4.1. SOURCES OF AIR POLLUTION
Air is everywhere around us and we need clean air for breathing. But did you know that as a result of the addition of some substances to air, it is increasingly becoming toxic for living organisms ? The contamination of air with unwanted substances, which have harmful effects on both plants and animals, is known as air pollution.
The substances that cause the contamination of air are called air pollutants.
Sources of air pollution
There are two source of air pollution are : (i) Natural sources and (ii) Man-made sources
You may have seen on television that during the summer season some forests catch fire. These fires are caused when, as a result of high temperatures, dead plant materials such as barks, twigs, and leaves, which are lying on the forest floor, start burning. These fires emit large amounts of smoke into the atmosphere, thereby polluting the air.
The other natural source of air pollution is volcanoes. Volcanoes emit large amounts of harmful gases and dust particles into the atmosphere, thus contributing to air pollution.
Although natural sources contribute to air pollution, did you know that human activities contribute the most toward air pollution ?
Human activities that cause air pollution include emissions from power plants, automobile exhausts, and factories; burning of fossil fuels and firewood, etc.
Let us now explore various air pollutants and their sources.
I. Carbon monoxide
Carbon monoxide is a toxic, colourless gas. It is produced by the incomplete burning of fossil fuels. It is mainly produced by vehicles.
Smog is formed by the combination of smoke and fog. It is a highly noxious mixture of pollutants that affects the health of living organisms. Smog is a common winter phenomenon in a large number of modern day cities such as Delhi.
III. Oxides of sulphur and Nitrogen
Sulphur dioxide and nitrogen dioxide are major oxides of sulphur and nitrogen that act as pollutants. These are released from petroleum refineries and also from power plants that use coal as a fuel.
Chlorofluorocarbons are also known as CFCs. They are used in refrigerators, air conditioners, and aerosol sprays. They cause damage to the ozone layer in the atmosphere.
V. Suspended Particulate Matter (SPM)
These are tiny particles that are produced on the burning of coal and petroleum. They are also released during industrial processes such as mining and making of steel.
4.2. EFFECTS OF AIR POLLUTION ON LIVING ORGANISMS
Air pollution has significant health effects on all living organisms including human beings.
Various air pollutants cause diseases that range from skin cancers to respiratory disorders. Let us examine in detail the effect that each pollutant has on living organisms.
I. Carbon monoxide
Carbon monoxide is a pollutant that is released as a result of the incomplete burning of fuels such as diesel and petrol. What effect does carbon monoxide have on the health of humans ?
Carbon monoxide combines with haemoglobin, which is present in the red blood cells, and decreases the oxygen-carrying capacity of blood.
II. Sulphur dioxide
Sulphur dioxide is a pollutant that is produced during the combustion of fuels such as coal. It causes many respiratory problems such as cough and throat irritation when inhaled in small amounts. Continuous exposure to sulphur dioxide may cause permanent damage to the lungs.
III. Nitrogen dioxide
Exposure to nitrogen dioxide causes damage to the lungs apart from other respiratory disorders.
Some of you may have seen a thick fog-like layer in the atmosphere during the winter months. This is smog. Smog is formed when smoke mixes with fog.
Smog is made up of many air pollutants such as the oxides of nitrogen. It causes breathing difficulties such as asthma, cough, and wheezing among children.
VI. Chlorofluorocarbons (CFCs)
Chlorofluorocarbons are responsible for damaging the ozone layer and have led to the formation of the ozone hole in the atmosphere. A rapidly depleting ozone layer allows the harmful UV radiations of the sun to reach the Earth, which is responsible for an increase in the cases of skin cancers.
VII. Suspended particles
Suspended particles are tiny particles that are produced because of the burning of fossil fuels. They trigger many respiratory diseases such as asthma and sneezing when inhaled.
The hair present in the nostrils prevents the suspended dust particles from entering our lungs. However, some dust particles are so small that they cannot be trapped in the nostrils and they enter the respiratory system.
4.3. EFFECT OF AIR POLLUTION ON NON-LIVING OBJECTS
All of us have seen the Taj Mahal, either in reality or in pictures. Did you know that the Taj Mahal is in danger because of rising air pollution levels ? Taking the Taj Mahal as a case study, let us explore how air pollution affects non-living objects such as buildings and monuments. The industries present around the Taj Mahal, especially the Mathura oil refinery, are primarily responsible for the damage caused to the monument.
Acid rains are very harmful. These rains cause widespread damage to several materials and property, especially to monuments, which undergo heavy corrosion as a result of these rains. Acid rains have corroded the marble of the Taj Mahal, a phenomenon also known as Marble-cancer.
