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Published December 2, 2014 | Supplemental Material
Journal Article Open

Insight into Acid−Base Nucleation Experiments by Comparison of the Chemical Composition of Positive, Negative, and Neutral Clusters


We investigated the nucleation of sulfuric acid together with two bases (ammonia and dimethylamine), at the CLOUD chamber at CERN. The chemical composition of positive, negative, and neutral clusters was studied using three Atmospheric Pressure interface-Time Of Flight (APi-TOF) mass spectrometers: two were operated in positive and negative mode to detect the chamber ions, while the third was equipped with a nitrate ion chemical ionization source allowing detection of neutral clusters. Taking into account the possible fragmentation that can happen during the charging of the ions or within the first stage of the mass spectrometer, the cluster formation proceeded via essentially one-to-one acid−base addition for all of the clusters, independent of the type of the base. For the positive clusters, the charge is carried by one excess protonated base, while for the negative clusters it is carried by a deprotonated acid; the same is true for the neutral clusters after these have been ionized. During the experiments involving sulfuric acid and dimethylamine, it was possible to study the appearance time for all the clusters (positive, negative, and neutral). It appeared that, after the formation of the clusters containing three molecules of sulfuric acid, the clusters grow at a similar speed, independent of their charge. The growth rate is then probably limited by the arrival rate of sulfuric acid or cluster−cluster collision.

Additional Information

© 2014 American Chemical Society. Received: May 14, 2014; Revised: September 25, 2014; Accepted: October 7, 2014; Published: November 18, 2014. We would like to 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 P. Carrie, L.-P. De Menezes, J. Dumollard, K. Ivanova, F. Josa, I. Krasin, R. Kristic, A. Laassiri, O.S. Maksumov, B. Marichy, H. Martinati, S.V. Mizin, R. Sitals, A. Wasem, and M. Wilhelmsson for their important contributions to the experiment and the tofTools team for support in mass spectrometry data analysis. This research has 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 no. 57360 and ERC Advanced "ATMNUCLE" grant no. 227463), theGerman Federal Ministry of Education and Research (project nos. 01LK0902A and 01LK1222A), the Swiss National Science Foundation (project nos. 200020_135307 and 206620_141278), the Academy of Finland (Center of Excellence project no. 1118615), the Academy of Finland (135054, 133872, 251427, 139656, 139995, 137749, 141217, 141451, 138951), the Finnish Funding Agency for Technology and Innovation, the V.is.l. Foundation, the Nessling Foundation, the Austrian Science Fund (FWF; project no. J3198-N21), the Portuguese Foundation for Science and Technology (project no. 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), the U.S. National Science Foundation (grants AGS1136479 and CHE1012293), the PEGASOS project funded by the European Commission under the Framework Programme 7 (FP7-ENV-2010-265148), and the Davidow Foundation.

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