1 air mile

On average, a plane produces a little over 53 pounds of carbon dioxide (CO2) per mile.

Airlines

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.)

Table 1. International departures by US airline
Airline Departures
American 1,695
Continental 1,157
Delta 860
United Airlines 827
Northwest 721
USAirways 543
Total 5,803
Aviation Industry Data, Office of Aviation and International Affairs,
Downloadable Data, Departures 2002, US Department of Transportation

Manufacturers

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.

Table 2. FAA aircraft registrations by leading airlines
Model American Continental Delta United Northwest USAirways Total as % total
B-737 77 255 71 94 0 92 589 21.6%
B-747 0 0 0 30 35 0 65 2.4
B-757 140 58 123 97 71 43 532 19.5
B-767 74 26 104 35 0 10 249 9.1
B-777 47 20 8 52 0 0 127 4.7
MD-88 0 0 120 0 0 0 120 4.4
MD-90 0 0 16 0 0 0 16 0.6
DC-9 338 0 0 0 134 0 472 17.3
F-28 4 0 0 0 0 0 4 0.1
A-300 34 0 0 0 0 0 34 1.2
A-319 0 0 0 55 59 93 207 7.6
A-320 0 0 0 97 71 75 243 8.9
A-321 0 0 0 0 0 28 28 1.0
A-330 0 0 0 0 29 9 38 1.4
Total 714 359 442 460 399 350 2,724 100%
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.

Table 3. Boeing aircraft in use
Model Planes (1) as % all planes (1) as % Boeing planes
B-737 589 21.6% 37.7%
B-747 65 2.4 4.2
B-757 532 19.5 34.1
B-767 249 9.1 15.9
B-777 127 4.7 8.1
Total 1,562 57.3% 100%
  1. From Table 2, FAA aircraft registrations by leading airlines

Average aircraft

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.

Table 4. Boeing aircraft capacity and fuel efficiency
Model Passengers Max fuel capacity (gal) Max range (mi) Fuel efficiency (gal/mi)
737-600 110 6,875 3,510 1.96
737-700 126 6,875 3,872 1.78
737-700ER 76 6,875 6,341 1.08
737-700C 120 6,875 3,688 1.86
737-800 162 6,875 3,521 1.95
737-900ER 180 7,837 3,682 2.13
Average 129 7,035 4,103 1.79
747-8 467 64,225 9,206 6.98
747-400 524 57,285 8,355 6.86
747-400ER 524 63,705 8,826 7.22
747-100 452 48,445 7,020 6.90
747-200 452 52,410 9,091 5.76
747-300 496 52,410 8,861 5.91
Average 486 56,413 8,560 6.61
757-200 200 11,489 4,488 2.56
757-300 243 11,466 3,907 2.93
Average 222 11,478 4,197 2.75
767-200ER 224 23,980 7,584 3.16
767-300ER 269 23,980 6,876 3.49
767-400ER 304 23,980 6,473 3.70
Average 266 23,980 6,978 3.45
777-200 400 31,000 6,024 5.15
777-200ER 400 45,200 8,861 5.10
777-200LR 301 47,890 10,875 4.40
777-300 451 45,200 6,922 6.53
777-300ER 365 47,890 9,126 5.25
Average 383 43,444 8,362 5.29
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.

Table 5. Weighted average capacity and fuel efficiency
Model as a % Boeing planes (1) Avg. fuel efficiency (gal/mi) (2) Avg. passengers (2)
B-737 37.7% 1.79 129
B-747 4.2 6.61 486
B-757 34.1 2.75 222
B-767 15.9 2.75 266
B-777 8.1 5.29 383
Weighted average 100% 2.75 218
  1. From Table 3, Boeing aircraft in use
  2. From Table 4, Boeing aircraft capacity and fuel efficiency

Jet fuel

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).

Combustion

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)

Given the molar ratio of 12 (Equation 3) and a mass ratio of 0.258 (Equation 6), we can determine that for every gram of jet fuel (aka, dodecane) consumed, 3.096 grams of carbon dioxide are produced: 

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)

Conclusion

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.

Heads up! We intentionally omitted an average emissions per passenger. Really, it would be an average per seat (since not every flight is full). Plus, most commercial airlines carry a significant amount of freight. However, with that said, if you allocate all the emissions to passengers, the plane is full, and you divide the pounds of carbon dioxide per mile by the average number of passengers from Table 4, Boeing aircraft capacity and fuel efficiency, you'll get 0.24 pounds of CO2 per passenger per mile.

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