Press releases – May 2016

FRANKFURTAerosol particles generated by human activity counteract the warming of the earth's atmosphere by greenhouse gases. However, this effect might be smaller than first thought, as many particles were already generated from tree emissions in pre-industrial times. This was the finding of a simulation carried out as part of the international CLOUD experiment, in which researchers from the Goethe University played a major role. The results are published in the form of three papers in the renowned journals "Science" and "Nature".

"These results are the most important so far by the CLOUD experiment at CERN", said CLOUD spokesperson Jasper Kirkby, Honorary Professor at the Goethe University. "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."

Professor Joachim Curtius from the Institute for Atmospheric and Environmental Sciences at the Goethe University added: "We believe that the newly discovered process will mean that we will have to reassess cloud formation in earlier times, as there must have been more particles present than we had previously assumed. There would therefore be less of a difference between the situation then and now than previously thought."

The CLOUD experiment is looking at how new aerosol particles form in the atmosphere and their effect on climate. As the aerosol particles increase, as is the case due to human activities, more sunlight is reflected and more cloud droplets form, making the clouds brighter. In order to estimate the cooling effect caused by anthropogenic influences, it is necessary to know the quantities of aerosols present in the pre-industrial age. As direct measurement is not an option, the effects are simulated through reliable laboratory tests such as the CLOUD experiment, and then applied to climate modelling.

In pre-industrial times, the organic compounds emitted by trees were a major contributing factor in the formation of aerosols. The researchers examined alpha-pinene, a substance that gives pine forests their characteristic pleasant smell. They are among the most important biogenic emissions. Alpha-pinene is rapidly oxidised on exposure to ozone and the ensuing reaction chains create some extremely low-volatility substances. However, these only occur in very small concentrations of around one molecule per one trillion air molecules.

The CLOUD experiments show that these extremely low-volatility organic compounds are very efficient at forming new particles. This process occurs under atmospheric conditions, even in the absence of sulphuric acid. It had been assumed that sulphuric acid was virtually always involved in particle formation in the atmosphere. The main source of sulphuric acid in the atmosphere is sulphur dioxide, which is generated by the burning of fossil fuels.

Furthermore, the researchers discovered that ions from cosmic rays strongly enhance the production rate of the organic particles - by a factor of 10-100 compared to particle formation without ions, provided the concentrations of the particle-forming gases are low. "Furthermore, our studies show that these low-volatility organic substances also dominate particle growth in unpolluted environments across the entire size range from clusters of just a few molecules all the way up to sizes of 50-100 nm, where the particles are large enough to be able to seed cloud droplets", explained Joachim Curtius. The growth rates accelerate as the particles increase in size, because more and more oxidation products, also those of higher volatility, are able to condense on the expanding particles. This process is described in quantitative terms with a condensation model for the various organic substances.

Why is this knowledge important for our understanding of the climate? This may well be a very important mechanism, because it is so efficient in terms of the formation of organic particles under natural conditions. As soon as the particles have formed, they grow through the condensation of other similar oxygenated organic compounds. The rapid growth of the newly-formed particles means that they lose a smaller percentage through collisions with pre-existing large particles. As a result more particles grow to sizes that have the potential to seed clouds and influence the climate.

Another paper that appears in the same issue of "Science" reports on observations from the observatory on the Jungfraujoch, which detected pure organic nucleation in the free troposphere. This proves the relevance of the CLOUD laboratory experiments for the atmosphere.

Here you can find an image to download.

Caption (fltr): Mario Simon, Martin Heinritzi, Andreas Kürten, Andrea Wagner and Joachim Curtius with the mass spectrometer they developed. This is used to measure the highly oxygenated multifunctional   organic molecules and molecule clusters, which are responsible for particle generation and particle growth in the recent CLOUD experiments.

Publications:

Kirkby, J. et al.: Ion-induced nucleation of pure biogenic particles, in: Nature, doi:10.1038/nature17953

Tröstl, J. et al.: The role of low-volatility organic compounds in initial particle growth in the atmosphere, in: Nature, doi:10.1038/nature18271.

