Composition and Structure of the Atmosphere

Atmosphere

Reason — The atmosphere is the blanket of air surrounding the Earth. It is made up mainly of nitrogen and oxygen. The ozone layer is a part of the atmosphere, while the lithosphere is the Earth's solid outer layer.

A: 78 B: 21

Reason — A clean, dry sample of air contains 78% nitrogen, 21% oxygen, and 1% other gases. Hence, A represents nitrogen (78%) and B represents oxygen (21%).

(i) The ash cloud is present at that altitude

Reason — The IMD statement refers to the ash plume suspended between 8.5 km and 15 km above sea level. Thus, 'affected altitude' means the height at which the ash cloud is present.

(ii) Both (a) and (b)

Reason — The volcanic ash cloud lies between 8.5 km and 15 km above sea level, away from the lower troposphere where weather occurs. Hence, it does not affect weather conditions over India.

(iii) All of the above

Reason — Volcanic ash is a cloud of fine particles released during an eruption. It damages aircraft engines, reduces visibility, and makes flying hazardous.

All of the above.

Reason — As altitude increases, air becomes thinner, reducing air pressure, oxygen, and temperature. Hence, camps are set up at intervals to help climbers acclimatize.

Both A and R are true and R is the correct explanation of A.

Explanation — The atmosphere is the most dynamic entity because large masses of air are constantly moving vertically and horizontally due to the Sun's unequal heating of the Earth's surface. This continuous movement keeps the atmosphere in a dynamic state.

Troposphere - Stratosphere - Mesosphere - Thermosphere

Reason — From the Earth's surface upward, these are the Troposphere (the lowermost and densest layer), the Stratosphere (up to about 50 km), the Mesosphere (up to about 80 km), and the Thermosphere, which includes the Ionosphere and the Exosphere.

Ionosphere

Reason — The Ionosphere, a part of the Thermosphere, extends up to about 400 km. It contains electrically charged particles (ions) that reflect radio waves back to the Earth's surface, enabling radio communication.

Both A and R are true and R is the correct explanation of A.

Explanation — The atmosphere is denser near the Earth's surface because the weight of the upper layers compresses the lower layers. As a result, about 90% of the total mass of the atmosphere lies within the lowest 20 km above the Earth's surface.

All of the above

Reason — Water vapour is added to the atmosphere by evaporation from oceans, lakes and rivers, by transpiration from vegetation and by respiration of animals. Hence all the given processes add water vapour to the atmosphere.

Meteoric dust particles reflect sunlight causing wispy clouds.

Reason — The Mesosphere extends up to about 80 km above the Earth's surface. Wispy clouds are seen in this layer due to sunlight reflected by meteoric dust particles. They are not weather clouds, as all weather phenomena occur only in the Troposphere.

All of the above

Reason — The atmosphere facilitates the cyclic exchange of gases between air, land, and water, maintains a suitable temperature by trapping heat, and protects the Earth from harmful ultraviolet rays of the Sun. Hence, all of the above are functions of the atmosphere.

Normal lapse rate

Reason — The Troposphere is characterised by a regular decrease in temperature with altitude. This decrease in temperature is known as the normal lapse rate. The average decrease is 1°C for every 166 metre altitude gained.

Ionosphere

Reason — The Ionosphere contains electrically charged particles called ions which create a sheet like display of light known as Aurora Borealis in the Northern Hemisphere and Aurora Australis in the Southern Hemisphere.

A is true but R is false.

Explanation — The troposphere is heated from below, not directly by incoming solar radiation. The Earth's surface absorbs the Sun's energy and then radiates heat upward, warming the air in the troposphere. Therefore, the assertion is true, but the reason is false.

Radiation Balance

Reason — Global warming causes precipitation changes, sea level rise, and an increase in diseases. It also leads to radiation imbalance, not radiation balance, by disturbing the balance between incoming and outgoing radiation. Hence, radiation balance is not a direct impact of global warming.

The blanket of air surrounding the Earth is known as the atmosphere.

The atmosphere is a mixture of many gases and tiny solid particles. Atmosphere contains-

1. 78% nitrogen gas
2. 21% oxygen gas
3. The remaining 1% of air is made up of Carbon dioxide, Water Vapour, Helium, Hydrogen, Argon etc.

The four layers of the atmosphere are-

1. Troposphere
2. Stratosphere
3. Mesosphere
4. Thermosphere

Thermosphere is the outermost layer of the atmosphere where the satellites orbit the earth.

