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There may be millions of tonnes of white hydrogen available for power. Since each reaction needs oxygen, could it deplete our air supply?
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Mike Follows
Sutton Coldfield, West Midlands, UK
In 1987, a well in the Malian village of Bourakébougou unexpectedly ignited when a worker lit a cigarette nearby. The incident drew the attention of a local entrepreneur, who investigated and discovered that the flames were caused by naturally occurring, or white, hydrogen seeping from underground.
White hydrogen is typically created through geological processes in which water reacts with iron-rich minerals, such as olivine, under conditions of high temperature and pressure. This sets it apart from grey hydrogen, which is derived from fossil fuels, and green hydrogen, which is produced using renewable energy sources.
Estimates differ, but the US Geological Survey suggests that there may be approximately 100,000 megatonnes of accessible white hydrogen worldwide. A back-of-the-envelope calculation suggests that there is about 1018 kilograms of oxygen in the atmosphere. Even if all the white hydrogen reacted instantly with oxygen, only 1 in about 1500 oxygen molecules would be involved.
Even if all the white hydrogen reacted instantly with oxygen, only 1 in about 1500 oxygen molecules would be involved
Guy Cox
Sydney, Australia
White, or mineral, hydrogen is that which occurs naturally underground. It was originally derived from water, but the oxygen from the water has been mineralised rather than released into the atmosphere.
The questioner’s thinking is presumably that when we burn other fuels – coal, oil or wood – they are created by plant photosynthesis, so an equivalent amount of oxygen to that consumed in combustion was released to the atmosphere when the fuel was formed.
But it isn’t so simple. In the case of wood, we can be fairly sure that the oxygen released when the wood was formed is still out there. Not so with fossil fuels and white hydrogen, since much of the oxygen released will subsequently have been mineralised in carbonate rocks such as limestone, chalk and dolomite. The Carboniferous period was when much of Europe’s coal deposits took shape, and also when huge deposits of limestone were formed.
So, burning white hydrogen won’t deplete atmospheric oxygen any more than burning fossil fuels such as coal, and has the bonus of not producing any carbon dioxide. Of course, “green” hydrogen would be even better.
Sam Edge
Ringwood, Hampshire, UK
The simple answer is no.
First of all, the atmosphere has a total mass of about 5.5 quadrillion tonnes. Even though most of this is nitrogen, this still means around a quadrillion tonnes of oxygen, so a few million tonnes of hydrogen fuel aren’t going to make much of a dent.
In any case, the oxygen in the atmosphere is constantly replenished by photosynthetic life forms. These convert CO2 and water into tissue, energy and oxygen. Burning hydrogen cleanly generates only water as the combustion product. (Burning fossil fuels and wood also generates a lot of water, along with CO2 and other nasties.) Some of this water and a very small proportion of the CO2 then becomes the feedstock for further photosynthesis.
A lot of research suggests that white hydrogen (hydrogen in the ground) will become as uneconomical for large-scale energy generation as petrochemical fossil fuels are becoming compared with renewables. So, it is likely that a hydrogen economy will pretty soon be using hydrogen split from water using renewable energy or, if it ever becomes feasible, from nuclear fusion. Hydrogen generated this way releases the same amount of oxygen as is consumed when burning it, so it will therefore be “oxygen-neutral”.
Correspondent Sam Edge amended/clarified some of the details in his answer.
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