As we know that air consists of a mixture of gases. By volume, about 78% of this mixture is nitrogen and about 21% is oxygen. Carbon dioxide, argon, methane, ozone and water vapour are also present in very small quantities.
When air is contaminated by unwanted substances which have a harmful effect on both the living and the non-living, it is referred to as air pollution.
The substances which contaminate the air are called air pollutants.
The sources of air pollutants are factories, power plants, automobile exhausts and burning of firewood and dung cakes.
Many respiratory problems are caused by air pollution.
Vehicles produce high levels of pollutants like carbon monoxide, carbon dioxide, nitrogen oxides and smoke. Carbon monoxide is produced from incomplete burning of fuels such as petrol and diesel. It is a poisonous gas. It reduces the oxygen-carrying capacity of the blood.
Other kinds of pollutants are chlorofluorocarbons (CFCs) which are used in refrigerators, air conditioners and aerosol sprays. CFCs damage the ozone layer of the atmosphere.
Power plants give out tiny ash particles which also pollute the atmosphere.
India's most famous tourist attraction, Taj Mahal located in Agra, has become a matter of concern. Experts have warned that pollutants in air are discolouring its white marble.
The industries located in and around Agra like rubber processing, automobile, chemicals and especially the Mathura oil refinery, have been responsible for producing pollutants like sulphur dioxide and nitrogen dioxide. These gases react with the water vapour present in the atmosphere to form sulphuric acid and nitric acid. The acids drop down with rain, making the rain acidic. This is called acid rain. Acid rain corrodes the marble of the monument. The phenomenon is also called “Marble cancer”. Suspended particulate matter, such as the soot particles emitted by Mathura oil refinery, has contributed towards the yellowing of the marble.
A part of the radiation that falls on the earth is absorbed by it and a part is reflected back into space. A part of the reflected radiation is trapped by the atmosphere. The trapped radiations further warm the earth.
The trapped heat warms the green house. The trapping of radiations by the earth's atmosphere is similar. That is why it is called the greenhouse effect. Without this process, life would not have been possible on the earth.
Plants utilise CO2 from the atmosphere for photosynthesis, thereby decreasing the amount of CO2 in the air. Deforestation leads to an increase in the amount of CO2 in the air because the number of trees which consume CO2 is reduced. Human activities, thus, contribute to the accumulation of CO2 in the atmosphere. CO2 traps heat and does not allow it to escape into space. As a result, the average temperature of the earth's atmosphere is gradually increasing. This is called global warming.
Global warming has become a major concern for governments worldwide.
Other gases like methane, nitrous oxide and water vapour also contribute towards this effect. Like CO2, they are also called greenhouse gases.
There are many success stories in our fight against air pollution.
The quality of air at various locations is monitored regularly by government and other agencies.
There is a need to switch over to alternative fuels instead of the fossil fuels for our energy requirements. These could be solar energy, hydropower and wind energy.
We saw that water is becoming scarce due to increase in population, industries and agricultural activities.
Whenever harmful substances such as sewage, toxic chemicals, silt, etc., get mixed with water, the water becomes polluted. The substances that pollute water are called water pollutants.
The water get polluted because of the towns and cities, through which the river flows, throw large quantities of garbage, untreated sewage, dead bodies, and many other harmful things, directly into the river. In fact the river is ‘dead’ at many places where the pollution levels are so high that aquatic life cannot survive.
These industries cause chemical contamination of water. The chemicals released include arsenic, lead and fluorides which lead to toxicity in plants and animals. The soil is also affected by impure water, causing changes in acidity, growth of worms, etc.
Water contaminated with sewage may contain bacteria, viruses, fungi and parasites which cause diseases like cholera, typhoid and jaundice. The bacteria present in the faeces of mammals are indicators of the quality of water. If water has these bacteria, it means that it has been contaminated by fecal matter. If such water is used by us, it can cause various infections.
Water which is suitable for drinking is called potable water. You have seen how various physical and chemical processes in the sewage treatment plants help to clean water before discharging it into water bodies.
How water can be made safe for drinking: