The formation of marine aerosols and cloud condensation nuclei—from which marine clouds originate—depends ultimately on the availability of new, nanometre-scale particles in the marine boundary layer. Because marine aerosols and clouds scatter incoming radiation and contribute a cooling effect to the Earth's radiation budget1, new particle production is important in climate regulation. It has been suggested that sulphuric acid—derived from the oxidation of dimethyl sulphide—is responsible for the production of marine aerosols and cloud condensation nuclei. It was accordingly proposed that algae producing dimethyl sulphide play a role in climate regulation2, but this has been difficult to prove and, consequently, the processes controlling marine particle formation remains largely undetermined3,4. Here, using smog chamber experiments under coastal atmospheric conditions, we demonstrate that new particles can form from condensable iodine-containing vapours, which are the photolysis products of biogenic iodocarbons emitted from marine algae. Moreover, we illustrate, using aerosol formation models, that concentrations of condensable iodine-containing vapours over the open ocean are sufficient to influence marine particle formation. We suggest therefore that marine iodocarbon emissions have a potentially significant effect on global radiative forcing.

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This work was funded by the European Commission, the Finnish Academy, the US Department of Energy and the National Development Plan and Environmental Protection Agency, Ireland.

Author information


  1. Department of Physics, National University of Ireland, Galway, Ireland

    • Colin D. O'Dowd
    •  & S. Gerard Jennings
  2. Division of Atmospheric Sciences, Department of Physical Sciences, University of Helsinki, P.O. Box 64, Helsinki, FIN-00014, Finland

    • Colin D. O'Dowd
    • , Liisa Pirjola
    •  & Markku Kulmala
  3. Departments of Environmental Science and Engineering and Chemical Engineering, California Institute of Technology, 1200 E. California Boulevard, Pasadena, 210-41, USA

    • Jose L. Jimenez
    • , Roya Bahreini
    • , Richard C. Flagan
    •  & John H. Seinfeld
  4. Finnish Institute for Occupational Health, Topeliuksenkatu 41a, Helsinki, FIN-00250, Finland

    • Kaarle Hämeri
  5. Helsinki Polytechnic Technology, PL 4020, FIN-00099, Helsinki, Finland

    • Liisa Pirjola
  6. Institute of Spectrochemistry and Applied Spectroscopy, Dortmund, 44139, Germany

    • Thorsten Hoffmann


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The authors declare that they have no competing financial interests.

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Correspondence to Colin D. O'Dowd.

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