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Proc Natl Acad Sci U S A. 2014 Oct 21;111(42):15019-24. doi: 10.1073/pnas.1404853111. Epub 2014 Oct 6.

Neutral molecular cluster formation of sulfuric acid-dimethylamine observed in real time under atmospheric conditions.

Author information

1
Institute for Atmospheric and Environmental Sciences, Goethe-University of Frankfurt, 60438 Frankfurt am Main, Germany; kuerten@iau.uni-frankfurt.de.
2
Department of Physics, University of Helsinki, 00014 Helsinki, Finland;
3
Institute for Atmospheric and Environmental Sciences, Goethe-University of Frankfurt, 60438 Frankfurt am Main, Germany;
4
Department of Physics, University of Helsinki, 00014 Helsinki, Finland; Helsinki Institute of Physics, University of Helsinki, 00014 Helsinki, Finland;
5
Institute for Atmospheric and Environmental Sciences, Goethe-University of Frankfurt, 60438 Frankfurt am Main, Germany; European Organization for Nuclear Research, CH-1211 Geneva, Switzerland;
6
Laboratory for Systems, Instrumentation and Modeling for Space and the Environment, University of Lisbon and University of Beira Interior, 1749-016 Lisbon, Portugal;
7
Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, 5232 Villigen, Switzerland;
8
Ionicon Analytik GmbH, 6020 Innsbruck, Austria; Institute for Ion Physics and Applied Physics, University of Innsbruck, 6020 Innsbruck, Austria;
9
Center for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, PA 15213;
10
Department of Physics, University of Helsinki, 00014 Helsinki, Finland; Helsinki Institute of Physics, University of Helsinki, 00014 Helsinki, Finland; European Organization for Nuclear Research, CH-1211 Geneva, Switzerland;
11
Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125;
12
Institute for Atmospheric and Environmental Sciences, Goethe-University of Frankfurt, 60438 Frankfurt am Main, Germany; Institute for Ion Physics and Applied Physics, University of Innsbruck, 6020 Innsbruck, Austria;
13
Tofwerk AG, 3600 Thun, Switzerland;
14
Department of Applied Physics, University of Eastern Finland, 70211 Kuopio, Finland; Finnish Meteorological Institute, 00101 Helsinki, Finland;
15
Department of Physics, University of Helsinki, 00014 Helsinki, Finland; Airmodus Ltd., 00560 Helsinki, Finland;
16
Solar and Cosmic Ray Research Laboratory, Lebedev Physical Institute, 119991 Moscow, Russia;
17
European Organization for Nuclear Research, CH-1211 Geneva, Switzerland;
18
Department of Physics, University of Helsinki, 00014 Helsinki, Finland; Institute for Ion Physics and Applied Physics, University of Innsbruck, 6020 Innsbruck, Austria;
19
Faculty of Physics, University of Vienna, 1090 Vienna, Austria;
20
Institute for Atmospheric and Environmental Sciences, Goethe-University of Frankfurt, 60438 Frankfurt am Main, Germany; Department of Physics, University of Helsinki, 00014 Helsinki, Finland;
21
School of Earth and Environment, University of Leeds, Leeds LS2 9JT, United Kingdom; and.
22
Department of Physics, University of Helsinki, 00014 Helsinki, Finland; Aerodyne Research Inc., Billerica, MA 01821.

Abstract

For atmospheric sulfuric acid (SA) concentrations the presence of dimethylamine (DMA) at mixing ratios of several parts per trillion by volume can explain observed boundary layer new particle formation rates. However, the concentration and molecular composition of the neutral (uncharged) clusters have not been reported so far due to the lack of suitable instrumentation. Here we report on experiments from the Cosmics Leaving Outdoor Droplets chamber at the European Organization for Nuclear Research revealing the formation of neutral particles containing up to 14 SA and 16 DMA molecules, corresponding to a mobility diameter of about 2 nm, under atmospherically relevant conditions. These measurements bridge the gap between the molecular and particle perspectives of nucleation, revealing the fundamental processes involved in particle formation and growth. The neutral clusters are found to form at or close to the kinetic limit where particle formation is limited only by the collision rate of SA molecules. Even though the neutral particles are stable against evaporation from the SA dimer onward, the formation rates of particles at 1.7-nm size, which contain about 10 SA molecules, are up to 4 orders of magnitude smaller compared with those of the dimer due to coagulation and wall loss of particles before they reach 1.7 nm in diameter. This demonstrates that neither the atmospheric particle formation rate nor its dependence on SA can simply be interpreted in terms of cluster evaporation or the molecular composition of a critical nucleus.

KEYWORDS:

aerosol particles; atmospheric chemistry; atmospheric nucleation; mass spectrometry

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