Study Shows Massive Eruption Thinned Earth’s Protective Ozone Layer

The January 2022 eruption of the Hunga Tonga-Hunga Ha’apai volcano in the South Pacific produced a shock wave felt around the world and tsunamis around the Pacific basin—some thousands miles distant. It created longer-term effects as well, changing the chemistry and dynamics of the earth’s atmosphere in the year following the eruption, according to a recent study by researchers from the University of Maryland and Harvard University.

Published last month in the Proceedings of the National Academy of Sciences, the research shows that the 12-hour undersea eruption led to unprecedented losses of up to 7% of the ozone layer over large areas of the Southern Hemisphere.

Driving those atmospheric changes, according to the study, was the sheer amount of water vapor injected into the stratosphere, a layer of the atmosphere that extends from 8 to 30 miles above Earth’s surface. It is here that the protective ozone layer shields the planet from the sun’s potentially harmful ultraviolet radiation.

“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, which is just an absolutely incredible amount of water from a single event,” said David Wilmouth, a project scientist at Harvard’s John A. Paulson School of Engineering and Applied Sciences and first author of the paper.

The 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, said Ross Salawitch, a professor at UMD ’s Earth System Science Interdisciplinary Center and co-author of the study.

“This eruption put us in uncharted territory,” said Salawitch, who also has appointments in the Department of Atmospheric and Oceanic and Science and the Department of Chemistry and Biochemistry. “We’ve never seen, in the history of satellite records, this much water vapor injected into the atmosphere.”

The Hunga Tonga-Hunga Ha’apai eruption was the largest explosion ever recorded in the atmosphere using modern equipment, far surpassing the biggest atomic bomb tests or other recent volcanic eruptions. It hurled aerosols and gases deep into the stratosphere and beyond, with some material reaching the lower mesosphere more than 30 miles above the Earth’s surface, altitudes never previously recorded from a volcanic eruption. Other studies found that the eruption increased water vapor in the stratosphere by 10% worldwide, with even higher concentrations in some areas of the Southern Hemisphere.

Wilmouth, Salawitch and the rest of the research team used data from the Microwave Limb Sounder (MLS) aboard the NASA Aura satellite to track not only how that water vapor moved across the globe but also to monitor temperature and levels of chlorine monoxide, ozone, nitric acid and hydrogen chloride in the stratosphere for the year following the eruption. They then compared those measurements to data collected by MLS from 2005 to 2021 prior to the eruption.

The team found that the injection of water vapor and sulfur dioxide changed both the chemistry and the dynamics of the stratosphere.

In terms of chemistry, the sulfur dioxide led to an increase of sulfate aerosols, which provided new surfaces for chemical reactions to occur.

“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,” said Wilmouth.

The increased sulfate aerosols and water vapor kicked off a chain of events in the complex atmospheric chemistry that led to widespread changes in the concentrations of a number of compounds, including ozone.

The extra water vapor also had a cooling effect in the stratosphere, leading to a change in circulation, which drove decreases in ozone in the Southern Hemisphere and an increase of ozone over the tropics.

The researchers found that the peak decrease in ozone occurred in October, nine months after the eruption.

“A key point our paper illustrates is that you can’t just perturb one component of the stratosphere and have that happen in isolation,” said Wilmouth. “The cycles are connected.”

The researchers hope to continue the study by following the impact of the volcano into 2023 and beyond as the water vapor moves from the tropics and midlatitudes to the Southern Hemisphere pole, where it has the potential to amplify ozone losses in the Antarctic. The water vapor is expected to stay elevated in the stratosphere for several years.

This article was based on a news release by Leah Burrows at Harvard University.