Tuesday, July 24, 2012

You Do The Math - Carbon Sequestering

Used to be you would see a lot of ads from businesses selling their services to offset your carbon footprint, an activity called carbon sequestering.  A few years ago I stopped seeing these ads, and I know why.  Today you'll see for yourself as You Do The Math!

From many, many sources I've learned that a gallon of gasoline weighs about 6 pounds.  How much of that is carbon?  Depends whether you have Summer or Winter gas, because Summer gasoline is less volatile, being made up of longer carbon chains than Winter gas.  But a good estimate is a chain of 6 carbon atoms.  As we'll see at the end of this blog, a 10 percent error is not a big deal.  It's a HUGE deal!

One of my wood piles, a decade of work doesn't begin to offset my carbon footprint:

Anyway...  these organic molecules tend to be linear carbon chains, with 2 hydrogen atoms per carbon, plus an extra hydrogen at both ends.  So, 6 carbon atoms would be accompanied by 14 hydrogen atoms.  Using approximate atomic weights of 12 for the carbon, and 1 for the hydrogen, we see:

C6H14 = (12 * 6) + (14 * 1) = 86

And the percentage of that which is carbon:

C6 / C6H14 = (12 * 6) / 86 = 72/86 = 83.7%

And for every gallon of gasoline this much is carbon:

83.7% of 6 pounds of gasoline = 5.02 pounds carbon

Empty car hauler snaking its way through Deal's Gap Tennessee, 50 miles south of the interstate, and headed further south.

How many gallons do you use a year?  It varies a lot, with an average US citizen driving 11,000 miles a year, but a suburbanite drives 20,000 miles while an urban dweller takes the subway or bus, and must figure out what percentage of the RTA's diesel bill he or she is responsible for.  Doesn't matter, urbanites can't sequester enough carbon without a lot of property to grow a small forest.

Why?  We shall see.  Take a (nearly) average American getting 22 miles per gallon and driving 11,000 miles a year.  That's 500 gallons of gas a year:

500 gallons * 5.02 pounds carbon per gallon = 2,510 pounds of carbon.

This source, http://www.talkabouttrees.org/docs/lesson9.pdf, says that roughly half of a tree is carbon by weight.

And there aren't many in New Mexico.  This is typical...    treeless scrubland:

2,510 pounds carbon * 2 pounds of tree per pound of carbon = 5,020 pounds of tree

That means the average American needs to grow a 5,000 pound tree each YEAR just to make up for his/her driving.  Can you say "bamboo"?  Because that's probably the only fast growing plant that would do the job.  That, and a quarter acre of land to plant this bamboo forest.

Very rare for Arizona, the Sedona area with some slow growing pine.  Still a desert, though.

But what about the electricity to power the home and workplace and the stores?  What about the manufacturing processes to make all the food and products we buy?  What about the diesel to transport these products in inefficient trucks? (trains are much more efficient)  What about the energy used to build stores, highways bridges and skyscrapers?  What about the raw materials for all these products and constructs, which must be mined, melted at two thousand degrees a few times, not just once?

Bridges upon bridges: Cincinnati, Ohio

Seems like every dollar we spend goes to energy.  And since 85% of the US's energy comes from fossil fuels (World Almanac, 2009 and the Energy Information Administration, EIA), we have a big carbon problem to figure out.  To make it easy, our fossil fuel usage in 2007 was about 40% oil, 23% coal and 23% natural gas.

To infinity and beyond...   Our nation is covered in food crops (the opposite of a carbon sequestering process).  This is western Kansas and eastern Colorado (back in 2003, before many droughts).

In 2007, again from the EIA and World Almanac 2009, Americans used 86.25 quadrillion BTU's of fossil fuels.  Of that, 39.82 were petroleum, 23.64 were natural gas and 22.77 were coal.  To find out how much carbon is released we need to convert from BTUs to carbon.  We also need to subtract carbon that is already sequestered.

According to the EIA, much of our fossil fuels are sequestered.  For instance, crude oil is turned into plastics, and made into various products from medical supplies to grocery bags to fleece clothing.  Well, as we know, these items can become litter, decompose slowly, and release carbon.  Point of fact, the continental sized plastic armada in the Pacific Ocean.

Plastics also end up in landfills, and they decompose, releasing methane, which certain municipalities suck out of the ground using extensive pipe systems.  They then burn it for energy, thus releasing carbon into the atmosphere.

