These are the sources which release some substances which are capable of undergoing chemical reactions in the atmosphere to generate air pollutants. Example Photochemical smog
(c) Man-made or Anthropogenic sources:
These are the sources which generate air pollutants by human activities Example Vehicular discharges, burning of fossil fuels, population explosion etc
(i) Vehicular discharges:
A mixture of CO, CO2, NOxand RH are emitted as exhaust gases from automobiles. They cause air pollution as such. Moreover, they also react with oxides of nitrogen in the presence of sunlight to produce highly toxic photochemical smog.
(ii) Burning of conventional fossil fuels:
Burning of coal, lignite, natural gas and combustion of petrol/diesel/CNG produces gaseous by-products like CO, S02 NOxwhich is toxic. They pollute the air and make it unfit for breathing.
(iii) Population explosion:
It creates the emission of Greenhouse gases, global warming, destruction and loss of forest cover and wildlife etc.
Air pollutants for which national ambient air quality standards have been given in India
The Central Pollution Prevention and Control Board, New Delhi, has provided the standard for ambient air quality in India under the Act of 1981.
The natural and man-made (synthetic) air pollutants and their consequences
(i) Carbon monoxide (CO):
Sources: Forest fires, agricultural burning, incomplete combustion of fuels, tobacco smoking, automobile exhausts, etc.
Effects: Toxicity, blood poisoning leading to death, increased proneness to accidents.
(ii) Sulphur dioxide (SO2)
Sources: Combustion of coal and petroleum products, sulphuric acid plants, power houses, metallurgical operations
Effects: Irritation of throat and eyes, suffocation, aggravation of asthma and chronic bronchitis.
(iii) Oxides of Nitrogen (NOx):
Sources: Nitric acid plants, automobile exhausts, explosives and fertiliser industries, power stations.
Effects: Headache, respiratory irritation, impairment of lung defences, corrosion of teeth, loss of appetite.
(iv) Mercury (mg) :
Sources: Mining and refining of Hg, industries linked with manufacture of medicinal products, pesticides which use organic mercurials.