This particulate matter released from Mathura oil refinery is responsible for the yellowing of the marble of the Taj Mahal.
What are we doing to protect the Taj Mahal or other monuments from the harmful effects of air pollution ? Let us find out.
The Supreme Court of India has taken many steps in the direction of protecting the Taj Mahal from pollution. It has directed the industries around the Taj Mahal to use cleaner fuels such as LPG (Liquefied Petroleum Gas) and CNG (Compressed Natural Gas). In addition, all vehicles have been ordered to switch-over to unleaded petrol. CNG and LPG are clean fuels. Hence, they do not produce soot on burning.
4.4. GREENHOUSE EFFECT AND GLOBAL WORMING
Have you seen a greenhouse in a nursery where plants are kept? A greenhouse is a structure that traps the sun’s heat and does not allow it to escape. This provides a warm atmosphere for the plants to grow.
We know that the sun’s rays keep the Earth’s surface warm. Some of the solar radiation is absorbed by the Earth, while a part of it is reflected back into space. This reflected radiation is trapped by the atmosphere of the Earth.
This phenomenon, which imitates the greenhouse of a nursery, is known as the greenhouse effect.
How does the greenhouse effect affect our environment ?
There are a few gases in the atmosphere that aggravate the greenhouse effect. These gases are called greenhouse gases. The levels of these gases in the atmosphere have increased as a result of increasing pollution levels. Carbon dioxide is one of the gases that cause the greenhouse effect.
Carbon dioxide (CO2) is a natural component of the atmosphere. How can a natural part of the Earth pose a threat to life ?
All of us know that plants absorb carbon dioxide from the atmosphere to synthesize their own food through the process of photosynthesis. However, as a result of deforestation, the number of trees has gone down drastically. This has reduced the uptake of carbon dioxide by trees, which in turn has led to an increase in its concentration in the atmosphere. The burning of fossil fuels further adds to the carbon dioxide levels in the atmosphere. As a result, more and more solar radiation is being trapped in the atmosphere, thereby leading to an increase in the Earth’s temperature. This warming-up of the Earth is termed as global warming. Other gases such as methane, nitrous oxide, and water vapour also contribute to the greenhouse effect.
What are the likely consequences of global warming ?
Global warming will result in extreme temperature conditions. There will be changes in the precipitation patterns that may lead to floods and droughts. The water trapped in the ice caps of the Polar Regions will start melting at a rapid rate, which will cause the sea levels to rise. Even a marginal increase in the temperature of the Earth (i.e., +0.5°C) may lead to serious disasters.
4.5. INITIATIVES TO REDUCE AIR POLLUTION AND GLOBAL WARMING
Air pollution and global warming pose a serious threat to the Earth.
What initiatives can we take to reduce these problems ?
The government of Delhi has taken several initiatives to reduce the levels of air pollution in the city. Delhi was ranked among the most polluted cities of the world till a few years ago. The air in the city was heavily laden with fumes and poisonous gases from automobiles. On the intervention of the Supreme Court, a decision was taken to introduce CNG (Compressed Natural Gas) as a fuel to run the public transport system of Delhi.
In addition, the use of unleaded petrol was made compulsory. The results of these initiatives reflected in the quality of air. The air in Delhi now is much cleaner as compared to the past. Thus, the use of CNG and unleaded petrol are a few of the measures that can be taken to reduce air pollution.
Measures to help combat air pollution
One measure of preventing air pollution and global warming involves the switching over from traditional fuels to alternative, cleaner fuels such as solar energy, wind energy, and hydropower energy. Unlike fossil fuels, these alternative sources of energy do not cause pollution and can be tapped from nature, where these are available in abundance.
The burning of dry leaves causes a lot of pollution. Therefore, instead of burning them, one can bury these leaves in a compost pit. The leaf compost thus obtained can be used as manure for plants.
Planting of trees is another measure that can be taken to reduce air pollution. Plants use carbon dioxide during photosynthesis. Thus, planting more trees will increase the utilization of carbon dioxide from the atmosphere. This will reduce the carbon dioxide concentration in the atmosphere and will help in reducing the growing effects of global warming. In India, Van Mahotsav is celebrated every year during the rainy season in the months of July and August. During this period, large scale plantation of trees is carried out.
4.6. WHAT IS WATER POLLUTION ?
The addition of harmful substances to water which causes its physical, chemical and biological properties to change is called water pollution.
The substances that pollute water are called water pollutants. Sewage, toxic chemicals, silt etc. are examples of water pollutants.
Sources of water pollution
All of you are aware that Ganga is one of the most important holy rivers of India. It supports the lives of millions of people living in the northern plains. According to a study by the WWF, Ganga is one of the ten most endangered rivers.
