Concern grows over pollution from jets

Newsweek recently had Richard Branson discussing how he plans to make airline travel green...

 

<div class='quotetop'>QUOTE(TonyPSchaefer @ Dec 20 2006, 09:31 AM) [snapback]364542[/snapback]</div>

Don't worry, when peak oil starts kicking in a few years, these problems will solve themselves.

 

<div class='quotetop'>QUOTE(HBO6 @ Dec 20 2006, 03:14 AM) [snapback]364478[/snapback]</div>

Interesting article. And a bit distressing, in that jets are already pretty fuel efficient due to jet fuel being one of their largest operating expenses.

Nonetheless...the distance from Denver to New York is about 1778 miles (per mapquest), which I can only imagine is a good deal more miles than the average SUV drives in a month. I just wish I knew how they got that figure. It makes it sound like jets generate a lot more CO2 than US autos (and a quick bit of searching proved inconclusive: 83000 or so SUVs in use, 24000 high altitude flights per day, each major airline carrier listing an active fleet of 400-700 planes, a sort of consensus that planes and cars emit about the same amount of co2 per passenger mile but plane journeys are much farther, etc..).

In any event, the poking about eventually led me to the union of concerned scientists website http://www.ucsusa.org/ which I'd never seen before, and, while not containing the source for this airplane study, has a lot of interesting info, including their number one tip for reducing your carbon footprint: buy a fuel efficient car.

And as for Tony's post, well, maybe we could harness the CO2 from Jets and put it into bombs. Then we could really (wait for it) ... drop carbon emissions.

 

<div class='quotetop'>QUOTE(HBO6 @ Dec 20 2006, 02:14 AM) [snapback]364478[/snapback]</div>

Always the nerd, I looked up the data and it appears that about 2.5% of total US energy consumption is for aviation, near as a I can tell. That's something around 8% of all liquid petroleum producs used in the US. Take 8% of US oil use, burn a good bit of it in the stratosphere - I could believe that might be an issue.

Further facts: Boeing says a loaded 747 gets about 53 passenger-miles per gallon, or roughly one-fifth the gas mileage of a full-loaded Prius. (That is, a gallon of fuel takes five passengers about 10 miles in a 747, but about 50 in a Prius). That 53 PMPG figure yields pretty much exactly the low-end carbon number cited in the article, assuming 22 lbs C02/gallon of fuel. (However, for an SUV to yield the low-end carbon number in the article, if it were driven at the US average 15,000 miles a year, it would have to get 31 MPG. So, the SUV they have in mind must be a Ford Escape Hybrid.)

At that PMPG mileage, a 6000 mile round trip from DC to California, for a family of four, would consume enough fuel to go 22,000 miles in a 48 mpg Prius.

All of that, of course, just pro-rates the jet's total fuel consumption / total passengers. Which is fair, I guess, but a bit ignorant -- the marginal impact of adding a person onto a plane is going to be far less than that. So, in some sense, if the jet's going to fly anyway, and it's not full, your decision to fly versus drive adds only a small increment to total C02 if you fly. That's quite unlike your decision to drive, where all the C02 is attributable to you.

How small is that marginal increment. That issue has already be quantified, in the context of fatter Americans requiring more jet fuel, here http://www.boingboing.net/2004/11/05/super...g_of_ameri.html

Based on the data there, plus some rummaging at the DOE, I calculate that the marginal fuel cost is about one-quarter of the average fuel cost. Roughly. So if you're of average weight (185 lbs with baggage was cited as the figure typically used by airlines), the incremental fuel that the jet burns to carry your weight is about one-quarter of the average for the entire plane and trip. So, on the margin, my family of four's decision to park the Prius and drive is roughly a wash, in terms of total additional fuel consumption for that trip,comparing the total additional fuel the jet burns (assuming our weight is average), versus the fuel the Prius would burn. Ignoring the fact that the fuel gets burned in the stratosphere.

Not sure how I would resolve the issue of average versus marginal fuel use. Guess I'd assume whatever made me feel better about the mode of transportation I had chosen.

