Welcome to the COMPETITIVE EXAM MCQs SERIES of ENVIRONMENTAL SCIENCE for UGC-NET/JRF, SLET, GATE, and other entrance tests – Structure and Composition of the Atmosphere.
Syllabus Outline
- Introduction to the Earth’s atmosphere and its layers.
- Composition of the atmosphere: Major and trace gases.
- Vertical distribution of temperature and pressure in the atmosphere.
- Atmospheric circulation: Global wind patterns, monsoons, and local winds.
- Atmospheric humidity and precipitation: Concepts of relative humidity, dew point, and different forms of precipitation.
- Atmospheric stability and adiabatic processes.
- Atmospheric optics: Phenomena like scattering, refraction, and reflection in the atmosphere.
- Greenhouse effect and global warming.
- Air pollution and its impact on the atmosphere.
- Ozone layer depletion and its environmental implications.
- Aerosols and their role in atmospheric processes.
- Atmospheric modelling and climate change predictions.
Quick Study Guide
The Earth’s atmosphere is a complex layer of gases surrounding our planet. Understanding how it works is essential for environmental science exams like the UGC NET and GATE.
1. Layers and Composition
- The Layers: The atmosphere is divided into four main layers based on temperature: the troposphere (where we live and where weather happens), the stratosphere (home to the protective ozone layer), the mesosphere, and the thermosphere.
- What It’s Made Of: The air is mostly Nitrogen (78%) and Oxygen (21%). However, tiny amounts of “trace gases”—like Carbon Dioxide, Methane, and Water Vapor—are incredibly important because they trap heat and control the planet’s temperature.
- Pressure and Temperature: As you go higher in the atmosphere, the air gets thinner, meaning air pressure drops. Temperature also changes drastically depending on which layer you are in.
2. Weather and Wind
- Global Winds: The sun heats the Earth unevenly. This uneven heating, combined with the Earth’s spin, creates global wind patterns that move heat and moisture around the world.
- Humidity and Rain: Warm air can hold more water vapour than cold air. When air cools down to a specific temperature (its “dew point”), the water vapour turns into liquid, causing rain, snow, or hail.
- Atmospheric Stability: This refers to whether a pocket of air naturally wants to rise or sink. Unstable air rises quickly, creating clouds and storms, while stable air resists moving and leads to clearer skies.
3. Light and Heat
- Atmospheric Optics: Gases in the atmosphere scatter sunlight. They scatter blue light more easily than other colours, which is why the sky looks blue. Larger particles, like water droplets, scatter all light equally, making clouds look white.
- The Greenhouse Effect: Certain gases act like a blanket, trapping the Earth’s heat and keeping the planet warm enough to live on. However, human activities are adding too many of these gases, trapping extra heat and causing global warming.
4. Pollution and Climate Change
- Air Pollution: Chemicals and particles released by human activity (like car exhaust and factory emissions) create smog, lower air quality, and harm human health.
- Ozone Depletion: Human-made chemicals (like CFCs from old refrigerants) have damaged the ozone layer in the stratosphere. This allows more harmful UV radiation from the sun to reach the surface.
- Aerosols: These are tiny floating particles, like dust, smoke, or soot. They can cool the Earth by reflecting sunlight into space, or warm it by absorbing heat. They are also necessary for clouds to form.
- Climate Models: Scientists use complex computer programs to simulate how the atmosphere behaves. This helps them predict future climate changes, rising sea levels, and extreme weather events.
Test Your Knowledge
This quiz contains the concept-based most frequently asked 25 MCQs of “Structure and Composition of the Atmosphere“. Each question has a single correct/most appropriate answer.
1. Assertion (A): The greenhouse effect is primarily due to water vapour in the atmosphere.
Reasoning (R): Water vapour is the most abundant greenhouse gas and traps a significant amount of heat radiated from the Earth’s surface.
a) Both A and R are true, but R is not the correct explanation of A.
b) Both A and R are true, and R is the correct explanation of A.
c) A is true, but R is false.
d) A is false.
2. The atmosphere contains various layers, each having a characteristic composition. The correct sequence starting from the Earth’s surface is:
a) Troposphere – Stratosphere – Mesosphere – Thermosphere
b) Stratosphere – Troposphere – Mesosphere – Thermosphere
c) Stratosphere – Mesosphere – Troposphere – Thermosphere
d) Mesosphere – Stratosphere – Thermosphere – Troposphere
3. Assertion (A): The troposphere is the densest layer of the atmosphere.
Reasoning (R): The weight of the air above compresses the air molecules in the troposphere, resulting in higher air density.
a) A is true, but R is false.
b) Both A and R are true, but R is not the correct explanation of A.
c) A is false.
d) Both A and R are true, and R is the correct explanation of A.
4. Assertion (A): The stratosphere is warmer than the troposphere.
Reasoning (R): The stratosphere contains a higher concentration of ozone, which absorbs and re-emits solar radiation, leading to an increase in temperature with altitude.
a) A is true, but R is false.
b) Both A and R are true, but R is not the correct explanation of A.
c) Both A and R are true, and R is the correct explanation of A.
d) A is false.
