Lightning: the spectacular beauty of chemistry

Lightning changes the chemistry of the atmosphere

Many of nature's phenomena have simple explanations. Many of us know, as it is more or less common knowledge, that an event as powerful as a thunderstorm is the result of the friction between air masses at cloud level. But it is worth going into detail: thunderstorms usually result from the collision of ice crystals and hail, which causes electrical discharges. The flash is an electrical flow, while the sound wave is caused by the violent heating of the air, producing temperatures five times hotter than the surface of the sun. The rapid rise in temperature causes an abrupt expansion of the air which, as a result, produces sound waves known as thunder. This beautiful dance of lightning and its thunder can leave you either mesmerised or frightened.

Now, let's get into the chemistry of thunderstorms...

It has been known for some time that lightning causes changes in the atmosphere, such as a decrease in the concentration of ozone, the gas that acts as a natural shield to the sun's ultraviolet radiation. However, in 2021, scientists at the University of Pennsylvania also discovered that lightning can in fact help eliminate air pollution. This is because it produces substances such as hydroxyl radicals (OH), which break down methane, one of the gases responsible for accelerating the greenhouse effect. According to experiments, between 2 and 16% of the cleaning capacity that occurs naturally around the planet is generated by lightning.

Other ongoing research suggests that the electrical activity of lightning can also accelerate the formation of raindrops and increase precipitation, and that it has the ability to form amino acids that may have been essential for the beginning of life on Earth.
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The effects of lightning also come down to earth

Lightning can also have a beneficial effect on soil quality. When it comes into direct contact with the ground at a speed of up to 400.000 kilometres per hour, the electric current – which reaches over 200.000 amperes – heats up the materials, producing strange glass shapes called fulgurites.

If the lightning hits sand, it produces fulgurites made up of silica, a chemical compound, shaped like a tube. They are only a few centimetres in diameter (lightning bolts are two to three centimetres wide), but quite long: the largest ever found was 8 metres long. When they land on rock, the lightning creates fulgurites on the surface, which resemble a thin shell.

When it reaches the ground, lightning can also cause fires, which is estimated to happen 100.000 times a year worldwide. However, there is a positive side to this too: when there is no material or human damage, and important ecosystems are not destroyed, these fires are beneficial in that they can contribute to the recycling of nutrients in the soil, through the NOx formed in the atmosphere and carried to the ground by the rain, which favours various species of fauna and flora.

The Grupo de Eletricidade Atmosférica (Atmospheric Electricity Group), a Brazilian organisation that is a world benchmark in atmospheric electricity research, reports that the amount of nitrogen compounds deposited in the soil by lightning varies between 1% and 20% of the total, which is significant in terms of fertility.

Between myth and reality

Without a plausible explanation, lightning was generally interpreted by ancient civilisations as divine manifestations. The Greeks considered them to be spears made by the Cyclops so that Zeus could punish humanity for its shortcomings. Roman generals wore laurel on their heads as an amulet against lightning. And in medieval Europe, the ringing of church bells was believed to protect against lightning. Of course, a tall tower with a metal bell was actually a very bad place to be during storms... In France, after 103 bellringers died over three decades from lightning strikes, the tradition was banned in 1786.

The big "magnets" for lightning are the height of the object, its pointed shape and its isolated location. As is the case with a tree. Therefore, one myth to avoid is seeking shelter under trees in the event of a thunderstorm. Being outside is generally a bad choice, as the ground itself conducts the lightning current. The best way to enjoy this natural phenomenon safely is to stay indoors or in a car with a sunroof, avoiding water and appliances connected to electricity.

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