2016, Lehtipalo, Katrianne, Rondo, Linda, Kontkanen, Jenni, Schobesberger, Siegfried, Jokinen, Tuija, Sarnela, Nina, Kürten, Andreas, Ehrhart, Sebastian, Franchin, Alessandro, Nieminen, Tuomo, Kulmala, Markku, Riccobono, Francesco, Sipila, Mikko, Yli-Juuti, Taina, Duplissy, Jonathan, Adamov, Alexey, Ahlm, Lars, Almeida, Joa˜o, Amorim, Antonio, Bianchi, Federico, Breitenlechner, Martin, Dommen, Josef, Downard, Andrew J., Dunne, Eimear M., Flagan, Richard C., Guida, Roberto, Hakala, Jani, Hansel, Armin, Jud, Werner, Kangasluoma, Juha, Kerminen, Veli-Matti, Keskinen, Helmi, Kim, Jaeseok, Kirkby, Jasper, Kupc, Agnieszka, Kupiainen-Määttä, Oona, Laaksonen, Ari, Lawler, Michael J., Leiminger, Markus, Mathot, Serge, Olenius, Tinja, Ortega, Ismael K., Onnela, Antti, Petäjä, Tuukka, Praplan, Arnaud, Rissanen, Matti P., Ruuskanen, Taina, Santos, Filipe D., Schallhart, Simon, Schnitzhofer, Ralf, Simon, Mario, Smith, James N., Tröstl, Jasmin, Tsagkogeorgas, Georgios, Tomé, António, Vaattovaara, Petri, Vehkamäki, Hanna, Vrtala, Aron E., Wagner, Paul E., Williamson, Christina, Wimmer, Daniela, Winkler, Paul M., Virtanen, Annele, Donahue, Neil M., Carslaw, Kenneth S., Baltensperger, Urs, Riipinen, Ilona, Curtius, Joachim, Worsnop, Douglas R., Kulmala, Markku

The growth of freshly formed aerosol particles can be the bottleneck in their survival to cloud condensation nuclei. It is therefore crucial to understand how particles grow in the atmosphere. Insufficient experimental data has impeded a profound understanding of nano-particle growth under atmospheric conditions. Here we study nano-particle growth in the CLOUD (Cosmics Leaving OUtdoors Droplets) chamber, starting from the formation of molecular clusters. We present measured growth rates at sub-3 nm sizes with different atmospherically relevant concentrations of sulphuric acid, water, ammonia and dimethylamine. We find that atmospheric ions and small acid-base clusters, which are not generally accounted for in the measurement of sulphuric acid vapour, can participate in the growth process, leading to enhanced growth rates. The availability of compounds capable of stabilizing sulphuric acid clusters governs the magnitude of these effects and thus the exact growth mechanism. We bring these observations into a coherent framework and discuss their significance in the atmosphere.

2016, Kirkby, Jasper, Duplissy, Jonathan, Sengupta, Kamalika, Gordon, Hamish, Williamson, Christina, Heinritzi, Martin, Simon, Mario, Yan, Chao, Almeida, João, Tröstl, Jasmin, Nieminen, Tuomo, Ortega, Ismael K., Wagner, Robert, Adamov, Alexey, Amorim, Antonio, Bernhammer, Anne-Kathrin, Bianchi, Federico, Breitenlechner, Martin, Brilke, Sophia, Chen, Xuemeng, Craven, Jill, Dias, Antonio, Ehrhart, Sebastian, Flagan, Richard C., Franchin, Alessandro, Fuchs, Claudia, Guida, Roberto, Hakala, Jani, Hoyle, Christopher R., Jokinen, Tuija, Junninen, Heikki, Kangasluoma, Juha, Kim, Jaeseok, Krapf, Manuel, Kürten, Andreas, Laaksonen, Ari, Lehtipalo, Katrianne, Makhmutov, Vladimir, Mathot, Serge, Molteni, Ugo, Onnela, Antti, Peräkylä, Otso, Piel, Felix, Petäjä, Tuukka, Praplan, Arnaud P., Pringle, Kirsty, Rap, Alexandru, Richards, Nigel A.D., Riipinen, Ilona, Rissanen, Matti P., Rondo, Linda, Sarnela, Nina, Schobesberger, Siegfried, Scott, Catherine E., Seinfeld, John H., Sipilä, Mikko, Steiner, Gerhard, Stozhkov, Yuri, Stratmann, Frank, Tomé, Antonio, Virtanen, Annele, Vogel, Alexander L., Wagner, Andrea C., Wagner, Paul E., Weingartner, Ernest, Wimmer, Daniela, Winkler, Paul M., Ye, Penglin, Zhang, Xuan, Hansel, Armin, Dommen, Josef, Donahue, Neil M., Worsnop, Douglas R., Baltensperger, Urs, Kulmala, Markku, Carslaw, Kenneth S., Curtius, Joachim

Atmospheric aerosols and their effect on clouds are thought to be important for anthropogenic radiative forcing of the climate, yet remain poorly understood1. Globally, around half of cloud condensation nuclei originate from nucleation of atmospheric vapours2. It is thought that sulfuric acid is essential to initiate most particle formation in the atmosphere3,4, and that ions have a relatively minor role5. Some laboratory studies, however, have reported organic particle formation without the intentional addition of sulfuric acid, although contamination could not be excluded6,7. Here we present evidence for the formation of aerosol particles from highly oxidized biogenic vapours in the absence of sulfuric acid in a large chamber under atmospheric conditions. The highly oxygenated molecules (HOMs) are produced by ozonolysis of α-pinene. We find that ions from Galactic cosmic rays increase the nucleation rate by one to two orders of magnitude compared with neutral nucleation. Our experimental findings are supported by quantum chemical calculations of the cluster binding energies of representative HOMs. Ion-induced nucleation of pure organic particles constitutes a potentially widespread source of aerosol particles in terrestrial environments with low sulfuric acid pollution.

2016, Berndt, Torsten, Richters, Stefanie, Jokinen, Tuija, Hyttinen, Noora, Kurtén, Theo, Otkjær, Rasmus V., Kjaergaard, Henrik G., Stratmann, Frank, Herrmann, Hartmut, Sipila, Mikko, Kulmala, Markku, Ehn, Mikael

Explaining the formation of secondary organic aerosol is an intriguing question in atmospheric sciences because of its importance for Earth’s radiation budget and the associated effects on health and ecosystems. A breakthrough was recently achieved in the understanding of secondary organic aerosol formation from ozone reactions of biogenic emissions by the rapid formation of highly oxidized multifunctional organic compounds via autoxidation. However, the important daytime hydroxyl radical reactions have been considered to be less important in this process. Here we report measurements on the reaction of hydroxyl radicals with a- and b-pinene applying improved mass spectrometric methods. Our laboratory results prove that the formation of highly oxidized products from hydroxyl radical reactions proceeds with considerably higher yields than previously reported. Field measurements support these findings. Our results allow for a better description of the diurnal behaviour of the highly oxidized product formation and subsequent secondary organic aerosol formation in the atmosphere.