June 13th, 2012 by Joshua S Hill
A new study has found that massive volcanic eruptions that took place over the past 70,000 years in Nicaragua could have injected enough gases into the atmosphere to temporarily thin the ozone layer. The study also concluded that if such an event took pace today, the amount of gases released could equal twice the amount of ozone-depleting halogen currently released into the stratosphere by manmade emissions.
Bromine and chlorine are gases that “love to react — especially with ozone,” said Kirstin Krüger, a meteorologist with GEOMAR in Kiel, Germany. “If they reach the upper levels of the atmosphere, they have a high potential of depleting the ozone layer.”
Krüger and her colleagues presented their findings at a scientific conference in Selfoss, Iceland at the American Geophysical Union’s Chapman Conference on Volcanism and the Atmosphere. Their research was a combination of field work, geochemistry, and existing atmospheric models to look at the previous Nicaraguan eruptions.
Steffen Kutterolf, a chemical volcanologist with GEOMAR and one of Krüger’s colleagues, was responsible for determining how much gas had been released during the eruptions. Kutterolf analysed gases that had been trapped in minerals crystallizing in the magma chambers and estimated the amount of gas within the magma prior to the eruptions.
Previous studies have estimated that in large, explosive eruptions — the type that sends mushroom clouds of ash kilometers high — up to 25 percent of the halogens ejected can make it to the stratosphere. For this study, the research team used a more conservative estimate of 10 percent reaching the stratosphere, to calculate the potential ozone layer depletion.
Taking an average from 14 Nicaraguan eruptions, Krüger and her colleagues found bromine and chlorine concentrations in the stratosphere jumped to levels that are equivalent to 200 percent to 300 percent of the 2011 concentrations of those gases. The Upper Apoyo eruption 24,500 years ago, for example, released 120 megatons of chlorine and 600 kilotons of bromine into the stratosphere.
Volcanic sulfate aerosols alone can lead to an ozone increase — if chlorine levels are at low, pre-industrial levels, Krüger said. But bromine and chlorine are halogens, gases whose atoms have seven electrons in the outer ring. To reach a stable, eight-electron configuration, these atoms will rip electrons off of passing molecules, like ozone. So when an eruption also pumps bromine and chlorine levels into the stratosphere, the ozone-depleting properties of the gases together with aerosols is expected to thin the protective layer.
“As we have bromine and chlorine together, we believe that this can lead to substantial depletion,” she said. “And this is from one single eruption.”
Because the effects are in the stratosphere, where the volcanic gases can be carried across the globe, eruptions of tropical volcanoes could lead to ozone depletion over a large area, Krüger said, potentially even impacting the ozone over polar regions.
Source: American Geophysical Union
Image Source: Steffen Kutterolf
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