Atmospheric CO2 and diurnal Asymmetry

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  • #1
johnbbahm
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Something that has bothered me is that CO2 appears to have a much greater role after dark than in the daytime. I was wondering if this is because of a CO2 population inversion during the sunlight hours.
I am thinking that Sunlight and daytime blue sky, excite atmospheric nitrogen,
The nitrogen vibration ally passes the energy to CO2, which spontaneously decays back to ground state.
In a CO2 laser, helium is added to speed up the decay of the .2 eV back to ground.
In the atmosphere, there is insufficient helium for this task, and so the CO2 energy cycle would slow down.
The evidence of something like this happening would be 9.6 and 10.6 um emission spectra,
present during sunlight hours, but not after dark.
Does anyone have a source for daytime vs nighttime infrared sky spectra?
 

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  • #2
haruspex
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CO2 appears to have a much greater role after dark than in the daytime.
Can you be more specific? E.g. in daylight hours the CO2 would be intercepting IR in both directions, whereas at night it is all from ground.
Sunlight and daytime blue sky, excite atmospheric nitrogen,
Not to any great extent, other than in extreme UV, surely?
 
  • #3
johnbbahm
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Can you be more specific? E.g. in daylight hours the CO2 would be intercepting IR in both directions, whereas at night it is all from ground.

Not to any great extent, other than in extreme UV, surely?
What I am thinking is that during the sunlight hours, the CO2 quickly gets into a population inversion state,
and a much lower percentage of CO2 molecules are available to intercept IR.
Since the observed diurnal asymmetry is roughly 3:1 night vs daytime warming,(Karl et al 1993) the effective daytime CO2
level would be around 320 ppm.
If this idea is correct, the evidence would be a greater level of 9.6 and 10.6 um atmospheric emissions, during sunlight hours than after sundown.
 
  • #4
DrClaude
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What I am thinking is that during the sunlight hours, the CO2 quickly gets into a population inversion state,
Why would you say that? First, sunlight is not strong enough (it is not laser light), and second, CO2 can't be considered as a two-level system. Even if there was significant excitation of the molecules, they could still absorb more at the same frequencies (absorption in the IR is mostly related to vibrational excitation).
 
  • #5
johnbbahm
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Why would you say that? First, sunlight is not strong enough (it is not laser light), and second, CO2 can't be considered as a two-level system. Even if there was significant excitation of the molecules, they could still absorb more at the same frequencies (absorption in the IR is mostly related to vibrational excitation).
Nitrogen does not need laser light to be excited, simply a photon in it's absorption band (Roughly 3.8 to 5 um)
CO2 does have a meta stable state at the .2 eV level, which can cause a population inversion and limit power in a laser.
Helium is used in the gas mixture, to allow more molecules to get back to ground state where they can be excited again.
The same forces are at work in the atmosphere, but without the helium.
If I am correct, then the excited nitrogen would be vibration ally exciting the CO2 to the .3 eV level, during the sunlight hours.
The evidence of this would be higher levels of 9.6 and 10.6 um bands in the daylight than at night.
 
  • #6
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CO2 does have a meta stable state at the .2 eV level, which can cause a population inversion
Please give a reference demonstrating that this can happen in the atmosphere.
 
  • #7
johnbbahm
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We know it happens at atmospheric range pressures in the lab, the question is why would it not happen in the atmosphere?
The real question is if the artifacts of these energy transitions are detectable,
i.e. are the 9.6 and 10.6 um bands more pronounced during the sunlight hours?
 
  • #8
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We know it happens at atmospheric range pressures in the lab, the question is why would it not happen in the atmosphere?
Because we don't have the specific pumping conditions needed for a CO2 laser in the atmosphere.
I asked for a reference, which means a peer-reviewed publication, not for "why not" questions.
 
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  • #9
johnbbahm
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Sorry, Most of the discussions of energy states of atmospheric nitrogen revolve around much higher energy states.
http://iopscience.iop.org/article/10.1088/1367-2630/11/6/065011/meta
This air fluorescence demonstrates that excited nitrogen exists in the atmosphere.
They even mention that,
"2.2. Fluorescence quenching
Non-radiative molecular de-excitation by collision with other molecules of the medium (collisional quenching) becomes very important even at moderate pressures."
The reasoning is that if we have excited atmospheric nitrogen, as it cycles back to ground state, it can pass energy
to any CO2 molecule it encounters, the question is weather this behavior is asymmetrical with day and night?
 
  • #10
haruspex
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the question is weather this behavior is asymmetrical with day and night?
It would clearly be a daytime effect, but is it strong enough to explain the observation you raised in post #1?

Anyway, as I mentioned in post #2, it is not clear what observation you have in mind. Can you be more precise about CO2 having a "greater rôle" at nght?
 
  • #11
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@johnbbahm: This has nothing to do with the claim of a population inversion, or CO2 in general. I closed this thread, if you find a reference discussing such a population inversion send me a message then I will open the thread again.
 
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