The troposphere is the lowermost and densest layer of the atmosphere. Its height varies from 18 km at the equator to 8 km at the poles.

Two characteristics of the troposphere are:

1. Seventy-five per cent of the atmosphere is found in the troposphere and its concentration decreases as we go higher from ground level.
2. The troposphere is heated more from below than from above.

The chief characteristics of stratosphere are-

1. The air is thin, cold, and dry. The temperature at the base is about −55°C.
2. The ozone layer lies in the stratosphere, mainly between 20 km and 50 km above the Earth's surface.
3. Ozone absorbs the Sun's ultraviolet radiation, causing the temperature to increase with altitude in the upper part of the stratosphere.
4. The lower stratosphere has very little water vapour and is almost free from weather disturbances, making it ideal for jet aircraft.
5. The temperature rises from about −60°C at the base to about 0°C at the stratopause.
6. The upper limit of the stratosphere is called the stratopause.

All the weather conditions occur in the troposphere.

The constituent gases of atmosphere which scientists consider responsible for climate change are Carbon dioxide, Methane, Chlorofluorocarbons, Ozone and Water Vapour.

Pratap did not feel any turbulence because aeroplanes generally fly in the lower stratosphere, where the weather is calm and stable. The troposphere, the layer below the stratosphere, contains all weather phenomena like storms and rain. Since the plane was flying above the troposphere (in the stratosphere), it did not experience the turbulence caused by the storm in Bhubaneswar.

Ozone layer is a stratospheric layer that absorbs the Sun's harmful ultraviolet (UV) rays and helps maintain stable temperatures in the lower atmosphere.

It is depleted by chemicals such as chlorofluorocarbons (CFCs), chlorine, bromine, and sulphur dioxide from volcanic eruptions, solar storms, and human activities. CFCs break down in the stratosphere, releasing chlorine atoms that destroy ozone.

The effects of ozone layer depletion are as follows:

1. Increased levels of harmful ultraviolet (UV) radiation reaching the Earth's surface.
2. Higher risk of skin cancer, eye damage (including cataracts), and weakened immune systems.
3. Damage to marine ecosystems.
4. Harm to crops, reducing agricultural productivity and causing food shortages.
5. Disruption of biogeochemical cycles, including the nitrogen, sulphur, and carbon cycles.
6. Changes in climate patterns by affecting atmospheric temperatures and rainfall.

The natural causes of ozone layer depletion are volcanic eruptions and solar flares.

No, ozone in the lower layer of the atmosphere (the troposphere) cannot make up for the loss of ozone in the ozone layer (the stratosphere). This is because ozone near the Earth's surface is a harmful pollutant, whereas ozone in the stratosphere forms a protective layer that absorbs the Sun's harmful ultraviolet (UV) rays.

Therefore, ozone in the lower atmosphere cannot replace or perform the protective function of the stratospheric ozone layer.

The rise in average mean temperature of the Earth on account of enhanced concentration of greenhouse gases in the atmosphere is known as global warming.

Some important Greenhouse gases are Carbon dioxide, Methane, Chlorofluorocarbons, Ozone and Water Vapour.

The atmosphere consists of concentric layers of air. On the basis of the characteristics of temperature and air pressure, it can be divided into four thermal layers — Troposphere, Stratosphere, Mesosphere and Thermosphere. The Thermosphere is divided into Ionosphere and Exosphere. The four layers are briefly described below:

1. Troposphere — It is the lowermost and densest layer. Its height varies from 18 km at the Equator to 8 km at the Poles.
2. Stratosphere — This layer lies above the Troposphere. It extends to a height of 50 km from sea level. The Ozone layer lies within the stratosphere. Ozone is generally found between the altitudes of 20 and 50 km.
3. Mesosphere — This layer lies above the Stratosphere. It extends to a height of 80 km from ground level.
4. Thermosphere — It lies above Mesosphere and consists of two parts:
   1. Ionosphere — It extends up to a height of about 400 km.
   2. Exosphere — It is the uppermost layer of the atmosphere. It lies between 400 to 1500 km above the earth.

The main components of the atmosphere are Nitrogen (78%) and Oxygen (21%). These two gases play a significant role in supporting life on Earth.

