CO2 and IR absoption

October 16th, 2009 at 4:03 am
Re: thefordprefect (#186),
"From what I have seen the logarithmic effect is usually explained by the absoption bands getting full - ie. no more radiation can be absorbed. Radiation is then absorbed by smaller absorptions bands and and by the under used width of the CO2 bands.
And the CO2 GH effect is vastly lessened by many of the bands falling within the H20 bands."
I don't konw where you have seen that but this explanation is not even wrong .
It is absolutely and totally forbidden that a band , any band gets "full" or "saturated" .
The population that is in an excited state is a CONSTANT for a given temperature (f.ex the CO2 15µ excited state represents 5 % of the total CO2 population at room temperatures) . This is prescribed by the MB distribution of the quantum states .
It doesn't depend on the number of molecules , the intensity of radiation or the age of the captain . Only temperature .
So whatever amount of IR you throw at a CO2 population , they will absorb it all and REEMIT .
They can't do anything else because they must do whatever it takes to keep the percentage of excited states constant .
Imagine a dam (CO2 molecules) and a lake whose level (percentage of excited states) is exactly at the top of the dam .
If you increase the flow in the lake (absorbed radiation) all that will happen is that the flow over the top of the dam (emitted radiation) will increase by exactly the same amount .
If you increase the height of the dam (temperature) , the level of the lake will go in a transient untill it gets to the new top and then it's again exactly like described above .
There is no "saturation" .

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