Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Present-day measurements yield insights into clouds of the past


Researchers have shown how fine particles are formed from natural substances in the atmosphere. These findings will improve our knowledge about clouds in the pre-industrial era and thus will contribute to a more accurate understanding of both the past and future evolution of our climate.

To assess the effect of human activity on climate, scientists must be able to compare today's climate with that of the pre-industrial era. One important aspect of this effort is to reconstruct the abundance and properties of clouds.

PSI researchers Jasmin Tröstl and Urs Baltensperger at the CLOUD chamber at CERN, in which they have studied the formation of aerosols in the atmosphere.

Paul Scherrer Institute/Markus Fischer

PSI researcher Federico Bianchi at the Jungfraujoch High Altitude Research Station, where he, together with colleagues, has studied the formation of aerosols in the atmosphere.

Paul Scherrer Institute/Gilles Martin

This matters because clouds can reflect sunlight and thus, to a certain extent, mask the warming of the Earth due to greenhouse gases. In turn, the formation of clouds is essentially determined by aerosol particles in the air on which water can condense to form cloud droplets. If more particles are available, more droplets can form, and that changes the characteristics of the clouds.

Aerosol particles have a variety of sources – ranging for example from desert dust to soot particles produced by burning wood or fossil fuels. In addition, aerosol particles can be formed in the atmosphere through a process known as nucleation, when gas molecules join together. Up to now, it was thought that this process was crucially dependent on sulfuric acid, which has only been present in large quantities in the atmosphere since the beginning of the industrialisation.

Aerosols from nature

„We have now been able to show that aerosol particles capable of seeding clouds can also arise from organic substances, such as those that are emitted by trees,“ explains Urs Baltensperger – head of the Laboratory for Atmospheric Chemistry at the Paul Scherrer Institute PSI and co-initiator of the project – who this year was honoured with the Spiers Memorial Award of the Royal Society of Chemistry for his research on aerosols in the atmosphere. „This means that even before the industrialisation aerosol particles were formed from gaseous precursors in the atmosphere – resulting in higher concentrations than had previously been assumed.“

„This does not necessarily mean that there were more clouds in those days than previously thought,“ adds PSI researcher Jasmin Tröstl. „But the clouds probably consisted of more and smaller droplets, so that they were brighter and reflected more sunlight back to space.“

These results were obtained within the framework of an extensive international research collaboration under the leadership of researchers at CERN and the PSI. The researchers carried out their experiments in the CLOUD chamber at CERN and at the Jungfraujoch High Altitude Research Station in the Swiss Alps. The CLOUD chamber is a cylindrical vessel, 4.3 metres high and 3 metres in diameter, in which a variety of atmospheric conditions can be very specifically replicated. The researchers introduced the substance pinene, which is emitted by trees, and were able to observe how aerosol particles formed inside the CLOUD chamber.

Aerosol formation in two stages

„We also characterised these processes with the help of mathematical models, through which we can understand how these particles are formed,“ Tröstl explains. „All in all, it is a very complicated process. First the pinene molecules are altered through reactions with oxidants such as ozone, and a multitude of similar but still different molecules – with varying degrees of 'stickiness' – are created.“ The „stickiest“, those that bind especially well with other molecules, can join together to form tiny particles. This is the first crucial step, because unless the particles reach a minimum size of around 1.7 nanometres, they simply evaporate again. With this, though, they are still too small to serve as the seeds of cloud droplets; for that, they need to be roughly 50 to 100 nanometres in size.

„In order for the particles to grow further, more molecules need to condense onto them– and this increasingly includes also the less „sticky“ ones which attach more easily to larger particles and are present in greater quantities,“ Tröstl says. „These results are the most important so far by the CLOUD experiment at CERN,“ stresses CERN researcher Jasper Kirkby, spokesperson of the CLOUD experiment. „When the nucleation and growth of pure biogenic aerosol particles is included in climate models, it should sharpen our understanding of the impact of human activities on clouds and climate.“

The two steps in the formation of new aerosol particles are described in the pair of articles in Nature. CERN researcher Jasper Kirkby is first author of the first Nature article; PSI researcher Jasmin Tröstl is first author of the second.

