Iodine in desert dust destroys ozone
New study shows iodine from desert dust can decrease ozone air pollution
but could prolong greenhouse gas lifetimes

Date:
December 22, 2021
Source:
University of Colorado at Boulder
Summary:
When winds loft fine desert dust high into the atmosphere, iodine
in that dust can trigger chemical reactions that destroy some air
pollution, but also let greenhouse gases stick around longer. The
finding may force researchers to re-evaluate how particles from
land can impact the chemistry of the atmosphere.



FULL STORY ==========================================================================
When winds loft fine desert dust high into the atmosphere, iodine in that
dust can trigger chemical reactions that destroy some air pollution,
but also let greenhouse gases stick around longer. The finding,
published today in the journal Science Advances, may force researchers
to re-evaluate how particles from land can impact the chemistry of
the atmosphere.


========================================================================== "Iodine, the same chemical added as a nutrient to table salt, is eating
up ozone in dusty air high in the atmosphere," said Rainer Volkamer,
a CIRES Fellow and professor of chemistry at CU Boulder. Volkamer led
the team that made precision atmospheric measurements by aircraft over
the eastern Pacific Ocean several years ago. The new finding, he said,
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.

"Our understanding of the iodine cycle is incomplete," Volkamer
said. "There are land-based sources and chemistry we didn't know about,
which we must now consider." 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 Volkamer. 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.

Volkamer handed the data to then-CU Boulder graduate student Theodore
Koenig, lead author on this study. Koenig describes those data as one
in a set of blurry photographs shared by atmospheric chemists around
the world. In one image, for example, "iodine seemed to correlate with
dust ... but not absolutely clearly," he said. Everywhere, dust seemed
to destroy ozone, but why? "Iodine and ozone clearly connect, but there
weren't any 'photos' of both with dust," said Koenig, who is now an air pollution researcher at Peking University in China.

The data from TORERO (the "Tropical Ocean Troposphere Exchange of Reactive Halogens and Oxygenated Hydrocarbons," a field campaign funded by the
National Science Foundation) captured those three characters together,
finally, in one image he said, and it was clear that where desert dust contained significant levels of iodine -- like dust from the Atacama and Sechura deserts in Chile and Peru -- the iodine was quickly transformed
into a gaseous form and ozone dropped to very low levels. But how did
that dust-based iodine transform? "The mechanism still remains elusive," Volkamer said. "That's future work." So the picture is another blurry
one, Koenig said, but still, the science is sharper than it was. "I
have more questions at the end of the project than at the start,"
he said. "But they're better, more specific questions." They're also
very important, for anyone interested in the future of the atmosphere,
Volkamer said. 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, 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!" ========================================================================== Story Source: Materials provided by
University_of_Colorado_at_Boulder. Note: Content may be edited for style
and length.


========================================================================== Journal Reference:
1. Theodore K. Koenig, Rainer Volkamer, Eric C. Apel, James F. Bresch,
Carlos A. Cuevas, Barbara Dix, Edwin W. Eloranta, Rafael
P. Fernandez, Samuel R. Hall, Rebecca S. Hornbrook,
R. Bradley Pierce, J. Michael Reeves, Alfonso Saiz-Lopez,
Kirk Ullmann. Ozone depletion due to dust release of iodine
in the free troposphere. Science Advances, 2021; 7 (52) DOI:
10.1126/sciadv.abj6544 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/12/211222153149.htm

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