CLOUD project at CERN investigates particle formation of isoprene in the troposphere
Aerosol particles in the atmosphere play a central role in cloud formation and consequently influence solar radiation on its way to Earth. An international team of scientists from the Universities of Vienna and Innsbruck is researching their formation and growth mechanisms. In a recent study as part of the CLOUD project at CERN, they discovered that the hydrocarbon molecule isoprene contributes very efficiently to the formation of new particles under the cold conditions of the upper troposphere and thus influences cloud properties globally. The results appear in the renowned journal Nature.
Aerosol particles cool the climate directly by backscattering sunlight and indirectly through their effect as cloud condensation nuclei by influencing the formation and reflective properties of clouds. The aerosol particles thus counteract the warming greenhouse gases such as CO2; however, the exact proportions are unclear.
Aircraft measurements over the past 20 years make it clear that particle formation occurs on a large scale in the upper tropical troposphere, e.g. over the Amazon. Particle formation refers to the spontaneous condensation of trace gases through nucleation. While the mechanisms for this are still largely unknown, recent satellite observations have shown unexpectedly high concentrations of the molecule isoprene at these altitudes. Isoprene is emitted by trees, particularly in the Amazon basin, where it is transported into the upper troposphere by convective processes. After methane, isoprene is the most frequently emitted hydrocarbon in the atmosphere.
In the CLOUD experiment, scientists have now been able to show for the first time that the oxidized organic molecules derived from isoprene form new particles very efficiently under the cold conditions of the upper troposphere - in the -50 °C range. Moreover, the nucleation rates increased 100-fold when the smallest amounts of sulphuric acid were added, which explains the high numbers of particles observed in the upper troposphere. The oxidation products of isoprene also contribute to rapid particle growth. The newly formed particles can therefore influence cloud properties and thus the climate. In a parallel article in Nature, the (newly) identified mechanisms are confirmed by direct atmospheric aircraft measurements.
"The results show that isoprene significantly controls the formation of new particles over large areas of the upper tropical troposphere, although it tends to inhibit the formation of new particles near the ground," explains aerosol physicist and co-author of the study Paul Winkler from the University of Vienna. As a result of the growth and sinking to lower altitudes, these particles apparently represent a source of condensation nuclei of global importance for low-lying continental and maritime clouds, which have a particularly strong influence on the radiation balance.
"We assume that the biosphere produced more cloud condensation nuclei in the clean atmosphere of pre-industrial times, which means that the difference to the polluted atmosphere of today is significantly smaller than previously assumed," says Armin Hansel from the University of Innsbruck. The new results provide an important contribution to a more precise understanding of many different mechanisms that contribute to global warming. It is therefore to be expected that air pollution control measures, in particular the reduction of SO2 emissions, will not contribute as much to global warming as previously thought.
About CLOUD
The CLOUD (Cosmics Leaving OUtdoor Droplets) experiment at CERN is investigating how new aerosol particles form and grow in the atmosphere. CLOUD is led by an international consortium - consisting of 21 institutions - in which Austrian researchers from the Universities of Vienna and Innsbruck are also involved. The CLOUD measurement chamber was developed with CERN know-how and thus achieves significantly better defined measurement conditions than other comparable experiments. In CLOUD measurement campaigns, the physical and chemical state of the particles and gases is characterized using a variety of different measuring instruments.
A team led by Paul Winkler from the Faculty of Physics at the University of Vienna is involved with a measuring device with which the aerosol dynamics in the size range of approx. 1 to 10 nanometers, which is relevant for particle formation, can be quantitatively investigated.
Armin Hansel’s group specializes in the measurement of trace gases. Armin Hansel’s research group at the Institute of Ion Physics and Applied Physics at the University of Innsbruck has developed special measurement methods in close cooperation with the spin-off company Ionicon Analytik GmbH. Hansel’s team is regarded as an international pioneer in the field of trace analysis, as this technical innovation from Tyrol delivers real-time results with extremely high detection sensitivity.
Original publications:
Shen, J., et al. New particle formation from isoprene under upper tropospheric conditions. Nature (2024).
DOI: https://doi.org/10.1038/s41586’024 -08196-0
Curtius, J. et al. Isoprene nitrates drive new particle formation in Amazon’s upper troposphere. Nature (2024)
DOI: https://doi.org/10.1038/s41586’024 -08192-4
