International research team cracks chemical code on how iodine helps form clouds

Cumulus clouds over the Atlantic Ocean [image credit: Tiago Fioreze @ Wikipedia]

The article says iodine’s ‘catalytic role in particle formation enhances its effects in the atmosphere wherever it goes, whether that role is eliminating protective ozone molecules or increasing cloud cover.’ But it’s not clear why this claim would be correct: ‘As sea ice melts in the Arctic, more iodine can enter the atmosphere, increase cloud cover and enhance warming effects on the region.’ Effects of cloud cover differ between high and low cloud, for example.
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An international team led by CU Boulder researchers has cracked the chemical code driving the formation of iodine particles in the atmosphere, revealing how the element contributes to increased cloud cover and depletes molecules in the Earth’s protective ozone layer, says Phys.org.

The research, conducted at the world’s largest particle physics laboratory, the European Organization for Nuclear Research (CERN), was published today in the journal Nature Chemistry.

It’s the first time that any experiment in the world has demonstrated the mechanism for how the gas-phase form of iodine—known as iodic acid—forms, and suggests it has an significant role in atmospheric particle formation.

It comes at a time when atmospheric iodine is increasing globally, with current levels triple what they were 70 years ago.

Researchers hope that this new knowledge on iodine’s atmospheric interactions can be added to global atmospheric and climate models to help scientists better understand its environmental impacts—such as increased cloud cover, which could exacerbate global warming-related thinning of Arctic sea ice.

“This paper establishes a link between the sources of iodine, how they are emitted into the atmosphere, and particle formation, which through subsequent growth, seeds clouds,” said Rainer Volkamer, co-lead author on the paper, professor of chemistry at CU Boulder and fellow at the Cooperative Institute for Research in Environmental Sciences (CIRES). “That link didn’t exist before, and now we have established that link at the molecular level.”

This missing mechanical link between iodine sources and atmospheric particle formation is a multi-step process. First iodine oxide radicals bond with themselves, then react with ozone and water to make iodic acid, with (singlet) oxygen and hypoiodous acid as co-products.

Iodine is a common and highly reactive element that forms radical species which undergo rapid chemical reactions lasting seconds to minutes in the atmosphere.

Most iodine found in the atmosphere comes from the ocean—where it exists as iodide, also present in table salt. Its three-fold increase in the atmosphere over the past 70 years is linked to an increase in anthropogenic air pollution: as harmful, ground-level ozone reacts with the ocean-based iodide, it releases volatile iodine gasses to the atmosphere.

While iodine has been studied for 150 years, it is only in the past two decades that researchers such as Volkamer have revealed its important role within the atmosphere. In 2020, Volkamer and CU Boulder and CIRES researchers published research showing how iodine reaches the stratosphere and eats away at the ozone that protects the planet from harmful UV radiation.

“Iodine is the new kid on the block, among other halogens, that play into the recovery of the ozone layer,” said Volkamer.

Full article here.
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Study: The gas-phase formation mechanism of iodic acid as an atmospheric aerosol source