I get some of the biggest reactions discussing global warming with people who aren’t familiar with the technical details when I ask:
How many pounds of CO2 does one gallon of gas produce when burned in a car engine?
Between 19 and 20.
It’s true. One gallon of gas weighs about 6.5 pounds. The process of burning literally means to combine with oxygen. So, the chemical reaction requires that the octane molecule combines with oxygen. The hydrogen and carbon of the octane molecules separate, combine with oxygen, and produce CO2 and H2O.
This is chemistry. You can’t argue with the science. You can nit-pick over whether you should assume perfect combustion for the example, which there never really is, or you can nit-pick over whether you’re discussing 93 octane premium or 87 octane regular, whether assuming “ideal conditions” in the real world is valid (which is always done in first approximations)… The Energy Information Authority uses molecular weights and percentages to conclude each gallon of gasoline produces 20 pounds of CO2, so it’s good enough for this discussion of the data behind the climate crisis.
EIA data, specifically a downloadable spreadsheet, gives the annual sales of transportation fuels from 1949 onward.
Motor gasoline, as broken out, is simply gasoline used in automobile engines. This does not include diesel fuel, nor aviation gasoline, nor jet fuel, nor “bunker fuel” used in ships. This is the resource used to support and fuel our “American” lifestyle of driving everywhere for everything in most places.
The data is provided in “thousand barrel” quantities, and a little more digging confirms that one barrel equals 42 gallons.
In 2008, the “preliminary” number of thousand barrels of motor gasoline used in the USA is 3,212,837
That’s equal to 134,959,154 thousand gallons of gasoline sold in the US in 2008 alone.
When you do the simple calculation for pounds CO2 emitted to transport our butts from points A to points B day in and day out, using 20 pounds CO2 per gallon, you get:
2,698,783,080,000 pounds of CO2, or
It’s important to remember that this is one year’s output of CO2 for one type of transportation fuel used in the US. It’s a big number. But, the atmosphere is big, too…. isn’t it? Well, yes, it is… and isn’t.
Using the “ideal gas law” let’s try to estimate how much space that would take up if it were the only gas at “room temperature” at one “atmosphere” of pressure. This is a completely theoretical exercise along the lines of “if you had enough balloons to capture all the CO2 coming out of every tailpipe on every US road…”
I found a handy-dandy discussion of the volume required for one gallon of gasoline’s CO2 contribution, in other words, the space required for 20 pounds using the “ideal gas law,” PV=nRT. That is, Pressure*Volume=n*R*Temperature, where n=number of “moles” of gas and R=Rydberg constant.
… and the volume eventually is found to be 172 cubic feet… per 20 pounds CO2.
For our 2008 example of our motor gasoline use,
2,698,783,080,000 pounds CO2/20 pounds CO2 * 172 cubic feet
=134,939,154,000 * 172 cubic feet
=23,209,534,488,000 cubic feet.
or 859,612,388,444 cubic yards…. or a 3 foot high blanket of CO2 on an area of 277,509 square miles.
That’s a large area, and we’re still only talking 2008 motor gasoline numbers.
The entire list of transportation fuels includes:
- Aviation Gasoline …………. 5,638 thousand barrels
- Distillate fuel oil (diesel) … 1,044,958
- Jet fuel ……………………….. 555,556
- Liquified petroleum gases … 5,348
- Motor Gasoline…………….. 3,212,837
- Residual Distillate fuel oil … 148,68
Residual Distillate fuel oil is the leftover “sludge” used by diesel cargo ships, a.k.a. “bunker fuel,” notoriously laden with sulfur compounds and other junk.
The EIA includes the volume of lubricants used in transportation too, but they’re not “burned” as transportation fuel, and I’m exploring the volume of CO2 emitted by our transportation ways, I’m not going to include them.
Diesel fuel produces about 22 pounds/gallon, propane and LNG for transportation somewhat less…
Just for a quick “back of the napkin” calculation, let’s continue to use 20 pounds of CO2 per gallon of “fuel.”
Total 2008 transportation fuel, adding up the totals above:
4,973,022 thousand barrels, which equals 208,866,924 thousand gallons of fuel
When burned, this fuel makes 2,088,669,240 tons CO2… enough to cover 429,545 square miles with a 3 foot thick blanket of pure CO2 gas at one atmosphere (sea level). Mind boggling, isn’t it?
This is what the authors of my 32 year old chemistry textbook meant by “prodigious consumption” of fossil fuels… and this does not yet include “space heating” or heating oil used for homes and commercial buildings, nor does it include electrical production. Nor does this include heat for industrial processes like smelting, manufacturing, etc.
Animals and plants maintain a carbon cycle which I won’t cover, other than to say that before the Industrial Revolution, CO2 concentrations were relatively constant. Humans and animals produced carbon biologically and through burning wood, and plants and oceans sequestered it. Now, burning fossil fuels to get from here to there, concentrations of CO2 are rising, and have been for some time.
Yes, there are 300 million people in the US. Yes, other more populous countries like China and India have already or will soon pass the US on total CO2 production per year. But, 2008 is just one year, and CO2 lasts a long time in the atmosphere, an estimated 100 yrs. Transportation fuels can be changed. The fuel for electrical production can be changed. Renewable energy sources can be used. These will be other topics for other posts.
If you want to think about global economic policies, think about the increased fuel usage arising from globalization. Despite video conferencing, international business travel drives air travel and its fuel consumption. Goods travel by boat from Asia, mostly, burning bunker fuel at amazing rates. Once on land, the vast majority of goods travel in trucks that average SIX miles per gallon on the highway, largely because roads have been built with tax dollars while freight rail infrastructure has been left to decay. Planning and zoning boards in towns adapt regulations to allow more big-box retailers to reap the benefit of increased property tax revenue from commercial zones, requiring highway expansions to accommodate increased truck and car traffic.
It’s a crazy cycle. And, if you look honestly at it, you should easily be able to conclude that federal, state, and local tax dollars have been used to subsidize the oil industry over time. The oil companies haven’t been out paving roads that I’ve been on to facilitate usage of their products. Our government has done that.