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Published August 25, 2011 | Supplemental Material
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Role of sulphuric acid, ammonia and galactic cosmic rays in atmospheric aerosol nucleation


Atmospheric aerosols exert an important influence on climate through their effects on stratiform cloud albedo and lifetime and the invigoration of convective storms. Model calculations suggest that almost half of the global cloud condensation nuclei in the atmospheric boundary layer may originate from the nucleation of aerosols from trace condensable vapours, although the sensitivity of the number of cloud condensation nuclei to changes of nucleation rate may be small. Despite extensive research, fundamental questions remain about the nucleation rate of sulphuric acid particles and the mechanisms responsible, including the roles of galactic cosmic rays and other chemical species such as ammonia. Here we present the first results from the CLOUD experiment at CERN. We find that atmospherically relevant ammonia mixing ratios of 100 parts per trillion by volume, or less, increase the nucleation rate of sulphuric acid particles more than 100–1,000-fold. Time-resolved molecular measurements reveal that nucleation proceeds by a base-stabilization mechanism involving the stepwise accretion of ammonia molecules. Ions increase the nucleation rate by an additional factor of between two and more than ten at ground-level galactic-cosmic-ray intensities, provided that the nucleation rate lies below the limiting ion-pair production rate. We find that ion-induced binary nucleation of H_(2)SO_(4)–H_(2)O can occur in the mid-troposphere but is negligible in the boundary layer. However, even with the large enhancements in rate due to ammonia and ions, atmospheric concentrations of ammonia and sulphuric acid are insufficient to account for observed boundary-layer nucleation.

Additional Information

© 2011 Nature Publishing Group, a division of Macmillan Publishers Limited. Received: 09 September 2010; Accepted: 24 June 2011; Published online: 24 August 2011. We thank CERN for supporting CLOUD with important technical and financial resources, and for providing a particle beam from the CERN Proton Synchrotron. We also thank J.-L. Agostini, S. Atieh, J. Baechler, D. Bloess, G. Bowden, A. Braem, T. Callamand, A. Castel, L.-P. De Menezes, G. Favre, L. Ferreira, L. Gatignon, D. Gregorio, M. Guinchard, E. Ivanova, F. Josa, I. Krasin, R. Kristic, A. Kuzmin, O. Maksumov, S. Mizin, R. Richter, R. Sitals, A. Vacca, R. Veenhof, A. Wasem and M. Wilhelmsson for their contributions to the experiment. This research has received funding from the EC Seventh Framework Programme under grant agreement no. 215072 (Marie Curie Initial Training Network, 'CLOUD-ITN') and ERC-Advanced Grant 'ATMNUCLE' no. 227463, the German Federal Ministry of Education and Research (project no. 01LK0902A), the Swiss National Science Foundation (project nos 206621_125025 and 206620_130527), the Academy of Finland Center of Excellence program (project no. 1118615), the Austrian Science Fund (FWF; project nos P19546 and L593), and the Russian Academy of Sciences and Russian Foundation for Basic Research (grant N08-02-91006-CERN). Author Contributions: J.A. performed the nucleation rate analysis. S.S. conducted the APi-TOF analysis. J.A., F.B., M.B., A. Downard, E.D., J. Duplissy, S.E., A.F., S.G., D.H., L.I., W.J., J.K., F.K., A. Ku¨ rten, A. Kupc, K.L., V.M., A.M., T.N., F.R., L.R., R.S., S.S., Y.S., G.T. and D.W. conducted the data collection and analysis. J.A., K.S.C., J.C., E.D., S.E., L.I., E.R.L. and F.S. performed the modelling. J.K. wrote the manuscript. U.B., K.S.C., J.C., J.K., M.K., J.H.S. and D.R.W. did data interpretation and editing of the manuscript. All authors contributed to the development of the CLOUD facility and analysis instruments, and commented on the manuscript.

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August 19, 2023
October 24, 2023