Notes On Air Pollution: Gaseous Pollutants - CBSE Class 11 Chemistry
Pollution is the harmful effect on the environment that can prove fatal to all living organisms. It is caused by the contamination of the air, water and soil by harmful substances, known as pollutants. Pollutants can be solid, liquid or gas, and originate from human actions and natural sources.   Air Pollution:   Air pollution takes place in two different layers of the earth’s atmosphere—the troposphere and the stratosphere. The troposphere is the lowest region of the earth’s atmosphere in which living organisms live.   Air Pollutants: There are two types of air pollutants     • Gaseous         Oxides of :                          → Sulphur                          → Nitrogen                          → Carbon                          → Hydrocarbons • Particulate                      → Dust                      → Mist                      → Smoke   The gaseous pollutants of the atmosphere are harmful gaseous oxides and oxidants. The particulate pollutants are dust, mist and smoke. The harmful gaseous oxides include the oxides of sulphur, nitrogen, and carbon, besides hydrocarbons.   Oxides of sulphur:  Burning sulphur containing fossil fuels produces the oxides of sulphur. The most common oxide among them is sulphur dioxide.   Harmful effects :  This gas is poisonous for living organisms and causes respiratory diseases like asthma, bronchitis and emphysema in humans. In plants, a high concentration of sulphur dioxide makes the flower buds stiff and makes them fall off,hampering its reproductive cycle. Coal combustion, ore smelters, petroleum refineries and diesel engines are some sources of sulphur dioxide.   Oxides of Nitrogen:  The most common pollutant of nitrogen gas, nitrogen dioxide, is produced when fossil fuels are burnt in high temperature like in automobile engines. Dinitrogen and dioxygen are the main constituents of air, and they form nitric oxide and nitrogen dioxide in high temperature.   Harmful effects:  Nitric oxide also reacts with the ozone in the earth’s atmosphere to form nitrogen dioxide. Nitrogen dioxide can cause respiratory diseases in children, irritate the eyes, lungs and throat, and damage the leaves of plants, affecting their photosynthesis.   Acid Rain:  An increase in the level of the oxides of sulphur and nitrogen makes the pH value of rain water drop below 5.6, causing acid rain. Acid rain washes away nutrients from plants, and is harmful for trees and agriculture. It causes respiratory diseases in humans and animals. Acid rain flows to rivers, lakes and oceans, and harms the ecosystem in them. The acid particles corrode metals and stones, damaging structures made of them. The Taj Mahal, the beautiful monument in India, is being disfigured and rendered lustreless by acid rain. Hydrocarbons:  Another air pollutant, hydrocarbons, is produced as a result of incomplete combustion of fuels in automobile engines. In animals, hydrocarbons can cause cancer, while in plants, they cause aging by breaking down tissues, which causes shedding of leaves, twigs and flowers.   Oxides of carbon:  Other major gas pollutants are the oxides of carbon, namely carbon monoxide and carbon dioxide. Carbon monoxide is produced by automobile exhaust and incomplete combustion of fossil fuels. This highly poisonous gas combines with haemoglobin in blood, forming carboxyhaemoglobin. it reduces the oxygen-carrying capacity of blood. This results in headache, weak eyesight and cardiovascular disorders. In extreme cases, it can also cause death. Carbon dioxide is the most commonly known air pollutant that is produced in respiration, burning of fossil fuels and decomposition of limestone. An increase in carbon dioxide leads to an increase in the average global temperature. This is known as global warming.   Global warming:  When the sun’s ray come towards the earth the atmosphere absorbs the harmful rays like ultra violet rays, and lets the rest pass to reach the earth’s surface. In response, the earth’s hot surface also sends back some infrared light, a part of which is sent back to space through the atmosphere. This process is very much similar to a greenhouse, where the glass holds the sun’s heat inside. Therefore, gases in the atmosphere that trap the sun’s heat are known as greenhouse gases. Water vapour, carbon dioxide, nitrous oxide and methane are some of the major greenhouse gases. When the level of greenhouse gases in the atmosphere increases, they trap more heat from the sun and also from the earth’s surface. As a result, the atmosphere becomes warmer. This is called global warming.