Bianchi, F. et al.: New particle formation in the free troposphere: A question of

chemistry and timing, in: Science, doi 10.1126/science.aad5456, 2016

Information: Prof. Dr. Joachim Curtius, Institute for Atmosphere and Environment, Goethe University, Campus Riedberg, Phone +49(0)69 798-40258, curtius@iau.uni-frankfurt.de.

This year the most important award in the field of metrology, the science of making precise measurements, was awarded to a team of five Frankfurt atomic physicists at Goethe University: Prof. Reinhard Dörner, Associate Prof. Dr. Till Jahnke, Dr. Maksim Kunitzki, Dr. Jörg Voigtsberger and Stefan Zeller. The Helmholtz award includes an endowment of Euro 20,000 and is awarded to European researchers every three years.

The award recipients succeeded in measuring the extremely weak binding energy of helium molecules with a previously unachievable precision. Chemistry teaches us that helium as a noble gas doesn't form bonds. However, this becomes possible under certain circumstances predicted by quantum theory. The study group under Dörner has measured this binding energy indirectly with the COLTRIMS reaction microscope developed at Goethe University. It can be used to measure the location and speed of decaying molecules at the same time with a high level of accuracy, and this data can be used to reconstruct the original configuration. The award winners focused on rare molecules composed of two or three helium atoms.

"It started with the German Research Foundation approving me for a Koselleck project with funding of over 1.25 million in 2009. This is a kind of venture capital, which the DFG uses to support experiments with a long lead time", Prof. Reinhard Dörner from the Institute for Nuclear Physics explains. Dr. Till Jahnke laid the foundation for the equipment, then doctoral candidate Jörg Voigtsberger took over the experiment and achieved initial successes. The next doctoral candidate, Stefan Zeller, was able to make significant improvements to the equipment and to further increase the precision. To do so, he had to direct the largest "photon canon" in Germany, the "Free Electron Laser FLASH" at the DESY research centre in Hamburg, at the extremely weakly bonded helium molecules. In this way he was able to determine the binding energy with a precision of a few nano-electron volts. This means that the binding energy of the helium molecules is one-hundred million times weaker than in a water molecule, for example.

The series of experiments culminated this past year with the dicovery of the so-called Efimov state for a helium molecule made up of three atoms. This comparatively huge molecule predicted 40 years ago by the Russian theorist Vitaly Efimov, can only exist in the tunnel effect established by quantum physics. The postdoc Maksim Kunitzki succeeded in making this measurement with the same equipment.

"All Helmholtz Award winners to date have significantly advanced the art of measuring and many of them are among the most renowned researchers in the field of metrology today", said Dr. Joachim Ullrich, President of the National Metrology Institute of Germany (PTB) and Chairman of the Helmholtz Fund. "We are confident that this will also hold true this time." Researchers at the University of Cambridge are also distinguished with the Helmholtz Award for their method of measuring individual molecules using nano-pores, a proven method in DNA analysis. They have created a method for theoretically detecting any number of different protein molecules in the same measurement. The award will be presented on 22 June 2016 in the conference centre of the National Metrology Institute of Germany (PTB).

The Frankfurt award winners have already received several other rewards for their work: In 2013 Till Jahnke was awarded the most important young scientistaward of the Deutsche Physikalische Gesellschaft, the Gustav Hertz Award. The following year, Reinhard Dörner was distinguished with the renowned Robert Wichard Pohl Award by the Deutsche Physikalische Gesellschaft.In 2015, Maksim Kunitski received an award from the "Frankfurter Förderverein für physikalische Grundlagenforschung".

A picture is available for downloading here: www.uni-frankfurt.de/61204234

Caption: Prof. Reinhard Dörner (left) and Maksim Kunitski in front of the equipment used to complete the outstanding work.

Information: Prof. Reinhard Dörner, Institut für Kernphysik, Max-von-Laue-Str. 1, Tel: (069) 798-47003, doerner@atom.uni-frankfurt.de