# About Cars - How Much Oxygen do They Use?

Mario Buildreps is a graduate engineer. Become aware of topics in a way you have never heard before.

## A Simple Question

Children sometimes ask adults questions where a simple answer doesn't fit. Like: how much air use all cars together?

All organisms on Earth share the same air as the cars we use. So, it looks a little bothersome that we still not seem to be aware about this and happily keep on travelling by car and plane, and using our own oxygen for something quite arbitrary, like going to a shopping mall.

How much air use all cars together? How hard is it to answer this question?

## The Power of Simple Calculations

Simple calculations can be very useful to put things back into perspective and to make clear how large a problem actually is. Even when a simple calculation is made on the back of a beer mat, it can still be very useful for describing the magnitude of an idea or a hypothesis.

Even when a simple calculation is not very accurate, it at least shows something as when we don't make the calculation, isn't it?

Many people look often unaccustomed to simple calculations, because they can be amazed how simple it can be to show an unimaginable 'difficult' issue in a simple way.

Simplicity and simple calculations have great power, and it doesn't need any fancy equipment or cumbersome scientific approach.

You only need the ratio and some figures that are available on internet.

## Oxygen Usage of Cars versus Humans

During operation an average car, with a cylinder displacement of let's say 2000 cm3, uses at an average rotation speed of 2,500 RPM, approximately 2.5 m3 of air per minute.

All these figures might say you not so much, but let's put this into perspective - a human being at rest consumes about 6 litre per minute, which is 400 times less than the car.

But there is more. The residual oxygen emitted by a car is just 2%. The residual oxygen emitted by Humans is about 16%. The oxygen usage of a car is much higher on top of its also much higher air consumption. So, it goes double!

The normal level of oxygen in the air is 21%, from which a human consumes 1/4 portion. While an average car consumes 9/10 portion of all oxygen in the air. The exhausted air of a car is almost useless for oxygen consuming organisms, except for plants that consume carbon dioxide.

So a car is hungry and thirsty for oxygen. Both. This doesn't look very promising!

## Air Becomes Unbreathable for Oxygen Consuming Organisms

A little bit depending of the degree of sophistication of the engine, the air, that has passed the engine of a car, becomes unbreathable for oxygen consuming organisms.

This means that air that is consumed by a car has to go somehow back into the ecosystem to be compensated by the vegetations like plants and trees, and of course the oceans. But besides tons of carbon dioxide, drop cars much more garbage, like particulate matter, into nature, without any message 'what to do with it'.

I think that everyone should be aware of this while driving around in a car. The air that your car is exhausting every second is unbreathable and has to be 'treated' by the surrounding nature to become breathable again, no matter how sophisticated your car is.

Only an 100% electrical car, like the wonderful Tesla Model S, that takes electricity from windmills or solar panels can be classified as fully clean to use. Although these cars were produced in factories and the windmills had to be produced as well. It is currently the best we can get.

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## Air Usage of a Car

Every car that has a four stroke engine, will displace half it's volume with every revolution. To explain how the principle of a four stroke engine works goes slightly too far in this Hub, but it has to do with the basic construction principle of this most commonly used engine type.

• Based upon information found in the data above, the average volume of the 1 billion cars around the world is around 2000 cm3 from which 1000 cm3 will be emitted into the air with every revolution.
• The average speed 1 billion cars travel annually will be around 60 km/h, which is a mix of city traffic, highway traffic and standstills at traffic lights and/or traffic jams. The typical revolution speed of an average engine at this speed is around 2,500 revolutions per minute.
• An average car travels about 15,000 km per year. That come down to the usage time of 250 hours per year.

The air displacement of a car in this typical average situation like sketched above will be 37,500 m3 per year (2.5 × 60 × 250).

## The Input For This Calculation

IssueAmount

Amount of Cars

1,000,000 (2010)

Average air usage per car per year

37,500 m3

Oxygen Usage

90% (19% of 21%)

Diameter Earth

6,371,000 m

Height Troposphere

10,000 m

## Volume of the Troposphere Counted on Ground Level

The majority of the cars are used at sea level, where air is the most dense, around 100 kPa. To compare the amount of oxygen in the higher regions of the Stratosphere that take part in the refreshment of the air through wind displacement, the air in the higher regions has to be 'compressed' to make it comparable at sea level.

The volume of the troposphere can be derived by extracting the volume of two spheres: ((12,777)³-(12,757)³) * π/6 ≈ 5,120,000,000 km³. This volume includes the air on ground level, but also the air on a height of 10 km where there is no breathable air anymore, so using this volume would be incomplete.

The pressure of the Troposphere is not uniform. The volume of the upper-air should be transformed into an equivalent of the air pressure on ground level, like I show on the picture. The most simple method with an acceptable accuracy is to divide the result of the formula above by two - which results in 2,560,000,000 km³.

## Results

 Resulting volume Troposphere 2,560,000,000 km³ Annual air usage one car 37,500 m³ Annual air usage all cars (1 billion in 2010) 37,500,000,000,000 m³ (37,500 km³) Annual air usage of all cars (%) 0.001465%

## Conclusion

According to the results of the above result, it would take 68,300 years until all air on Earth would have gone through the engines of all present cars.

According to the Hirsch Report personal used vehicles powered by a combustion engines consume around 55% of the oil use worldwide.

This indicates within certain variations that it would take around 40,000 years until all planet's air has passed oil driven combustion engines, which puts the climate issue into another perspective. It looks not so much, but it's just one of the many man-made polluters around.

The question is then, would Earth be able to handle this? I don't know. But when you add all other harm that is done to Earth that all adds up to one huge man-made devastation, I think Earth isn't feeling too well about this attitude of humans.

In most cities the air became simply unbreathable. Debates about the climate are just nonsense, better stop to drive cars and stop to use airplanes.

Well, that's it folks!

Frank Mancuso on December 17, 2018:

2 things to consider 1. The oxygen level needs to fall by 3% to end life as we know it.2. The machines that sequester CO2 and convert it back to oxygen are broken, forests half gone, phytoplankton almost half gone. I would love to see a new calculation getting us to 18% considering the above plus fire, from other combustion, factories, power plants, methane from animal production.