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.