September 2024
by Charlie Paullin, Virginia Mercury
James Madison University professor Mace Bentley had a friend living on the Eastside of Atlanta who noticed his VCRs and TVs going on the fritz after several lightning strikes during thunderstorms that would move west across the sprawling Southeast city. It was a comparatively minor issue.
A fire chief of a nearby station told Bentley and a colleague that he “hardly” had “enough trucks to send out for these fires that are occurring from lightning strikes.” That, and other anecdotal evidence, spurred Bentley to dig into the data.
When they surveyed data sets, Bentley said, “We found … there’s more lightning that’s occurring downwind from the city. It looked like the city was actually enhancing lightning and producing this.”
Bentley has continued that research, now with a focus closer to Virginia. In July, he published findings that show from 2006 to 2020, between the months of May and September as pollution levels increased from cities, including the Washington D.C. metro area, lightning strikes also increased. The research offers a look at the potential, present day impact of climate change in the region.
“Most of the research on climate change, most of the press, is global climate change. We didn’t want to think about climate change from the standpoint of what is going to happen 20 years from now,” Bentley said. “We want to see: Are humans impacting the climate right now and where and how much?”
The research included reviewing lightning strike data gathered from the National Lightning Detection Network. The locations of those strikes were traced back to where storm events were observed to have traveled.
Bentley then looked up hourly air quality monitoring data from the U.S. Environmental Protection Agency to find levels of particulate matter 2.5 and particulate matter 10, tiny carcinogens that are 2.5 and 10 microns in diameter, respectively, which come from tailpipe emissions, industrial and manufacturing activity and several other sources.
The research then determined when there were high levels of Convective Available Potential Energy, or CAPE, a metric used to measure the atmospheric conditions that are ripe for lightning activity. As the CAPE increases with hot humid air at the ground level and cooler air above, when pollution enters the mix during those “dog days of summer,” Bentley said, it leads to more lightning flashes.
Bentley and his team found that pollution is “affecting thunderstorm development, electrification and thunderstorm intensity over time,” Bentley said, noting the right CAPE conditions are needed before pollution can create more lightning strikes.
“We can’t say, ‘oh, it’s a polluted day, so we’re going to get thunderstorms.’ That’s not the case. Pollution is like an accelerant,” Bentley said. “Once you get a thunderstorm, it’s like a fire accelerant.”
But even at low, medium and high levels of CAPE, the research further found that increased pollution levels still produced more lightning strikes, showing “the pollution is really playing a fundamental ingredient in electrifying these storms,” Bentley said.
The Washington D.C. area lightning strikes also happened the most on Thursdays, later in the week, after people have been commuting to work and driving around and enough pollution has built up, before winding back down over the weekend — all while CAPE levels remained the same.
“It’s like when you turn on the heat on your stove, the water doesn’t boil instantaneously. It takes a while. That heat has to transfer to the water, and then finally gets hot and boils,” Bentley said. “The same thing happens with cities.”
The research also found that size of the pollutant didn’t matter; it was the volume of them within the atmosphere that counted. Larger cities like D.C. can also impact regional communities, like Fredericksburg, Charlottesville and Richmond, the data also found, with winds strong enough to push a storm around. Smaller cities can also have an impact on surrounding communities, just at a smaller scale, Bentley added.
The storms are ones that pop up on a moment’s notice and may last for about an hour, Bentley said, much like the one on Aug. 26, wherein Cardinal Elementary School in Richmond was struck by lightning and caught fire around 6:54 p.m.
According to the Wakefield office of the National Weather Service, temperatures reached 93 degrees with a relative humidity of 93% that day. The storm formed at about 6 p.m. northwest of Richmond before rain fell at 6:10 pm. And temperatures cooled as the storm disappeared on the Southeast side of the city around 7 p.m.
Though Bentley said he wasn’t exactly sure exactly how pollution levels may have influenced it, he added, “I think it could have very well been associated” with the air quality.
Sam Wray, meteorologist with the Wakefield office of the National Weather Service, said he wasn’t able to speak to the findings of the research, but acknowledged that isolated storms like those popping up in the summer time generally “is not really an uncommon thing.”
The storms in Hurley and Whitewood in Southwest Virginia in 2021 and 2022, respectively, led to devastating flooding, and are examples of quickly formed storms dumping inches of rain in a short period, Bentley acknowledged. Those storms were a few hours longer and located in rural areas with less traffic than an urban environment, but pollution in those areas can come from far away distances, like smoke from the fires in Canada did last year, leading to health warnings across the state. The toxins can then become trapped by the surrounding mountainous terrain, Bentley added, similarly to the smog issues mountain-bound communities in California’s Los Angeles County deal with.
The research on D.C.-area cities is similar to findings Bentley made in Kansas City and in Bangkok, Thailand; the common denominator is the pollution, Bentley said.
“You could probably go around the world where you have different particle sizes impacting the atmosphere, but if the content remains relatively the same, you might get this similar electrification for a thunderstorm.”
There’s two ways to address the matter, Bentley said.
“Lower pollution levels through multitudes of innovative technologies we’ve got,” Bentley said.
Also key: Helping hot cities cool off.
“And also put in more green space so that you make the heat island cooler.”
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