PAUL SCHERRER INSTITUTE
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IMAGE: HOUSSNI LAMKADDAM, RESEARCHER IN THE LABORATORY FOR ATMOSPHERE CHEMISTRY AT PSI, IN THE EXPERIMENTAL DEVICE. show more CREDIT: PAUL SCHERRER INSTITUT / MAHIR DZAMBEGOVIC
Researchers at the Paul Scherrer Institute PSI have investigated for the first time how chemical reactions in clouds can influence the global climate. They found that isoprene, the dominant non-methane organic compound emitted into the atmosphere, can be a major contributor to the formation of organic aerosols in clouds. They published their results today in Science Advances.
Aerosols, a mixture of solid or liquid particles that float in the air, play an important role in the earth’s climate. Aerosols come from either natural or human sources. They influence the radiation balance of the earth by interacting with sunlight and forming clouds. However, their effect remains the most significant uncertainty in climate models.
A very common substance in the atmosphere is isoprene, an organic compound whose reactions in the gas phase are relatively well understood. Isoprene is given off by trees and can produce aerosols when oxidized. How isoprene and its reaction products react in cloud droplets is still largely unknown. For this reason, researchers at the Paul Scherrer Institute PSI used a type of flow-through reactor with wetted walls along with the most advanced mass spectrometers to investigate what could be chemically happening for the first time in clouds under atmospherically relevant conditions.
“With our experimental set-up, we can for the first time precisely investigate the distribution of organic vapors at the air-water interface under environmental conditions,” says Houssni Lamkaddam, researcher in the Laboratory for Atmospheric Chemistry at PSI. “With our apparatus we can now simulate what happens in clouds.”
What exactly happens in clouds?
In the special device, a so-called wetting reactor, a thin film of water is held on the inside of a quartz tube. A gas mixture containing, among other things, isoprene, ozone and so-called hydroxyl radicals is fed into the glass bottle. UV lamps are installed around the glass cylinder to simulate daylight conditions for some of the experiments.
With this setup, the researchers found that up to 70 percent of the isoprene oxidation products can be dissolved in the water film. The subsequent aqueous oxidation of the dissolved species generates significant amounts of secondary organic aerosols. On the basis of these analyzes, they calculated that the chemical reactions that take place in clouds are responsible for up to 20 percent of secondary organic aerosols worldwide.
“This is another important contribution to a better understanding of the processes in the atmosphere,” summarizes Urs Baltensperger, scientific director of the Laboratory for Atmospheric Chemistry at PSI. The earth’s radiation balance is a very important factor in the entire climate process and thus also in climate change. “And aerosols play a decisive role in this,” says the atmospheric researcher. While aerosols form cloud droplets, this study shows that clouds can also form aerosols through the aqueous chemistry of organic vapors, a process that is known for sulfate aerosols but is also shown here for the organic fraction. This new experimental setup, which was developed at PSI, opens up the possibility of studying aerosol formation in clouds under almost atmospheric conditions so that these processes can ultimately be included in climate models.
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Text: Paul Scherrer Institute / Sebastian Jutzi
About PSI
The Paul Scherrer Institute PSI develops, builds and operates large, complex research facilities and makes them available to the national and international research community. The research focus of the institute lies in the areas of matter and materials, energy and the environment as well as human health. PSI is committed to training future generations. That is why around a quarter of our employees are post-docs, postgraduates or trainees. PSI employs a total of 2100 people, making it the largest research institute in Switzerland. The annual budget is around CHF 400 million. The PSI is part of the ETH domain, the other members are the two Federal Technical Institutes ETH Zurich and EPFL Lausanne as well as Eawag (Swiss Federal University for Aquatic Science and Technology), Empa (Federal Laboratories for Materials Science and Technology) and WSL (Swiss Federal University for Forest, Snow and Landscape Research).
Original publication
Large contribution of isoprene cloud chemistry to the secondary organic aerosol
H. Lamkaddam, J. Dommen, A. Ranjithkumar, H. Gordon, G. Wehrle, J. Krechmer, F. Majluf, D. Salionov, J. Schmale, S. Bjeli ?, KS Carslaw, I. El Haddad, U Baltensperger
Advances in Science, March 24, 2021
DOI: 10.1126 / sciadv.abe2952
From EurekAlert!
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