Aerosols high in the mountains

Additionally, the researchers investigated aerosol particle formation under real atmospheric conditions at the Jungfraujoch High Altitude Research Station. Situated at more than 3500 meters above sea level, this station lies above the lowest layer of the atmosphere – the planetary boundary layer. Aerosol particles from the planetary boundary layer can also be found at this altitude, because they can be carried up with the rising air. Additionally, newly formed particles can be found here, whose origin was inexplicable – until now. „Naturally, in contrast to the experiment at CERN, we could not limit ourselves to one individual substance as the precursor for the aerosol particles,“ explains Federico Bianchi, who took part in this project during his time as a researcher at the PSI and now works at the University of Helsinki. „In the process, we observed for the first time in a natural setting the formation of aerosol particles from sulfuric acid and ammonia. More importantly, we also were able to observe the formation of new aerosol particles from purely organic substances.“ Thus the results of the CLOUD chamber and Jungfraujoch measurements agree in showing that aerosol particles are indeed formed from purely organic precursors.

„Incidentally,“ Bianchi adds, „we could only observe aerosol formation on the Jungfraujoch at certain times, because the precursor molecules also come out of the lower atmospheric layers, and it appears that the conditions for this aerosol formation are only favourable within a time window of around two days following their ascent out of the planetary boundary layer.“

Bianchi is first author of the paper in Science, which presents the results of the Jungfraujoch studies.

Synergies between laboratory and field

The researchers used the same instruments for the observations on the Jungfraujoch and for the measurements in the CLOUD chamber. The heart of the system is a mass spectrometer – a complex piece of equipment with which many thousands of different chemical substances can be distinguished from each other. The device used was manufactured by the Swiss company TOFWERK AG in Thun. „This machine made it possible to determine the chemical composition in a matter of seconds,“ Bianchi says.

The publications also show how important it is to link laboratory and field experiments. Measurements in the lab allow for detailed investigations of individual mechanisms, but only a field experiment can provide information about whether or not this process is relevant in the real atmosphere. „And,“ says Urs Baltensperger, „the Jungfraujoch is one of the best sites worldwide to study this kind of process in the real free troposphere, thanks to its location, the clean air, and its infrastructure.“

Text: Paul Scherrer Institute/Paul Piwnicki

Participating institutions:

The experimental collaboration behind this research comprises 21 institutes: Aerodyne Research, California Institute of Technology, Carnegie Mellon University, CERN, Finnish Meteorological Institute, Goethe University Frankfurt, Helsinki Institute of Physics, Karlsruhe Institute of Technology, Lebedev Physical Institute, Leibniz Institute for Tropospheric Research, Paul Scherrer Institute, Tofwerk, University of Beira Interior, University of Eastern Finland, University of Helsinki, University of Innsbruck, University of Leeds, University of Lisbon, University of Manchester, University of Stockholm and University of Vienna.

The Jungfraujoch High Altitude Research Station is operated by the International Foundation High Altitude Research Stations Jungfraujoch and Gornergrat (HFSJG).

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 institute's own key research priorities are in the fields of matter and materials, energy and environment and human health. PSI is committed to the training of future generations. Therefore about one quarter of our staff are post-docs, post-graduates or apprentices. Altogether PSI employs 2000 people, thus being the largest research institute in Switzerland. The annual budget amounts to approximately CHF 370 million. PSI is part of the ETH Domain, with the other members being the two Swiss Federal Institutes of Technology, ETH Zurich and EPFL Lausanne, as well as Eawag (Swiss Federal Institute of Aquatic Science and Technology), Empa (Swiss Federal Laboratories for Materials Science and Technology) and WSL (Swiss Federal Institute for Forest, Snow and Landscape Research).


Prof. Dr. Urs Baltensperger, Head of the Laboratory for Atmospheric Chemistry,
Paul Scherrer Institute, 5232 Villigen PSI, Switzerland
Telephone: +41 56 310 24 08, mobile: +41 79 679 6534, e-mail: [German, English]

Dr. Jasmin Tröstl, Laboratory for Atmospheric Chemistry,
Paul Scherrer Institute, 5232 Villigen PSI, Switzerland
Mobile: +41 76 665 16 65, e-mail: [German, English]

Dr. Federico Bianchi, current address: Physics Dept., University of Helsinki, Finland
Telephone: +358 40 326 87 23, e-mail: [Italian, English]

Prof. Dr. Jasper Kirkby, CERN, EP Department, 1211 Genf, Switzerland
Telephone: +41 22 767 45 93, mobile: +41 75 411 40 19, e-mail: [English]

Original publications:

Ion-induced nucleation of pure biogenic particles
Jasper Kirkby et al.; Nature 26 May 2016

The role of low-volatility organic compounds in initial particle growth in the atmosphere
Jasmin Tröstl et al.; Nature 26 May 2016

