The Combustion Conundrum

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The Combustion Conundrum

Everybody loves a cheery campfire, and a big bonfire is even more fun, but exactly how much carbon are you releasing into the atmosphere every time you light up a pile of logs? Usefully, the average 10-year-old Christmas tree (when dry) weighs about the same as the average bundle of pre-split, kiln-dried firewood: about 18 pounds. One pound of carbon in wood, when burned, releases 1.6 pounds of CO2 (carbon dioxide). This is because combustion is an oxidative process and pulls oxygen (O2) out of the atmosphere to combine with the carbon.

So, your average Christmas tree, or a campfire that burns one bundle of wood, has the capability of putting about 30 pounds of CO2 into the atmosphere. The combustion of wood in a campfire or bonfire is inefficient, though, and perhaps only 50% to 80% of that carbon is actually turned into gas.

For a pile of 250 Christmas trees, this means that of a possible 7,500 lbs of CO2, a “back of the envelope” guess is that probably more like 4,000 to 5,000 pounds of CO2 from that pile is released. The rest stays in solid form as ash and charcoal.

This sounds pretty bad. But if you want to get some perspective about our cultural problems with CO2, let’s do a comparison with a different carbon-based fuel that we burn all day every day: gasoline.

A gallon of gasoline weighs eight pounds, and releases almost 18 pounds of CO2 when burned—and gas burns much, much more efficiently than wood.

An 80-mile round trip to Grandma’s house (say, from Salt Lake City to Ogden) in a vehicle averaging 25 miles per gallon will release 57 pounds of CO2, about the same as two to four bundles of firewood. One hundred people driving to Ogden for Thanksgiving liberates about as much carbon as a pile of 250 Christmas trees burning.

Now, if you want to drive to Moab for a weekend vacation, the 470-mile round trip in an average pickup truck (15 mpg) will release 600 lbs of CO2, just for that one trip. A fuel-efficient car (40+ mpg) will release more like 200 lbs.

Zion National Park is over a 600-mile round trip from Salt Lake City. Your Ford pickup is liberating 730 lbs of CO2 for that trip, and your Honda Fit is releasing about 275 lbs.

Now consider that Salt Lake County contains just over a million people. The average U.S. per capita consumption of gasoline is 423 gallons (that’s for every man, woman, and child in the nation). Divide that by 365 and you can ballpark the amount of gas burned in the valley every day. 1.6 gallons per person times a million people, so that’s 1.6 million gallons of gasoline burned, every single day.

Multiply that by 18 pounds of CO2 per gallon of gas, and just our normal commuting and driving around doing errands in the valley liberates more than 28 million pounds of carbon dioxide PER DAY. That’s over a million bundles of firewood (or Christmas trees). Also remember that gasoline is fossil carbon, not carbon that was in the air 10 to 50 years ago that got made into a tree and then re-released into the atmosphere. Burning wood is, at least in theory, carbon-neutral.

And this is only gasoline we’re talking about here. When you factor in coal-fired power plants and natural gas for heating homes and businesses, our carbon footprint becomes even more extravagant.

We can see the flames of a campfire, but these other sources of combustion are “invisible: — we don’t often think about how much fossil carbon is released just in the name of keeping our electrical grid running, or our houses warm in the winter. Your smartphone runs on fossil carbon.

Contemplating all of this causes crippling anxiety and a feeling of powerlessness, but this is the way I see things: Excoriating yourself about burning a campfire or a bonfire because of our overall carbon footprint is like deciding not to drink water from your tap because there’s a big leak in the main out on the street, and thousands of gallons of water are running away down the gutter every hour. Just as, if you are thirsty and need water to nourish your body, drink it, but don’t waste it—if you need a campfire to soothe your soul, or a bonfire to bring cheer to your community, burn the wood, but do it with mindfulness. We change the world an inch at a time, and you are only one small human. Do what you can: Take public transport, ride your bike, invest in renewable energy sources, and vote for people who share these values. Tend your life and set an example for others, and always have a good ghost story to share at the campfire.

 
 
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