The river Ganga is practically dead at many places. This is because the pollution levels in the river are so high that it cannot support any life form. The portion of the river that flows through the city of Kanpur is a stretch that is completely dead.
The factors that have contributed to the increase in the pollution levels of the river are
• Dumping of large quantities of garbage into the river
• Releasing of untreated sewage water into the river
• Throwing of dead bodies into the river
• Washing, bathing, and defecating near the shores of the river
• Throwing flowers and idols of gods and goddesses into the river
• Dumping non-biodegradable substances such as polythene bags into the river.
These are common factors that are responsible for polluting the rivers of our country. In addition, factories manufacturing fertilizers, detergents, leather goods, and paints that are located near a river, throw their industrial wastes and toxic chemicals into the river. This makes the water of the river unfit for use by living organisms.
In order to address all the above mentioned problems, the Ganga Action Plan was launched in the year 1985 with the purpose of reviving the river. However, unplanned urbanisation and industrialization has taken its toll on the river and it has been damaged beyond repair.
4.7. EFFECTS OF WATER POLLUTION ON LIVING ORGANISMS
I. Industrial waste
In the absence of proper treatment facilities for industrial wastes, most of these wastes are directly dumped into the rivers. The industrial wastes from oil refineries, chemical factories, sugar mills, and fertilizer plants carry toxic substance such as arsenic, lead, mercury, and fluoride. These substances cause toxicity in plants and animals.
They also pollute the soil by increasing its acidity, decreasing its fertility, and affecting the growth of worms which are beneficial for the soil.
II. Pesticides and fertilizers
We know that fertilizers and pesticides are a farmer’s friends as these help in killing the pests and weeds and increasing the fertility of the soil. The chemicals that are contained in these pesticides and fertilizers get dissolved in the water and eventually get washed away to the water bodies. They also seep into the ground and pollute the ground water.
On entering the water bodies, these pesticides and fertilizers increase the nutrient content of the soil as they contain various nutrients. This accelerates the growth of algae in the water bodies. You may have observed that some water bodies appear green in colour. This is because of the excessive growth of algae in water.
When these algae die, they are decomposed by the action of micro-organisms that are present in water. Consequently, the number of these micro-organisms in water bodies increases. Since they consume a large quantity of oxygen that is present in the water, it leads to a decrease in the levels of oxygen. The absence of oxygen eventually leads to the death of the living organisms.
Sewage is waste water that contains faecal matter, urine, food wastes, detergents, and other solid substances. Sewage contains many disease-causing pathogens such as bacteria, fungi, viruses, and parasites. When drinking water gets contaminated with sewage water, these harmful organisms enter the bodies of the living organisms and cause several diseases. Some of the diseases caused by the drinking of contaminated water and the names of the respective causal organisms are listed in the table.
Name of the disease
Amoebic dysenter y
Sever al bacteria are present in the faeces of mammals. If the water is contaminated with faeces, then these bacteria function as indicator organisms for the quality of water i.e., the number of these faecal bacteria indicates the extent to which the water is contaminated by faecal matter.
4.8. CONSERVATION AND PURIFICATION OF WATER
Water is a precious resource and we need to conserve it. Water can be conserved by following the simple principle of reduce, reuse, and recycle. This can be practiced easily at homes. Some examples are
• Reusing the waste water from the kitchen (water that has been used to wash vegetables etc.) to water the plants in the garden
• Reusing the water after washing clothes to wipe the floor or to clean the car
• Turning the tap off while brushing or shaving
• Checking for leaky taps and fixing them up
Thus, we can reduce the total amount of water consumed by us by recycling and reusing most of the waste water for other purposes.
The waste water from industries first needs to be treated in sewage treatment plants. This water can then be used for growing plants and other industrial purposes.
Purification of water
Potable water is the water that is safe for drinking. Although the water may look clean on mere observation, it may contain disease-carrying micro-organisms. In order to prevent the occurrence of diseases, this water has to be cleaned and only then can it be used safely for drinking.
Methods to purify water
I. Physical methods
Filtration : It is one of the common methods used for removing impurities from water. A simple filter paper can be used to obtain clean water. Candle-type filters that are commonly used in households are also based on the principle of filtration.
Boiling : Boiling the water helps in killing the germs present in water.
II. Chemical Methods
Adding chlorine to water is one of the most commonly used methods of purifying water. Chlorine, when used in the prescribed amount, kills the germs present in water and makes it safe for consumption. You may have observed that tap water sometimes appears milky. This is because it contains chlorine.
Adding bleaching powder helps in purifying water.