Why is CO2 considered to be a greenhouse gas but N2 O2 and Ar are not?

Answer 1

Each gas absorbs energy from the sun, some more efficiently than others. Symmetric gases, such as O₂, N₂, and Ar neither absorb or emit infrared radiation and are not contributors. Water vapor is the worst offender, but we cannot do without water! That leaves CO₂, methane, ozone, and a few others that, fortunately, do not occur in any abundance.

Answer 2

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Why is CO2 considered to be a greenhouse gas but N2 O2 and Ar are not?

Answer 3

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One form of spectroscopy you may not have considered is mass spectroscopy. If your gas is pure then the parent ion will reveal its identity (match isotope pattern to computer simulated and the MS in the data bank). Helium leak detectors are little mass spectrometers that detect He^+ (4amu). If your gas is a mixture you may have to run it through a GC (GC MS). But I guess you're thinking about IR spectroscopy but it is limited for the analysis of simple gases: atomic gases eg Ar, Ne (Hg(g) cannot of course have any vibrations; homnucler diatomics such as O2 and N2 also do not absorbed in the IR (which is useful for creatures living on Earth) this is because there is no dipole moment change accompanying the vibration ↔O=O↔. For a heteronuclear diatomic (NO, CO, HCl(g): the bane of undergrad phys chem lab!) the stretch is IR active and is characteristic of the gases and has rotation fine structure (P,Q,R bands) pressure 1 atm pathlength 10 cm (gas cell) gives a beautiful spectrum. More complicated molecules have at least one active IR band (the asymmetric stretches) examples are CO2 (it is not called a greenhouse gas for nothing) H2O (that keeps us warm at night) CH4 (natural gas contributes to the greenhouse effect; don't blame the cows!) SF6. These species are often not present in large conc so pathlengths up to miles with reflecting mirrors can be used. In space I presume the pathlength could be several light years (OH• detected in space; Hertzberg a Canadian Noble prize winner wrote the book on the subject). For the homonuclear diatomics you presumably can use Raman spectroscopy because the stretch is active (different selection rule). The use of lasers make R routine now. You could also put your gas in a special glass tube and put a discharge through it which will break it into the constituent elements so probably only good for the Group 18 gases and simple diatomics (eg H2). The atomic emission spectrum (Ne red) is characteristic of the gas. Mixtures can also be tolerated up to a point. [Google the various terms here for more info.]

Answer 4

Is Oxygen A Greenhouse Gas

Answer 5

Is Argon A Greenhouse Gas

Answer 6

Heather,

The definition of a greenhouse gas is one that will absorb significant amounts of infrared radiation, and therefore keep this energy in the atmosphere. It turns out that due to the physics of the molecules, CO2 will do this, and therefore we call it a greenhouse gas, but the other three gases you mentioned will not.

The reason for this is complicated, but I'll try to make it as simple as I can: In order to absorb IR radiation, a molecule must be able to bend in a way that creates a positive side of the molecule and a negative side of the molecule. A CO2 molecule, having THREE atoms (with one of them different than the other two), is able to "wiggle" in such a way as to make that happen. In contrast, the other three molecules can't do this in any way that will create positive and negative ends. So CO2 can absorb this energy while many other molecules cannot.

Answer 7

The greenhouse effect refers to things in the atmosphere that act like a greenhouse; that is, they pass the sun's radiation to earth but reflect the longer wavelength radiation the earth reflects back out into space, so those rays (infrared or heat) are trapped on earth, just as in a greenhouse the glass roof traps heat. CO2 will do this, but N2, O2, Ar won't.

Answer 8

Carbon Dioxide (CO2) is a compound gas. N2 is Nitrogen, O2 is Oxygen, and Ar is Argon; they all exist in nature. CO2 is produced by burning fossil fuel. This is done by cars; but more of it is from volcano's, wildfires, and such.