Aircraft and CO2

Are planes so polluting?

We recently read on the Nouvel Observateur website:

"I would like a Paris-Bangkok return trip in a recent, well-filled plane". This is what a traveler who is very concerned about combating the greenhouse effect could ask their travel agency. On an airplane, a passenger emits an average of 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.

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Preliminaries:

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

We came up with 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.

However, kerosene, fuel for reactors, is heavier than gasoline (see its properties here: properties of petroleum fuels ). Let us take a number of carbon atoms of 12, that is to say a 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.

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

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

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

What current mainstream car is capable of such low consumption? None without hesitation!

And yet the article drives the point home 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 following the same reverse procedure, a gasoline car emitting 100 g of CO2 / km will consume 100 * 100 / 2.3 = 4.3 L / 100… Very few gasoline vehicles are capable of a such consumption..I am obviously not talking about urban traffic! 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: What current car is capable of such consumption? None (bis)!

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.passenger . In any case, and according to the initial figure of 1 tonne of CO2 for a Paris / New-York return trip, the plane still consumes less than the cars.

Not so polluting, large carriers are full!

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

The major problem of the future is the increase in world traffic, whether land, sea or air! Accusing planes or boats to exonerate the use of personal cars 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 so much?

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