The clean air is very essential for human life and human health. It should be free from pollutants in any form. The pollutants may be in the form of solid, liquid or gaseous form. Any considerable change in the composition of air may affect the living system of the humans.
Air Pollution is defined as the pollution in the atmospheric air, due to the presence of solid, liquid, or gaseous material and causes the problems to humans, living systems, plants etc.
A Pollutant is defined as a material (or substance) which creates the air pollution and in the form of liquid, gaseous or solid. Generally, any pollutant, solid, liquid or gaseous material affects the atmospheric air considerably and creates harmful effects on the environment.
1.2. STRUCTURE AND COMPOSITION OF ATMOSPHERE
The atmosphere of earth is a layer of gases, surrounding the planet Earth, which is retained by gravitational force of the earth. It extends to about 500 km from the Earth's*Structure of Atmosphere
Earth's atmosphere can be divided into five main layers. From the lowest to highest, these layers are,
1. Troposphere (0 to 12 km)
2. Stratosphere (12 to 50 km)
3. Mesosphere (50 to 80 km)
4. Thermosphere (80 to 500 km)
5. Exosphere (above 500 km)
1. Troposphere is the nearest gaseous layer and the lowest layer of the atmospheric Earth, extending from the Earth's surface up to an average distance of about 12 km. This altitude actually varies from about 9 km (30000 ft) at the poles to 17 km (56,000 ft) at the equator, with some variations due to weather.
Solar radiation is the main heat source, and the ground level and hence, the temperature decreases with increase in height of the troposphere.
The rate at which the temperature.
2. Stratosphere
The Stratosphere is the second layer of Earth's atmosphere, just above the troposphere (Tropopause - TP)and below the mesosphere, extending to 50 km (SP).
The temperature increases gradually from about -80 °C to 0 °C between the Tropopause (TP) to (SP). The increase in temperature is due to the absorption of Ultra - Violet Radiation from the sun by oxygen and ozone, which restricts turbulence and mixing. There is very little water vapor at this layer.
Ozone layer is the layer in the stratosphere which exists between 20 km, 40 km above the earth's surface. Hence, stratosphere is sometimes referred as ionosphere.
Ozone layer protects all Ultra - Violet, Ultra - Violet Radiation from the Sun.
The atmospheric pressure at the top of the stratosphere 1 (Tropopause) is approximately equal to times the 1000 pressure at the sea level.
The stratosphere is almost completely free from clouds and other forms of weather. However, Polar stratospheric or Nacreous clouds are occasionally seen in the lower parts of the stratosphere, where the air is cold. This is the highest layer that a Jet-Powered Aircraft can be accessed.
3. Mesosphere
The Mesosphere is the third layer from the Earth's surface, extending from stratosphere of about 50 km to 80 km from the ground surface. It is the coolest place of the earth's atmosphere and has an average temperature of about -85 °C. The top level of the mesosphere is called Menopause (MP) and just below the menopause, the air is highly cold. Within the mesosphere, the temperature decreases with increasing altitude. This is due to the increasing cooling by CO, relative emission and due to decreasing solar heating.
The mesosphere lies above the maximum altitude for aircraft and below the minimum altitude for orbital spacecraft. It has been only accessed through the use of sounding rockets. As a result, it is the most poorly understood part of the atmosphere.
The stratosphere, mesosphere and the lowest part of the atmosphere is collectively referred as 'Middle Atmosphere', which has the altitudes approximately from 10 km to 100 km above the earth's surface.
4. Thermosphere is the zone above and extends that an altitude of about 80 km up to 500 km. The height of van considerably due to the changes in solar activity lies at the lower boundary of the exosphere Co. The lower part of the
(from 80 to 480 above the earth's surface) contains many ions, and electrons. Cosmic rays and radiations from the sun pro the ions, and this part of the thermosphere is called ionosphere.
5. Exosphere
The outermost layer (or region) of the atmosphere, beyond the height of 500 km and above, is called Exosphere. It is a low density, high temperature region with minimum atomic collisions. The exosphere merges with the emptiness of outer space, where there is no atmosphere.
This layer is mainly composed of extremely low densities of H₂, He and other heavier molecules such as N, O, and CO. The exosphere is located too far above the Earth, for any meteorological factor to be possible. Most of the satellites, orbiting the earth, are located in the exosphere.
2. Other layers
Within the primary layers, which are differentiated by temperature, several secondary layers are also distinguished by other properties, and as follows.
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