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Alpine ice shows iodine increase

Posted on 15 November 2018

Analysis of iodine trapped in Alpine ice has shown that levels of atmospheric iodine have tripled over the past century, which partially offsets human-driven increases in the air pollutant, ozone.

Analysis of the Alpine ice by scientists at the University of York, Université Grenoble Alpes and Desert Research Institute shows that iodine concentration began to increase after the Second World War following the growth in motor vehicles and electricity generation.

Nitrogen oxide emissions from vehicles and power plants since the 1950s increase surface ozone, and this reacts with chemicals in seawater to release more iodine into the atmosphere, which partially, but not completely, destroys some of these harmful gases.

Professor Lucy Carpenter said: “Iodine's role in human health has been recognised for some time - it is an essential part of our diets.

“Its role in climate change and air pollution, however, has only been recently recognised, and up until now, there have been no historical records of iodine in populated regions such as Europe.

“Due to the difficulty in accessing this kind of data, the impact of iodine in the atmosphere is not currently a feature of the climate or air quality models that predict future global environmental changes.”

The study in the European Alps has now provided new long-term insight into the role of iodine on the delicate balance of ozone in the atmosphere.

Ozone in the lower atmosphere acts as an air pollutant and greenhouse gas, but it is also the main driver of iodine emissions from the ocean. Once released into the atmosphere iodine acts to destroy this ‘bad’ ozone.

The more ozone humans produce, the more iodine is released from the ocean, which can then help destroy the ozone produced by humans. This means that iodine levels in the ocean can, at least partially, act to keep ozone in the lower atmosphere in check, but there is not enough to counter all of the production.

Dr Tomás Sherwen, who worked on this research in the Wolfson Atmospheric Chemistry Laboratories, said: “We can now start to think about factoring in our knowledge of iodine chemistry into climate and air quality models to help us better predict what the future of our atmosphere will look like around the globe.”

The research is published in Proceedings of the National Academy of Sciences of the United States of America.