosphere—tens of thousands of tons per year by the time they began to be phased out.

Giuliana: Well, in , a young chemist named Mario Molina joined the lab of F. Sherry had a bunch of different projects available, but Mario was most interested in CFCs and what they might be doing in the atmosphere. Rather than strictly focusing on fundamental chemistry questions, Mario says, he wanted to study something with a potential societal impact. Mario Molina: These were very stable, very safe chemicals. But we decided anyhow to take a look and see if we could predict what would happen to these chemicals in the environment.

So it was a question out of scientific curiosity that led us to explore the consequences. Mario Molina: So the conclusion then was that, well, they will eventually find their way into the stratosphere, into the ozone layer or above.

Giuliana: The ultraviolet light liberates single chlorine atoms from CFCs called chlorine radicals. At first, these solo chlorines react with other compounds to form so-called reservoir gases, like chlorine nitrate and hydrogen chloride.

Unlike the radicals, these are pretty stable. No problems yet? Giuliana: Not yet. Giuliana: More chlorine radicals. And these radicals run amok in the ozone layer. This leaves you with a molecule of diatomic oxygen, or O 2 , and a chlorine monoxide radical. When this radical collides with a single, free oxygen atom hanging out in the ozone layer, the result is a second O 2 molecule and the original chlorine radical. As Mario explains:. Mario Molina: Just a single chlorine atom could destroy tens of thousands of ozone molecules because it would be continuously recycled.

And so that was what led us to the hypothesis, then, that these industrial compounds, as stable as they were, they could significantly affect the ozone layer. Giuliana: Although there was a lot of stigma back then about scientists talking to the media, Mario and Sherry Rowland realized that their discovery was too important to keep within the confines of a scientific society. In addition to presenting their scientific results, they called for a complete ban on the substances.

They spent the ensuing years continuing to talk to the press and testifying before Congress. So we learned about communicating to the media and we also contacted decision makers in government. Giuliana: It certainly garnered a lot of attention. DuPont, which was the major manufacturer of CFCs, publicly challenged the conclusions and spent millions of dollars on ad campaigns and lobbying Congress to try and convince the public that CFCs were safe.

But despite this pushback, the National Academy of Sciences decided to commission a report to look into the possibility that these chemicals were harming the environment. Giuliana: Well, in , just two years after Mario and Sherry published their groundbreaking study, the National Academy released their report, which used models of atmospheric chemistry and transport to unequivocally verify the calculations that Mario and Sherry carried out.

At this point, scientists were only making sparse measurements of the ozone layer, but they were becoming more aware of the potential catastrophe that CFCs could bring about. Other countries followed suit, and this work led to the establishment of the Montreal Protocol in , which is pretty widely thought of as the most influential environmental policy ever enacted—it was signed by parties.

Susan Strahan: All the nations of the world signed on to the Montreal Protocol. Every single one is a signatory. Giuliana: Well, there was a lot of support for creating the World Health Organization in And in , for example, the Framework Convention on Climate Change—the precursor to the Kyoto Protocol—had signatories.

Was that foreshadowing, perhaps? Might we hear more about that later? Giuliana: Oh, for sure. Kerri: Wait. Giuliana: Yeah, and remember how I said the CFC-based propellant bans were enacted without a whole lot of direct measurements of ozone?

Dorea Reeser: Hey there, Dorea Reeser here. This is our last Stereo Chemistry episode of the year, so it seemed like a good time to take stock and thank you, our listeners, for following along all year long. This year, you heard stories about underwater robots monitoring our oceans, the innovative chemistries in rocket fuel that never actually made it into rocket fuel, and an in-depth look at the life and legacy of John B. You can check it out at cenm. Again, for all the biggest news of gathered together in one place, go to cenm.

Giuliana: Before the break, we were talking to Mario Molina, a chemist who won the Nobel Prize for helping show how chlorofluorocarbons, or CFCs, were destroying the ozone layer. Kerri: Right. Going back to , British scientists had been measuring ozone levels above Antarctica using something called a Dobson spectrophotometer. The numbers the British scientists were seeing were pretty consistent, with some natural variability.

Way faster than what Mario Molina and Sherry Rowland had predicted. Giuliana: In fact, the levels were so low that Joe Farman, the lead scientist on the project, thought that his instrument was broken. Are you familiar with the term polar night? Giuliana: Solid logic. It refers to the time of year where the sun disappears entirely for months at a time. It gets so cold during polar night that what little moisture exists in the stratosphere freezes into tiny ice crystals.

Those crystals can then accumulate in what are called polar stratospheric clouds. These ice crystals also contain a lot of nitric acid, and they form in the lower reaches of the stratosphere. During polar night, clouds form in the low stratosphere that are full of ice crystals and nitric acid. Giuliana: Totally. Now, you remember those reservoir gases I mentioned? Kerri: So these previously inert gases are reacting and creating a buildup of chlorine in the stratosphere?

Then, when the sun begins to come up in the Antarctic spring, its UV rays start breaking apart the chlorine molecules to create chlorine radicals, and the ozone depletion begins. This whole process really only happens between August and October—as polar night ends and spring begins.

Once the stratosphere starts warming, the ice crystals melt and wind patterns shift, allowing the hole to essentially close up until the next year. This reaction mechanism—the one involving the ice crystals in the polar clouds—was first proposed by Susan Solomon, an atmospheric chemist, then with the National Oceanic and Atmospheric Administration. She led the US Antarctic expedition that helped confirm this mechanism. Giuliana: There were other groups looking at ozone at the time.

This satellite was orbiting Earth and creating global maps of ozone, but there was a problem. So those data were flagged as bad and rejected. Giuliana: Yeah, and some Japanese scientists in Antarctica were making their own measurements, too.

But none of this information was really being shared around. When NASA went back and reprocessed their flagged data, it revealed the true extent of the ozone hole—an area of low ozone concentrations roughly the size of the continental United States.

Kerri: So maybe we could have been working to solve the ozone problem sooner if folks had been more forthcoming with their data?

But whatever you believe, the discovery of the ozone hole certainly galvanized the world into action. It involved two aircraft decked out with a suite of scientific sensors, 25 total flights, and something like scientists looking at the data. Basically, there were a bunch of prevailing theories about why the ozone hole formed and why it went away and came back every year. To put those theories to the test, all of these scientists descended on Punta Arenas, the southernmost city in Chile, to try and collect the data needed to settle things.

Susan Strahan was a year away from completing her PhD in chemistry when she first heard about the ozone hole. Having spent her PhD working on instrumentation, she was attracted to the idea of tackling a massive problem with real societal implications.