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4 Air Do you know? Our earth is surrounded by a huge blanket of air called atmosphere. All living beings on this earth Carbon dioxide depend on the atmosphere for their survival. It released in the provides us the air we breathe...

4 Air Do you know? Our earth is surrounded by a huge blanket of air called atmosphere. All living beings on this earth Carbon dioxide depend on the atmosphere for their survival. It released in the provides us the air we breathe and protects us from atmosphere creates a the harmful effects of the sun’s rays. Without this green house effect by blanket of protection, we would be baked alive by the trapping the heat heat of the sun during day and get frozen during radiated from the night. So it is this mass of air that has made the earth. It is therefore temperature on the earth liveable. called a greenhouse gas and without it the COMPOSITION OF THE A TMOSPHERE earth would have been too cold to live in. Do you know that the air we take in while breathing is However, when its actually a mixture of many gases? Nitrogen and oxygen level in the are two gases which make up the bulk of the atmosphere increases atmosphere. Carbon due to factory smoke dioxide, helium, or car fumes, the heat ozone, argon and retained increases the hydrogen are found temperature of the in lesser quantities. earth. This is called Apart from these global warming. This gases, tiny dust rise in temperature causes the snow in particles are also coldest parts of the present in the air. The world to melt. As a pie chart gives you the result the sea level percentage of different rises, causing floods in constituents of air (Fig. 4.1). the coastal areas. Nitrogen is the most There may be drastic plentiful gas in the air. When changes in the climate we inhale, we take some of a place leading to amount of nitrogen into our extinction of some lungs and exhale it. But plants and animals in plants need nitrogen for their the long run. Fig. 4.1: Constituents of Air survival. They can not take Reprint 2024-25 nitrogen directly from the air. Bacteria, that live in the soil and roots of some plants, take nitrogen from the Do you know? air and change its form so that plants can use it. Oxygen is the second most plentiful gas in the air. When air is heated, it Humans and animals take oxygen from the air as they expands, becomes breathe. Green plants produce oxygen during lighter and goes up. photosynthesis. In this way oxygen content in the air Cold air is denser and remains constant. If we cut trees then this balance heavy. That is why it gets disturbed. tends to sink down. Carbon dioxide is another important gas. Green When hot air rises, plants use carbon dioxide to make their food and cold air from release oxygen. Humans or animals release carbon surrounding area dioxide. The amount of carbon dioxide released by rushes there to fill in humans or animals seems to be equal to the amount the gap. That is how air circulation takes used by the plants which make a perfect balance. place. However, the balance is upset by burning of fuels, such as coal and oil. They add billions of tons of carbon dioxide into the atmosphere each year. As a result, the increased volume of carbon dioxide is affecting the earth’s weather and climate. ytivitcA Read and Ponder: Is global warming a serious issue in today’s world? AIR 21 Reprint 2024-25  STRUCTURE OF THE ATMOSPHERE Our atmosphere is divided into five layers starting from the earth’s sur face. These are T roposphere, Stratosphere, Mesosphere, Thermosphere and Exosphere (Fig. 4.2). Troposphere: This layer is the most important layer of the atmosphere. Its average height is 13 km. The air we breathe exists here. Almost all the weather phenomena like rainfall, fog and hailstorm occur in this layer. Stratosphere: Above the troposphere lies the stratosphere. It extends up to a height of 50 km. This layer is almost free from clouds and associated weather phenomenon, making conditions most ideal for flying aeroplanes. One important feature of stratosphere is that it contains a layer of ozone gas. We have just learnt how it protects us from the harmful effect of the sun rays. Mesosphere: This is the third layer of the atmosphere. It lies above the stratosphere. It extends up to the height of 80 km. Meteorites burn up in this layer on entering from the space. Thermosphere: In thermosphere temperature rises very rapidly with increasing height. Ionosphere is a part of this Fig. 4.2: Layers of the Atmosphere layer. It extends between 22 OUR ENVIRONMENT Reprint 2024-25 80-400 km. This layer helps in radio transmission. In fact, radio waves transmitted from the earth are reflected back to the earth by this layer. Let’s do Exosphere: The upper most layer of the atmosphere For ten days note is known as exosphere. This layer has very thin air. down weather report Light gases like helium and hydrogen float into the from a local space from here. newspaper and observe the changes WEATHER AND CLIMATE occurring in the weather. “Is it going to rain today?” “Will it be bright and sunny today?” How many times have we heard this from anxious cricket fans speculating the fate of a One Day match? If we imagine our body to be a radio and the mind its speaker, weather is something that fiddles Do you know? with its control knobs. Weather is this hour-to-hour, day to day condition of the atmosphere. A hot or humid