The ozone layer is a layer of ozone particles
dispersed between 11,80 and 18,64 miles (19
and 30 km) altitude in the stratosphere. The
concentration of ozone in the ozone layer
is usually below 10 parts per million ozone.
The ozone layer is essential for life on Earth
as it absorbs ultraviolet radiation (UV) from
the Sun.
The unique physical properties of ozone
allow the ozone layer to act as a sunscreen
for our planet, providing an invisible filter
to help protect all forms of life against
danger ultraviolet rays. Most UV radiation
entering the atmosphere is absorbed by ozone
and prevented from reaching the Earth's surface.
Ozone is created in the stratosphere over
the tropics and stratospheric winds transport
around the Earth. Ozone (O3) is composed of
three oxygen atoms (O). The ozone molecules
are able to absorb ultraviolet rays and they
decompose in oxygen (an oxygen molecule (O2))
and a free oxygen atom (O). when the solar
radiation strikes an oxygen molecule (O2)
that absorbs UV rays and creates two oxygen
atoms (O) by dividing into two. If it comes
in contact with another molecule of oxygen
(O2), so they can regenerate a molecule of
ozone (O3). This process is known as
photolysis. Ozone is also naturally broken
down in the stratosphere by sunlight and by
a chemical reaction with various compounds
containing nitrogen, hydrogen and chlorine.
These chemicals occurs naturally in the atmosphere
in very small amounts.
Volcanic eruptions can alter the amount
of ozone in the atmosphere as was the case
during the eruption of Mount Pinatubo and
Hudson, 1991. Then it's the same for
the solar activity influence on concentration
of stratospheric ozone.
The anomaly of the stratospheric
ozone about latitude since 1978. Source NOAA
The
Hole in the Ozone Layer
The diminishing ozone
layer occurs when the natural balance
between the production and destruction
of stratospheric ozone is tilted in
favor of the destruction. Although
natural phenomena can cause temporary
ozone loss, chlorine and bromine released
from man-made compounds such as CFC
are now accepted as the main cause
of this depletion.
The "hole"
in the ozone layer is not a hole in any
real sense of the word, but a thinning
of the amount of ozone in the stratosphere
(From 11 to 18,64 miles (19 to 30 kilometers)
above the surface of the Earth) and mostly
over the Antarctic and Arctic during the
end of the winter. However, in some regions,
the thinning of the amount of ozone is
more important than the other and it is
in these areas where the term "hole
in the ozone layer" is strictly used.
During the spring in the Southern
Hemisphere, there is an ozone depletion
in the stratosphere over Antarctica,
with losses up to 60 %. This is
because each winter the polar
vortex isolates the air located
in polar latitudes of the rest of
the Earth's atmosphere and at very
low temperatures in winter (below
-112°F (-80°C)) because
it's dark permanently. When
it is very cold during the Polar
Nights, PSC
(Polar Stratospheric Clouds)
form in the polar stratosphere.
And as the sunlight returns to the
pole during early spring then by
the action of ultraviolet (UV) while
the PSC that formed the winter destroys
ozone and is not replaced as this
season there is not new supply of
atmospheric ozone. It is at the
end of the spring atmospheric circulation
changes, and the ozone that comes
from the tropical atmosphere replenishes
the polar atmosphere. The hole in
the ozone layer over Antarctica
is formed every year since the early
1970s.
Since 1970 the hole has grown,
in the sense that more and more
ozone is destroyed. But from the
observations made by the SAGE and
HALOE satellites, it was found that
the rate of decrease of the ozone
layer in the upper atmosphere has
been reduced since 1997.
From the graph
above, we have the data of two various
instrumentations aboard the same satellite.
The total of the ozone is represented
by a deformed column and of shaded
off color.
The profile of the ozone is converted
in volume to obtain a cutting of surface
of pressure
by latitude. Both observable data
concern the southern hemisphere, they
appear in a polar spelling projection,
on a superficial topographic support.
A video giving an explanation of
the ozone layer
Winters with low temperatures in Antarctica
favor the concentration of these molecules
in the atmosphere inert form. But as soon
as the sunlight starts, with the action
of UV rays, chlorine becomes active and
reacts with ozone molecules. There is
a catastrophic chain reaction : a single
chlorine atom can destroy released 100.000
ozone molecules. However, the stratospheric
ozone layer is our only protection from
ultraviolet radiation.
WARNING Patricia
Régnier helped me correct mistakes,
please you to visit her
blog
I’m not english speaker, some improprieties
can appear to english masters.
Could you help me reporting by mail any fault
you read. Thank you for all.
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