Lightning is as beautiful as it is deadly. It also passes gas. Well, sort of. The lightning bolts that streak across the sky during thunderstorms emit a gas found in car exhaust -- nitrogen oxide (NO). This gas can adversely affect air quality and trigger respiratory illnesses in humans, but how lightning-generated nitrogen oxide affects the atmosphere is less clear.
For the first time, a team of scientists used high-frequency satellite observations to create an experiment that can detect lightning and its impact on the air. The team found that thunderstorms simultaneously produce both pollutants and critical chemicals that help cleanse the Earth's atmosphere.
Lightning strikes generate extremely hot temperatures that break apart nitrogen and oxygen molecules in the air. This molecular disruption creates nitrogen oxide, nitrogen dioxide (NO₂), and other types of nitrogen oxide gas. These are some of the same air pollutants that cars, power plants, and other fossil fuel combustion generates. In turn, nitrogen oxides create ozone pollution.
"Lightning globally makes up 10 to 15 percent of total nitrogen oxides released into the atmosphere," University of Maryland atmospheric scientist Kenneth Pickering said in a statement.
While there is significantly more human-generated pollution in the atmosphere, lightning releases nitrogen oxides at much higher altitudes. At these heights, lightning can create ozone, a pungent, pale blue gas. More ozone can lead to more air pollution in the upper atmosphere, the same way that car exhaust generates ozone pollutants near the ground.
Sometimes, the ozone lightning creates can be transported down to Earth's surface, affecting the air quality hundreds of miles away from the original storm. This effect is generally exacerbated during the summer, when temperatures climb higher and more ozone is produced.
"Lightning's effects on climate during the summer season are comparable to anthropogenically [human] created nitrogen oxides, which is why we wanted to study storms during June," explained atmospheric research scientist Dale Allen.
However, lighting doesn't just create this high-level atmospheric pollution. It also triggers the formation of hydroxyl radicals. These important molecules help cleanse the Earth's atmosphere by breaking down greenhouse gases like methane and background levels of ozone pollution that didn't originate from a more local, human-produced source.
So, how does this mix of air cleaning hydroxyl radicals and air polluting ozone unfold in the atmosphere?
To find out, Allen and Pickering used data captured by NASA's Tropospheric Emissions: Monitoring of POllution (TEMPO) instrument. TEMPO was launched in 2023 and tracks air pollutants from 22,000 miles above the Earth.
In late June, the team carefully monitored thunderstorms as they moved across the eastern United States using TEMPO. Typically, the satellite tracks air pollutants every hour. Instead, Pickering and Allen's experiment took measurements of the nitrogen dioxide associated with each storm at 10-minute intervals.
By measuring nitrogen dioxide every 10 minutes, they observed the complicated atmospheric processes happening live inside of each thunderstorm.
"This is the first time this kind of research has been conducted at such a temporal frequency," Pickering said. "Thunderstorms evolve on a rapid basis. They often build up, intensify, and die within an hour's time. These short interval observations give us better snapshots of what actually happens during a storm."
With this experiment and data from NOAA's Geostationary Lightning Mapper satellite instruments, the team counted lightning flashes as they happened. According to Allen, this provides "a more accurate idea of how much nitrogen dioxide each flash of lightning produces during a storm and how long it sticks around afterward."
Additionally, the experiment offers insight into the chain reaction that connects the polluting nitrogen oxides to the air-cleaning hydroxyl radicals.
"We believe that when storms get more intense, lightning flashes get shorter and produce less nitrogen oxide per flash," said Allen. "This study will give us a chance to prove that. Understanding how the footprint of lightning will change in a world of intensifying weather extremes is essential to formulate climate models for the future."
The preliminary data from this experiment has not been peer reviewed, but added analysis could help improve climate models that impact daily life here on Earth. The gases produced by lightning can travel on long "conveyor belts of moving air" and possibly influence the air quality far from where storms originally occurred, Allen noted. Lightning also occasionally contributes to ground-level ozone, which is a primary component of smog that can trigger asthma and other respiratory diseases.
"For people living in mountainous areas like Colorado, this information can be very important as lightning does make a significant contribution to surface ozone at higher terrain altitudes," Pickering said. "It could make a difference in how meteorologists predict air quality during and after storms in such regions."
The experiment also provides a look into the atmosphere's ability to naturally break down pollutants, including methane and other harmful hydrocarbons responsible for global warming.
"With better data comes better predictions, and potentially better ways to protect our health and environment from both natural and human-made pollution," Allen said.