Question
Which of the following gases has the lowest residence time ?
The correct answer is
$\text{CH}_4$
Identifying Gas with Lowest Residence Time
The residence time of a gas in the atmosphere is the average time it spends there before being removed or transformed. Gases with shorter residence times are removed more quickly.
Comparing Atmospheric Residence Times
Let's examine the approximate atmospheric residence times for the given gases:
| Gas | Approximate Residence Time (Years) |
|---|---|
| $\text{CO}_2$ | 100 - 200 |
| $\text{N}_2\text{O}$ | ~114 |
| CFCs | Decades to Millennia (Highly Variable) |
| $\text{CH}_4$ | 8 - 12 |
Conclusion on Residence Time
Comparing the residence times:
- Methane ($\text{CH}_4$) has the shortest residence time, typically around 8 to 12 years.
- Carbon Dioxide ($\text{CO}_2$) and Nitrous Oxide ($\text{N}_2\text{O}$) have significantly longer residence times.
- Chlorofluorocarbons (CFCs) generally have very long atmospheric lifetimes, often much longer than $\text{CO}_2$ or $\text{N}_2\text{O}$.
Therefore, methane ($\text{CH}_4$) is the gas with the lowest residence time among the options provided.
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Important Questions from Global Environmental Issues
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- Stratospheric ozone absorbs UV radiations principally in the wavelength range
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