Acid Rain and Green house effect

Question 1 What is green house effect? State its importance for us?

Question 2 Name few greenhouse gases?

Question 3 What depletes the ozone layer in the atmosphere?

Question 4 What are the harmful effects of the depletion of ozone layer?

Question 5 Describe the threat to Taj Mahal monument due to air pollution?

Question 6 What is acid rain? How is acid rain caused? What are the harmful effects of acid rain?

Question 7 What is global warming? What are the harmful effects of global warming?

Acid Rain

The burning of fossil fuels like coal and oil in factories, thermal power plants and oil refineries, and petrol and diesel in motor vehicles produce acidic gases like sulphur dioxide and nitrogen oxides which go into air and pollute it.

Sulphur dioxide reacts with water vapour present in the atmosphere to form sulphuric acid whereas nitrogen oxides react with water vapour present in the atmosphere to form nitric acid.

Acid rain is that rain which contains small amounts of acids formed from acidic gases like sulphur dioxide and nitrogen oxides present in polluted air.

Acid rain causes great damage to living and non-living things.

Harmful effects of Acid Rain

(1) Acid Rain Destroys Forests

(a) Acid rain damages the forest trees by destroying their leaves.

(b) It causes the leaves of trees to turn yellow and fall off.

(c) In the absence of leaves, the roots of trees cannot absorb water from the soil. And due to lack of water the trees die.

(d) Acid rain also damages a lot of crop plants every year and causes a big loss to the farmers.

(e) Acid rain makes the soil acidic. This acidic soil is not good for the growth of crop plants.

 

(2) Acid Rain Kills Aquatic Animals Such as Fish

Acid rain causes the water in ponds, lakes and rivers to become much more acidic and unsuitable for the survival of aquatic animals and plants. Due to high acidity of water, the aquatic animals such as fish get killed.

(3) Acid Rain Corrodes the Statues, Buildings and Historical Monuments and Damages them Slowly

The statues, buildings and monuments are made of marble or limestone, etc. The acids present in acid rain react with the carbonates present in marble and limestone of a statue, building or monument and corrode it slowly (dissolve it slowly). In this way, acid rain makes the statues, buildings and monuments to crumble away slowly.

The Case of Taj Mahal

The Taj Mahal at Agra (near Delhi) is a beautiful historical monument made of pure, white marble . The experts have warned that air pollution around Taj Mahal area is discolouring its white marble and also corroding it slowly. This poses a threat to the beauty of Taj Mahal.

The Mathura Oil Refinery near Agra as well as the various industries in and around Agra are emitting gaseous pollutants such as sulphur dioxide and nitrogen oxides into the air which cause acid rain. The acids present in acid rain react with the marble (calcium carbonate) of Taj Mahal monument and corrode it slowly. The slow corrosion (or eating up) of marble of a monument by acid rain is also known as Marble Cancer. The suspended particulate matter such as soot particles emitted in the smoke from Mathura Oil Refinery is discolouring the pure white marble of Taj Mahal by turning it yellowish. The Supreme Court of India has ordered all the industries in Agra to switch over to cleaner fuels like CNG and LPG to reduce air pollution.

It is not only the living things (such as humans, other land animals, aquatic animals like fish, trees and crop plants, etc.) which are affected by air pollution, even the non-living things (such as soil, statues, buildings and historical monuments) get affected by air pollution.

Greenhouse Effect

The greenhouse is a structure or building made of glass walls and glass roof in which the plants that need protection from cold weather are grown . The glass walls and glass roof of a greenhouse allow the sun’s heat rays to go in freely but do not allow the inside heat to go out. In this way, more and more of sun’s heat rays are trapped inside the greenhouse due to which the temperature in the greenhouse rises. So, even without an internal supply of heat, the temperature inside a greenhouse becomes higher than that outside. This heat is beneficial for the growth of plants inside the greenhouse (when the outside temperature is very low during winter season). Thus, greenhouse acts as a heat trap (which traps sun’s heat energy). 

