Air Absorbing IR Radiation
Most recent answer: 03/29/2013
- Alex (age 16)
UK
Mike W.
(published on 03/29/2013)
Follow-Up #1: greenhouse gases
- Brigitte (age 25)
Montreal
Hi Brigitte- I've moved your question to follow-up a more closely related thread.
To answer the new parts:
Those IR-absorbing gases do have some heat capacity associated with the same modes that do the absorbing. At a given temperature, the average thermal energy of a CO2 molecule is a little more than that of an O2 molecule for that reason. However, there's not a consistent simple connection between those properties, since molecules can have modes that pick up thermal energy but don't contribute to the IR absorption.
I guess you can do a simple IR-absorption experiment without any lab equipment. It's not very expensive to buy an IR meter, but it's even cheaper if you don't insist on the name. Those little ear thermometers you get in the drugstore measure temperature via IR radiation. I bet you could rig up some setup with one of them to test gases for IR absorption.
Here's a possibility. Use a covered ceramic pot of water kept barely boiling on an electric stove as an IR source. I say ceramic because it's likely to absorb/emit IR better than metal. The water in the pot is just to keep the temperature steady near the boiling point. The cover is to avoid having too much water vapor come out. A vent fan would help with that. An electric stove is preferable because it won't give off various combustion products (including CO2) to confuse things, unlike a gas stove. (You could use yourself as an IR source, but the pot will give more radiation and be easier to detect.)
Mount the ear thermometer, with its little plastic sensor cover, some distance away, pointed toward the pot. Adjust the distance until the reading comes out in the thermometer's range. I bet you can see the reading change if you blow water vapor or CO2 between the stove and the thermometer.
It's possible that you could do the same thing just by feeling the radiant heat with your hand instead of a thermometer, but you'd have to be sure that the blowing gases weren't directly cooling it.
Please let us know if this works!
Mike W.
(published on 09/07/2013)