Ozone 101: What Is the Ozone Hole?

Ozone 101: What Is the Ozone Hole?

Narration: Kathleen Gaeta

Transcript:

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Have you ever heard that

something called the ozone layer

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is thinning? Or that your

aerosol hairspray is what's

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causing it? Or that it leads to

more severe sunburns and UV

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rays? This is referring to the

ozone hole. But what exactly

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does it all mean? Welcome to

ozone 101. The ozone holes

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proper name is actually the

Antarctic ozone hole because

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when it forms it forms over

Antarctica. But before we get

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into what that is, let's first

talk about what ozone itself is.

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Ozone is a gas comprised of

three oxygen atoms, about 90% of

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the Earth's ozone exists in the

stratosphere, the layer of the

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atmosphere that extends from

eight to about 30 miles above

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the earth's surface. In fact,

the stratosphere is often

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referred to as the ozone layer.

Ozone acts as a sunscreen around

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the Earth filtering out harmful

ultraviolet radiation or UV

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rays, which are mainly absorbed

in the stratosphere. Without an

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ozone layer, UV radiation would

sterilize the Earth with a

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damaged but still present ozone

layer, there will be more

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sunburns, more skin cancer cases

increased cases of eye damage

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the wilting and loss of trees

and plants and significantly

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lessened crop yields. Suffice it

to say ozone is pretty important

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for the planet. So what causes

the ozone hole? There are

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several major factors that

together lead to the destruction

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of ozone, thus creating the

ozone hole. Those factors are

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one very strong winds around the

South Pole, or the polar vortex

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to the sun's rays, three

chlorine and bromine compounds

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from ozone depleting substances,

and for cold temperatures below

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negative 109 degrees Fahrenheit

in the stratosphere, which form

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a specific kind of cloud polar

stratospheric clouds. The polar

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vortex forms in the southern

hemisphere stratospheric during

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the winter as temperatures drop.

And when sunlight returns to

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Antarctica and late winter and

early spring, temperatures are

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still cold enough to form polar

stratospheric clouds. And now

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there's also sunlight. Chemical

reactions take place on the

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cloud particle surfaces,

converting unreactive forms of

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chlorine and bromine into

reactive chemicals. The vortex

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acts as a sort of container

confining the contents of the

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Antarctic stratosphere within

its bounds allowing the reactive

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chlorine and bromine compounds

to destroy ozone molecules.

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That's when depletion can occur

on a large scale with the

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presence of sunlight. The

reactive chlorine and bromine

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compounds produced during winter

begin to deplete ozone molecules

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by stealing one of their oxygen

atoms leaving just oxygen gas or

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otoo. In its wake. As long as a

polar stratospheric clouds are

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present, these reactions will

occur over and over again until

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the ozone is nearly gone. This

forms what we call the ozone

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hole. But that's really a

misnomer. It's actually more of

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a thin layer. In mid to late

spring, the vortex begins to

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break up and the polar air

depleted of ozone is mixed back

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into the rest of the Southern

Hemisphere. The ozone hole is

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gone. Ozone depletion has still

occurred. It's just no longer

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all concentrated in one small

area. It spread around the

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atmosphere. So why is the ozone

hole bigger and longer lasting

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and certain years? Well, it all

comes down to weather, just like

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some winters are colder and

longer than others on the

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Earth's surface. The same goes

for weather in the stratosphere.

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If the Antarctic stratosphere

stays cold, the polar vortex and

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the ozone hole within it will

persist. And in years with cold

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springtime temperatures, the

polar vortex and the ozone hole

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are large.

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Make no mistake, ozone depletion

is not a natural thing. It stems

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from human emissions of

chemicals called

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chlorofluorocarbons or CFCs. In

the early 1900s refrigerators

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use toxic gases like ammonia and

methyl chloride as refrigerants.

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Unfortunately, this led to

fatalities as the toxic gases

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leaked out of the appliances. So

the search began for a non toxic

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and non flammable chemical that

can be used as a refrigerant.

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Thus the CFC was born. There are

many types of CFCs but the two

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most common are CFC 11 and CFC

12. In the 1930s, the production

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and consumption of CFCs began to

skyrocket. By the early 1980s,

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over 300 million pounds of CFC

11 alone were being released

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into the atmosphere each year.

Then, in 1985, British

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researcher Joe Farman and his

colleagues published their

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research on large seasonal ozone

losses over Antarctica. Thanks

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to the combined efforts of the

quick acting science community

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industry and policymakers the

Montreal Protocol was signed in

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1987, restricting the production

and consumption of CFCs. Every

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nation on earth has now signed

the Montreal Protocol. So for

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the record, your hairspray and

aerosol deodorant hasn't been

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harming ozone since these laws

went into effect in the 80s. But

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why do we still see an ozone

hole today? First CFCs have

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lifetimes of 50 to 100 plus

years and it will take some time

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for the concentration of CFCs in

the atmosphere to drastically

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decline. Second, there are still

CFCs being released into the

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atmosphere today. For example,

as an old refrigerator or air

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conditioning unit deteriorates

in a landfill, the CFCs within

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are slowly released. From the

time a CFC is released into the

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air, it takes about five years

for its impact to be felt over

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Antarctica, where depletion will

occur. The CFCs emitted at the

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surface eventually rise into the

tropical stratosphere. The ozone

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in the stratosphere blocks most

of the sun's UV radiation, so

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the CFCs have to rise above most

of the ozone layer before

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sunlight can then break them

down. Once they get high enough

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solar radiation releases the

chlorine most of which

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eventually goes into ozone, say

forms like hydrochloric acid and

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chlorine nitrate. When these

compounds make their way to

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Antarctica, those chemical

reactions start up. And if

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you're wondering why Antarctica

these reactions are unique to

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the polar regions, because of

their extreme low temperatures,

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and presence of polar

stratospheric clouds, one

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chlorine atom can destroy 1000s

of ozone molecules, and millions

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of tons of CFCs were pumped into

the atmosphere from the 1920s

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through the early 1990s. As CFC

concentrations in the atmosphere

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continue to decline, the ozone

hole is expected to gradually

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become less severe, and

scientists expect the Antarctic

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ozone to recover back to healthy

levels around the year 2070.