5. Which gas is responsible for the blue colour of the sky?
a) Carbon dioxide
b) Oxygen
c) Nitrogen
d) Water vapour
6. Which gas is the third most abundant in Earth’s atmosphere?
a) Nitrogen
b) Argon
c) Oxygen
d) Carbon dioxide
7. Which gas is responsible for the red colour of the sunset?
a) Carbon dioxide
b) Nitrogen
c) Oxygen
d) Ozone
8. The Coriolis effect is caused by:
a) Ocean currents
b) Earth’s rotation
c) Atmospheric pressure differences
d) Greenhouse gases
9. The dew point is the temperature at which:
a) Water evaporates from surfaces
b) Dew forms on surfaces
c) Air becomes saturated with water vapour
d) Rainfall occurs
10. The layer of the atmosphere that contains the ozone layer is located approximately:
a) 0-10 kilometres above Earth’s surface
b) 100-500 kilometres above Earth’s surface
c) 10-50 kilometres above Earth’s surface
d) 50-100 kilometres above Earth’s surface
11. The layer of the atmosphere where most meteoroids burn up upon entering is the:
a) Thermosphere
b) Mesosphere
c) Stratosphere
d) Troposphere
12. The mesosphere is the layer of the atmosphere where:
a) Most weather phenomena occur
b) The temperature increases with altitude
c) Satellites orbit the Earth
d) The auroras (Northern and Southern Lights) occur
13. The term albedo refers to:
a) The density of air in the atmosphere
b) The reflection of solar radiation from Earth’s surface
c) The absorption of carbon dioxide by plants
d) The amount of ozone in the atmosphere
14. The ozone layer is important for protecting life on Earth because it:
a) Absorbs harmful ultraviolet radiation
b) Regulates the Earth’s climate
c) Absorbs carbon dioxide
d) Produces oxygen through photosynthesis
15. Assertion (A): The ozone layer benefits life on Earth.
Reasoning (R): The ozone layer absorbs harmful UV radiation from the Sun, preventing it from reaching the Earth’s surface and protecting living organisms.
a) Both A and R are true, but R is not the correct explanation of A.
b) A is false.
c) Both A and R are true, and R is the correct explanation of A.
d) A is true, but R is false.
16. The atmospheric layer that contains the ozone layer is warmer than the layer below it due to:
a) Emission of greenhouse gases
b) Advection of warm air from the equator
c) Conduction of heat from Earth’s surface
d) Absorption of solar radiation by ozone
17. Which of the following is not a primary air pollutant?
a) Ozone
b) Nitrogen dioxide
c) Carbon monoxide
d) Sulfur dioxide
18. Which weather conditions are most conducive to the formation of photochemical smog?
a) Foggy and misty weather
b) Hot and humid weather
c) Cold and dry weather
d) Windy and rainy weather
19. The tropopause is the boundary between which two atmospheric layers?
a) Troposphere and stratosphere
b) Stratosphere and mesosphere
c) Thermosphere and exosphere
d) Mesosphere and thermosphere
20. The process by which a gas changes directly into a solid is called:
a) Sublimation
b) Condensation
c) Evaporation
d) Deposition
21. The layer of the atmosphere where the International Space Station orbits is the:
a) Thermosphere
b) Mesosphere
c) Stratosphere
d) Troposphere
22. In a close ecosystem, across its boundaries:
a) Both energy and mass cannot be transferred
b) Mass can transfer, but energy cannot transfer
c) Both energy and mass can transfer
d) Energy can transfer, but mass cannot transfer
23. Assertion (A): The ozone hole is primarily caused by human activities.
Reasoning (R): Certain chemicals, such as chlorofluorocarbons (CFCs), released by human activities, can deplete the ozone layer, leading to the formation of an ozone hole.
a) A is false.
b) A is true, but R is false.
c) Both A and R are true, and R is the correct explanation of A.
d) Both A and R are true, but R is not the correct explanation of A.
24. The layer of the atmosphere where weather phenomena occur is the:
a) Mesosphere
b) Troposphere
c) Thermosphere
d) Stratosphere
25. The atmospheric layer where the Northern and Southern Lights occur is the:
a) Thermosphere
b) Mesosphere
c) Stratosphere
d) Troposphere
Previous: Fundamentals of Environmental Sciences
Next: Laws of thermodynamics
References
- Erach Bharucha (2017). Environmental Studies, Universities Press, 4th edition
- Richard Goody (1995). Principles of Atmospheric Physics and Chemistry, Oxford University Press, 1st Edition.
- Frederick K. Lutgens, Edward J. Tarbuck, Redina L. Herman (2019). The Atmosphere: An Introduction to Meteorology, Pearson, 14th edition.
- John H. Seinfeld, Spyros N. Pandis (2016). Atmospheric Chemistry and Physics: From Air Pollution to Climate Change, John Wiley & Sons, 3rd edition.
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