Göran Frank
Director of graduate studies
Enhanced organic mass fraction and decreased hygroscopicity of cloud condensation nuclei (CCN) during new particle formation events
Author
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.
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.
Department/s
- Nuclear physics
- MERGE: ModElling the Regional and Global Earth system
Publishing year
2010
Language
English
Publication/Series
Geophysical Research Letters
Volume
37
Document type
Journal article (letter)
Publisher
American Geophysical Union (AGU)
Topic
- Subatomic Physics
Status
Published
ISBN/ISSN/Other
- ISSN: 1944-8007