NASA experiment reveals a powerful natural force cleans the atmosphere

Over two summer days in June 2012, a NASA aircraft called DC-8 daringly flew at a speed of 200 meters per second through deep clouds and threw itself into the eye of a tumultuous thunderstorm.

DC-8 undertook this harrowing journey for one primary purpose: to understand lightning’s ability to clean Earth’s atmosphere. The specific kinds of measurements performed here “are the first-ever in thunderstorms,” William H. Brune tells Inverse. Brune is one of the authors of a new study detailing DC-8’s findings and a professor of meteorology at Pennsylvania State University.

What the craft found on this intrepid journey could change the course of atmospheric science as we know it. But more immediately, these measurements hold some pretty strange implications for how we can best face the climate crisis.

What’s new — This daring atmospheric experiment is detailed in a new study published Thursday in the journal Science. In the study, the scientists explain how DC-8 measured certain oxidizing elements in the storm clouds after visible lightning flashes and following less-visible electric discharges from within the thunderstorm.

The storm in question took the form of electrified anvil clouds hanging over northeastern Colorado. These flat-topped clouds, named for their resemblance to a blacksmith’s anvil, often indicate the presence of volatile, high-energy storm systems — including thunderstorms.

The findings reach new heights in atmospheric science by measuring lightning’s ability to generate the oxidizing elements hydroxide (OH) and the hydroperoxyl radical HO₂. The scientists refer to this direct oxidizing process using the formula LHO_x. These oxidants play a role in cleansing greenhouse gases from our atmosphere.

Brune and his colleagues’ new research underscores for the first time the sheer amount of hydroxide produced by this little-studied oxidizing process.

“If LHO_x is an important source of global OH, then it stands to reason that OH produced by the well-known method — a combination of ozone, water vapor, and UV solar radiation — must be less than is currently assumed,” Brune says. Jena Jenkins, a Ph.D. student at Penn State University and a co-author on the study, contributed to Brune’s responses to Inverse.

Ultimately, the oxidization occurring within electrified anvil clouds may produce up to 12 percent of all hydroxide found globally, a finding which shocked the researchers.

“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,” Brune says.

Why is lightning helpful for Earth?

The two oxidants that are the central focus of this study, OH and HO_2, have an important role in cleansing pollutants — including greenhouse gases — from Earth’s atmosphere.

Previous scientific research has mostly focused on lightning’s indirect impact on the atmosphere through the production of nitric oxide (NO), which, in turn, generates OH as well as the greenhouse gas ozone — a major contributor to smog.

This indirect process, known as LNO_x, is essential to the atmosphere’s ability to clean itself.

“LNO_x has been well studied in atmospheric measurements and laboratory studies for more than 40 years,” Brune says.

But much less is known about LHO_x — the subject of this study.

“There have been only a few modeling and laboratory studies for OH and HO₂ generated by electrical discharges,” Brune says, which the study refers to as LHO_x.

Behind the scenes — The NASA aircraft, DC-8, conducted 32 flights over Oklahoma and Colorado between May and June of 2012.

However, the researchers honed in on one specific experiment, which occurred over the course of June 22-23, 2012 in the skies above Colorado.

According to the study, the aircraft flew in and “spiraled up” outside the growing storm cell in the cloud, which was electrified by lightning. Using special instruments, DC-8 measured the amount of LHO_x after each lightning flash, as well as after less-visible electric discharges.

Meanwhile, dozens of researchers on the ground simultaneously measured the LHO_x using equipment known as a lightning mapping array, which involves the detection of high-frequency radio waves. Brune was among the ground crew, taking measurements every 0.2 seconds — or every 40 meters of distance that the aircraft traversed above.

“I was one of [approximately] 40 scientists, most operating instruments to measure different chemical species or environmental parameters, onboard the DC-8 when the pilots flew it through these thunderstorm anvils,” Brune recalls.

It’s this groundbreaking combination of in-air flight and on-ground measurements that made the experiment work, according to Brune.

“We are going to need more of this type of interdisciplinary research to better understand LHO_x and its potential importance to atmospheric oxidation processes,” Brune says.

Why it matters — The study has major implications for the climate crisis, according to the researchers.

“Climate is sensitive to amounts of greenhouse gases,” Brune explains. Greenhouse gases include ozone, which occurs at high altitudes — precisely where thunderstorms occur, too. Greenhouse gas emissions are one of the major driving forces behind global warming. Furthermore, the global OH — one of the oxidizing elements measured in this study — is integral to a process known as atmospheric oxidation.

Atmospheric oxidation is “the process by which the atmosphere cleans itself, often creating ozone and particle pollution in the process,” Brune says.

“So understanding global OH and its sensitivity to climate change is a big deal.”

One key takeaway from the study is that warmer climates will likely yield more intense storms — and more lightning — possibly increasing the contribution of OH to global oxidation processes.

But is there a direct link between this lightning-driven process and global warming? We don’t have enough data to prove there is such a link yet, according to the scientists.

“Any thoughts of LHO_x increasing as climate changes are just speculation,” Brune says.

Ultimately, the researchers conclude that “LHO_x could be contributing to regional and global oxidation well beyond the storm cloud anvils.”

What’s next — There’s still a lot of uncertainty hanging in the air — literally.

In the study, the scientists acknowledge that their estimates of lightning’s contribution to global oxidation — specifically through LHO_x — may be “uncertain by perhaps a factor of ten.”

To reduce these uncertainties, the scientists will need to take their experiments into the skies once more, with more sophisticated measuring equipment and using an aircraft that will measure clouds at a variety of altitudes.

Brune also suggests that scientists “determine the impact of LHO_x on global OH and possible changes with climate” by including “LHO_x generation in global chemical transport and climate models.”

Factoring this lightning-driven process into climate models could help scientists better predict how future thunderstorms may alter global air pollution and better understand our changing climate.

Abstract: Lightning increases the atmosphere’s ability to cleanse itself by producing nitric oxide (NO), leading to atmospheric chemistry that forms ozone (O3) and the atmosphere’s primary oxidant, the hydroxyl radical (OH). Our analysis of a 2012 airborne study of deep convection and chemistry demonstrates that lightning also directly generates the oxidants OH and the hydroperoxyl radical (HO2). Extreme amounts of OH and HO2 were discovered and linked to visible flashes occurring in front of the aircraft and to subvisible discharges in electrified anvil regions. This enhanced OH and HO2 is orders of magnitude more than any previous atmospheric observation. Lightning-generated OH in all storms happening at the same time globally can be responsible for a highly uncertain but substantial 2-16% of global atmospheric OH oxidation.