Question

Which among the following is NOT a greenhouse gas?

• A. CO2
• B. CH3
• C. CO
• D. O3

Hint:

Greenhouse Gases:
Direct Primary GHGs = $\text{CO}_2, \text{CH}_4, \text{N}_2\text{O}, \text{O}_3, \text{CFCs}, \text{H}_2\text{O}$ vapor.
NOT Direct GHGs = Carbon Monoxide (CO), Nitrogen gas ($\text{N}_2$), Oxygen ($\text{O}_2$).

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Atmospheric radiation physics and greenhouse gases: Carbon monoxide (CO) is a short-lived indirect atmospheric pollutant without strong infrared absorption bands, unlike direct primary GHGs ($ ext{CO}_2, ext{CH}_4, ext{N}_2 ext{O}, ext{O}_3, ext{H}_2 ext{O}$).

Step 2: Detailed Explanation:
Evaluating atmospheric greenhouse gases (GHGs):
1. Direct Greenhouse Gases: Possess vibrational infrared-active molecular structures that absorb and re-emit terrestrial infrared thermal radiation:
- Carbon Dioxide ($\text{CO}_2$)
- Methane ($\text{CH}_4$ written as $\text{CH}_3$ radical proxy in options)
- Tropospheric Ozone ($\text{O}_3$)
- Nitrous Oxide ($\text{N}_2\text{O}$) and Water Vapor ($\text{H}_2\text{O}$).
2. Carbon Monoxide (CO) (C): A toxic indirect air pollutant; it lacks strong direct radiative forcing properties and is NOT classified as a primary greenhouse gas.

Step 3: Final Answer:
Therefore, CO is NOT a greenhouse gas, matching option (C).