The Unexpected Chemistry of Lightning — Waterbury Roundabout

Aug. 25, 2022  |  By Kenrick Vezina

To say that lightning “divides” the sky is not pure poetry. A single shot contains about a billion joules of energy, or about 280 kilowatt hours of electricity, and could power a modern American household for more than nine days. Moreover, it is enough to explode the very molecules that make up the atmosphere and temporarily blur its composition.

Oxygen is one of these molecules. Oxygen in the atmosphere is diatomic, meaning it normally exists as pairs of oxygen atoms with a strong double bond. But lightning rips these paired atoms apart, and in the ensuing chaos, some give up monogamy. The result is ozone, made up of three oxygen atoms.

Ozone in the stratosphere protects the planet from the carcinogenic effects of excess ultraviolet solar radiation. It’s also the cause of the “electric sting” in the air after a particularly active thunderstorm, or – less dramatically – when using a copier.

Most of the air around us is made up of another diatomic molecule: nitrogen. Nitrogen makes up about 78% of the atmosphere, oxygen about 21%, and the rest is a bag of gases, including carbon dioxide. Nitrogen is also one of the most abundant elements in your body. It is used to build the paired bases – the “letters” – of DNA. It is necessary to build amino acids, which build proteins, which build… well, ultimately, all life on Earth.

Yet despite its apparent abundance, entire ecosystems can be strangled by low nitrogen availability. That’s because free-floating nitrogen molecules have a powerful triple bond — even stronger than the double bond of oxygen pairs — that makes them so completely codependent that it renders them chemically inert. Atmospheric nitrogen is useless to plants and animals without outside intervention.

And this is perhaps the only context in which a bacteria in the roots of an alfalfa plant, a fertilizer manufacturing plant, and the elemental wrath of Zeus have something in common: they can all “fix” the ‘nitrogen. Nitrogen fixation is the process by which atmospheric nitrogen separates and recombines with other elements to form compounds that plants and other life forms can use.

Among living things, only a limited selection of bacteria and other microorganisms have the biochemical tools necessary to perform nitrogen fixation. Of these, some live freely in the soil, while others have formed close relationships with plants. A prime example is the rhizobium bacteria found in nodules on the roots of legumes – peas, the aforementioned alfalfa, and wild species such as American peanuts. In northern boreal forests, cyanobacteria that colonize mosses are an important source of nitrogen for the ecosystem.

Not surprisingly, much of today’s nitrogen fixation also occurs in industrial fertilizer plants. They combine nitrogen and methane under high heat and pressure to form ammonia and other compounds. The wide availability of nitrogen-based fertilizers has been a boon to farmers. But, in a classic case of too much of a good thing, nitrogen-rich runoff from farms can also cause entire lakes to be strangled by algal blooms.

Of course, the heat used in industrial nitrogen processing is mild compared to the 50,000 degree Fahrenheit fury of a lightning strike. Even the strong triple bond of nitrogen is not enough to withstand such an infusion of energy. In the momentary chemical melee that follows a lightning strike, some newly unique nitrogen atoms join with eligible oxygen atoms to form nitrogen oxides. These are washed away by rain, soak into the soil and can be taken up by thirsty plants. The short-term role of lightning in the nitrogen cycle appears to be minor, representing little more than an occasional ecological problem. advantage, especially in our region relatively poor in thunderstorms. On a deeper time scale, however, the role of lightning was probably fundamental.

Lightning helped shape the chemistry of early Earth and may well have provided the spark (literally) needed to make essential elements like nitrogen and phosphorus available to early organisms, before the evolution of fixing bacteria. nitrogen.

So when we experience the primal thrill that only a late summer thunderstorm can bring, it bodes more than just a break from the heat: it’s the presence of remarkable chemistry – potentially capable of changing the planet.

Kenrick Vezina is a freelance writer, naturalist, and storyteller based in the Greater Boston area. The Outside Story is attributed to and edited by Northern Woodlands magazine and sponsored by the Wellborn Ecology Fund of the New Hampshire Charitable Foundation.

Robert M. Larson