On calculating CO2 weight

06 Aug 2008

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Dear Umbra,

I know CO2 is a gas as other greenhouse gases are, and gases are sometimes lighter than air. So I'm wondering: how can gases be weighed in tons? That's a hell of a lot of gas to weigh even one ton, let alone the millions of tons that are reported to be causing climate change. (No, I'm not Oklahoma Sen. James Inhofe in disguise.)

James N.
Oklahoma City, Okla.

Dearest James,

Science. It is confusing. Oh, for the Dark Ages, when all was explained by unquestioned religious authorities, and the common people never needed to have a critical thought.

The unbearable heaviness of being.

I, too, have puzzled over the concept of "tons" of carbon dioxide. Not only how, but why? Why are we talking about the weight of this gas when most of us, including yourself, have trouble picturing how much carbon dioxide is in a ton (and can't imagine how a gas can get this hefty to begin with)? As it happens, the how and why are connected. Today, I will try to explain these entwined matters and help us all understand a little more about the elephantine gas portions entering our atmosphere. Wish me luck.

The overall problem regarding the planet is that greenhouse-gas concentration in the atmosphere is increasing. Greenhouse gases like CO2 trap and radiate sunlight and heat, so as more of them enter the atmosphere, the global mean temperature rises. To discover, chart, and study the problem -- and then talk to each other about it -- scientists everywhere need to measure atmospheric gases in the same way. It turns out that weight and mass are some of the easiest standard measurements to use.

But how can we quantify something that looks like nothing? Carbon dioxide and other gases are made of atoms -- and everything made of atoms has mass. Each carbon atom, for example, has an atomic mass of 12 (because each has six protons and six neutrons in its nucleus, if you must know). The two oxygen atoms in a CO2 molecule have mass as well. By using these factoids and other standardized measures such as the "mole" (no relation to the TV series), scientists have a way to calculate the tonnage of CO2 produced by humankind's bad habits. So what is a mole, you badger? If I tried to describe it, all the actual scientists who are still reading this would fall down laughing, so I leave that to you and your own research, dear readers. Suffice it to say that a mole of carbon dioxide weighs 44 grams. When enough grams of CO2 pile up, you've got a ton.

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As to how the gas coming from your personal fossil-fuel combustion can be weighed -- well, do you remember chemical equations? Scientists have calculated how much CO2 results from all kinds of chemical reactions, from burning fuel in your car to burning natural gas (aka methane) in your furnace, all using chemical equations. Here's the equation for burning methane in the presence of oxygen: CH₄ + 2O₂ => CO₂ + 2H₂0. (I know it's pretty meaningless to all us liberal arts majors, but I just want us to occasionally be near some actual Science.) That's "one" methane on the left, turning into "one" CO2 and some water on the right. (I think we've now gotten close enough to actual Science and can step back to a safe distance.)

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And, yes, a ton is a lot of anything, including carbon dioxide. But the atmosphere itself is quite immense -- with a total mean mass of 5.1480 x 10¹⁸ kilograms, according to the National Center for Atmospheric Research. Today, there are about 385 parts per million of carbon dioxide in the atmosphere,* or some 782 gigatons of carbon -- a gigaton being a billion metric tons. Before the Industrial Revolution, the level was about 280 ppm.

In other words, the time to act has long been before us and is now starting to be behind us. Alas.

Heavily,
Umbra

*[Correction, 06 Aug 2008: This article originally stated that there are about 367 parts per million of carbon dioxide in the atmosphere, but according to NOAA, the current number is closer to 385 ppm.]

Yours is to wonder why, hers is to answer (or try). Please send Umbra any nagging question pertaining to the environment -- but first check out her FAQs!

The claims made in this column may not reflect the views of this magazine. Neither the magazine nor the author guarantees that any advice contained in this column is wise or safe. Please use this column at your own risk.

Umbra Fisk is Grist Research Associate II, Hardcover and Periodicals Unit, floors 2B-4B.

Comments: (19 comments)

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by intimidavid at 5:28 AM on 06 Aug 2008

Carbon Offset

Umbra,

Do you know how much carbon a tree would 'offset?'

