Thunderstorms containing extremely high concentrations of two critical oxidants were captured by a storm-chasing aircraft.
Lightning has the potential to help flush toxins from the atmosphere.
Researchers report online in Science that observations from a storm-chasing plane show that lightning can produce a large number of air-cleaning chemicals known as oxidants. Oxidants help to clean the environment by interacting with chemicals such as methane to form molecules that are more water soluble or stickier, causing them to rain out of the atmosphere or stick to the Earth’s surface more easily.
Researchers realized that lightning releases nitric oxide, which can cause oxidants like hydroxyl radicals to form. However, no one had ever seen lightning specifically produce a large number of these oxidants.
A NASA jet weighed two oxidants in storm clouds over Colorado, Oklahoma, and Texas in May and June 2012. The hydroxyl radical, abbreviated as OH, was one of them. The other was the hydroperoxyl radical (HO2), which was a similar oxidant. In some sections of these clouds, the combined concentration of OH and HO2 molecules produced by lightning and other electrified regions of air reached thousands of parts per trillion. Previously, the maximum concentration of OH in the atmosphere was just a few parts per trillion.
“We didn’t expect to see any of this,” says William Brune, an atmospheric scientist at Penn State University. “We shelved the data … because it was just so extreme.” But lab experiments later showed that electricity really could generate such large quantities of OH and HO2, helping confirm these oxidant signals were real.
Since there are an estimated 1,800 lightning storms raging around the world at any given time, Brune and colleagues calculated that lightning could account for 2 percent to 16 percent of atmospheric OH. More thunderclouds would be required to get a more accurate estimate. As climate change causes more lightning, understanding how lightning affects atmospheric chemistry will become increasingly relevant.