title: New particle formation in the free troposphere: A question of chemistry and timing.
abstract: New particle formation (NPF) is the source of over half of the atmosphere's cloud condensation nuclei, thus influencing cloud properties and Earth's energy balance. Unlike in the planetary boundary layer, few observations of NPF in the free troposphere exist. We provide observational evidence that at high altitudes, NPF occurs mainly through condensation of highly oxygenated molecules (HOMs), in addition to taking place through sulfuric acid-ammonia nucleation. Neutral nucleation is more than 10 times faster than ion-induced nucleation, and growth rates are size-dependent. NPF is restricted to a time window of 1 to 2 days after contact of the air masses with the planetary boundary layer; this is related to the time needed for oxidation of organic compounds to form HOMs. These findings require improved NPF parameterization in atmospheric models.
authors.affiliation: Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, 5232 Villigen, Switzerland. Institute for Atmospheric and Climate Science, ETH Zurich, 8092 Zurich, Switzerland. Department of Physics, University of Helsinki, 00014 Helsinki, Finland. federico.bianchi@psi.ch urs.baltensperger@psi.ch.
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authors.affiliation: Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, 5232 Villigen, Switzerland.
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authors.affiliation: Department of Physics, University of Helsinki, 00014 Helsinki, Finland.
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authors.affiliation: Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, 5232 Villigen, Switzerland.
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authors.affiliation: Empa, Swiss Federal Laboratories for Materials Science and Technology, 8600 Dübendorf, Switzerland.
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authors.affiliation: Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, 5232 Villigen, Switzerland. WSL (Swiss Federal Institute for Forest, Snow and Landscape Research) Institute for Snow and Avalanche Research SLF, 7260 Davos, Switzerland.
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authors.affiliation: Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, 5232 Villigen, Switzerland.
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authors.affiliation: Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, 5232 Villigen, Switzerland.
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authors.affiliation: Department of Physics, University of Helsinki, 00014 Helsinki, Finland.
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authors.affiliation: Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, 5232 Villigen, Switzerland.
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authors.affiliation: Department of Physics, University of Helsinki, 00014 Helsinki, Finland.
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authors.affiliation: Department of Physics, University of Helsinki, 00014 Helsinki, Finland. Helsinki Institute of Physics, University of Helsinki, 00014 Helsinki, Finland.
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authors.affiliation: Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, 5232 Villigen, Switzerland.
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authors.affiliation: Tofwerk, 3600 Thun, Switzerland.
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authors.affiliation: Department of Physics, University of Helsinki, 00014 Helsinki, Finland.
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authors.affiliation: Department of Physics, University of Helsinki, 00014 Helsinki, Finland.
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authors.affiliation: Institute for Atmospheric and Environmental Sciences, Goethe University Frankfurt, 60438 Frankfurt am Main, Germany.
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authors.lastname: Kürten
authors.affiliation: Department of Physics, University of Helsinki, 00014 Helsinki, Finland.
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authors.lastname: Manninen
authors.affiliation: Institute for Atmospheric and Environmental Sciences, Goethe University Frankfurt, 60438 Frankfurt am Main, Germany.
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authors.lastname: Münch
authors.affiliation: Department of Physics, University of Helsinki, 00014 Helsinki, Finland.
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authors.affiliation: Department of Physics, University of Helsinki, 00014 Helsinki, Finland.
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authors.lastname: Petäjä
authors.affiliation: Institute for Atmospheric and Environmental Sciences, Goethe University Frankfurt, 60438 Frankfurt am Main, Germany.
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authors.lastname: Rondo
authors.affiliation: Institute for Atmospheric and Environmental Sciences, Goethe University Frankfurt, 60438 Frankfurt am Main, Germany.
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authors.affiliation: Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, 5232 Villigen, Switzerland.
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authors.lastname: Weingartner
authors.affiliation: Institute for Atmospheric and Environmental Sciences, Goethe University Frankfurt, 60438 Frankfurt am Main, Germany.
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authors.affiliation: Department of Physics, University of Helsinki, 00014 Helsinki, Finland. Aerodyne Research, Billerica, MA 01821, USA.
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authors.lastname: Worsnop
authors.affiliation: Department of Physics, University of Helsinki, 00014 Helsinki, Finland.
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authors.affiliation: Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, 5232 Villigen, Switzerland.
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authors.affiliation: Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, 5232 Villigen, Switzerland. federico.bianchi@psi.ch urs.baltensperger@psi.ch.
authors.forename: U
authors.initials: U
authors.lastname: Baltensperger