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| Titel |
Development and chamber evaluation of the MCM v3.2 degradation scheme for β-caryophyllene |
| VerfasserIn |
M. E. Jenkin, K. P. Wyche, C. J. Evans, T. Carr, P. S. Monks, M. R. Alfarra, M. H. Barley, G. B. McFiggans, J. C. Young, A. R. Rickard |
| 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 ; 12, no. 11 ; Nr. 12, no. 11 (2012-06-15), S.5275-5308 |
| Datensatznummer |
250011242
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| Publikation (Nr.) |
 copernicus.org/acp-12-5275-2012.pdf |
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| Zusammenfassung |
| A degradation mechanism for β-caryophyllene has recently been released
as part of version 3.2 of the Master Chemical Mechanism (MCM v3.2),
describing the gas phase oxidation initiated by reaction with ozone, OH
radicals and NO3 radicals. A detailed overview of the construction
methodology is given, within the context of reported experimental and
theoretical mechanistic appraisals. The performance of the mechanism has been
evaluated in chamber simulations in which the gas phase chemistry was coupled
to a representation of the gas-to-aerosol partitioning of 280
multi-functional oxidation products. This evaluation exercise considered data
from a number of chamber studies of either the ozonolysis of
β-caryophyllene, or the photo-oxidation of
β-caryophyllene/NOx mixtures, in which detailed product
distributions have been reported. This includes the results of a series of
photo-oxidation experiments performed in the University of Manchester aerosol
chamber, also reported here, in which a comprehensive characterization of the
temporal evolution of the organic product distribution in the gas phase was
carried out, using Chemical Ionisation Reaction Time-of-Flight Mass
Spectrometry (CIR-TOF-MS), in conjunction with measurements of NOx,
O3 and SOA mass loading. The CIR-TOF-MS measurements allowed
approximately 45 time-resolved product ion signals to be detected, which were
assigned on the basis of the simulated temporal profiles of the more abundant
MCM v3.2 species, and their probable fragmentation patterns. The evaluation
studies demonstrate that the MCM v3.2 mechanism provides an acceptable
description of β-caryophyllene degradation under the chamber conditions
considered, with the temporal evolution of the observables identified above
generally being recreated within the uncertainty bounds of key parameters
within the mechanism. The studies have highlighted a number of areas of
uncertainty or discrepancy, where further investigation would be valuable to
help interpret the results of chamber studies and improve detailed
mechanistic understanding. These particularly include: (i) quantification of
the yield and stability of the secondary ozonide (denoted BCSOZ in MCM v3.2),
formed from β-caryophyllene ozonolysis, and elucidation of the details
of its further oxidation, including whether the products retain the
"ozonide" functionality; (ii) investigation of the impact of NOx
on the β-caryophyllene ozonolysis mechanism, in particular its effect
on the formation of β-caryophyllinic acid (denoted C137CO2H in
MCM v3.2), and elucidation of its formation mechanism; (iii) routine
independent identification of β-caryophyllinic acid, and its
potentially significant isomer β-nocaryophyllonic acid (denoted
C131CO2H in MCM v3.2); (iv) more precise quantification of the
primary yield of OH (and other radicals) from β-caryophyllene
ozonolysis; (v) quantification of the yields of the first-generation hydroxy
nitrates (denoted BCANO3, BCBNO3 and BCCNO3 in MCM v3.2) from the
OH-initiated chemistry in the presence of NOx; and (vi) further
studies in general to improve the identification and quantification of
products formed from both ozonolysis and photo-oxidation, including
confirmation of the simulated formation of multifunctional species containing
hydroperoxide groups, and their important contribution to SOA under
NOx-free conditions. |
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