There is nothing more compelling to many than watching a lightning storm in the summer as bolts streak across the night sky. Parents and children lie on beds and look out the windows, counting the seconds between flashes and thunder to see how far away each strike was.
An intense summer thunderstorm can also be a cathartic event. Once the show is over, and the rain stops, the air feels refreshed. Has there been a change in the air from the lightning? Yes, and Mother Nature uses the power of a thunderstorm to clean the air and the upper atmosphere.
The Research
NASA isn’t only in the business of space travel. It also looks closely at our atmosphere and how it is evolving. Its DC-8 Earth Science Laboratory airplane frequently flies over the US central plains to intercept thunderstorms and analyze the molecular make-up of air going into and out of them. The goal is to understand the influence lightning strikes and powerful convection currents have on the atmosphere’s chemical composition. Why? So scientists and ecologists can learn even more about urban air pollution and greenhouse gas production.
An Encouraging Discovery
One of the most important discoveries found after analyzing collected data is the quantity of large, concentrated spikes surrounding thunderstorms of a compound called the hydroxyl (OH) radical. Hydroxyl is the Earth’s primary oxidant and key to the air’s ability to cleanse itself. The researchers’ latest work on these spikes suggests that lightning has a greater effect on the atmosphere than previously thought.
A tree or water tower struck by lightning is not the only thing damaged by the intense heat and energy each bolt emits. Every molecule in a bolt’s vicinity is torn apart by the force into its component atoms. Most of these molecules will be molecular oxygen (O2) and dinitrogen (N2) – the two primary components of air. As these atoms cool and recombine, they often do so with new partners, forming new molecules, like hydroxyl.
A Deeper (though still pretty shallow) Dive into the Chemistry
According to William Brune, an atmospheric chemist at Penn State University who was one of the scientific leads of a study by the DC-8 Earth Science Laboratory’s crew, with each lightning strike, “there is very unique chemistry going on there. The main gas people know about and measure is nitric oxide, NO.”
After a strike, NO undergoes a series of reactions with oxygen and nitrogen atoms and other molecules. Two of the main molecules that result are nitrogen dioxide and ozone. The Earth experiences more than three million lightning strikes daily, so their impact on the upper atmosphere and ozone levels is greater than previously thought.
According to Mary Barth with the US National Center for Atmospheric Research, ozone is a pollutant at the ground level and can cause health problems. In the upper atmosphere, however, when produced by thunderstorms, it is a greenhouse gas. Ozone, like some other major greenhouse gases, such as water vapor, carbon dioxide, and methane, allows much of the solar energy from the sun to pass through the atmosphere and warm the surface. They also absorb the outgoing energy and redirect it to Earth’s surface, further warming up the atmosphere.
Mother Nature’s Response
Mother Nature balances the spike in Nitric Oxide (NO) concentration caused by lightning(which initiates a cascade of reactions that can up the air’s supply of ozone) by boosting the creation of the atmosphere’s primary cleansing oxidant, the hydroxyl radical, at the same time.
The hydroxyl (OH) radical is made up of one hydrogen atom and one oxygen atom with a free (unpaired) electron. It is one of the most reactive gases in the atmosphere and acts as a detergent to break down other gases and remove toxic gasses like carbon monoxide, and volatile organic compounds (VOCs). It is also the main check on the concentration of methane in the atmosphere, the second most potent greenhouse gas to carbon dioxide. In other words, the hydroxyl radial plays a key role in the oxidation of the atmosphere, air quality, and climate.
Lightning isn’t the only way OH is formed. Ultraviolet sunlight reacts with water vapor and ozone in the lower atmosphere to produce it. This occurs particularly over the tropics. Scientific evidence shows tropical regions expanding, so this natural factory for OH could grow as well.
Humankind may be contributing to global warming and poorer air quality, but Mother Nature has put in place countermeasures to help.
Sources: Maria Mith/Medium, Climate and atmospheric science/NPJ, nature.com, Earth Observatory/NASA, weather.gov