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Experiments on Greenhouse Gases

by physicsdude30
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physicsdude30
#1
Mar16-10, 09:38 PM
P: 37
Note: This isn't intended to be a Global Warming thread but rather a Greenhouse Gases thread (they're not the same thing), so please let's not talk about Global Warming because I don't want it closed. I'm very interested on any feedback or thoughts anyone may have for my experiments.


Galileo would test things out for himself. We've all heard about greenhouse gases, but then I've heard some say they don't exist or that CO2 isn't one of them. So I thought it would be lots of fun to test this out for myself.

As you've probably noticed, during the daytime it's warmer than at night, so the Sun's rays warm the earth. You've probably noticed that the higher elevations aren't as warm, which is because there's "less atmosphere" up there. Also, just like some foods warm up better in the microwave than others, because of how the microwaves excite the molecules, scientists say sunlight warms up some gases like CO2 better than N2 or O2. So my train of thought is just like in the Medical Field where they test a new medicine by using an experiment and control group, it could be done with two glass jars the same with the difference being CO2 between them, then measure temperatures. This is what I've tried so far, so check it out and let me know what you think?

The two glass jars I used



First I decided to use CO2 gas from dry ice. I put some ice in a separate glass of water and let it fog over.



I let the fog catch in the experimental jar. Both the jars were sealed off, let sit overnight to allow CO2 to dissipate, and then temperatures taken during the sunlight the next day. This is what I got. Need some feedback?:



Next I thought it would be interesting to try match stick smoke. I rinsed out both jars and dried them, then held some burning match sticks above the upside down experimental jar. Although more than "CO2 gas" was in the jar, I thought it was appropriate enough of a test since one of the ways among many it gets into the atmosphere is "burning substances". I let both jars sit over night so they could have the chance to be the same temperature. The next day when both of them were in sunlight this is what I got:



Why I thought about testing match stick smoke:



Just looking for feedback on these experiments!
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sylas
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Mar17-10, 08:43 AM
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Quote Quote by physicsdude30 View Post
Note: This isn't intended to be a Global Warming thread but rather a Greenhouse Gases thread (they're not the same thing), so please let's not talk about Global Warming because I don't want it closed. I'm very interested on any feedback or thoughts anyone may have for my experiments.
You would also be interested in the thread Need Help: Can You Model CO2 as a Greenhouse Gas (Or is This Just Wishful Thinking?), which was also starting out about experiments at home or in schools. There are some links and descriptions there.

One essential thing with a good experiment is to understand the theory that it is testing. This doesn't depend on anything particularly associated with the banned topics, since it is simply on the thermodynamics of radiation and gases; not about how things change as concentrations of gases alter, so it isn't about "change" so much as the elementary physics behind, which ought not be at all controversial; though it can be a good exercise to figure out how to test it. However, final word on that will lie with mentors. I'll proceed without any concerns for changes to climate -- only a look at how gases like CO2 interact with heat and radiant energy.

... scientists say sunlight warms up some gases like CO2 better than N2 or O2.
Actually, that's not really accurate. Scientists say that thermal infrared radiation heats up CO2 better than N2 or O2. The difference is important. The important thing about gases like CO2 is that they DON'T get heated up by sunlight, but they do absorb infrared radiation (in some bands).

That is, the essential feature is that they are transparent to sunlight and opaque to infrared. I especially recommend looking at the first experiments done in the mid nineteenth century by John Tyndall, who first discovered this surprising property. It was, at that time, completely unexpected and quite shocking to the discoverers. (See msg #10 of that other older thread.)

Just looking for feedback on these experiments!
Nice work! Well done. However, I am not at all sure, at this stage, of the reasons for your results. One tricky problem is that glass is also partially opaque to infrared radiation. It may make a difference what your jars are made of. Theoretically, the difference with the CO2 is that it will interact more strongly with the thermal infrared radiation from the surrounds. In some cases this might even have a cooling effect, if the jar is heated mainly by contact with a hot surface, and the gases are able to radiate that heat more effectively. But out in the open as you have done, it makes sense to think that there's extra energy being absorbed from the thermal radiation. But I can't be sure.