You will be surprised weather may make one irritable. A pleasant, breezy to know that the weather may make one cheerful and even plan for an earth receives only 1 outing. Weather can change dramatically from day to in 2,000,000,000 day. However, the average weather condition of a place parts of the sun’s for a longer period of time represents the climate of a energy. place. Now do you understand why we have daily weather forecasts. Temperature The temperature you feel everyday is the temperataure of the atmosphere. The degree of hotness and coldness of the air is known as temperature. Thermometer: The temperature of the Measures Barometre: Measures atmosphere changes not only the temperature atmospheric pressure between day and night but also from season to season. Summers are hotter than winters. An important factor that influences the distribution of temperature is insolation. Insolation is the incoming solar energy intercepted by the earth. The amount of insolation Rain Gauge: Measures Wind Vane: Shows the the amount of rainfall direction of the wind decreases from the equator towards the poles. Therefore, the Fig. 4.3: Weather Instruments AIR 23 Reprint 2024-25  Do you know? temperature decreases in the same manner. Now do you understand why poles are covered with snow? If The standard unit of the earth’s temperature rises too high, it would become measuring too warm for some crops to grow. Temperature in cities temperature is degree is much higher than that of villages. The concrete and Celsius. It was metals in buildings and the asaphalt of roads get invented by Anders heated up during the day. This heat is released during Celsius. On the Celsius scale the the night. water freezes at 0°C Also, the crowded high rise buildings of the cities and boils at 100°C. trap the warm air and thus raise the temperature of the cities. Air Pressure You will be surprised to know that air above us presses Do you know? us with a great force on our bodies. However, we don’t even feel it. This is because the air presses us from all On the moon there is directions and our body exerts a counter pressure. no air and hence no Air pressure is defined as the pressure exerted by the air pressure. weight of air on the earth’s surface. As we go up the Astronauts have to layers of atmosphere, the pressure falls rapidly. The air wear special pressure is highest at sea level and decreases with height. protective space suits Horizontally the distribution of air pressure is influenced filled with air when by temperature of air at a given place. In areas where they go to the moon. If temperature is high the air gets heated and rises. This they did not wear creates a low-pressure area. Low pressure is associated these space suits, the with cloudy skies and wet weather. counter pressure In areas having lower temperature, the air is cold. It exerted by the body of the astronauts would is therefore heavy. Heavy air sinks and creates a high make the blood vessels pressure area. High pressure is associated with clear and burst. The astronauts sunny skies. would bleed. The air always moves from high pressure areas to low pressure areas. Wind The movement of air from high pressure area to low Do you know? pressure areas is called wind. You can see wind at work as it blows dry leaves down the pavement or uproots A wind is named after trees during a storm. Sometimes when the wind blows the direction from gently you can even see it blowing away smoke or fine which it blows, e.g. dust. At times wind can be so strong that it is difficult the wind blowing from to walk against it. You must have experienced it is not the west is called easy to hold an umbrella on a windy day. Think of westerly. some other examples when strong winds have created 24 OUR ENVIRONMENT Reprint 2024-25 problems for you. Winds can be 90°N High Pressure broadly divided into three types. Polar Easterlies 1. Permanent winds – The trade winds, westerlies and easterlies 60°N Sub-Polar Low Pressure are the permanent winds. P r e v a i l i n g We s t e r l i e s These blow constantly 35°N Sub - Tropical High Pressure (Horse Latitudes) throughout the year in a 30°N 23.5°N T r o p i c o f C a n c e r particular direction. Northeast Trade Winds 2. Seasonal winds – These 0° Equatorial Low Pressure (Doldrums) winds change their direction Southeast Trade Winds T rop i c of C apri co r n 23.5°S in different seasons. For 30°S Sub - Tropical High Pressure (Horse Latitudes) example monsoons in India. 35°S Prevailing We s t e r l i e s 3. Local winds – These blow only during a particular 60°S Sub-Polar Low Pressure period of the day or year in a Polar Easterlies small area. For example, land High Pressure and sea breeze. Do you recall the 90°S hot and dry local wind of northern planes of India? It is called loo. Fig. 4.4: Major Pressure Belts and Wind System CYCLONE – NATURE’S FURY Odisha, located on the eastern seacoast of India is prone to cyclones that originate in the Bay of Bengal. On 17-18 October 1999, cyclone hit five districts of the state. Another supercyclone occurred on the 29 October 1999, that devastated large portions of the state. The damages caused were mainly due to three factors: wind velocity, rain and Destruction caused by a cyclone tidal surge. The winds of upto 260 km. per hour lasted for over 36 hours. These high velocity winds uprooted trees and damaged the kutcha houses. Roof tops of several industrial sheds