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Published October 17, 2013 | Supplemental Material + Published
Journal Article Open

Molecular understanding of sulphuric acid–amine particle nucleation in the atmosphere


Nucleation of aerosol particles from trace atmospheric vapours is thought to provide up to half of global cloud condensation nuclei. Aerosols can cause a net cooling of climate by scattering sunlight and by leading to smaller but more numerous cloud droplets, which makes clouds brighter and extends their lifetimes. Atmospheric aerosols derived from human activities are thought to have compensated for a large fraction of the warming caused by greenhouse gases. However, despite its importance for climate, atmospheric nucleation is poorly understood. Recently, it has been shown that sulphuric acid and ammonia cannot explain particle formation rates observed in the lower atmosphere3. It is thought that amines may enhance nucleation, but until now there has been no direct evidence for amine ternary nucleation under atmospheric conditions. Here we use the CLOUD (Cosmics Leaving OUtdoor Droplets) chamber at CERN and find that dimethylamine above three parts per trillion by volume can enhance particle formation rates more than 1,000-fold compared with ammonia, sufficient to account for the particle formation rates observed in the atmosphere. Molecular analysis of the clusters reveals that the faster nucleation is explained by a base-stabilization mechanism involving acid–amine pairs, which strongly decrease evaporation. The ion-induced contribution is generally small, reflecting the high stability of sulphuric acid–dimethylamine clusters and indicating that galactic cosmic rays exert only a small influence on their formation, except at low overall formation rates. Our experimental measurements are well reproduced by a dynamical model based on quantum chemical calculations of binding energies of molecular clusters, without any fitted parameters. These results show that, in regions of the atmosphere near amine sources, both amines and sulphur dioxide should be considered when assessing the impact of anthropogenic activities on particle formation.

Additional Information

© 2013 Nature Publishing Group, a division of Macmillan Publishers Limited. This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License. Received 4 March; accepted 17 September 2013; Published online 6 October 2013. We thank J.-L. Agostini, P. Carrie, L.-P. De Menezes, F. Josa, I. Krasin, R. Kristic, O.S. Maksumov, S.V. Mizin, R. Sitals, A. Wasem and M. Wilhelmsson for their contributions to the experiment, and D. Hanson and P. McMurry for discussions on their unpublished measurements of ambient gas-phase amines. We thank the CSC Centre for Scientific Computing in Espoo, Finland, for computer time, and J. Pierce and P. Paasonen for discussions. We thank CERN for supporting CLOUD with technical and financial resources, and for providing a particle beam from the CERN Proton Synchrotron. This research received funding from the EC Seventh Framework Programme (Marie Curie Initial Training Network 'CLOUD-ITN' no. 215072, MC-ITN 'CLOUD-TRAIN' no. 316662, ERC-Starting 'MOCAPAF' grant 57360 and ERC-Advanced 'ATMNUCLE' grant 227463), the German Federal Ministry of Education and Research (projects 01LK0902A and 01LK1222A), the Swiss National Science Foundation (projects 200020_135307 and 206620_130527), the Academy of Finland (Center of Excellence project 1118615), the Academy of Finland (135054, 133872, 251427, 139656, 139995, 137749, 141217 and 141451), the Finnish Funding Agency for Technology and Innovation, the Väisälä Foundation, the Nessling Foundation, the Austrian Science Fund (FWF; projects P19546 and L593), the Portuguese Foundation for Science and Technology (project CERN/FP/116387/2010), the Swedish Research Council, Vetenskapsrådet (grant 2011-5120), the Presidium of the Russian Academy of Sciences and Russian Foundation for Basic Research (grants 08-02-91006-CERN and 12-02-91522-CERN), and the US National Science Foundation (grants AGS1136479 and CHE1012293).

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