Вадим Дудченко
Администратор портала

Iodine, the same chemical added as a nutrient to table salt, is an atmospheric trace element emitted from oceans that efficiently destroys ozone. Low ozone in airborne dust layers is frequently observed but poorly understood. New research led by the University of Colorado, Boulder, shows that dust is a source of iodine, indicated by aircraft observations of iodine monoxide ions inside lofted dust layers from the Atacama and Sechura deserts in Chile and Peru. The finding has implications for not only air quality, but climate, too — iodine chemistry can make greenhouse gases stick around longer and should give us pause to re-think geoengineering schemes involving dust.

A valley in the Atacama Desert in Chile. Image credit: S. McMurtrey / CC BY-SA 4.0.

Atmospheric researchers have long been interested in the observation that dusty layers of air are often very low in the air pollutant ozone, which, when concentrated, can damage people’s lungs and even crops.

It seemed that some kind of dust-surface chemistry was eating up ozone, but no one had been able to show that happening in laboratory experiments.

“Others have speculated about this, but there’s been a lot of doubt,” said Professor Rainer Volkamer, a researcher at the University of Colorado, Boulder.

By contrast, lab experiments have long shown that a gaseous form of iodine can gobble up ozone, but there were only hints of a connection between dust and iodine.

There were other tantalizing hints about the process in a dataset from 2012, from a series of aircraft flights offshore Chile and Costa Rica.

Dust seen blowing offshore from South America had striking levels of gaseous iodine.

“Dust seemed to destroy ozone, but why? Iodine and ozone clearly connect, but there weren’t any ‘photos’ of both with dust,” said Theodore Koenig, an air pollution researcher at Peking University.

The data from the Tropical Ocean Troposphere Exchange of Reactive Halogens and Oxygenated Hydrocarbons (TORERO) field campaign captured those three characters together, finally, in one image and it was clear that where desert dust contained significant levels of iodine, like dust from the Atacama and Sechura deserts, the iodine was quickly transformed into a gaseous form and ozone dropped to very low levels.

“So the picture is another blurry one, but still, the science is sharper than it was. I have more questions at the end of the project than at the start. But they’re better, more specific questions,” Koenig said.

“They’re also very important, for anyone interested in the future of the atmosphere,” Professor Volkamer added.

“Iodine’s reactions in the atmosphere are known to play a role in reducing levels of OH, for example, which can increase the lifetime of methane and other greenhouse gases.”

“Perhaps more importantly, various geoengineering ideas involve injecting dust particles high into Earth’s atmosphere, to reflect incoming solar radiation.”

“There, in the stratosphere, ozone is not a pollutant; rather, it forms a critical ozone layer that helps shield the planet from incoming radiation.”

“If iodine from dust was chemically transformed into an ozone-depleting form in the stratosphere,” Professor Volkamer said.

“Well, that’d not be good, as it could delay the recovery of the ozone layer. Let’s avoid adding anthropogenic iodine into the stratosphere!”

The study was published in the journal Science Advances.

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Theodore K. Koenig et al. 2021. Ozone depletion due to dust release of iodine in the free troposphere. Science Advances 7 (52); doi: 10.1126/sciadv.abj6544

 



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