and other houses were also blown away. Power supply and telecom lines snapped completely. Heavy rain occurred under the influence of the cyclone for three days continuously. These rains led to flooding in the major rivers of Odisha. The cyclonic winds caused tidal waves that swept 20 km. inland and brought massive destruction to the coastal areas. The 7 to 10 m high tidal wave intruded suddenly and caused massive damage to the standing paddy crops. AIR 25 Reprint 2024-25  The cyclone originated as a “depression” in the Gulf of Thailand, near east of Port Blair, on 25 October 1999 and gradually moved in a northwestward direction. It intensified into a supercyclone and hit the area between Erasama and Balikuda in Odisha on 29 October at 10.30 a.m. The supercyclone swept the entire coast of Odisha including the cities of Bhubaneshwar and Cuttack and 28 coastal towns. About 13 million people were affected. A large number of livestock were killed. Standing crops of paddy, vegetables and fruits were heavily damaged. Due to salinisation caused by tidal surge, large tracts of agricultural land have turned infertile. Large tracts of sal, teak and bamboo plantations have disappeared. The mangrove forests between Paradeep and Konark vanished. Moisture Cold When water evaporates from land and different air Warm water bodies, it becomes water vapour. Moisture air in the air at any time, is known as humidity. When the air is full of water vapour we call it a humid day. As the air gets warmer, its capacity to hold the water vapour increases and so it becomes more and more humid. On a humid day, clothes take longer to dry and sweat from Cyclonic Rainfall our body does not evaporate easily, making us feel very uncomfortable. When the water vapour rises, it starts cooling. The water vapour condenses causing formation Moist of droplets of water. Clouds are just masses of air such water droplets. When these droplets of water become too heavy to float in air, then they come down as precipitation. Jet planes flying in the sky leave a white trail behind them. The moisture from their engines Relief (Orographic) Rainfall condenses. We see trails of this condensed moisture for some time when there is no air movement to disturb it. Precipitation that comes down to the earth in liquid form is called rain. Most of the ground water comes from rainwater. Plants help preserve water. When trees on hill sides are cut, rainwater Warm flows down the bare mountains and can cause air flooding of low lying areas. On the basis of mechanism, there are three types of rainfall: the Convectional Rainfall convectional rainfall, the orographic rainfall and Fig. 4.5: Types of Rainfall the cyclonic rainfall (Fig. 4.5). 26 OUR ENVIRONMENT Reprint 2024-25  Rainfall is very important for the survival of plants and Do you know? animals. It brings fresh water to the earth’s surface. If rainfall is less – water scacity and drought occur. On the Other forms of other hand if it is more, floods take place. precipitation are snow, sleet, hail. Exercises 1. Answer the following questions. (i) What is atmosphere? (ii) Which two gases make the bulk of the atmosphere? (iii) Which gas creates green house effect in the atmosphere? (iv) What is weather? (v) Name three types of rainfall? (vi) What is air pressure? 2. Tick the correct answer. (i) Which of the following gases protects us from harmful sun vays? (a) Carbon dioxide (b) Nitrogen (c) Ozone (ii) The most important layer of the atmosphere is (a) Troposphere (b) Thermosphere (c) Mesosphere (iii) Which of the following layers of the atmosphere is free from clouds? (a) Troposphere (b) Stratosphere (c) Mesosphere (iv) As we go up the layers of the atmosphere, the pressure (a) Increases (b) Decreases (c) Remains the same (v) When precipitation comes down to the earth in the liquid form, it is called (a) Cloud (b) Rain (c) Snow 3. Match the following. (i) Trade Winds (a) Incoming solar energy (ii) Loo (b) Seasonal wind (iii) Monsoon (c) Horizontal movement of Air (iv) Wind (d) Layer of ozone gas (e) Permanent wind (f) Local wind 4. Give reasons. (i) Wet clothes take longer time to dry on a humid day? (ii) Amount of insolation decreases from equator towards poles? AIR 27 Reprint 2024-25 5. For fun. (i) Solve this Crossword puzzle with the help of given clues: Across Down 6. An Indian tree having extraordinary 1. Amount of water vapour in air quality of providing oxygen round the 2. Condensation of water vapours around clock dust particles in atmosphere 8. Gas present in atmosphere occupying 3. Example of local wind blowing in summer only 0.03% by volume in northern india 11. Outermost layer of atmosphere 4. Short term changes in atmosphere 12. Mixture of many gases 5. Precipitation in liquid form 14. Life giving gas 7. Blanket of air around the earth 15. Air in motion 9. Instrument to measure pressure 16. An indian tree valued highly for 10. Incoming solar radiation medicinal properties 13. Reduces visibility in winters 18. Gas protecting us from harmful sunrays 17. It is....... time when sun is overhead 19. Low pressure area 28 OUR ENVIRONMENT Reprint 2024-25  (ii) Make a weather calendar for one week. Use pictures or symbols to show different types of weather. You can use more than one symbol in a day, if the weather changes. For example, the sun comes out when rain stops. An example is given below: Day Weather 1. Sunny day 2. 3. 4. 5. 6. 7. AIR 29 Reprint 2024-25