by A recent study published in the Proceedings of the National Academy of Sciences (PNAS) reveals that the eruption of the Hunga Tonga-Hunga Ha’apai volcano on January 15, 2022, had a significant impact on the ozone layer. The eruption, which took place in the South Pacific, caused shockwaves felt worldwide and triggered tsunamis in several countries, including Tonga, Fiji, New Zealand, Japan, Chile, Peru, and the United States. Researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and the University of Maryland found that the eruption led to unprecedented losses in the ozone layer, reducing its levels by up to 7% across large areas of the Southern Hemisphere.
The key factor driving these atmospheric changes was the immense amount of water vapor that was injected into the stratosphere by the underwater volcano. The stratosphere, located approximately 8 to 30 miles above the Earth’s surface, is where the protective ozone layer resides. David Wilmouth, a project scientist at SEAS and first author of the study, described the eruption as extraordinary, as it injected around 300 billion pounds of water into the typically dry stratosphere – an unprecedented amount from a single event.
According to Ross Salawitch, a professor at the University of Maryland, this eruption put researchers in uncharted territory. The magnitude of water vapor injected into the atmosphere had never been seen in satellite records before. The study is the first to examine the downstream consequences of the eruption on broad regions of both hemispheres in the months following the event, using satellite data and a global model.
The eruption of the Hunga Tonga-Hunga Ha’apai volcano was the largest ever recorded in the atmosphere. It propelled aerosols and gases deep into the stratosphere, with some reaching the lower mesosphere at altitudes exceeding 30 miles above the Earth’s surface, a level never before recorded from a volcanic eruption. Previous studies have shown that the eruption increased water vapor in the stratosphere by 10% globally, with even higher concentrations in certain areas of the Southern Hemisphere.
To track the movement of water vapor and its effects on the stratosphere, Wilmouth, Salawitch, and the research team utilized data from the Microwave Limb Sounder (MLS) aboard the NASA Aura satellite. They monitored the temperature and levels of various compounds, including chlorine monoxide (ClO), ozone (O3), nitric acid (HNO3), and hydrogen chloride (HCl), for a year following the eruption. The measurements were compared to data collected by the MLS from 2005 to 2021 prior to the eruption.
The researchers discovered that the injection of water vapor and sulfur dioxide (SO2) caused significant changes in the chemistry and dynamics of the stratosphere. The presence of SO2 resulted in an increase in sulfate aerosols, which provided new surfaces for chemical reactions to occur. The increased sulfate aerosols, combined with the presence of water vapor, triggered a cascade of events in the complex atmospheric chemistry, leading to widespread changes in the concentrations of various compounds, including ozone.
Additionally, the extra water vapor had a cooling effect in the stratosphere, altering circulation patterns. This change in circulation contributed to decreases in ozone levels in the Southern Hemisphere and an increase in ozone over the tropics. The researchers noted that the peak decrease in ozone occurred in October, nine months after the eruption.
Currently, the research team intends to continue studying the impact of the volcano into 2023 and beyond. They will track the movement of the water vapor from the tropics and mid-latitudes to the Southern Hemisphere pole, where it has the potential to amplify ozone losses in the Antarctic. The elevated levels of water vapor in the stratosphere are expected to persist for several years.
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