Question about spectral absorption of CO2

[William Gaatjes]

http://forums.anandtech.com/showthread.php?t=2063387

In this tread i posted a question but i think i am better of here.

The global warming people mention greenhouse gases, but what i know is that in a greenhouse it is aways very humid. Afcourse one wants to increase the carbon dioxide in a greenhouse because carbon dioxide is part of a plants diet. i have always wondered what the spectral absorption and reflection is of carbon dioxide. Does anybody know ?

 

[CycloWizard]

I don't recall the specific values, but its primary absorption peak happens to coincide with the minimum in the water absorption spectra. I think it was somewhere in the near IR range, but it's been years since I really read much about it.

 

[beginner99]

hAfcourse one wants to increase the...eaningful argument but good to as an analogy.

 

[Paperdoc]

This site:

http://chemlinks.beloit.edu/Warming/moviepages/IRconc.htm

has an animated display of CO2 absorption depending upon the concentration, but you can see where the three main groups of peaks are. From a global warming perspective, probably the most troublesome is the band around 666 wavenumbers. This is the lower-energy (longer wavelength) area in which emissions occur from lower-temperature materials on the earth's surface. The "low-grade heat" this represents fails to penetrate through our atmosphere to outer space because it is absorbed by gases like CO2, held in the atmosphere, and re-radiated in random directions. This is the basis of the Greenhouse Effect. Water has a similar effect on different infrared wavelengths.

The Greenhouse Effect does not depend directly on the humidity of the greenhouse. In a REAL greenhouse used for plant growing, the actual main barrier to the escape of low-grade heat out of the greenhouse is the glass or plastic covering. But the term also is applied to the same mechanism when one considers the earth as a whole with a "covering" of our atmosphere with its mixture of several gases. Among them several like water and CO2 are very effective at trapping the low-grade heat waves so they cannot escape outside our "greenhouse", earth. The more of these gases there are in that atmosphere, the more effective that is at trapping the heat on the earth's surface.

Within limits of course, as beginner99 points out, more CO2 may be beneficial to plants since it is their primary source of nutrients for building carbohydrate molecules for growth. For that reason one might project that, as global warming continues and CO2 and H2O levels rise in the atmosphere, plants will grow even larger and become a more important life class on the planet. Even though we use plants as food ourselves, humans probably will NOT do so well because those conditions are optimal for plants, not people. As many have said, global warming will not kill the planet. Lifeforms will continue to thrive on this earth. They just won't be the ones that we prefer.

 

[William Gaatjes]

This site:

http://chemlinks.beloit.edu/Warming/moviepages/IRconc.htm

has an animated display of CO2 absorption depending upon the concentration, but you can see where the three main groups of peaks are. From a global warming perspective, probably the most troublesome is the band around 666 wavenumbers. This is the lower-energy (longer wavelength) area in which emissions occur from lower-temperature materials on the earth's surface. The "low-grade heat" this represents fails to penetrate through our atmosphere to outer space because it is absorbed by gases like CO2, held in the atmosphere, and re-radiated in random directions. This is the basis of the Greenhouse Effect. Water has a similar effect on different infrared wavelengths.

The Greenhouse Effect does not depend directly on the humidity of the greenhouse. In a REAL greenhouse used for plant growing, the actual main barrier to the escape of low-grade heat out of the greenhouse is the glass or plastic covering. But the term also is applied to the same mechanism when one considers the earth as a whole with a "covering" of our atmosphere with its mixture of several gases. Among them several like water and CO2 are very effective at trapping the low-grade heat waves so they cannot escape outside our "greenhouse", earth. The more of these gases there are in that atmosphere, the more effective that is at trapping the heat on the earth's surface.

Within limits of course, as beginner99 points out, more CO2 may be beneficial to plants since it is their primary source of nutrients for building carbohydrate molecules for growth. For that reason one might project that, as global warming continues and CO2 and H2O levels rise in the atmosphere, plants will grow even larger and become a more important life class on the planet. Even though we use plants as food ourselves, humans probably will NOT do so well because those conditions are optimal for plants, not people. As many have said, global warming will not kill the planet. Lifeforms will continue to thrive on this earth. They just won't be the ones that we prefer.

Woeha, if i was religious, i would have thought that you just found the antichrist. :

6 protons. 6 neutron. 6 electrons. Carbon C-12 it is.
i love coincidences. Now if we only can find buckyballs (twenty hexagons and twelve pentagons) up in the air then we have 2012 and christians and doom believers can go wild

But to be serious again, thank you very much to all posters.

I found some information myself after another poster replied as well.
If i understand correctly and partially do it from the head i would get around 15um ?
That does not sound right.

I found this site : http://www.chemguide.co.uk/analysis/ir/background.html#top
http://www.chemguide.co.uk/analysis/ir/fingerprint.html#top

In this picture it is mentioned what is absorbed by our atmosphere, does anybody know if it is correct ?
http://mc2.gulf-pixels.com/wp-content/uploads/2009/07/Electromagnetic-Spectrum2.jpg

Even though we use plants as food ourselves, humans probably will NOT do so well because those conditions are optimal for plants, not people. As many have said, global warming will not kill the planet. Lifeforms will continue to thrive on this earth. They just won't be the ones that we prefer.

If global warming is true or not, i totally agree. That must not happen until humanity is able to adjust quick to every hazardous change in the environment. Something i suspect that is inevitable to happen.

 

[Paperdoc]

The absorption bands in the picture are approximately correct. You see that the atmosphere will allow penetration of low-frequency radio waves and of visible light. It partially absorbs lower-frequency microwaves (this is why some satellite TV signals and internet transceivers can be disturbed by rain, etc - they operate in the low microwave region) and high-frequency infrared close to visible red. This latter band includes the absorption peaks for CO2 over 3500 wavenumbers, and that's why they are less important for global warming. But other lower infrared frequencies are blocked and trapped near the earth's surface by the atmosphere.

The "wavenumbers" unit is an odd unit of "frequency" used in IR spectroscopy. Wavenumbers is just the inverse of the wavelength measured in cm. Because multiplying a wavenumber value by a constant (the velocity of light in cm/second) gives you frequency of the radiation (in Hertz) directly, it is used like a measurement of frequency. Higher wavenumbers means higher frequency and energy. The units of wavenumbers are just (cm)^-1. So the 666 wavenumber peak I mentioned for CO2 has a wavelength of 1/666 cm, or 1000/666 milli-cm (not a commonly used unit!) or 10/666 milli-m (better known as millimeters), or 10,000/666 micro-meters. That's 16 microns, same as you got.