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Sci Adv. 2018 Nov 28;4(11):eaat9744. doi: 10.1126/sciadv.aat9744. eCollection 2018 Nov.

Ion-induced sulfuric acid-ammonia nucleation drives particle formation in coastal Antarctica.

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INAR-Institute for Atmospheric and Earth System Research, P.O. Box 64, 00014 University of Helsinki, Finland.
Finnish Meteorological Institute, Erik Palménin aukio 1, 00560 Helsinki, Finland.
Laboratory of Environmental Physics, Institute of Physics, University of Tartu, Tartu 50090, Estonia.
CERN, CH1211 Geneva, Switzerland.
Aerodyne Research Inc., Billerica, MA 01821, USA.
Goethe University Frankfurt, Institute for Atmospheric and Environmental Sciences, 60438 Frankfurt am Main, Germany.


Formation of new aerosol particles from trace gases is a major source of cloud condensation nuclei (CCN) in the global atmosphere, with potentially large effects on cloud optical properties and Earth's radiative balance. Controlled laboratory experiments have resolved, in detail, the different nucleation pathways likely responsible for atmospheric new particle formation, yet very little is known from field studies about the molecular steps and compounds involved in different regions of the atmosphere. The scarcity of primary particle sources makes secondary aerosol formation particularly important in the Antarctic atmosphere. Here, we report on the observation of ion-induced nucleation of sulfuric acid and ammonia-a process experimentally investigated by the CERN CLOUD experiment-as a major source of secondary aerosol particles over coastal Antarctica. We further show that measured high sulfuric acid concentrations, exceeding 107 molecules cm-3, are sufficient to explain the observed new particle growth rates. Our findings show that ion-induced nucleation is the dominant particle formation mechanism, implying that galactic cosmic radiation plays a key role in new particle formation in the pristine Antarctic atmosphere.

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