Question

Which one or more of the following is/are greenhouse gas(es)? 

• A. Methane
• B. Water vapour
• C. Sulphur dioxide
• D. Nitrous oxide

Hint:

Common greenhouse gases to remember for GATE Ecology: {CO$_2$, CH$_4$, N$_2$O, and H$_2$O}. Gases like SO$_2$ mainly cause cooling via aerosols, not greenhouse warming.

Answer 1

The Correct Option is A, B, D

Greenhouse gases are components of the atmosphere that contribute to the greenhouse effect by absorbing and emitting radiation within the thermal infrared range. Let's analyze each option to determine which are greenhouse gases:

1. Methane (CH₄): Methane is a well-known greenhouse gas. It is emitted from natural sources as well as human activities such as livestock management and agriculture. It has a significant impact on Earth's climate system due to its capacity to trap heat.
2. Water vapour (H₂O): Water vapour is the most abundant greenhouse gas in the earth's atmosphere. Although it acts as a feedback rather than a direct radiative forcing agent, it contributes significantly to the greenhouse effect by amplifying the effects of other greenhouse gases.
3. Sulphur dioxide (SO₂): Sulphur dioxide is not a greenhouse gas. Although it plays a role in atmospheric chemistry and can lead to acid rain, it does not significantly trap heat in the atmosphere. It can actually lead to cooling effects by forming aerosols that reflect sunlight.
4. Nitrous oxide (N₂O): This is a potent greenhouse gas. It is emitted from agricultural practices, fossil fuel combustion, and various industrial activities. It absorbs heat and contributes to global warming.

Based on the analysis above, the correct options that are greenhouse gases are:

• Methane
• Water vapour
• Nitrous oxide

Therefore, the correct answer is Methane, Water vapour, and Nitrous oxide.

Answer 2

Step 1: Recall the definition of greenhouse gases.
Greenhouse gases are atmospheric gases that absorb and emit infrared radiation, thereby trapping heat in the Earth’s atmosphere and contributing to the greenhouse effect.
Step 2: Analyze option (A) — Methane.
Methane (CH$_4$) is a major greenhouse gas with a high global warming potential.
It absorbs infrared radiation effectively and contributes significantly to climate change.
Hence, (A) is correct.
Step 3: Analyze option (B) — Water vapour.
Water vapour (H$_2$O) is the most abundant greenhouse gas in the atmosphere.
It plays a crucial role in regulating Earth’s temperature through strong absorption of infrared radiation.
Hence, (B) is correct.
Step 4: Analyze option (C) — Sulphur dioxide.
Sulphur dioxide (SO$_2$) primarily contributes to aerosol formation and has a cooling effect by reflecting sunlight.
It is not considered a greenhouse gas.
Hence, (C) is incorrect.
Step 5: Analyze option (D) — Nitrous oxide.
Nitrous oxide (N$_2$O) is a potent greenhouse gas with a long atmospheric lifetime.
It absorbs infrared radiation and contributes to global warming.
Hence, (D) is correct.
Step 6: Conclusion.
The gases that act as greenhouse gases among the given options are: \[ \boxed{(A),\ (B)\ \text{and}\ (D)} \]