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by Gustavion at 9:29 AM on 06 Aug 2008

innumeracy, density

"I know it's pretty meaningless to all us liberal arts majors"

Um, not all... some people who are "liberal arts majors" major in physics, chemistry, and so on. Some of these (like me) also study theatre, art, and so on. Some people who are "liberal arts majors" major in things like theatre, art, and so on. Some (though few) of these also study physics, chemistry, and so on.

Why is it socially acceptable (or worse, "cute") to profess ignorance and incompetence in things scienc-ey, but not socially acceptable to profess ignorance or incompetence in the humanities-ey?

From my reading (I used to teach physics to reluctant college students), it seems that our friend not-James Inhofe is confusing density with weight... you know, the whole "ton of feathers [not dense] vs. ton of lead [dense, same weight]" thing: one cubic yard of air that we breathe weighs about the same as a quart of water.

by mihan at 10:37 AM on 06 Aug 2008

"Weighing" the air

As a hot air balloonist, I am very aware of the "weight" of air. After all, we fly by filling a balloon with heated air, which weighs less than (but NOT zero) the surrounding air, and therefore floats. Same principle as a boat--it may weigh a lot, but it's lighter than the equivalent volume of water, so it floats to the top.

Another reason I am aware of the mass (to use the Science word)of the air is this: if you ever stand in front of the seemingly weightless balloon as it floats a foot or two off the surface, and it is moving toward you, get out of the way! It will mow you down like a semi. The balloon and basket and the people in it have some weight/mass, but the big item is the air inside the balloon--about 3 tons of air!!

If you have ever seen a hot air balloon, here's a way to visualize the "weight" of CO2: Balloons come in a range of sizes, but I'll use the typical sport balloon her for example, a "size 7." This balloon contains 77,000 cubic feet of air. At sea level, 77,000 cubic feet of air weighs 6237 pounds! CO2 is actually a bit heavier than air, so if I filled my balloon with pure CO2 (at sea level, standard temperature, blah, blah, the gas inside would weigh/mass 9562 pounds, or nearly 5 tons.

Of course, the CO2 in the atmosphere is mixed in with all the other gases.

So there you have it--if you want a visual image, 5 tons of CO2 is just about an (unheated) hot-air balloon full.

by gosner at 10:49 AM on 06 Aug 2008

propane

The combustion of one gallon of LPG or propane produces 12.64 pounds of CO2 gas.

You might ask why if a galon of propane weighs 4.22 pounds, how can that be. It's because it combines with the oxigen provided by the air.

That is the fuel I displace most when I install solar heaters. A commercial pool 25 x 12.5 meters can produce well over 100 tons of CO2 a year in mild climates.

by solar greg at 11:34 AM on 06 Aug 2008

Don't forget other GHGs

Some of them are much more effective at trapping solar radiation as heat than CO2.

So saith the bachelor of science (in journalism, gotta love Cal Poly). g

Eat what you grow, grow what you eat

by PermieWriter at 12:23 PM on 06 Aug 2008

The Blue Barrel

We had the same thoughts about how to visualize a tonne of CO2 here at Reduce the Juice so we came up with the Blue Barrel. We calculated how much CO2 would it take to fill a commonly found 50 gallon drum (our Blue Barrel) and found it was 0.4kg. From there we have been able to create fabulous images that really drive home the concept of emissions reduction. One litre of gasoline is 6 Blue Barrels!

Check out the photos at http://www.reducethejuice.ca/foundation/bluebarrel.htm

Reduce the Juice!

by tsauren at 12:46 PM on 06 Aug 2008

Weight and volume of carbon

Out of sight/out of mind?
Here's another way to look at it - a "medium sized" power plant that produces 300 MW a year also produces close to 2 million tons of carbon dioxide a year, which would take a "square" balloon that was over half a mile on each side to hold it.

Chris Plum

by cnplum at 1:40 PM on 06 Aug 2008

Now, when reported in parts per million........

385 doesn't sound like a whole lot. But when reported in Billions of tons, it does.