New particle formation in the free troposphere: a question of chemistry and timing
Federico Bianchi et al.; Science 26 May 2016

Weitere Informationen: - Online version of this press release including additional images for download - Particle formation in the atmosphere - Climate research at the particle accelerator (in German only) - News from the smog chamber: mechanisms of particle formation in the atmosphere unveiled - Mystery solved: how fine particulates are formed in the air

Dagmar Baroke | idw - Informationsdienst Wissenschaft

Further reports about: Atmosphere CERN PSI Paul Scherrer aerosol particles droplets

More articles from Physics and Astronomy:

nachricht Sharpening the X-ray view of the nanocosm
23.03.2018 | Changchun Institute of Optics, Fine Mechanics and Physics

nachricht Drug or duplicate?
23.03.2018 | Fraunhofer-Institut für Angewandte Festkörperphysik IAF

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Space observation with radar to secure Germany's space infrastructure

Satellites in near-Earth orbit are at risk due to the steady increase in space debris. But their mission in the areas of telecommunications, navigation or weather forecasts is essential for society. Fraunhofer FHR therefore develops radar-based systems which allow the detection, tracking and cataloging of even the smallest particles of debris. Satellite operators who have access to our data are in a better position to plan evasive maneuvers and prevent destructive collisions. From April, 25-29 2018, Fraunhofer FHR and its partners will exhibit the complementary radar systems TIRA and GESTRA as well as the latest radar techniques for space observation across three stands at the ILA Berlin.

The "traffic situation" in space is very tense: the Earth is currently being orbited not only by countless satellites but also by a large volume of space...

Im Focus: Researchers Discover New Anti-Cancer Protein

An international team of researchers has discovered a new anti-cancer protein. The protein, called LHPP, prevents the uncontrolled proliferation of cancer cells in the liver. The researchers led by Prof. Michael N. Hall from the Biozentrum, University of Basel, report in “Nature” that LHPP can also serve as a biomarker for the diagnosis and prognosis of liver cancer.

The incidence of liver cancer, also known as hepatocellular carcinoma, is steadily increasing. In the last twenty years, the number of cases has almost doubled...

Im Focus: Researchers at Fraunhofer monitor re-entry of Chinese space station Tiangong-1

In just a few weeks from now, the Chinese space station Tiangong-1 will re-enter the Earth's atmosphere where it will to a large extent burn up. It is possible that some debris will reach the Earth's surface. Tiangong-1 is orbiting the Earth uncontrolled at a speed of approx. 29,000 km/h.Currently the prognosis relating to the time of impact currently lies within a window of several days. The scientists at Fraunhofer FHR have already been monitoring Tiangong-1 for a number of weeks with their TIRA system, one of the most powerful space observation radars in the world, with a view to supporting the German Space Situational Awareness Center and the ESA with their re-entry forecasts.

Following the loss of radio contact with Tiangong-1 in 2016 and due to the low orbital height, it is now inevitable that the Chinese space station will...

Im Focus: Alliance „OLED Licht Forum“ – Key partner for OLED lighting solutions

Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP, provider of research and development services for OLED lighting solutions, announces the founding of the “OLED Licht Forum” and presents latest OLED design and lighting solutions during light+building, from March 18th – 23rd, 2018 in Frankfurt a.M./Germany, at booth no. F91 in Hall 4.0.

They are united in their passion for OLED (organic light emitting diodes) lighting with all of its unique facets and application possibilities. Thus experts in...

Im Focus: Mars' oceans formed early, possibly aided by massive volcanic eruptions

Oceans formed before Tharsis and evolved together, shaping climate history of Mars

A new scenario seeking to explain how Mars' putative oceans came and went over the last 4 billion years implies that the oceans formed several hundred million...

All Focus news of the innovation-report >>>



Industry & Economy
Event News

New solar solutions for sustainable buildings and cities

23.03.2018 | Event News

Virtual reality conference comes to Reutlingen

19.03.2018 | Event News

Ultrafast Wireless and Chip Design at the DATE Conference in Dresden

16.03.2018 | Event News

Latest News

For graphite pellets, just add elbow grease

23.03.2018 | Materials Sciences

Unique communication strategy discovered in stem cell pathway controlling plant growth

23.03.2018 | Agricultural and Forestry Science

Sharpening the X-ray view of the nanocosm

23.03.2018 | Physics and Astronomy

Science & Research
Overview of more VideoLinks >>>