#### Summary

Pollution is the harmful effect on the environment that can prove fatal to all living organisms. It is caused by the contamination of the air, water and soil by harmful substances, known as pollutants. Pollutants can be solid, liquid or gas, and originate from human actions and natural sources.   Air Pollution:   Air pollution takes place in two different layers of the earth’s atmosphere—the troposphere and the stratosphere. The troposphere is the lowest region of the earth’s atmosphere in which living organisms live.   Air Pollutants: There are two types of air pollutants     • Gaseous         Oxides of :                          → Sulphur                          → Nitrogen                          → Carbon                          → Hydrocarbons • Particulate                      → Dust                      → Mist                      → Smoke   The gaseous pollutants of the atmosphere are harmful gaseous oxides and oxidants. The particulate pollutants are dust, mist and smoke. The harmful gaseous oxides include the oxides of sulphur, nitrogen, and carbon, besides hydrocarbons.   Oxides of sulphur:  Burning sulphur containing fossil fuels produces the oxides of sulphur. The most common oxide among them is sulphur dioxide.   Harmful effects :  This gas is poisonous for living organisms and causes respiratory diseases like asthma, bronchitis and emphysema in humans. In plants, a high concentration of sulphur dioxide makes the flower buds stiff and makes them fall off,hampering its reproductive cycle. Coal combustion, ore smelters, petroleum refineries and diesel engines are some sources of sulphur dioxide.   Oxides of Nitrogen:  The most common pollutant of nitrogen gas, nitrogen dioxide, is produced when fossil fuels are burnt in high temperature like in automobile engines. Dinitrogen and dioxygen are the main constituents of air, and they form nitric oxide and nitrogen dioxide in high temperature.   Harmful effects:  Nitric oxide also reacts with the ozone in the earth’s atmosphere to form nitrogen dioxide. Nitrogen dioxide can cause respiratory diseases in children, irritate the eyes, lungs and throat, and damage the leaves of plants, affecting their photosynthesis.   Acid Rain:  An increase in the level of the oxides of sulphur and nitrogen makes the pH value of rain water drop below 5.6, causing acid rain. Acid rain washes away nutrients from plants, and is harmful for trees and agriculture. It causes respiratory diseases in humans and animals. Acid rain flows to rivers, lakes and oceans, and harms the ecosystem in them. The acid particles corrode metals and stones, damaging structures made of them. The Taj Mahal, the beautiful monument in India, is being disfigured and rendered lustreless by acid rain. Hydrocarbons:  Another air pollutant, hydrocarbons, is produced as a result of incomplete combustion of fuels in automobile engines. In animals, hydrocarbons can cause cancer, while in plants, they cause aging by breaking down tissues, which causes shedding of leaves, twigs and flowers.   Oxides of carbon:  Other major gas pollutants are the oxides of carbon, namely carbon monoxide and carbon dioxide. Carbon monoxide is produced by automobile exhaust and incomplete combustion of fossil fuels. This highly poisonous gas combines with haemoglobin in blood, forming carboxyhaemoglobin. it reduces the oxygen-carrying capacity of blood. This results in headache, weak eyesight and cardiovascular disorders. In extreme cases, it can also cause death. Carbon dioxide is the most commonly known air pollutant that is produced in respiration, burning of fossil fuels and decomposition of limestone. An increase in carbon dioxide leads to an increase in the average global temperature. This is known as global warming.   Global warming:  When the sun’s ray come towards the earth the atmosphere absorbs the harmful rays like ultra violet rays, and lets the rest pass to reach the earth’s surface. In response, the earth’s hot surface also sends back some infrared light, a part of which is sent back to space through the atmosphere. This process is very much similar to a greenhouse, where the glass holds the sun’s heat inside. Therefore, gases in the atmosphere that trap the sun’s heat are known as greenhouse gases. Water vapour, carbon dioxide, nitrous oxide and methane are some of the major greenhouse gases. When the level of greenhouse gases in the atmosphere increases, they trap more heat from the sun and also from the earth’s surface. As a result, the atmosphere becomes warmer. This is called global warming.

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