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| Titel |
Composition and temporal behavior of ambient ions in the boreal forest |
| VerfasserIn |
M. Ehn, H. Junninen, T. Petäjä, T. Kurtén, V.-M. Kerminen, S. Schobesberger, H. E. Manninen, I. K. Ortega, H. Vehkamäki, M. Kulmala  , D. R. Worsnop |
| 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 ; 10, no. 17 ; Nr. 10, no. 17 (2010-09-09), S.8513-8530 |
| Datensatznummer |
250008764
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| Publikation (Nr.) |
 copernicus.org/acp-10-8513-2010.pdf |
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| Zusammenfassung |
| A recently developed atmospheric pressure interface mass spectrometer
(APi-TOF) measured the negative and positive ambient ion composition at a
boreal forest site. As observed in previous studies, the negative ions were
dominated by strong organic and inorganic acids (e.g. malonic, nitric and
sulfuric acid), whereas the positive ions consisted of strong bases
(e.g. alkyl pyridines and quinolines). Several new ions and clusters of ions were
identified based on their exact masses, made possible by the high
resolution, mass accuracy and sensitivity of the APi-TOF. Time series
correlograms aided in peak identification and assigning the atomic
compositions to molecules. Quantum chemical calculations of proton
affinities and cluster stabilities were also used to confirm the
plausibility of the assignments. Acids in the gas phase are predominantly
formed by oxidation in the gas phase, and thus the concentrations are
expected to vary strongly between day and night. This was also the case in
this study, where the negative ions showed strong diurnal behavior, whereas
the daily changes in the positive ions were considerably smaller. A special
focus in this work was the changes in the ion distributions occurring during
new particle formation events. We found that sulfuric acid, together with
its clusters, dominated the negative ion spectrum during these events. The
monomer (HSO4−) was the largest peak, together with the dimer
(H2SO4 · HSO4−) and trimer
((H2SO4)2 · HSO4−). SO5− also
tracked HSO4− at around 20% of the HSO4−
concentration at all times. During the strongest events, the tetramer and a
cluster with the tetramer and ammonia were also detected. Quantum chemical
calculations predict that sulfuric acid clusters containing ammonia are much
more stable when neutral, thus the detection of a single ion cluster implies
that ammonia can be an important compound in the nucleation process. We also
believe to have made the first observations of an organosulfate (glycolic
acid sulfate) in the gas phase. This ion, and its cluster with sulfuric
acid, correlates with the HSO4−, but peaks in the early afternoon,
some hours later than HSO4− itself. A list of all identified ions
is presented in the supplementary material, and also a list of all detected
masses not yet identified. |
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