Previous Year Question
With reference to “water vapour”, which of the following statements is/are correct?
It is a gas, the amount of which decreases with altitude.
Its percentage is maximum at the poles.
Select the answer using the codes given below.
Correct Answer: A
Detailed Solution
Statement 1 is correct:
Water vapour is a variable gaseous component of the atmosphere.
It enters the atmosphere mainly through evaporation from oceans, seas, rivers, lakes and soil, as well as through transpiration from plants.
Most atmospheric water vapour is concentrated close to Earth’s surface in the lower troposphere.
With increasing altitude, temperature and air pressure generally decrease, and the atmosphere’s capacity to hold water vapour declines. Its amount therefore decreases rapidly with altitude.
Besides facilitating cloud and precipitation formation, water vapour is also an important greenhouse gas.
Statement 2 is incorrect:
The percentage of water vapour is not maximum at the poles.
It is generally higher in warm and humid tropical regions because both temperature and evaporation are high.
Cold polar air has a very limited capacity to hold moisture. Consequently, the amount of water vapour in the polar regions is extremely low.
Atmospheric water-vapour content may vary from nearly zero to approximately 4%, depending upon location and time.