Abstract
The formation of secondary particles in the atmosphere accounts for more than half of global cloud condensation nuclei. Experiments at the CERN CLOUD (Cosmics Leaving OUtdoor Droplets) chamber have underlined the importance of ions for new particle formation, but quantifying their effect in the atmosphere remains challenging. By using a novel instrument setup consisting of two nanoparticle counters, one of them equipped with an ion filter, we were able to further investigate the ion-related mechanisms of new particle formation. In autumn 2015, we carried out experiments at CLOUD on four systems of different chemical compositions involving monoterpenes, sulfuric acid, nitrogen oxides, and ammonia. We measured the influence of ions on the nucleation rates under precisely controlled and atmospherically relevant conditions. Our results indicate that ions enhance the nucleation process when the charge is necessary to stabilize newly formed clusters, i.e., in conditions in which neutral clusters are unstable. For charged clusters that were formed by ion-induced nucleation, we were able to measure, for the first time, their progressive neutralization due to recombination with oppositely charged ions. A large fraction of the clusters carried a charge at 1.5 nm diameter. However, depending on particle growth rates and ion concentrations, charged clusters were largely neutralized by ion-ion recombination before they grew to 2.5 nm. At this size, more than 90 % of particles were neutral. In other words, particles may originate from ion-induced nucleation, although they are neutral upon detection at diameters larger than 2.5 nm. Observations at Hyytiälä, Finland, showed lower ion concentrations and a lower contribution of ion-induced nucleation than measured at CLOUD under similar conditions. Although this can be partly explained by the observation that ion-induced fractions decrease towards lower ion concentrations, further investigations are needed to resolve the origin of the discrepancy.
| Original language | English |
|---|---|
| Pages (from-to) | 15181-15197 |
| Journal | Atmospheric Chemistry and Physics |
| Volume | 17 |
| Issue number | 24 |
| DOIs | |
| Publication status | Published - 21 Dec 2017 |
| MoE publication type | A1 Journal article-refereed |
Funding
Acknowledgements. We thank the European Organization for Nuclear Research (CERN) for supporting CLOUD with important technical and financial resources and 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 contributions to the experiment. This research was supported by the EC Seventh Framework Programme (Marie Curie ITN CLOUD-TRAIN, no. 316662; advanced grant, ATMNUCLE, no. 227463; consolidator grant NANODYNAMITE, no. 616075; starting grant QAPPA, no. 335478; starting grant MOCAPAF, no. 257360; MC-COFUND CERN-COFUND-2012, no. 600377), EC Horizon 2020 (Marie Skłodowska-Curie Individual Fellowships Nano-CAVa, no. 656994; starting grant COALA, no. 638703), German Federal Ministry of Education and Research (nos. 01LK1222A and 01LK0902A), Presidium of the Russian Academy of Sciences and Russian Foundation for Basic Research (grants 08-02-91006-CERN and 12-02-91522-CERN), US Department of Energy (no. DE-SC0014469), Swiss National Science Foundation (206620_141278, 200020_135307, 200021_140663, 206021_144947/1), Austrian Science Fund (J3198-N21, L593, P19546), Portuguese Foundation for Science and Technology (CERN/FP/116387/2010), Swedish Research Council (2011-5120), US National Science Foundation (AGS1136479, AGS1447056, AGC1439551, CHE1012293), Natural Environment Research Council (NE/J024252/1, NE/K015966/1), Royal Society (Wolfson Merit Award), Dreyfus Award (EP-11-117), European Funds for Regional Economic Development (Labex-Cappa grant, ANR-11-LABX-0005-01), Nessling Foundation, Finnish Funding Agency for Technology and Innovation, Väisälä Foundation, Caltech Environmental Science and Engineering grant (Davidow Foundation), French National Research Agency, Nord-Pas de Calais, and the Academy of Finland (nos. 299574, 1118615, 135054, 133872, 251427, 139656, 139995, 141451, 137749, 141217, 138951).