Just before an onslaught of heavy rain, howling wind, and thundering lightning, there’s often a sharp, distinctive odor in the air. That’s the smell of ozone being carried down from higher altitudes by a storm’s downdrafts.
High in the stratosphere, the second layer of the earth’s atmosphere, ozone acts as a protective shield. This is why the ozone hole, first discovered above Antarctica in the 1980s, is a big deal. Back then, chlorofluorocarbons (CFCs) released into the atmosphere from aerosols, like hairspray, as well as refrigerants, produced a chemical reaction that dissolved portions of the ozone layer.
At ground level in the troposphere – the innermost layer of the atmosphere where we live – this colourless gas can cause people a host of respiratory issues. It can also act as a greenhouse gas and contribute to warming the planet.
“It’s not as strong as carbon dioxide (CO2) or methane, but that’s where it has the biggest impact on heating the earth,” said Victoria Treadaway, a Ph.D. candidate at the University of Rhode Island’s Graduate School of Oceanography (GSO). Treadaway discussed the role of thunderstorms in creating and moving ozone within the atmosphere, and the impacts to climate during the Bay Informed monthly public lecture series held on July 20.
Researchers are finding that storms, especially as they become more intense due to a warming climate, may play a bigger role than previously thought in contributing to “bad” ozone trapped in the troposphere.
Inside the storm, ice particles formed at higher altitudes are super active. They create charges in the same way as when you rapidly rub socked feet over a carpet to create static electricity, said Treadaway. In this case, the result is lightning.
Lightning, she said, produces NOx, nitrogen oxides – namely nitric oxide (NO) and nitrogen dioxide (NO2), which are key players in forming ozone. “So you’re most likely making ozone in the storm that can make its way to the upper troposphere.”
Since the troposphere is the only place in our atmosphere where weather happens, storm clouds typically form an anvil shape where the top levels off due to falling temperatures and air pressure at the “tropopause” – the boundary between the troposphere and stratosphere.
This distinction is important because when storms are strong enough they can break through this barrier and pop into the stratosphere. This allows that protective ozone to be brought down into the troposphere where it will act like greenhouse gas instead.
“There’s a lot going on in these complex systems. What we do know, which is the same for hurricanes, is that the storms are going to get more intense,” she said, referring to a study that suggests more intense storms are increasingly going to penetrate the stratosphere, in turn bringing more stratospheric ozone into the troposphere. “That’s what we do know … We don’t know about the frequency.”
Nor is it certain how much ozone is being produced by these storms and transported across atmospheric boundaries.
Treadaway took part in a field campaign in 2012 to look at big, deep thunderstorm systems across the U.S. and better understand the chemistry going into and coming out of these storms. Data obtained during this study has been used to improve chemistry-climate models to project future climate and air quality.
“The goal of the study is to get a handle on what’s happening because we really don’t know. We don’t know how much NOx we’re actually making,” she said. She added that scientists also don’t fully understand the chemistry of the air people breathe because of the complex dynamics between fossil fuel outputs and natural emissions, such as plants, that are also essential in creating ozone. “As we change our emissions that chemistry will change.”
“We’re trying to understand the chemistry of where we live so we can understand the chemistry inside the storms and what comes up so modelers can tell us what climate change is going to do for the storms.”
The Bay Informed Discussion Series is sponsored in part by Rhode Island Sea Grant in partnership with URI’s Graduate School of Oceanography. This series is held every third Thursday of the month at 7 p.m. at GSO’s Bay campus in Narragansett. These events are designed for the community to get involved and learn more about ongoing research.
The next event will be on August 17: The Carbon Cycle and Climate
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Meredith Haas | Rhode Island Sea Grant Research Communications Specialist