Lightning and sub-visible discharges produce molecules that cleanse the atmosphere – sciencedaily

Lightning bolts break down nitrogen and oxygen molecules in the atmosphere and create reactive chemicals that affect greenhouse gases. Now, a team of atmospheric chemists and lightning scientists have discovered that lightning and, surprisingly, sub-visible discharges that cannot be seen by cameras or with the naked eye produce extreme amounts of the hydroxyl radical – OH – and the hydroperoxyl radical – HO2.

The hydroxyl radical is important in the atmosphere because it initiates chemical reactions and breaks down molecules like methane, a greenhouse gas. OH is the primary driver of many compositional changes in the atmosphere.

“Initially we looked at these huge OH and HO2 signals found in the clouds and asked, what is wrong with our instrument? said William H. Brune, distinguished professor of meteorology at Penn State. We assumed there was noise in the instrument, so we removed the huge signals from the dataset and put them away for further study. “

The data came from an instrument on a plane flying over Colorado and Oklahoma in 2012 and examining the chemical changes thunderstorms and lightning make to the atmosphere.

But a few years ago, Brune took the data off the shelf, saw that the signals were really hydroxyl and hydroperoxyl, and then worked with a graduate student and a research associate to see if those signals could be produced by sparks and discharges visible in the laboratory. . Then they reanalyzed the Thunderstrom and Lightning dataset.

“With the help of an excellent undergraduate intern,” said Brune, “we were able to relate the huge signals seen by our instrument flying through the storm clouds to the lightning measurements taken from the ground. .

The researchers report their findings online today (April 29) at Science First version and the Journal of Geophysical Research – Atmospheres.

Brune notes that planes avoid flying through the cores of rapidly rising thunderstorms because it is dangerous, but can sample the anvil, the upper part of the cloud that propagates outward in the direction of the wind. Visible lightning occurs in the part of the anvil near the thunderstorm core.

“Throughout history, people were only interested in lightning because of what they could do on the pitch,” said Brune. “Now there is growing interest in weaker electric shocks in thunderstorms that lead to lightning.”

Most lightning never hits the ground, and lightning that remains in clouds is particularly important in affecting ozone, and important greenhouse gases, in the upper atmosphere. It was known that lightning can split water to form hydroxyl and hydroperoxyl, but this process had never been observed before in thunderstorms.

What initially confused Brune’s team was that their instrument recorded high levels of hydroxyl and hydroperoxyl in areas of the cloud where there was no visible lightning from the aircraft or ground. Laboratory experiments have shown that a weak electric current, much less energetic than that of visible lightning, can produce these same components.

While the researchers found hydroxyl and hydroperoxyl in areas with sub-visible lightning, they found little evidence of ozone and no evidence of nitric oxide, which requires the formation of a lightning bolt. visible. If subvisible lightning occurs regularly, then the hydroxyl and hydroperoxyl created by these electrical events must be included in the atmospheric models. Currently, they are not.

According to the researchers, “OH (hydroxyl) generated by lightning in all storms occurring in the world may be responsible for a very uncertain but substantial global atmospheric oxidation of OH from 2% to 16%” .

“These results are very uncertain, in part because we don’t know how these measures apply to the rest of the globe,” Brune said. “We only flew over Colorado and Oklahoma. Most thunderstorms occur in the tropics. The whole structure of storms in the high plains is different from those in the tropics. Clearly we need more measurements. airways to reduce this uncertainty. “

The National Science Foundation, NASA, and the National Oceanic and Atmospheric Administration supported this work.

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Material provided by Penn State. Original written by A’ndrea Elyse Messer. Note: Content can be changed for style and length.

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