Checking my math

In finishing last month's Scientific American at the mall, I read an article about the future of hybrid vehicles. It was interesting, and, as always, Steggie and I are proud to have gotten on at the ground floor. The most interesting, and most sobering, part of this article was a table comparing all the different hybrid models currently out there. The final column listed annual CO2 emissions, assuming the cars are driven 15000 miles a year (which is about how much I drive) and using the (optimistic) EPA estimates of fuel efficiency (55 mpg).

The statistic for a Toyota Prius, which is indisputably the BEST car out there, is an overwhelming 3.5 tons of CO2 a year. I was astounded. Of course, I couldn't leave this number alone. With a little stoichiometry, I determined that this amounted to 0.47 lb of CO2 a mile. That's actually even more astounding. With a little more stoichiometry, this time using a more reasonable estimate of fuel efficiency (50 mpg), I determined that Steggie emits 23.3 pounds of carbon for every gallon of gas. Yikes!

I must admit, I was skeptical. A gallon of gas can't weigh anything near that much! Of course, all the extra weight must come from atmospheric oxygen taking part in the combustion, but still! So I searched the internet and was overjoyed to find this site which tells you how much carbon a given car will emit. They present results in g/km, but after still more stoichiometry, I found that Steggie emits 0.4258 lb/mile. Unfortunately, Scientific American is only too right. I guess (grudgingly) that makes sense. After all, oxygen is a lot heavier than hydrogen, and with combustion, the carbons are exchanging their hydrogens for oxygens (in a manner of speaking).

Wow. How frightening. Now I'm even more glad to be pioneering this hybrid technology. How much does your car chalk up for global warming?