breaking down of ozone layer in stratosphere layer

1. BREAKING DOWN OF OZONE
LAYER IN Stratosphere Layer
BY
U.MUKUND
9D
CHEMISTRY 2nd term project.

2. INDEX
• The Stratosphere
• The Ozone Layer
• Ozone Chemistry
• Use of Ozone
• What is a Ozone Hole
• What is Stratospheric Ozone Depletion?
• Breaking Down of Ozone Layer in
Stratosphere
• The Role of Polar Stratospheric Clouds

3. The Stratosphere
• The stratosphere is the second major layer
of Earth's atmosphere, just above the troposphere,
and below the mesosphere. About 20% of the
atmosphere's mass is contained in the
stratosphere.
• The stratosphere is stratified in temperature, with
warmer layers higher and cooler layers closer to
the Earth. The increase of temperature with
altitude, is a result of the absorption of the Sun's
ultraviolet radiation by ozone.
• The border between the troposphere and
stratosphere, the tropo pause, marks where this
temperature inversion begins.
• Near the equator, the stratosphere starts at 18 km
59,000 ft; at mid latitudes, it starts at 10–13 km
33,000–43,000 ft and ends at 50 km 160,000 ft; at
the poles, it starts at about 8 km 26,000 ft.

4. The Ozone Layer
• The ozone layer or ozone shield is a region of
Earth's stratosphere that absorbs most of
the Sun's UV radiation.
• It contains high concentrations ozone (O3) in
relation to other parts of the atmosphere,
although still small in relation to other gases in
the stratosphere.
• The ozone layer contains less than 10 parts per
million of ozone, while the average ozone
concentration in Earth's atmosphere as a whole is
about 0.3 parts per million.
• The ozone layer is mainly found in the lower
portion of the stratosphere, from approximately 20
to 30 kilometers above Earth, although the
thickness varies seasonally and geographically.

5. Ozone Chemistry
• Ozone, a molecule consisting of three oxygen
atoms, was first discovered in the 1830s by the
German scientist Christian Schönbein. He
identified a new compound in laboratory
experiments using oxygen, and named the
molecule “ozein,” meaning “to smell” in Greek.
In 1881, John Hartley experimented with ozone
and found that it strongly absorbed ultraviolet
light . He compared the absorption spectrum of
ozone to the spectrum of sunlight as seen from
the Earth’s surface and found that they
matched exactly.
• O3 + light → O2 + O
• O + O3 → 2 O2
• Net: 2 O3 + light → 3 O2

6. Use of Ozone
• For nearly a billion
years, ozone molecules in the
atmosphere have protected life on
Earth from the effects of ultraviolet
rays. The ozone layer resides in the
stratosphere and surrounds the entire
Earth. ... As a result, the amount of
UV-B reaching Earth's surface is
greatly reduced.

7. What is a Ozone Hole
• A region of marked thinning of the
ozone layer in high latitudes,
chiefly in winter, attributed to the
chemical action of CFCs and other
atmospheric pollutants. The resulting
increase in ultraviolet light at
ground level gives rise to an
increased risk of skin cancer.

8. What is Stratospheric Ozone
Depletion?
• Ozone depletion describes two distinct but related
phenomena observed since the late 1970s: a steady decline of
about 4% in the total amount of ozone in
Earth'sstratosphere (the ozone layer), and a much larger
springtime decrease instratospheric ozone around Earth's
polar regions.
• Ozone depletion describes two distinct but related
phenomena observed since the late 1970s: a steady decline of
about four percent in the total amount
of ozone in Earth‘s stratosphere (the ozone layer), and a much
larger springtime decrease in stratospheric ozone around
Earth's polar regions. The latter phenomenon is referred to as
the ozone hole. In addition to these well-known stratospheric
phenomena, there are also springtime polar tropospheric
ozone depletion events.

9. Breaking Down of Ozone Layer
in Stratosphere
• Once in the atmosphere, CFCs drift slowly
upward to the stratosphere, where they
are broken up by ultraviolet radiation,
releasing the chlorine that catalytically
destroys ozone. In the graphic below, the
destructive cycle of a chlorine atom is shown.
UV radiation breaks off a chlorine atom from a
CFC molecule.

11. The Role of Polar Stratospheric
Clouds
• Polar stratospheric clouds or PSCs, also known as nacreous
clouds , are clouds in the winter polar stratosphere at
altitudes of 15,000–25,000 meters (49,000–82,000 ft). They
are best observed during civil twilight when the sun is
between 1 and 6 degrees below the horizon as well as
in winter and in more northerly latitudes. They are implicated
in the formation of ozone holes. The effects on ozone depletion
arise because they support chemical reactions that produce
active chlorine which catalyzes ozone destruction, and also
because they remove gaseous nitric acid,
perturbing nitrogen and chlorine cycles in a way which
increases ozone destruction.