Class 9 Atmosphere and air

### Topics to be covered

=> General introduction
=> The breathe of life:AIR
=> The role of the atmosphere in climate control
=> The movement of air:WINDS
=> Rain

### 𝐆𝐞𝐧𝐞𝐫𝐚𝐥 𝐢𝐧𝐭𝐫𝐨𝐝𝐮𝐜𝐭𝐢𝐨𝐧

Life on Earth is dependent on many factors like we know need an ambient temperature, water, and food. The resources that are available on the Earth and the energy from the Sun are necessary to meet the basic requirements of all life-forms on the Earth.

color{green}("𝐖𝐡𝐚𝐭 𝐚𝐫𝐞 𝐭𝐡𝐞𝐬𝐞 𝐫𝐞𝐬𝐨𝐮𝐫𝐜𝐞𝐬 𝐨𝐧 𝐭𝐡𝐞 𝐄𝐚𝐫𝐭𝐡?")

These are the land, the water and the air.

color{green}(•) The outer crust of the Earth is called the lithosphere.

color{green}(•) Water covers color{red}(75%) of the Earth’s surface. It is also found underground. These comprise the hydrosphere.

color{green}(•) The air that covers the whole of the Earth like a blanket, is called the atmosphere.

color{green}(•) Living things are found where these three exist. This life-supporting zone of the Earth where the atmosphere, the hydrosphere and the lithosphere interact and make life possible, is known as the biosphere.

color{green}(=>) Living things constitute the biotic component of the biosphere.

color{green}(=>) The air, the water and the soil form the non-living or abiotic component of the biosphere.

### 𝐓𝐡𝐞 𝐁𝐫𝐞𝐚𝐭𝐡 𝐨𝐟 𝐋𝐢𝐟𝐞: 𝐀𝐢𝐫

color{green}(=>) Air is a mixture of many gases like nitrogen, oxygen, carbon dioxide and water vapour.

color{green}(=>) In planets such as Venus and Mars, where no life is known to exist, the major component of the atmosphere is found to be carbon dioxide. In fact, carbon dioxide constitutes up to color{red}(95-97%) of the atmosphere on Venus and Mars.

color{green}(=>) Eukaryotic cells and many prokaryotic cells, need oxygen to break down glucose molecules and get energy for their activities. This results in the production of carbon dioxide.

color{green}(=>) Another process which results in the consumption of oxygen and the concomitant production of carbon dioxide is combustion. This includes not just human activities, which burn fuels to get energy, but also forest fires.

Despite this, the percentage of carbon dioxide in our atmosphere is a mere fraction of a percent because carbon dioxide is color{red}("‘𝐟𝐢𝐱𝐞𝐝’") in two ways:

(i) Green plants convert carbon dioxide into glucose in the presence of Sunlight and

(ii) many marine animals use carbonates dissolved in sea-water to make their shells.

### 𝐓𝐇𝐄 𝐑𝐎𝐋𝐄 𝐎𝐅 𝐓𝐇𝐄 𝐀𝐓𝐌𝐎𝐒𝐏𝐇𝐄𝐑𝐄 𝐈𝐍 𝐂𝐋𝐈𝐌𝐀𝐓𝐄 𝐂𝐎𝐍𝐓𝐑𝐎𝐋

color{green}(=>) The atmosphere keeps the average temperature of the Earth fairly steady during the day and even during the course of the whole year.

color{green}(=>) The atmosphere prevents the sudden increase in temperature during the daylight hours. And during the night, it slows down the escape of heat into outer space.

color{green}(=>) Despite that, on the surface of the moon, with no atmosphere, the temperature ranges from color{red}(–190^o C) to color{red}(110^o C).

### 𝐓𝐇𝐄 𝐌𝐎𝐕𝐄𝐌𝐄𝐍𝐓 𝐎𝐅 𝐀𝐈𝐑: 𝐖𝐈𝐍𝐃𝐒

color{green}(=>) All the naturally occurring phenomena are the result of changes that take place in our atmosphere due to the heating of air and the formation of water vapour.

color{green}(=>) Water vapour is formed due to the heating of water bodies and the activities of living organisms.

color{green}(=>) The atmosphere can be heated from below by the radiation that is reflected back or re-radiated by the land or water bodies.

color{green}(=>) On being heated, convection currents are set up in the air.

When air is heated by radiation from the heated land or water, it rises. But since land gets heated faster than water, the air over land would also be heated faster than the air over water bodies.

While in coastal regions during the day, the air above the land gets heated faster and starts rising. As this air rises, a region of low pressure is created and air over the sea moves into this area of low pressure. The movement of air from one region to the other creates winds. During the day, the direction of the wind would be from the sea to the land.

At night, both land and sea start to cool. Since water cools down slower than the land, the air above water would be warmer than the air above land.

Similarly, all the movements of air resulting in diverse atmospheric phenomena are caused by the uneven heating of the atmosphere in different regions of the Earth.

Besides this there are various other factors that influence these winds – the rotation of the Earth and the presence of mountain ranges in the paths of the wind are a couple of these factors.

### 𝐑𝐀𝐈𝐍

color{green}(=>) When water bodies are heated during the day, a large amount of water evaporates and goes into the air

color{green}(=>) Some amount of water vapour also get into the atmosphere because of various biological activities. This air also gets heated.

color{green}(=>) The hot air rises up carrying the water vapour with it.

color{green}(=>) As the air rises, it expands and cools. This cooling causes the water vapour in the air to condense in the form of tiny droplets. This condensation of water is facilitated if some particles could act as the color{red}("‘𝐧𝐮𝐜𝐥𝐞𝐮𝐬’") for these drops to form around. Normally dust and other suspended particles in the air perform this function.

color{green}(=>) Once the water droplets are formed, they grow bigger by the ‘condensation’ of these water droplets

color{green}(=>) . When the drops have grown big and heavy, they fall down in the form of rain.

color{green}(=>) Sometimes, when the temperature of air is low enough, precipitation may occur in the form of snow, sleet or hail.

color{green}(•) Rainfall patterns are decided by the prevailing wind patterns. In large parts of India, rains are mostly brought by the southwest or north-east monsoons.

color{green}(•) color{red}("‘𝐃𝐞𝐩𝐫𝐞𝐬𝐬𝐢𝐨𝐧𝐬’") in the Bay of Bengal have caused rains in some areas (Figure 14.2).