1. Oxygen gas helps in burning and breathing. Without breathing oxygen, most living things cannot survive.
2. Nitrogen dilutes the oxygen and slows down the process of oxidation.
3. It is essential for all living things but they cannot use it directly from the atmosphere. Plants obtain it from the soil and animals obtain nitrogen by eating plants or other animals.
4. Nitrogen and Oxygen indirectly help in retaining the necessary warmth on the earth and helps in the circulation of water vapour—the source of rainfall.

(i) We find it difficult to breathe when we climb mountains because the layers of atmosphere become thinner at high altitudes. This means that there is less pressure to push the air into the lungs and a lower percentage of Oxygen in the air. This makes it harder to breath.

(ii) The atmosphere is the most dynamic entity because of its composition. Large masses of air are being moved up and down and across the surface of the Earth.

(iii) The troposphere is characterised by regular decrease in temperature with altitude. This decrease in temperature is known as normal lapse rate. The average decrease is 1°C for every 166 metre altitude gain. This temperature variation is responsible for many turbulences which result in all weather phenomena taking place in the troposphere.

Below diagram shows the Greenhouse Effect:

Conversion of forest land into agricultural land cause global warming in the following ways:

1. Reduction of Carbon Dioxide Absorption: Forests absorb carbon dioxide (CO₂) from the atmosphere in large amount. When forests are cut down to create agricultural land, this ability to absorb CO₂ is reduced. As a result, more carbon dioxide remains in the atmosphere, which contributes to global warming.

2. Release of Stored Carbon: When trees are cut and often burned to clear the land, the carbon stored in trees is released into the atmosphere in the form of carbon dioxide, further increasing the concentration of greenhouse gases. This extra CO₂ traps more heat and raises the Earth's average temperature.

Thus, deforestation for agriculture both reduces CO₂ absorption and increases CO₂ emission, making it a major cause of global warming.

Construction of high rise buildings cause global warming in the following ways:

1. It increases energy consumption as high-rise buildings require large amounts of electricity for lighting, heating, cooling, and operating elevators. Much of this energy is often generated from burning fossil fuels, which releases carbon dioxide (CO₂) into the atmosphere.

2. The construction process itself (manufacturing cement, steel, etc.) releases a significant amount of greenhouse gases, further adding to global warming.

Fossil fuel production cause global warming in the following ways:

1. Burning fossil fuels like coal, oil, and natural gas releases large amounts of carbon dioxide (CO₂) and other greenhouse gases into the atmosphere.

2. These gases trap heat from the sun, leading to a rise in the Earth's temperature, which is the main cause of global warming.

Transportation industry cause global warming in the following ways:

1. Vehicles like cars, trucks, ships, and airplanes burn fossil fuels (petrol, diesel, aviation fuel), releasing large amounts of carbon dioxide (CO₂) and other greenhouse gases into the atmosphere.

2. These gases trap heat and lead to a rise in the Earth's temperature, contributing to global warming.

No single layer of the atmosphere is more significant than the others. Each layer has a unique and important role in supporting life on Earth.

The troposphere supports life and is where weather occurs. The stratosphere contains the ozone layer, which protects us from harmful ultraviolet (UV) rays. The mesosphere burns up most meteoroids before they reach the Earth. The thermosphere absorbs high-energy solar radiation and is where many satellites orbit. The exosphere is the outermost layer and gradually merges into space.

Therefore, all the layers of the atmosphere are interconnected and equally important for maintaining Earth's environment and protecting life.

Global warming is caused by the increase in greenhouse gases in the atmosphere due to human activities. Gases such as carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) trap the Sun's heat in the atmosphere, causing the Earth's average temperature to rise. This is known as the greenhouse effect.

To preserve the atmosphere and reduce global warming, people can:

1. Reduce carbon emissions by using public transport, cycling, walking, or renewable energy instead of fossil fuels.
2. Conserve energy by switching off lights and appliances when not in use and using energy-efficient devices.
3. Support sustainable agriculture by reducing food waste and encouraging eco-friendly farming practices.
4. Conserve water by using it wisely and preventing wastage.
5. Follow the 3Rs - Reduce, Reuse, and Recycle to minimize waste and pollution.

One significant effect of climate change that affects me is the increasing frequency of heatwaves. Rising temperatures make summers much hotter, causing discomfort, dehydration, and heat-related illnesses. They also increase electricity consumption due to greater use of cooling appliances and can affect daily life and productivity.