Ozone Layer Depletion Video Lecture | Chemistry for JEE Main & Advanced

[Trace]Gotta get ready.
That hole in the ozone layer you know that's
some serious stuff.
[Julian] Hey that's not a thing anymore
[Trace] WHAT?
IT'S GONE?!
Howdy chlorofriendocarbons, you've found your
way to DNews, thanks for that!
Welcome!
I'm Trace.
If you are a Millennial, you've probably spent
your whole life hearing about the "hole" in
the ozone layer.
Before you can understand the hole, though,
you gotta know what the ozone layer is.
The ozone layer isn't really its own thing,
instead 90 percent ozone floats around the
stratosphere: about 6 to 30 miles above our
heads.
Ozone is three oxygen atoms linked together1,3,
Oh-three.
When in the stratosphere, ozone absorbs harmful
UV-B radiation, protecting us and other life
here on the ground (in the troposphere).
In the late 19th and early 20th centuries,
people were just beginning to harness the
power of refrigeration using toxic gasses
like ammonia, methyl chloride, and sulfur
dioxide.
In 1928, an enterprising inventor at General
Motors created a non-toxic chemical for refrigeration
called CFC -- chlorofluorocarbon.
It was patented as Freon by DuPont, and sold
in air conditioners, fridges, bug sprays,
spray paints, hair conditioners, and healthcare
products.
At it's peak companies were making a million
metric tons of CFCs every year.
Then, in a 1974 study in Nature found this
great nontoxic refrigerant was wreaking havoc
on the atmospheric ozone layer.
Sure, at sea level, CFCs are nontoxic and
safe for humans, but if they get into the
upper atmosphere, they're subject to photodissociation:
where UV radiation breaks a Chlorine atom
off the CFC!
If that free chlorine finds a molecule of
ozone (O-three) it will react with it, destroying
the ozone by ripping off one of its oxygen
atoms to make Chlorine Monoxide, leaving regular
old O2, or oxygen, in its wake.
Then the Chlorine Monoxide gets hit by UV
and broke up again… so it has to find another
O3 molecule to stabilize it…and the cycle
repeats itself.
It's bad.
In 1977, we were studying the ozone layer
and it was fine.
By 1981, there were hints something was amiss.
Then in 1984, scientists suddenly registered
a giant hole in the ozone layer.
They published their findings and in 1987,
the Montreal Protocol was signed, beginning
the phasing out CFCs shortly thereafter.
Meanwhile even though the house was clearly
on fire, Du Pont and other companies insisted
everything was fineand fought tooth and nail
to keep CFCs legal.
But they finally relented after scientific
evidence became indisputable.
A looming environmental disaster that pitted
corporations against the scientific community…
where have I heard that before?
Though CFCs can hide in the atmosphere for
40 to 150 years, without the emission of new
CFCs, eventually that free chlorine cycle
will stop.
If the chlorine runs into some methane
up there, it would break it up forming hydrogen
chloride which is stable enough to rain
down to Earth.
In 2015, about 30 years after the Protocol
was signed, the ozone hole reached the largest
size EVER.
But since that peak (due mostly to volcanic
eruptions that sprew bromine, another Ozone
depleting gas), scientists have finally started
to see the ozone layer repair itself!
A study published in Science this year found
the hole had decreased in size from the year
2000, and most of that decrease was specifically
because of the Montreal Protocol!!
International Policy, for the win!
Without the chlorine wafting up into the stratosphere,
ozone was able to form naturally -- when UV
light breaks up regular old oxygen from O2
into O3.
Without the chlorine to mess it up, this process
could restart!
It can still be messed up by volcanic eruptions,
but overall without our meddling, the ozone
layer may someday be back to normal!
Based on this new study, the Ozone layer might
be back to 1980 levels by 2040!
You can actually see how the Ozone layer is
doing right now, on NASA's website!
We'll put the link in the description for
you.
Of course, this is science, so we can't have
all happy endings.
We still need AC and fridges, and the replacement
gas, HFCs, are a potent greenhouse gas.
So now, global warming is a concern.
Sigh.
We can never win.
But hey, at least that thing we fought for
as kids is getting better, right?
But...why is there air in the first place?