Cheers -- sylas
Bystander
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Mar20-10, 02:29 PM
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You will want to consider the effect of the difference in thermal conductivity between air and CO2. You may be looking at nothing more than the difference in how effectively the two thermometers are cooled by the two differenct gas envelopes.

physicsdude30
#4
Mar22-10, 06:10 PM
P: 37
Experiments on Greenhouse Gases

Quote Quote by sylas View Post
Nice work! Well done. However, I am not at all sure, at this stage, of the reasons for your results. One tricky problem is that glass is also partially opaque to infrared radiation. It may make a difference what your jars are made of. Theoretically, the difference with the CO2 is that it will interact more strongly with the thermal infrared radiation from the surrounds. In some cases this might even have a cooling effect, if the jar is heated mainly by contact with a hot surface, and the gases are able to radiate that heat more effectively. But out in the open as you have done, it makes sense to think that there's extra energy being absorbed from the thermal radiation. But I can't be sure.
Thanks for the input. Although, I'm not sure why the glass would throw it off, since both jars are made of glass and still there was a difference.




If glass blocked some of the infared, there was still a consistant difference in temperatures between them; I'd try changing the order of what the bottles were and a couple of times. So I'm thinking if there is an issue of internal validity, there'd be something else? (That picture of the jars above shows the sun's rays at different angles, however when I actually recorded the temperatures I made sure it was the same angle for both when I had the control on the right vs. left hand sides)

What are your thoughts?
physicsdude30
#5
Mar22-10, 06:18 PM
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Quote Quote by Bystander View Post
You will want to consider the effect of the difference in thermal conductivity between air and CO2. You may be looking at nothing more than the difference in how effectively the two thermometers are cooled by the two differenct gas envelopes.
You make a point. Experiment 2 with the smoke isn't pure CO2; that was mostly meant to test burning substances. However, wouldn't gas from the dry ice be CO2? What percentage of CO2 is dry ice? Since I let it fog over from another container and into the experiment jar, I would think it gave it enough time to be the same air pressure as the other jar, then I sealed it off after letting it sit for 5 seconds. Then considering the smoke jar wasn't much behind in difference from control jar, I'm not so sure that the original temperatures of how I obtained the gases before it was sealed off made much of a difference?

Do you know if they sell bottled CO2?
Bystander
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Mar23-10, 03:35 PM
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Quote Quote by physicsdude30 View Post
(snip)... , I'm not so sure that the original temperatures of how I obtained the gases before it was sealed off made much of a difference?
(snip)
I say, "thermal conductivity," and you say, "original temperatures." Before I commit to further investment of my time, let's clarify whether this is running against the clock (science fair, extra credit project for an earth science class), or open-ended (you really are doing this to answer your own questions on the topic(s) of atmospheric gas properties. I ain't gonna try sorting out the differences between "thermal conductivity" and "temperature" for you while staring at a deadline.
physicsdude30
#7
Mar24-10, 06:43 PM
P: 37
Quote Quote by Bystander View Post
I say, "thermal conductivity," and you say, "original temperatures." Before I commit to further investment of my time, let's clarify whether this is running against the clock (science fair, extra credit project for an earth science class), or open-ended (you really are doing this to answer your own questions on the topic(s) of atmospheric gas properties. I ain't gonna try sorting out the differences between "thermal conductivity" and "temperature" for you while staring at a deadline.
I think there must have been a misunderstanding. What I was trying to say is "air pressure" is a factor to be considered. Since the match stick smoke was still hot and the dry ice fog cold while the lid was sealed off, when cooling down/warming up I was wondering if their air pressures could change slightly while in the jars. However, then I thought after sitting outside for a day and in the sun both the warmer and colder gases were a couple of degrees higher compared to the control jar, so I don't think that was an issue. That's also why I asked if they sell canned CO2 air to anyone who wants it.

That's all that I meant by that.

I'm also just doing these experiments for my own enjoyment, no school projects.
DarioC
#8
Mar27-10, 12:28 AM
P: 187
Actually your experiment is quite good, especially considering how simple and intuitive it is.

The visible and UV radiation go through the glass and heat up the interior air and also are absorbed by the material of the thermometers. The heat loss is by IR radiation that doesn't penetrate glass very well, but the variation you are seeing IS likely to be caused by the different gas inside being so opaque to IR at certain wavelengths.

You could also put them in a cardboard box to move them to a quiet cooler room, darkish I should think, and record the rate of cooling of the two containers. That would be even closer to the effect of "greenhouse warming."

