Air Pollution: Origin, Nature, Size and Impact of Air Pollution!
Air pollution is the result of the combined effects of several pollutants. These pollutants are associated with each other and also react with other elements, therefore, it is difficult to categories them, but for proper understanding they can be divided into the following categories on the basis of their origin, nature, size, impact, etc.
1. According to origin, particulate matter can be divided into two types, viz., natural and man-made. The natural form of particulate matter is the result of volcanic dust and gases, mineral dust and sea-salt crystals. Another class of natural particulate matter is smoke from forest and grass fires.
Living plants release pollens and spores into the air, which are organic compounds. From forest trees certain hydrocarbons called terrenes are also released into the atmosphere.
Man-made particulate matter comes from many sources, but its major source is the combustion of hydrocarbon fuels—petroleum products, coal, peat and wood. Combustion of solid wastes is another source. Other kinds of matter introduced into the atmosphere are industrial chemicals, fly ash, refining fossil fuels, mining and smelting ores, as well as pollutants discharged through quarrying, farming activities, etc. Use of various types of solvents and also radioactive elements are the cause of air pollution created by man.
2. Another classification, according to origin, is (i) primary and (ii) secondary pollutants. The primary pollutants are those gaseous and other solid micro particles inducted to the atmosphere. These pollutants are emitted and as such are not found in the air. The most important gaseous pollutants are carbon monoxide, oxides of sulfur, hydrogen sulfide, hydrocarbons, oxides of nitrogen, ozone and other oxidants. Secondary pollutants are the result of chemical reactions.
Evidences and experiments indicate that exhaust gases of automobiles contribute more in the formation of secondary pollutants. For example, oxides of nitrogen produced in the combustion of petroleum and other fuels emitted into the atmosphere, yield ozone in the presence of sunlight. It is to be noted that ozone is not emitted as such into the atmosphere but formed only from primary pollutants.
3. According to chemical composition, air pollutants can be divided into organic and inorganic pollutants. Others have divided them into solid, liquid and gaseous pollutants. The gaseous pollutants are carbon monoxide, sulfur dioxide, hydrogen sulfide and organic sulfide, hydrogen fluoride, hydrogen chloride, oxides of nitrogen, aldehydes and organic acids, etc. Particulate pollutants consist of both solid and liquid particles. They vary in size from 0.01 micron to 20 microns. Dust, fume, mist, spray and smoke are included in this category.
4. According to source type, pollutants can be classified as being produced from:
(ii) Transportation emissions,
(iii) Industrial processes,
(iv) Use of solvents, and
Combustion processes yield particulates such as fly ash and smoke and oxides of sulfur and nitrogen.
The amount of sulfur dioxide emitted depends upon the contents in the fuel. High temperature processes such as thermal fixation of atmospheric nitrogen yield larger quantities of oxides of nitrogen. Carbon monoxide is also emitted from combustion. The other contaminants that are produced by combustion include acids and aldehyde.
The simplest form of combustion is the use of fuels in domestic use. In most developing countries, including India, wood, coal, cow-dung and kerosene are commonly used for cooking. All these materials yield carbon dioxide, carbon monoxide, sulfur dioxide, etc.
Automobiles may be considered as the main source of air pollution, especially in urban areas. Automobile exhausts release smoke and to a certain extent lead particles also. Smoke contains the gaseous pollutants carbon monoxide, hydrocarbons and oxides of nitrogen.
The pollutants emitted by petrol and diesel driven vehicles are as follows:
Pollutants Emitted by Petrol and Diesel Driven Vehicles:
The rapid rate of industrialisation has resulted in more and more air pollution. Various industrial processes release almost all types of pollutants into the air. Some industries like cement, iron and steel, fertiliser, petrochemical, etc., are of great concern because of the difficulty in controlling the emission of pollutants from them.
Acid rain has become a great threat to the environment. The use of solvents is increasing with the growing use of paints, spray, polish, etc. Due to the presence of hydrocarbons in these materials, air pollution is caused, which is dangerous for health. Similarly, spray of pesticides in agriculture is also responsible for air pollution even in rural areas.
Nuclear material, when released into the air, is hazardous for all living organisms. Nuclear weapon testing’s, nuclear reactors, chemical processing plants, research institutes and hospitals contribute many radio nuclides to the atmosphere.