It's all smoke and mirrors. It seems probable that generating as much CO2 as we do isn't such a good idea. We probably should reduce that.

Is it an "emergency"? For environmentalists everything is an emergency. Their natural global outlook is negative.

Victory in Pattani

by MAD MAC at 1:44 AM on 07 Aug 2008

Poor Umbra, having to answer math ?s so much!

I have profound pity for you. Every freaking question you have been asked recently would probably make a MIT graduate flinch for the calculations you have to explain to us lay people.

Grist should give you a pay raise, medal and vacation for having to answer all of those damn math questions. Bless you!

"For as long as space endures, and for as long as living beings remain, until then may I too abide, to dispel the misery of the world." - Shantideva

by mtvyfan at 7:34 AM on 07 Aug 2008

Where did that fuel go???

Solar Greg makes a point similar to my thought here. Let's see-- I fill the gas tank in my car that gets 28 mpg, I drive 28 miles and... HEY, a gallon of gas is missing! Where the heck did it go? Oh that's right-- it went into the air! And it weighed something, didn't it? Solar Greg refines this startling observation to point out that the burning can make my original gallon weigh more than it did as a liquid. But start with the weight of the fuel because it all goes into the air.

by ccbrewster at 9:26 AM on 07 Aug 2008
[ Parent ]

Weighing a gas

Gas is "weightless" only in the simple sense that a kid's balloon doesn't seem to have weight. But this is similar to a water balloon having no weight when you drop it in a swimming pool. The atmosphere is pressing down on the earth just as the oceans do, because of the gravitational attraction between the earth and these fluids. Add more gas to a pressurized tank, and the tank's weight increases. All molecules have mass, and therefore weight.

by ccbrewster at 9:43 AM on 07 Aug 2008

Science!

As a scientist, I'm quite fond of the first paragraph. ;)

Well done on the explanation Umbra, keep it up. :)

by freeztar at 10:56 AM on 07 Aug 2008

Mole

"So what is a mole, you badger? If I tried to describe it, all the actual scientists who are still reading this would fall down laughing, so I leave that to you and your own research, dear readers."

A mole is a very simple thing. It is just 6.02 x 10^23 atoms or molecules of anything. It has no units because it is a counting number, like a dozen.

Imagine a dozen carbon dioxide molecules. Then imagine 5.01 x 10^22 of those dozens. That is a mole of carbon dioxide molecules.

a sibilant intake of breath

by sindark at 7:20 AM on 08 Aug 2008

Scientific notation

For those not familiar with scientific notation 6.02 x 10^23 is the same as:

602,000,000,000,000,000,000,000

a sibilant intake of breath

by sindark at 7:25 AM on 08 Aug 2008

See, oh two!

Well done, Umbra. I relish the rodent references.

I also appreciate the equation CH4 + 2O2 => CO2 + 2H20

CH4 is a hydrocarbon. We buy the hydrocarbons, which are mostly carbon (75 to 90%) because hydrogen is light. But CO2 is only 27% carbon by weight.

So for each pound of fuel you buy, you make about 3 pounds of CO2! Save a little hydrocarbon, save a lot of greenhouse gas.

Toad the 12 sprocket

by thollandpe at 1:39 PM on 08 Aug 2008

And the CO2 content of the dollar?

"Carbon Footprint of Your Dollar"

"... for every dollar paid (or received) each time in 2007 an average of about 136 grams of carbon, or 499g of CO2 were released to the environment."

http://edro.wordpress.com/2008/08/05/carbon-footprint-for ...

by LGT at 12:58 AM on 11 Aug 2008

How about gallons?

It helps me to think of a gas in terms of gallons. A mole of any gas is 22.4 liters (at "standard temperature and pressure," as scientists say). According to my calculations, one pound of carbon dioxide equals about 61 gallons.

I've read that burning one gallon of gasoline results in emission of about 19 pounds of carbon dioxide.

This means that burning one gallon of gasoline results in emission of about 1,200 gallons of carbon dioxide.

Something to think about each time you fill up your gas tank.

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by pacinopeer at 2:59 AM on 14 Aug 2008

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The Ton Also Rises

On calculating CO2 weight