Role of sulphuric acid, ammonia and galactic cosmic rays in atmospheric aerosol nucleation

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Atmospheric aerosols exert an important influence on climate1 through their effects on stratiform cloud albedo and lifetime2 and the invigoration of convective storms3. Model calculations suggest that almost half of the global cloud condensation nuclei in the atmospheric boundary layer may originate from the nucleation of aerosols from trace condensable vapours4, although the sensitivity of the number of cloud condensation nuclei to changes of nucleation rate may be small5, 6. Despite extensive research, fundamental questions remain about the nucleation rate of sulphuric acid particles and the mechanisms responsible, including the roles of galactic cosmic rays and other chemical species such as ammonia7. Here we present the first results from the CLOUD experiment at CERN. We find that atmospherically relevant ammonia mixing ratios of 100 parts per trillion by volume, or less, increase the nucleation rate of sulphuric acid particles more than 100–1,000-fold. Time-resolved molecular measurements reveal that nucleation proceeds by a base-stabilization mechanism involving the stepwise accretion of ammonia molecules. Ions increase the nucleation rate by an additional factor of between two and more than ten at ground-level galactic-cosmic-ray intensities, provided that the nucleation rate lies below the limiting ion-pair production rate. We find that ion-induced binary nucleation of H2SO4–H2O can occur in the mid-troposphere but is negligible in the boundary layer. However, even with the large enhancements in rate due to ammonia and ions, atmospheric concentrations of ammonia and sulphuric acid are insufficient to account for observed boundary-layer nucleation.

At a glance


  1. Plots of nucleation rate against H2SO4 concentration.
    Figure 1: Plots of nucleation rate against H2SO4 concentration.

    Neutral, GCR and charged (pion beam) nucleation rates are shown at 1.7nm diameter, J1.7, as a function of sulphuric acid concentration at 38% relative humidity. a, Rates at 292K; b, rates at 248K (blue) and 278K (green). The NH3 mixing ratios correspond to the contaminant level (<35p.p.t.v. at 278 and 292K; <50p.p.t.v. at 248K). Triangles, Jch; filled circles, Jgcr; open circles, Jn. The predictions of the PARNUC model30 for binary H2SO4–H2O charged nucleation, Jch, are indicated by the coloured bands. The fitted curves are drawn to guide the eye. The error bars indicate the estimated total statistical and systematic 1σ measurement uncertainties, although the overall factor 2 systematic scale uncertainty on [H2SO4] is not shown.

  2. Plots of nucleation rate against negative ion concentration.
    Figure 2: Plots of nucleation rate against negative ion concentration.

    Nucleation rates as a function of negative ion concentration at 292K and [H2SO4] = 4.5×108cm−3 (purple line), and at 278K and [H2SO4] = 1.5×108cm−3 (green line). Triangles, Jch; filled circles, Jgcr; open circles, Jn. All measurements were made at 38% relative humidity and 35p.p.t.v. NH3. Neutral nucleation rates, Jn, were effectively measured at zero ion pair concentration (ion or charged-cluster lifetime <1 s). The curves are fits of the form J = j0+k[ion]p, where j0, k and p are free parameters. The error bars indicate only the point-to-point 1σ errors; the nucleation rates and ion concentrations each have estimated overall scale uncertainties of ±30%.

  3. Ion cluster composition.
    Figure 3: Ion cluster composition.

    a–d, The chemical composition of charged nucleating clusters at 248K (<35p.p.t.v. NH3) (a), 278K (<35p.p.t.v. NH3) (b), 292K (<35p.p.t.v. NH3) (c) and 292K (230p.p.t.v. NH3) (d). The cluster spectra are averaged over the steady-state nucleation period. To simplify the figures, only the overall envelopes are shown for organic species. The concentrations are approximately corrected for detection efficiency.

  4. Plots of nucleation rate against NH3 concentration.
    Figure 4: Plots of nucleation rate against NH3 concentration.

    Nucleation rates are shown as a function of ammonia mixing ratio. a, At 292K and [H2SO4] = 1.5×108cm−3 (curves) and 4.3×107cm−3 (straight lines); b, at 278K and [H2SO4] = 6.3×107cm−3. All measurements were made at 38% relative humidity. Triangles, Jch; filled circles, Jgcr; open circles, Jn. The fitted lines are drawn to guide the eye. The bars indicate 1σ total errors, although the overall ammonia scale uncertainty of a factor 2 is not shown.

  5. Nucleation rate comparison.
    Figure 5: Nucleation rate comparison.

    Comparison of CLOUD data with measurements of the nucleation rate of new particles as a function of [H2SO4] in the atmospheric boundary layer (pale filled circles8, 33 and pale open circles32) and with recent laboratory experiments at room temperature (grey19 and orange29 lines). The CLOUD data (large, darker symbols and lines) show the galactic cosmic ray nucleation rates, Jgcr, measured at 248K (blue), 278K (green) and 292K (red) and at NH3 mixing ratios of <35 p.p.t.v. (open green and red circles), <50p.p.t.v. (open blue circles), 150p.p.t.v. (filled blue and green circles) and 190 p.p.t.v. (filled red circles). The bars indicate 1σ total errors, although the overall factor 2 scale uncertainty on [H2SO4] is not shown. The measurements at 278 and 292K bracket the typical range of boundary-layer temperatures, whereas those at 248K reflect exceptionally cold conditions. Ion-induced nucleation in the boundary layer is limited by the ion-pair production rate to a maximum of about 4cm−3s−1.