CO2 is used as a cooling agent for small temperature chambers, but the tanks available are quite large, probably not practical for your use.

If your source for dry ice is easily available that is about as good as it gets
Jon Richfield
#9
Apr30-10, 08:58 AM
P: 258
Quote Quote by physicsdude30 View Post
Thanks for the input. Although, I'm not sure why the glass would throw it off, since both jars are made of glass and still there was a difference.
Congratulations on your attitude and your experiments.
A few points to consider, but remember that you are the one who got off your butt and I am typing this sitting down!

Controls:
I agree that dry ice is the best source of CO2 for practical purposes. But the CO2 you get is very high in water from condensation (hence the fog) and water is a far more powerful IR absorber than CO2. If you have no way of drying the CO2, then you could put a few ccs of water in each jar to make sure that they contain the same amount.

It would be good to swap thermometers with each experiment to make sure that they have the same calibration. Commercial domestic thermometers often don't match very well.

If it doesn't stretch your resources, try more jars, to see what degree of variation you get with the SAME treatment. Even better if you could get a nice young lady to help you by labelling the jars A,B,C,D... and not telling you what is in each jar till after the experiment. (Blind experiments reduce bias. With a little ingenuity you can manage a double blind experiment, not telling her what is in each jar, so that it does not matter whether she knows what outcome you want or not.)

You might like to try jars with a few other chemicals in them, such as a few drops of alcohol (meths) or rubbing alcohol (isoprop) etc.

Good luck and have fun!

Jon
BioBen
#10
May24-10, 09:35 AM
P: 29
Do you have any idea what are the CO2 levels (in ppm or in percentage) in each jar ?
physicsdude30
#11
May24-10, 09:28 PM
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Quote Quote by BioBen View Post
Do you have any idea what are the CO2 levels (in ppm or in percentage) in each jar ?
No I don't, but if I had more sophisticated equipment to measure it then that would be neat.
Saladsamurai
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Jul18-10, 10:42 PM
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I am reviving this thread because I have been looking around for some "scholarly" articles on an experiment like this but have yet to find one. Anyone know of anyone who has authored any papers on this matter? As in, performed an actual experiment like this and recorded results?
Bored Wombat
#13
Jul25-10, 09:04 AM
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Quote Quote by DarioC View Post
You could also put them in a cardboard box to move them to a quiet cooler room, darkish I should think, and record the rate of cooling of the two containers. That would be even closer to the effect of "greenhouse warming."
The other thing that would affect this is that the thermal conductivity of CO₂ is 105 mW/(m.K), but the thermal conductivity of N₂ is 24 mW/(m.K) (at one atmosphere and 0C).

So you would get an underestimate of the greenhouse effect of CO₂, or even the CO₂ cooling faster if you get a situation where heat transfer by conductivity is a similar order of magnitude to that by radiation.
Bored Wombat
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Jul25-10, 09:08 AM
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Quote Quote by Saladsamurai View Post
I am reviving this thread because I have been looking around for some "scholarly" articles on an experiment like this but have yet to find one. Anyone know of anyone who has authored any papers on this matter? As in, performed an actual experiment like this and recorded results?
The greenhouse effect has been understood for a century or so. I expect the scholarly papers from when this sort of thing was first investigated would not have been archived electronically.
Bystander
#15
Jul26-10, 12:45 PM
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Quote Quote by Bored Wombat View Post
The other thing that would affect this is that the thermal conductivity of CO₂ is 105 mW/(m.K), but the thermal conductivity of N₂ is 24 mW/(m.K) (at one atmosphere and 0C).
"105?" CRC reformatted and failed to proofread again? CO2 thermal conductivity is a little more than half that of air.

So you would get an underestimate of the greenhouse effect of CO₂, or even the CO₂ cooling faster if you get a situation where heat transfer by conductivity is a similar order of magnitude to that by radiation.
"Overestimate."
Jon Richfield
#16
Jul26-10, 12:56 PM
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Quote Quote by Bystander View Post
"105?" CRC reformatted and failed to proofread again? CO2 thermal conductivity is a little more than half that of air.

"Overestimate."
That sounds right to me!
Well spotted!
Bored Wombat
#17
Jul26-10, 08:07 PM
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Quote Quote by Bystander View Post
"105?" CRC reformatted and failed to proofread again? CO2 thermal conductivity is a little more than half that of air.

