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| Titel |
Organic Aerosol Nucleation and Growth at the CERN CLOUD chamber |
| VerfasserIn |
Jasmin Tröstl, Katrianne Lethipalo, Federico Bianchi, Mikko Sipilä, Tuomo Nieminen, Robert Wagner, Carla Frege, Mario Simon, Ernest Weingartner, Martin Gysel, Josef Dommen, Urs Baltensperger |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250093505
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| Publikation (Nr.) |
 EGU/EGU2014-8297.pdf |
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| Zusammenfassung |
| It is well known that atmospheric aerosols influence the climate by changing Earth’s radiation
balance (IPCC 2007 and 2013). Recent models have shown (Merikanto et al. 2009) that
aerosol nucleation is one of the biggest sources of low level cloud condensation nuclei. Still,
aerosol nucleation and growth are not fully understood. The driving force of nucleation and
growth is sulfuric acid. However ambient nucleation and growth rates cannot be explained by
solely sulfuric acid as precursor. Recent studies have shown that only traces of precursors like
ammonia and dimethylamine enhance the nucleation rates dramatically (Kirkby et al. 2011,
Almeida et al., 2013). Thus the role of different aerosol precursor needs to be studied
not only in ambient but also in very well controlled chamber experiments. The
CLOUD (Cosmics Leaving OUtdoor Droplets) experiment enables conducting
experiments very close to atmospheric conditions and with a very low contaminant
background.
The latest CLOUD experiments focus on the role of organics in aerosol nucleation and
growth. For this purpose, numerous experiments with alpha-pinene have been conducted at
the CERN CLOUD chamber. Several state-of-the-art instruments were used to cover the
whole complexity of the experiment. Chamber conditions were set to 40% relative
humidity and 5°C. Atmospheric concentrations of SO2, O3, HONO, H2O and
alpha-pinene were injected to the chamber. Different oxidation conditions were used,
yielding different levels of oxidized organics: (1) OH radicals, (2) Ozone with the OH
scavenger H2 (pure ozonolysis) and (3) both. SO2 was injected to allow for sulfuric acid
production. Optical UV fibers were used to enable photochemical reactions. A
high field cage (30 kV) can be turned on to remove all charged particles in the
chamber to enable completely neutral conditions. Comparing neutral conditions to the
beam conditions using CERN’s proton synchrotron, the fraction of ion-induced
nucleation can be studied. Using the beam, different ion concentrations can be
simulated, from the planetary boundary layer to the upper troposphere (Kirkby et al.
2011).
Precursor concentration and oxidiation products were measured with one proton transfer
reaction time-of-flight mass spectrometer (precursor concentration), two atmospheric
pressure interface time-of-flight mass spectrometer (APi-ToF, charged cluster composition)
and two chemical ionization APi-ToF (neutral cluster composition and concentration).
Aerosol formation and growth rates were determined using particle size magnifier (size rage:
1-3 nm), neutral air ion spectrometer (size rage: 0.8 -30 nm), nano scanning mobility
particle sizer (size rage: 5-80 nm) and several low cut-off condensation particle
counters.
The presented results will include nucleation and growth rates depending on
oxidized organics and sulfuric acid concentration. Another focus will be on the
contribution of organics to aerosol growth. For this, different size ranges will be
considered. The results will also include the influence of ions on nucleation and
growth.
References:
Almeida, J., et al. Nature 502.7471 (2013): 359-363.
IPCC, 2007: Climate Change 2007: The Physical Science Basis.
IPCC, 2013: Climate Change 2013: The Physical Science Basis.
Kirkby, J., et al. Nature 476.7361 (2011): 429-433.
Merikanto, J., et al. Atmospheric Chemistry and Physics 9.21 (2009): 8601-8616. |
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