Air pollution began in the earliest stage of human civilization. It dates back to the discovery of fire and its various use in various activities. However, air pollution has become aweful in modern times. The air we breathe these days in not as pure as it was hundreds of years before.
The principal sources of air pollution are: powerplants, automobiles, industries, burning of water etc. The pollutants discharged from them may be classed as (a) common dust, ash, smoke, soot, dense fog and solid and liquid particulate materials; (b) gases like carbon dioxide, ammonia, chloride, fluorides and sulphides of hydrogen, oxide of nitro- gen, nitric acid etc. The extremely tiny particles of solid and liquid float in air in the form of aerosols
For producing power huge amount of coal and petrolium oil are burnt in the power plants. The smoke emitted from the chimneys contains carbon monoxide, silver oxide and oxides of nitrogen etc. All these are poisonous gasses. Besides sulphur dioxide is produced from burning of fossil fuels.
The automobiles like cars and other motor transport give out the highest amount of carbon monoxide into the atmosphere. The diesel car exhaust emits oxide of nitrozen and other gases containing particles of lead which pollutes the biosphere.
The industries give out large amount of water containing dust of metallic power and such other injurious substances.
Burning of agricultural waste and forests create thick fog like smoke and pollute the atmosphere.