Have you ever heard that something called the ozone layer
is thinning? Or that your aerosol hairspray is what's
causing it? Or that it leads to more severe sunburns and UV
rays? This is referring to the ozone hole. But what exactly
does it all mean? Welcome to ozone 101. The ozone holes
proper name is actually the Antarctic ozone hole because
when it forms it forms over Antarctica. But before we get
into what that is, let's first talk about what ozone itself is.
Ozone is a gas comprised of three oxygen atoms, about 90% of
the Earth's ozone exists in the stratosphere, the layer of the
atmosphere that extends from eight to about 30 miles above
the earth's surface. In fact, the stratosphere is often
referred to as the ozone layer. Ozone acts as a sunscreen around
the Earth filtering out harmful ultraviolet radiation or UV
rays, which are mainly absorbed in the stratosphere. Without an
ozone layer, UV radiation would sterilize the Earth with a
damaged but still present ozone layer, there will be more
sunburns, more skin cancer cases increased cases of eye damage
the wilting and loss of trees and plants and significantly
lessened crop yields. Suffice it to say ozone is pretty important
for the planet. So what causes the ozone hole? There are
several major factors that together lead to the destruction
of ozone, thus creating the ozone hole. Those factors are
one very strong winds around the South Pole, or the polar vortex
to the sun's rays, three chlorine and bromine compounds
from ozone depleting substances, and for cold temperatures below
negative 109 degrees Fahrenheit in the stratosphere, which form
a specific kind of cloud polar stratospheric clouds. The polar
vortex forms in the southern hemisphere stratospheric during
the winter as temperatures drop. And when sunlight returns to
Antarctica and late winter and early spring, temperatures are
still cold enough to form polar stratospheric clouds. And now
there's also sunlight. Chemical reactions take place on the
cloud particle surfaces, converting unreactive forms of
chlorine and bromine into reactive chemicals. The vortex
acts as a sort of container confining the contents of the
Antarctic stratosphere within its bounds allowing the reactive
chlorine and bromine compounds to destroy ozone molecules.
That's when depletion can occur on a large scale with the
presence of sunlight. The reactive chlorine and bromine
compounds produced during winter begin to deplete ozone molecules
by stealing one of their oxygen atoms leaving just oxygen gas or
otoo. In its wake. As long as a polar stratospheric clouds are
present, these reactions will occur over and over again until
the ozone is nearly gone. This forms what we call the ozone
hole. But that's really a misnomer. It's actually more of
a thin layer. In mid to late spring, the vortex begins to
break up and the polar air depleted of ozone is mixed back
into the rest of the Southern Hemisphere. The ozone hole is
gone. Ozone depletion has still occurred. It's just no longer
all concentrated in one small area. It spread around the
atmosphere. So why is the ozone hole bigger and longer lasting
and certain years? Well, it all comes down to weather, just like
some winters are colder and longer than others on the
Earth's surface. The same goes for weather in the stratosphere.
If the Antarctic stratosphere stays cold, the polar vortex and
the ozone hole within it will persist. And in years with cold
springtime temperatures, the polar vortex and the ozone hole
are large.
Make no mistake, ozone depletion is not a natural thing. It stems
from human emissions of chemicals called
chlorofluorocarbons or CFCs. In the early 1900s refrigerators
use toxic gases like ammonia and methyl chloride as refrigerants.
Unfortunately, this led to fatalities as the toxic gases
leaked out of the appliances. So the search began for a non toxic
and non flammable chemical that can be used as a refrigerant.
Thus the CFC was born. There are many types of CFCs but the two
most common are CFC 11 and CFC 12. In the 1930s, the production
and consumption of CFCs began to skyrocket. By the early 1980s,
over 300 million pounds of CFC 11 alone were being released
into the atmosphere each year. Then, in 1985, British
researcher Joe Farman and his colleagues published their
research on large seasonal ozone losses over Antarctica. Thanks
to the combined efforts of the quick acting science community
industry and policymakers the Montreal Protocol was signed in
1987, restricting the production and consumption of CFCs. Every
nation on earth has now signed the Montreal Protocol. So for
the record, your hairspray and aerosol deodorant hasn't been
harming ozone since these laws went into effect in the 80s. But
why do we still see an ozone hole today? First CFCs have
lifetimes of 50 to 100 plus years and it will take some time
for the concentration of CFCs in the atmosphere to drastically
decline. Second, there are still CFCs being released into the
atmosphere today. For example, as an old refrigerator or air
conditioning unit deteriorates in a landfill, the CFCs within
are slowly released. From the time a CFC is released into the
air, it takes about five years for its impact to be felt over
Antarctica, where depletion will occur. The CFCs emitted at the
surface eventually rise into the tropical stratosphere. The ozone
in the stratosphere blocks most of the sun's UV radiation, so
the CFCs have to rise above most of the ozone layer before
sunlight can then break them down. Once they get high enough
solar radiation releases the chlorine most of which
eventually goes into ozone, say forms like hydrochloric acid and
chlorine nitrate. When these compounds make their way to
Antarctica, those chemical reactions start up. And if
you're wondering why Antarctica these reactions are unique to
the polar regions, because of their extreme low temperatures,
and presence of polar stratospheric clouds, one
chlorine atom can destroy 1000s of ozone molecules, and millions
of tons of CFCs were pumped into the atmosphere from the 1920s
through the early 1990s. As CFC concentrations in the atmosphere
continue to decline, the ozone hole is expected to gradually
become less severe, and scientists expect the Antarctic
ozone to recover back to healthy levels around the year 2070.