27 February 2014

Danish chemist cracks code for cloud creation

Environmental chemistry

The role of clouds in global warming is something of a foggy area for climate researchers. This is partly because relatively little is understood about cloud formation. Atmospheric chemists at the University of Copenhagen have now revealed an important factor in this process. They have demonstrated how emissions from trees and other plants can develop into particles that serve to bind water. The researchers hope that these newfound insights will make it possible to predict climatic changes with greater accuracy than is possible today.

Needed good explanation for how clouds could form

Clouds are commonly perceived as water vapour floating in the atmosphere. But the truth is more complex. Water vapour can only condense into cloud if there is something for it to condense upon. Atmospheric chemists describe these elements of cloud formation as 'cloud seeds' or cloud condensation nuclei (CCN). This is where the story once ended, according to Kjærgaard, Professor at the University of Copenhagen's Department of Chemistry

- Clouds are basically airborne particles of which there are inherently enormous quantities, but chemists have had difficulty explaining how a great many of these particles came into existence. Their most likely origin is volatile organic compounds, or VOCs. VOCs are gases, and we have not had a sufficient explanation of the chemical mechanisms that allow these gases to form particles. Now we do, explains Professor Kjærgaard, who together with research groups in Germany, Finland and the United States, has now published the discovery in the prestigious journal Nature.

Cloud seeds from plant gasses

The gases Kjærgaard refers to, volatile organic compounds, 'VOCs', are naturally emitted by plant life. Therefore, they are primarily composed of carbon. And therein lies the chemists' problem. Cloud seeds are large particles that need to consist of oxygen rich molecules, as oxygen acts almost magnetically on water. Earlier research had demonstrated that the carbon rich VOCs rapidly halt their growth when they interact with urban air.

The breakthrough came when a team of climate researchers based at Forschungszentrum Jülich in Germany studied what happened to VOCs if they were allowed to grow in clean air. Suddenly, they grew large.

The right theory at the right time

Kjærgaard has years of experience under his belt in calculating the transformation of chemical substances found in the atmosphere. For him, the German results were momentous. He knew the people behind the research and could see that their experiments pointed towards unknown chemical reactions. Using his theoretical background, he was able to quickly conduct the calculations that explained the Germans' results. And this is how he came to be invited to become a co-author of the Nature article.

"I hope that we will soon be able to apply this knowledge about cloud seeds in climate models

Henrik Kjaergaard


Dept. of Chemistry

University of Copenhagen

- Results from the Jülich experiment demonstrated that VOCs could grow to become large. But they didn't reveal how. Our theoretical calculations were able to do so. I hope that we will soon be able to apply this knowledge about cloud seeds in climate models, says Kjærgaard.

A tide table for cloud genesis

Before climate researchers can use the new findings to predict climate developments, Kjærgaard must iron out some important details. VOCs are often blown in over cities from forested areas. Therefore, one needs to know how fast they develop to cloud seeds when mixed with various concentrations of pollutants.

- Enormously complex calculations need to be performed to reveal how cloud seeds develop under different conditions. One can't muck about with this in a climate model. Therefore, our ambition is to create the ultimate cloud seed table. Something a bit like a tide table, says Professor Henrik Kjærgaard.

The most important task in years to come

Kjærgaard refers to the development of this table as one of the most important research assignments within his area of expertise in coming years. Consequently, he has teamed up with Associate Professor Solveig Jørgensen of University of Copenhagens Department of Chemistry and Academy Research Fellow Theo Kurten of Helsinki University.

For additional brainpower, the trio are planning to bring five new students aboard. They will assist with the many calculation tasks and get their first taste of what it's like to be part of a research group.

Read the scienctific article in Nature


Professor Henrik Kjærgaard
Mail: hgk@chem.ku.dk
Phone: +45 35 32 03 34

Communications officer Jes Andersen
Mail: jean@science.ku.dk
Mobile: 30 50 65 82