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). CO₂ dominates due to vast emissions from fossil fuels, while others are trace gases.
Current Concentrations
| Gas | Concentration (2024-2025) | Notes |
|---|---|---|
| CO₂ (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 CO₂ vastly outnumbers others volumetrically.
Option Breakdown
-
(A) CO₂: 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 CO₂’s role in photosynthesis ties to its prevalence.
