Study examines how massive 2022 eruption changed stratosphere chemistry and dynamics

The Hunga Tonga-Hunga Ha'apai volcano erupted in the South Pacific on January 15, 2022. It sent shock waves around the world and caused tsunamis in Tonga, Fiji, New Zealand, Japan, Chile, Peru, and the United States.

According to a new study from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and the University of Maryland, the eruption changed the chemistry and dynamics of the stratosphere in the year that followed. This caused the ozone layer to lose up to 7% of its thickness over large parts of the Southern Hemisphere, which had never happened before. The study was published in the Proceedings of the National Academy of Sciences.

According to the study, those changes in the atmosphere were caused by the huge amount of water vapor that the underwater volcano put into the air. The stratosphere is about 8 to 30 miles above the surface of the Earth. It is where the protective ozone layer is located.

Project scientist at SEAS and lead author of the paper David Wilmouth said, "The Hunga Tonga-Hunga Ha'apai eruption was truly extraordinary in that it injected about 300 billion pounds of water into the normally dry stratosphere. That is just an absolutely incredible amount of water from a single event."

“This eruption took us to places we have never been before,” said Ross Salawitch, co-author of the study and professor at the University of Maryland’s Earth System Science Interdisciplinary Center. "We've never seen, in the history of satellite records, this much water vapor injected into the atmosphere and our paper is the first that looks at the downstream consequences over broad regions of both hemispheres in the months following the eruption using satellite data and a global model."
It is known that the Hunga Tonga-Hunga Ha'apai eruption was the biggest blast ever seen in the sky. Aerosols and gases were thrown high into the atmosphere by the explosion. Some of it got to the lower mesosphere, which is more than 30 miles above the Earth's surface. This is the highest level of material that has ever been found from a volcano erupting. Studies done in the past found that the eruption raised the amount of water vapor in the atmosphere by 10% around the world, and in some parts of the Southern Hemisphere, the levels were even higher.

Aura's Microwave Limb Sounder (MLS) helped Wilmouth, Salawitch, and the rest of the research team track how the water vapor moved around the world. They also kept an eye on the temperature and amounts of chlorine monoxide (ClO), ozone (O3), nitric acid (HNO3), and hydrogen chloride (HCl) in the stratosphere for a year after the eruption. Then, they matched those readings to information MLS had gathered from 2005 to 2021, which was before the eruption.

That adding water vapor and sulfur dioxide (SO2) changed the chemistry and the movement of things in the atmosphere, the team found. To explain this chemically, the SO2 caused more sulfate particles to form, which gave chemicals new places to react.

"Certain reactions that might not happen at all or only happen slowly can happen faster if there are aerosols available on which those reactions can take place," stated Wilmouth. "The injection of SO2 from the volcano allowed sulfate aerosols to form and the presence of water vapor led to the additional production of sulfate aerosols."

The rise in sulfate particles and water vapor set off a chain of events in the atmosphere's complicated chemistry that changed the amounts of many chemicals, including ozone everywhere.

There was less ozone in the southern hemisphere and more over the tropics because of the change in airflow caused by the extra water vapor. This caused the stratosphere to cool down.

The most ozone was lost in October, which was nine months after the earthquake, according to the experts.

"We had this enormous increase in water vapor in the stratosphere with modest increases in sulfate that set off a series of events that led to significant changes in temperature and circulation, ClO, HNO3, HCl, O3, and other gases," said Wilmouth.

Next, the scientists want to keep studying by keeping an eye on the volcano's effects through 2023 and beyond. They want to see how the water vapor moves from the tropics and midlatitudes to the poles of the Southern Hemisphere, where it could make ozone losses worse in the Antarctic. It is believed that the water vapor will stay high in the atmosphere for a number of years.

James Anderson, the Philip S. Weld Professor of Atmospheric Chemistry at SEAS, Freja Østerstrøm, and Jessica Smith all wrote parts of the study together.