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Author information


  1. CERN, CH-1211 Geneva, Switzerland

    • Jasper Kirkby,
    • Jonathan Duplissy,
    • André David,
    • Stefan Haider,
    • Serge Mathot,
    • Pierre Minginette &
    • Antti Onnela
  2. Goethe-University of Frankfurt, Institute for Atmospheric and Environmental Sciences, 60438 Frankfurt am Main, Germany

    • Joachim Curtius,
    • João Almeida,
    • Sebastian Ehrhart,
    • Luisa Ickes,
    • Andreas Kürten,
    • Linda Rondo,
    • Daniela Wimmer &
    • Fabian Kreissl
  3. SIM, University of Lisbon and University of Beira Interior, 1749-016 Lisbon, Portugal

    • João Almeida,
    • Antonio Amorim,
    • Jorge Lima,
    • Sandra Mogo,
    • Paulo Pereira &
    • Antonio Tomé
  4. University of Leeds, School of Earth and Environment, LS2-9JT Leeds, United Kingdom

    • Eimear Dunne &
    • Kenneth S. Carslaw
  5. University of Helsinki, Department of Physics, FI-00014 Helsinki, Finland

    • Jonathan Duplissy,
    • Alessandro Franchin,
    • Stéphanie Gagné,
    • Siegfried Schobesberger,
    • Mikael Ehn,
    • Heikki Junninen,
    • Katrianne Lehtipalo,
    • Jyri Mikkilä,
    • Tuomo Nieminen,
    • Tuukka Petäjä,
    • Mikko Sipilä,
    • Joonas Vanhanen,
    • Douglas R. Worsnop &
    • Markku Kulmala
  6. Helsinki Institute of Physics, University of Helsinki, FI-00014 Helsinki, Finland

    • Jonathan Duplissy,
    • Stéphanie Gagné &
    • Mikko Sipilä
  7. University of Vienna, Faculty of Physics, 1090 Vienna, Austria

    • Agnieszka Kupc,
    • Aron Vrtala,
    • Paul E. Wagner &
    • Paul M. Winkler
  8. Ionicon Analytik GmbH and University of Innsbruck, Institute for Ion and Applied Physics, 6020 Innsbruck, Austria

    • Axel Metzger,
    • Martin Breitenlechner,
    • Armin Hansel,
    • Daniel Hauser,
    • Werner Jud &
    • Ralf Schnitzhofer
  9. Paul Scherrer Institut, Laboratory of Atmospheric Chemistry, CH-5232 Villigen, Switzerland

    • Francesco Riccobono,
    • Federico Bianchi,
    • Josef Dommen,
    • Hansueli Walther,
    • Ernest Weingartner &
    • Urs Baltensperger
  10. Leibniz Institute for Tropospheric Research, 04318 Leipzig, Germany

    • Georgios Tsagkogeorgas,
    • Frank Stratmann &
    • Heike Wex
  11. University of Milan, Department of Inorganic, Metallorganic, and Analytical Chemistry, 20133 Milan, Italy

    • Federico Bianchi
  12. California Institute of Technology, Division of Chemistry and Chemical Engineering, Pasadena, California 91125, USA

    • Andrew Downard,
    • Richard C. Flagan &
    • John H. Seinfeld
  13. Lebedev Physical Institute, Solar and Cosmic Ray Research Laboratory, 119991 Moscow, Russia

    • Alexander Kvashin,
    • Vladimir Makhmutov &
    • Yuri Stozhkov
  14. University of Eastern Finland, FI-70211 Kuopio, Finland

    • Ari Laaksonen
  15. NOAA Earth System Research Laboratory, Boulder, Colorado 80305, USA

    • Edward R. Lovejoy
  16. Finnish Meteorological Institute, FI-00101 Helsinki, Finland

    • Yrjo Viisanen
  17. Aerodyne Research Inc., Billerica, Massachusetts 01821, USA

    • Douglas R. Worsnop


J.A. performed the nucleation rate analysis. S.S. conducted the APi-TOF analysis. J.A., F.B., M.B., A. Downard, E.D., J. Duplissy, S.E., A.F., S.G., D.H., L.I., W.J., J.K., F.K., A. Kürten, A. Kupc, K.L., V.M., A.M., T.N., F.R., L.R., R.S., S.S., Y.S., G.T. and D.W. conducted the data collection and analysis. J.A., K.S.C., J.C., E.D., S.E., L.I., E.R.L. and F.S. performed the modelling. J.K. wrote the manuscript. U.B., K.S.C., J.C., J.K., M.K., J.H.S. and D.R.W. did data interpretation and editing of the manuscript. All authors contributed to the development of the CLOUD facility and analysis instruments, and commented on the manuscript.

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    The file contains Supplementary Text and Data, Supplementary References and Supplementary Figures 1-4 with legends.


  1. Report this comment #63713

    Norman Morgan said:

    Time-resolved molecular measurements reveal that nucleation proceeds by a gatit base-stabilization mechanism involving the stepwise accretion of ammonia molecules. Ions increase the nucleation rate by an additional factor of between two and more than ten at ground-level galactic-cosmic-ray intensities, provided that the nucleation rate lies below the limiting ion-pair production rate.

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