Cloud-forming particles don’t need sulfuric acid to assemble, trio of studies show | May 30, 2016 Issue - Vol. 94 Issue 22 | Chemical & Engineering News
  • CORRECTION: The credit line on the photo accompanying this story was updated on May 31, 2016, to reflect the correct photographer. The photo is credited to Gilles Martin/Paul Scherrer Institute, not Federico Bianchi.
Volume 94 Issue 22 | p. 7 | News of The Week
Issue Date: May 30, 2016 | Web Date: May 26, 2016

Cloud-forming particles don’t need sulfuric acid to assemble, trio of studies show

Findings could have implications for modeling climate effects
Department: Science & Technology
News Channels: Analytical SCENE, Environmental SCENE, Organic SCENE
Keywords: atmospheric chemistry, aerosols, atmosphere, sulfuric acid
At the Jungfraujoch research station, Bianchi uses a mass spectrometer to detect molecules that form aerosols.
Credit: Gilles Martin/Paul Scherrer Institute
Scientist Bianchi at Jungfraujoch in snow-covered swiss mountains, standing with a mass spectrometer.
At the Jungfraujoch research station, Bianchi uses a mass spectrometer to detect molecules that form aerosols.
Credit: Gilles Martin/Paul Scherrer Institute

Atmospheric aerosols, particles once thought to need human-generated sulfur dioxide to form, can form from other naturally occurring compounds alone, according to a series of new reports (Nature 2016, DOI: 10.1038/nature18271 and 10.1038/nature17953; Science 2016, DOI: 10.1126/science.aad5456).

The discovery of this additional avenue for aerosol formation has significant implications for modeling the effects of these particles on climate. The studies also imply that the preindustrial atmosphere was cloudier than once thought.

Formation and growth of aerosols are some of the most poorly understood aspects of atmospheric science. Yet these particles’ importance is hard to overstate. Aerosols can seed cloud formation, and they also have detrimental effects on human respiratory and cardiovascular health. Because they reflect and scatter sunlight, aerosols are also likely responsible for an as-yet-unknown amount of global cooling that climate scientists think has somewhat counteracted the effects of global warming.

Previously, scientists had thought that sulfuric acid, which is largely produced in the atmosphere by the oxidation of sulfur dioxide, was essential for aerosol formation. Sulfur dioxide spews into the atmosphere from oil and gas burning and, to a lesser extent, from volcanoes and marine plankton.

But now, experiments that are part of the Cosmics Leaving Outdoor Droplets (CLOUD) project run by CERN, the European Organization for Nuclear Research, have expanded researchers’ knowledge about aerosol formation and growth mechanisms. The facility uses a proton accelerator to simulate the high-energy cosmic rays that shower Earth.

A team led by Urs Baltensperger of Paul Scherrer Institute and Jasper Kirkby, a particle physicist at CERN and a founder of CLOUD, studied the molecule α-pinene. When oxidized, this compound, which is emitted by pine trees, forms various types of highly oxygenated molecules (HOMs).

Research led by Kirkby showed that, under simulated pristine, sulfur-free atmospheric conditions, the ozonolysis of α-pinene leads to the condensation of nanometer-scale aerosol particles. The team also found that cosmic rays enhance this aerosol production by up to two orders of magnitude. Baltensperger led an additional study of the growth of these particles.

Another team led by Federico Bianchi, also at Paul Scherrer Institute, and Baltensperger studied atmospheric samples at a research station in the Swiss Alps. Their observations, made with mass spectrometers and particle counters, back up the CLOUD experiments: The researchers found that similar aerosols were produced in an unpolluted mountain atmosphere when the atmosphere contained high levels of HOMs.

The new studies show that these organic compounds can enable the nucleation of new particles, says Paul O. Wennberg, an atmospheric chemist at Caltech. This is important for understanding Earth’s atmospheric processes. Wennberg emphasizes: “Remember that at the core of every cloud or raindrop is one of these particles.”

This article has been translated into Spanish by and can be found here.

Chemical & Engineering News
ISSN 0009-2347
Copyright © American Chemical Society
William Thomson (May 26, 2016 6:30 AM)
How is this a surprise? Did clouds not form before SO2 emissions?

So the highly oxidized products of biogenic emissions that form nascent particles have hydrophilic properties? Call Nature!

What is disappointing is the failure to reference the discovery of oligomers in SOA from the Johnston group at Delaware. Without that, none of this work is possible.
Gilles Martin (May 30, 2016 6:25 AM)
Could you please correct the credits for the photo, it should be "Gilles Martin"? You can check on that website for the original credits:

Thank you.


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