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The Ozone Layer: Importance and the Harmful Effects of Thinning

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  • 0:05 Ozone Is Beneficial
  • 1:17 CFCs Break Down Ozone
  • 2:58 Early Discoveries
  • 4:14 Policy to Protect Ozone
  • 5:17 Lesson Summary
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Lesson Transcript
Instructor: Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

In this lesson, you will learn the importance of the ozone layer and how it is depleted. You will also study the research and policy that has been instrumental in its recovery.

Ozone Is Beneficial

You probably don't realize that every time you step outside, ozone, a gaseous molecule of three oxygens, makes it possible for you to do so without reaping the harmful effects of the sun's radiation. This helpful ozone is found in the stratosphere, which is the atmospheric layer just above where life exists and weather occurs.

When that same gaseous ozone is found in our lower layer (called the troposphere), it is considered an air pollutant and is very harmful to human health. However, we need it in the stratosphere because even at the low concentration of 12 parts per million, ozone is so effective at absorbing the sun's UV radiation that this small amount is plenty enough to protect us on Earth.

Just how harmful is UV radiation? In humans, UV radiation causes skin cancer and cataracts. UV radiation also affects the fertility of other animals, as well as the viability of their offspring. Plants are affected by UV radiation because it affects their ability to grow and develop correctly. As you'll see later, UV radiation also influences how chemicals break down and react, and this can lead to catastrophic changes in environments and ecosystems.

CFCs Break Down Ozone

You've likely heard about the ozone hole or thinning of the ozone layer, but you may not know what causes these problems. These discoveries came about through many years of scientific research, so let's take a trip back in time to gain a better understanding of how the ozone layer has been affected by human activity.

It all began in the 1960s when scientists noticed that their measurements of ozone in the atmosphere were lower than what their models predicted they should be. The scientists believed that either naturally or artificially created chemicals were somehow depleting the ozone.

It turns out that these chemicals were something called chlorofluorocarbons, or CFCs. These are compounds used for refrigerants, fire extinguishers, and aerosol propellants. CFCs were invented in the 1920s and were originally thought to be environmentally friendly, but in fact, they break down ozone in the presence of UV radiation.

What happens is this: a chlorine molecule from the CFC is released from the compound by the UV radiation. It then reacts with an ozone molecule (O3), leaving a molecule of oxygen gas (O2) and a molecule of chlorine monoxide (ClO). The chlorine on this molecule is free to react with a single oxygen atom and then breaks away, leaving another O2 molecule and the free chlorine atom. This chlorine atom is now floating around the stratosphere, ready to break apart another ozone molecule into atmospheric oxygen, continuing the cycle.

Early Discoveries

Ok, so now that we know how CFCs break apart ozone, let's go to the early 1970s where CFCs are being mass produced at an annual rate of one million metric tons and growing by 20% each year!

In 1974, two scientists named Sherwood Rowland and Mario Molina were able to demonstrate how CFCs were splitting ozone molecules into atmospheric oxygen and chlorine monoxide molecules, and this work earned them the 1995 Nobel Prize in chemistry. Their research helped put new policy into motion, and by 1979, the U.S. and other countries had banned CFCs in aerosol sprays, but not for other uses.

Fast forward to 1985 when a new and shocking discovery sparked action across the world. British scientists, who had been measuring ozone concentrations at a research station in Antarctica since the 1950s, discovered that the ozone above this region had declined by as much as 60% in the previous ten years. This extremely thin layer of ozone above the region became known as the ozone hole, and over the next several years, it was confirmed that CFCs were the cause of so much thinning.

Policy to Protect Ozone

Let's jump one more time, now to the Montreal Protocol of 1987. When it was originally drafted, 24 different nations signed this treaty agreeing to reduce CFC production by at least 50%. Since then, five more agreements have followed up this original one with more severe cuts to CFC production and other ozone-depleting chemicals. At present, it includes almost 200 different signatory nations from all over the world.

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