| |
You are here: Experts > Science > Environmental Issues > Global warming/Climate Change > CO2
Expert: David B. - 10/28/2009
Question
QUESTION: We are teaching our primary and secondary students about Climate Change, and of course we hear a lot about tons of CO2 being released into the air.
I haven't found anyone to explain how CO2 is measured---I can't imagine that carbon and oxygen could possibly weigh so much. Is it measured based on the weight of fossil fuels being burned? Or what? Thank you very much.
-Laura
ANSWER: Hi Laura,
The specific techniques of measuring CO2 are not my expertise, but hopefully my limited knowledge will be of some use.
There are of course estimates out there of the amount of fossil fuels being burned, but the concentration of CO2 in the atmosphere is measured directly and continuously by hundreds of monitoring stations around the world.
The oldest and most famous of these is the "Keeling curve" from the Mauna Loa observatory in Hawaii. Basically Dr. Keeling took a sample of air then used a technique called mass spectroscopy to find the concentration. It basically involves emitting radiation through the sample and measuring how much got absorbed, then comparing this absorbance % to a control. It is a bit interesting that the very property that makes CO2 significant as a greenhouse gas is the property used to measure its concentration.
Measurements can also be taken from satellites, again using the properties of CO2's radiative absorption. The most notable of these satellites is NASA's Aqua. There is also a Japanese satellite named Ibuki; NASA had planned to launch a similar craft this February, but unfortunately the launch failed and it never reached orbit.
Good luck with your unit on climate change. I have some experience in explaining science to elementary school students, so if you have any other questions feel free to contact me again.
Regards,
David Brooks
---------- FOLLOW-UP ----------
QUESTION: Thank you very much David. I think I understand the bit about concentration of CO2...what I don't get is the actual WEIGHT...when they say that we can save a certain number of TONS of CO2 by walking instead of driving.
Is that really the molecular weight added up, or is the weight calculated by the amount of fossil fuel which would have been used to produce so much C02?
It's a little hard to make my question clear. Sorry for the extra trouble!
-Laura
Answer
Ah, sorry I understand now.
There are two ways you can talk about this: either the weight of CO2, or the weight of carbon. Both of them are indeed based on the molecular weights. As you can imagine, since C and O are fairly close to the same weight, then if you talk about weight of CO2 you're going to get a number about 3x larger than if you were to just talk about the weight of carbon (O2 is 32 and carbon is 12, so it's actually 3.6x larger)
So in essence, the answer to your question is "both": mass is conserved, so if you have 1 ton of coal (which is almost pure carbon), then burning it will put about 1 ton of carbon into the atmosphere. Since the carbon combined with O2, however, you are actually getting closer to 3.6 tons of carbon dioxide.
As you can imagine, this can lead to some confusion, as some people will talk about a mass of "carbon emitted" and fail to specify if they're talking about CO2 or just the carbon itself. Generally the numbers you hear are in reference to CO2, but a global warming skeptic for instance may choose to talk about the weight of carbon alone in order to make the numbers sound lower.
Hope this answered your question better; if not feel free to ask another follow up.
Cheers
David Brooks
PS: reading back on your original question, I'm wondering if it may help your students to first go over the difference between "mass" and "weight". Sometimes it's hard to wrap your mind around the idea that a gas--which seems weightless when it's floating around you--has a "weight" of several tons. Imagining the gas as tiny particles with mass flying and bouncing off each other in space may help.
In the rest of the world the mass of a gas is almost always given in grams. But since Americans have a paralyzing phobia of the metric system we always convert grams to pounds. Not the best way to talk about a gas, and indeed you'll never see a foreigner talking about a certain amount of gas in Newtons. In fact they tend to think we're a bit nutty for always insisting on using units of force when it would really be more appropriate to use units of mass.
Add to this Answer Ask a Question
|
|
