Atmosphere

The atmosphere is composed of gases, water vapour, dust particles and smoke. The gases include nitrogen, oxygen, argon, carbon dioxide, neon, ozone, hydrogen, helium and methane. Nitrogen (78%) and oxygen (21%) are the two main gases while other gases are found in very small quantities. The heavier gases like oxygen, water vapour and dust particles are found in the lower layers of the atmosphere.

Smoke, salts and carbon monoxide are the three impurities found in the atmosphere.

On the basis of composition, density and temperature, the different layers of the atmosphere are:

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

Two importance of the atmosphere are:

1. It maintains the earth's temperature by keeping it warm even at night.
2. Protection from harmful ultraviolet rays of the sun.

The earth's atmosphere traps the heat energy that comes from the sun and prevents the earth from becoming too cold at night. This is known as the greenhouse effect. There are gases which absorb the heat energy and maintain a liveable temperature on the earth. Theses gases are called the greenhouse gases. Some of them are carbon dioxide (CO₂), nitrous oxide (N₂O), chlorofluorocarbons (CFCs), methane (CH₄) and water vapour.

The excess accumulation of greenhouse gases in the atmosphere disturbs the energy balance. This can increase the heat and cause rise in air temperature. This increase in air temperature due to excessive concentration of greenhouse gases is called global warming.

Three impacts of global warming are:

1. Rise in sea level — Increase in air temperature would speed up the melting of glaciers, ice caps and other icebergs in the northern and southern parts of the world which will lead to the rise in sea level and the flooding of coastal areas.
2. Change in agriculture — Increase in air temperature may affect the world food production as the change in the rainfall pattern would affect crop yields and types of crops cultivated.
3. Climate change — As the earth heats up, the world climatic pattern will change. Floods, storms, heat waves, fires and droughts could also become more common.

The vertical column thickness of the ozone layer above 220 DU is considered normal but when thickness of the ozone layer in the stratosphere falls below 220 DU, then it is termed as ozone hole.

The aim of the Montreal Protocol is to phase out the use of ozone-depleting substances and to find or develop non-toxic substances by adopting the following methods:

1. Safe disposal of air conditioners and old refrigerators at recycling yards.
2. Avoiding ozone depleting substances from being released into atmosphere.
3. Properly disposing ozone-depleting substances as environmentally hazardous waste.

1. In the atmosphere, the density of air decreases with increase in height.
2. All weather phenomena occurs in the troposphere.
3. A greenhouse is a glass house used to grow plants in cold areas.
4. A rise in sea level due to global warming will cause flooding of coastal areas.
5. Dobson Unit is used to measure the thickness of ozone layer.

1. Global Warming
2. Greenhouse Effect
3. Ozone Hole
4. Carbon Footprint
5. Stratosphere

Greenhouse gases are gases which absorb heat energy that comes from the sun and prevents the earth from becoming too cold at night and thus maintain a liveable temperature on the earth. The excess accumulation of greenhouse gases increases the heat and cause rise in air temperature and finally lead to global warming.

The ozone layer absorbs the harmful ultraviolet rays of the sun and thus protects life on earth. The depletion of the ozone layer will result in more ultraviolet rays reaching the earth's surface. This can cause serious damage to different forms of life as it can cause skin cancer, eye cataract, immune deficiency and respiratory illness.

The envelope of air consisting of a mixture of colourless, odourless and tasteless gases, which surrounds the earth is called atmosphere.

Nitrogen and Oxygen are the two main gases found in the atmosphere.

Mesosphere is the coldest layer of atmosphere.

True.

Inside a greenhouse, the air temperature is more than it is outside.

oxygen

ionosphere

carbon dioxide

afforestation

chlorofluorocarbons

False.

Corrected Statement — The composition of air in the atmosphere is not uniform and varies from place to place and from time to time.

True.

True.

False.

Corrected Statement — Reduction in deforestation is a way to control global warming.

True.