Methane and CO2 atmospheric lifetime math problem

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1. Nov 24, 2013

courtneywetts

1. The problem statement, all variables and given/known data

On a per-molecule basis, methane is 26 times more effective as an infrared absorber than is CO2. Calculate the corresponding ratio on a per-unit-mass basis, and compare it with the 20-year GWP for methane. What's the reason for any discrepncy you find?
(CO2 atmospheric lifetime = 1000 years, GWP relative to CO2 is 1 in 20 years)
(Methane atmospheric lifetime = 11 years, global warming potential relative to CO2 in 20 years is 23)

2. Relevant equations

3. The attempt at a solution

I am not sure how to start this problem. I think I need to make a ratio between methane and CO2 but am not sure if that is right or how to do so.

2. Nov 26, 2013

Hollumber

It gives you the ratio between their effectiveness per molecule. How to change this ratio considering the effectiveness per mass instead of molecule?

3. Nov 26, 2013

haruspex

Suppose 1 molecule of CO2 has absorption rating X.
Complete the following:
1 molecule of methane has absorption rating ...
1 molecule of methane has mass ... atomic units
1 molecule of CO2 has mass ... atomic units
... atomic units of CO2 has absorption rating X
1 atomic unit of CO2 has absorption rating ...
1 atomic unit of methane has absorption rating ...