Air pollutants present in the atmosphere are generally in the form of gases or particles. So, air pollution caused by gaseous pollutants or particulate pollutants can be controlled by different methods.
1. Methods To Control Gaseous Air Pollutants
- Combustion
Combustion method is used for controlling those air pollutants which are present in the form of organic gases or vapours. By combustion the organic air pollutants are converted into relatively less harmful products such as carbon dioxide and water. - Absorption
In this method, the polluted air is passed through a tank containing a suitable liquid absorbent. The liquid absorbent absorbs the gaseous pollutants present in air. In this way, gaseous pollutants are removed from polluted air and air becomes clean. - Adsorption
In this method, the pollute air is passed through a porous solid adsorbent kept in a suitable container. The solid adsorbents adsorbs the gaseous pollutants present in air and make it clean.
2. Methods To Control Particulate Air Pollutants
a) Electrostatic Precipitator
This method is used to remove dust particles, soot and fly-ash from air. An electrostatic precipitator is a cylindrical body having negatively charged electrode (cathode) at its centre. The outer plate of the electrostatic precipitator is made anode by connecting it to the positive terminal of source of current. When a high voltage of 30,000 to 100,000 V is applied, the polluted air present in the electrostatic precipitator gets negatively charged. These negatively charged particles are attracted towards the positively charged outer plate and settle there. These particles can be removed from the outer plate by water or vibration of the electrodes.
b) Fabric Filters
In this method, the polluted air containing particulate pollutants is passed through fabric filters. During passage of polluted air through fabric filters, the particulate pollutants present in air get trapped by filters and air becomes clean.
c) Wet Scrubbers
This method is used to remove those particulate pollutants from air which are soluble in water. In this method, water is sprayed on the polluted air containing particulate pollutants such as dust, soot and fly ash. The water washes away the particulate pollutants present in air and make it clean.
d) Mechanical Devices
The particulate pollutants present in polluted air can also be removed by using mechanical devices which work on following two principles:
Gravity: – In this process, the air containing particulate pollutants is kept undisturbed for sometime in a chamber. During this process, many particles of pollutants settle down due to gravity of earth. In this way air becomes clean.
Sudden change of direction of flow: – The particulate pollutants can also be removed from polluted air by suddenly changing the direction of flow of polluted air.
Apart from the above given methods, air pollution can also be controlled by following methods:
Setting up of industries at a distance from residential areas.
Use of tall chimneys in factories.
- Development and use of non-combustible sources of energy such as wind energy, solar energy, nuclear energy and tidal energy.
- Plantation of more and more trees along road sides and homes.
- Development and use of better designed engines, equipments and hearths in industries and homes.
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