Searching for ozone in a storm

Lightning, monsoon rains don't necessarily mean clean air

Sue Vorenberg |

8/22/2008 - 8/23/08

The air might seem deceptively fresh after one of New Mexico’s lightning-laden summer monsoons, but don’t be fooled.

That sweet, earthy smell of desert rain could also be accompanied by a natural source of ozone, created through an as-yet mysterious process inside thunderclouds, said Ken Minschwaner, an atmospheric physics researcher and associate professor at New Mexico Tech.

"Ozone, when it's up in the stratosphere is a good thing, because it filters out harmful ultraviolet light and prevents it from getting to the Earth's surface," Minschwaner said. "But when ozone is close to the surface it's not such a good thing. It's very toxic and very reactive. It can have long-term effects on health and even lead to death sometimes."

Minschwaner and other researchers at Tech's Langmuir Laboratory, which studies lightning and thunderstorms, have been collecting data all summer in an attempt to understand evidence linking lightning storms to natural ozone production.

The group first noticed something odd going on with lightning and ozone while participating in a summer 2006 international study.

In that study, researchers were trying to determine and map how much human-caused ozone pollution, which comes from burning fossil fuels and other sources, was hanging in the air across the Americas.

During one of the weather balloon launches for that study, the instruments were sucked into a strong thunderstorm, he said.

"And what we saw there were extremely high amounts of ozone," Minschwaner said.

Ozone is created when a low-level electric current splits O2, the oxygen in the air we breathe, apart. That split oxygen then rebinds with other O2 to form O3, also known as ozone, he explained.

Instruments on the ground during that balloon launch showed there was a lot of electrical activity in the thunderstorm, indicating that the lightning, or the charge in the clouds, had probably created the ozone, he said.

But, while people on the ground have also long-noted the smell of ozone in storms, until that eureka moment, there wasn't any hard scientific evidence that the phenomenon was actually occurring.

Still, one incident is not enough to build up any sort of scientific proof. So this summer, Minschwaner and other Tech students and researchers have been re-examining the phenomenon to figure out what's happening, he said.

"All summer we've been making a conscious effort to launch into these sorts of thunderstorms," Minschwaner said. "And we have some early results back. Some results show elevated ozone in these storms, but others don't. So we know it doesn't happen every time, but we don't know why."

It's possible the balloons didn't reach the right part of the cloud, or that something was different about the electrical makeup of some of the clouds that didn't show elevated ozone levels, he said.

"In one incident the balloon and the instruments were actually struck by lightning," Minschwaner said. "You can't get closer to a storm than that."

In that case, there was a high level of ozone, he added, noting in the usual evasive scientific way that after gathering data all summer the evidence is "very strong" that lightning clouds are creating ozone.

And that could well play into an entirely unrelated study by Emory University and the University of Georgia indicating that lightning storms elevate symptoms of asthma, said Stefanie Ebelt Sarnat, an assistant research professor in the Rollins School of Public Health at Emory University.

"Our study looked at the occurrence of thunderstorms and asthma exacerbation, and we found that on days following thunderstorms, there was a 3 percent increase in asthma-related emergency room visits," Ebelt Sarnat said. "That's significant. It's not that many people on a given day, but with a large population, and considering these are only the most severe cases, that's a significant health impact."

In that research, scientists noted that storm winds blow pollen and other particles into the air prior to rainfall, which is a source of asthma irritation, she said.

"Most people think that storms wash the air and decrease pollutants, but rain and wind can actually increase particles," Ebelt Sarnat said. "For instance, when pollen comes in contact with rain drops, that can burst the pollen into smaller fragments that are more easily inhalable and also cause greater irritation."

On hearing about the work at Tech, though, Ebelt Sarnat said ozone could also be playing a strong role in that asthma and thunderstorm connection.

"Ozone is definitely an asthma irritant," Ebelt Sarnat said. "And we haven't looked much at that atmospheric relationship. I'm certainly curious about that, especially if ozone is building up locally on the ground."

The possibility also intrigued Minschwaner, who said that was an excellent reason to further study the phenomenon.

Another reason for the ongoing study of the pheonomenon is so that lawmakers can get a more realistic understanding of how much ozone is created from human pollution, versus how much is just occurring naturally, he said.

"Understanding the relative strengths of these mechanisms is important for policy decisions," Minschwaner said. "You don't want to impact the economy with extra measures if the ozone is coming from a natural source."

He added, however, that natural ozone likely only makes up a small fraction of overall ozone pollution amounts.

"This is a small piece of a larger problem," Minschwaner said.

It will probably take at least six months to crunch the data after the Tech team finishes collecting its data through August. After that, though, Minschwaner said he hopes to have a much greater understanding of what's going on, and perhaps he will be able to find a way to quantify how much ozone could be produced by any particular storm, he said.

"The question still is what's making the ozone," Minschwaner said. "It's not made by hot-channel lightning, but by lower-level electric charges, like the blue glow of electricity when you turn out the lights. So in the cloud we want to know what's happening. Is it the types of lightning branches? Is it some sheath surrounding the lightning? I should have a lot more to say in six months."

Contact Sue Vorenberg at svorenberg@sfnewmexican.com.