The sun is an extremely hot object due to which the heat rays emitted by the sun are of shorter wavelengths. The shorter wavelength heat rays coming from the sun can pass through the glass walls and glass roof of a greenhouse and go inside it. The inside objects of glasshouse are much less hot (than the sun), so they emit heat rays of longer wavelengths.

The longer wavelength heat rays emitted by the inside objects of the greenhouse cannot pass through the glass walls and glass roof of a greenhouse and go out. Thus, glass is a material which allows sun’s heat rays to come in but does not allow heat rays to go out. This is called greenhouse effect. Due to the presence of a carbon dioxide layer around the earth, our atmosphere acts like the glass roof of an ordinary greenhouse and allows sun’s heat rays the earth’s atmosphere. This is why it is called greenhouse effect.

Carbon dioxide gas present in the atmosphere allows the heat rays of the sun to pass through it and reach the earth but prevents the heat rays reflected from the earth’s surface and its objects from passing out of the atmosphere into space. In this way, the sun’s heat rays remain trapped in the earth’s atmosphere and warm it up .

The warming up (or heating up) of the earth’s atmosphere due to the trapping of Sun’s heat rays by carbon dioxide gas in the atmosphere, is called greenhouse effect.

The warming (or heating) of the earth produced by greenhouse effect is important for the existence of life on the earth. This is because it is due to the warming of earth by the greenhouse effect that the earth has become a habitable planet having millions of different life forms on it.

If there were no warming up of the earth’s atmosphere due greenhouse effect produced by carbon dioxide gas in the atmosphere, the whole earth would have been  converted into an extremely cold planet, making the existence of life difficult on it.

 

The problem arises when the amount of carbon dioxide gas in the atmosphere increases too much leading to the excessive heating of earth and its atmosphere.

(a) Carbon dioxide is added to the atmosphere mainly by the burning of fossil fuels like coal petroleum products (like kerosene, petrol, diesel, LPG) and natural gas.

(b) Carbon dioxide is removed from the atmosphere by the plants and trees for making food by photosynthesis.

These two opposing processes keep the amount of carbon dioxide in the atmosphere fairly constant. These days, the fossil fuels are being burned at a very rapid rate (to meet the energy requirement of increasing population) due to which the amount of carbon dioxide gas in the atmosphere is increasing day by day. At the same time, the number of plants and trees (which remove carbon dioxide gas from the atmosphere through photosynthesis) is decreasing day by day due to deforestation and damage by acid rain.

Due to the rapid burning of fossil fuels and decrease in forests (plants and trees), the amount of carbon dioxide gas in the atmosphere is increasing steadily. The extra carbon dioxide present in the atmosphere is trapping more heat energy of the sun due to increased greenhouse effect. And because of increased greenhouse effect, the temperature of earth’s atmosphere is increasing day by day. If the proportion of carbon dioxide gas in the atmosphere goes on increasing like this, then the temperature of earth’s atmosphere will also rise further. This will lead to the excessive heating of the earth.

Global Warming

The undue rise in the temperature of earth’s atmosphere due to excessive greenhouse effect produced by increasing amounts of carbon dioxide gas in the atmosphere, is called global warming.

Global warming is harmful to us:

(1) Global Warming Can Cause Sea-Levels to Rise Dramatically

The rise in temperature of atmosphere due to excessive greenhouse effect or global warming will melt the enormous amount of ice lying on the poles of the earth. The huge amount of water produced by the melting of polar in seas and oceans, and flood the low-lying areas of the earth. This will cause damage to life and property.

(2) Global Warming Can Reduce Rainfall in Some Areas of the Earth Leading to Droughts

This can cause the death of many plants and animals, and turn large areas of the earth into semi-deserts.

Global warming has become a major concern for all the governments of the world because an increase in the earth’s atmospheric temperature by even as little as 0.5°C can have serious consequences for all.

Greenhouse gases: Those gases which can trap sun’s heat rays in the earth’s atmosphere by producing greenhouse effect leading up to the heating of earth’s atmosphere, are called greenhouse gases.

Carbon dioxide, Methane, Nitrous oxide, Chlorofluorocarbons and Water vapour, are all greenhouse gases. Carbon dioxide is the main greenhouse gas.