Q.5 The decreasing order of concentration of green house gases (GHGs) in the
atmosphere is :
(A). CO2
(B). CH4
(C). CFCs
(D). N2O
Choose the correct answer from the options given below:
1. (A), (B), (C), (D).
2. (A), (C), (B), (D).
3. (B), (A), (D), (C).
4. (C), (B), (D), (A).
Decreasing Order of Greenhouse Gas Concentrations: CO2 > CH4 > N2O > CFCs
The correct answer to the query is option 1: (A), (B), (C), (D), ranking CO₂ > CH₄ > CFCs > N₂O by atmospheric concentration.
Why Concentration Matters
Atmospheric concentration measures GHGs in parts per million (ppm) or parts per billion (ppb), reflecting their abundance rather than warming potency (GWP). COâ‚‚ dominates due to vast emissions from fossil fuels, while others are trace gases.
Current Concentrations
| Gas | Concentration (2024-2025) | Notes |
|---|---|---|
| COâ‚‚ (A) | ~424-427 ppm | Highest by far; rose from 280 ppm pre-industrial. |
| CH₄ (B) | ~1,900 ppb (1.9 ppm) | Second; from agriculture, leaks.​ |
| N₂O (D) | ~340 ppb (0.34 ppm) | Lower; from fertilizers, soils.​ |
| CFCs (C) | <1 ppb (0.001 ppm) | Lowest; phased out by Montreal Protocol.​ |
This order holds as COâ‚‚ vastly outnumbers others volumetrically.
Option Breakdown
-
(A) COâ‚‚: Leads at over 420 ppm, comprising ~0.04% of air; primary GHG by volume.
-
(B) CH₄: ~100x less than CO₂ but potent; total ~1.9 ppm equivalent.​
-
(C) CFCs: Ultra-trace (<0.001 ppm); high GWP but negligible concentration.​
-
(D) N₂O: ~0.00034%; between CH₄ and CFCs in abundance.​
Common Confusions
Options like 4 reverse to CFCs first, mixing GWP (where CFCs excel) with concentration. Exams test volume, not potency. For biology students, note COâ‚‚’s role in photosynthesis ties to its prevalence.
