Massive Flying Laboratory Uncover Secrets of Marine Life’s Influence on Cloud Formation

The view from the DC-8 research aircraft flying through the Marine Boundary Layer, the part of the atmosphere near the ocean surface where the ocean affects processes such as cloud formation. Credit: Sam Hall

Ocean Life helps produce clouds, but existing clouds keep new ones at bay

Stand on the ocean shore and take a deep breath of the salt spray and you will smell the unmistakably pungent scent of the sea. That ripe, almost rotten scent? It’s sulfur.

Marine plankton breathe more than 20 million tonnes of sulfur into the air each year, mainly in the form of dimethyl sulfide (DMS). In the air, this chemical can change to sulfur acid, which helps produce clouds by providing a site for the formation of water droplets. Across the oceans of the world, this process affects the entire climate.

But new research from the University of Wisconsin-Madison, the National Oceanic and Atmospheric Administration and others reveals that more than a third of the DMS emitted by the sea can never help the formation of new clouds, because it is lost to the clouds themselves. The new findings dramatically change the current understanding of how marine life influences clouds and could change the way scientists predict how cloud formation responds to changes in the oceans.

Gordon novak

First author of the study Gordon Novak pictured with the National Oceanic and Atmospheric Administration chemical detection equipment used in the study. Credit: Courtesy of Gordon Novak

By reflecting sunlight back into space and controlling precipitation, clouds play an important role in the global climate. Predicting them accurately is essential for understanding the effects of climate change.

“It turns out that this cloud-forming story was really incomplete,” says Tim Bertram, professor of chemistry at UW-Madison and lead author of the new report. “Over the past three or four years, we’ve challenged parts of this story, both through lab experiments and large-scale field experiments. Now we can better connect the dots between what is emitted by the ocean and how you form those particles that encourage cloud formation. “

Along with collaborators from 13 other institutions, Gordon Novak, a graduate student from UW-Madison, constructed the analysis which was published on October 11, 2021 in the Proceedings of the National Academy of Sciences.

A few years ago, this group of collaborators, led by Patrick Veres at NOAA, discovered that in the process of becoming sulfuric acid, DMS first turns into a molecule known as HPMTF, who had never been identified before. For the new study, the team used ">Nasaplanes equipped with instruments to capture detailed measurements of these chemicals over the ocean, both inside clouds and under sunny skies.

“It’s a huge DC-8. It’s a flying laboratory. Essentially, all the seats have been removed and very precise chemical instrumentation has been installed which allows the team to measure, at very low concentrations, both the molecules emitted into the atmosphere and all the chemical intermediates ”, explains Bertram.

From the flight data, the team found that HPMTF easily dissolves in water droplets from existing clouds, which permanently removes this sulfur from the cloud nucleation process. In cloudless areas, more HPMTF survives to become sulfuric acid and help form new clouds.

Hosted by collaborators from Florida State University, the team took these new measurements into account in a large global model of the chemistry of the oceanic atmosphere. They found that 36% of the sulfur in DMS is lost in the clouds in this way. Another 15% of sulfur is lost through other processes, so less than half of the sulfur in marine plankton released as DMS can help nucleate clouds.

“This loss of sulfur in the clouds reduces the rate of formation of small particles, therefore it reduces the rate of formation of the cloud nuclei themselves. The impact on the brightness of clouds and other properties will need to be explored in the future, ”says Bertram.

Until recently, researchers largely ignored the effects of clouds on chemical processes over the ocean, in part because it is difficult to get good data from the cloud layer. But the new study shows both the power of the right instruments to obtain this data and the important roles clouds can play, even influencing the processes that give rise to the clouds themselves.

“This work has really reopened this area of ​​marine chemistry,” says Bertram.

Reference: “The rapid removal of the oxidation products of dimethyl sulfide limits the production of SO condensation nuclei and clouds in the marine atmosphere” Gordon A. Novak, Charles H. Fite, Christopher D. Holmes, Patrick R. Veres, J. Andrew Neuman, Ian Faloona, Joel A. Thornton, Glenn M. Wolfe, Michael P. Vermeuel, Christopher M. Jernigan, Jeff Peischl, Thomas B. Ryerson, Chelsea R. Thompson, Ilann Bourgeois, Carsten Warneke, Georgios I. Gkatzelis, Mathew M. Coggon, Kanako Sekimoto, T. Paul Bui, Jonathan Dean-Day, Glenn S. Diskin, Joshua P. DiGangi, John B. Nowak, Richard H. Moore, Elizabeth B. Wiggins, Edward L. Winstead, Claire Robinson, K. Lee Thornhill, Kevin J. Sanchez, Samuel R. Hall, Kirk Ullmann, Maximilian Dollner, Bernadett Weinzierl, Donald R. Blake and Timothy H. Bertram, October 11, 2021, Proceedings of the National Academy of Sciences.
DOI: 10.1073 / pnas.2110472118

This work was supported in part by the National Science Foundation (GEO grants AGS 1822420 and CHE 1801971), NASA (grants 80NSSC19K1368 and NNX16AI57G), and the United States Department of Agriculture (grant CA-D-LAW-2481-H) .

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