Particulate pollution along shipping lanes leading out of Singapore correlates with increased lightning activity, according to University of Washington and NASA atmospheric scientists.

“And right along the ship track, that’s where the lightning was. Right smack on top of it,” said Professor Robert Holzworth, of the University of Washington’s Department of Earth and Space Sciences. “There was a clean spot right next to the tracks where you could say, ‘Hey! It’s the same weather, but over the trip tracks we have twice as much lightning.’”

Holzworth says the tracks stand out because the air off that part of Asia is relatively clear.

Holzworth, along with Joel Thornton of the UW’s Department of Atmospheric Sciences, Katrina Virts of the NASA Marshall Space Flight Center and formerly with the UW, and Todd Mitchell of the UW’s Joint Institute for the Study of the Atmosphere and Ocean, produced the scientific paper on how ship exhaust is increasing the intensity of thunderstorms.

Top: Red shows a larger presence of lightning in the atmosphere over 12 years. Bottom: Ship pollutants in the air over shipping lanes out of Singapore. Diagrams: UW/NASA study.

The tiny particulates, referred to as aerosols, are coated with water forming a mist, which makes up clouds. But unlike water droplets without particulates, the ones containing air pollution are actually smaller, lighter, and move up higher into the atmosphere and freeze. The ice particles become electrically charged, and that can lead to lightning.

“Ice likes to freeze on something,” said Holzworth. “Freezes a lot faster if there’s something like a piece of dust or an aerosol to freeze onto.”

Holzworth heads the World Wide Lightning Location Network, and the ship track correlation was found based on 12 years of data Virts examined using a higher resolution version of the lightning data.

The correlation between pollution and lightning over the shipping lanes is interesting, but it’s the bigger research that could come next that may have a much bigger impact.

“It could well help us understand and feed into the global warming questions about weather,” Holzworth said.