Iodine in desert dust destroys ozone

news7g12/27/2021

3 3 minutes read

New CU Boulder study shows that iodine from desert dust can reduce ozone air pollution but could extend greenhouse gas lifespan

Peer-reviewed publications

COLORADO UNIVERSITY IN POVERTY

Atacama Desert photographed from an airplane. — **PICTURE DESCRIPTION: ATACAMA DESERT PHOTO FROM THE AIR.** see more CREDIT: PHOTO CREDIT: SAM HALL

As the wind sweeps fine desert dust high into the atmosphere, the iodine in that dust can trigger chemical reactions that destroy some air pollution, but also make greenhouse gases stick around longer. The discovery, published today in the journal Scientific advances, could force researchers to re-evaluate how particles from the soil can affect the chemistry of the atmosphere.

“Iodine, the same chemical that is added as a nutrient in table salt, is eating up the ozone layer in the atmosphere,” said Rainer Volkamer, a member of CIRES and professor of chemistry at CU Boulder. lots of dust in the atmosphere. Volkamer led the team that made precise atmospheric measurements by plane over the eastern Pacific Ocean a few years ago. The new finding has implications for not only air quality but also climate – iodized chemistry can make greenhouse gases last longer, and we should pause to rethink our plans, he said. geotechnical planning related to dust.

“Our understanding of the iodine cycle is incomplete,” Volkamer said. “There are sources and soil-based chemicals that we weren’t aware of, which we now have to look at.”

Atmospheric researchers have long been interested in the observation that airborne dust layers are often very low in ozone, which causes air pollution, which when concentrated can be harmful to human lungs and even crops. . It appears that some form of dust surface chemistry has corroded the ozone, but no one has been able to prove that is happening in lab experiments. Others have speculated on this, but there are plenty of doubts, Volkamer said. In contrast, laboratory experiments have long shown that a form of iodine gas can corrode ozone – but there have only been hints of a link between dust and iodine.

There are other interesting hints about this process in a dataset from 2012, from a series of aircraft flights off the coast of Chile and Costa Rica. The dust seen blowing off the coast of South America has a surprising concentration of iodine in the gaseous form. Volkamer gave the data to CU Boulder PhD student Theodore Koenig, lead author of the study. Koenig describes the data as one of a series of fuzzy images shared by atmospheric chemists around the world. In one image, for example, “iodine seems to correlate with dust … but not quite so clearly,” he said. Everywhere, dust seems to destroy the ozone layer, but why? “Iodine and ozone are clearly connected, but there aren’t any ‘pictures’ of the two,” said Koenig, now an air pollution researcher at Peking University in China.

Data from TORERO (“Tropical Ocean Convective Atmospheric Exchange of Halogen Reactions and Oxidized Hydrocarbons”, a field campaign funded by the National Science Foundation) captured those three figures together , finally, in an image he said, and apparently where dust deserts contain significant amounts of iodine – like the dust from the Atacama and Sechura deserts in Chile and Peru – iodine quickly turns into a gas and ozone dropped to a very low level. But how does that dusty iodine change? “The mechanism is still elusive,” Volkamer said. “It’s future work.”

So the photo is another blurry one, says Koenig, but still, the science is sharper than it is. “I have more questions at the end of the project than at the beginning,” he says. “But those are better, more specific questions.”

They are also important, for anyone interested in the future of the atmosphere, Volkamer said. Atmospheric iodine reactions are known to play a role in reducing OH levels, which can, for example, increase the lifetime of methane and other greenhouse gases. Perhaps more importantly, various geoengineering ideas involve sending dust particles high up into the Earth’s atmosphere, to reflect incoming solar radiation. There, in the stratosphere, ozone is not a pollutant; rather, it forms an important “ozone layer” that helps shield the planet from incoming radiation.

If the iodine from the dust were chemically converted into a form of ozone destruction in the stratosphere, Volkamer said, “that wouldn’t be good, because it could delay the ozone layer’s recovery. Avoid adding toxic iodine to the stratosphere! ”