Our Cover and action of CFC's on it

Twelfth Day of August, 2011

Beautiful atmosphere

Earth is surrounded by a blanket of air, which we call the atmosphere. It reaches near or over 600 kilometers (372 miles) from the surface of the Earth, so we are only able to see what occurs fairly close to the ground. Early attempts at studying the nature of the atmosphere used clues from the weather, the beautiful multi-colored sunsets and sunrises, and the twinkling of stars. With the use of sensitive instruments from space, we are able to get a better view of the functioning of our atmosphere.

Life on Earth is supported by the atmosphere, solar energy, and our planet's magnetic fields. The atmosphere absorbs the energy from the Sun, recycles water and other chemicals, and works with the electrical and magnetic forces to provide a moderate climate. The atmosphere also protects us from high-energy radiation and the frigid vacuum of space.

The envelope of gas surrounding the Earth changes from the ground up. Four distinct layers have been identified using thermal characteristics (temperature changes), chemical composition, movement, and density.

The layers of atmosphere

Troposphere

The troposphere starts at the Earth's surface and extends to about 15 kilometers (9 miles) high. This part of the atmosphere is the most dense. As you climb higher in this layer, the temperature drops from about 17 to -52 degrees Celsius. Almost all weather is in this region. The tropopause separates the troposphere from the next layer. The tropopause and the troposphere are known as the lower atmosphere.

Stratosphere

The stratosphere starts just above the troposphere and extends to 50 kilometers (31 miles) high. Compared to the troposphere, this part of the atmosphere is dry and less dense. The temperature in this region increases gradually to -3 degrees Celsius, due to the absorbtion of ultraviolet radiation. The ozone layer, which absorbs and scatters the solar ultraviolet radiation, is in this layer. Ninety-nine percent of "air" is located in the troposphere and stratosphere. The stratopause separates the stratosphere from the next layer. Usually Aeroplanes use this layer for transportation.

Mesosphere

The mesosphere starts just above the stratosphere and extends to 85 kilometers (53 miles) high. In this region, the temperatures again fall as low as -93 degrees Celsius as you increase in altitude. The chemicals are in an excited state, as they absorb energy from the Sun. The mesopause separates the mesophere from the thermosphere.

The regions of the stratosphere and the mesosphere, along with the stratopause and mesopause, are called the middle atmosphere by scientists. This area has been closely studied on the ATLAS Spacelab mission series.

Ionoshpere

This region comes intermediate to mesosphere and thermosphere where all the elements are in inonic form and this helps in all modes of communication (television, radio, mobiles etc), electro magnetic radiation is present in this layer. This is the region where the space shuttles entering earth gets heated up.

Thermosphere

The thermosphere starts just above the mesosphere and extends to 600 kilometers (372 miles) high. The temperatures go up as you increase in altitude due to the Sun's energy. Temperatures in this region can go as high as 1,727 degrees Celsius. Chemical reactions occur much faster here than on the surface of the Earth. This layer is known as the upper atmosphere.

The upper and lower layers of the thermosphere will be studied more closely during the Tethered Satellite Mission (TSS-1R).

CloroFluroCarbons:

Chlorofluorocarbon (CFC) is an organic compound that contains carbon, chlorine, and fluorine, produced as a volatile derivative of methane and ethane. A common subclass is the hydrochlorofluorocarbons (HCFCs), which contain hydrogen, as well. Freon is DuPont's brand name for CFCs, HCFCs and related compound

Chemical structure of CFC

They are a class of synthetic chemicals that are odourless, non-toxic, non-flammable, and chemically inert. CFC’s were first synthesized in 1892, but no use was found for it until the 1920s. Their stability and apparently harmless properties made CFCs popular as propellants in aerosol cans, as refrigerants in refrigerators and air conditioners, as degreasing agents, and in the manufacture of foam packaging. They are now known to be partly responsible for the destruction of the ozone layer. In 1987, an international agreement called the Montréal Protocol was established; it was one of the first global environmental treaties and it banned the use of chemicals responsible for ozone damage, such as CFCs in aerosols and refrigerants.

When CFCs are released into the atmosphere, they drift up slowly into the stratosphere, where, under the influence of ultraviolet radiation from the Sun, they react with ozone (O₃) to form free chlorine (Cl) atoms and molecular oxygen (O₂), thereby destroying the ozone layer which protects the Earth's surface from the Sun's harmful ultraviolet rays. The chlorine liberated during ozone breakdown can react with still more ozone, making the CFCs particularly dangerous to the environment. This has indeed been observed, especially over Antarctica. As a consequence, levels of genetically harmful ultraviolet radiation have increased. CFCs can remain in the atmosphere for more than a hundred years. Replacements for CFCs are being developed, and research into safe methods for destroying existing CFCs is being carried out.

CFC,s and their catalytic action on Ozone(O3)

Courtesy: NASA