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Göran Frank

Director of graduate studies

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Enhanced organic mass fraction and decreased hygroscopicity of cloud condensation nuclei (CCN) during new particle formation events


  • Ulrike Dusek
  • Göran Frank
  • J. Curtius
  • F. Drewnick
  • J. Schneider
  • A. Kürten
  • Diana Rose
  • Meinrat O. Andreae
  • S. Borrmann
  • Ulrich Pöschl

Summary, in English

In a forested near-urban location in central Germany, the

CCN efficiency of particles smaller than 100 nm decreases

significantly during periods of new particle formation. This

results in an increase of average activation diameters, ranging

from 5 to 8% at supersaturations of 0.33% and 0.74%,

respectively. At the same time, the organic mass fraction in

the sub-100-nm size range increases from approximately 2/3

to 3/4. This provides evidence that secondary organic aerosol

(SOA) components are involved in the growth of new

particles to larger sizes, and that the reduced CCN efficiency

of small particles is caused by the low hygroscopicity of

the condensing material. The observed dependence of

particle hygroscopicity (k) on chemical composition can

be parameterized as a function of organic and inorganic

mass fractions (forg, finorg) determined by aerosol mass

spectrometry: k = korg forg + kinorg finorg. The obtained value

of korg ~ 0.1 is characteristic for SOA, and kinorg ~ 0.7 is

consistent with the observed mix of ammonium, sulfate

and nitrate ions.


  • Nuclear physics
  • MERGE: ModElling the Regional and Global Earth system

Publishing year





Geophysical Research Letters



Document type

Journal article (letter)


American Geophysical Union (AGU)


  • Subatomic Physics




  • ISSN: 1944-8007