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| Titel |
Observation of neutral sulfuric acid-amine containing clusters in laboratory and ambient measurements |
| VerfasserIn |
J. Zhao, J. N. Smith, F. L. Eisele, M. Chen, C. Kuang, P. H. McMurry |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 11, no. 21 ; Nr. 11, no. 21 (2011-11-02), S.10823-10836 |
| Datensatznummer |
250010161
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| Publikation (Nr.) |
 copernicus.org/acp-11-10823-2011.pdf |
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| Zusammenfassung |
| Recent ab initio calculations showed that amines can enhance atmospheric
sulfuric acid-water nucleation more effectively than ammonia, and this
prediction has been substantiated in laboratory measurements. Laboratory
studies have also shown that amines can effectively displace ammonia in
several types of ammonium clusters. However, the roles of amines in cluster
formation and growth at a microscopic molecular scale (from molecular sizes
up to 2 nm) have not yet been well understood. Processes that must be
understood include the incorporation of amines into sulfuric acid clusters
and the formation of organic salts in freshly nucleated particles, which
contributes significantly to particle growth rates. We report the first
laboratory and ambient measurements of neutral sulfuric acid-amine clusters
using the Cluster CIMS, a recently-developed mass spectrometer designed for
measuring neutral clusters formed in the atmosphere during nucleation. An
experimental technique, which we refer to as Semi-Ambient Signal
Amplification (SASA), was employed. Sulfuric acid was added to ambient air,
and the concentrations and composition of clusters in this mixture were
analyzed by the Cluster CIMS. This experimental approach led to
significantly higher cluster concentrations than are normally found in
ambient air, thereby increasing signal-to-noise levels and allowing us to
study reactions between gas phase species in ambient air and sulfuric acid
containing clusters. Mass peaks corresponding to clusters containing four
H2SO4 molecules and one amine molecule were clearly observed, with
the most abundant sulfuric acid-amine clusters being those containing a C2-
or C4-amine (i.e. amines with masses of 45 and 73 amu). Evidence for C3-
and C5-amines (i.e. amines with masses of 59 and 87 amu) was also found,
but their correlation with sulfuric acid tetramer was not as strong as was
observed for the C2- and C4-amines. The formation mechanisms for those
sulfuric acid-amine clusters were investigated by varying the residence time
in the inlet. It was concluded that the amines react directly with neutral
clusters and that ion-induced clustering of sulfuric acid cluster ions with
amines was not a dominant process. Results from ambient measurements using
the Cluster CIMS without addition of sulfuric acid have shown that the
sulfuric acid-amine clusters were reasonably well correlated with sulfuric
acid tetramer and consistent with the SASA experiments at the same Boulder
sampling site. Also, clusters that contain C2- or C4-amines were more
abundant and better correlated with sulfuric acid tetramer than other types
of amine containing clusters. However, ambient measurements of sulfuric
acid-amine clusters remain difficult and highly uncertain because their
concentrations are only slightly above background levels, even during
nucleation events. |
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