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01 June 2010 @ 10:46 am
How much does a forest of smoke weigh?  
Last night, spike mused curiously on how much the smoke from the Quebec forest fires weighs. I thought about it for a while and realized that I didn't think I had enough information even to estimate. How much does a particle of smoke weigh? How many particles in the air normally? How many particles per cubic foot are represented by 1 mile visibility? Then spike pointed out that it might be easier to go at it from the other side: how much does a tree weigh and how much of that turns into smoke? We didn't have much information there, either, but the numbers were a little more graspable, so here's what we came up with:

We guessed that the "average" tree weighs about 1000 (10^3) pounds, there are about 10^9 trees burning, that about 1% of a tree's weight turns into smoke, etc, etc. Our final calculation was that there were about 100,000 tons of smoke resulting from those fires, which I actually think represents a dropped zero somewhere, and, obviously some wild guesses. I decided I wanted to know more, so I went to the internet for some numbers that represent real data, even if they still lead to an estimate:
The Energy Policy Act of 1992 gives us 700 trees/acre in a forest (varies by type, but this is close enough for government work), and there are 100,000 acres of trees on fire = 70,000,000 trees (7x10^7 - so we were off by 2 orders of magnitude on that one, at 10^9)

Wiki Answers gives the average weight of a tree at 1500lbs (we thought 1000)

According to http://burningissues.org/lukebiomass.html:

"Burning a kilogram (2.2lbs.) of wood in a new wood stove will produce about 130 grams of carbon monoxide, 51 grams of hydrocarbons (including up to 10 grams of carcinogenic benzene), 21 grams of fine particulates, and about 0.3 grams of the highly carcinogenic poly cyclic organic hydrocarbons (EPA, 1984, Larson, 1993). Wood burning also produces from 10 to 167 milligrams of highly carcinogenic dioxins per kilogram of fuel burning (Abelson). Wood burning is responsible for about 3 percent of the total suspended particulates, 6 percent of the total carbon monoxide, and 51 percent of the highly carcinogenic polycyclic organic matter produced by all US sources (EPA, 1986)"

Giving us 21grams of smoke per 1kg of wood = .021 = 2% (we guessed 1%)

So, finally, we have:
7x10^7 trees
*1500lbs/tree
*.02 pounds of smoke/pound of tree =
21x10^7 pounds (or just over 1 million tons) of smoke

ish. Or, not too far off!
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Deloresdebsquared on June 1st, 2010 03:21 pm (UTC)
Very cool! I remember an example like this in college. Eddy Merckx was a champion cyclist (Tour de France, etc.) and our task was to figure out how much energy he burned in an hour. We of course then translated it to alcohol, for the now-famous "beers per hour" energy replenishment metric.
Blue Gargantuabluegargantua on June 1st, 2010 03:29 pm (UTC)

It was really weird driving back into Boston after a weekend of clear sunny skies and suddenly realizing I couldn't actually seen the Boston skyline.

later
Tom
lazyzlazyz on June 1st, 2010 06:00 pm (UTC)
I'd no idea Quebec is burning.