Stratosphere

The 2nd layer of the earth atmosphere, Stratosphere is explained in detail in this presentation....

1. The Earth’s Atmosphere بِسْمِ ٱللَّٰهِ ٱلرَّحْمَٰنِ ٱلرَّحِيمِ Prepared By: Talha Liaqat BS chemistry, KFUEIT

2. Different layers of the atmosphere The atmosphere is comprised of layers based on temperature. These layers are the troposphere, stratosphere, mesosphere and thermosphere. A further region at about 500 km above the Earth's surface is called the exosphere.

3. Stratosphere The stratosphere is the 2 nd  layer of Earth's atmosphere  as you go upward. The troposphere the lowest layer, is right below the stratosphere. The next higher layer above the stratosphere is the mesosphere. The bottom of the stratosphere is around 10 km (6.2 miles or about 33,000 feet) above the ground at middle latitudes.

4. Stratosphere The top of the stratosphere occurs at an altitude of 50 km (31 miles). Ozone, an unusual type of oxygen molecule that is relatively abundant in the stratosphere Ozone heats this layer as it absorbs energy from incoming ultraviolet radiation from the Sun. Temperatures rise as one moves upward through the stratosphere.

5. Temperatures rise as one moves upward through the stratosphere. This is exactly the opposite of the behavior in the troposphere in which we live, where temperatures drop with increasing altitude. Commercial jet aircraft fly in the lower stratosphere to avoid the turbulence which is common in the troposphere below. Stratosphere

6. Chemical composition of Stratosphere Most of the compounds released at the Earth's surface do not reach the stratosphere, instead they are: decomposed by the main tropospheric oxidants (hydroxyl radicals - OH, nitrate radicals - NO 3 , ozone - O 3 ) broken down by sunlight deposited back to the surface of the Earth in rain or as particles trapped in the cold tropopause.

7. Inorganic compounds in the stratosphere Stratospheric chemistry is dominated by the chemistry of ozone between 85 and 90% of all the ozone in the atmosphere is found in the stratosphere. Ozone is formed when sunlight breaks down molecular oxygen (O 2 ) in the stratosphere into oxygen atoms (O).  The highly reactive oxygen atoms then react with more molecular oxygen to form ozone (O 3 ).    Compounds such as ozone, nitrogen oxides, nitric acid, sulphuric acid, chlorofluorocarbons halogens are the dominant chemicals in the stratosphere.

8. Volacanic Eruptions Volcanic eruptions can inject large quantities of gases and particles directly into the stratosphere. The particles such as and sulphur dioxide (SO 2 ) which is converted to sulphuric acid (H 2 SO 4 ) emitted include silicates and sulphates and these absorb sunlight in the stratosphere.  It lead to a temporary warming in the stratosphere and a temporary cooling in the troposphere.  These effects on temperature can last around 1 - 2 years.

9. The Ozone Layer The ozone layer or ozone shield is a region of Earth's stratosphere that absorbs most of the Sun's ultraviolet radiation. It contains a high concentration of ozone (O 3 ) in relation to other parts of the atmosphere, although still small in relation to other gases in the stratosphere. The ozone layer is mainly found in the lower portion of the stratosphere, from approximately 15 to 35 km above Earth, although its thickness varies seasonally and geographically.

10. The Ozone Layer

11. The Ozone Layer

12. Depletion of Ozone Layer The ozone layer can be depleted by free radical catalysts. Free radicles including nitric oxide (NO), nitrous oxide (N 2 O), hydroxyl (OH), atomic chlorine (Cl), and atomic bromine  (Br). The concentrations of chlorine and bromine increased markedly. Man made organo-halogen compounds include especially chlorofluorocarbons  (CFCs) and bromofluorocarbons. 

13. Depletion of Ozone Layer These highly stable compounds are capable of surviving the rise to the stratosphere. While Cl and Br radicals are liberated by the action of ultraviolet light. Each radical is then free to initiate and catalyze a chain reaction. Each chain reaction is capable of breaking down over 100,000 ozone molecules.

14. Ozone Hole Nitrous oxide  is the largest ozone-depleting substance, and is expected to remain the largest throughout the 21st century. The breakdown of ozone in the stratosphere results in reduced absorption of ultraviolet radiation.  Unabsorbed and dangerous ultraviolet radiation is able to reach the Earth's surface at a higher intensity. Depletion of the protective ozone layer in the upper atmosphere (stratosphere) is Called Ozone Hole.