 

Branson's article

 

<div class='quotetop'>QUOTE(Delta Flyer @ Dec 20 2006, 10:58 AM) [snapback]364583[/snapback]</div>

Decent article. The two here-and-now changes amounted to not using the engine while moving slowly over the ground, and planning your travel to be more efficient in traffic jams. Good advice for anybody.

 

It isn't just engines. The airframes need to be improved. A flying wing is more efficient than the standard air plane shape.

 

The numbers don't make any sense! A fully loaded 373-300 carries 27,512 pounds of jet fuel. IF ALL the fuel when burned turned into CO2 the at 840 pounds of C02 only 32 passengers (no pilot or stews) at the higher rate that would be 16 passengers.

Perhaps it should have read for the plane on that trip would be those numbers which means at the lower end considering 200 passengers 4.2 pounds per or at the higher end 8.3 pounds per passenger. Again IF ALL the fuel turned into CO2 these number would apply, but they don't. I would guess only a 1/3 of the fuel turns into C02.

373 fuel capacity 20,105 Liters (5311.17 gallons)
JP4 weighs 62% of water
A full load of fuel weighs 27,512 pounds

Faulty data :angry:

 

<div class='quotetop'>QUOTE(madams @ Dec 21 2006, 11:30 AM) [snapback]365110[/snapback]</div>

The rule of thumb is that burning a gallon of gasoline yields about 22 lbs of C02. Most of the weight is the 02, which of course comes from the air, not the fuel tank. You can predict the ratio of the weight of C02 to the weight of the gas pretty closely by ignoring the hydrogen, as (16+16+12)/12 , the molecular weight of (O+O+C)/C. That's not exactly right but it gets the gist of it;. Botton line is that the C02 has about 3.5x more mass than the gasoline that generated it. I'm sure that's about right for kerosene or jet fuel as well.

The weight of a gallon of gas may vary depending on octane and formulation, but 6.2 lbs would be average.

Chevron says that almost all US jets use kerosene-type jet fuel (Jet A) and lists the weight at 6.76 lbs per US gallon. Though no doubt that may vary with the exact formulation as well. From what little I know about it, it would make sense to me that refined kersoene-type jet fuel would weigh more than gasoline. In anycase, I'm taking Chevron's figure for it.

http://www.chevron.com/products/prodserv/f...htm#performance

So, starting from your listed fuel capacity, I estimate that burning that entire tank would generate about 125,000 lbs of C02. At 840 lbs/person, thats about 148 people, or pretty nearly the capacity of that plane, I think. No idea whether it would take a full tank to get to Denver, but if so, the numbers seem about right to me.

 

We should just make strong catapults.

http://youtube.com/watch?v=WDZsfllhrrM

And big pillows.

 

So is this all about fuel usage and no mention of cloud seeding and contrails? Albeit it is so far considered a small effect but it is an effect and it all adds up.

 

<div class='quotetop'>QUOTE(F8L @ Dec 22 2006, 03:06 AM) [snapback]365584[/snapback]</div>

No, I was just tring to do some calculation. The gist of the USA Today article was that a) air travel is growing fast, and B) releasing exhaust directly into the stratosphere appears more damaging that releasing it at ground level, for the reasons you mentioned. I just wanted to get a handle on how much of US energy use aviation accounts for and then to figure out whether, for a long trip with my family, I'd generate more C02 by flying than by driving. (Completely ignoring the issue of where that C02 is released). I think the answer is, that if I only count my marginal impact on jet fuel consumption (that is, just the added weight of my familiy, on a plane that's going to be flying anyway), then it's about a wash. If I count the average (jet fuel consumed / N of passengers), then no, flying produces vastly more C02. Like many accounting issues of this type, there's no natural solution -- no one "right" way to pick between average and marginal impact as reflecting my "true" impact in choosing to fly rather than drive -- so that's as far as I could take the analysis. In terms of carbon footprint, flying my family somewhere is with certainty no better than driving, and could be viewed as a whole lot (ie, 4x) worse than driving if I accept full responsibility for the average C02 per passenger instead of just my marginal contribution. Throw in the additional issue of releasing exhaust directly into the stratosphere and I think the answer is, for my family of four, with a Prius, drive rather than fly, when feasible.