What would happen if the air in all car tyres was released?

By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

04 December 2022

Kimani wa Karanja from Mombasa asks: “Suppose all air inflated in cars and aeroplanes tyres [as well as] foot balls etc worldwide is released; would there be excess air in circulation? What would be the effects?”

The short answer is nothing would change. This is because that air was originally in the atmosphere before it was pumped into those tubes and tyres. Perhaps the question should then be asked in a reversed manner, thus: what is the effect of removing air from the atmosphere and compressing it into small enclosures?

To answer that, we need to find out how much air has been enclosed in tubes and tyres in relation to the quantity in the atmosphere. The starting point is the mass of air in a car tyre. This can be calculated from the following known typical quantities: volume of a car tyre is about 10 litres and pressure inside is about 2 atmospheres (30 PSI).

These values combined with the density of air at 2 atmospheres of pressure give a mass of about 25g of air per tyre. So, a car with four tyres should have a total of about 100g of air in them.

The next step is to find out how much air there is in all the cars in the world. There are about 1.5 billion cars, therefore, altogether, the tyres carry about150 billion grammes or 150 million kilograms or 150,000 tonnes of air. This isn’t a lot of mass: it can be carried by one ship!

But how does it compare with all the air in the rest of the atmosphere? In December 2010, I did an estimate of the total mass of the air in the entire earth’s atmosphere. The calculation started with the air pressure near the earth’s surface; this was expressed as force per unit area. Then the force was multiplied by the total surface area of the planet. The result was the changed to mass using the gravitational intensity on earth.

The answer came to 500 quadrillion tonnes; that is, the number 5 followed by 17 zeroes. 150,000 tonnes pales into insignificance when compared to the mass of the atmosphere. It is 0.00000000003 per cent! Hence, removing such a miniscule amount wouldn’t have any observable effect…

Nevertheless, meteorologists are acutely aware of the butterfly effect: The idea that a butterfly flapping its wings somewhere in, say, the Amazon forest can cause changes in air currents that eventually trigger a typhoon in a faraway place like, say, Japan!