WEBVTT FILE

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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.