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| Titel |
The potential role of organic peroxides in laboratory new particle formation |
| VerfasserIn |
Matthias Hummel, Boris Bonn |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250041429
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| Zusammenfassung |
| New particle formation in the atmosphere belongs to the currently most discussed
aspects of atmospheric aerosols with significant implications for cloud formation and
microphysics, once these particles have grown beyond about 50Â nm in particle
diameter. If these particles act as cloud condensation or ice nuclei they can affect the
radiation budget at the Earths surface and cause climate couplings important to
understand when aiming to predict climate change scenarios. One aspect widely
discussed is the potential contribution of organic trace gases from anthropogenic
and biogenic sources. From earlier studies it is known that secondary ozonides
formed in the reaction of carbonyl compounds and the so-called stabilised Criegee
Intermediates (stabCI) act as nucleation inducing molecules. However their gas-phase
concentration prevents their activation. Because of that additional compounds are
required for activation and subsequent growth at the very smallest sizes with a
strong Kelvin effect present. Here we focussed on the role of organic peroxy radicals
(RO2) and the so-called stabilized Criegee Intermediate (stabCI) in laboratory new
particle formation during ethene-ozone reactions in the presence of excess nopinone.
Ethene was used because of its well-known chemical reactions. In order to check the
influence of RO2, the peroxy radicals were varied by the addition of different nitrogen
oxide concentrations. A flow-chamber set-up in a walk in cold chamber was used at
atmospheric pressure and room temperature. 176Â ppb of ethene and 543Â ppb of nopinone
were dispersed in a synthetic air flow of 20Â LÂ min-1. Additionally varying mixing
ratios of ozone (87-108Â ppb) and of nitrogen oxide (0.5-100Â ppb) have been added,
too. The total particle number concentration (Dp > 2.7 nm) was monitored at a
fixed reaction time of 147Â s at the end of the tube. The observed particle number
concentrations could be reproduced by gas phase and aerosol nucleation kinetics
with an organic nucleation mechanism reasonably well. This mechanism assumes
the nucleation to be started by secondary ozonides (SOZ) and activated by either
organic peroxy radicals or the stabCI with a preference to the RO2 molecules from
nopinone-OH oxidation. This indicates that high molecular weight radicals are
likely to play a significant role in organic new particle formation at least in the
laboratory. In general we observed a clear reduction of particles activated when
increasing NO up to a nearly supression at an NO mixing ratio of 100 ppb. This
reduction appeared in three distinct sections: (a) a first one at low NO mixing ratios
(NOÂ |
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