Can we measure the volatility?

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Air quality and climate are influenced by chemical processes in the atmosphere, with biogenic carbon playing an important role. In the journal Nature Geoscience, an international research team with the participation of physicists from Innsbruck is now presenting for the first time an overview of the organic carbons in the atmosphere over a forest area in the USA. A third of the total amount therefore consists of compounds that have not yet been measured.

In the summer of 2011, the National Center for Atmospheric Research in the USA assembled the most modern measuring instruments in Colorado to track down all the carbon in the atmosphere from biological sources. Researchers from the University of Innsbruck were there. They installed their electronic nose - a highly specialized device for measuring volatile organic compounds - at the foot of a 26-meter-high measuring tower. The field test took place in a largely untouched pine forest in the Rocky Mountains. The Innsbruck team around Armin Hansel and Thomas Karl worked with a proton exchange reaction time-of-flight mass spectrometer (PTR-ToF-MS), with which high-resolution measurements can be carried out and the carbon fluxes in the Can record atmosphere. This device was developed in Innsbruck and was used for the first time in the field test. "The PTR-TOF-MS can measure the tiniest amounts of organic trace substances in the air," explains Armin Hansel from the Institute for Ion Physics and Applied Physics at the University of Innsbruck. It is therefore particularly suitable for recording the carbon compounds given off by trees. During photosynthesis, around one percent of the carbon dioxide absorbed by the plant is released back into the atmosphere as volatile organic compounds. “With our method, we can measure these volatile trace substances particularly well, while the other instruments were more specialized in the less volatile compounds,” says Armin Hansel.

Follow the air currents

With a special measuring method - the so-called Eddy Covariance method - the Innsbruck researchers were able to continuously monitor the concentration of the various carbon compounds. For this purpose, up to ten measurements per second were carried out and the data later correlated with the wind speed. "In this way we can analyze the air movements in the atmosphere and follow the transport of the carbon compounds in slow motion," says Thomas Karl from the Institute for Atmospheric and Cryospheric Sciences. In this way, the researchers determined the volatile carbon compounds present over a certain forest area, depending on the wind direction. The most frequently measured chemical substances were monoterpenes and 2-methyl-3-buten-2-ol. The terpenes are responsible for the odor characteristic of coniferous forests.

On the trail of reaction products

From the data, the researchers were also able to read what happens to the carbons emitted by the trees in the atmosphere. “We wanted to know which compounds the carbons form and how gradually less and less volatile molecules are formed that later adhere to aerosols or condense on the ground and on plants.” This is not an easy task, because these carbon compounds form a large number of different oxidation products. For the first time, the research work provides a detailed picture of what organic carbon the coniferous forest releases, how it is oxidized in the atmosphere and where it ends up. Surprisingly, the proportion of previously unmeasured carbon compounds makes up a whole third of the total recorded amount. This creates the basis for creating a measurement-based budget for the local organic carbon budget for the first time.


The work was financially supported by the Austrian

Science Fund FWF and the Austrian Academy of Sciences.



Publication: Comprehensive characterization of atmospheric organic carbon at a forested site. James F. Hunter et al. Nature Geoscience 2017

DOI: 10.1038 / ngeo3018 (Link:


BLOCKING PERIOD: September 4, 2017, 5:00 p.m.