1 air mile
On average, a plane produces a little over 53 pounds of carbon dioxide (CO2) per mile.
To figure out how much carbon dioxide is produced by a plane flying one mile in the air, we're going to need to look at the technical details of a bunch of planes. However, how do we know what planes to look at, and how will we weight the different performance data?
To answer those questions, we decided to select a bucket of industry-leading airlines, see what planes they fly, and weight the technical details of each plane according to that plane's popularity.
There are plenty of ways to measure industry leadership, but we used the number of international departures from US airports as our measure of popularity. Here are the most popular US-based airlines in 2002 as reported by the Department of Transportation. (We know it's old data, and the airline industry has definitely seen some ups and downs since 2002. If you have better data, let us know.)
Aviation Industry Data, Office of Aviation and International Affairs,
Downloadable Data, Departures 2002, US Department of Transportation
Now that we have an idea who our industry leaders are (a rough idea because the data is years old!), we can see what planes they use. Determining which planes are used by our industry leaders will tell us what technical data we need to gather.
To determine the most popular US aircraft manufacturer, we looked at the airlines' FAA aircraft registrations. These figures aren't perfect. Just because a plane is registered doesn't mean it's in use. However, we can't really adjust for that, and, after all, it is in the company's best interest to use all of their planes.
|Model||American||Continental||Delta||United||Northwest||USAirways||Total||as % total|
|Airline Certificate Information, US Federal Aviation Administration|
Based on Table 2, FAA aircraft registrations by leading airlines, we can see that nearly 60% of the planes registered in the US are made by Boeing. We can also determine the mix of Boeing aircraft in use.
|Model||Planes (1)||as % all planes (1)||as % Boeing planes|
Now, we're ready to calculate the efficiency of an average aircraft using Boeing as the representative manufacturer. Within each 7-series, there are multiple models, and for one model there are multiple cabin configurations. A two class configuration was chosen where available because we believed this was probably their most popular configuration - first class and coach.
To compute the fuel economy of each plane as gallons per mile, we divided the stated maximum fuel capacity in gallons by the stated maximum range in statute miles (miles we drive in a car). Since Boeing's reported maximum range would have to include takeoff, flight, and landing we figured this was a simpler approach than using a more complex multivariate equation. In their technical details, Boeing wants to overstate both the range and the fuel capacity. Hopefully, any overstating will wash out in the division to create a close or conservative figure.
|Model||Passengers||Max fuel capacity (gal)||Max range (mi)||Fuel efficiency (gal/mi)|
|Boeing's Website, Aircraft Technical Details|
We know Boeing planes represent the industry (Table 2, FAA aircraft registrations by leading airlines). We know the mix of Boeing models (Table 3, Boeing aircraft in use), and we know the average fuel efficiency of each Boeing model (Table 4, Boeing aircraft capacity and fuel efficiency).
We're ready to calculate the fuel efficiency of an average aircraft. In geek speak, we're going to calculate a weighted average.
|Model||as a % Boeing planes (1)||Avg. fuel efficiency (gal/mi) (2)||Avg. passengers (2)|
Now that we know the fuel efficiency of an average aircraft (2.75 gal/mi), we're ready for a little chemistry.
In a turbine engine, jet fuel is mixed with air and combusted. The hot gases created by the combustion reaction in the engine exit the engine at high speeds and create thrust in the opposite direction. This moves the plane forward.
There are many types of jet fuel, and there are no standard chemical formulas. Not only does the chemical composition of jet fuel depend upon the crude oil from which it was refined, but most jet fuels contain additives like antioxidants, static inhibitors, corrosion inhibitors, and more. However, despite all their differences, the primary ingredient of most jet fuels is kerosene.
Kerosene is a mixture of hydrocarbons with the formula CvH2v+2 and carbon numbers mostly in the C9 - C16 range. For our calculations, we'll assume kerosene (aka, jet fuel) is dodecane, C12H26. In a 1991 survey, the Air Force determined dodecane was the most prevalent hydrocarbon in kerosene. Dodecane has a density of 0.75 g/mL (2,839.06 g/gal).
We're finally ready to calculate the pounds of carbon dioxide produced by a plane.
Jet fuel (aka, kerosene) (aka, dodecane) is burned in a typical combustion reaction where it's combined with atmospheric oxygen (O2) to create carbon dioxide (CO2) and water (H20). Of course, other elements in the air such as nitrogen and carbon dioxide are burned in the engine as well as oxygen. Those other element will create other molecules like nitrates and ozone, but we'll ignore them in our calculations.
The chemical formula for our reaction is:
C12H26 + O2 -> CO2 + H2O (1)
Of course, we need to balance it so the same number of elements enter and exit our reaction:
2C12H26 + 37O2 -> 24CO2 + 26H2O (2)
In the equation above, we can see that 24 molecules of carbon dioxide are produced for every two molecules of jet fuel (aka, dodecane):
24 m CO2 / 2 m C12H26 = 12 m CO2/m C12H26 (3)
However, dodecane and carbon dioxide have different molecular masses. We need to calculate the molecular mass of carbon dioxide, the molecular mass of dodecane, and the ratio between the two:
(1 m * 12.011 amu) + (2 m * 15.999 amu) = 44.009 amu (4)
(12 m * 12.011 amu) + (26 m * 1.008 amu = 170.337 amu (5)
44.009 amu / 170.337 amu = 0.258 (6)
12 * 0.258 = 3.096 g CO2 / g C12H26 (7)
Using the density of dodecane (2,839.06 g / gal), we can calculate our average fuel economy from Table 5, Weighted average capacity and fuel efficiency in grams of dodecane per mile:
2.75 gal/mi * 2,839.06 g C12H26/gal = 7,807.42 g C12H26/mi (8)
Now, given that 1 gram of dodecane produces 3.1 grams of carbon dioxide, we can calculate how much carbon dioxide an average plane produces to fly one mile in the air:
7,807.42 g C12H26/mi * 3.096 g CO2/g C12H26 * 1 lb/453.59 g = 53.29 lbs CO2/mi (9)
There you have it! To the best of our ability, on average, one air mile produces 53.3 pounds of carbon dioxide. One flight from New York, NY to Los Angeles, CA (about 2,450 miles) generates a little over 65 short tons of carbon dioxide.