Lightning May Wash Pollution Out of the Air With a Chemical Dubbed ‘Detergent of the Atmosphere’

The oxidizing chemicals hydroxyl and hydroperoxyl may clean the skies of harmful pollutants by reacting with them

A photo of lightning striking the ground against a moody purple sky
As the NASA aircraft DC-8 flew into the storm and collected data after each lightning flash, the researchers found that the concentrations of hydroxyl and hydroperoxyl produced by visible lightning and other regions that were electrically charged soared up to thousands of parts per trillion. Mathias Krumbholz via Wikicommons under CC BY-SA 3.0

To understand how lightning rids the atmosphere of pollutants, researchers flew a NASA jetplane into the eye of the storm, reports Maria Temming for Science News.

The study, published last week in the journal Science, marks the first time scientists have demonstrated lightning bolts and less visible electric charges produce large amounts of chemical oxidizing elements, hydroxyl (OH) and hydroperoxyl (HO2).

Oxidants are great at breaking down greenhouse gases. The highly reactive hydroxyl, dubbed the "detergent of the atmosphere," is know for its ability to almost oxidize every chemical found in the troposphere. When hydroxyl reacts with methane, for example, it easily dissolves in water and falls back to Earth as rain, ultimately clearing the atmosphere of chemicals that exacerbate global warming, reports Science News.

In 2012, researchers flew through electrified anvil storm clouds at 200 meters per second over Colorado, Oklahoma and Texas to see how lightning could clean the atmosphere, reports Tara Yarlagadda for Inverse. After each lightning flash, the researchers found the concentrations of hydroxyl and hydroperoxyl increased by thousands of parts per trillion, Science News reports. The researchers concluded that anvil clouds may also produce 2 to 16 percent of all hydroxide found on Earth, reports Inverse.

"We are surprised by the extreme amounts of OH and HO2 generated in thunderstorm anvils and cores. They are orders of magnitude larger than any previous atmospheric HO2 or OH measurement," study author William H. Brune, a meteorologist at Pennsylvania State University, tells Inverse.

Their data was shelved for years before it was examined again because the researchers did not think the high number of oxidants was caused by lightning—at first. Instead, the team thought the readings indicated an issue with their study instruments. Because they were able to take measurements from the sky and ground simultaneously, the researchers found they had demonstrated lightning's role in atmospheric oxidation when they compared the two datasets.

"With the help of a great undergraduate intern, we were able to link the huge signals seen by our instrument flying through the thunderstorm clouds to the lightning measurements made from the ground," Brune says in a statement.

Overall, the researchers suspect that hydroxyl and hydroperoxyl could be contributing to global oxidation, Inverse reports. However, the researchers are planning another similar experiment to measure oxidation again using more sophisticated equipment. Because their study focused on only a specific region in the atmosphere, they're also hoping to use an aircraft that can measure clouds at various altitudes in future work, Inverse reports. The researchers' efforts could help scientists further understand how thunderstorms may change air pollution and how this phenomenon plays into changing climate.

"These results are highly uncertain, partly because we do not know how these measurements apply to the rest of the globe," said Brune in a statement. "We only flew over Colorado and Oklahoma. Most thunderstorms are in the tropics. The whole structure of high plains storms is different than those in the tropics. Clearly, we need more aircraft measurements to reduce this uncertainty."

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