Different layers of atmosphere
Troposphere
A steady decrease in temperature occurs from the ground temperature to about 210 K with the increase in altitude in this region. Due to a fall of pressure and density of air, the temperature falls. This feature extends to about 12 km from the surface and its upper limit is called tropopause. This lies between 10-20 km above the Earth's surface.
Stratosphere
This region extends up to 50 km above the Earth's surface. The upper limit of this region is called stratopause. This is a region of ozone activity and is known as ozonosphere. It is characterized by increase in temperature with increase in altitude. The rise in temperature in this region is due to ozone present in this region, which absorbs the ultraviolet radiation of the Sun. The concentration of ozone varies between 1 to 5 ppm by volume. The maximum temperature attained in the stratopause is about 270 K.
Mesosphere
This region extends from 50 km to 85 km in altitude. The temperature once again decreases rapidly in the region to about 160 K. The upper limit of the mesosphere is called mesopause.
Thermosphere
This is the last region of the atmosphere and extends above 85km. It is characterized by continuous rise in temperature.
Role of Ozone Layer
The stratosphere or ozonosphere protects the Earth from the infrared/ultraviolet radiation coming from the Sun. Ozone absorbs U.V. radiations and prevents most of them in reaching the Earth's surface.O3 
O + O2
Also, O2 + hv
The above naturally occurring chemical reactions show how ozone is simultaneously being formed and destroye.
Depletion of ozone layer
The influx of several substances into the atmosphere such as CFCs, halons and oxides of nitrogen caused by human activity, have disturbed the equilibrium between formation and destruction of ozone. These gases react with ozone to destroy it. The rate at which ozone is being destroyed is much faster than the rate at which it is being formed. Factors accelerating the ozone depletion are due to the influx of several substances into the atmosphere, such as:
Effect of Chlorofluorocarbons (Freons)
The use of chlorofluorocarbons gases (CFC) is posing a grave threat to the existence of ozone in the stratosphere. CFCs have a wide range of applications due to their properties like non-corrosiveness, non-inflammability, low toxicity and high chemical stability. They are used as refrigerants, propellants in aerosol sprays, foaming agents in plastic manufacturing, fire extinguishing agents and solvents for cleaning electronic and metallic components etc. The main CFCs in use are Freon 1 (CFCl3) Freon 12 (CCl2F2), Freon 22 (CHCl2F), Freon 113 (CCl2FCClF2) and Freon 114 (CClF2CClF2).
CFCs are chemically inert gases. Once these enter the atmosphere they do not react with any substance and thus cannot be eliminated. By gradual evaporation from their source, they float unchanged upwards and eventually enter the stratosphere.In stratosphere, they absorb the U.V. radiations and break up liberating free chlorine atom. The chlorine atom reacts with O3 to form chlorine monoxide (ClO), which further combines with O to give oxygen.
Thus, we find that element chlorine (Cl) that destroys O3 is regenerated at the end. A single chlorine atom can thus destroy millions of O3 molecules which eventually result in depletion of ozone.
Use of Halons
Halons are bromofluorocarbons that are used as fire extinguishers and pesticides. Halons produce bromine atoms by a similar process, causing the destruction of a very large number of ozone molecules.
Oxides of nitrogen
The sources of oxides of nitrogen are mainly emissions from chemical and metal fabrication plants, agricultural fertilizers, automobile emissions, electric power plants and explosion of thermonuclear weapons in the atmosphere. NO molecule also catalytically converts O3 to O2 like Cl and Br atoms. The mechanism for the destruction of the ozone layer is:
Here, NO is a catalyst (used and returned) while NO2 and O (oxygen free radical) are intermediates (created and destroyed).
Effect of depletion of ozone layer
The depletion of ozone layer poses a severe threat to mankind. Along with the above-mentioned gases, other pollutants such as methane (CH4), carbon dioxide (CO2) have caused a hole in the ozone layer. A hole or a decreased concentration of ozone in stratosphere results in the influx of increasing U.V. radiations reaching the surface of Earth. Medical scientists have pointed out that larger exposure to U.V. radiations, due to decrease in ozone concentration, leads to 2% increase in risk to skin cancer. U.V. radiation also tend to damage the immune system which may lead to increased viral infections. Excessive exposure to U.V. radiations also damages vegetation, aquatic animals and plants.
Problem
4. Which parts of the atmosphere does the temperature increase with increasing altitude? Is this important?
Solution
The parts of atmosphere where temperature increases with increasing altitude are stratosphere and thermosphere. The increase in temperature is important in the region called the stratosphere, which also houses the ozonosphere. As we go upwards from the Earth, a fall of pressure and density of air causes the temperature to fall. However after approximately 12 km the phenomenon is reversed.
The stratosphere is characterized by increase in temperature with increase in altitude, primarily due to it being a region of ozone activity. Ozone gas present in this region absorbs much of the harmful ultraviolet radiation of the Sun and prevents most of them in reaching the Earth's surface. The ozonosphere also gives the greenhouse effect by trapping heat in this layer, keeping the Earth warm.