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| Titel |
Formation of highly oxidized multifunctional compounds: autoxidation of peroxy radicals formed in the ozonolysis of alkenes – deduced from structure–product relationships |
| VerfasserIn |
T. F. Mentel, M. Springer, M. Ehn, E. Kleist, I. Pullinen, T. Kurtén, M. Rissanen, A. Wahner, J. Wildt |
| 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 ; 15, no. 12 ; Nr. 15, no. 12 (2015-06-18), S.6745-6765 |
| Datensatznummer |
250119837
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| Publikation (Nr.) |
 copernicus.org/acp-15-6745-2015.pdf |
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| Zusammenfassung |
It has been postulated that secondary organic particulate matter plays a
pivotal role in the early growth of newly formed particles in forest areas.
The recently detected class of extremely low volatile organic compounds
(ELVOC) provides the missing organic vapors and possibly contributes a
significant fraction to atmospheric SOA (secondary organic aerosol). The sequential rearrangement of
peroxy radicals and subsequent O2 addition results in ELVOC which are
highly oxidized multifunctional molecules (HOM). Key for efficiency of such
HOM in early particle growth is that their formation is induced by one
attack of the oxidant (here O3), followed by an autoxidation process
involving molecular oxygen. Similar mechanisms were recently observed and
predicted by quantum mechanical calculations e.g., for isoprene. To assess
the atmospheric importance and therewith the potential generality, it is
crucial to understand the formation pathway of HOM.
To elucidate the formation path of HOM as well as necessary and sufficient
structural prerequisites of their formation we studied homologous series of
cycloalkenes in comparison to two monoterpenes. We were able to directly
observe highly oxidized multifunctional peroxy radicals with 8 or 10 O atoms
by an Atmospheric Pressure interface High Resolution Time of Flight Mass
Spectrometer (APi-TOF-MS) equipped with a NO3−-chemical ionization (CI) source.
In the case of O3 acting as an oxidant, the starting peroxy radical is formed
on the so-called vinylhydroperoxide path. HOM peroxy radicals and their
termination reactions with other peroxy radicals, including dimerization,
allowed for analyzing the observed mass spectra and narrowing down the likely
formation path. As consequence, we propose that HOM are multifunctional
percarboxylic acids, with carbonyl, hydroperoxy, or hydroxy groups arising
from the termination steps. We figured that aldehyde groups facilitate the
initial rearrangement steps. In simple molecules like cycloalkenes,
autoxidation was limited to both terminal C atoms and two further C atoms in
the respective α positions. In more complex molecules containing
tertiary H atoms or small, constrained rings, even higher oxidation degrees
were possible, either by simple H shift of the tertiary H atom or by
initialization of complex ring-opening reactions. |
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