How exactly does CO2 behave as a greenhouse gas?

[falcon32]

Hi everyone,

This is my very first post here, so hi!

I've got a few questions about CO2 that maybe a physics buff can help me out with. I understand the basics about CO2 warming the atmosphere via absorption and re-emission (radiatively or kinetically) of Outgoing Longwave Radiation...but can't find any in-depth details on the mechanics of it.


Conceptually, and considering only EM energy of the proper wavelength to excite CO2 molecules...

1. What percent of CO2 molecules transfer their absorbed energy kinetically, and what percent radiate?

2. Of the molecules that do radiate, what percent of these radiate a wavelength with lower energy than the one originally absorbed?

3. If lower energy is emitted, is CO2 opaque with respect to it?

These questions bring me to...

4. If CO2 is not saturated, would it absorb completely, and never emit (black when viewed in absorption bandwidth)? That is, below an effective saturation point, do we get total conversion into kinetic, not photonic?

I understand by Beer-Lambert that there is no true technical, 'saturation' point because of the logarithmic relationship, but for the sake of argument, (to help me grasp the subject) pretend there is.

Thanks, appreciate the help!

 

[falcon32]

So far, one hundred and forty-two people have viewed this post. Of these, zero have replied.

It seems I have found a question no one is capable of answering. :P

 

[mathman]

http://www.ess.uci.edu/~prather/IPCC/2001IPCC_Chap04-PratherEhhalt.pdf

You might want to look at the above. Also Google "greenhouse gases chemistry".

I suspect that you got no responses, since it takes a specialist in this area to answer your questions.

 

[LostConjugate]

I will try to give some answers.

1. What percent of CO2 molecules transfer their absorbed energy kinetically, and what percent radiate?

Kinetically? You mean between each other? They transfer the kinetic energy between each other until it is all radiated away.

2. Of the molecules that do radiate, what percent of these radiate a wavelength with lower energy than the one originally absorbed?

100%

3. If lower energy is emitted, is CO2 opaque with respect to it?

Not sure, depends on the frequency.

4. If CO2 is not saturated, would it absorb completely, and never emit (black when viewed in absorption bandwidth)? That is, below an effective saturation point, do we get total conversion into kinetic, not photonic?

Perfect Black Bodies are not possible, so no.