Which of the following is NOT a greenhouse gas?

Question

Accepted Answer

Explanation:

1. Definition: A greenhouse gas (GHG) is one that absorbs outgoing longwave (infrared) radiation, trapping heat in the atmosphere.

2. Check each option:
- (1) Methane: $\mathrm{CH_4}$ — a potent greenhouse gas with high global warming potential.
- (2) Carbon dioxide: $\mathrm{CO_2}$ — the primary long-lived greenhouse gas from combustion and respiration.
- (3) Nitrous oxide: $\mathrm{N_2O}$ — a powerful greenhouse gas and ozone-depleting substance.
- (4) Nitric oxide: $\mathrm{NO}$ — a reactive nitrogen oxide (NOx) involved in atmospheric chemistry (ozone formation/destruction) but it does not significantly absorb outgoing longwave radiation and is not classified as a greenhouse gas.

3. Conclusion: Nitric oxide (option 4) is NOT a greenhouse gas.

FINAL_ANSWER: d

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