I also have some disagreement with the EIA on asphalt.  They say 100% of the oil in asphalt is sequestered indefinitely.  Then explain why it dries up, cracks, and needs to be replaced?  Heck, just walk across a shopping mall's parking lot on a sunny, 95 degree day, and you can smell it evaporating.

Here's a typical suburban road in an upper middle class neighborhood, without much oil.

Coal is a little more easy to figure.  The EIA says that 6% of coal coke is converted to oils and tars, of which 75% is sequestered.  This means that 4.5% of coke is sequestered.  In 2007 the EIA says the US imported and consumed 30 trillion BTUs of coal coke.  For coal itself, 22.77  quadrillion BTUs were used in 2007.

There's also the soot from coal. much like soot from diesel trucks.  They say this is not a greenhouse gas.  However, it does cause global warming, as it lowers the albedo of the Earth.  I've read that carbon soot resting on ice and snow is actually responsible for a few percentage points of the total global warming.

The southern half of California is no help in the tree department... so dry, so dead.

To make things simple, let's ignore all coal coke, and figure coal only.  Anthracite coal has 62.1 pounds of carbon per million BTUs, while bituminous, sub-bituminous and lignite have less carbon, at 56.0, 57.9 and 58.7, respectively.  Let's use the smallest figure in order to fend off skeptics.

(22.77 quadrillion BTU / 1 million ) * 56.0 = 1.275 trillion pounds

Divide by the approximate US population:

1.275 trillion pounds / 315 million = 4,048 pounds of carbon

Multiply by 2 and we get 8,000 pounds of tree.  Add that to the 5000 pounds for gasoline, and we already have 13,000 pounds.  Hmmm...   not looking good.

Seriously, this is Oregon's scenic byway.  Oregon is either arid, or slow growing pine.

On to natural gas.  Some of that is turned into products, however, we used more BTUs of natural gas than coal.  Thankfully, natural gas has the lowest carbon content of all fossil fuels, at 31.9 pounds per million BTU.

(23.64 quadrillion BTU / 1 million ) * 31.9 = 741 billion pounds

Divide by the approximate US population:

741 billion pounds / 315 million = 2,353 pounds of carbon

Multiply by 2 and we get 4,700 pounds of tree.  Add that to the 13,000 pound subtotal for coal and gasoline, and we have 17,700 pounds.   This is equal to two H1 Hummers plus one Honda Accord (or five and a half Accords).

This is an annual figure!   Safe to say it's not possible to sequester your carbon.  Especially if you're a suburbanite who drives twice as far as average and spends twice as much money on airfare, housing and goodies to fill your house with.  We're talking 35,400 pounds of tree.  Good thing you have bigger yards.

But is your yard big enough to grow one of these 3000 ton Giant Sequoias?  That's 6 million pounds, and would offset your carbon footprint for 169 years.   But, it takes 2000 years to grow one of these.  Too bad the government is considering logging these forests this year (2012).

Let's move on to petroleum in general, not just gasoline.  In 2007 the US used 39.82 quadrillion BTUs of petroleum, and the EIA lists crude oil and petroleum products have 44.7 pounds of carbon per million BTU.  This is a catch all for aviation gas, jet fuel, automobile gas, diesel, fuel oil, kerosene, liquified petroleum gas (LPG), petroleum coke and more.  These are between 40 and 48 pounds of carbon per million BTU, with coke being higher at 61.4, so the figure of 44.7 for petroleum in general seems just right.

(39.82 quadrillion BTU / 1 million ) * 44.7 = 1.78 trillion pounds

Divide by the approximate US population:

1.78 trillion pounds / 315 million = 5.650 pounds of carbon

Multiply by 2 and we get 11,300 pounds of tree.  Add that to the 4,700 pounds for natural gas and the 8,000 pounds for coal, and we have 24,000 pounds.  That's two African elephants!

Wallowa Valley, Oregon has some carbon sinks.

However, most of Oregon is either arid cattle country...

... or arid forests that burned to the ground recently:

The point is...    don't bother sequestering your carbon.  Maybe use less carbon.   Eh....   that won't work either.   You would need one of those zero energy homes and a bicycle.  Not gonna happen.   

Just pray that Canada and Siberia both thaw, and the tundra is replaced by trees.  That's our only hope.  After all, together they are about 8 million square miles, almost two Europes put together.

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