Scientists are shocked to discover how much lightning can clean the atmosphere.

Lightning may play a much bigger role than previously thought in a fundamental process that cleanses our atmosphere of pollutants, according to the results of a new study.

An electric discovery

A new research published in the journal Science suggests that electrical storms produce large amounts of molecules called oxidant radicals that break down gases such as carbon monoxide and methane in the atmosphere. These air pollutants can contribute to global warming and damage the ozone layer.

Carbon monoxide and methane make their way into the atmosphere from both natural and industrial sources. Methane is produced by the decay of plants, but is also released by oil and gas development and agriculture. Carbon monoxide and other hydrocarbon pollutants can be produced by industry and fires.

But natural processes in the atmosphere, driven largely by sunlight, produce molecules called radicals, the most important of which is hydroxyl. These molecules are chemically very active (which means they are much more likely to react with other molecules) and can react with pollutants to form new compounds that are harmless or that can more easily attach to water and be rained out from the air.

Reception

At first we didn’t believe the signals we were receiving. They were so big, a thousand times bigger than the biggest we’ve ever seen”. New research led by William Brune, a distinguished professor of meteorology at Penn State University, has found that lightning produces many more molecules than previously understood. His work suggests that more than 10 per cent of the atmosphere’s supply of these cleaning radicals could be produced by lightning storms. The work involved flying a NASA DC-8 research aircraft through deep convective thunderstorms to collect data. According to Brune, it wasn’t as dangerous as it sounds. “It was a lot of fun, actually. The pilots are just amazing. They know what they’re doing. They know how to keep the plane safe. But it’s really interesting because you get to see deep convection, which is very, very strong,” he said.

“We were doing this study in 2012, flying over the central United States and trying to look at what was going into the storms in terms of chemistry, what was coming off the top,” Brune said. “And to our surprise, we saw very, very, very large amounts of OH [hydroxyl molecules]. At first we couldn’t believe the signals we were getting. They were so big, a thousand times bigger than the biggest we’ve ever seen.” The data collected by the aircraft was compared to data collected by radio receivers on the ground that monitor flashes in the clouds. The two sets of data confirmed the production of high levels of hydroxyl radicals by the lightning.

“Lo and behold, the two data sets overlapped in terms of where the lightning was occurring,” Brune said. Hydroxyl radicals are produced when lightning energy breaks up water vapour in the atmosphere. “You can think of water with a hydrogen atom removed and then it wants that hydrogen back,” Brune said. “So it becomes very reactive as it goes and tries to get that hydrogen back.” This means that the hydroxyl radical is very prone to reacting with methane or carbon monoxide molecules. Brune admits that it is difficult to assess the effectiveness of this process on a global scale. The results of this study are based on a limited number of flights over a small section of the United States. There is still much more information that needs to be gathered to create a global picture. But Brune believes that hydroxyl generated by lightning has a substantial impact worldwide.

Previous researches

Previous models suggested that lightning was not a significant contributor to the cleanup process. “Our best estimate now is anywhere from two per cent, which is quite important, to more than 10 per cent, which is quite important to the total amount of atmospheric cleaning,” he said. These estimates could change as the planet warms. Some climate change models suggest an increase in thunderstorm activity, which would mean the production of more hydroxyls and thus more atmospheric cleanup in the future. Other climate models suggest that there may not be as many lightning strikes, but that they will be more intense, which would also alter the numbers.

An update is required

In any case, future models of global pollution and climate change will need to take this new understanding of atmospheric cleanliness into account. Existing models may need updating, for this as well for other climate change-related topics.

“If the OH generated by lightning is 10 per cent effective, the models that estimate the other part are 10 per cent too high,” Brune said. “And so that’s going to cause people to think very hard about how do you put something that’s created by a flash into a model? A very difficult problem.”

 

 

Read the full articles here:

  1. Economy, November 2021, Scienziati scioccati, i fulmini possono pulire l’atmosfera (https://www.economymagazine.it/economy/2021/11/01/news/scienziati-scioccati-i-fulmini-possono-pulire-l-atmosfera-96562/);
  2. W. H. Brune, P. J. McFarland, E. Bruning, S. Waughd, D. MacGorman, D.O. Miller, J. M. Jenkins, X. Ren, J. Mao, J. Peischl, in Science, May 2021, Extreme oxidant amounts produced by lightning in storm clouds (https://www.science.org/doi/10.1126/science.abg0492)
  3. William Brune for Penn State University, April 2021 Lightning and subvisible discharges produce molecules that clean the atmosphere (https://www.psu.edu/news/research/story/lightning-and-subvisible-discharges-produce-molecules-clean-atmosphere/)