Scientists made an important step in order to better understand the relationships between vegetation and climate.
So-called extremely low-volatility organic compounds, which are produced by plants, could be detected for the first time during field and laboratory experiments in Finland and Germany. These organic species contribute to the formation of aerosol that can affect climate and air quality, they report in this week's issue of the journal Nature. The results may help to explain discrepancies between observations and theories about how volatile organic compounds produced by vegetation are converted into atmospheric aerosol – especially over forested regions.
Forests emit large amounts of volatile organic compounds (VOC). Their reaction products form the so-called secondary organic aerosol. In this case, gases are converted into particles that reflect solar radiation or act as nuclei for cloud droplets. These processes have a major influence on the climate and are therefore of special scientific interest. However, the model calculations have been very inaccurate, as there are still large gaps in our knowledge concerning the role of the compounds emitted by plants during the transition between gaseous and solid state. As long as these processes are poorly understood, it is difficult to give accurate predictions. This uncertainty also affects all climate models.
Large uncertainties do primarily exist regarding the growth of newly formed particles towards cloud nuclei on which water condenses, thus initiating the formation of clouds. The particle growth in the diameter range between about three and one hundred nanometers requires low-volatile organic vapors, as has been speculated. These "extremely low-volatility organic compounds (ELVOC)" have been hardly detected so far and their possible formation pathways are very speculative. Latest progress in the measurement techniques made their detection possible. Until recently, these compounds could not be measured because they are very short-lived. As soon as these molecules collide with a surfaces, they remain adsorbed and cannot be detected in the gas phase by analytical instruments. To prevent this, the ELVOCs are directly ionized under atmospheric conditions in the gas phase, and subsequently transported as an electrically charged ELVOC-molecule into the sensor (mass spectrometer), where the detection takes place. This powerful analytical method using mass spectrometric detection is called CI-APi-TOF (chemical ionization - atmospheric pressure interface time -of-flight mass spectrometry).
The newly released study by scientists from Finland, Germany, the USA and Denmark consists of several parts. The field measurements were carried out at the station of the University of Helsinki in Hyytiäla in southern Finland, which is typical for boreal forests, which cover eight percent of the earth's surface. The main part of the study comprises laboratory investigations performed in a reaction chamber at the Research Center Jülich. The Jülich Plant Atmosphere Chamber (JPAC) is a 1.5-cubic-meter glass chamber under controlled conditions of temperature, humidity and irradiation. "We have focused our efforts on the oxidation of α-pinene, because it accounts for about half of global monoterpene emissions," explains Dr. Mikael Ehn from the University of Helsinki, who is the first author of this study and did the pioneering work for the discovering of ELVOCs. Every forest visitor can recognize these compounds as the typical fir needle smell. "We managed to present the first molecular evidence of a direct and ubiquitous source of ELVOCs arising from the oxidation of monoterpenes and other volatile organic compounds in the gas phase." This produces vapors with relatively large molecules containing many hydrogen atoms as well as approximately the same number of oxygen as carbon atoms. "The results suggest that about 10 percent of the reacting VOC mass is converted tosecondary organic aerosol over the tree tops. Previous estimates were based on a share of less than 5 percent. This shows that the role of ozone (the oxidant of α-pinene and other monoterpenes) has been underestimated. There is still quite large uncertainty in climate models at this point," the lead author states. Mikael Ehn has been working on this study over four years and is glad that the international cooperation in the large team has made it possible not only to detect these new compounds but also to explain the mechanism that leads to the formation.
Measurements in the chemistry laboratory of the Leibniz Institute for Tropospheric Research (TROPOS) in Leipzig have also contributed to this result. The researchers let the needle scent α-pinene react with both "normal" ozone (16O3) and "labeled", heavier ozone (18O3), in order to determine the portion of heavy oxygen atoms (18O) in the formed ELVOCs. "These experiments allowed us a first insight into the formation mechanism of these compounds and provide the basis for a series of further experiments," as Dr. Torsten Berndt from TROPOS explains. Chemists from TROPOS investigate reactions of OH and other radicals since many years. The hydroxyl radical consisting of one hydrogen and one oxygen atom, is one of the most common free radicals in the air and is therefore often referred as the detergent of the atmosphere.
The new findings help to explain a significant part of the organic mass of aerosol particles in the air, which had remained mysterious to the scientists so far. Changes in the ratio of ozone to OH radicals could be an additional anthropogenic influence on the atmosphere. The formation of the new ELVOCs influences cloud formation and hence the climate, the scientists conclude. The new findings will help to better estimate different land use effects and especially the effects of vegetation on the climate . As a result, the climate models can be improved, which had not sufficiently taken into account the growth of nanoparticles caused by these compounds produced in boreal regions.
Publication: Mikael Ehn, Joel A. Thornton, Einhard Kleist, Mikko Sipila, Heikki Junninen, Iida Pullinen, Monika Springer, Florian Rubach, Ralf Tillmann, Ben Lee, Felipe Lopez-Hilfiker, Stefanie Andres, Ismail-Hakki Acir, Matti Rissanen, Tuija Jokinen, Siegfried Schobesberger, Juha Kangasluoma, Jenni Kontkanen, Tuomo Nieminen, Theo Kurtén, Lasse B. Nielsen, Solvejg Jørgensen, Henrik G. Kjaergaard, Manjula Canagaratna, Miikka Dal Maso, Torsten Berndt, Tuukka Petäjä, Andreas Wahner, Veli-Matti Kerminen, Markku Kulmala, Douglas R. Worsnop, Jürgen Wildt & Thomas F. Mentel (2014): A large source of low-volatility secondary organic aerosol. Nature, 506, 476-479. 27 February 2014. http://www.nature.com/doifinder/10.1038/nature13032
The research was funded by the Emil Aaltonen foundation, the US Department of Energy Office of Science, the European Research Council (ATMNUCLE), the European Commission (PEGASOS) and the Academy of Finland Center of Excellence.
Dr. Mikael Kristian Ehn (en. + fi.)
University of Helsinki
Dr. Torsten Berndt, Prof. Hartmut Herrmann
Leibniz Institute for Tropospheric Research (TROPOS)
phone +49-341-2717-7032, -7024
Tilo Arnhold, TROPOS Public Relations
Laboratory investigations on particle formation and early growth at TROPOS: http://www.tropos.de/en/research/atmospheric-aerosols/process-studies-on-small-spacial-and-temporal-scales/secondary-aerosol-formation/new-particle-formation-nucleation/laboratory-investigations-on-particle-formation-and-early-growth/
older press releases:
A new atmospherically relevant oxidant of sulphur dioxide - Nature (press release, 08 August 2012): http://www.colorado.edu/news/releases/2012/08/08/cu-led-team-discovers-new-atmospheric-compound-tied-climate-change-and
Tilo Arnhold | TROPOS
Research sheds new light on forces that threaten sensitive coastlines
24.04.2017 | Indiana University
NASA sees the end of ex-Tropical Cyclone 02W
21.04.2017 | NASA/Goddard Space Flight Center
More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.
Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...
Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.
"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...
The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.
Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...
The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...
Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.
Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...
20.04.2017 | Event News
18.04.2017 | Event News
03.04.2017 | Event News
24.04.2017 | Physics and Astronomy
24.04.2017 | Materials Sciences
24.04.2017 | Life Sciences