Question

Why is carbon dioxide a greenhouse gas while nitrogen and oxygen are not? Consider the structures of these molecules and the absorption of light.

Answer 1

Ans.

A greenhouse gas is a gas that absorbs and re-emits energy in the infra red region.

Carbon dioxide is a greenhouse gas because it can absorb and re-emit IR radiation. Carbon dioxide has three vibrational modes which are IR active. Therefore, it can absorb IR radiation and re-emit IR radiation. Therefore, it is a greenhouse gas.

Whereas, diatomic molecules like nitrogen gas and oxygen gas are linear molecules with only one vibrational mode which is IR inactive. So, nitrogen gas and oxygen gas are IR inactive and they are not greenhouse gas.