Formation of iodic acid influences global climate

Iodine, which enters the atmosphere from the world’s oceans, destroys ozone and contributes to cloud formation. As part of an international research collaboration, the team led by Armin Hansel from the Institute for Ion Physics and Applied Physics at the University of Innsbruck explained the detailed reaction pathway by which the gaseous iodic acid (HIO3) is formed in the atmosphere.

This is a central intermediate step in the cycle in which iodine enters the atmosphere from the world’s oceans, forms aerosols and in the course of this destroys ozone, according to the University of Innsbruck’s press release. The study was published in the renowned journal Nature Chemistry.

Iodine acts as a catalyst in ozone depletion

In a previous study, Armin Hansel and his research group were able to show that iodic acid is the key substance that leads to particle and cloud formation. Iodine acts as a catalyst in the destruction of ozone, it is not consumed in this process.

Uni Innsbruck

Ion physicist Armin Hansel

The study was carried out with the help of the large-scale experiment CLOUD. CLOUD is located at the nuclear research center CERN, where the atmosphere is simulated in a large chamber. It investigates how, under carefully controlled conditions, reactive gases form aerosol particles and grow into cloud condensation nuclei.

Global warming accelerates the process

“The chemical processes involved in the iodine cycle are particularly critical because the amount of iodine that has entered the atmosphere since 1950 has more than tripled. Iodine is formed when ozone (O3) reacts with iodide (I-) dissolved in seawater. Human activities have led to an increase in ground-level ozone and to strong warming,” explained Hansel.

Thinner ice in the Arctic means more water-dissolved iodide comes into contact with ozone and releases iodine. Both effects would increase the iodine emissions, says the scientist. These increasing global emissions could therefore further accelerate the melting of sea ice in the Arctic, so it is a self-reinforcing effect.

Das CLOUD Experiment am CERN

CERN, Maximilian Brice

The CLOUD experiment was carried out at CERN

The individual steps leading to the formation of iodic acid were decoded by the research group with great experimental effort at CERN near Geneva and through field measurements at the Maido Observatory in Reunion. Quantum chemical calculations were necessary to confirm the reactivity of the individual conversion steps.

Chemical processes of global importance

“Iodine is a critical trace element that has a significant impact on tropospheric photochemistry, i.e. the chemical reactions that take place there under the influence of light. These ultimately affect the climate. Iodine dissolved in the sea goes into the gas phase, is then involved in the formation of aerosol particles and is then released back into the gas phase or washed out of the atmosphere,” says Hansel.

Of particular interest to chemists is the fact that gaseous iodine forms reactive radicals in the atmosphere, which actually only affect photochemistry near the coast or over the oceans. In the process, ozone – an air pollutant – is destroyed. Because iodine can be transported over long distances in aerosol particles and released far from iodine sources, the iodine cycle has global implications.

Tyrolean pioneers for the CLOUD experiment

For the CLOUD experiments, the Innsbruck research group led by Armin Hansel developed special measurement methods in close cooperation with the spin-off company Ionicon Analytik GmbH. Hansel’s team is considered an international pioneer in the field of trace analysis, as this technical innovation from Tyrol delivers results with extremely high detection sensitivity in real time.

The CLOUD research team consists of numerous working groups from all over Europe and North America and is financially supported by the European Union and numerous national sponsors – including the Austrian research funding agency FFG.

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