Aircraft and CO2

Are planes so polluting?

We recently read on the Nouvel Observateur website:

"I would like a round trip Paris-Bangkok in a plane of recent and well filled invoice". This is what a traveler very concerned about fighting the greenhouse effect could ask his travel agency. By plane, a passenger emits on average 140 grams of CO2 per kilometer, against 100 on average by car, recalls the French Institute of the Environment (Ifen) in a summary on the contribution of air transport to the greenhouse effect. Even taking into account emissions from car manufacturing and petroleum refining, the aircraft rejects 16% more carbon dioxide per passenger.

Even in the best conditions of filling, type charter flight, a return Paris-New York corresponds to the rejection of a tonne of CO2 per passenger, says Ifen in the latest issue of Environmental Data. The most polluting flights are the shortest.

CO releases2 are not the only contribution of air transport to the greenhouse effect, Ifen continues. The planes also reject nitrogen oxides and water vapor which promotes the formation of contrails.
The work of Patrick Minnis at NASA's Langley Research Center has shown that these trails form cirrus that retain heat.

Global air transport accounts for 2,5% of global CO emissions2 related to fossil energy consumption. The room for maneuver to improve the energy efficiency of the aircraft is very limited, underlines the Ifen article. As a result, with increasing traffic, the impact on the climate will intensify. "

Our analyzes on air transport

This news is however completely wrong. Here is the proof by calculations.

Read also: Thèse des Mines de Paris: fuel oil and water combustion


I recently calculated the mass releases starting from the complete (and ideal) combustion equation.

We arrived at the following figures: An engine consuming 1 L of gasoline will therefore reject a little more than a kilo of water and 2.3 kg of CO2.

Now kerosene, the fuel for reactors, is heavier than gasoline (see its properties here: properties of petroleum fuels ). Let's take a carbon atom number of 12, that is one forumthe average chemical level of C12H26.

According to the combustion formulas, it comes:

Application to kerosene. n = 12
[C12H26] = 12 12 * + = 26 1 170 * g / mol.
The mass of CO2 released per mole of kerosene consumed is: 44 * 12 = 528 g.
The ratio of kerosene mass consumption to CO2 emissions is 528/170 = 3.10

This means that for 1 kilo of kerosene consumed 3.1 kilograms of CO2 are emitted.

The details of the combustion calculations are on this page: combustion equations and CO2 hydrocarbon emissions

What does this article say?

According to this one: a round trip Paris-New York rejects 1 ton of CO2 per passenger.

Read also: Water injection in Daimler Benz engines on Messerschmitt aircraft

This means that 1000 / 3.1 = 322 kilograms of kerosene were consumed, or 322 / 0.8 = 402 L because the density of kerosene is around 0.8.

The distance Paris New York is 5850 km approximately 5850 * 2 = 11700 km for a round trip.

402 L for 11 km… this gives us an average consumption per passenger of 700 L per 3.43 km.

Which current consumer car is capable of such low consumption? None without hesitation!

And yet the article pushes the nail a little further:

"An airplane traveler emits approximately 140 grams of CO2 per kilometer, compared to 100g / km for a motorist."

Here then ? Assuming that the motorist is alone in his vehicle and using the same reverse approach, a petrol car emitting 100 g of CO2 / km will consume 100 * 100 / 2.3 = 4.3 L / 100… Very few petrol vehicles are capable of such consumption..I'm not obviously talking about urban traffic! The reality is rather close to double…

Another reasoning would say that the plane consumes 40% more than the car, or conversely that the car consumes 28% less than the plane…

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A small digital application with the figure of 3.43 L per 100 km for the consumption of an airplane gives a consumption of a vehicle of 3.43 * 0.72 = 2.46 L / 100.

Again: Which current car is capable of such consumption? None (twice)!

Note: The filling rate average of European cars is between 1.2 and 1.6 person / car, a correction of the calculations is therefore possible thanks to these figures to obtain the emissions or the average consumption for cars in g of CO2 per km.passenger or L / 100km.passager . In all cases, and according to the initial figure of 1 tonne of CO2 for a round trip Paris / New-York, the plane remains less consumer than cars.

Not so polluting, large carriers are full!

Here I stop to say that it seems to me that the figures announced in this article are either false or that air transport, mass over long distances, is less polluting than road transport…Yet the authors of the article did not really state that.

The major problem of the future is the increase in global traffic, whether by land, sea or air! Accusing planes or boats to make the use of the private car less guilty is common and very misleading! The real questions are: do we need to fly so much? Do we need to buy halfway around the world? Do we need to take our car as much?

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