Friday, 17 April 2020

"Does warm nitrogen emit infra red?"

Is a question I have been asking myself recently. My guess was "yes, of course it does, that's why warm air feels warm" but it's always best to Google this sort of thing.

Turns out, it does:

The bottom line here is pretty simple. After doing some sky observing, [people at the Mount Wilson Observatory and Washburn Observatory] found a large IR interference from the open sky. This was chased back to a Nitrogen band at 10,300 Angstroms [= 1 micron/micrometre = in the middle of the range of solar infrared radiation]. It varies over the night, dimming as the sky cools, and increases again just before sunrise. It varies with zenith angle too. It is strong and bright.

So my questions are simple and few:

1) Is it not the case that
“That which emits, absorbs” at the same band?

2) Does that not mean Nitrogen is an infrared absorber and emitter?

3) Does that not mean Nitrogen fits the definition of a “greenhouse gas”? (wrong as the term may be).

4) Doesn’t this kind of screw up the whole “Only CO2 Matters!” mantra? (That already ignores water vapor…)

That’s really the whole thrust of this posting. IF Nitrogen (not to mention all its ions and N3 and atomic forms) has a bunch of IR bands, doesn’t that kind of play Hob with the whole CO2 thesis? And there is ample evidence for Nitrogen having a bunch of IR bands.


Ralph Musgrave said...

If a gas, Nitrogen or any other gas, absorbs heat from the sun during the day and emits it during the night, strikes me there is no effect on global warming because that effect simply reduces the extent to which heat from the sun is absorbed by the surface of planet Earth during the day and emitted back out into space at night.

To qualify as a greenhouse gas, the gas has to let thru short wave length infra red, but block longer wave infra red, which is what most of the radiant heat trying to leave planet Earth consists of at night. CO2 qualifies but Nitrogen does not, seems to me.

View from the Solent said...

your #1. Yes. A molecule only absorbs IR of certain frequencies, corresponding to its resonant frequencies. Hence IR spectroscopy.

Similarly it only emits IR on those same frequencies.

Mark Wadsworth said...

RM, mmmm. Not sure if that is all entirely correct, either by Warmenist consensus or my own understanding. But probably not far off.

VFTS, thanks. That wasn't 'my' question. I just copied the whole post from a post I found on another blog. It was his rhetorical question.

Graeme said...

Have you looked at Clive Best's blog. A physicist who worked at CERN. He did a lot of work a few years ago trying to work through "the science".

Bayard said...

RM, any gas that is absorbing long wave infra red radiation, but not short wave IR, is a greenhouse gas. If nitrogen absorbs IR in the same sort of wavelength as CO2, it too is a greenhouse gas. All gases re-emit the IR they absorb, so, in fact the IR is not blocked but scattered. There used to be a handy infographic produced by the IPCC, which illustrated this very point, but now it has vanished off the internet, I suppose because the "official" science switched to CO2 "absorbing" IR.

Bayard said...

Mark, looking up about something else entirely, I discovered that water vapour is less dense than air, so will rise through air, even if it is at the same temperature as the air, so it may be that the whole IR radiation/greenhouse effect is bollocks and the earth is cooled by water vapour rising and then condensing (clouds are water droplets, not water vapour) and giving up its latent heat of vapourisation, and acting like a giant refrigerator.

Mark Wadsworth said...

G, yes, I have often ended up at Clive Best's blog.

B, second comment, of course. Most nitrogen or oxygen in air is molecular, N2 or O2, heavier than H2O. Nobody's sure if water has overall cooling or warming effect. Commonsense and raw temperatures say overall cooling, but close to neutral.

Dinero said...

Not all absorbers emit at the absorbed frequency. Objects absorb ultraviolet and emit infrared.

Mark Wadsworth said...

Din, that is clearly true, but you're looking at it the wrong way round.

The assumption is, if something (like N2, O2) can emit IR at certain wavelengths, then they can also absorb IR at the same wavelengths. Either that is true or it isn't, and I assume it is.