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[John Galt]

A typical passenger vehicle emits about 4.6 metric tons of carbon dioxide per year.

I think you need to check your numbers. A typical passenger vehicle consumes about 4,600 POUNDS (not tons) of gasoline per year. If every pound of that gasoline burned resulted in a pound of CO2, I would be very surprised. But, even if it did, that is 1,000 times less CO2 that 4.6 metric tons...

 

[RobStow]

I think you need to check your numbers. A typical passenger vehicle consumes about 4,600 POUNDS (not tons) of gasoline per year. If every pound of that gasoline burned resulted in a pound of CO2, I would be very surprised. But, even if it did, that is 1,000 times less CO2 that 4.6 metric tons...

The guy you were responding to never said anything about how much fuel a typical passenger vehicle consumes - he said it produces 4.6 tonnes of CO2.

You, however, said it consumes 4600 lbs of fuel and somehow magically produces "1,000 times less CO2 than 4.6 metric tons".

You are very, very wrong because burning 4600 lbs of gasoline or diesel produces significantly MORE than 4.6 tonnes of C02. The CO2 produced by burning long chain hydrocarbons like octane, nonane, decane, etc vastly exceeds the mass of the initial fuel.

Gasoline is not pure octane by any stretch, but lets pretend it is just to keep things simple.
Burning octane, assuming nice clean ideal combustion to keep it simple is:
2 * C8H18 + 25 O2 ==> 16 CO2 + 18 H2O
In terms of atomic mass units that corresponds to
228 amu of Octane + 800 amu of Oxygen ==> 704 amu CO2 + 324 amu Water

Using those proportions, if you burn 4600 lbs of Octane you'll produce 14204 lbs of CO2 ... which is 6.44 tonnes.

 

[John Galt]

The guy you were responding to never said anything about how much fuel a typical passenger vehicle consumes - he said it produces 4.6 tonnes of CO2.

You, however, said it consumes 4600 lbs of fuel and somehow magically produces "1,000 times less CO2 than 4.6 metric tons".

You are very, very wrong because burning 4600 lbs of gasoline or diesel produces significantly MORE than 4.6 tonnes of C02. The CO2 produced by burning long chain hydrocarbons like octane, nonane, decane, etc vastly exceeds the mass of the initial fuel.

Gasoline is not pure octane by any stretch, but lets pretend it is just to keep things simple.
Burning octane, assuming nice clean ideal combustion to keep it simple is:
2 * C8H18 + 25 O2 ==> 16 CO2 + 18 H2O
In terms of atomic mass units that corresponds to
228 amu of Octane + 800 amu of Oxygen ==> 704 amu CO2 + 324 amu Water

Using those proportions, if you burn 4600 lbs of Octane you'll produce 14204 lbs of CO2 ... which is 6.44 tonnes.

Now you've made me go look it up. I don't think either answer is correct. I also think he changed his original post from 4,600 tonnes, which is why I originally thought it ridiculous, but can't prove that so there you go. Maybe he saw my post and changed it...

I work for the world's largest reseller of vehicles. An average vehicle actually is driven about 15,000 miles per year, which at 20mph comes to 766 gallons / 4,600 lbs. Thus, I had assumed he meant pounds of gasoline, not tonnes of exhaust.

When people say nonsensical things the only thing to do is look it up. You are correct only as far as burning 1 lb of gasoline "creates" more than 1 lb of CO2. In fact it results in approximately 20 lbs. https://www.fueleconomy.gov/feg/contentIncludes/co2_inc.htm

So... If the hypothetical "average vehicle" does in fact burn 766 gallons/4,600 POUNDS of gasoline, that would result in approximately 92,000 lbs of CO2, or 46 tonnes. Note too that 46 tonnes could have been a mistake in his calculations, shifting the decimal point by two places. That's a lot more than 6.44 tonnes, but not even in the neighborhood of 4,600 tonnes - which I still think is what he originally posted...

Cheers.