Iodine chemistry will play major role in controlling tropospheric ozone over Arctic: Study

Published on Sep 15, 2022 08:31 PM IST

The research was carried out during the ship-based ‘Multidisciplinary Drifting Observatory for the Study of Arctic Climate (MOSAIC)’ expedition

The Arctic expedition (HT PHOTO)
The Arctic expedition (HT PHOTO)
ByNamrata Devikar

A recent study has highlighted that iodine chemistry plays a major role in controlling tropospheric ozone over the Arctic. Tropospheric ozone – a harmful pollutant formed when sunlight alters various chemicals emitted by human beings – is found nearest to the ground. The research was carried out during the ship-based ‘Multidisciplinary Drifting Observatory for the Study of Arctic Climate (MOSAIC)’ expedition – the largest polar expedition in history - and the study was published in the international journal, Nature Geosciences, on September 15, 2022. The goal of the MOSAIC expedition was to take the closest look ever at the Arctic as the epicentre of global warming, and gain fundamental insights for better understanding of global climate change. Hundreds of researchers from 20 countries made observations between March and October 2020 onboard the German research icebreaker, Polarstern, as it set sail from Norway and spent a year drifting through the Arctic ocean trapped in ice. The researchers showed that iodine enhances springtime tropospheric ozone depletion.

Dr Anoop Mahajan, a researcher from the city-based Indian Institute of Tropical Meteorology (IITM) who was part of the expedition, said that stratospheric ozone depletion, especially in the Antarctic, has been well reported. “The main driver for stratospheric ozone depletion over the Antarctic is the anthropogenic emissions of chlorofluorocarbons (CFCs). However, similar, but shorter-lived, ozone depletion events are seen close to the surface of the Earth. During these depletion events, ozone concentrations drop to nearly zero. Until recently, these surface depletion events were thought to occur mainly because of catalytic depletion by a single type of halogen - bromine, which is emitted into the atmosphere from the sea-ice region,” said Mahajan. Unlike bromine, the effect of another halogen species, iodine, has not been well understood or quantified.

“Observations show that iodine enhances springtime tropospheric ozone depletion in the Arctic. Using a chemical model, it is seen that the chemical reactions between iodine and ozone are the second highest contributor to the loss of surface ozone, after the loss initiated by ozone photolysis, and ahead of bromine. This changes the decades’ old paradigm on the drivers of Arctic photochemical ozone loss,” Mahajan said. Arctic photochemical ozone loss is loss of ozone due to various chemical reactions that take place during the presence of sunlight.

The research also underlined the atmospheric increase in iodine loading due to enhanced anthropogenic ozone-induced ocean iodine emissions. As Arctic sea-ice is expected to thin and shrink in the near future, it will probably lead to increases in iodine emission, further reducing tropospheric ozone over the region.

“The iodine which is released from the sea can actually help in tropospheric ozone depletion over the Arctic circle. However, the iodine which humans receive from natural sources will not be reduced in this process. And so, the results of the study indicate that iodine chemistry could play an increasingly important role in future and must be considered for accurate quantification of the ozone budget in the Arctic,” said Mahajan.

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