BREAKING DOWN OF OZONE LAYER IN Stratosphere Layer

BYU.MUKUND

9DCHEMISTRY 2nd term project.

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

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.

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.

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

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.

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.

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.

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.

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.