Newswise – 85 percent of Earth’s air is found in the lowest layer of its atmosphere, the troposphere. However, major gaps remain in our understanding of the atmospheric chemistry that drives changes in the composition of the troposphere.

A particularly important gap in our knowledge is the formation and dispersion of secondary organic aerosols (SOAs), which impact the planet’s radiation balance, air quality and human health. But that gap is closing, thanks to groundbreaking discoveries by an international team of researchers led by the U.S. Department of Energy’s (DOE) Argonne National Laboratory, Sandia National Laboratories, and NASA’s Jet Propulsion Laboratory (JPL).

The scientists describe their results in one new paper published this month in Nature Geosciences.

The team focused on a class of compounds known as Criegee Intermediates (CIs). Researchers suspect that CIs play a crucial role in the formation of SOAs when they combine via a process called oligomerization. But until now, no one had directly identified the chemical signatures of this process in situ.

“First, we found that CI chemistry may play a larger role in changing the composition of the troposphere than current atmospheric models account for – probably by an order of magnitude.” — Carl Percival, researcher at NASA’s JPL

Using the most advanced methods available to detect gas-phase molecules and aerosols in the atmosphere, the team conducted field measurements in the Amazon rainforest, one of the most important SOA areas on Earth. There they found clear evidence consistent with reactions of a Criegee intermediate containing carbon, hydrogen and oxygen (CH).2OO).

“This discovery is extremely significant because we were able to make direct connections between what we actually saw in the field, what we expected with the oligomerization of CIs, and what we were able to characterize and theoretically determine in the laboratory,” explained Rebecca L . Caravan, an assistant chemist at Argonne and first author of the paper.

These field observations represent just one component of the innovative science made possible by collaboration between laboratories.

“In addition to the field measurements, we were able to use the world’s most advanced experimental methods to directly characterize the Criegee intermediate reactions. We have used the most advanced theoretical kinetics to predict reactions that we cannot directly measure. And we used the most advanced global chemistry modeling to assess the effects we would expect from oligomerization in the troposphere based on these kinetics,” said Craig A. Taatjes, a combustion chemist at Sandia.

This combination of components led to some extremely important findings.

“First, we found that CI chemistry could play a larger role in changing the composition of the troposphere than current atmospheric models account for – probably by an order of magnitude,” said Carl Percival, a researcher at NASA’s Jet Propulsion Laboratory. “Second, the updated modeling we conducted based on our work produced only a fraction of the oligomerization signatures we observed in the field.”

This could mean that CI chemistry could be driving even more transformations in the troposphere, or that other, as yet unidentified, chemical mechanisms are at work.

“We still have a lot of work to do to fully define the role of CI reactions in the troposphere,” Caravan concluded. “But these findings significantly expand our understanding of a potentially important pathway of SOA formation in the most important layer of Earth’s atmosphere.”

In addition to Caravan, Argonne authors also include Ahren Jasper and Stephen Klippenstein.

Funding for the Argonne and Sandia work was provided by the Basic Energy Sciences program of the DOE’s Office of Science and the National Nuclear Security Administration. NASA funded the research conducted at the Jet Propulsion Laboratory.

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