Iodine, the same chemical that is added as a nutrient to table salt, is an atmospheric trace element emitted from the oceans that is efficient at destroying ozone. Low ozone levels in airborne dust layers are often observed but poorly understood. New research, led by the University of Colorado, Boulder, shows that dust is a source of iodine, as indicated by airplane observations of iodine monoxide ions in bloated layers of dust from the Atacama and Sechura deserts in Chile and Peru. The result not only affects air quality, but the climate too – iodine chemistry can hold greenhouse gases longer and should give us a break to rethink geoengineering programs with dust.
Atmospheric researchers have long been interested in the observation that dusty layers of air often contain very low levels of air pollutant ozone, the concentration of which can damage lungs and even plants.
It appeared that some kind of chemistry was consuming ozone from the dust surface, but no laboratory experiments had shown it to do so.
“Others speculated about it, but there were many doubts,” said Professor Rainer Volkamer, a researcher at the University of Colorado at Boulder.
Laboratory experiments, on the other hand, have long shown that a gaseous form of iodine can gobble up ozone, but there has only been evidence of a connection between dust and iodine.
Further tantalizing clues to the process came from a 2012 data set from a series of airplane flights off the coast of Chile and Costa Rica.
Dust that was blown off the coast from South America contained striking amounts of gaseous iodine.
“Dust seemed to destroy ozone, but why? Iodine and ozone are clearly related, but there were no ‘photos’ of either with dust, ”said Theodore Koenig, air pollution researcher at Peking University.
The data from the Tropical Ocean Troposphere Exchange of Reactive Halogens and Oxygenated Hydrocarbons (TORERO) field campaign eventually captured these three characters in one picture, and it was clear that where desert dust contained significant amounts of iodine, like dust from the Atacama and In the Deserts by Sechura the iodine was quickly converted into a gaseous form and the ozone sank to very low levels.
“So the picture is blurry again, but the science is still sharper than it was. I have more questions at the end of the project than at the beginning. But these are better, more specific questions, ”said Koenig.
“They are also very important to anyone interested in the future of the atmosphere,” added Professor Volkamer.
“It is known that the reactions of iodine in the atmosphere, for example, play a role in reducing OH, which can increase the lifespan of methane and other greenhouse gases.”
“Perhaps more importantly, various geoengineering ideas involve bringing dust particles high into the 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 protects the planet from incident radiation. “
“If iodine from dust in the stratosphere were chemically converted into an ozone-depleting form,” says Professor Volkamer.
“Well, that wouldn’t be a good thing as it could delay the recovery of the ozone layer. Let’s avoid adding anthropogenic iodine to the stratosphere! “
the to learn was published in the magazine Scientific advances.
Theodore K. Koenig et al. 2021. Ozone depletion through the release of dust from iodine into the free troposphere. Scientific advances 7 (52); doi: 10.1126/sciadv.abj6544