"Overestimate."
Quite right. 14.65 mW/(m.K) and Overestimate.

Thanks for that: I thought that last time I'd had this discussion it had come out the other way, and was thinking that I'd made a mistake then.
reasonmclucus
#18
Aug16-10, 12:54 AM
P: 194
Are you familiar with the experiment IR expert R.W. Wood conducted in 1909? He used two identical greenhouses with one being reflective of IR and the other transparent.

XXIV. Note on the Theory of the Greenhouse
By Professor R. W. Wood (Communicated by the Author)

THERE appears to be a widespread belief that the comparatively high temperature produced within a closed space covered with glass, and exposed to solar radiation, results from a transformation of wave-length, that is, that the heat waves from the sun, which are able to penetrate the glass, fall upon the walls of the enclosure and raise its temperature: the heat energy is re-emitted by the walls in the form of much longer waves, which are unable to penetrate the glass, the greenhouse acting as a radiation trap.

I have always felt some doubt as to whether this action played any very large part in the elevation of temperature. It appeared much more probable that the part played by the glass was the prevention of the escape of the warm air heated by the ground within the enclosure. If we open the doors of a greenhouse on a cold and windy day, the trapping of radiation appears to lose much of its efficacy. As a matter of fact I am of the opinion that a greenhouse made of a glass transparent to waves of every possible length would show a temperature nearly, if not quite, as high as that observed in a glass house. The transparent screen allows the solar radiation to warm the ground, and the ground in turn warms the air, but only the limited amount within the enclosure. In the "open," the ground is continually brought into contact with cold air by convection currents.

To test the matter I constructed two enclosures of dead black cardboard, one covered with a glass plate, the other with a plate of rock-salt of equal thickness. The bulb of a themometer was inserted in each enclosure and the whole packed in cotton, with the exception of the transparent plates which were exposed. When exposed to sunlight the temperature rose gradually to 65 oC., the enclosure covered with the salt plate keeping a little ahead of the other, owing to the fact that it transmitted the longer waves from the sun, which were stopped by the glass. In order to eliminate this action the sunlight was first passed through a glass plate.

There was now scarcely a difference of one degree between the temperatures of the two enclosures. The maximum temperature reached was about 55 oC. From what we know about the distribution of energy in the spectrum of the radiation emitted by a body at 55 o, it is clear that the rock-salt plate is capable of transmitting practically all of it, while the glass plate stops it entirely. This shows us that the loss of temperature of the ground by radiation is very small in comparison to the loss by convection, in other words that we gain very little from the circumstance that the radiation is trapped.

Is it therefore necessary to pay attention to trapped radiation in deducing the temperature of a planet as affected by its atmosphere? The solar rays penetrate the atmosphere, warm the ground which in turn warms the atmosphere by contact and by convection currents. The heat received is thus stored up in the atmosphere, remaining there on account of the very low radiating power of a gas. It seems to me very doubtful if the atmosphere is warmed to any great extent by absorbing the radiation from the ground, even under the most favourable conditions.

I do not pretent to have gone very deeply into the matter, and publish this note merely to draw attention to the fact that trapped radiation appears to play but a very small part in the actual cases with which we are familiar.

http://www.wmconnolley.org.uk/sci/wood_rw.1909.html

The results were originally published in Philosophical Magazine which despite the name was a leading scientific journal of its day. J.J. Thomson, Albert Einstein and Niels Bohr all published in the magazine.

You will notice that the greenhouse that was transparent to IR initially heated faster than the other one because of the higher energy radiation coming in from the sun which didn't enter to greenhouse that reflected IR.


In your experiment you need to consider the water vapor content of the air because water vapor heats and cools slower than CO2 or other atmospheric gases. Water vapor holds a substantial amount of heat which has traditionally been called "latent" heat although some scientists call it "heat of enthalpies". Latent heat is the substantial amount of heat energy absorbed when water goes from a solid to a liquid and then to a gas. The latent heat of one gram of water vapor is approximately equal to the amount of heat necessary to raise the temperature of 620 grams of water 1 C.

A 3% concentration of water vapor in the air is equivalent to a dew point (the temperature at which water vapor will condense on objects of that temperature) of 65 F. At this temperature water vapor contains approximately half of the heat in the air sample which is why air with dew points of 65 or higher is more likely to produce severe storms than air with lower dew points.


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