Air

The Earth is surrounded by a blanket of air called the atmosphere, held by gravity. It contains about 78 percent nitrogen, 21 percent oxygen and small amounts of argon, carbon dioxide, water vapour and dust. Carbon dioxide traps heat radiated by the Earth, creating the greenhouse effect, and its increase is causing global warming. The atmosphere has five layers: the troposphere, where weather occurs, with an average height of 13 km; the stratosphere, up to about 50 km, which contains the protective ozone layer; the mesosphere, where meteorites burn up; the thermosphere, with the ionosphere that reflects radio waves; and the outermost exosphere. Weather is the day-to-day condition of the atmosphere, while climate is its average over many years. Temperature depends on insolation, the incoming solar energy. Air pressure decreases with height, and winds blow from high pressure to low pressure areas. Winds may be permanent, like the trade winds, westerlies and easterlies, seasonal, like the monsoons, or local, like the loo. Moisture in the air condenses into clouds and falls as convectional, orographic or cyclonic rainfall.

Detailed Worksheet: Air Section A - Definitions (10 marks) 1. What is the atmosphere? Why does it stay around the Earth? (2 marks) 2. Define weather and climate. (2 marks) 3. What is insolation? (2 marks) 4. What is air pressure? How does it change with height? (2 marks) 5. What is humidity? What is meant by precipitation? (2 marks) Section B - Calculations and Applications (15 marks) 6. The atmosphere contains 78 percent nitrogen and 21 percent oxygen by volume. In a room containing 500 cubic metres of air, find the volume of nitrogen and oxygen. What percentage is left for all other gases? (3 marks) 7. The temperature in the troposphere falls by about 6.5 degrees C for every 1 km rise in height. If it is 30 degrees C at sea level, find the temperature at a height of 4 km and at 8 km. (3 marks) 8. Arrange the layers of the atmosphere from the Earth's surface upwards and give the approximate height of the troposphere and stratosphere. (3 marks) 9. Classify these winds as permanent, seasonal or local: trade winds, monsoon, loo, westerlies, easterlies, land breeze. (3 marks) 10. Name the type of rainfall in each case: (i) heavy afternoon showers in equatorial regions (ii) rain on the windward side of the Western Ghats (iii) rain due to the meeting of warm and cold air masses. (3 marks) Section C - Diagrams (10 marks) 11. Draw a labelled diagram of the layers of the atmosphere with their approximate heights and one feature of each. (4 marks) 12. Draw a labelled diagram showing orographic (relief) rainfall over a mountain, marking the windward and leeward sides. (3 marks) 13. Draw a pie chart showing the composition of the atmosphere: nitrogen 78 percent, oxygen 21 percent, others 1 percent. (3 marks) Section D - Analysis and Higher-order Thinking (15 marks) 14. The amount of carbon dioxide in the atmosphere is rising. (i) Name two human activities that release it. (ii) Explain the greenhouse effect. (iii) What is global warming? (iv) Give two possible effects of global warming. (v) Suggest two ways to reduce it. (5 marks) 15. Mountaineers climbing Mount Everest carry oxygen cylinders and warm clothes. (i) Why does air become thinner at high altitudes? (ii) Why is it colder? (iii) Why do aeroplanes fly in the lower stratosphere? (iv) Why are deserts very hot by day and cold at night? (5 marks) 16. A city has many cars, factories and few trees. (i) What kind of air pollution is likely? (ii) What are its effects on health? (iii) What is smog? (iv) Suggest three steps to keep the air clean. (5 marks) Instructions: Time allowed 2 hours. Attempt all sections. Label diagrams clearly and write heights in kilometres.